Marine engines have high thermal efficiency, good economy, and are conducive to start-up and adaptability to various types of ships. They were used as propulsion power for ships shortly after they came out. Play a role in promoting the development of society. So, how many types of marine engines are there? Here are some answers.
Low-speed diesel engine
Two-stroke diesel engine
Four-stroke diesel engine
Directly drive the propeller, to make the propeller have high propulsion efficiency, a slower speed is required. The medium diesel engine powers the propeller through the gearbox. Gearboxes 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 higher 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.
A diesel engine that completes a working cycle through two strokes of the piston is called a two-stroke diesel engine. The oil engine completes a working cycle and the crankshaft makes only one revolution. Compared with a four-stroke diesel engine, it has improved working power. In terms of the specific structure and working principle, There are also big differences.
The basic structure of a two-stroke diesel engine is the same as that of a four-stroke diesel engine. The main difference lies in the valve train. Two-stroke diesel engines do not have an intake valve, and some do not even have an exhaust valve. Instead, a scavenging port and an exhaust port are provided in the lower part of the cylinder; or a scavenging port and exhaust valve mechanism are provided. A scavenging pump is driven by a moving part and a scavenging tank for storing compressed air is specially set up, and the gas distribution is completed by the cooperation of the piston and the airport, thereby simplifying the structure of the diesel engine. The figure shows the working principle of a two-stroke diesel engine. The scavenging pump is attached to one side of the diesel engine, and its rotor is driven by the diesel engine. Air is sucked in from the pump, compressed and discharged, stored in a scavenging tank with a larger volume, and maintained a certain pressure in it.
The work of a diesel engine is completed by the four processes of suction, compression, work, and exhaust, which constitute a working cycle. A marine diesel engine in which the piston goes through four processes to complete a working cycle is called a four-stroke diesel engine.
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