In combustion, heat release parameter (or gas expansion parameter) is a dimensionless parameter which measures the amount of heat released by an adiabatic combustion process. [1] [2] It is defined as
where
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
The gas expansion ratio is simply defined by
which is related to by