Rocket Propulsion Elements, 9th Edition

CHAPTER 9LIQUID PROPELLANT COMBUSTION AND ITS STABILITY

In this chapter, the complexities of combustion chamber phenomena found in liquid bipropellant thrust chambers are treated. We describe combustion behavior and its analysis in general terms, together with several types of combustion instability with their resulting undesirable effects, and discuss semiempirical remedies on how to avoid these effects. An objective here is to operate at very high combustion efficiencies while preventing any occurrence of disruptive or destructive combustion instabilities. Thrust chambers need to operate with stable combustion over a wide range of operating conditions. Further treatment of these subjects can be found in Refs. 9–1 to 9–7.

Liquid propellant combustion is very efficient in well‐designed thrust chambers. Combustion efficiencies of between 95 to 99.5% are typical, in contrast to turbojets or ordinary furnaces which may range from 50 to 97%. Such high efficiencies stem from the very fast reaction rates at high combustion temperatures resulting from the thorough mixing of fuel and oxidizer (from proper injection flow distributions, uniform atomization, and turbulent gas diffusion). Losses arise from nonuniform mixture ratios resulting in incomplete burning or inadequate mixing. Combustion efficiencies can be well below 95% in very small bipropellant thrust chambers or small gas generators because their injectors lack sufficient injection orifices or elements for proper mixing.