
MDI has developed two types of piston engine powered by the expansion of compressed air: one runs on compressed air alone, the other uses liquid fuel to supplement the compressed air. Under 50kph (31mph) it uses air only. Over that speed the on-board compressor refills the compressed air tanks.
The existing MiniCat vehicle has a horizontally-opposed 800cc four cylinder engine.
The above details were extracted from various on-line sources, mainly Green Car contress.
To find out more, put >> tata air car << into Google and you will find many reports and articles on this interesting subject.