There is an interesting futurist website entitled “Evolution Shift” authored by David Houle that recently reported on “the Air Car.” If you haven’t yet heard of the Air Car, from Moteur Developpment International in France, you aren’t alone. We’d heard of MDI’s Air Car, but when we set out to really research the development, we learned there is a surprising lack of information available, other than a handful of online forum commentaries and the company’s own website.
Apparently the car’s engine runs on compressed air, and the prototype is reputed to have a range of several hundred kilometers. In recent months, the company website has announced a hybrid design – on their “how it works” page they claim the engine now has the ability to run on gasoline or air, or a combination of both. This is all very interesting, but let’s focus on the notion of compressed air as a way to store energy to propell a vehicle. How much energy can you store?
Basically, if you expend a certain amount of horsepower-hours (1.3 horsepower hours = one kilowatt-hour) pumping air into the tank, at a certain efficiency – say 90% – for the compressor, then that amount of energy is available to turn the wheels. Any more than that is creating energy from nothing.
One way to store hydrogen on a vehicle is to compress the gas into a pressure vessel, and when we looked at the energy required to compress hydrogen to 5,000 PSI, the energy we expended to compress the gas was equivalent to 5% of the energy in the hydrogen, and the biggest 5,000 PSI tank we could find for a vehicle (it was 24″ diameter, 28″ long, and weighed 600 pounds) only held 4.0 kilograms of hydrogen, containing energy of about 700,000 BTUs. This suggests a large 5,000 PSI tank of air would hold (.05 x 700,000) about 35,000 BTUs, which is the energy equivalent of less than a third of one gallon of gas. Even at 100% efficiency releasing compressed air into the air car’s motor to create traction, this will not give you any meaningful range.
The Air Car claims to have a unique engine design, and perhaps there are engineering innovations in this design that will have utility for stretching combustible fuels – but when it comes to running a car on compressed air, consider me a giant skeptic.
What is significant about Houle’s post is his comment “What the compressed air car points to is the fact that humanity has the technological capability of solving our energy problems as they relate to transportation.” Whether or not cars will ever run on compressed air – they probably won’t – is missing this point. Automobiles are poised to make a technological leap as significant as Henry Ford’s Model T. Over at General Motors, VP of R&D Larry Burns calls it “the new automotive DNA.”
We are on the verge of seeing the automobile completely reinvented – with zero pollution and using flexible sources of fuel, of course, but also with radically improved safety features, and autopilot. That innovations such as the air car are being experimented is one example of the unfolding revolution in automotive transportation. The automobile age is about to get very, very interesting.