Some of the earliest gas engines ever built that ran on brown's gas, town gas, natural gas, and white gas, and other petrol distillates, used the implosion or "vacuum" to PULL the piston to the top, instead of the other way around. I have seen pictures of the russian built units that date back to the 1700's as they were incredibly LARGE, they move incredibly SLOW, and have a LAUGHABLE amount of horsepower, and consumed tons of metal and floor-space.
they were fired with a rotating flame/torch setup, where the opening in the cylinder lead to a chamber with a rotating outer tube, and one side, the side opposite of the cylinder, has a torch. the torch lights the candle inside, and the tube rotates, the openings line up with the cylinder now, and the flame is now exposed to the inside of the cylinder. it ignites the fuel, and as the fuel burns, it "Pulls" the piston to the top of the cylinder.
Keep in mind that these early attempts at engines did indeed run, but rather slow (50 to 100 or so RPM) and had minimal horsepower, as it was NOT a compression type otto-cycle engine.
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