Infrastructure:

Unlike CNG, LPG does not require elaborate and expensive pipeline networks for distribution. CNG distribution is done via pipelines where the gas is supplied to the dispensing stations from a central pumping station under high pressure. LPG on the other hand is transported in tankers and can be stored in stand-alone facilities. LPG dispensing equipment is simple & cheap and can be operated with minimum support infrastructure. The dispensing of LPG is done from storage tanks at the pump and is not dependent on pipelines or gas pressure like CNG.

Filling Time:

Based on the pressure, the waiting time for filling of CNG varies, and usually customers have to wait in long queues for their turn. It takes between 4-5 minutes to fill each car with a tankful of CNG. Further, the filling time increases with the decrease in quantity of fuel in the storage tank. LPG, on the other hand, has a much faster filling process and takes about 2-3 minutes at the most (like Petrol & Diesel).

Weight & Space:

CNG cylinders are bigger and heavier as they need to store compressed gas (which is much less dense than LPG) under high pressure. In small vehicles, fitting a large 12 Kg CNG cylinder will leave no room for any luggage at all. Additionally, a 12 Kg CNG cylinder filled with 10 Kg of gas will weigh close to 100 Kg. All that weight behind the rear axle means the car will bottom out quiet frequently, especially with 5 people on-board. LPG cylinders are thinner and smaller, as the fuel is stored in liquid form inside the cylinder at much lower pressures. For the same volume, LPG requires a tank that is 1/3 times that of CNG. Toroidal Cylinders are also available which fit snugly into the spare wheel well of the car.

Power:

Small cars like the Maruti Alto have an engine bhp of 46 and torque of 62 Nm. With CNG about 15% of that peak power is lost, which would equate to a 39 bhp petrol engine. With LPG, the power loss is lesser at about 10%, which makes it equivalent to a 41.5 bhp petrol engine. The usage of LPG does not necessitate a sacrifice in power. Also, since LPG is pressurized at a mere 5-7 bars, it does not require drag inducing heavy tanks, which is the bane of CNG. With CNG, as the quantity of gas reduces in the tank, engine power also reduces simultaneously and pressure creating systems have to be installed in order to maintain engine power at optimum levels (thereby adding to the cost of conversion to CNG). On the other hand, LPG does not face this problem of power reduction right until the last drop is consumed. LPG has a better calorific power of 66.1 Mega Joules per Kilogram as compared to CNG (47.7 Mega Joules per Kilogram).

Safety:

Unlike CNG, which is pressurized at 200 bars, LPG is pressurized at 5-7 bars, which makes it as safe as conventional fuels. The automotive use of LPG has an excellent safety record and various crash tests and fire tests have proved that, owing to the strength and integrity of the fuel tank, it is safer than petrol and at par with diesel. The conversion of vehicles to LPG should only be undertaken by a competent person working in accordance with the prescribed standards.

Cost of Conversion:

CNG kits are more expensive than LPG kits owing to an additional number of parts and the CNG storage tank. A good LPG kit for a car like a Maruti Alto or Wagon-R will cost about Rs. 25,000, while a good sequential CNG kit for the same will cost about Rs. 40,000.