Previous Year Question

Compressed Natural Gas (CNG) is essentially Natural Gas compressed to a high pressure. Compression does not fundamentally change its chemical composition; its principal hydrocarbon remains Methane (CH₄).

Under the Indian IS 15958:2012 specification for automotive CNG, the minimum Methane content is prescribed as 90%. The same specification limits the amounts of Ethane and higher hydrocarbons.

Methane is the simplest alkane. Its molecular formula is CH₄, consisting of one Carbon atom bonded to four Hydrogen atoms.

Ethane, Propane and Butane may occur in Natural Gas in smaller quantities, but they are not the principal constituent of CNG.

A useful distinction is between CNG and LPG. CNG is predominantly Methane-rich gas, whereas LPG is mainly associated with Propane and Butane.

CNG is also used as a vehicle fuel because its combustion can produce comparatively lower particulate and certain other pollutant emissions than conventional petrol or diesel.