ABSTRACT
Hybrid propellant rocket engine (HPRE) has certain characteristics that are different from solid-propellant rocket engine (SPRE) and liquid-propellant rocket engine (LPRE). The grain configuration plays an important role in deciding the level of thrust and thrust law, apart from the composition of propellants. Combustion instability is an important and difficult phenomenon that can occur in that case of hybrid rocket engine. The chapter describes low-frequency combustion instabilities, which can be divided into three categories, namely, feed system coupled instabilities, chuffing, and intrinsic low-frequency instabilities (ILFLs). It considers a typical liquid oxidizer and solid fuel hybrid rocket engine, which consists of a combustion chamber, a nozzle, a liquid propellant tank, a propellant feed system, an atomizer and an igniter. In the case of solid fuel grains with a high metal loading or a heavily sooting fuel, heat transfer to the fuel grain surface due to thermal radiation plays a very important role that affects the regression rate of the fuel grain.
