Undergraduate Research on Peculiarities of the Combustion of Ecologically Clean Paraffin Wax Fuels in Hybrid Propellant Rocket Engines

Abstract

The paper describes the student-faculty research of the combustion of non-conventional bio-derived fuels in a lab-scale Hybrid Propellant Rocket Engine (HPRE). The long-term goal of the senior capstone project is to study specific features of combustion of nonconventional bio-derived hybrid propellant rocket fuels such as paraffin, beeswax, and lard, which are non-toxic and non-explosive with different oxidizers. Combustion of above fuels with additives (aluminum powder) was studied as well. The study was concentrated on the obtaining of regression rates (velocities of the combustion) for the listed propellants, and investigating losses of melted unburned bio-derived fuels. Such fuels could replace conventional toxic and explosive fuels, and are planned to be used on the NASA sounding rockets. A lab-scale HPRE, test fixture and instrumentation system have been designed, manufactured, assembled and used for the research and analysis of combustion. More than 60 tests were performed to study the specific features of combustion using paraffin and bee's wax. The results of the study were presented at 51 st AIAA Meeting and Exhibits, and SciTech, 52 nd Aerospace Sciences Meeting. This paper summarizes 2013/14 research results on the combustion of paraffin and paraffin with aluminum powder; represents new findings, such as regression rate formulas for paraffin wax combustion with 10% of aluminum powder obtained for two different diameters of the grain ports; the paper also illuminates the study of the losses of unburned paraffin wax and discusses novel methodology of the prediction of losses of unburned fuel based on the measurements of the temperature of the exhaust plum of combustion products. Nomenclature T-Thrust, N e u -Velocity of combustion products at nozzle exit, m/s e A -Exit area of the nozzle, m 2 e p -Pressure at the exit of the nozzle, Pa P -Pressure in the combustion chamber, psig a p -Ambient pressure, Pa k -Mass oxidizer-to-fuel ratio st k -Stoichiometric mass oxidizer-to-fuel ratio 1 Professor, 2 Figure 1. Simplified diagram of HPRE Figure 2. Simplified schematic of the combustion in HPRE 2 R -Gas constant sp I -Specific impulse m/s or s f m  -Mass flow rate of fuel, kg/s ox m  -Mass flow rate of oxidizer, kg/s p m  -Mass flow rate of propellant, kg/s f G -Average mass flux of fuel through the grain port, g/cm 2 s ox G -Average mass flux of oxidizer through the grain port, g/cm 2 s p G -Average mass flux of propellant through the grain port, g/cm 2 s i A -Cross-sectional area of injector, m 2 a -Jet coefficient m u -Velocity on the axis of the plume of the combustion products, m/s  r -Regression rate, mm/s in d -Initial port diameter (before fuel burnout), cm fin d -Final port diameter (after fuel burnout), cm * A -Nozzle throat area, m 2  -Specific heat ratio