Comparison Between Two-stroke and Four Stroke Diesel Engines

In a four stroke diesel engine, the piston travels four strokes to complete a working cycle, with two strokes (intake and exhaust), and the function of the piston is equivalent to an air pump. In a two-stroke diesel engine, for every revolution of the crankshaft, the piston completes a working cycle every two rows of travel, and the intake and exhaust processes are completed using compression and a part of the working process, so the piston of a two-stroke diesel engine does not have the function of an air pump. Due to the different number of strokes and ventilation methods in each working cycle of the two diesel engines, each has its own characteristics when compared.

(1) The advantages of four stroke diesel engine

1. Low heat load. Due to the large interval between power strokes, the thermal load at the piston, cylinder, and cylinder head of a four stroke diesel engine is lower than that of a two-stroke diesel engine. It is more advantageous in preventing thermal fatigue (referring to parts that are damaged due to long-term high temperature effects and reduced mechanical performance) compared to two-stroke diesel engines.

2. The ventilation process is more complete than that of a two-stroke diesel engine, with clean exhaust emissions and higher inflation efficiency.

3. Due to low heat load, it is easy to adopt exhaust gas turbocharging to increase the power of diesel engines.

4. Good economic performance. Due to the complete ventilation process and sufficient utilization of thermal energy, the fuel consumption rate is relatively low. Due to its structural characteristics, the lubricating oil consumption rate of a four stroke diesel engine is also relatively low.

5. The working conditions of the fuel system are good. Due to the fact that the crankshaft only sprays oil once every two revolutions, the service life of the plunger pair of the fuel injection pump is longer than that of a two-stroke diesel engine. During operation, the thermal load of the fuel injection nozzle is lower and there are fewer malfunctions.

(2) The advantages of two-stroke diesel engines

1. When the structural and operational parameters of a diesel engine are basically the same, comparing its power, for a non turbocharged diesel engine, the output power of a two-stroke diesel engine increases by about 60% to 80% compared to a four stroke diesel engine. From the principle of circulation, it seems that a two-stroke diesel engine has twice the power output compared to a four stroke diesel engine. In fact, due to the opening of an air port on the cylinder wall of a two-stroke diesel engine, the effective stroke is reduced, there is a loss in the air exchange process, and driving the scavenging pump requires power consumption. As a result, the power can only be increased by 60% to 80% C

2. The structure of two-stroke diesel engine is relatively simple, with few components, no or only partial valve structures, making maintenance and upkeep convenient.

3. Due to the short interval between power strokes, the diesel engine operates relatively smoothly. Four stroke diesel engines and two-stroke diesel engines each have their own advantages, and their applications in production are different. Two stroke diesel engines are commonly used on ships.

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