This category is for two-cycle internal combustion engines, not four-cycle engines. Two-cycle engines mostly use reciprocating piston layouts, but rotary types have been designed, built, and run. All two- and four-cycle engines can use Otto or Diesel cycles, and the four stages of operation and combustion (compression, ignition, expansion, exhaust) occur sequentially in time, in a common spatial area and part of the engine, a combustion chamber, usually via a piston. But in two-cycle engines, these stages occur in two cycles, not four: 1) a combined compression/ignition cycle, and then, 2) a combined expansion/exhaust cycle.
More information