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Discussion Starter #1
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.
 

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Discussion Starter #3
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.
 

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Crazy Idea

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.
 

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Discussion Starter #5
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.
 

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I think this needs to be thought through

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.
 

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Discussion Starter #7
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.
 

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Discussion Starter #8 (Edited)
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.
 

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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.
 

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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.
 

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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.
 

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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.
 

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Discussion Starter #14
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.
 

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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.
 

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Discussion Starter #16
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.
 

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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...
 

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Discussion Starter #20
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.
 
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