Fuel mass fraction

This article is about combustion. For flight vehicle fuel weight, see fuel 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.^[1] As fuel is burned in a combustion process, the fuel mass fraction is reduced. The definition reads as

${\displaystyle Y_{F}={\frac {m_{F}}{m_{\rm {tot}}}}}$

where

• ${\displaystyle m_{F}}$ is the mass of the fuel in the mixture
• ${\displaystyle m_{\rm {tot}}}$ is the total mass of the mixture