Frequently Asked Questions (FAQs) on CNG


All spark-ignited engines can be converted to CNG, but a specially designed conversion kit is required for the purpose. The kit consists of a cylinder to be fixed in the boot of the car and other equipment to allow gas flow into the engine.


Yes, even after conversion to CNG, the vehicle continues to be fitted with the petrol carburetor and fuel tank. The vehicle can therefore run on dual fuel, either on CNG or petrol, whenever desired,simply by flicking a switch on the dashboard.


The cost of converting a vehicle to CNG depends on its type and make. Broadly, it varies between Rs 30,000 to Rs 50,000 (approximately).


CNG cylinders are manufactured from a special steel alloy and are seamless in construction. Their compact size allows them to easily fit even in a small car. An empty CNG cylinder with a 50 litre-water-carrying capacity weighs 48 kg (approximately), with a length of 835 mm and a diameter of 316 mm. The 50 litre capacity cylinder is the one most regularly used; cylinders with 45 litre, 55 litre, 60 litre and 65 litre capacity are used as well.


A cylinder with a 50 litre water-carrying capacity is capable of carrying approximately 9 kg of CNG. This is equivalent to 12.5 litres of petrol and will allow a run of about 150-160 km to a medium-sized 1300 CC car. An electronic fuel gauge fitted on the dashboard as part of the conversion kit indicates the quantity of CNG left in the cylinder.


CNG cylinders are designed and built in such a way so as to withstand high pressure. The maximum pressure in a CNG cylinder is up to 200 kg/cm2 (g) (about 2840 pounds per square inch (gauge) or psi[g] ). CNG cylinders are safe as they are manufactured as per specific requirements and tested before use,in accordance with international specifications and standards, and are duly approved by the Chief Controller of Explosives. Moreover, they are provided with a pressure relief device (PRD) that consists of a fusible plug and a burst disc that ruptures in case of inadvertent high pressure and temperature.


CNG kit gives years of trouble-free operation. It doesn't require frequent servicing. Just as for all other fuels, it is advised to have routine services. An authorized person should be consulted for service. As per Gas Cylinder Rules, 1981, the cylinder should undergo hydro-stretch testing every 3 years to check pressure tolerance.


Owing to CNG's distinct features, it does not contaminate or dilute crankcase oil, giving a new lease of life to the engine. The absence of any lead content in CNG helps avoid lead fouling of plugs, thereby enhancing plug life. One of the important benefits of CNG is that upon entering the engine in the form of a gas (and not as a spray or mist like other fuels), it doesn't disturb the presence of lubricating oil in the engine, and reduces chances of wear and tear.


CNG is an environment-friendly fuel. The natural gas is mainly composed of methane and its exhaust emissions consist of water vapour and a negligible fraction of carbon monoxide. The absence of carbon and other particulates result in negligible amount of harmful elements in exhaust fumes.


CNG provides easy starting, reliable idling and smooth acceleration. The acceleration of a CNG vehicle is a bit slower, which is due to a power loss of 5-15%. This can be minimized by proper tuning on CNG (e.g. advancing the spark timing) to take advantage of the high octane rating of the fuel.

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