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.
The working fluid entering the cylinder is pure air. Since the resistance of the diesel engine intake system is small, the intake end pressure pa = (0.85 ~ 0.95) p0, which is higher than that of the gasoline engine. The inlet end temperature Ta = 300 ~ 340K, which is lower than the gasoline engine.
Since the compressed working medium is pure air, the compression ratio of the diesel engine is higher than that of the gasoline engine (generally -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 000K, which greatly exceeds the diesel. Auto-ignition temperature (about 520K).
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 5,000~9 000 kPa, and the highest temperature reaches 1 800~2 000K. Since the diesel engine is self-ignited by compression, the diesel engine is called a compression ignition engine.
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.
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