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

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

Gas expansion ratio

The gas expansion ratio is simply defined by

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

which is related to ${\displaystyle \alpha }$ by ${\displaystyle r=1-\alpha .}$

See also

• Zel'dovich number

References

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