If GM wants to offer a range extending mechanism that has zero emissions, but cheaper than a fuel cell, then they should look into the Rotary Air Engine developed by Engineair.

http://www.engineair.com.au/index.htm

They are looking for ODM and OEM partners to help them expand their market reach, and the Chevy Volt platform would be a good fit. Individuals would just need a compressor at home, and a refill would only take minutes, instead of charging for hours.

See also an air car from MDI / Tata

http://www.technologyreview.com/Energy/20071/

Yes, I've seen the articulated connecting rod design for the air car's piston engine, giving it much better torque. That car is already being exported to some European countries as well. There is a youtube video of that air car being driven around - I was surprised to hear it pop-pop-pop along, like a 2 stroke.

I like the rotory air engine, because it is extremely light weight for the horsepower it generates, so it would make a great, cheap, clean and lightweight range extender for REV's.

I think it's clear that an air powered engine is a winner - the issue, as with an electric motor, is the energy storage. The MDI / Tata article above mentioned an on-board motor to recharge the compressed air tank, much like the ICE generator on the Volt.

So here's the crazy idea - instead of a piston ICE driving a compressor, how about direct injection of fuel & oxidizer into the compressed air tank? I don't know enough to say what would the burn be like under high pressure. But if it does burn cleanly, I can't think of a more efficient way to recharge the pressure, if you're going to use liquid fuel.

My only reason for suggesting the rotary air engine is that it is emissions free, assuming your home compressor runs off renewable energy. Any addition of fuels (except for hydrogen) leads you to staying with current ICE technologies.

I think GM should keep this approach in their hip pocket, because Arizona and California are pushing the federal government to grant them waivers to accelerate the time tables for requiring low / no emissions vehicles in their states. This approach is low tech and ready to go now.

I suppose an on-board compressor that plugs into any outlet is a way to have unlimited range, but a large reservoir home compressor would allow rapid refills of your vehicle at home.

While I do think the rotary air engine itself is a cool device, I would be very surprised it it would be reasonable for this application. The big issues are, how much energy can you store in say a one cubic meter volume? What is the efficiency of converting that stored energy to mechanical energy? What is the expected energy loss from heat flow out of the pressurized tank? Can you recover mechanical energy from the cars motion and re-pressurize the tank? What is the efficiency of that?

These things need to be answered before the air engine can be reasonably compared. Besides it will take energy to compress the air to begin with, which will likely have to come from electric or chemical energy.

One of the feature of using a battery or capacitor is the efficiency of energy storage and conversion, both in terms of unit mass and unit volume.

I don't mean to sound like a jerk, but at first glance, this device doesn't appear to accomplish the desired goals.

While I do think the rotary air engine itself is a cool device, I would be very surprised it it would be reasonable for this application. The big issues are, how much energy can you store in say a one cubic meter volume? What is the efficiency of converting that stored energy to mechanical energy? What is the expected energy loss from heat flow out of the pressurized tank? Can you recover mechanical energy from the cars motion and re-pressurize the tank? What is the efficiency of that?

These things need to be answered before the air engine can be reasonably compared. Besides it will take energy to compress the air to begin with, which will likely have to come from electric or chemical energy.

One of the feature of using a battery or capacitor is the efficiency of energy storage and conversion, both in terms of unit mass and unit volume.

I don't mean to sound like a jerk, but at first glance, this device doesn't appear to accomplish the desired goals.

Yes, those are exactly the right questions to ask, and compared to batteries, it is less efficient in all the aspects you list. The benefit of this approach over batteries, is that a pressure tank can be rapidly refilled, whereas, today's batteries require at least 4 hours to achieve an 80% recharge, which causes the "range anxiety" that turn car buyers off from buying 100$ BEV's.

I only suggest pursuing this approach, because CA and AZ are pushing for a ZERO emissions vehicle to be sold immediately, and compressed air is the only rapid refill tech readily available, that is also affordable.

Of your list of questions, the only one that I can answer for sure is:
"Can you recover mechanical energy from the cars motion and re-pressurize the tank?" Answer: The existing regenerative braking system would simply recharge the batteries for later use, and not bother converting the electricity into pressurized air.

I think it's clear that an air powered engine is a winner - the issue, as with an electric motor, is the energy storage. The MDI / Tata article above mentioned an on-board motor to recharge the compressed air tank, much like the ICE generator on the Volt.

So here's the crazy idea - instead of a piston ICE driving a compressor, how about direct injection of fuel & oxidizer into the compressed air tank? I don't know enough to say what would the burn be like under high pressure. But if it does burn cleanly, I can't think of a more efficient way to recharge the pressure, if you're going to use liquid fuel.

Your crazy idea is now a start-up:

http://zeropollutionmotors.us/

They burn fuel to heat the compressed air, getting crazy range and mileage over compressed air alone.

Since CARB is expecting 7,500 ZEV's from automakers, I believe this rotary air engine could replace the gasoline ICE range extender in the Volt, and meet CARB's ZEV mandate.

Your crazy idea is now a start-up:

http://zeropollutionmotors.us/

They burn fuel to heat the compressed air, getting crazy range and mileage over compressed air alone.

I did see that, and thought "my crazy idea is now a start-up". Instead of burning the fuel *inside* the tank, as I had proposed, they have a separate chamber between the tank and the rotary engine. This allows combustion at lower pressures.

Just like the Volt, you get high efficiency, plug-in and regen capability, and a range-extender. The big difference in my mind is that car companies are made up of mechanical engineers. So if the same thing can be done mechanically instead of electrically, maybe that would be easier at some level. It certainly would be less expensive.

A lot of unanswered questions about this rotary air motor. Their website doesn't tell you much, but what it does tell you is that it seems to be only for low HP applications. So is it scalable? How much PSI in storage does it require and what volume? How many HP? Any performance charts?

One problem I see with these compressed air motors is simply leaks in the system. Anybody who was owned a compressor and lines to run air tools knows that they always leak down when you're not using them. That's why you shut the power off to the compressor when you leave for the night otherwise it will run all night. I can see leaks being a constant head ache as the vehicle ages.

At first glance this sounds like a perfect idea, as an RE. The more I thought of it though it is missing the point of why the range extender exists. My thought of why there is a range extender is not so much of getting the extra miles, but being able to utilize another energy source when I cannot plug-in. I would be commuting with this car within it's range most of the time, so mileage isn't as important. It's those long trips that it becomes more important. So, at least to me, using compressed air as an RE is as useful to me as not having an RE at all.

That said when the time comes that gas stations/supermarkets also have places where you can plug in your car this would become, it seems, an excellent way to extend the range.

So, at least to me, using compressed air as an RE is as useful to me as not having an RE at all.


Just to clarify, in this thread, we're talking about a car that uses compressed air instead of a battery, to drive an engine that runs on compressed air. The range-extender part comes in when you burn fuel, and use the exhaust gases to drive the same engine.

Just as in the Volt, such an air car is "gas-optional" since you can plug it in to recharge the air tank.

There are many ways to incorporate this rotary air engine:

- Air engine is main drive component with ICE back-up when tanks are depleted
- Batteries are primary drive component with rotary air engine as the range extender (electric refill using onboard compressor)
- ZPM approach in which blend of air and gasoline is used

I agree with Joshua, that many mechs would gravitate to any of these configs, being far more comfortable with pneumatics over electronics. I believe many would like it simply because it is extremely simple, safe, cheap and achievable today.

I'm not sure that a compressed air tank is as safe as a battery. The issue is how fast the energy is released in a crash situation. A compressed air tank would become a rocket.

However, I'm sure that there are ways around this problem!!!! For instance, in addition to a strong outer shell, the compressed air tank could be filled with some kind of air-permeable foam material that has very high tensile strength. If the outer shell were breached, this inside material would limit how fast the air could be released.

I'm not sure that a compressed air tank is as safe as a battery. The issue is how fast the energy is released in a crash situation. A compressed air tank would become a rocket.

However, I'm sure that there are ways around this problem!!!! For instance, in addition to a strong outer shell, the compressed air tank could be filled with some kind of air-permeable foam material that has very high tensile strength. If the outer shell were breached, this inside material would limit how fast the air could be released.

Modern Marvels, or one of those other type shows, showed that a carbon fiber tank would just tear along a seem, instantly bursting all its pressure at once with no shrapnel. Even metal tanks would burst all at once at those pressures.

Beyond tomorrow has a good episode on both the MDI piston compressed air motor and the rotary compressed air motor.

YouTube Beyond Tomorrow (http://youtube.com/watch?v=QmqpGZv0YT4)

I truly hope this technology makes it to the street. I think it would make a great and inexpensive city car. Just one more weapon in the fight against burning fossil fuels.

Great find Jason!

What a great video.

I like the rotary engine better...I think it could be quieter,more reliable and have better low end torque. Maybe similar to an electric motor?

Although the MDI concept of preheating the air to increase pressure using petro is also really good. Did they infer something like 900 miles on one tank of gas and air?

Seems like a viable concept...

Great find Jason!

What a great video.

I like the rotary engine better...I think it could be quieter,more reliable and have better low end torque. Maybe similar to an electric motor?

Although the MDI concept of preheating the air to increase pressure using petro is also really good. Did they infer something like 900 miles on one tank of gas and air?

Seems like a viable concept...

I think the rotary air engine would make a great range extender. If you connect the rotary motor shaft to a generator shaft, you could produce a smooth flow of electricity to maintain a charge in the batteries, and the batteries could quickly handle various loads on the vehicle.

I think the rotary air engine would make a great range extender. If you connect the rotary motor shaft to a generator shaft, you could produce a smooth flow of electricity to maintain a charge in the batteries, and the batteries could quickly handle various loads on the vehicle.

Hmmm... I like it! The range extender is also zero emissions and would only take a few minutes to refill at any 110volt outlet.

Seems to easy...what are we missing here?

You will need very large air tanks on-board because air cannot hold much energy. Also, when you compress air very fast you have to get rid of a LOT of heat. Just remember, the energy is the same amount. You can't expect to use a 110 V outlet for 5 minutes to fill compressed tanks and go further than you can for the same voltage and time (assume the same current) to fill up batteries. You will actually go further on the batteries because the efficiency is greater!

You can have pre-compressed air tanks at the gas station and fast charge but then again you need the infrastructure, tanks, way to get rid of all the heat, etc. Without the infrastructure you are in the same boat as everything else - can't extend the range when you're in a hurry.

I love the idea of using compressed air by the way. Should be great for over-crowded cities like those found in India. However, just go right to the wheels, no hybrid needed - too expensive.

You will need very large air tanks on-board because air cannot hold much energy.

Quantum Tech and Boeing are collaborating on 10 kpsi (700 bar) compression systems (for hydrogen, but of course would work with air). Tanks would be smaller than current tech.


Also, when you compress air very fast you have to get rid of a LOT of heat. Just remember, the energy is the same amount.

Any home / industrial compression system you buy will "handle" the heat, either by its ability to store the heat or quickly transfer it out.


You can't expect to use a 110 V outlet for 5 minutes to fill compressed tanks and go further than you can for the same voltage and time (assume the same current) to fill up batteries.

I can expect to buy an air motor and tank for a lot less money than 200 miles worth of batteries. We are talking range extender here. An air motor and tank would be cheaper to buy and run than an ICE, and certainly cleaner, and would work in all climates - no cold start issues.


You can have pre-compressed air tanks at the gas station and fast charge but then again you need the infrastructure, tanks, way to get rid of all the heat, etc. Without the infrastructure you are in the same boat as everything else - can't extend the range when you're in a hurry.

True, but a compressed air system would be cheaper than an electricity fast charge station and wouldn't require special hook ups from the utilities.


I love the idea of using compressed air by the way. Should be great for over-crowded cities like those found in India. However, just go right to the wheels, no hybrid needed - too expensive.

You are pulling that assessment right out of your ass. A compressed air system is cheaper than any full parallel or series hybrid system you could name. Tata Motors and ZPM are proving that with their upcoming designs.

Any home / industrial compression system you buy will "handle" the heat, either by its ability to store the heat or quickly transfer it out.


As I understand it, compressing a gas does generate extra heat, while decompressing a gas makes things cold. It's been a long time since I took thermodynamics... but it seems to me that if these two things happen at different times or different places, then that heat differential energy is lost.

Someone else (on this thread?) mentioned using the compressor waste heat in the home as a hot water heater.

It makes so much sense to attach a burn chamber between the pressure tank and the air motor. The decompressed gas is cold, but is heated up by the burning fuel, which also increases the pressure with its exhaust.

This exhaust could be routed either to the air motor, or back into the pressure tank.

Quantum Tech and Boeing are collaborating on 10 kpsi (700 bar) compression systems (for hydrogen, but of course would work with air). Tanks would be smaller than current tech.

Jason, you make it sound like 700 bar is brand new technology. I was talking about 700 bar in my example. They are using it all the time now. Where have you been? Also, you do realize that having 700 bar worth of hydrogen is a lot different than having 700 bar worth of air. Right? One will get a Volt sized car to go around 300 miles while the air will be significantly less. I guess we should start with how far you want to go and how big do you think the tanks will have to be? I think you will discover that the tanks will be a heck of lot bigger than you think. If you need help I can calculate it for you.



Any home / industrial compression system you buy will "handle" the heat, either by its ability to store the heat or quickly transfer it out.

If you take your empty tank and high pressure hoses and connect a 700 bar (that's 10,000 psi folks) source of compressed air to it and go from 0 psi to 10,000 psi in 5 minutes what do you think will happen? I have a hint. HEAT, lots of it. No, not just at the out-board compressor.




I can expect to buy an air motor and tank for a lot less money than 200 miles worth of batteries. We are talking range extender here. An air motor and tank would be cheaper to buy and run than an ICE, and certainly cleaner, and would work in all climates - no cold start issues.

Well you sound convinced. I would say go out there and build a Volt killer. How about before you do that you visit YouTube and check out the latest air-car technology. Does that look like it's ready to kick the Volt's butt? Answer: not ready. If it were clearly better technology don't you think the engineers and scientists would be all over it? The big problems are the size of the tank (please calculate it first before telling me it's not a problem) and the amount of losses you get from the process. First you have electricity then you fire up a 10,000 psi compressor notice how hot everything gets? Even your home compressor going up to only 90 psi gets very hot. Multiply that by a huge factor. That heat is wasted energy. Then you have to run an air motor with all it's efficiency losses. Remember, for the battery system you go from electricity to battery to motor. You also get some heating but not like the air compressor. Anyway, your retort was not what I was talking about. I got the impression that the poster felt that they could just plug the car in and 5 minutes later would have hundreds of miles of range. I mean, that's the purpose of the range extender, right? I wanted to clarify that getting a Volt to go 400 miles (the range of the range extender) using an air motor and tank is not a simple matter. Do you agree that it will take a lot more energy than what can be provided with a 110 volt plug and 5 minutes? If you are not sure I can calculate that for you as well.



True, but a compressed air system would be cheaper than an electricity fast charge station and wouldn't require special hook ups from the utilities.

Jason, I wish you would think sometimes before you write. Since we are talking about a range extending situation let's draw a picture of our seniero. We are on the highway somewhere and people come in to range extend their vehicles. There are three stations. One is a fast charge station for EVs, one is a fast charge station for an air motor range extender and one is a normal station giving out gas. All drivers want to go 400 miles after they are done and they want to do it fast. One hundred cars are serviced at each station. All cars are around the same size. Here are the questions:

1) What station needs the least amount of energy? Surprise surprise it's the battery station! Why? Because it has the most efficient process: electricity - battery - motor. Next is the air motor and last is the nasty and inefficient ICE.

2) What is the easiest? Pumping around 7 gallons of gas. What could be easier than that?

Why do you think you wouldn't need around the same amount of energy? If you are going to instantaneously deliver that 10,000 psi air to the car in 5 minutes you are going to need more energy and more power than delivering the equivalent milage to the batteries. Maybe you're talking about having huge storage tanks and smaller compressors on-site compressing 10,000 psi air all day and night and then transfer that stored energy to the car's tank when needed. Fine. I will just counter with my electrical storage system that fills the station's batteries all day and night (with even less energy and power than that required by the air system - efficiency) and deliver that power to the car when needed. I would much rather have to deal with a bank of batteries than high pressure (10,000 psi) compressors, tanks, hoses, mechanical breakdowns, oil changes, blow-outs, etc. I guess you just like that stuff. Like how you enjoy playing with all the extra hydrogen parts (another thread).



You are pulling that assessment right out of your ass. A compressed air system is cheaper than any full parallel or series hybrid system you could name. Tata Motors and ZPM are proving that with their upcoming designs.

Pulling out of my butt? Here is what I wrote:

"I love the idea of using compressed air by the way. Should be great for over-crowded cities like those found in India. However, just go right to the wheels, no hybrid needed - too expensive."

Jason, have you been hitting the pipe extra hard today? I think you argue just to argue. Are you really some kid yanking my chain? That's what I have thought for quite a while but figure your questions and retorts are what many people actually think. Don't think you got me. I just think you represent the misinformed masses. I mean really, you can't be serious with all this. If you are then I apologize. Anyway, I said that the air car would be great for over-crowded cities in India because it IS cheap. It won't go that far and the performance will not be that good at first (see YouTube and visit the websites of the manufacturers) but it's clean and somewhat simple. I was saying that a hybrid car with a air motor would be too expensive for the Indian market. Agree? Just take the air motor and go to the wheels. Just like Tata motors. Hello?

Jason, you make it sound like 700 bar is brand new technology. I was talking about 700 bar in my example. They are using it all the time now. Where have you been? Also, you do realize that having 700 bar worth of hydrogen is a lot different than having 700 bar worth of air. Right? One will get a Volt sized car to go around 300 miles while the air will be significantly less. I guess we should start with how far you want to go and how big do you think the tanks will have to be? I think you will discover that the tanks will be a heck of lot bigger than you think. If you need help I can calculate it for you.

Actually, 5 kpsi (350 bar) is common, 10 kpsi (700 bar) is much more recent. I understand hydrogen is being used as a fuel and not a pressure source.


If you take your empty tank and high pressure hoses and connect a 700 bar (that's 10,000 psi folks) source of compressed air to it and go from 0 psi to 10,000 psi in 5 minutes what do you think will happen? I have a hint. HEAT, lots of it. No, not just at the out-board compressor.

This is what I love about dealing with you Texas, as you clearly are NOT technically trained in thermodynamics. Heat is only created / lost during the initial pressurization of the gas, so the home compressor would slowly build up pressure and heat until 10 kpsi is reached. Whatever the temp / pressure of the gas in the 10 kpsi tank may be, when you transfer it into another tank (for this discussion, let's assume home compressor tank is significantly larger than the vehicle tank, so that the pressure drop is insignificant) it will be the same or less temp / pressure in your vehicle. Let me state that more plainly, transferring a pressurized gas from one tank to another does NOT heat the gas, it will, in fact end up at a lower temp / pressure than in the original tank, just like discharging a big capacitor to a small capacitor, leaving them both at a lower voltage.


Well you sound convinced. I would say go out there and build a Volt killer. How about before you do that you visit YouTube and check out the latest air-car technology. Does that look like it's ready to kick the Volt's butt? Answer: not ready. If it were clearly better technology don't you think the engineers and scientists would be all over it? The big problems are the size of the tank (please calculate it first before telling me it's not a problem) and the amount of losses you get from the process. First you have electricity then you fire up a 10,000 psi compressor notice how hot everything gets? Even your home compressor going up to only 90 psi gets very hot. Multiply that by a huge factor. That heat is wasted energy. Then you have to run an air motor with all it's efficiency losses. Remember, for the battery system you go from electricity to battery to motor. You also get some heating but not like the air compressor. Anyway, your retort was not what I was talking about. I got the impression that the poster felt that they could just plug the car in and 5 minutes later would have hundreds of miles of range. I mean, that's the purpose of the range extender, right? I wanted to clarify that getting a Volt to go 400 miles (the range of the range extender) using an air motor and tank is not a simple matter. Do you agree that it will take a lot more energy than what can be provided with a 110 volt plug and 5 minutes? If you are not sure I can calculate that for you as well.

A air motor / generator would perform better than a gasoline ICE, especially under cold start conditions.


Jason, I wish you would think sometimes before you write. Since we are talking about a range extending situation let's draw a picture of our seniero. We are on the highway somewhere and people come in to range extend their vehicles. There are three stations. One is a fast charge station for EVs, one is a fast charge station for an air motor range extender and one is a normal station giving out gas. All drivers want to go 400 miles after they are done and they want to do it fast. One hundred cars are serviced at each station. All cars are around the same size. Here are the questions:

1) What station needs the least amount of energy? Surprise surprise it's the battery station! Why? Because it has the most efficient process: electricity - battery - motor. Next is the air motor and last is the nasty and inefficient ICE.

2) What is the easiest? Pumping around 7 gallons of gas. What could be easier than that?

Why do you think you wouldn't need around the same amount of energy? If you are going to instantaneously deliver that 10,000 psi air to the car in 5 minutes you are going to need more energy and more power than delivering the equivalent milage to the batteries. Maybe you're talking about having huge storage tanks and smaller compressors on-site compressing 10,000 psi air all day and night and then transfer that stored energy to the car's tank when needed. Fine. I will just counter with my electrical storage system that fills the station's batteries all day and night (with even less energy and power than that required by the air system - efficiency) and deliver that power to the car when needed. I would much rather have to deal with a bank of batteries than high pressure (10,000 psi) compressors, tanks, hoses, mechanical breakdowns, oil changes, blow-outs, etc. I guess you just like that stuff. Like how you enjoy playing with all the extra hydrogen parts (another thread).

The EV station would be the most costly to implement, and the electric vehicle would be the most costly to buy.


Pulling out of my butt? Here is what I wrote:

"I love the idea of using compressed air by the way. Should be great for over-crowded cities like those found in India. However, just go right to the wheels, no hybrid needed - too expensive."

Jason, have you been hitting the pipe extra hard today? I think you argue just to argue. Are you really some kid yanking my chain? That's what I have thought for quite a while but figure your questions and retorts are what many people actually think. Don't think you got me. I just think you represent the misinformed masses. I mean really, you can't be serious with all this. If you are then I apologize. Anyway, I said that the air car would be great for over-crowded cities in India because it IS cheap. It won't go that far and the performance will not be that good at first (see YouTube and visit the websites of the manufacturers) but it's clean and somewhat simple. I was saying that a hybrid car with a air motor would be too expensive for the Indian market. Agree? Just take the air motor and go to the wheels. Just like Tata motors. Hello?

Claiming that air cars are too expensive compared to EV's is absolute BS, and you know it.

I thought the air engine range extender was super cool so I did a little research. Here are some thoughts:

1) The piston air engine is noisy and becomes less efficient as rpms increase. The rotary air engine is more efficient and quiet but lacks the attention of well funded engineers.

2) The cost of a compressed air refueling station would be significantly less than a shipping container full of Lith-ion batts.

3) Preheating the compressed air with a small gas or diesel burner has more than doubled the estimated range of the Tata car and is now considered a requirement. This would make an E-REV a three fuel vehicle. Too complicated for the average Joe.

4) Maybe using a small air engine with a small tank and onboard compressor could help run the heat pump and/or other accessories. It could refill simultaniously when the car is plugged in. Then the accessories could run on electricity only when the air tanks are empty and by then the car would be using the ICE anyway. It might extend the range of EV mode alot in extreme weather conditions and night driving. Just a thought.

5) The best idea is to use an over unity magnetic motor. (joke)

I have a severe case of strep throat and my doctor gave me a narcotic for pain relief so I may just be completely out of my mind.

Guys, I know you really want the air engine to work as a viable range extender but there is a long way to go. It's not just the limitations due to technology but due to physical constraints and the need to follow the laws of physics. Please read the following and this will get us closer to where we need to be so we can continue our debate and maintain focus:

http://en.wikipedia.org/wiki/Compressed_air_energy_storage

"Energy density and efficiency
Compressing air heats it up and expanding it cools it down. Therefore practical air engines require heat exchangers in order to avoid excessively high or low temperatures and even so don't reach ideal constant temperature conditions. Nevertheless it is useful to describe the maximum energy storable using the isothermal case, which works out to about 110 kJ/m3-N at 24°Celsius. One m3-N is one cubic meter of gas volume at normal, i.e. atmospheric pressure, conditions. Thus if 1.0 m3 of ambient air is very slowly compressed into a 5-liter bottle at 200 bar, the potential energy stored is 583 kJ (or 0.16 kWh). A highly efficient air motor could transfer this into kinetic energy if it runs very slowly and manages to expand the air from its initial 200 bar pressure completely down to 1 bar (bottle completely "empty" at ambient pressure). Achieving high efficiency is a technical challenge both due to nonlinear energy storage and the thermodynamic considerations. If the bottle above is emptied down to 10 bar, the energy extractable is about 330 kJ. The efficiency of isothermal compressed gas storage is theoretically 100% but in practice the process is not isothermal and the two engines (compressor and motor) have additional types of losses.
A standard 200 bar 5 liter steel bottle has a mass of 7.5 kg, a superior one, 5 kg. Bottles reinforced with, or built from, high-tensile fibers such as carbon-fiber or kevlar can be below 2 kg in this size, consistent with the legal safety codes. 1 m3 of air contained inside such a full bottle has a mass of 1.2250 kg. Thus, theoretical energy densities are from roughly 70 kJ/kg for a plain steel bottle to 180 kJ/kg for an advanced fiber-wound one, whereas practical achievable energy densities for the same containers would be from 40 kJ/kg to 100 kJ/kg. Comparing to the data given for rechargable batteries, this makes the advanced fiber-reinforced bottle example comparable to the lead-acid battery in terms of energy density and advanced battery systems are several times better. Batteries also provide nearly constant voltage over their entire charge level, whereas the pressure of compressed air storage varies greatly with charge level. It is technically challenging to design air engines to maintain high efficiency and sufficient power over such a wide range of pressures. Compressed air can transfer power at very high rates, which is a principle objective of transportation prime-movers, for acceleration and deceleration; particularly for hybrid vehicles.
Advantages of compressed air over electric storage are the longer lifetime of pressure vessels compared to batteries and the lower toxicity of the materials used. Costs are thus potentially lower, however advanced pressure vessels are costly to develop and safety-test and at present are more expensive than mass-produced batteries.
As with electric technology, it must be stressed that compressed air energy storage depends on external energy sources and overall consumption can only be as "clean" as these."

I think it sums it up very nicely.

Texas,

Wiki's write-up is out of date, and their authors only optimize on the efficiency of the systems, and NOT the economics. You can rehash those obsolete arguments all you want, but customers are going to flock to these vehicles produced by Tata Motors and ZPM.

It is cheaper to buy an compressed air vehicle than a BEV.

It is cheaper to build out the infrastructure to support a compressed air vehicle than a BEV.

Given how much lighter a compressed air vehicle will be over a BEV, I suspect operation of the two vehicles would be a wash. BEV may expend energy more efficiently, but their greater weight would consume more energy. Only highway driving would be more efficient for a BEV.

I guess we will just have to take your word for it, Jason. The physics are wrong. Compressing air is the most efficient and cost effective path to take. Hummm. Why only one tiny prototype out there? Probably because nobody knows anything. You don't need to give us any calculations supporting anything or any specifics on how they work. Just say so. Nice argument. Thus, I think it's time to say... LATD (lets agree to disagree).

I guess we will just have to take your word for it, Jason. The physics are wrong. Compressing air is the most efficient and cost effective path to take. Hummm. Why only one tiny prototype out there? Probably because nobody knows anything. You don't need to give us any calculations supporting anything or any specifics on how they work. Just say so. Nice argument. Thus, I think it's time to say... LATD (lets agree to disagree).

I didn't say that compressed air was most efficient, just the most economical. Those two things aren't always closely correlated. Again, your lack of technical expertise is glaringly obvious, as you can't seem to decouple the two.

It is cheaper to buy an compressed air vehicle than a BEV.

It is cheaper to build out the infrastructure to support a compressed air vehicle than a BEV.

You can look up the prices for the Tata Motors vehicle and compare it to the Tesla Roadster yourself, no calculations needed.

As for the quantity of compressed air vehicles on the road, the engineers who designed the air piston engines spent 10 years trying to develop a configuration with enough low end torque to work. ZPM is one upping the tech by including a compressed air heater. The rotary air engine is perfect as a source to power a generator, as it will provide smooth constant power for a given rpm.

These approaches will be played out in the next few years, so you will only have to sit and watch, as EV's struggle to reduce price, and alternatives to EV's gobble up the market opportunities.

lol. You have really lost it now, Jason! If you go all the way back I said that the air car could be very inexpensive. Can't you read? I just said the performance that you get would be poor. If you were to attempt to make an air car that matched the Tesla's performance, the air car would be more expensive. That's why nobody, but your imagination, is trying to build one. Hello?

You think that air is a simple substance that is easy to work with. Sorry but just because you studied ideal gases in high school doesn't make you prepared for the real world. In the real world gases do not behave exactly isothermally or adiabatically. However, a good start would be to use the adiabatic model because of the extremely fast changes in state (compressing enough air in 5 minutes to move the Volt several hundred miles). Hate to tell you this Jason but when you compress a gas you heat it up. Sure if you do it very slowly and use the isothermal model of extracting the heat to the environment then the gas can be modeled not to gain heat. However, if you use real gases and work them extremely hard they will heat up. No, not just at the point of the compressor. Where did you get that? I'll give you a nice simple example - the bicycle pump. When you pump that baby nice and fast does it get hot? Well guess what, If you check the hoses and the tire they also get hot! Go and try it.

The example you are using where you can use massive heat exchangers to cool the compressed gas to follow a more isothermal process only works if you are using the gas at the outputted pressure. Get it? When you start with an empty tank and start up the compressor the air in the tank is at lower pressure. Lets say you stop when the air in the tank is at 100 psi. OK? Now let it sit for a while to cool it off (yes, it will get hot if you do it fast enough) now when you start up the compressor again and cool the exit air to room temperature you now begin to compress the air that is in the tank! Get it? Every time the compressor puts new air in the tank that air will be compressed further in the next compressor cycle (if it has pistons - continuously for a turbine). That is only one of the reasons the air heats up.

Again, air heats up when you compress it and cools when you expand it. If you do it very fast it's more apparent. Now let's add even more real world conditions. Since you are moving the air very quickly and moving over all kinds of imperfections you will have friction effects. Like moving a gas through a valve body at high speeds. Heats up! I think that is easy to imagine. No? You also get the transferred heat from the compressor to the air that needs to be extracted by your heat exchangers (more efficiency losses).

Jason, the reality is that air is a complex gas whose properties are deeply governed by temperature, pressure, volume, and yes time. We can start discussing enthalpy and entropy if you like but since you have not even grasped the basics of how gases behave I think that is a bit premature. Just remember the bike pump and multiply that by hundreds of times. Heat! Now if you are talking about putting an on-board compressor in the car... More Heat! Also, when you are running the car and the compressed air is being expanded you also have to deal wit the cold (expanding gasses get cold). Air is very complex. Don't "high school" it down. I didn't even get into the fact that air can hold a lot of water. If you ever tried to paint a car in the North you would understand what I'm talking about.

The main problem with using compressed air for transportation is that it needs lot's of volume, even at 10,000 psi and the heat losses due to compression make the process inefficient. Sure it works but you have to compare it to all the other options before deciding if it will be the golden child solution. Sorry, it will not be that solution. Waving your fist in the air and writing about my technical expertise are not going to change the facts.

Go ahead and say your last words on my posts and be done. Then go out and build your air car beast! Good luck, you're going to need it. The Tesla is ready and waiting your challenge.

Texas,

You are intentionally ignoring what I've told you several times. Air compression would happen slowly into a stationary reservoir, but then be quickly transfered from that reservoir to the vehicle. I know you want to stay fixated on what happens when you compress air initially, but myself and equipment makers are talking about simple high pressure air TRANSFER.

Also, you can sprinkle big thermodynamic words around in your posts, but your understanding of thermodynamics has been demonstrated to be grossly lacking - everyone has seen it now, so stop embarassing yourself.

Finally, if I were to design a compressed air vehicle to compete with the Tesla Roadster, I would have an electric drive system with plug-in supercapacitor / battery mix energy storage system and a compressed air motor generator to extend the range. That vehicle would be light, cheap, quicker and better handling than the Tesla Roadster.

You've just been schooled.

That was your comeback? Very weak and of course having no numbers or theory to support your delusions. You fail to even describe how you are going to implement this super compressed air motor extended range system that will compete against the Tesla. Range? Tank size? Cost? Nothing. You just said it will work in the face of all the other talk to the contrary. Even physics, reality, other web links, etc. Nope, Jason knows. I wonder if you're not in a straight jacket somewhere typing with your nose. You're just plain wrong, as usual.

Oh, how am I lacking in my understanding of thermodynamic principals? Perhaps you can "school me". Of course you realize there are at least two ways to get the air in the car's tank compressed to 10,000 psi. Right? You can compress on the fly or have a large tank that is at a higher pressure. Both are different animals. I love how you said:

"for this discussion, let's assume home compressor tank is significantly larger than the vehicle tank, so that the pressure drop is insignificant"

This clearly shows you have no idea how real systems work and that you have no grasp on how much energy we are talking about storing. You should realize that if you're going to pressurize an automotive tank to 10,000 psi that you have to have a big enough station tank at a higher pressure to do so. What size are you talking about? What pressures? Costs? How about for the 100 car example? Not cheap. The bigger the tank the stronger the walls have to be. You know that, right? Probably not. Just use a big enough tank and you don't have to worry about any pressure drop. Right? The reality is that the station's tanks would be extremely expensive to make very large. A real system would probably have a reasonable sized tank pre-pressurized to some level and then use an in-line compressor to get the car's tank to the 10,000 psi level. You have obviously never dealt with a 10,000 psi gas before. Not simple, not cheap. If you ever bothered to run some numbers or cost anything out you would have came to that conclusion a long time ago. Using compressed air does sound like a great and simple solution. However, when you start talking about long range and great performance the costs go way up. Why can't you grasp that?

Funny that you say I should stop using my "big words". I have always wondered how you can keep being so blatantly wrong on so many posts yet keep coming back for more. You really do think you're right! Amazing.

If I just got schooled by you then I guess my graduation gift bag should include a bag of suckers and a rubber diaper.

Texas,

If you want to understand how to pressurize multiple cars from a single tank, then go down to your local tire service shop and look at the giant air tank that they have to fill dozens of tires everyday. They don't have a compressor inline between the tank and the vehicle, and the tank has dozens of times the volume of a single tire.

You are flailing, as similar solutions exist all around, if you care to look and learn, but you don't. You are desparate for a circumstance in which air must be compressed as it is put into the vehicle, but that is not how service stations operate, so you are left empty handed - as none of your thermodynamic arguments apply.

Ever see how large the tanks are that hold gasoline beneath the ground? A similarly sized pressure vessel could be placed beneath the ground, and pumps could maintain the pressure in the tank.

Alright! We finally got a physical specification out of you. That didn't hurt, did it? Ok:

1) Tank size - same size as a standard gasoline holding tank - 10,000 to 15,000 gallons. Let's choose 10,000 gallons - easiest, cheapest. See link below.

2) Maximum Pressure - 10,000 psi Plus the delta of the minimum and maximum set points of the compressor. Non-continuous compressor operation. Unknown.

3) Compressor size - multistage, intercooled, rated at 10,000 psi Plus delta of setpoint.

4) Cost of large tank - unknown

5) Cost of compressor - unknown

Ok, now we can start the calculations! First you need to decide on the set points. You stated that it will work like a gas station tank filling up tires so that system has set points. I'm guessing you forgot about that. Since running the compressor at continuous operation would be extremely inefficient (above and beyond the huge inefficiencies due to waste heat). I'm assuming for the moment that the tank is large enough and able to remove the heat of compression fast enough so as not to cause hot air to be pumped into the cars (No heat you said).

Ok, Jason, at what pressures would you like to turn the compressor on and off. Minimum would be 10,000 plus normal pressure drops. Remember, the lower the maximum limit the closer the pump must run to continuos operation. Less time to remove the heat of compression. You can design a fancy tank (station) cooling system. However, it will add to the expense.

I hope if anyone is reading this (I'm sure just about everyone has long given up on us) that they realize that the gas station tank filling tires will not quite model what we are talking about. For one the tire pressures are only about 50 psi but sometimes they have to fill up a bike tire at 100 psi or run some power tools so they have a much higher upper limit on the compressor. If the smallest tire to be filled is 50 psi that is the MINIMUM possible setting on the compressor. If you ever ran a compressor tank at 50 psi and tried to pump up a tire to 50 psi you will realize it's not as fast as when the compressor tank is set at 100 psi. This also explains how the air motor performance decreases as the pressure in the car's tank begins to decrease. No sir! We are not talking 50 psi but 10,000 psi - that's 200 times more! Next is the volume. Just a little bit more than a car tire. No? ;)

Jason, still think this is a simple and inexpensive system? lol. You probably do. However, after you decide on the initial delta we can then know the upper pressure on the tank and you can then start the calculation. Jason, do you know anything about the factor of safety? It's just a silly thing engineers use to make sure something will not break at the intended load. Usually a factor of safety will be about 3. Thus, your huge tank will not have to just hold 10,000 psi plus the delta but must be tested and certified at a much higher pressure. I bet you will not believe how big and expensive your tank is going to be. You might just fall out of your chair! In fact, You can save yourself some effort and call up a tank manufacturer and ask them to quote you on a tank with the interior volume that you already specified - same size as a standard gas station gasoline holding tank. Give them the maximum set pressure for the compressor and wait for the answer (please let them know you are not going to buy the tank and that it's for a school project or something - don't waste their time) In the mean time please let me know what you want for the delta.

Oh, I found a picture of a 2,600 gallon tank that is rated at 9,000 psi to be used to store liquid hydrogen. Not even close to what we need - 10,000 gallons minimum and over 10,000 psi. Well, this picture is worth a thousand words but to give you an idea, the walls are 13.4 inches think of stainless steel!

http://www.prentex.com/gallery6.php

I also found a picture of your air powered Tesla killer! lol

http://www.fmcsa.dot.gov/images/nurse-tanks.jpg

Yeah, the tanks would need to be big! lol

Jason, now you know why I was talking about in-line compression more than the storage system idea. I didn't realize you were serious about the tank. I didn't realize you had no idea what you were proposing. Well, actually I kind of did. Oh, I am embarrassed... For you. ;)



Size of average gas station tank:
http://ask.metafilter.com/23497/How-many-gallons-does-the-average-gas-stations-underground-gas-tank-hold
10,000 to 15,000 gallons.

This also explains how the air motor performance decreases as the pressure in the car's tank begins to decrease.

You still don't get it. A compressed air tank in a vehicle would throttle the escaping air to a much lower pressure, so that the pressure vessal wouldn't be "running on empty" until the entire tank has reached this lower pressure.


...the walls are 13.4 inches think of stainless steel!

Today's high pressure vessals are made of carbon fiber (with an gas impermiable membrane on the inside), which is many times stronger than steel. Stainless steel is the weakest of all steels, at about 1/3 the strength of high strength steel. An engineer would know that - again, your lack of technical training is showing.


Jason, now you know why I was talking about in-line compression more than the storage system idea.

I know why you kept trying to inject compression into the process, because you've wasted your breath in countless posts trying to create a heat problem, where there is none.

No one is jumping in to save you, as they know better than me not to argue with fools.

It figures you didn't answer the question. Jason, what is the delta? Once we have that value we can then get that tank quoted. Both carbon fiber and steel (whatever material you want). It will be extremely expensive either way. You thinking what? 1/8 thick for the tank? lol. You will continue to skirt around the issue until the tank quote (for the size and pressure and now the material you specified) is provided by a licensed vendor. I think we are getting closer to the destruction of your air car dreams. Don't chicken out now. You can keep questioning my technical abilities but that's not going to change reality. Let's keep the focus. It's better for you to know now than to waste even more time on this. I know you like to move all over the place but let's concentrate on one thing at a time. Now, the tank. If the tank is doable then we can move on from there. Agree?

It figures you didn't answer the question. Jason, what is the delta? Once we have that value we can then get that tank quoted. Both carbon fiber and steel (whatever material you want). It will be extremely expensive either way. You thinking what? 1/8 thick for the tank? lol. You will continue to skirt around the issue until the tank quote (for the size and pressure and now the material you specified) is provided by a licensed vendor. I think we are getting closer to the destruction of your air car dreams. Don't chicken out now. You can keep questioning my technical abilities but that's not going to change reality. Let's keep the focus. It's better for you to know now than to waste even more time on this. I know you like to move all over the place but let's concentrate on one thing at a time. Now, the tank. If the tank is doable then we can move on from there. Agree?

The cost of the tank is certainly cheaper than building 1 MW charging stations that feed straight off the high power lines from utilities, which is what I've been stipulating this whole time - that a compressed air infrastructure is cheaper to build than a rapid recharge electric infrastructure. As for the vehicle tank, here is a quote for a 4,500 psi carbon fiber tank for $650, and that's retail, so you know that a high production volume tank intended for automobiles would be cheaper, regardless of the higher pressure / volume.

Carbon Fiber Tank quote (http://www.pyramydair.com/cgi-bin/accessory.pl?accessory_id=350)

You will be on the losing end of this argument, as we will see compressed air filling stations long before we see high power electric charging stations.

I hesitate to jump into this duel, but couldn't resist throwing in my 2-cents.

I do not like compressed air for one reason: It is not efficient. You lose energy compressing and expanding the air.

Yes, I realize that ICE engines are also not efficient, I just think investing in infrastructure for such an inefficient technology is not a good idea. If the plan is to have compressed air stations like gas stations with energy supplied by electricity, you will have to deliver even more energy into those stations than you would if they were directly filling batteries (because batteries are more efficient).

I'm not going to try to change anyone's mind, I just don't have compressed air in my dream for a future energy infrastructure.

I do not like compressed air for one reason: It is not efficient. You lose energy compressing and expanding the air.


Being a power electronics engineer, I am also quite enamoured with the idea of electrical cars. But all I've seen of air engines suggests that they can be of very high efficiency.

Here's another link - FedEx is looking at integrating this into their delivery trucks to get regenerative braking:
http://www.greencarcongress.com/2007/12/parker-hannifin.html

Being a power electronics engineer, I am also quite enamoured with the idea of electrical cars. But all I've seen of air engines suggests that they can be of very high efficiency.

Here's another link - FedEx is looking at integrating this into their delivery trucks to get regenerative braking:
http://www.greencarcongress.com/2007/12/parker-hannifin.html

Josh, thanks for this find - some people just can't handle the feasibility of mechanical energy storage systems, and this is a great example of how one can work with today's low cost tech.

Josh, thanks for this find - some people just can't handle the feasibility of mechanical energy storage systems, and this is a great example of how one can work with today's low cost tech.

I could not find a reference to efficiency in that article in a quick scan. It appeared to be a hydraulic hybrid vehicle, but I honestly did not read the article thoroughly.

I'm not saying it won't work, I'm just saying I doubt it is an efficient way of using electrical energy.

Any references to efficiency of those systems would be interesting. I've seen roundtrip battery/motor efficiency numbers in the 80-90% range. From outlet to wheels through the batteries and motor at around 80-90%. What would be the efficiency of electrical outlet to wheels in a compressed air system? I haven't been able to find a number for that.

Here is a link again to the company that Jason found earlier in this thread:

http://zeropollutionmotors.us/?page_id=43

They're claiming 106mpg

Here is a link again to the company that Jason found earlier in this thread:

http://zeropollutionmotors.us/?page_id=43

They're claiming 106mpg

I've seen that, but they are not telling you how efficient the process is going from electricity to compressed air to mechanical energy transfer to wheels. They are just talking about how much fuel is used (it's not clear from this website what the fuel is used for, normal ICE-type combustion or just heating the gas during the expansion step). Those are the numbers I can't find.

You guys still haven't figured out that air cars are a scam? Ok, I'm only half kidding. Like I said before, they may be good for some markets - like a crowded city in India but...

First, I'm going to compare the new Air Car to a very inexpensive VW Polo TDi. Why am I doing that? Well, isn't that really what the air car is doing? Think about it. The air car uses compressed air to run a piston engine. Before the air is used it's first heated with gasoline. Ok, sounds great. Use the heat energy in gasoline to expand a gas and drive a cylinder. Hummmm, sounds similar to a turbo diesel. Here's what happens there... Compressed air (compressed right there - no need to mess with an outside air compressor, external tanks, huge on-board carbon fiber tanks, losses, air compression stations, etc. - wasted energy from the engine is used to run the compressor - ingenious) is forced into a cylinder where a liquid petroleum fuel is used to heat the compressed air and that expanding air is used to drive a piston engine. Sounds strangely similar, don't you think? Texas, that's just insane! No way! Well let me give you some specifications on the two cars. One using compressed air with gas for heating (Air Car - the one given by the poster above) and the other using a turbo diesel (VW Polo TDi):

Air Car : VW Polo TDi
Weight - 1873 lbs : 2483.8 lbs Polo is 25% heavier
HP - 75 hp : 73 hp almost the same hp
Max Speed - 95 mph (other site says 70 mph) : 106 mph
Fuel economy - 106 mpg (claimed) : 72.6 mpg

Now if you look there is not that much difference. If you add about 25 percent to the fuel milage because the Polo is heavier you get around 90 mpg. Relax Jason, I'm not claiming that is correct only that you have to take into account the Polo is 25% heavier. Also, the Air Car specifications have never been verified.

Now here's the killer. The turbo diesel is very highly developed to use the fuel as efficiently as possible. Sure the Air Car will not have those heat losses with the compressed air but it WILL have those heat losses when it burns the gas to heat the compressed air. Tell me that's not the case. I dare you.

Now, you have to add the energy to compress the air in the first place. Remember, there are several things that have to go on to get the air compressed. In the Turbo diesel engine it's all right there next to the engine using wasted heat. To compress the air you have to:

1) Use grid electricity to turn an electric motor (95% efficient).

2) Connect to an air compressor to compress the air (lots of heat is generated inside of the compressor heating the air and the friction of the compressor itself adds to that heat - intercoolers will be needed. Remember that you have to compress to at least 4500 psi. This is not as simple as filling up your 100 psi tank back in the garage, folks.

3) Compress the air in a tank up to 4500 psi. The progressively introduced air further compresses the air in the tank and more heat is generated. Mechanical work is converted to heat.

4) This compressed air located in the station's holding tank(s) is then used to fill up the air tank in the Air Car. Don't forget - after you are done doing that you have to now fill up the gasoline tank! The Air Car hold 8 gallons of fuel - 2 more than the Volt!

5) Don't forget that the compressed air has to run through filters to remove debris (friction losses) must be dried using water traps (friction losses) and must be controlled with pressure and flow controls (friction losses)

What do you all think? Is all that worth the trouble? If you take into account all the energy needed to do that I'm guessing the VW would do better! The VW doesn't need any air filling station, advanced carbon fiber tanks or the space they require. Please tell me where I'm off-base using real numbers, not pulling things out of the air (PI - Pun Intended).

The Air Car is probably a complete waste of time. The cost of the carbon fiber tanks (if you go to 10,000 psi the costs go even higher) for both the cars and the air stations and the dangers they pose makes it seem like fools errand. You be the judge. Oh, did I tell you that the carbon fiber tanks, per DOT, only have a 15 year life and must be water tested every 5 years. Not sure what the regulations are going to be but there WILL be regulations. The pressures are just too high.

Later on I'm going to kill off the dream of using an air motor in the Volt for a range extender. I will also show how it will be impossible to build an air car that could compete against the Tesla! I have the numbers and the analysis that just might raise a few eyebrows. Jason, I know you are going to say it isn't so. However, let me offer you this tip before you continue with your crazy delusion... Calculate how much energy is stored in compressed air at 10,000 psi. Pull out your thermodynamic books, hit the web or ask your professor if you must. When you get that look up how much energy the Tesla can hold, or how much energy is available for the Volt's ICE (6 gallons of gasoline - 30 to 40 percent efficiency - from heat losses). I think it's time to close up the folder on this project. It's just about time to wake up from the air car dream.

I did find one reference to energy efficiency of compressed air energy storage (it's reference 1 on the wikipedia page on compressed air energy storagehttp://www.bine.info/pdf/publikation/projekt0507englinternetx.pdf). In that reference they are projecting the possibility of 70% efficiency if heat recovery is used (store the heat from the compression step to heat the gas during the expansion step). This would, in principle, allow grid energy storage using compressed air without the need to use natural gas to heat the air during the expansion. If that could be demonstrated, it would be a very cool way of storing baseline grid energy for peak demand. It's very difficult to imagine doing the same thing in a practical manner for a mobile application and there is no discussion of trying to do so that I've seen. That is why current systems use fuel to heat the gas during expansion.

Although I still don't have numbers for grid to wheels energy efficiency for a compressed air car, I can say with some level of confidence that it will be below 70%, probably well below. Long term, good for large scale grid storage where you can use heat recovery, but I'll stick with my opinion that building infrastructure for such an inefficient use of energy for cars is not a good idea compared to batteries.

Texas,

The vehicles are already selling in India and Europe, and soon North America - there is no vaporware, as they are already on the roads.

IIRC, Eaton is also working on Hydraulic Hybrids.

Here is a PDF on the Parker Hannifin Ford pickup.

http://www.epa.gov/oms/technology/420f04024.pdf

Texas,

The vehicles are already selling in India and Europe, and soon North America - there is no vaporware, as they are already on the roads.

Really? Are there test drive reports? Consumer feed back? I went to this site for Indian auto sales in the country and found nothing about air powered cars, except in a link called "Models Awaited" for the Tata Air Car that had no info about the car. http://auto.indiamart.com/auto-industry/ So then I went to the Tata Motors site and found absolutely nothing mentioning the Air Car. It's not even in the concepts shown section. If they're building it, they don't want anybody to know.http://www.tatamotors.com/landing/ After that I went to the MDI site thinking maybe they are selling them in Europe, but their site only show the MiniCAT in testing and developement and the OneCAT as a concept car. All other models are shown as artist's sketches. No mention of where to buy or road tests. Again, if they're selling these things, they don't want anybody to know. http://www.mdi.lu/eng/affiche_eng.php?page=minicats

So I must be lost. Point me to the dealership.

Funny, the MDI website is completely changed as well, and I can't find their vehicles either. It is easy enough to find all the past articles discussing their sale in distribution in India and Europe, and the YouTube videos of the piston air car driving around, but I can no longer find webpages for the vehicles themselves.

Alas, we all wake up from the air car dream. Good morning everyone. I must say, this has been an excellent discussion. It forced me to look deeply into the internal energies of different systems and to then compare and estimate approximate performance and conditions based on this simple concept:

"You can't squeeze blood from a turnip"

You cannot ask a transportation system to do more than the energy contained within it. From checking things out I have come to a few surprising conclusions. 1) Compressing air does not greatly increase it's ability to perform useful work (compared to liquid fuels or compressed hydrogen gas). 2) Carbon-hydrogen bonds have an amazing amount of energy. Gasoline has an unbelievable 124,884.4 BTUs per gallon! Compare that to liquid hydrogen at 34,947.7 BTSs per gallon. However that liquid hydrogen is 3 times lighter and it's conversion to electricity is very efficient and of course very clean. Unfortunately, storing liquid hydrogen has it's own problems but you can conclude that it would be very worthwhile to design airplanes that use liquid hydrogen as the fuel because of it's huge energy to weight ratio (1 lb of hydrogen is equivalent to 1.78 liters of gasoline)

In conclusion, when a new transportation system is proposed the first thing one should do is calculate the amount of energy the proposed design can hold. Then, based on the weight and shape of the vehicle and an estimation of the system inefficiencies you can quickly get a good feel for the possible performance. Look at possible losses of energy from friction or from the conversion of different types of energy (electrical to mechanical, chemical to heat, etc.). Remember that the change in the internal energy of a system is equal to the amount of energy added by heating the system minus the amount lost as a result of the work done by the system on it's surroundings (1st Law of Thermodynamics - conservation of energy). It can be expressed as:

change Internal Energy = change Heat - Work done by the system

If you assume a reversible process (can get back to the starting point) you can write it as:

change U = T x change in S - P x change in V

Where:

U - Internal Energy
T - System Temperature (generalized force)
S - Entropy (generalized displacement or amount of order)
P - Pressure (directed force or mechanical force)
V - Volume (directed displacement or actual physical size)

If this is interesting to you please Google thermodynamics. You can grasp the concepts in a short time with very little math knowledge but it will take a lifetime to master the details. If you want a very entertaining introduction to all things energy please check out Rick Miley's series of YouTube videos. He has a Masters in Mechanical Engineering (MSME) and the lessons are geared at the absolute beginner. He will grow on you (Thanks for the great job Rick!):

http://www.youtube.com/user/SmileyOil

Here's a highly relevant study that explores the thermodynamics of the air car charging & expansion:

http://www.efcf.com/reports/E14.pdf

Keep in mind that using fuel exhaust (from a secondary combustion chamber between the storage tank and the air motor) is a totally different game.

Joshua, Thank you for the great link. However, next time can you give that to us at the start of the thread? It would have saved me so much trouble. ;) Kidding, I enjoyed doing the analysis.

Ok, now that we have the great Ulf Bossel backing up the numbers (also check out his hydrogen economy report http://www.efcf.com/reports/E21.pdf) we can get to it. First let's take a look at the latest and greatest high pressure storage system for automobiles:

http://www.qtww.com/products/haft/hydrostorage.php

Quantum makes this unit and it can store approximately 155 liters (inner physical volume) of hydrogen (or lets assume air) at 10,000 psi (700 bar). You probably have all seen the cut-away view of hydrogen concept cars with this unit installed. If not, please take the time to get an idea of the size of this unit compared to the vehicle. It's important to know the size because when I show how much compressed air storage would be needed for different scenarios you will be more able to appreciate the quantitiy.

From Ulf's paper you can calculate that for air compressed at 10,000 psi you get the value of .108 kwh/l (20 C, 300 l, 300 bar = 51 MJ). If you multiply that by the tank size you get 16.7 kWh. Hey, that's just about the capacity of the Volt's battery! However, even if you could get anywhere near as much energy to the wheels as you can with a battery-to-controller-to-motor configuration of the Volt you would only be able to get around 50 miles of range per Quantum tank set. those things are quite big, don't you think? Just to keep from having arguments I'm going to assume that the air motor and battery have the same efficiency (even though I know the air motor is worse - as shown by Ulf).

Ok, how does this all stack up when compared to other options brought up in this thread? Not good for the Air Car, rest in peace. At the start of this thread I suggested that the Air Car would be good for something like a small over-crowded city in India. Ulf also suggests that it might be good for short range transportation. Mind you I do love the air car concept, unfortunately compressed air cannot hold enough energy to make things interesting. Let's compare by showing how many Quantum tank sets would be needed to match the requirements when air motor technology is used (remember that you get 16.7 kWh per Quantum tank set filled with compressed air at 10,000 psi):


Air Car vs. Tesla: Winner - Tesla

The Air car needs at least 3.4 Quantum tank sets! The Tesla's battery pack can hold 56 kWh of energy and that goes directly to the controller and on to the drive motor. You also get the benefit of regerative braking! I'm even being extremely generous not taking into account the air motor's minimum 15% energy losses as outlined by Ulf. Where are you going to put all those tanks? It's not like you can make a molded tank. The tank must be in approximately the current shape in order to withstand the extreme pressures. Ok, we can put one where the current battery pack sits, one in the front... Hummm. I'm guessing impossible to build. Don't forget you need room for the Air motor and it has to match the Tesla's horsepower rating! The motor must be multi-staged and intercooled at each stage, as shown by Ulf.


Air Car vs. Volt: Winner - Volt

For air car technology to be used for the range extender in the Volt at least 5 Quantum tank sets would be needed! The just-reduced 6 gallon ICE gas tank holds 219.6 kWh of energy but as we know the ICE only outputs around .40 percent of that. I'll also assume 100 percent efficiency for the air motor (I can be so generous because the game is not even close). Thus, Let's say the 6 gallons of gas has 87 kWh. Gasoline is quite amazing. Obviously this air car motor extended range concept is impossible to build but maybe if we use a trailer... I suggest we call it the Jason trailer.

I could go on about the hydrogen car but lets just say it can hold 4 - 5 kg of hydrogen in that Quantum tank and that holds an impressive 189.86 kWh! I also didn't realize just how inefficient the hydrogen to electricity conversion was but apparently it is not very good. Well, let's just say that the hydrogen filled tank can hold over 10 times the energy that the compressed air filled tank can hold. Wow! Let's call that the Jason Extreme. ;)

If you multiply that by the tank size you get 16.7 kWh. Hey, that's just about the capacity of the Volt's battery!

Here, you finally admit that you can store enough energy in compressed air on board to operate a vehicle. BTW, they usually have 3 of these tanks in the MDI Air Car. Now you can probably understand why ZPM would claim something like a 1,000 mile range by adding an air heater to the system. You also leave out how much lighter full air tanks are compared to a comparable amount of batteries for a given amount of energy storage - once again - bad science. At this point, you should be able to see how bad NiMH batteries are for transportation systems. Boy, I would hate to be the early adopter holding the NiMH bag at this stage - suckers.

As for your comparisons with the Tesla Roadster and the Chevy Volt, once again, you keep leaving economics out of the equation, to give the customer the "feasibility value" they care about. The Tesla Roadster is $100K, so no one would recover the $$$$ in saved gasoline over its lifetime. The Chevy Volt is also more expensive than the Air Car, so far more people are going to buy the Air Car, if their transportation needs are local.

I shouldn't even remind Texas of the hydraulic system that was just created to give conventional vehicles regenerative braking - it would fry his mind.


I could go on about the hydrogen car but lets just say it can hold 4 - 5 kg of hydrogen in that Quantum tank and that holds an impressive 189.86 kWh! I also didn't realize just how inefficient the hydrogen to electricity conversion was but apparently it is not very good. Well, let's just say that the hydrogen filled tank can hold over 10 times the energy that the compressed air filled tank can hold. Wow! Let's call that the Jason Extreme. ;)

Another vacuous statement from Texas. Once the serial hybrid config gets cost reduced, fuel cell vehicles will become common place. I am starting to think that rapid recharge batteries won't become a reality, so it will be the only option for consumers who want to travel beyond their vehicle's range in a day.

I'm convinced that compressing air from the grid is impractical because of the aforementioned inefficiency of air compression.

However, I do see a middle ground where air cars deliver 2-3 times the efficiency of internal combustion engines when run purely on fuel from your local gas station. Part of that efficiency improvement is reduced friction in the motor, and another part is the ability to provide regenerative braking using a small compressed air tank.

This configuration is simple and cheap, which might allow it to be offered in higher volume than a series hybrid, which in turn might allow it to save more gasoline in the end.

For someone who wants to reduce their use of petroleum, but can't afford to buy a vehicle with any type of batteries or hydrogen, the Air Car is a perfect solution. If I had teenagers, I would buy them an Air Car, because it is cheap, requires no maintenance, and I know they couldn't go very far.

and I know they couldn't go very far.

Is that why you said air car technology would be great for a range extender? Jason, I think you should stick to topics that cannot be proven wrong. Topics like politics, religion, unsolved scientific subjects, etc. These topics might never be able to be proven wrong and thus you would never have to admit that you were wrong.

I understand that you would probably rather die than to say that you were wrong. You dug your heels in so deep on this topic that you are now cornered like a rat. What does a cornered rat do? It attacks. Your inability to allow yourself to admit when you are wrong makes any debate with you worthless. That is why I no longer wish to debate with you on ANY subject. I may feel obligated to say something from time to time and will do so when I think it's necessary.

Go ahead and write your last words and talk about how untrained I am, how I use stupid formulas or that I'm a dime-a-dozen engineer (a complement by the way - even an average engineer can do amazing things) or whatever crap you wish to write. Enjoy and good luck.

Texas,

We only need to wait and see how effectively each of these technologies penetrates the markets, but you are not willing to allow technologies to compete. You want to set your own criteria for future growth and disallow anything that resides outside those criteria from competing. Clearly, you are intimidated by other possibilities and will do anything to undermine them, whereas, someone comfortable within themselves would be happy to see many ideas tried.

I find most liberals are actually illiberal, seeking to suppress contrarian points of view. There's nothing like a non-conformist who insists everyone thinks like themselves.

No, I'm only against wasting time talking about things that violate the laws of physics (unless for educational purposes) or are so impractical that diverting significant resources towards them would not only waste time but keep decision makers from doing what they are supposed to do - make decisions.

We are at a point in history where most sane people are looking for an energy transition and there are multiple options out there but no obvious silver bullet. I'm just trying to weed out the obviously bad ideas (like using compressed air as a range extender) so that everyone can focus on real, practical options.

Of course I have my favorites are you implying that you don't? However, I listen to all arguments and try to see both short-term and long-term implications of each option. I just want us Americans to come up with a workable plan and get on it. If a majority decide to go with hydrogen fuel cells and to start building out the infrastructure I would say, "Ok, a decision has been made. Let's get to work!" Even if 20 years down the road it turned out to be a poor choice we would at least have a sustainable system where we would not have to purchase foreign oil for the bulk of our transportation energy needs. Great! Of course, I would still drive a pure EV that's charged from my personal solar panels (unless an even better technology comes along) but so what. We still have some freedoms in America the last time I checked.

Coward, you only deem other alternatives as wasteful, because you don't want the feasibility of your preferred solutions to see the light of day. For policy makers to make decisions, they must see the various technologies market tested, which is what is happening today. Since a 100% BEV costs $100K, it is clear that EV's are nowhere near ready for broad acceptance in our economy, while less attractive solutions like ethanol from corn and hydrogen from natural gas is.

I do have my favorites, but having succeeded in high tech by iterating a tech through less preferred incarnations, until you reach the ultimate solution, I KNOW how to best drive a broadly accepted answer to existing problems - YOU do NOT.

Hey Lyle, What's the banning policy here? Jason has clearly lost his grip with reality. I'm sure the real juicy expletives are on their way. I can hardly wait. I have already decided to not debate with him any longer but I'm guessing he would like to continue insulting me from behind his computer screen. Anyway, I have already hit the virtual ignore button. I'm also hoping his mother takes away his computer privileges. ;)

As usual, you try to bully until you get hit back, then you scream for help from the school teacher. Bullies are the biggest cowards.

I always thought that cowards were people that insulted others on the Internet because they didn't have to worry about the consequences. I can guarantee that you wouldn't be insulting me if we were standing in front of each other. When you write something pretend you are in the same room as the other person. I played sports my whole life and always enjoyed healthy banter. However, there is a point when it's no longer healthy and it becomes down right insulting. When that happens I guess you can imagine what happens. You do understand the dynamics right?

I have my full name listed at the top of every post, how 'bout you? Further, your insistence on trying yet another intimidation tactic just reinforces that you are a bully, and used to brow beating people into compliance. Not getting any traction with me though, huh? Must be pretty frustrating for someone like you who's used to getting your way by force.

I'll let you in on a little secret - those who tried those tactics with me in person no longer get in my face, as they aren't prepared to go as far as I'm willing. Like you, they run for the school teacher.

Any and all these techs are going to be necessary to quickly move our economy from one with a severe energy trade deficit to a trade balance. Those who interfere are only trying to line their own pockets, while wrapping themselves in a thin veneer of sophistication and altruism, which you reveal yourself to be more and more each day.

How far ARE you willing to go? I'm guessing "those" who tried to get into your face but who no longer do (notice a pattern?) head for the hills because they probably realized you are slightly off kilter, ever think of that? Funny, I also have this feeling. Something like, "Oh no, he's a stalker." If I ask you real nice will you just go away? Seriously dude, take your medication!

If Texas and Jason can stop squabbling for a minute, I would like to insert some technical data.

Some good news and some bad news about compressed air energy storage.

First, the good.

If energy is cheap, compressed air beats out current generation LI batteries hands down for energy density per unit weight. See http://en.wikipedia.org/wiki/Energy_density

Note that compressed air has an energy density of 0.512 MJ/kg by weight at about 0.14 MJ/liter at 300 bar (4500 psi). Compare to LI's current density of about 0.25 MJ/kg. I think the volumetric energy density is about 0.3 MJ/L.

If you can compress the air to 600 bar (9000 psi), you about double the energy density again in both weight and volume. That's 4 times the energy density per unit weight of LI and about equal the volumetric density.

Now the bad news -
There are two problems. The first is efficient compression. Thermodynamic limitations start to kick in. About all that a state-of-the-art 4-stage inter-cooled compressor can do is 85%. This is very sophisticated industrial technology, usually reserved for compressors rated at 100's of HP.

So you might think, why can't a compressed air station just have a big tank and compressor (like they do for filling tires) and air engine owners just pull up, scan their credit card, and fill up?

Answer - filling a low pressure tank from a high pressure tank is very inefficient, energy-wise. Ultimately, my figures show that it could waste up to 50% of the energy. For those with thermodynamics training, this would be an isenthalpic, irreversible pressure reduction. This was actually a test question one of my thermo classes from long ago, so I remember it well.

Here is the way to think about it.

You put in X amount of work to compress Y lbs of air to 10000 psi in a tank. You connect that tank to a second tank that is at 0 psi. You open the valve. Air flows through the valve from one tank to the other tank until both are at 5000 psi. Let them set and assume ambient temperature again. Now you want to re-empty one tank and put the air back in the other tank at 10,000 psi again, just like you started. You will have to put in about X/2 more work to get the system back in its original state. During the filling process, you lost X/2 energy to entropy increases.

This will happen anytime you fill an empty tank from a high pressure tank through a valve. There are two ways to avoid this entropy loss. The first, and simplest, is to fill the empty tank directly with the compressor.

To fill up one 16 kW-hr air tank in 6 minutes (0.1 hours). (16/0.1)/0.85 = 188 kilowatt-motor to fill up your tank. The equivalent of your local Shell station would have to have several hundred kW of compressors to serve multiple vehicles. This gets to be pretty outrageous.

The second is to have an air turbine in the filling stream that "expands" the air to the lower pressure of the empty tank, recovering a portion of the lost work from the expansion and generating some electricity. I'm not sure how much recovery you could get, but let's just say for calculation's sake that it were 50% of available. That would reduce the entropy losses to 25%. This means the net W2W efficiency would be 0.75 x 0.85 = 63%. A lot better than hydrogen's W2W, but not as good as current technology LI batteries.

One key advantage of BEV's is that they can plug into the electric grid pretty much everywhere and re-charge, with minimal hassle and waste. The battery's high-tech, but the charging technology is mainstream.
To re-charge an air car by plugging into an outlet, you'd need a little 1 HP 10,000 psi onboard compressor (with the 4-stage intercooling).

That will take some mechanical breakthroughs that make future LI battery nanowire concepts look simple by comparison.

The second problem is trying to get more energy density out of compressed air than already available. It basically means even higher pressures. We'd have to go to 20,000 psi to get another density doubling. The storage tanks, compressors, etc. start to get pretty hairy at that pressure. the case of diminishing returns kicks in.

Compressed air does have some long-term potential in the wind-energy market, where 5 MW wind turbines could direct-drive the compressors, store the air in deep underground reservoir, and realize a bunch of efficiency improvements.

In conclusion, Jason's right about this being a pretty interesting idea, but it would be a short-term solution while power is still cheap and LI batteries are still improving. When electricity gets more pricey, W2W efficiency issues will dominate and and electro-chemical energy storage solutions will probably win-out.

hvacman,

Yes, I agree. I believe that compressed air tech will gain a temporary foothold in our vehicle markets, which will put more price pressure on battery tech. Simple emissions standards won't force people to batteries, if batteries are still expensive, so they will turn to simpler things like hydraulics and pnuematics.

Hey hvacman, nice analysis. Ah, the beautiful numbers. You sound like a man of reason. Let me ask you this... Say you have two 16 kWh drive train systems with similar final horsepower ratings (say 75 hp). These systems are installed in two cars using the same aerodynamic body and tires:

System 1 - Air Car technology (2010 expected technology):

This drive train system has the latest 10,000 psi carbon fiber tank technology, multistage intercooled air motor (need both the multistage and intercooling to get anywhere near isothermal expansion), mechanical transmission to drive wheels. It has all the electronics including digital pressure and flow control as well as all the associated high pressure lines, pumps, valves, safety systems etc.

System 2 - Battery technology (2010 expected technology):

This drive train system has the latest, safe lithium-ion battery technology (A123 or similar) contained in it's customized battery pack. It's connected to a high efficiency controller and AC drive motor. It has all the necessary connections including plug-in port, battery environmental controls, wiring, safety systems, etc.


Results Predictions:

1) Which system would have the higher volumetric energy density (remember that the entire storage system must be considered. Since giving the gas a high potential energy requires it to be constrained at extremely high pressures I feel this is a important consideration. The main tank used for the Ford hydrogen concept car has only a 5,000 psi tank but the walls are 2 inches thick of kevlar and carbon fiber (this is the only thickness data I could find). If we were to include the entire system (motor, storage, electronics, transmission, etc.) How would that change?

2) Which system would be cheaper to produce in large volumes?

3) What would be the final real-world plug-to-wheel efficiency of each system? How would this effect the operating costs of the system?

4) How far would each system go starting with a full charge(regeneration braking not considered, although essentially free for the electric system)?

5) Which system would have lower maintenance costs? Remember that current high pressure vessels transported on US streets have a life of 15 years and must be water tested every 5 years (not sure what the new regulations would be but there will be regulations).


Anyway, curious as to what you feel are the answers to these questions.

Good question(s). Sound's like something from my PE exam way back when. You aren't with the board of registration, doing a surprise re-check on my license, are you?

How about if some other engineering-type steps up to the numbers plate and takes a swing? My office manager keeps mumbling something in my ears about "billable hours". Until I can figure out how to charge GM for this analysis, it'll have to wait a bit.

Keith

Good question(s). Sound's like something from my PE exam way back when. You aren't with the board of registration, doing a surprise re-check on my license, are you?

How about if some other engineering-type steps up to the numbers plate and takes a swing? My office manager keeps mumbling something in my ears about "billable hours". Until I can figure out how to charge GM for this analysis, it'll have to wait a bit.

Keith

oops - double clicked on the reply.

Haven't run any numbers yet, but here is a link to an interesting paper that reviewed the well-to-wheels efficiency of hydrogen, LI batteries, and air. I haven't studied it much, but it may have a good start to many of the answers.

http://www.efcf.com/reports/E18.pdf

You might note that intercooling is required during compression. The air motor requires heating between stages to be isothermal.

Haven't run any numbers yet, but here is a link to an interesting paper that reviewed the well-to-wheels efficiency of hydrogen, LI batteries, and air. I haven't studied it much, but it may have a good start to many of the answers.

http://www.efcf.com/reports/E18.pdf

You might note that intercooling is required during compression. The air motor requires heating between stages to be isothermal.


Oh, my bad. I thought the multistage motor heat exchangers were still called intercoolers because they are so similar physically. What are they called? interheaters? lol. Anyway, here's what Ulf's report states:

"As expected, the highest efficiency is obtained when the expansion process proceeds close to the isothermal limit. From an energetic standpoint, the best results may be obtained by using a multistage expansion motor with heating between stages.

-Figure 7 T-s-diagram of a four-stage expansion compared to a single-stage expansion (point 4) -

The thermodynamics of a four-stage expansion with three heat exchangers has been analyzed. As the cold exhaust is released into the atmosphere, nature will take care of the final heat exchange to restore the original ambient conditions. It's assumed that all heat exchangers are sized to raise the temperature of the air exhaust of all but the last stage to 20°C. This is not easily accomplished on hot
summer days, but may be possible under cold weather conditions."


hvacman, sorry about the questions. Others can feel free to add their analysis. My intentions are actually to explore the viability of an air car for the application I originally suggested - car for a crowded city like those found in India. Reading the report that you linked to I noticed the following:

"However, because of the different densities hydrogen
compression requires 15 times more energy than air compression for identical initial volumes and identical pressure limits."

Is this correct? Anyone? It seems like a mistake. Anyway if true the hydrogen car is even worst off than I thought before. I would like to see a real-world test of this. If true, that would make the hydrogen car highly impractical (as the author states). I need confirmation! lol. Anyway, back on topic. The author then states:

"Compressed air vehicles, if engineering hurdles can be overcome, promise an efficiency equal to that of FCVs. However, the lower energy density of compressed air will limit the maximum range of such cars to values appropriate only for in-city commuting. "

That agrees with my previous post results. Compressed air has very low amounts of stored energy per volume when compared to other technologies. If I would have included all these inefficiencies in my analysis (I didn't need to in order to prove the point) it would make the number of Quantum units go up by quite a bit.

If the author is also correct in stating that his example car would go 133 km on lithium-ion but only 46 km on compressed air then the example I used in a previous post would make the 16 kWh air car highly impractical, even for city driving. The lithium-ion to compressed air drive distance ratio would be an amazing 2.9 to 1 Let me use my previous Volt example:


Volt:

16 kWh battery pack - distance traveled: Approximately 50 miles (assume the set points can be opened up slightly for BEV operation).



Air Car:

16 kWh Battery pack - distance traveled: 50 / 2.9 = 17.3 miles!


Wow, that figure along with honest answers to my previous questions would just about guarantee that we will never see a practical Air Car. I think the author may have exaggerated a bit. It just couldn't be that bad for the Air Car. Could it? I will need to see the actual data from the Tata Air Car, if it ever makes it to production, to see for myself. Anyone still feel the Air Car has a chance? Things are looking very grim.

Once again, you fail to compare the cost of a 16 kWhr battery / motor vehicle with a compressed air tank and air motor.

Below is a link to an article that shows how hydraulic systems (similar to air / pnuematic systems) are already deployed with FedEx with Eaton providing a hydraulic system for garbage trucks which is completely free of electric motors and batteries:

Link to article (http://www.nytimes.com/2008/04/27/automobiles/27TRUCK.html?_r=2&ref=automobiles&oref=slogin&oref=slogin)

As EV's come at a steep premium, we will see the proliferation of mechanical energy storage systems in heavy vehicles with lots of stop and go driving requirements.

Formula one is now using a mechanical energy storage system for their races - the flywheel:

Formula One Link (http://www.ecogeek.org/content/view/1580/69/)

All these things put price pressures on battery suppliers to compete.

Once again, you fail to compare the cost of a 16 kWhr battery / motor vehicle with a compressed air tank and air motor.

Below is a link to an article that shows how hydraulic systems (similar to air / pneumatic systems) are already deployed with FedEx with Eaton providing a hydraulic system for garbage trucks which is completely free of electric motors and batteries:

Link to article (http://www.nytimes.com/2008/04/27/automobiles/27TRUCK.html?_r=2&ref=automobiles&oref=slogin&oref=slogin)

As EV's come at a steep premium, we will see the proliferation of mechanical energy storage systems in heavy vehicles with lots of stop and go driving requirements.

Oh did I? Here's what I wrote a few posts back. Look at my questions 2 and 3:


"Let me ask you this... Say you have two 16 kWh drive train systems with similar final horsepower ratings (say 75 hp). These systems are installed in two cars using the same aerodynamic body and tires:

System 1 - Air Car technology (2010 expected technology):

This drive train system has the latest 10,000 psi carbon fiber tank technology, multistage intercooled air motor (need both the multistage and intercooling to get anywhere near isothermal expansion), mechanical transmission to drive wheels. It has all the electronics including digital pressure and flow control as well as all the associated high pressure lines, pumps, valves, safety systems etc.

System 2 - Battery technology (2010 expected technology):

This drive train system has the latest, safe lithium-ion battery technology (A123 or similar) contained in it's customized battery pack. It's connected to a high efficiency controller and AC drive motor. It has all the necessary connections including plug-in port, battery environmental controls, wiring, safety systems, etc.


Results Predictions:

1) Which system would have the higher volumetric energy density (remember that the entire storage system must be considered. Since giving the gas a high potential energy requires it to be constrained at extremely high pressures I feel this is a important consideration. The main tank used for the Ford hydrogen concept car has only a 5,000 psi tank but the walls are 2 inches thick of kevlar and carbon fiber (this is the only thickness data I could find). If we were to include the entire system (motor, storage, electronics, transmission, etc.) How would that change?

2) Which system would be cheaper to produce in large volumes?

3) What would be the final real-world plug-to-wheel efficiency of each system? How would this effect the operating costs of the system?

4) How far would each system go starting with a full charge(regeneration braking not considered, although essentially free for the electric system)?

5) Which system would have lower maintenance costs? Remember that current high pressure vessels transported on US streets have a life of 15 years and must be water tested every 5 years (not sure what the new regulations would be but there will be regulations).


Anyway, curious as to what you feel are the answers to these questions."


Well, I asked the question but did not get a response. What are your estimations of the cost of a 155 liter 10,000 psi carbon fiber tank (thickness more than 2 inches thick) with associated multi stage and multi interheated (still not sure of the name for this) air motor with associated control electronics and high pressure devices? When you are done with that tell me if that's worth the 17.3 miles you will get from that.

I'm ready to go to the minute details on this. Let's get going! From the required tank size, to operating cost. Just throw out some numbers for me. Propose the air car or range extender that you mentioned in earlier posts and let's get to work.

Oh, an now you are tying to slide yourself into an almost insignificant hydraulic / pneumatic device as a way of vindicating your original position? Do you realize that the link posted before is for a non electrical system that can store the braking energy and allow that energy to help get the vehicle moving again? A sort of a non-electrical regen system. Do you know how much energy that is? Well, get in a truck and step on the brakes. How far did you go? You will get about 75% (that is what an electrical regen system gets) of that energy back. Is that a long distance? Did I ever say that was impossible? Does that violate the laws of physics or have an unrealistic system volume? No, no, no, no and no. Shame on you.


Here, I will state it clearly:

1) A BEV will be cheaper to purchase and operate than a vehicle using air car technology. From golf cart to Tesla class. You don't think so? How about you propose a practical air car vehicle and let's work on the costs.

2) If you then propose to include a liquid fuel air heating system to the air car to increase the volume of the compressed air in order to extend range (what seems like the next plan for air car developers) then I claim it will be far cheaper to purchase and operate a vehicle that uses a turbo ICE. It will emit less CO2 as well!


Summary:

If you want an inexpensive-to-purchase and operate environmentally friendly short-range vehicle that uses no petroleum fuel buy a small BEV city car. Think Tata with a small motor and battery.

If you want an inexpensive to purchase and operate vehicle that has more range but uses some petroleum fuel buy a small turbo ICE car. Think Tata with a tiny and efficient VW turbo diesel. Do you think you will be able to heat the compressed air for the air motor using a petroleum fueled air heater better and more efficiently than the highly developed VW turbo diesel (both are mechanical devices that use compressed air and liquid petroleum fuels to expand gases to push pistons). Fat chance. You'll get more efficient use of fuel inside the cylinder of that diesel than you will outside of the cylinder with the proposed air heater.

Texas,

You can set up your strawmen as much as you want, fudging numbers to achieve your outcome - I wouldn't expect anything better of you.

As I posted above, mechanical energy systems are finding their way into Formula One and FedEx delivery fleets, and compressed air will find its place(s) as well. All these things are going to have applications where heavy and expensive battery packs just won't be feasible.

You can go hang out with all the other sideliners, who are missing out on the real innovations in this industry - people so steeped in their text books, that they can't contribute to future advancements. You will forever be a spectator of advancements, cheering only for what is provided to you, not made by you.

Well, I look forward to seeing you on YouTube driving your Air Car. For that matter I look forward to seeing any production Air Car on YouTube or anywhere else. I can't wait to see real world data. Unfortunately, I think I'm going to have to wait a while. Anyway, Good luck! Let's agree to disagree.

Link to Eaton's hydraulic series hybrid (http://www.eaton.com/EatonCom/ProductsServices/Hybrid/SystemsOverview/SeriesHydraulic/index.htm)

As a new member to this formum, I don't know which one of you started this food-fight, but knock it off. If you'd both get off the name-calling kick, you'd see that both of you post the most interesting and informative messages on the forum.

Jason, Texas' numbers look ball-park right - the odds aren't good that a straight compressed-air energy system as proposed by the Air Car will actually ever pencil out economically.

Texas, I know you may hate to hear it, but Jason's on to something here with this hydraulic concept. Very interesting.

It looks like Eaton's system actually stores energy in two closed hydraulic fluid/air compression tanks (called accumulators). As the hydraulic pump/motor increases system pressure, fluid enters the high pressure tank and compresses the air.

It taps energy by drawing hydraulic oil off the hi pressure tank, allowing the air to expand and reduce pressure. Because the tanks will be steel, have a large surface area, and are exposed to ambient air, there is adequate heat transfer to make both the air compression and expansion cycles work isothermally without all the intercooling/heating.

This is a very creative way to simplify the entire compressed air energy-storage thermodyamic cycle using off-the-shelf components and great idea for commercial vehicles. Liquids are a lot easier/more efficient to mechanically pump than gasses are to mechanically compress.

On the negative side, the energy density per unit volume will be very low, as there has to be two tanks, not one (it is a closed system), and the pressures have to work with standard hydraulic pressures in the 2000 psi range. This would limit its all-hydraulic range probably to dynamic braking energy recovery and some engine power boosting.

I'll have to see if I can dig up the operating efficiencies of hydraulic pumps and motors so we can get a W2W efficiency calc.

Keith

hvacman,

It appears that Engineair has some competition:

APT Air Engine (http://www.youtube.com/watch?v=CuKJqzFjlog&feature=related)

20krpm Wolfhart Air Motor (http://www.youtube.com/watch?v=gFbKINlXzRk)

Air cars will still find their niche. I think they would be most feasible as range extenders for PHEV's in cities demanding zero emissions vehicles.

Hydraulics find their greatest feasibility in very heavy vehicles where the equivalent battery tech would weigh tons and costs tens of thousands alone. You are correct that they will only be used as a regenerative braking / launch assist system.

one small addition - Eaton actually charges the accumulators with nitrogen. About the same performance as air without the corrosion problems.

We've looked at many ways of extending the range of the Volt:

Fuel Cells of different kinds
Compressed air
Hydraulics
Flywheels
Diesel
Gasoline
Etc.


But we've failed to see the obvious! Right in front of our face! Time tested for thousands of years.

What we need is renewable, highly efficient, reliable, reusable horse power right...?

Ok so lets use a horse. We could pull it in a trailer behind the Volt until needed. Using a small hose we could harness some of the methane and using a fuel cell convert it into electricity.
If the battery goes dead. Grab the horse out of the trailer and pull the Volt anywhere you want to go. Using slight regenerative braking during the horse pull maneuver, the main systems like AC could remain fully functional. I've done some preliminary calculations that prove this is the most efficient and environmentally friendly range extender concept.

(Sorry...couldn't help myself. I'll be seeing my phychiatrist tomorrow)

You forgot:

solar
twisted rubberband
wind-sail
nuclear fission
nuclear fusion
harnessed pigeons
reindeer
sled dogs
south pacific islanders carrying the Volt on long poles like their chief
coal-fire

hvacman,

Actually, it is possible to have a plug-in hydraulic regenerative braking system, if you have a separate electric pump precharge the hydraulic tank while the vehicle is parked. Not sure how much one could gain, but it would be cheaper than petroleum.

We've looked at many ways of extending the range of the Volt:

Fuel Cells of different kinds
Compressed air
Hydraulics
Flywheels
Diesel
Gasoline
Etc.


But we've failed to see the obvious! Right in front of our face! Time tested for thousands of years.

What we need is renewable, highly efficient, reliable, reusable horse power right...?

Ok so lets use a horse. We could pull it in a trailer behind the Volt until needed. Using a small hose we could harness some of the methane and using a fuel cell convert it into electricity.
If the battery goes dead. Grab the horse out of the trailer and pull the Volt anywhere you want to go. Using slight regenerative braking during the horse pull maneuver, the main systems like AC could remain fully functional. I've done some preliminary calculations that prove this is the most efficient and environmentally friendly range extender concept.

(Sorry...couldn't help myself. I'll be seeing my phychiatrist tomorrow)

Eric, Now that's thinking outside the box. lol.

...and if we go with a cow-based version, GM could call it the People-Mooover.

Sorry, just had to milk it for one more joke. Time to stop beating a dead horse.

...and if we go with a cow-based version, GM could call it the People-Mooover.

Sorry, just had to milk it for one more joke. Time to stop beating a dead horse.

with the cow based version, you could also install a methane based generator!

The formal phrase for that type of methane generation is "enteric fermentation". It is actually considered a major source of global warming.

The People Mooover would be a huge hit in the dairy industry. An earth-friendly, bio-grass-powered dairy vehicle that delivers both farm-fresh milk and garden fertilizer while reducing global warming. And if they cross the Guernsey with the Holstein, it would literally be a "hybrid". And the device to collect the methane gas would give new meaning to "plug-in".

Help....this thread's going downhill fast ....

Help....this thread's going downhill fast ....

... then stop posting, as you serve only as Texas' crutch, when he needs a PE to back up his BS.

I provided a couple responses to your posts, to which you didn't even respond:

1) I showed two youtube videos of new air motors beyond what engineair has offered

2) I posited that a separate plugin electric compressor could actually charge a hydraulic system while parked

Feel free to regain focus at any time.

Supercapacitors like Maxcell's Boostcap (http://www.maxwell.com/ultracapacitors/products/modules/bmod0063-125v.asp) with a 2 - 5KWh battery is a better solution than hydraulic for regen/partial acceleration only in heavy duty vehicles. They need a little voume to bring the price down.

Supercapacitors like Maxcell's Boostcap (http://www.maxwell.com/ultracapacitors/products/modules/bmod0063-125v.asp) with a 2 - 5KWh battery is a better solution than hydraulic for regen/partial acceleration only in heavy duty vehicles. They need a little voume to bring the price down.

Perhaps, but, as you say, cost is always the problem with battery / cap tech.

... then stop posting, as you serve only as Texas' crutch, when he needs a PE to back up his BS.


Jason is poking a stick in the back of Texas who is hard at work at his desk. Hair all askew with dark circles around his eyes from lack of sleep Texas gently swats away the stick and without turning from the hundreds of papers haphazardly shuffled about the desk says with a low comforting voice, "Jason, stop bothering me and go play with your air car." Jason's face twists up with dissatisfaction as he turns and skips out of the room. "I'll show him!", he says under his breath.

Perhaps, but, as you say, cost is always the problem with battery / cap tech.

The large format ultracapacitor modules are very new and extremely low volume to this point and battery cost has always been a problem but that is debatable today. While these costs can reasonably be expected to continue to drop, low tech cost won't change much. The high power, high cycle demands of heavy duty urban vehicles like buses, garbage trucks, etc are ideally suited for the capacitor/high power battery configuration. I must confess to not having much knowledge of Maxwell or Nesscap costs, but their recent agreements give the impression those costs are coming in line.

The large format ultracapacitor modules are very new and extremely low volume to this point and battery cost has always been a problem but that is debatable today. While these costs can reasonably be expected to continue to drop, low tech cost won't change much. The high power, high cycle demands of heavy duty urban vehicles like buses, garbage trucks, etc are ideally suited for the capacitor/high power battery configuration. I must confess to not having much knowledge of Maxwell or Nesscap costs, but their recent agreements give the impression those costs are coming in line.

Batteries, supercaps and fuel cell tech may very well win out, but fortunately, hydraulic, pneumatic and flywheel techs compete in a way that forces the price of battery, supercap and fuel cell tech to get low or die - gotta luv free markets.

More evidence that pnuematic systems are cheap and readily available now:

Air assist vehicles (http://www.chicagotribune.com/business/chi-mxa0504aircarsmay04,0,3345883.story)

Folks, don't get lost in the Air Car scam. Please research this entire thread before you jump on the bandwagon.

Firstly, nobody is denying how important compressed air is for certain applications. I love compressed air and use it almost every day. I spray paint with it, run other pneumatic tools like drills, sanders, etc. I have also used it extensively for automation projects. It's clean, fast acting and powerful. You can design pneumatic circuits much like you design electrical circuits. Please Google pneumatics to get a basic idea of how this works.

However, what I am saying is that compressed air cannot hold much energy. If you read this forum you will see exactly how little energy it can hold when compared to other storage systems like liquid fuels, hydrogen, batteries, etc. I love compressed air but you will not see a practical air car that has any sort of usable range ever. A few may be produced and sold but they will never compete with plain turbo diesels, BEVs, or hybrid electrics.

Compressed air is not the solution for our transportation problems. They might be used for a non-electrical regen system or even a small boost system. Why? Compressed air is amazing! Wonderful! I love and use it almost every day! It's a shame that it has very low energy density. Fact of life. No amount of research can change that fact. Many people cannot give up the Air Car dream but I think if you get all the facts and run a few calculations you will see the truth.

Compressed air ... might be used for a non-electrical regen system or even a small boost system.

At least you are finally conceding the usefullness of compressed air for transportation applications where the benefit is obvious even to small children.

Now, the next step is to get you to understand the concept of feasibility vs. efficiency. Batteries are efficient, but not affordable, and therefore, they are not currently feasible for most car buyers. Compressed air is not as efficient as batteries, but the low cost of the vehicle and the compressed air makes them feasible for a segment of the market. As I've stated before, if I had driving aged children, I would buy them a compressed air vehicle, because their top speed is low and the fuel, maintenance and insurance is cheap.

Jason, Please show me where I said compressed air is not useful for anything. Good luck. I just said it's not useful for powering a practical car (not just for a few miles) or that it's impossible for use as a range extender. You still feel it will work! Baffling!

That said, I stand by my prediction that you will not see a practical Air Car. Time will tell. I don't want to start up another silly argument with you. I feel one way you feel the other. let's check back in 5 years and see who had a better understanding of energy.

If you stop telling people compressed air is the next great thing in car transportation I'll stop reminding them of compressed air's energy storage limitations. How about you hold off until one car is released that people can test? Is that too much to ask?

If a couple automakers are already going to field compressed air vehicles in which the compressed air motor is the primary drive source, then the use of a compressed air motor as a range extender is, without question, feasilble, because one only needs 70 hp continuously to recharge a small battery pack for good performance. When one plugs in to recharge the small battery pack, they would also be running a compressor to charge the air tanks.

Fine, let's just wait and see when these cars come out and are independently tested. According to you I should soon be proven wrong.

Just to add my kick to this dead horse, even assuming this would make a car that performs well with long range, it's a terrible waste of energy due to the losses in compression/decompression.

Just to add my kick to this dead horse, even assuming this would make a car that performs well with long range, it's a terrible waste of energy due to the losses in compression/decompression.

Certainly, through higher efficiencies, there is an opportunity for batteries to provide lower fuel (electricity) costs per mile, so the air motors will be putting price pressure on the upfront cost of batteries, so that batteries will be able to compete on overall costs.

You have to think of the power that the air motor brings to the marketplace by putting price pressures on other alternative forms of transportation energy. I like the Tesla Roadster, the Aptera, the Volt, etc., but I don't want consumers to face a steep upfront costs of BEV's and series hybrids. The poor are once again stuck with the worst choices, but air cars give them a feasible alternative to keeping their old chevy's on the road.

Certainly, through higher efficiencies, there is an opportunity for batteries to provide lower fuel (electricity) costs per mile, so the air motors will be putting price pressure on the upfront cost of batteries, so that batteries will be able to compete on overall costs.

You have to think of the power that the air motor brings to the marketplace by putting price pressures on other alternative forms of transportation energy. I like the Tesla Roadster, the Aptera, the Volt, etc., but I don't want consumers to face a steep upfront costs of BEV's and series hybrids. The poor are once again stuck with the worst choices, but air cars give them a feasible alternative to keeping their old chevy's on the road.

Good point.

Thanks for pointing me to this thread Jason... But I didn't know I was going to find another "cat fight" between you and Texas :p

Anyhow, I almost read all the comments.

For me the application of Air motors is for a RE, yes it's not the most efficient way to store energy, that's why we have battery, but it a cheap way to acheive it and 0 emission as a bonus.

Some of the Air motor talked here are more or less efficient to transpose that energy.

But I think is worth trying instead saying it can't work.

Thanks for pointing me to this thread Jason.

No problem.


For me the application of Air motors is for a RE, yes it's not the most efficient way to store energy, that's why we have battery, but it a cheap way to acheive it and 0 emission as a bonus.

But I think is worth trying instead saying it can't work.

Amen, brother.

See today's New York Times story

http://www.nytimes.com/2008/07/09/business/worldbusiness/09greencar.html?ex=1373256000&en=3a9a8a42affd240d&ei=5124&partner=permalink&exprod=permalink

The Air Car's first use will be as a "tethered" transport, used by businesses or parents who like that the vehicle is extremely low maintenance, troube-free, cheap to buy and operate and can't go very far from home.

See today's New York Times story

http://www.nytimes.com/2008/07/09/business/worldbusiness/09greencar.html?ex=1373256000&en=3a9a8a42affd240d&ei=5124&partner=permalink&exprod=permalink


Here is what your article claims:

"Mr. Negre’s engine will be offered as an option in Tata Motor’s new production model, the Nano, next year. The Nano, a minicar with an ultralow price tag, was introduced in January and is primarily aimed at the Indian market. Mr. Negre said a full tank of compressed air would cost about $3 and provide about 200 kilometers, or 125 miles, of driving. The tank could be filled by gas station compressors used for inflating tires, or a built-in compressor powered by plugging in to an electrical outlet, he said."

Do you really believe that? I hope not because it's impossible. There is no way on earth you can get enough pressure from a gas station compressor to get enough energy to travel 125 miles into tanks that would fit in that car. It's a physical impossibility. What are standard gas station compressors normally rated at? 200 psi? 300 psi? He should have said by specially built and extremely expensive compressors. The on-board compressor will need to run for many hours just to get 10 km worth of energy (wonder how they will deal with the massive amount of generated heat). I'm looking forward to seeing this air motor option and the market acceptance of it. I predict complete and utter failure. Let's place our bets on this as well. One dollar anyone? Let's review the success of the air car when we review the hydrogen vs. quick-charge battery battle in 5 years.

Tex,

Put me down for another dollar.

but, thanks to PV = nRT, releasing compressed air makes cold. That means that air conditioning systems should be really cheap in this car!

but, thanks to PV = nRT, releasing compressed air makes cold. That means that air conditioning systems should be really cheap in this car!

I guess Canadian brethrens and other more northerly folks would now freeze much more quickly inside this car when airconditioning are seldom ever needed. Compressing the air will revive them, but then decompressing the air would freeze them slowly, :D

I guess Canadian brethrens and other more northerly folks would now freeze much more quickly inside this car when airconditioning are seldom ever needed. Compressing the air will revive them, but then decompressing the air would freeze them slowly, :D

The compressed air is not passed through the cabin. It moves from the tank, through the motor and out the exhaust.

The compressed air is not passed through the cabin. It moves from the tank, through the motor and out the exhaust.


Oh, Jason. You do realize that the engine's required heat exchangers are going to be extremely cold don't you? Just like a current ICE is hot and needs to be thermaly issolated from the cabin yet is used for cabin heating the air motor will also need to be thermally issolated and can be used to cool the cabin. Will be welcomed in the hot areas around India. ;)

The on-board compressor will also need to be thermally isolated because it will extremely hot during the several hours of operation needed to fill up the compressed air tanks.

Sorry, but you just can't get away from the laws of thermodynamics.

Interesting discussion on the thermodynamics and efficiency of compressed air energy storage. Link (http://canada.theoildrum.com/node/3473#more)

hvacman,

You do like to use a lot of kerosene with your fires, don't you?

Interesting discussion on the thermodynamics and efficiency of compressed air energy storage. Link (http://canada.theoildrum.com/node/3473#more)



Nice article and great comments afterwards. I like how pumped storage hydro is becoming so popular as a viable energy storage system. One glaring thing that was not brought up (or I didn't see it) is when comparing the costs of pumped storage hydro to batteries you have to look at the life time of each. Once you build the pumped storage hydro facility it can produce for hundreds of years! The batteries? Not so much. ;) The turbines in the hydro plants now use water bearings and they last almost forever! Very rugged and proven performance all around the world.

It is amazing how much people talk about things they know so little about. I own a commercial paintball field and I have a Bauer 6000 p.s.i. air compressor. I have 4 large tanks attached to the compressor that holds 1800 cubit feet of compressed air. When the tanks were empty it took the compressor 5 hours to completely fill the tanks to a pressure of 4500 p.s.i. I use the compressor every week and it takes 30 minutes to fill the tanks back to 4500 p.s.i. when the pressure drops to 4000 p.s.i. I fill small paintball tanks with the larger tanks and it takes 10 seconds to fill a 48 cubit inch tank to 3000 p.s.i. This pressure will shoot 500 to 600 rounds of paintballs (depending on the marker).

I have actually thought about using my system to run an air motor, but I could not find a motor that was efficient enough to make it worthwhile. I hope this information helps.

It is amazing how much people talk about things they know so little about. I own a commercial paintball field and I have a Bauer 6000 p.s.i. air compressor. I have 4 large tanks attached to the compressor that holds 1800 cubit feet of compressed air. When the tanks were empty it took the compressor 5 hours to completely fill the tanks to a pressure of 4500 p.s.i. I use the compressor every week and it takes 30 minutes to fill the tanks back to 4500 p.s.i. when the pressure drops to 4000 p.s.i. I fill small paintball tanks with the larger tanks and it takes 10 seconds to fill a 48 cubit inch tank to 3000 p.s.i. This pressure will shoot 500 to 600 rounds of paintballs (depending on the marker).

I have actually thought about using my system to run an air motor, but I could not find a motor that was efficient enough to make it worthwhile. I hope this information helps.





It's amazing how people can talk so much and not say anything. ;) I guessing maybe a few of us are trying to figure out what you are trying to say. Are you saying that because you have experience with filling up paintball guns that you are qualified to justify the viability of an air-car drivetrain? To be honest, from your post I'm not even sure if you are for or against the idea! The first paragraph seems like you are for it and the second seems like you are against it. So, dear enlightened compressed air physicist please fill the void caused by our ignorance. If you could, please use real thermodynamic principles. I know that since you can shoot 500 rounds of paintballs with compressed air you might be temped to conclude that a two ton car can be driven around the around the world but when you do the math the size of the required tanks makes the dream a nightmare. It's all about the energy. From shooting paintballs to shooting rockets into space they all have to follow the laws of thermodynamics.