First viable compressed air car: get 200-300km per tank of air.

http://www.businessweek.com/autos/content/mar2007/bw20070319_949435.htm?chan=rss_topDiscussed_ssi_5

by gscott • 18 years ago

22 18 18 years ago

smanek• 18 years ago

Compressed air has great power density, but awful energy density. I.e., you can unload power very quickly from it but can't store much at all.

Looking at this http://www.popularmechanics.com/automotive/new_cars/4217016.... popular mechanics article, this engine uses 340 Liters of air (under STP) compressed at 4350 PSI.

If my math is right, that only provides a theoretical maximum of about 55 MJ of energy, which is about the same as about 1.5 liters of gasoline.

A combustion engine runs at about 20% efficiency and, if memory serves, compressed air engines at around 30%. But let's give MDI the benefit of the doubt and assume their engines are 50% efficient.

That means this car claims to be able to go 200-300KM (125-185 miles) on the equivalent of about 4 Liters (or 1 gallon) of gasoline.

Now, getting 150 miles/gallon isn't physically impossible, but it seems pretty difficuly and does raise some red flags to me. And that's assuming they have a 50% efficient engine, which is extraordinarily unlikely. Assuming a 30% efficient engine, this car is doing the equivalent of 250 miles/gallon.

elad2• 18 years ago

Maybe part of the explanation is that it's very light-weight - the car in the photo looks tiny, it says it's made of fiberglass, and my guess is that the engine must also weigh much less than a comparable internal combustion engine (you don't need as much metal to contain the combustion...).

Of course, that probably comes with a heavy price to passenger safety. Fiberglass won't give you any protection in a crush. That may be the reason why Tata is involved and not some European manufacturer. The Euro market has some serious safety regulations.

mynameishere• 18 years ago

Fiberglass won't give you any protection in a crush

Damn, just put the tank of air in front. Any wreck will cause a mighty explosion balancing out the various vectors involved. I haven't done (and couldn't do, really) the math, but this seems perfectly reasonable.

khafra2• 18 years ago

The Quasiturbine engine can be run on compressed air, and in transportation applications, it should (http://qtusa.promci.qc.ca/QTEfficaciteComparative.html) have better than 50% efficiency.

But great power density and awful energy density sounds like something an engineer should work with a little before declaring viability: A hybrid design with some other power source having high energy density, even if it can't deliver it very quickly.

tx3• 18 years ago

I suspect you're underestimating efficiency of both types of engines. Diesels, for instance, are always above 30% and air-compressed should be a lot higher: they don't have an enormous energy loss in a form of heat compared to diesels.

tx3• 18 years ago

Ok, we won't be burning gasoline in a vehicle, we'll be burning it to compress air when refueling.

For similar reasons I don't get the fuss about electric "zero-emission" cars. Zero? Like electricity just magically comes out of nowhere...

jcl2• 18 years ago

Most likely we wouldn't be burning gasoline to compress air for these cars: gas is expensive. Instead, we'd probably use electricity derived from coal, natural gas, or nuclear, with the possibility of better sources in the future.

"Zero-emission" is a reasonable description, as the car itself doesn't give off emissions while running. If you're going to include the emissions given off in the process of producing the fuel, a gasoline-based solution is suddenly much worse, as you need to include the emission costs of finding, extracting, refining, and transporting the gas.

asp742• 18 years ago

It's like software. If you cleanly separate the front-end and back-end it's very easy to tune and swap out the back-end without the user noticing.

tx3• 18 years ago

Like your analogy! :) The bigger picture is that we're approaching an energy crisis. That's why gas is getting more expensive, and that is why there is even an interest in these cars to begin with: the message isn't to "separate front end and back end" but to appeal to people who want to save money on energy costs, i.e. gasoline. But it won't work, because gasoline is just the medium, the real beef here is energy, and it's not going to get cheaper because we need more and more of it. It's not only gasoline that's getting expensive, my gas and electric bills are ahead of inflation as well.

"Solutions" covered by the press aren't really solving the problem, they're just shifting it around. "Wow! We have an air-powered car!" - without an explanation where the energy to compress that air is going to come from...

run4yourlives2• 18 years ago

Not all of us burn stuff to make electricity. In BC, all our power is hydro.

rw• 18 years ago

What we don't need are more dams in our waterways.

softwarejim• 18 years ago

"tubular chassis that is glued not welded"

Oh yeah I feel safe already. I wonder what its crash rating will be?

dmix• 18 years ago

That felt like reading a press release.

First viable compressed air car: get 200-300km per tank of air.

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