The working process of diesel engines is actually the same as that of gasoline engines, and each working cycle also undergoes four strokes of intake, compression, power and exhaust.
The piston moves from the lower stop point to the upper stop point, the inlet and exhaust valves are closed, and the piston compresses the air suction in the first stroke in the combustion chamber, increasing the temperature and pressure of the air. At the end of this process, the air temperature in the cylinder is about 500 to 700 ° C, and the pressure is 27 to 49 atmospheres.
The piston moves from the upper stop point to the lower stop point, and the inlet and exhaust valves remain closed. At the end of the compression process, the injector injects the high-pressure fuel into the cylinder, mixes it with high-temperature and high-pressure air, and the temperature is higher than the diesel spontaneous ignition point, generating combustion on its own, generating a large amount of thermal energy, and causing the temperature and pressure in the cylinder to rise sharply.
The high temperature and high- pressure gas pushes the piston down, drives the crankshaft rotation through the connecting rod, and does external work. The maximum combustion pressure of this process is about 60 to 90 atmospheres, and the maximum temperature is 1700 ~ 2000 °C. With the expansion of the action, the thermal energy is converted into mechanical energy, the pressure and temperature of the gas in the cylinder drop sharply, and at the end of the expansion, the pressure in the cylinder drops to 4 atmospheres, and the temperature drops to 600 ~ 900 °C.
The piston moves from the lower stop point to the upper stop point, at which point the intake valve closes and the exhaust valve opens. After the expansion is over, the gas in the cylinder has lost the ability to do work, called exhaust gas. In order for fresh air to re-enter the cylinder, exhaust gases need to be discharged. The exhaust gas is squeezed upward by the piston and passes through the exhaust valve to the outside of the cylinder. At the end of the schedule, the pressure in the cylinder is about 1.03 to 1.08 atmospheres, and the temperature is about 350 to 600 °C. At this point, the piston returns to the upper stop point, the four-stroke diesel engine completes a work cycle, and the crankshaft rotates twice.
Compared with the gasoline engine, the diesel engine has more torque than the gasoline engine at low speeds, and the power will is more powerful, especially when climbing a large truck to drive several tons is more suitable than the gasoline engine.
And because the diesel engine eliminates the process of ignition, there is no spark plug, and one less part is less likely to fail. And the energy efficiency ratio of the diesel engine is a distance higher than that of the gasoline engine, energy consumption is 45%-60% of the gasoline engine, thermal efficiency is also higher than gasoline, the calorific value of diesel fuel is relatively high, burning the same quality of diesel released more energy than gasoline, that is to say, the same displacement of diesel trucks will save about 30% of the oil than gasoline trucks, fuel economy is one-third higher than gasoline engines, for large trucks to use diesel engines can save a lot of costs. In general, the structure of the diesel engine is relatively simple, the low-speed torque is large, the fuel economy is good, and it is most suitable for large trucks.