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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

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

where

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

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

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

The ratio of burnt gas to unburnt gas temperature is

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

Gas expansion ratio

The gas expansion ratio is simply defined by

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

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

See also

• Zel'dovich number

References

1. Williams, Forman A. "Combustion theory." (1985).
2. Linan, Amable, and Forman Arthur Williams. "Fundamental aspects of combustion." (1993).
3. Clavin, P. (1985). Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Progress in energy and combustion science, 11(1), 1-59.

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