In combustion, heat release parameter (or gas expansion parameter) is a dimensionless parameter which measures the amount of heat released by an adibatic combustion process.[1][2] It is defined as

where
is the adiabatic flame 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

Gas expansion ratio
The gas expansion ratio is simply defined by

which is related to
by 
References
- ↑ Williams, Forman A. "Combustion theory." (1985).
- ↑ Linan, Amable, and Forman Arthur Williams. "Fundamental aspects of combustion." (1993).
- ↑ Clavin, P. (1985). Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Progress in energy and combustion science, 11(1), 1-59.