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