Methane fuel impurities threaten reusable rocket engine lifespans
A new study reveals that contaminants in methane fuel—like ethane and carbon dioxide—cause dangerous carbon buildup inside rocket engines during flight, reducing cooling efficiency and shortening engine life. The finding matters for companies developing reusable launch vehicles, as it forces a choice between expensive fuel purification or accepting higher maintenance costs.
Originaltitel: Pyrolysis stability of different methane fuel qualities for regenerative cooling rocket engines usage
<p>The rapid development of reusable launch vehicles (RLVs) has shifted attention towards methane as a rocket fuel, motivated by its balance of storability, performance, and the possibility of in-situ resource utilisation. Compared to kerosene-based fuel (e.g. RP-1), methane burns more cleanly and generates less soot. Compared to liquid hydrogen, it is easier to handle and store while still offering favourable propulsive efficiency and cooling performance compared to RP-1. However, impurities in methane derived from natural gas or biogas—such as ethane, propane, and carbon dioxide—may reduce this fuel’s thermal stability. Under rocket-like thermal conditions, methane can break down and deposit carbon (“coke”) on cooling channel walls. This reduces heat transfer, increases wall temperature, and shortens the lifetime of engines. If non-purified methane is to be used, its stability must be fully understood. This paper presents results from the MERiT project, a collaboration between KTH Royal Institute of Technology and GKN Aerospace. A series of controlled experiments examined the catalytic pyrolysis stability of methane with various impurity contents. Nickel 201 and Inconel 600 samples were heated to 800 °C at 200 kPa(A) while gas mixtures containing methane and different proportions of ethane, propane, and CO<sub>2</sub> were tested at a flow rate of 50 ml/min. Hydrogen production, coke deposition, and visual inspection were used to assess pyrolysis stability. The results demonstrate that propane, with concentrations as low as 2%, leads to a visually observable increase in cooking. Ethane also increases pyrolysis rates, though its effect is more moderate compared to propane. The effects of ethane and propane are both exponential in character across the 0–10% range. CO<sub>2</sub> demonstrated varying effects based on the samples used; however, regardless of the sample material, its effects were limited in increasing coke formation compared to ethane and propane. These findings suggest that while some level of ethane and CO<sub>2</sub> may be tolerated, propane must be removed if methane from natural gas is to be used in regenerative rocket nozzles.</p>