Liquid Layer Combustion Instabilities in Paraffin-Based Hybrid Rocket Fuels

Abstract

Hybrid rocket engines are a promising technology for a variety of applications, but their use has been hindered in the past due to some disadvantages derived from the characteristic diffusive flame mechanism. However, most of these drawbacks can be solved through a correct design process. In particular, the recent discovery of the so-called liquefying fuels allows to obtain higher regression rates due to a different combustion mechanism. The liquid layer combustion process of paraffin-based fuels in combination with gaseous oxygen has been visualized with different optical techniques in a 2D single slab burner at both sub- and super-critical pressure conditions. Fuel slab configuration and composition and oxidizer mass flow rate have been varied to understand their influence on the phenomenon. In all the tests, the flame is characterized by a wave-like structure, whose frequencies and wavelengths are determined by using decomposition algorithms. At elevated operating pressures, the flame becomes unsteady and highly turbulent.