Marine main engines work under full load conditions most of the time, and sometimes under variable load conditions. Ships often sail in turbulence, so marine diesel engines should be able to work reliably under the conditions of trim 15° ~ 25° and heel 15° ~ 35° . Most ships use supercharged diesel engines (see internal combustion engine supercharging), and low-power non-supercharged diesel engines are only used on small boats. Low-speed diesel engines are mostly two-stroke engines, medium-speed diesel engines are mostly four-stroke engines, and high-speed diesel engines have both. The scavenging forms of marine two-stroke diesel engines include backflow scavenging, port - valve DC scavenging and opposed piston port scavenging. High-power medium and low-speed diesel engines widely use heavy oil as fuel, and high-speed diesel engines still use light diesel.
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