Diesel engine is widely used because of its high thermal efficiency, high power, low fuel consumption and economy compared with gasoline engine. It is mainly used as the power of tractors, large automobiles, diesel locomotives and civil construction, excavators, loaders, fishing boats, diesel generator sets and agricultural machinery. Diesel oil is a complex mixture of hydrocarbons with a carbon atom count of about 10-22. Mainly from crude oil distillation, catalytic cracking, hydrocracking, viscosity cracking, coking and other processes produced by the blending of diesel distillate (also need to be refined and added additives). Diesel is divided into two categories: light diesel (boiling point range of about 180℃ ~ 370℃) and heavy diesel (boiling point range of about 350℃ ~ 410℃). The most important thing in the performance of diesel oil is ignition and fluidity, and its technical indicators are cetane number and freezing point, respectively. The main performance of diesel oil in China's current specifications requires the sulfur content to be controlled at 0.5%-1.5%. The main characteristics and working principle of synchronous generator

Diesel is classified according to the freezing point, light diesel has 10, 0, -10, -20, -35 five grades, heavy diesel has 10, 20, 30 three grades.

Diesel density

The density of No. 0 diesel oil is between 0.84 and 0.86g/cm³ at the standard temperature of 20 ° C.

The working process of the diesel engine is actually the same as that of the gasoline engine, and each working cycle also experiences four strokes of intake, compression, work and exhaust. However, because the fuel used in diesel engine is diesel, its viscosity is larger than gasoline, it is not easy to evaporate, and its spontaneous combustion temperature is lower than gasoline, so the formation and ignition mode of combustible mixture are different from gasoline engines.

Diesel engines suck in pure air during the intake stroke. When the compression stroke is near the end, the diesel oil is raised to more than 10MPa by the injection pump, injected into the cylinder through the injector, and mixed with the compressed high temperature air in a very short time to form a combustible mixture. Due to the high compression ratio of the diesel engine (generally 16-22), the main maintenance air pressure of the automotive engine in the cylinder at the end of compression can reach 3.5-4.5MPa, and the temperature can reach 750-1000K(while the gasoline engine's mixture pressure at this time will be 0.6-1.2MPa, and the temperature can reach 600-700K). Well above the spontaneous combustion temperature of diesel. Therefore, after the diesel oil is injected into the cylinder, it immediately ignits itself after mixing with the air in a very short time. The air pressure in the cylinder rose rapidly to 6-9MPa, and the temperature also rose to 2000-2500K. Under the push of high pressure gas, the piston moves down and drives the crankshaft to rotate and do work, and the exhaust gas is also discharged into the atmosphere through the exhaust pipe.

The ordinary diesel engine is driven by the engine camshaft, and the diesel is transported to the cylinder fuel chamber by means of a high-pressure oil pump. This way of oil supply should change with the change of engine speed, and the amount of oil supply under various speeds can not be done. The common rail injection system of electronically controlled diesel engine, which has been more and more widely used, can better solve this problem.

The common rail injection fuel supply system is composed of high pressure oil pump, common oil supply pipe, fuel injector, electronic control unit (ECU) and some pipeline pressure sensors. Each injector in the system is connected to the common oil supply pipe through its own high pressure oil pipe, and the public oil supply pipe plays the role of hydraulic pressure storage. When working, the high pressure oil pump transmits the fuel to the public oil supply pipeline at high pressure. The high pressure oil pump, pressure sensor and ECU work in a closed loop to achieve accurate control of the oil pressure in the public oil supply pipe, and change the phenomenon that the oil supply pressure changes with the engine speed. Its main characteristics have the following three aspects:

1, injection timing and fuel metering are completely separate, injection pressure and injection process by the ECU timely control.

2, according to the working condition of the engine to adjust the injection pressure of each cylinder, injection starting point, duration, so as to pursue the control point of injection.

3, can achieve a high injection pressure, and can achieve diesel pre-injection.

Compared with gasoline engines, diesel engines have a low fuel consumption rate (average 30% lower than gasoline engines), and the diesel price is lower, so the fuel economy is better; At the same time, the speed of the diesel engine is generally lower than that of the gasoline engine, and the torque is larger than that of the gasoline engine, but its mass is large, the noise is large when working, the manufacturing and maintenance costs are high, and the emissions are worse than that of the gasoline engine. However, with the development of modern technology, these shortcomings of diesel engines are gradually being overcome, and now not senior cars have begun to use diesel engines.