CHARACTERISTIC LENGTH AND COMBUSTION EFFICIENCY OF ALUMINIZED SOLID FUEL FOR HYBRID ROCKET

Abstract

This study investigates the effects of enlarged aft-chamber volume of a hybrid rocket and of aluminum powder added to solid fuel. To confirm the aluminum powder ignition, we conduct flame temperature analysis and scanning electron microscopy (SEM) analysis of the residue. Solid fuel used for the experiment is microcrystalline wax and 3 μ.m aluminum powder. Combustion experiments are conducted with three aft-chamber lengths of 55, 75, and 115 mm. Only one length of solid fuel is used. Results demonstrate that the regression rate tends to increase by adding aluminum powder. Furthermore, a high regression rate is obtained in the region of low oxidizer mass flux. However, the increase in the aft-chamber does not affect the regression rate. The combustion efficiency increases concomitantly with increased aft-chamber volume and increased characteristic length. Addition of the aluminum powder raises the rate of increase of combustion efficiency against the characteristic length. Under the characteristic length conditions used for this study, the combustion efficiency is low and insufficient. When aluminum powder is added, temperature analysis shows a rise in the flame temperature near the nozzle exit. By analyzing the residue around the nozzle after combustion using SEM, we confirmed the presence of shells of aluminum particles that had been ignited and burned. Temperature analysis and SEM analysis results suggest that the aluminum powder ignited and burned. However, Al powder ignition is not a phenomenon occurring only in the combustion chamber.