Performance and Analysis of Vortex Oxidizer Injection in a Hybrid Rocket Motor

Abstract

Abstract : A hybrid rocket motor is a type of rocket motor where fuel is placed in a combustion chamber as a solid, and then gaseous or liquid oxidizer is injected. When the two mix and are ignited, the surface of the fuel burns and the gases produced in the combustion develop thrust. Hybrid rocket motor performance is dictated by the rate at which the fuel burns. Fuel burn rate (or regression rate) can be increased by increasing oxidizer flow speed over the burning fuel surface. This is because flow over the burning surface creates shear stress which facilitates fuel and oxidizer mixing. One method for improving shear stress and thus regression rate is to induce an oxidizer vortex in the combustion chamber. The subject of this research is a method for inducing vortical flow that combines vortex and axial oxidizer injection within a cylindrical, interior burning fuel grain. A hybrid motor test stand has been developed to test both axial and vortex oxidizer flow configurations as well as any combination of the two. The apparatus is capable of measuring thrust, oxidizer flow rate, and chamber pressure. This, along with physical measurements of fuel grains, allows the determination of fuel regression rate, combustion efficiency, and specific impulse, all key rocket performance parameters. The apparatus is also equipped with millisecond scale combustion analyzers to measure the gases in the combustion products, to include CO, CO2, NOx, and unburned hydrocarbons. The high sample rate of these analyzers sheds light on vortex hybrid combustion processes as well as the phenomenon which could lead to combustion instability. Overall, this research is focused on identifying a possible way to increase hybrid rocket performance in order to bring this very safe and efficient type of propulsion to maturity.