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I know that Jet-A is the fuel most often used for turbofans, but is there something else that these engines can burn? (ethanol, LPG, methane, butane, 100LL, etc.) Basically, can a turbofan burn anything, or are there limits in terms of temperature, combustibility, and so forth? also, which fuel out of any you can think of would be the most powerful/fuel-efficient?

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    $\begingroup$ Related: Why do jet engines use kerosene rather than gasoline? $\endgroup$ – fooot May 22 '17 at 19:28
  • $\begingroup$ Possible duplicate of Why do jet engines use kerosene rather than gasoline? $\endgroup$ – Jan Hudec May 22 '17 at 19:44
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    $\begingroup$ Not a turbofan, but the same principals. The military version of the Rolls Royce Gnome had a long list of fuels that could be used when "needs must" with an inspection required following flight. There was an even longer list of basically any liquid that will burn with on octane less than petroleum that could be used in war time with an engine strip following. I can't find a copy of it but do remember that it included cooking oil of many types, fuel oil and diesel. $\endgroup$ – Simon May 22 '17 at 20:02
  • $\begingroup$ I do not see the related question answering this question. Very closely related, to be sure, but that question asks, "Why Jet fuel, rather than gasoline?", whereas this question asks, "What can turbofans burn?" $\endgroup$ – J Walters May 22 '17 at 20:21
  • $\begingroup$ Regarding turbine engines, not merely turbofans, I know some are approved for various types of aviation gasoline, and I have heard an anecdotal report of a turbine engine having been "unwittingly" operated burning 5606 hydraulic fluid. There are certainly quite a list of types of fuel that can be burned with varying degrees of success and engine and component longevity. $\endgroup$ – J Walters May 22 '17 at 20:24
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As explained in Why do jet engines use kerosene rather than gasoline?, turbines can burn almost anything, but the lubricating properties of kerosene make the fuel pump simpler as it is otherwise hard to keep high-pressure pump lubricated.

Temperature limiting is simply a matter of sufficiently lean mixture and cooling air stream along the combustor walls.

And most efficient depends on criteria. For money it is definitely kerosene (Jet-A). Actually, Jet-A is an excellent match overall. It is relatively dense (~0.8 kg/l) while still having good specific energy (~43 MJ/kg; so fuels tanks are not too big), lubricates (good for fuel pumps), has quite high flash point (low risk of fire when handling) and is a large fraction of crude oil (C8–C16 (gasoline is just C6–C8) so it is cheap).

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  • $\begingroup$ Most efficient is in terms of fuel storage(how much can I put in X space) and combustibility(How would I need to change the mixture to be similar to burning Jet-A?). $\endgroup$ – Nicholas May 23 '17 at 19:42
  • $\begingroup$ @Nicholas, for comparing things, you need to either select one criterion, or give each some weight. However, Jet-A is probably optimal for any combination practically useful in aviation. $\endgroup$ – Jan Hudec May 23 '17 at 21:01
  • $\begingroup$ Indeed. If you intend to use a fuel that has a flame and hot gas temperature that differs too much from it's design fuel, it would require a redesign of the combustion section as usually only about 20% of the air that goes into the 'core engine' (through the compressor section) is actually used for burning and the rest is used to protect/cool the combustion chamber. This is needed, because unlike piston engines, it is a continuous burn. $\endgroup$ – Chris V May 25 '17 at 12:39
  • $\begingroup$ Not quite anything; fuels with solid combustion products are generally excluded (solid at normal jet engine operating temperatures, that is), because the solid particles in the exhaust do bad things to the turbine blades. This is why zip fuel (jet fuel with boron compounds mixed in for added oomph) never really took off (pun intended) - that, and also the fact that both the boron-containing additives and the exhaust produced by a zip-fuel-burning engine proved to be hideously toxic. $\endgroup$ – Sean May 27 '18 at 1:42
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Jet-A is most common, however, we regularly used mixtures or pure 100LL in the arctic in Twin Otters and Caravans. Specifically the Caravan was approved for limited 100LL operation.

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