Injection Effects in Hybrid Rocket Engines

Abstract

There exists a growing interest in Hybrid rocket engines over the last years. Lots of research has been done on hybrids in general and on topics like combustion efficiency and stability in detail. But only minor work has been done on the design and performance of the injector type. This is especially important since combustion stability can be closely linked to the type of injector and configuration of the pre-combustion chamber. In the present paper a detailed review on earlier work regarding combustion stability has been done. Hot flow experiments have been carried out to evaluate the performance of different injector types including impingement, showerhead and swirl injectors. Characteristic velocity, ISP efficiency and regression rates during hot fire tests are evaluated and compared. Combustion stability is evaluated by means of Fast-Fourier Transformations and spectrograms of the pressure signals. Impingement injectors with high impingement angles produce unstable flow fields which excite vortex shedding and the Helmholtz acoustic mode of the combustion chamber.