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

${\displaystyle \alpha ={\frac {T_{b}-T_{u}}{T_{b}}}}$

where

• ${\displaystyle T_{b}}$ is the burnt gas temperature
• ${\displaystyle T_{u}}$ is the unburnt mixture temperature.

In typical combustion process, ${\displaystyle \alpha \approx 0.7-0.9}$. For isobaric combustion, using ideal gas law, the parameter can be expressed in terms of density,^[3] i.e.,

${\displaystyle \alpha ={\frac {T_{b}-T_{u}}{T_{b}}}={\frac {\rho _{u}-\rho _{b}}{\rho _{u}}}.}$

The ratio of burnt gas to unburnt gas temperature is

${\displaystyle {\frac {T_{b}}{T_{u}}}={\frac {\rho _{u}}{\rho _{b}}}={\frac {1}{1-\alpha }}.}$

See also

• Zel'dovich number

References