6 ms·
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
by smanek 18y 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.html 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.
- elad 18y agoMaybe 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 18y agoFiberglass 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.
- olefoo 18y agoOr use the compressed air to fill a whole vehicle airbag that triggers on items on a collision path. This would mean that your safety systems are highly dependent on software and effective sensors, but hey, cheap car.
- elad 18y agoIt would also mean that your level of protection depends on the amount of air in your tank. As someone who chronically forgets to fill-up, I wouldn't like that idea...
- khafra 18y agoThe Quasiturbine engine can be run on compressed air, and in transportation applications, it should (http://qtusa.promci.qc.ca/QTEfficaciteComparative.html 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.
- tx 18y agoI 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.