Investigation of usage of different methane fuel qualities for rocket engines with respect to pyrolysis stability : Effects of ethane, propane and carbon dioxide

Liquid methane as a rocket propellant has been a point of interest in recent years for its favourable properties both as a fuel and coolant, as well as its potential for in-situ production. As a part of ESA’s Future Launcher Preparatory Programme, GKN Aerospace and KTH Royal Institute of Technology are undertaking the MERiT project, for the characterization of methane in rocket nozzle cooling channels, which also involves the investigation of the effects of various methane fuel components such as ethane, propane and carbon dioxide in the context of the pyrolysis stability of methane-based fuels in rocket nozzle cooling channels. The impact of these components on methane pyrolysis stability is tested using a rig that simulates rocket nozzle cooling channel conditions. Nickel 201 samples were used to achieve the catalytic pyrolysis of methane at 800 °C under 200 kPa pressure, at a flow rate of 50 ml/min. Gas chromatography and real-time sensors measured hydrogen content and other pyrolysis products, while weight measurements and visual inspections quantified carbon deposition. Increased amounts of all tested components increased pyrolysis rates, leading to higher amounts of coke formation. Carbon dioxide was found to mostly influence pyrolysis onset, and its effects are less significant in later stages of pyrolysis. Propane, compared to ethane, caused a larger increase in pyrolysis rates, with even very low propane concentrations causing significant coke deposition. However, mixtures with lower concentrations of ethane had comparable levels of coke formation to pure methane. For ethane and propane, an exponential relationship was found between the impurity levels and the integrals of measured hydrogen curves in the 0% - 10% impurity range.