Piston engines are typically four-stroke (intake, compression, power, exhaust) or two-stroke (intake/compression, power/exhaust). Three strokes would not be applicable.
However, rotary engines such the Wankel might be describable as three-stroke, depending on their configuration and operating sequence.
A Web search on "three stroke engines" gives lots of (mis)information. (Me too maybe.)
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Three-Stroke Engines
Re: three stroke
