Calorific Value (CV)

Calorific value is the quantity of heat energy released when a unit mass or volume of fuel undergoes complete combustion with oxygen. It is the single most important specification for any fuel — gaseous, liquid, or solid — because it determines how much useful energy a buyer receives per rupee paid. Two conventions exist: Gross Calorific Value (GCV), also called Higher Heating Value (HHV), counts the latent heat released when water vapour in the combustion products condenses to liquid; Net Calorific Value (NCV), or Lower Heating Value (LHV), excludes this latent heat because the water vapour normally exits as exhaust before condensing.

For gaseous fuels the value is expressed in MJ/Nm3 (megajoules per normal cubic metre at 0 deg C and 1 atmosphere), while solid and liquid fuels use MJ/kg or kcal/kg. Typical Indian benchmarks: raw biogas at 60% methane has a GCV of around 21-23 MJ/Nm3; compressed biogas at 90%+ methane reaches 35-40 MJ/Nm3, matching fossil CNG; natural gas sits at 38-42 MJ/Nm3; LPG at 46 MJ/kg; diesel at 45.5 MJ/kg; tyre pyrolysis oil at 38-42 MJ/kg (close to industrial fuel oil); and carbon black at 28-32 MJ/kg.

The methane fraction directly governs biogas calorific value because methane carries 35.8 MJ/Nm3 (NCV) while CO2 contributes zero. A simple linear relationship holds: NCV of biogas in MJ/Nm3 is approximately 35.8 multiplied by the methane fraction. This is why upgrading from 60% to 90% methane raises energy density by 50%, allowing the same cylinder volume to deliver 50% more vehicle range.

NCV is the standard basis for pricing CBG, CNG, and PNG in India, and for calculating engine fuel efficiency. SATAT contracts denominate CBG in kilograms with an implicit minimum calorific value tied to the IS 16087:2016 methane specification. Producers who fail to meet calorific value incur penalty deductions; consistently undershooting can trigger contract termination.