Diesel engine working principle

The working process of a diesel engine is actually the same as that of a gasoline engine. Each working cycle also goes through the four strokes of intake, compression, power and exhaust.
The diesel engine inhales pure air during the intake stroke. When the compression stroke is nearing the end, the diesel oil pressure is increased to more than 10MPa through the injection pump, and is injected into the cylinder through the injector. It mixes with the compressed high-temperature air in a short period of time to form a combustible mixture. Due to the high compression ratio of diesel engines (usually 16-22), the air pressure in the cylinder can reach 3.5-4.5MPa at the end of compression, and the temperature can reach as high as 750-1000K (while the mixture pressure of gasoline engines at this time will be 0.6-1.2MPa , the temperature reaches 600-700K), which greatly exceeds the auto-ignition temperature of diesel. Therefore, after diesel is injected into the cylinder, it immediately ignites and burns after mixing with air in a very short time. The air pressure in the cylinder rapidly rose to 6-9MPa, and the temperature also rose to 2000-2500K. Driven by high-pressure gas, the piston moves downward and drives the crankshaft to rotate to perform work. The exhaust gas is also discharged into the atmosphere through the exhaust pipe.
The oil supply system of an ordinary diesel engine is driven by the engine camshaft, and the diesel is delivered to the fuel chamber of each cylinder with the help of a high-pressure oil pump. This oil supply method changes with the change of engine speed, and the optimal oil supply amount cannot be achieved at various speeds.
The common rail injection fuel supply system consists of a high-pressure fuel pump, a common fuel supply pipe, a fuel injector, an electronic control unit (ECU) and some pipeline pressure sensors. Each fuel injector in the system communicates with the public fuel supply through its own high-pressure fuel pipe. The common fuel supply pipes are connected to each other, and the common fuel supply pipe plays a role in hydraulic pressure accumulation for the injectors. When working, the high-pressure oil pump delivers fuel to the public oil supply pipe at high pressure. The high-pressure oil pump, pressure sensor and ECU work in a closed loop to accurately control the oil pressure in the public oil supply pipe, completely changing the relationship between the oil supply pressure and the change of the engine speed. Phenomenon. Its main features include the following three aspects:
1. Injection timing and fuel metering are completely separated, and the injection pressure and injection process are controlled by the ECU in a timely manner;
2. The fuel injection pressure of each cylinder, fuel injection starting point, and duration can be adjusted according to the engine working conditions, thereby pursuing the best control point of fuel injection;
3. It can achieve high fuel injection pressure and pre-injection of diesel fuel.