From Popular Mechanics
In the video above, the team builds a piston engine and fires it up while filming it in super slow motion. The result is that you can clearly see each step of the process as the engine goes through its cycle. The Warped Perception folks experiment with using isopropyl alcohol and acetylene as fuels instead of gas, and the engine clearly doesn’t care too much for those.
Ha ha that was too cool!
Pretty interesting.
From a science standpoint, there are a few issues not addressed.
Different fuels would require different fuel/air combinations to be used to make the engine run properly. This would require changes in the carberation and possibly the the gap on the spark plug to be modified.
For example, alcohol as a fuel. It's obvious way too much liquid is being drawn into the combustion chamber, also known as flooding or running rich. The guy is lucky the engine didn't fail or blow up since liquids do not compress much. If the engine had kept running for any length of time, the piston, piston rod, valves or even the entire head could have broken or even exploded if too much liquid built up in the combustion chamber.
Acetylene, which exists in a gas state at normal temperatures, would also require conversions to the engine to run properly. Think of changing your gas burning engine to a natural gas burning engine. Significant changes would need to be made to the carberation system in order for the engine to run properly with natural gas.