Heat release parameter

In combustion, heat release parameter is a dimensionless parameter which measures the amount of heat released by an adiabatic combustion process. 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, 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