Air–fuel Ratio

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	\(\large{lbm}\)	\(\large{kg}\)