Stoichiometric Air–Fuel Ratio

Theoretical AFR from elemental composition: AFR = (11.53·C + 34.34·(H − O/8) + 4.32·S) / 100, for mass fractions expressed in percent.

CombustionFuel

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Formula, assumptions, and limits

AFR_\text{stoich} = \frac{11.53 C + 34.34 \left(H - \tfrac{O}{8}\right) + 4.32 S}{100}

Symbol	Meaning	Unit
$C$	Carbon mass %	% m/m
$H$	Hydrogen mass %	% m/m
$O$	Oxygen mass %	% m/m
$S$	Sulphur mass %	% m/m
$AFR$	Stoichiometric air-fuel ratio	kg air / kg fuel

Source: Heywood - Internal Combustion Engine Fundamentals

Theoretical AFR from elemental composition: AFR = (11.