Fuel mass fraction

In combustion physics, fuel mass fraction is the ratio of fuel mass flow to the total mass flow of a fuel mixture. If an air flow is fuel free, the fuel mass fraction is zero; in pure fuel without trapped gases, the ratio is unity. As fuel is burned in a combustion process, the fuel mass fraction is reduced. The definition reads as


 * $$Y_F = \frac{m_F}{m_{\rm{tot}}}$$

where
 * $$m_F$$ is the mass of the fuel in the mixture
 * $$m_{\rm{tot}}$$ is the total mass of the mixture