From what I know, it seems good, so why does no one use butane as a rocket fuel?
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1I think it can be chalked up to the intense conservativeness of the aerospace industry. All hydrocarbons end up being somewhat similar to each other. – ikrase Oct 31 '20 at 18:19
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It would seem to me that, for full-scale rockets, using a fuel which is not liquid at room temperature and pressure is an unnecessary complication. Yes, LOX is used as an oxidizer, but that's because there's no other choice (and LOX is not terribly dangerous to handle unpressurized). I don't doubt that hobbyists somewhere have at one time used butane as a fuel, though. – Dan Nov 01 '20 at 21:58
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Hydrocarbons are largely interchangeable when it comes to performance, and as long as no single one beats kerosene with a large enough margin, the hassle of changing infrastructure is generally not worth it.
Compared to RP-1, butane has slightly (very slightly) higher specific impulse, and somewhat lower density, largely cancelling each other out.
Butane comes up short, since if sacrificing some density for Isp is beneficial, why not go all the way with methane? And if sacrificing density is unacceptable, more highly refined compounds like syntin gives you the same Isp boost, with even a little higher density as an added bonus.
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Butane also has a boiling point of around 0°C. So while not cryogenic, it's a cold liquid that will require refrigeration, insulated storage, and handling of boiloff, giving it much the same complexity of a cryogenic fluid compared to one like RP-1. Despite that, it's not really cold enough to be a much more effective coolant (unless you subcool it, at which point you're even closer to methane). – Christopher James Huff Oct 31 '20 at 20:16
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Side reaction propensities depositing material inside the engine are important consideration. Also see Density of propylene when used as rocket fuel and advantages (if any) over RP-1? and especially What actually is RP-1, and how is it different from any other hydrocarbon liquid fuel? and all the others linked there, especially Vector-R's LP-1 and -2 engines use liquid propylene as fuel with LOX, advantages and distinctions from kerosene or propane? – uhoh Nov 01 '20 at 00:00
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1I am seeing a pattern here as there are questions discussing about incompatibility of lower hydrocarbons as rocket fuel: propane; ethene and now butane. Are there any reasons/rules for not using lower hydrocarbons as rocket fuel? – Nilay Ghosh Nov 01 '20 at 12:35
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1@NilayGhosh: I suspect we'll run out of non-duplicate questions soon enough. – Joshua Nov 01 '20 at 17:12
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4@Joshua: I hope so, since the number of possible compounds this question could be asked about explodes rapidly once you start adding more carbons. :) – Ilmari Karonen Nov 01 '20 at 18:48
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Will simpler hydrocarbons burn cleaner (less soot?) than more complicated ones? Maybe for less maintenance on reusable engines? – Kozuch Mar 25 '21 at 19:27