The Effect of Arcjet Preheating on the Sooting Characteristics of Methane

The potential for improvement in the performance of electric rocket motors (arcjets) using methane as a propellant has been limited by sooting or choking and the resulting fouling of the rocket. If its sooting characteristics can be mitigated by rocket motor design or operational conditions, then its use as a propellant gas can be realized. For orbital transfer, we propose to investigate whether operational conditions, particularly preheating of the electric rocket motor, can be used to prevent fouling. For preheating purposes, hydrogen will be used to bring a 14 kw arcjet up to operational temperature. Methane will be introduced as the propellant gas by going through a series of H2/CH4 mixture compositions for 100-percent hydrogen to 100-percent methane. Sooting characteristics will be monitored by periodic disassembly and inspection of the arcjet motor internal surfaces. During actual operational testing, a spectrograph with an imaged-intensified diode array detector will be used to measure the emission spectra from the rocket motor exhaust plume. To monitor the effect of the appearance of soot, the exhaust plume emission spectrum will be studied to determine any spectral changes due to black body emission from soot.