FREQUENTLY ASKED QUESTIONS
What is CNG?
CNG stands for Compressed Natural Gas. It is a gaseous fuel and is a mixture of
hydrocarbons, mainly methane in the range of 95%. Due to its low density, it is compressed
to a pressure of 200 bar to enhance the vehicle on-board storage capacity.
Is CNG Safe?
Yes, it is safe. The properties of CNG make it a safe fuel. It is lighter than air, and
hence in case of leakage it disperses into the atmosphere rapidly. Its high auto-ignition
temperature of 540 degrees centigrade as against petrol’s 360 degrees centigrade makes it
even more safe fuel. CNG also has a narrow inflammability range of 5% to 15%, making it much
safer than other fuels.
Which type of vehicles can be converted into CNG ?
All spark-ignited engines can be converted to CNG, for which a specially designed conversion
kit is required for the conversion process. The kit consists of a cylinder to be fixed in
the boot of the car and other equipment’s to allow gas flow into the engine.
Can a car, which is fitted with CNG kit, run on petrol after its CNG gets over?
Yes, after conversion to CNG the vehicle can run on petrol whenever desired simply by
flicking a switch on the dashboard.
What are the dimensions and weight of a CNG cylinder?
CNG cylinders are manufactured from a special steel alloy and are seamless in construction.
Their compact size allows them to easily fit into a small car. An empty CNG cylinder with a
50 litre-water-carrying capacity weighs 48 kg (approximately), and has a length of 835 mm
and a diameter of 316 mm. The 50 litre capacity cylinder is the one most regularly used in
CNG kits but cylinders with 45 litre, 55 litre, 60 litre and 65 litre capacity are used as
well.
What is the capacity of a cylinder, and mileage from one fill? How does one get to know the
quantity of CNG left in the cylinder?
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
kms. for a medium sized 1300 CC car. An electronic fuel gauge fitted on the dashboard which
is part of the conversion kit indicates the quantity of CNG left in the cylinder.
What is the pressure of CNG in a cylinder? Is refuelling of a cylinder safe, given the pressure?
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 bar. 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 (CCoE). 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 extremely high pressure
and temperature.
Will my fuel expenses reduce after conversion to CNG?
Yes, the fuel bill on the basis of average running of vehicle reduces substantially when
compared to other conventional fuels. Price of CNG is lesser than other fuels and also it
enhances the mileage of your vehicle, making it the most economical fuel.
Will I lose my boot space if I convert my car to CNG?
On an average, vehicle owners lose about one third of their boot space when a car is
converted to CNG. The boot space also depends upon the size of vehicle and cylinder make.
However people who wish to convert to CNG can still install carriers on their vehicles to
compensate for the lost boot space.
Does CNG have any harmful effect on the engine?
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. As CNG enters the engine in the form of a gas
(and not as a spray or mist like other fuels), no carbon is generated during the combustion
of CNG reducing the chances of wear and tear.
Is CNG environmentally friendlier than any other fuel?
Yes, it is. As CNG mainly consists of methane which is the simplest hydrocarbon, it is a
much cleaner and efficient fuel. The use of CNG significantly reduces harmful exhaust gas
emissions like carbon monoxide, nitrogen dioxide and sulphur dioxide which causes harmful
diseases like cancer, asthma etc. CNG also helps in reducing the effects of global warming.
Are cylinders used for filling CNG safe?
Cylinders used for storing gas are designed with very high safety factor in accordance with
global standards. These cylinders are tested and certified for usage by statutory
authorities and each cylinder is defined with an expiry date of usage after which they are
to be tested again for safe use. These cylinders have been designed to take impact of
collision in case of accidents. However, as per Gas Cylinder Rules, 1981, the cylinder
should undergo hydro-stretch testing every 3 years to check pressure tolerance.
Does CNG kit require servicing ?
CNG kit is safe and simple. It 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.
Impact of CNG kit on the payload of a vehicle.
Factory fitted CNG vehicles have the same payload that of a diesel vehicle, however in case
of retro fitment payload of the vehicle is reduced to the tune of cylinders weight only.