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Hypothetically, if:

  • one got stuck somewhere at a remote airport
  • the jet aircraft or airliner they are flying had a 1/3 tank full of the proper jet A1 fuel
  • there was a tanker at the airport with 1/3 gasoline or petrol and another with diesel (the one used in trucks and passenger cars)

Would filling up the tanks and mixing all three fuels be safe for the operation of the jet engine, given that jet engines can burn any fuel?

Would the pilots expect to cover as much distance if they needed all the fuel to reach their closest destination safely to refuel?

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    $\begingroup$ Gas (mo-gas or AVGAS) in a jet engine would be very destructive. The best thing to do in that situation is have the correct fuel flown in or trucked in. Better to sit and wait than experience a flame-out or rapid disassembly mid-air. $\endgroup$
    – Ron Beyer
    Mar 20, 2019 at 19:52
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    $\begingroup$ No you can use gasoline in some engines in special circumstances. The PT-6 allows it. It's mostly bad for pumps like barrel pumps that depend on the fuel for lubrication. Jets fuels called Wide Cut are actually kerosene avgas blends. You can also run a PT-6 on "arctic diesel", which is an extra clean diesel used in the far north, sort of a near-kerosene. $\endgroup$
    – John K
    Mar 20, 2019 at 21:19
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    $\begingroup$ As a back of the napkin calculation, let's say that airliner of yours has a maximum endurance of 8 hours. (Small airliners almost certainly have less; large ones definitely have more.) 1/3 of that is about 2½ hours. Leave a one hour reserve at landing, that's 1½ hours of usable fuel. 1½ hours at 500 kt gets you an operating range of 700-750 nm, or around 1300 km. If you're willing to dip into the reserve (which you shouldn't be, but probably isn't half as bad as a random mix of different fuels), you get more like 2000 km before running out of fuel. Now where's that airport located, again? $\endgroup$
    – user
    Mar 21, 2019 at 9:09

1 Answer 1

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While turbine engine can be made to burn almost any fuel, a specific engine might not run with fuel it is not tuned for for several reasons:

  • The high pressure fuel pumps only work with stuff that is sufficiently lubricating. They don't use grease, because it would be too easily washed out at the operating pressure, and the pressure is needed because the fuel is injected directly into the combustors at the highest pressure present in the engine. This rules out too much gasoline—note that spark-ignition engines, even when they have direct injection, inject during suction, so at low pressure.

    With little enough gasoline, the pumps wouldn't mind, and I heard some militaries had backup plan for diesel engines—which have the same issue—to mix gasoline with some oil as an emergency fuel. However to know how much gasoline is safe somebody would have to test it and nobody is going to sacrifice a very expensive piece of equipment that is a turbine engine for a test with so little value as this since there is no shortage of proper jet fuel.

  • Each fuel has different heat of combustion, so it needs to be metered differently to keep the engine within the rather narrow range of operating pressures and temperatures. If the heat of combustion is too low, the pressure won't be enough to keep the turbine spinning and the engine will flame out, and if it is too high, the pressure will exceed the capability of the compressor which will stall and the engine will either flame out or go through a cycle of stalls that will thoroughly destroy it.

    The adjustment might be as “simple” as updating the firmware in the FADEC, but it is still a lot of work to do all the necessary measurements and then do all the tests for the modification and since there is no practical use, nobody did.

  • The length of the combustor also has to match the speed of combustion, so if that is different enough, you need a differently built engine altogether.

So the engine will probably tolerate some different fuel mixed in the tanks, but nobody can tell you how much exactly, because it wasn't tested.

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