Rough surfaces in rocket engines trigger fuel breakdown, threatening cooling systems
Researchers have identified a critical failure mode in methane-fueled rocket engines: surface roughness accelerates fuel decomposition in cooling channels, leaving insulating carbon deposits that degrade thermal performance. The finding matters because it affects engine reliability and lifespan—particularly for reusable rockets and additive manufacturing, where surface imperfections are common.
Originaltitel: Effect of surface roughness on cooling channel fouling in methane fueled rocket engines
<p>The effects of surface roughness, e.g. due to additive manufacturing or various wear mechanisms, is an active field of research, in particular for aerospace propulsion. With respect to rocket propulsion, such effects include performance changes of turbopump components and increasing pressure drop in cooling channels. An area that has not yet received significant attention is the effect of surface roughness on the thermo-catalytic decomposition of hydrocarbon fuels in cooling channels of, e.g. rocket engines or hypersonic aero engines. Although the decomposition of methane on rocket engine candidate materials and the resulting carbon depositions has been under active investigation in recent years, research mentioning the effect of surface roughness is sparse at best. The thermal decomposition of fuel, also known as pyrolysis, is a complex chemical process that can be catalyzed by materials such as nickel, iron and copper, which are common elements used in alloys for rocket engines and nozzles. Carbon deposited on, e.g. cooling channel walls has a thermal conductivity of a factor 100-1000 lower than that of copper and therefore effectively acts as a thermal insulator. Due to this, it has the potential to increase wall temperatures and thereby thermo-mechanical damage. The pyrolysis process depends on temperature, flow rate (or residence time), pressure, catalytic material, the area of the material exposed to the flow as well as the history of this material. High surface roughness materials may influence catalytic activity by increasing the number of active sites via surface area as well as the activity of the available catalytic sites. This is especially relevant given the increasing use of additive manufacturing in aerospace industry. The aim of this work is therefore to provide new data on the effects of surface roughness on fuel pyrolysis in components of aerospace propulsion systems. In this work, we focus on the experimental investigation of the effect of surface roughness on methane pyrolysis and the resulting carbon depositions. The candidate materials considered are nickel alloys Haynes 230 and Inconel 625 and are prepared by both additive and subtractive manufacturing methods resulting in a surface roughness range from Ra=0.40μm to Ra=11.24μm. This work is carried out as part of the MERiT+ project, a cooperation between KTH Royal Institute of Technology, GKN Aerospace Sweden and Siemens Energy, which is funded by the Swedish National Space Agency.</p>