# Air–fuel Ratio

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Air–fuel ratio, abbreviated as AFR, is the mass ratio of air to fuel mixture present in an internal combustion engines. Because it is a ratio, it is unitless.

## Air–fuel ratio formula

 $$\large{ AFR = \frac {m_a} {m_f} }$$

### Where:

$$\large{ AFR }$$ = air–fuel ratio

$$\large{ m_a }$$ = air mixture

$$\large{ m_f }$$ = fuel mixture