PRINCIPAL AND INDEPENDENT COMPONENT ANALYSIS OF HYBRID COMBUSTION FLAME

Hybrid rocket engines are a promising technology for a variety of applications, due to their advantages with respect to solid and liquid propulsion systems. However, their use has been hindered in the past due to the low regression rate performance associated with classical polymeric hybrid fuels. The discovery of high regression rate hybrid fuels has renewed the interest in hybrid rocket propulsion. The increase in regression rate is caused by a different combustion mechanism, which still needs to be fully understood. Since 2013, many optical investigations on the so-called liquefying hybrid fuels have been done at the German Aerospace Center, Institute of Space Propulsion in Lampoldshausen, Germany, in order to better understand the mechanism responsible for droplet entrainment. The liquid layer combustion process of paraffin-based fuels in combination with gaseous oxygen has been visualized with different optical techniques in a two-dimensional single slab burner. Tests have been performed under both sub- and supercritical pressure conditions. The fuel slab configuration and composition and oxidizer mass flow rate have also been varied to understand their influence on the phenomenon. The latest results of this research are presented and discussed in this work. In all of the tests, the flame is characterized by a wave-like structure, whose frequencies and wavelengths are determined by using decomposition algorithms. Droplet formation is observed mainly during the transients. At elevated operating pressures, the flame becomes unsteady and highly turbulent. Many flame bursting and blowing events are also visualized.