Reposting my own spin from my Facebook post......dunno if I'm breaking the rules but the machine below consists of an "output" engine on the right being fed fuel via a Stayputnik. The Stayputniks have a very low max temperature of 1200 degrees....if both of the "input" engines to either side are ignited, and only both, then it will be destroyed and cut off the fuel supply to the output engine. This is a logical NAND gate, at which point you have Turing completeness. Unfortunately they're one-use-only, but they can certainly be used to construct a calculator circuit. In a practical implementation the fuel tanks feeding the input engines would be replaced by fuel lines (signals) coming from other parts of the circuit, and the fuel line feeding the "output" engines would all go to one massive tank with enough fuel to handle the "propagation delay" of the entire circuit.
