Calorific values of LPG and CNG:
Compared to gasoline-powered vehicle, CNG powered vehicles are safer and more efficient. CNG is cheapest, cleanest and so less impacting on the environment. As CNG is lighter than air it distributes faster and proportionately in air.
Both CNG and LPG, because of presence of methane gas that burns readily in air and having low ignition temperature, have the risk of catching fire when the nozzle of the cylinder is left open or in case of any kind of leakage. The storage space required for the cylinders that are kept in isolation for their safety in both the types of gases is more compared to liquid fuels. In both the gases, the consumption is more as compared to liquid fuels like petrol and diesel. Moreover, extra modification of vehicle is required for installation of CNG cylinders in the vehicles.
LPG was thought to be an only clean fuel till the arrival of CNG. Nowadays CNG has replaced most of the petrol and diesel run vehicles. Also, CNG has been accepted as a clean fuel but due to its volatility in nature they have not been used as cooking gas, since it has high auto-ignition temperature (540°C) and a narrow range of flammability of 5 to 15%.