Editing Hybrid-propellant rocket (section)

== Combustion==
The governing equation for hybrid rocket combustion shows that the [[Hybrid Rocket Fuel Regression|regression rate]] is dependent on the oxidizer mass flux rate, which means the rate that the fuel will burn is proportional to the amount of oxidizer flowing through the port. This differs from a solid rocket motor, in which the regression rate is proportional to the chamber pressure of the motor.<ref name=Humble_etal_1995/>

:<math>\dot{r}=a_oG^n_o</math>

:where <math>\dot{r}</math> is the regression rate, {{mvar|a}}{{sub|o}} is the regression rate coefficient (incorporating the grain length), {{mvar|G}}{{sub|o}} is the oxidizer mass flux rate, and {{mvar|n}} is the regression rate exponent.<ref name=Humble_etal_1995/>

As the motor burns, the increase in diameter of the fuel port results in an increased fuel mass flow rate. This phenomenon makes the oxidizer to fuel ratio (O/F) shift during the burn. The increased fuel mass flow rate can be compensated for by also increasing the oxidizer mass flow rate. In addition to the O/F varying as a function of time, it also varies based on the position down the fuel grain. The closer the position is to the top of the fuel grain, the higher the O/F ratio. Since the O/F varies down the port, a point called the [[stoichiometric]] point may exist at some point down the grain.<ref name=Humble_etal_1995/>