In combustion, heat release parameter (or gas expansion parameter) is a dimensionless parameter which measures the amount of heat released by an adiabatic combustion process. It is defined as
q = T a d − T u T u {\displaystyle q={\frac {T_{ad}-T_{u}}{T_{u}}}}
where
T a d {\displaystyle T_{ad}} is the adiabatic flame temperature
T u {\displaystyle T_{u}} is the unburnt mixture temperature. In typical combustion process, q ≈ 2 − 7 {\displaystyle q\approx 2-7} . For isobaric combustion, using ideal gas law, the parameter can be expressed in terms of density, i.e.,
q = T a d − T u T u = ρ u − ρ a d ρ u . {\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
T a d T u = 1 + q . {\displaystyle {\frac {T_{ad}}{T_{u}}}=1+q.}
Gas expansion ratio The gas expansion ratio is simply defined by
r = ρ u ρ b {\displaystyle r={\frac {\rho _{u}}{\rho _{b}}}}
which is related to α {\displaystyle \alpha } by r = 1 + q . {\displaystyle r=1+q.}
See also Zel'dovich number
References