Compression ignition

Compression ignition is the combustion mode of a diesel engine, where fuel ignites from the heat of air compressed in the cylinder rather than from a spark. The piston compresses the charge to roughly 35 to 45 bar and 700 to 900 K, above the autoignition temperature of the injected fuel, so combustion begins after a short ignition delay once injection starts near top dead center. Marine two-stroke low-speed engines and most four-stroke diesels run this way. High-pressure dual-fuel engines such as the MAN ME-GI and the WinGD X-DF-A keep the diesel cycle on gas by injecting it at high pressure with a small pilot, which is why they avoid the methane slip of Otto-cycle types.