Introduction to Marine Diesel Engine Accessories Differences between High, Medium and Low Speed Marine Diesel Engines

The general marine engine belongs to the category of low-speed engine, and the engine speed is generally below 800rpm (except for special speedboats), because the marine engine needs to be matched with the propeller, and the propeller speed is about 600-800rpm. Considering the matching efficiency value, too high engine speed is not beneficial to this; Other engines for large cargo ships or cruise ships burn heavy oil (oil with poor Z). These engines are generally two-stroke low-speed engines. Of course, there are also high-power four stroke medium speed engines. Medium speed engines are generally used as auxiliary engines on ships for power generation.

Methods and Steps

1. Differences between high, medium and low speed marine diesel engines:

The marine engine speed range above 3000 rpm is high speed engine, 1500-3000 is medium speed engine, and below 1500 is low speed engine.

2. Low speed diesel engines are mostly two-stroke engines, medium speed diesel engines are mostly four stroke engines, and high-speed diesel engines are both. The scavenging forms of marine two-stroke diesel engines include return scavenging, port valve direct scavenging and opposed piston port scavenging. Heavy oil is widely used as fuel in high-power medium and low-speed diesel engines, while light diesel is still used in high-speed diesel engines.

3. Low speed diesel engine directly drives the propeller. In order to make the propeller have high propulsion efficiency, it requires a lower speed. Medium and high speed diesel engines drive the propeller through the gear reducer, and the gearbox is generally equipped with a reversing mechanism to reverse the propeller, but low speed diesel engines and some medium speed diesel engines can reverse themselves. Medium and high speed diesel engines are also electrically driven by generators - motors - propellers.