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This category is for Diesel cycle internal combustion engines, not Otto cycle engines. Diesel engines mostly use reciprocating piston layouts, but rotary types have been designed, built, and run. All two- and four-cycle engines can use Diesel or Otto 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. In Diesel engines, compression is higher and causes auto ignition, so Diesels are also called compression ignition engines, while Ottos are called spark ignition engines.