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Answered 2015-07-14 11:51:37
Two and Four Stroke EnginesPartially because of the way things are counted. Up and Down count as two, so it's pretty well impossible to have an odd number. That means the bare minimum is two, i.e. there is a power stroke every time the piston goes up and down. The next practical option is to have a power stroke every other time the piston goes up and down, i.e. the four stroke. The extra two strokes are used to more efficiently clear the exhaust gasses from the cylinder and cut the waste of unburned fuel that escapes to the exhaust system. Nobody has ever figured out a practical reason why you would want to have a power stroke every third time. What would those other strokes accomplish?

wankel made an engine which is now in the Mazda rx8 which is a rotary engine,in which the piston rotates,rather than go up and down

Also a rotary has not got a piston it has a ROTOR that ROTATES around a bore.(like a block in a 4 or 2 Stroke) a rotor has 3 sides that pass a intake port, a sparkplug chamber and an exhaust port.

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