# Why is the maximum adiabatic temperature found for an equivalence ratio a bit higher than 1?

Why does the peak adiabatic temperature usually happen for an equivalence ratio a bit higher than 1? I think it had something to do with the probability of each fuel molecule finding a corresponding oxidizer, and the fact that the molecular weight of the fuel is generally higher than that of the oxidizer.

• Just a guess, but is it because nitrogen in the air is inert, and you have to "waste" a bit of the heat from combustion to heat it up? It's a small effect, relative to the heat of combustion, so my guess is the the max temperature would be ever-so-slightly to the carbon-rich side of the equivalence ratio. Jul 10, 2015 at 6:05
• > [...] $\phi = 1.1$ was chosen because the flame temperature for many fuel peaks not at the stoichiometric value but between $\phi = 1.0$ and $\phi = 1.1$ owing to lower mean specific heats of the richer products. The maximum temperature for acetylene-air peaks, for example, at a value of $\phi = 1.3$.$^{[1]}$ ## References 1. Irwin Glassman, Richard A. Yetter, Combustion, 4th ed; Academic Press: New York, 2008 Apr 13, 2021 at 13:07