Understanding regression rate characteristics of CO2 as an oxidizer compound in paraffin based hybrid rocket motors

Abstract

CO2 is considered as a major combustion product in nature. However, CO2 can only burn with metallic powders due to high reactivity levels of metals compared to carbon. Therefore, Metal/CO2 combustion mechanism can be a potential propellant candidate for Mars Ascent Vehicles. In-situ CO2 can be used in Mars atmosphere reduces required Earth-based propellant mass. Propellant combination in this hybrid rocket motor consist of paraffin wax based solid fuel including metallic aluminium and magnesium. CO2 is mixed with N2O in various percentages by mass as the motor oxidizer. The goal of this research is to understand the maximum CO2 percentage by mass can be ignited with selected propellant combination (classical hybrid rocket motor). Maximum CO2 is achieved as 75% in oxidizer mixture by using 60% Magnesium 40% Paraffin solid fuel. Oxidizer flow rate at 75% CO2 is obtained as 60 g/s. Aluminum based solid fuels has maximum CO2 percentage of 50%. Magnesium provides better ignition characteristics with CO2. Therefore, the ignition boundary in mass flow rate vs. CO2 percentage is presented for both Al and Mg fuels. Regression rate characteristics does not change with the addition of CO2 in nitrous. Combustion efficiency of Mg based experiments are higher than Al and above 90%. Ignition results indicate that CO2 percentage can be increased with changing internal ballistics of hybrid motor. Paraffin/Metal/CO2 propellant combination can be a potential candidate for Mars Ascent Vehicles.