First viable compressed air car: get 200-300km per tank of air.
businessweek.com
businessweek.com
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.
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.
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.
This would mean that your safety systems are highly dependent on software and effective sensors, but hey, cheap car.
As someone who chronically forgets to fill-up, I wouldn't like that idea...
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.
Oh yeah I feel safe already. I wonder what its crash rating will be?
For similar reasons I don't get the fuss about electric "zero-emission" cars. Zero? Like electricity just magically comes out of nowhere...
"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.
"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...
But if you assume the problem is "How can we relieve market pressure on our most constrained resource?", air and electric cars are a solution. The hope is that by diversifying the sources of energy used for transportation, we can continue to use oil for other purposes that we haven't found cost-effective replacements for yet -- like plastics and jet fuel.
So while the cars won't solve the energy crisis by themselves, maybe they'll buy us enough time to reach the "then a miracle occurs" discovery that does solve it. Or, failing that, maybe they'll help civilization make a slow transition to reduced consumption, rather than a sharp crash.