Air–fuel Ratio

on . Posted in Fluid Dynamics

Air–fuel ratio, abbreviated as AFR, a dimensionless number, is the mass ratio of air to fuel mixture present in an internal combustion engines.  Because it is a ratio, it is unitless. Fuel doesn't burn on its own. It has to be mixed with air. AFR tells you how many parts of air are mixed with each part of fuel. For example, a 12:1 AFR (or just 12) means the mixture is 12 parts air to one part fuel. Gasoline engines typically run around 14.7 AFR.


Air–fuel ratio formula

\(\large{ AFR = \frac {m_a} {m_f} }\)
Symbol English Metric
\(\large{ AFR }\) = air–fuel ratio \(\large{dimensionless}\)
\(\large{ m_a }\) = air mixture \(\large{lbm}\) \(\large{kg}\)
\(\large{ m_f }\) = fuel mixture \(\large{lbm}\) \(\large{kg}\)


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Tags: Power Equations Air Equations