In combustion, heat release parameter (or gas expansion parameter) is a dimensionless parameter which measures the amount of heat released by the combustion process.[1][2] It is defined as
where
is the burnt gas temperature
is the unburnt mixture temperature.
In typical combustion process, . For isobaric combustion, using ideal gas law, the parameter can be expressed in terms of density,[3] i.e.,
The ratio of burnt gas to unburnt gas temperature is