Heat release parameter

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. It is defined as

$q={\frac {T_{ad}-T_{u}}{T_{u}}}$

where

• $T_{ad}$ is the adiabatic flame temperature
• $T_{u}$ is the unburnt mixture temperature.

In typical combustion process, $q\approx 2-7$. For isobaric combustion, using ideal gas law, the parameter can be expressed in terms of density, i.e.,

$q={\frac {T_{ad}-T_{u}}{T_{u}}}={\frac {\rho _{u}-\rho _{ad}}{\rho _{u}}}.$

The ratio of burnt gas to unburnt gas temperature is

${\frac {T_{ad}}{T_{u}}}=1+q.$

Gas expansion ratio

The gas expansion ratio is simply defined by

$r={\frac {\rho _{u}}{\rho _{b}}}$

which is related to $\alpha$ by $r=1+q.$

See also

• Zel'dovich number