Theoretical and Experimental Analysis of Liquid Layer Instability in Hybrid Rocket Engines

Abstract

Combustion behavior of different hybrid rocket fuels has been analyzed in the frame of this research. Tests have been performed in a 2D slab burner configuration with windows on two sides. Four different liquefying Paraffin-based fuels, Hydroxyl Terminated Polybutadiene (HTPB) and High-density Polyethylene (HDPE) have been tested in combination with gaseous oxygen (GOX). Experimental high speed video data has been analyzed manually and with the Proper Orthogonal Decomposition (POD) technique. Application of POD enables the recognition of the main structures of the flow field and combustion flame appearing in the video data. These results include spatial and temporal analysis of the structures. For liquefying fuels these spatial values can be related to the wavelengths associated to the Kelvin Helmholtz Instability (KHI). A theoretical long-wave solution of the KHI problem shows good agreement with the experimental results. Distinct frequencies found in the POD analysis can be related to vortex shedding phenomena and acoustic combustion oscillations.