Again, one of those hypothetical scenarios, it might sound silly but here is the idea.
The device would be composed of two chambers connected with a hammer valve. The first chamber is the reservoir in which pure Alcohol (Ethanol) and pressurized air would be stored. The idea is also to heat this chamber externally (via gas stove) to force alcohol to evaporate and homogeneously mix with the pressurized air. I have no clue is this even safe! It would be calculated how much of liquid alcohol could be poured into this chamber. I know that a liquid evaporates harder when pressure is increased.
The second chamber is the combustion chamber in which the ignition system would be installed. This chamber may or may not have a piston at the exit. One way valve would be between this chamber and a hammer valve.
I was thinking about two types of ignition systems. First one could be a regular taser, or a device that produces spark oscillations constantly. As for the second type of ignition, I was thinking about some material that has electrical resistance and glows red hot while electric current passes through it. Perhaps a modified car cigarette lighter. It would have to operate for a longer time and not fail after a few seconds.
After the ignition system is switched on and the reservoir is filled with Alcohol and pressurized air, you would fire this device by activating the hammer valve which is supposed to spray this Alcohol/Air mixture at the ignition system in the second chamber. Hopefully there would be a reaction.
As for the reservoir, honestly I am not sure if this thing could explode. Pressurizing a flammable liquid plus heat sounds like a bad day.
Here is the illustration.
