The six-stroke engine was developed to improve fuel efficiency and reduce emissions compared to conventional four-stroke engines. It operates with two additional strokes: in one, water is injected into the hot cylinder and turns to steam, forcing the piston down. In the other, the steam is exhausted up. This captures wasted heat to improve efficiency. Issues include potential engine damage from thermal expansion and needing separate water tanks. However, benefits are 40-60% reduced fuel use and lower emissions than four-stroke engines.