Algodoo

Press S briefly to start.

This engine does not use any sort of commands or scripts, all 'legal' mechanisms. This engine models how a real 4-stroke combustion engine works in real life, except that this one just magically deletes the waste or exhaust materials (the small red balls) instead of routing it into an exhaust pipe.
I modeled the fuel of gas by glueing multiple small circles that overlap into a single large circe and then "combusting" it by killing that bigger circle.

If you are wondering why there are only 4 pieces of fuel loaded, it is because that is how long the engine can run thus far as there is a timing issue i am yet to fix. For some reason, even though there is inifinite friction, the circles still somehow slip off each other thereby throwing off precise timing making the engine unusable

Update 1: Increased flywheel density for more angular momentun