Good one. In theory it's straigthforward. A squirt of fuel in a piston, BOOM. More and hotter gas than from a bottle. With a modern fuel injector, a pump and a fan to aid the mixing it's just a bit of creative thinking for the control spark.

I did think about it, in more ways than 1. I even did think about Walther Turbines and Wet Heater Torpedo's.

One straightforward problem.

Most event organisers , and more important, venue's don't allow combustion engines and such.