Effects of NO in oxidant and initial temperature on working characteristics of MON-X/MMH liquid space thruster.

With the progress of deep space exploration activities, low freezing point propellants are required to ensure the normal operation of aerospace engines in deep space environments. Blending NO and nitrogen tetroxide is a commonly used method to decrease freezing point of propellant, which is called MON-X. Researches on MON-X/methyl hydrazine thruster with impinging injection and influences of initial temperature are rare, and there hasn't been a comparison between nitrogen tetroxide/methyl hydrazine thrusters and MON-X/methyl hydrazine thrusters. In order to study the operation characteristics of nitrogen tetroxide/methyl hydrazine and MON-25/methyl hydrazine bipropellant thrusters with impinging injection and investigate the influence of initial temperature on performances, simulation model was developed for a 25 N thruster, starting and stable working process of thrusters was numerically simulated with different oxidant types and initial temperatures. The results show that NO in the oxidant leads to differences in operating characteristics of nitrogen tetroxide thruster and MON-25 thruster. During starting and stable operating processes, dominant reactions of methyl hydrazine dehydrogenation are self-decomposition of methyl hydrazine and extraction of H from methyl hydrazine by NO₂, respectively. The main reactions that affect the temperature rise of combustion chamber are the oxidation of CH₃ to H₂O by OH, as well as small molecule oxidation-reduction reactions such as CO generated by HCN and OH. In a stable operating state, the smaller mass fraction of N₂O₄ in MON-25 leads to a lower temperature in the middle of the cylindrical section of MON-25 thruster than that in nitrogen tetroxide thruster. The combustion chamber pressure of MON-25 thruster does not change significantly in the initial temperature range from 293 K to 263 K. When the initial temperature of MON-25 thruster is 243 K and lower, severe lost on working performance of thruster occurred due to the impact of temperature on propellant gasification.