Diesel engines types used in boats. More complicated than I could imagine.
30 Types of Marine Diesel Engines Explained
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Type of use
A marine diesel engine is put to different uses onboard. Broadly, they can be used in the following two manners:
Marine propulsion engine
When a marine diesel engine is used to turn the propeller and move the ship, it becomes a
marine propulsion engine and is popularly known as the main engine. The engine can be run at various speeds as per need.
Diesel generator
A marine diesel engine is also coupled to an alternator and used to generate electric power onboard. There is usually more than one of these onboard and multiple generators may be put into use during critical operations. Such diesel generators are also known as auxiliary engines.
Marine Diesel Generator
Number of strokes
We define a stroke as the travel of the piston from one end of the cylinder to the other end. Engine cylinder operations such as induction, compression, combustion (power stroke) and exhaust gas removal occur with the help of piston strokes. Based on the number of strokes it takes to complete one power stroke, an engine is classified as:
Two-stroke engine
In a two-stroke engine, a power stroke occurs every two strokes or one revolution of the engine crankshaft. The four operations are completed within one revolution. As a result, two-stroke engines provide a higher power-to-weight ratio, greater stability, simpler construction and are more compact compared to a four-stroke marine diesel engine.
Four-stroke engine
A four-stroke engine needs two complete revolutions of the crankshaft for one power stroke. The four aforementioned cylinder operations occur in four separate strokes in this type of engine.
Due to the fewer power strokes per revolution, these engines are more fuel efficient as the fuel has more time for complete combustion. It also requires less lubrication and is generally more durable than a two-stroke engine. All these qualities make four-stroke engines a more eco-friendly alternative.
Single-acting or double-acting
Reciprocating-type engines are further classified into single-acting and double-acting cylinder engines. In single-acting engines, power stroke occurs on one side of the piston, but it occurs on both sides in a double-acting engine.
There are two combustion spaces and a double piston is used to seal both of them. Power stroke takes place on the upward as well as downward stroke. In the case of a two-stroke double-acting engine, there are two power strokes per crankshaft revolution. Double-acting engines are not as popular as their counterpart as the lower combustion space can be difficult to seal.
A double-acting engine is different from an opposed-piston engine in which there is only one combustion space and two pistons on either side of it.