Zeldovich number

${\displaystyle \beta ={\frac {E_{a}}{RT_{b}}}\cdot {\frac {T_{b}-T_{u}}{T_{b}}}}$

where

• ${\displaystyle E_{a}}$ is the activation energy of the reaction
• ${\displaystyle R}$ is the universal gas constant
• ${\displaystyle T_{b}}$ is the burnt gas temperature
• ${\displaystyle T_{u}}$ is the unburnt mixture temperature.

In terms of heat release parameter ${\displaystyle \alpha }$, it is given by

${\displaystyle \beta ={\frac {E_{a}}{RT_{b}}}\alpha }$

For typical combustion phenomena, the value for Zel'dovich number lies in the range ${\displaystyle \beta \approx 8-20}$. Activation energy asymptotics uses this number as the large parameter of expansion.

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