There are more and more types and quantities of electric equipment, among which not onlyFire pump, spray pump and other fire-fighting equipment, as well as living pump, elevator and other electrical equipment that need reliable power supply. In order to meet the reliability of power consumption of these equipment, when the municipal power grid cannot provide two independent power supplies, the method of using diesel generator sets as standby power supply is widely used in the design.
The diesel engine must go through four thermodynamic processes of air intake, compression, expansion and exhaust before it can return to its original state,
Make the diesel engine continuously produce mechanical work, and the above four thermodynamic processes are called a working cycle.
Intake stroke
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Intake strokeThe purpose of is to inhale fresh air to prepare for fuel combustion.To achieve air intake, both inside and outside the cylinder
The differential pressure is formed.Therefore, in this stroke, the exhaust valve is closed, the inlet valve is opened, and the piston moves from top dead center to bottom dead center
The volume in the square cylinder gradually expands and the pressure decreases. The gas pressure in the cylinder is about 68-93kPa lower than the atmospheric pressure.At large
Under the action of air pressure, fresh air is sucked into the cylinder through the intake valve. When the piston reaches the bottom dead center, the intake valve is closed
End of stroke.[1]
compression stroke
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The purpose of the compression stroke is to increase the pressure and temperature of the air in the cylinder and create conditions for fuel combustion.Due to inlet and outlet
The valves have been closed, the air in the cylinder is compressed, and the pressure and temperature rise accordingly. The degree of increase depends on the degree of
The degree of compression is slightly different for different diesel engines.When the piston is close to top dead center.Air pressure in cylinder reaches
3000-5000kPa, the temperature reaches 500-700 ℃, which is much higher than the autoignition temperature of diesel engine.
1.3 Expansion (power) stroke
When the piston moves up to the end, the fuel injector starts to inject diesel into the cylinder, mixing with air to form a combustible mixture.Juxtaposition
That is, spontaneous combustion. At this time, the pressure in the cylinder rapidly rises to about 6000-9000kPa, and the temperature reaches 1800-2200 ℃.At temperature
Driven by high pressure gas, the piston moves down to the dead center and drives the crankshaft to rotate for work.As the gas expands
The pressure of the plug downward gradually decreases until the exhaust valve is opened.
Exhaust stroke
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The purpose of the exhaust stroke is to remove exhaust gases from the cylinder.power stroke After completion, the gas in the cylinder has become exhaust gas, and its temperature
The temperature drops to 800-900 ℃, and the pressure drops to 294-392kPa.At this time, the exhaust valve is opened, the inlet valve is still closed, and the piston
Moving from bottom dead center to top dead center, exhaust gas is discharged out of the cylinder under the action of residual pressure in the cylinder and piston thrust.When the piston
When the top dead center is reached again, the exhaust process is completed.
2.1 Arrangement and firing sequence of single row diesel engine cranks
aboutMulti cylinder engineIn order to torque, each cylinder should work in turn according to the uniform clearance, so that the crankshaft is evenly stressed and runs smoothly;
At the same time, in order to balance the inertia force generated by the piston, connecting rod and crankshaft in motion, the arrangement of the crank must be symmetrical.
The so-called crank arrangement refers to the angle and distance between the connecting rod journals of the crankshaft.It is related to the type of engine, number of cylinders
The working order is related.yesFour stroke engineFor example, the crankshaft rotates for two cycles (i.e. 720
o) Every cylinder should
Complete a cycle.In order to ensure uniform operation, the working stroke of each cylinder must be evenly distributed at 720
O Within the crankshaft angle.
ifMulti cylinder engineIf the number of cylinders is I, the crank angle interval H should be
H=720
o
/I
2.2 Firing sequence of V-type engine
V-type engine is equivalent to two single row engines sharing one crankshaft.But the firing interval of V-type engine is the same as that of V-type engine
The included angle K is related.The cylinder angle is usually determined according to the uniform firing interval.[1]
