CNG engine use in India

http://en.wikipedia.org/wiki/Compressed_natural_gas

CNG is CNG and not an engine. It is an alternative fuel. There is a coversion kit (98% Italian) and it automatically starts your engine on petrol and immediately switches to CNG.

The switch-over switch gives you the option to switch over from CNG to petrol & vice versa.

When they say there are bringing out 3-wheelers/4-wheelers on CNG, it means the kit is factory fitted and you've paid for it else, you take the 3/4-wheeler to a Conversion Centre and covert to CNG by paying USD 500/-.(which comprises of a conversion-kit,switch-over switch and a storage cylinder mounted inside your car trunk with complete job work).

In a 4-wheeler the storage cylinder capacity lets you drive 85-90 Km till you refill again.That means you go out to your work and return back home filling from gas station.When you go to the gas station there are min. 8 cars ahead of you in line so you've to take the time factor - a disadvantage but an advantage since it is 65% cheaper than petrol.In a 3-wheeler the storage cylinder is small so 3-wheeler has to go more frequent to filling. In a 2-wheeler there is no place to put the storage cylinder . Some fabricated their own storage cylinder (more like a hand-held fire extinguisher type) but who'd pay USD500 for the kit and run 10 times in day to fill CNG, so it was found not viable on a 2 wheeler.

Yes the power on CNG is less compared to petrol but you get used to it while driving since you are saving 65% on your monthly petrol account.