DiesOtto is Mercedes-Benz's brand name for its Homogeneous Charge Compression Ignition (HCCI) engine.
The DiesOtto engine controls in-cylinder temperature and pressure conditions very precisely so that a fuel/air mixture can ignited by the heat generated by compression. Exhaust gas is retained in the combustion chamber to heat the incoming charge (a process called 'internal exhaust gas recirculation') and the engine has a variable compression ratio.
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