CNG is a form of bio-gas and its combustion produces petty low harmful gases on contrast with petrol and diesel.
It is lighter than air and disappears when evolved in atmosphere. In India the effective use of CNG can be seen in several cities and states like Delhi, Lucknow, Kanpur and many more.
CNG is compatible only with the CNG supportive vehicles. In present days the manufacturing of all kind of vehicles is done with the provision of petrol/diesel as well as CNG supported mechanism.