Is it safe to mix different types of fuels in a jet engine?
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.