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How The Engine Works Dec 27, 2019

How the engine works

The engines are divided into piston engines, ram engines, rocket engines, and turbine engines.

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 intake system of the diesel engine, the end pressure of the intake air is pa = (0.85 ~ 0.95) p0, which is higher than that of the gasoline engine. Intake end temperature Ta = 300 ~ 340K, which is lower than that of gasoline engines.

Compression stroke

Because the compressed working medium is pure air, the compression ratio of a diesel engine is higher than that of a 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 000K, which greatly exceeds the autoignition temperature of diesel (about 520K).

Work stroke

When the compression stroke is nearing the end, under the action of a high-pressure oil pump, diesel is injected into the cylinder combustion chamber at a high pressure of about 10 MPa through an injector, and after a short period of time, it mixes with air and ignites itself. The pressure of the gas in the cylinder rises rapidly, up to 5 000-9 000 kPa, and the highest temperature is 1 800-2 000 K. Because the diesel engine burns itself by compression, it 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 temperature is lower than that of a gasoline engine. Generally Tr = 700 ~ 900K. For a single-cylinder engine, the speed is uneven, the engine works unevenly, 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. To solve this problem, the flywheel must have a sufficiently large moment of inertia, which in turn will lead to an increase in the mass and size of the entire engine. The use of a multi-cylinder engine can make up for these shortcomings. Modern cars use four-, six-, and eight-cylinder engines