How to divide marine diesel engine parts into low speed and high speed

Marine diesel engines are generally divided into high-speed, medium-speed and low-speed diesel engines. The main performance indicators of the three types of diesel engines are listed.

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, 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 reflux scavenging, port-valve direct current 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.

The low-speed diesel engine directly drives the propeller. In order to make the propeller have high propulsion efficiency, a lower speed is required. Medium and high-speed diesel engines drive propellers through gear reduction boxes. Gear boxes are generally equipped with a reverse mechanism to achieve propeller reversal, but low-speed diesel engines and some medium-speed diesel engines can reverse themselves. Medium and high-speed diesel engines also realize electric transmission through generator-motor-propeller. When high power is required, multiple engines can also be used in parallel, and only one main engine can be used for low-speed navigation, thereby improving operating economy and reliability. When two main engines are installed on the same ship, they are divided into left and right engines according to the installation position and the steering of the propeller.

The main development trend of marine diesel engine parts is: improving supercharging technology (two-stage supercharging, ultra-high supercharging and supplementary combustion supercharging, etc.) to increase the single engine power; improving the combustion process, burning low-quality fuel oil and using waste heat to Improve economy; improve reliability and extend service life; use fault prediction and monitoring to realize automatic remote control of diesel engines.