It seems like all expander cycle engines currently in operation or in development use liquid hydrogen as fuel. The answer to this question indicates that RP1 won't work for EC engines because of its poor heat transfer properties.

I'm wondering if the same applies to cryogenic hydrocarbon fuels such as methane or propane. Intuitively, it seems like they should work fine. Also, the paper linked in this answer seems to indicate the oxygen can be used to drive pumps in a dual expander cycle - so, I'm guessing methane and propane can as well.

So, the question: are there any reasons for why methane or propane are a not a good idea to use in an EC engine?

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    $\begingroup$ In a closed cycle, and where the surface area/volume ratio is suitable $\endgroup$
    – user20636
    Commented Feb 5, 2020 at 7:21
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    $\begingroup$ Yeah, based on my calculations from here it seems like an open expander cycle is pretty much out. $\endgroup$
    – irakliy
    Commented Feb 5, 2020 at 19:26
  • $\begingroup$ IMHO the problem with RP-1 is that it will coke before you get enough energy/temperature to efficiently feed a turbine. Methane has a much higher coking temperature (>1000°C) and even propane might be used up to ~700 °C. Heat transfere properties are a nice bonus if you want to build huge engines but with enough high surface area vs mass flow one can always get high energies/temperatures. Moreover methane can be expanded to much lower temperatures without condensing when compared to propane/RP-1. $\endgroup$
    – Christoph
    Commented Feb 24, 2020 at 16:46


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