A friend and I while in High School had the idea to use electric solenoids instead of camshafts. The air idea is much better than our idea.
I saw a story of a man who added two more strokes to a four stroke engine. He invented a 6 stroke engine. After the intake/compression/power/exhaust strokes, water would be allowed into the hot cylinder. With valves closed, the water would use the heat in the cylinder to convert the water to steam and cause another power stroke (#5). The last stroke (#6) would expel the water/steam and set up for the next fuel intake.