Future Rocket Engines: Liquid Methane as a Fuel and its Implications on Rocket Nozzles

The operating benefits in combination with the good cooling capabilities of methane makes it ideal for rocket engines and is therefore brought forward as an alternative fuel in European rocket engines. Before combustion the fuel is lead through cooling channels in the rocket nozzle in order to cool it to withstand the high heat load from the rocket flame. Fuels with a high content of methane can contain different sorts of impurities and furthermore undergo thermal cracking at high temperatures that leave deposits on the metal surface that in turn increases the pressure loss and decreases the heat transfer, which ultimately can lead to failure of the rocket nozzle.

Furthermore, methane undergoes thermal cracking at high temperatures. Cryogenic experiments with methane have been performed in parts of the world (foremost the USA) but in other parts of the engine where copper materials are used. Quantitative information on the heat transfer characteristics for nickel-alloy steels under influence of hydrocarbon fuels at high pressure and temperature, as for the cooling of rocket nozzles, is to a high degree unavailable in the open literature. To close this gap GKN have initiated the research project MERiT (MEthane in Rocket nozzle cooling channels - conjugate heat Transfer measurements) where a high heat flux thermal stability test rig for rocket nozzle cooling channels will be designed, built and operated at the Royal Institute of Technology (KTH). With the use of the test rig the industry and academia will be able develop necessary knowledge of the heat transfer characteristics and material influence at relevant operating conditions in order to maintain and gain new market shares in future rocket propulsion systems.