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How the engine works
- Aug 28, 2018 -

The engine is divided into a piston engine, a ramjet engine, a rocket engine, and a turbine engine.

Working process: intake-compression-injection-combustion-expansion work-exhaust.

Intake stroke

The working fluid entering the cylinder is pure air. Due to the low resistance of the diesel engine intake system, the intake end pressure pa = (0.85 ~ 0.95) p0, higher than the gasoline engine. The intake end temperature Ta = 300 ~ 340K, lower than the gasoline engine.

Compression stroke

Since the compressed working medium is pure air, the compression ratio of the diesel engine is higher than that of the gasoline engine (generally ε = 16 to 22). The pressure at the end of compression is 3,000 to 5,000 kPa, and the temperature at the end of compression is 750 to 1 000 K, which greatly exceeds the autoignition temperature of diesel (about 520 K).

Power stroke

When the compression stroke is nearing the end, under the action of the high-pressure oil pump, the diesel fuel is injected into the cylinder combustion chamber through the injector at a high pressure of about 10 MPa, and then spontaneously ignited and burned after being mixed with the air in a short time. The pressure of the gas in the cylinder rises rapidly, up to 5,000 to 9 000 kPa, and the maximum temperature is 1 800 to 2 000 K. Since the diesel engine is self-ignited by compression, the diesel engine is called a compression ignition engine.

Exhaust stroke

The exhaust of a diesel engine is basically the same as that of a gasoline engine, except that the exhaust gas temperature is lower than that of a gasoline engine. Generally Tr = 700 ~ 900K. For a single-cylinder engine, the speed is not uniform, the engine is not stable, and the vibration is large. This is because only one of the four strokes is work, and the other three strokes are strokes that consume power to prepare for work. In order to solve this problem, the flywheel must have a sufficiently large moment of inertia, which in turn leads to an increase in mass and size of the entire engine. A multi-cylinder engine can make up for the above shortcomings. Modern cars use four-cylinder, six-cylinder and eight-cylinder engines.