Diesel engines are engines that burn diesel fuel for energy release.
It was invented by the German inventor Rudolf Diesel in 1892. In honor of the inventor, Diesel is referred to by his surname Diesel, and the Diesel engine is also called the Diesel engine.
The working principle of four-stroke diesel engine
The working process of a diesel engine is actually the same as that of a gasoline engine. Each working cycle also goes through four strokes: intake, compression, power and exhaust.
1. Intake stroke
The working medium entering the cylinder is pure air.
Because the diesel engine intake system resistance is small, the intake terminal pressure Pa = (0.85~0.95) P0, higher than gasoline engine.
Intake terminal temperature Ta=300~340K, lower than gasoline engine.
The task of the intake is to fill the cylinder with fresh air.
When the intake stroke begins, the piston is at the top dead center, leaving some exhaust gas in the combustion chamber inside the cylinder.
When the crankshaft rotates the elbow, the connecting rod moves the piston from top dead center to bottom dead center, and at the same time, the intake valve is opened by means of a transmission mechanism connected to the crankshaft.
As the piston moves downward, the volume above the piston in the cylinder increases: the air pressure in the cylinder is lower than the pressure in the intake pipe, so that the outside air is constantly filling the cylinder.
2. Compression stroke
Because the compressed working medium is pure air, the compression ratio of diesel engine is higher than that of gasoline engine (generally ε=16~22).
The pressure at the end of compression is 3 000~5 000kPa, and the temperature at the end of compression is 750~1 000K, which is much higher than the spontaneous combustion temperature of diesel oil (about 520K).
3. Power stroke
When the compression stroke is near the end, under the action of the high pressure oil pump, the diesel fuel is injected into the cylinder combustion chamber at a high pressure of about 10Mpa through the injector. After mixing with the air in a very short period of time, it will ignite and burn itself immediately.
The pressure of the gas in the cylinder rises rapidly, up to 5 000~9 000kPa, and the highest temperature reaches 1 800~2 000K.
Because the diesel engine is self-ignition combustion by compression, it is called compression ignition engine.
4. Exhaust stroke
The exhaust of diesel engine and gasoline engine are basically the same, but the exhaust temperature is lower than gasoline engine.
Generally the Tr = 700 ~ 900 k.
For a single cylinder engine, its speed is not uniform, the engine work is not stable, vibration.
This is because only one of the four strokes is doing work; the other three are strokes that consume power in preparation for work.
To solve this problem, the flywheel must have a large enough moment of inertia, which in turn leads to an increase in overall engine mass and size.
The use of multi-cylinder engine can make up for the above deficiencies.
Most modern cars use four -, six - and eight-cylinder engines.
Because the working principle of diesel engine is its own compression gas, rely on combustion to generate power, and drive the flywheel rotation, for the next work to store energy, produce more waste gas pollution, so gradually more and more cars to switch to gasoline or even new energy to replace diesel.
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