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Working Principle Of Four Stroke Diesel Engine DESCRIPTION:
- Dec 17, 2018 -

The working principle of four-stroke diesel engine is the same as that of gasoline engine. Each working cycle consists of intake stroke, compression stroke, work stroke and exhaust stroke. Comparing with gasoline, diesel engine uses compression ignition (compression ignition) with spark plug ignition because of its low spontaneous combustion temperature and high viscosity, which is not easy to evaporate.

(1) Intake stroke

The working substance entering the cylinder is pure air. Because the resistance of intake system of diesel engine is small, the intake terminal pressure pa= (0.85-0.95) P0 is higher than that of gasoline engine. The intake terminal temperature Ta = 300-340K, which is lower than that of gasoline engine.

(2) Compression stroke

Because the compressed working substance is pure air, the compression ratio of diesel engine is higher than that of gasoline engine (e=16-22). The pressure at the end of compression is 3 000-5 000 kPa and the temperature at the end of compression is 750-1 000 K, which is much higher than the spontaneous combustion temperature of diesel oil (about 520 K).

(3) Work stroke

When the compression stroke is close to the end, under the action of high pressure oil pump, diesel oil is injected into the cylinder combustion chamber at high pressure of about 100 MPa through the injector, which combusts spontaneously after mixing with air in a short time. The pressure of the gas in the cylinder rises rapidly, reaching a maximum of 5 000-9 000 kPa and a maximum temperature of 1 800-2 000 K. Because the diesel engine is self-ignited by compression, it is called compression-ignition engine.

(4) Exhaust stroke

The exhaust gas of diesel engine is basically the same as that of gasoline engine, but the exhaust temperature is lower than that of gasoline engine. Tr = 700-900K. For a single cylinder engine, its speed is not uniform, the engine works unsteadily and the vibration is large. This is because only one of the four strokes does work, and the other three strokes consume power to prepare for work. In order to solve this problem, the flywheel must have enough inertia, which will lead to the increase of the mass and size of the whole engine. Multi-cylinder engine can make up for the above shortcomings. Modern automobiles mostly use four-cylinder, six-cylinder and eight-cylinder engines.