The advantages of diesel engines are high torque and good economic performance. The working process of diesel engines has many similarities with gasoline engines, and each working cycle also experiences four strokes of intake, compression, power, and exhaust. However, since the fuel used in diesel engines is diesel, its viscosity is higher than that of gasoline, it is not easy to evaporate, and its auto-ignition temperature is lower than that of gasoline. Therefore, the formation and ignition method of combustible mixture are different from those of gasoline engines. The main difference is that the mixture in the cylinders of a diesel engine is compression ignited rather than ignited. When the diesel engine is working, air enters the cylinder. When the air in the cylinder is compressed to the end point, the temperature can reach 500-700 ℃, and the pressure can reach 40-50 atmospheres. When the piston is close to the top dead center, the fuel injector of the fuel supply system injects fuel into the cylinder combustion chamber with extremely high pressure in a very short period of time. , the violent expansion produces explosive force, which pushes the piston downward to do work. At this time, the temperature can reach 1900-2000 ℃, the pressure can reach 60-100 atmospheres, and the torque generated is very large, so diesel engines are widely used in large diesel equipment.

The characteristics of traditional diesel engines: good thermal efficiency and economy, diesel engines use compressed air to increase the air temperature, so that the air temperature exceeds the self-ignition point of diesel, then inject diesel, diesel spray and air to mix and ignite and burn by itself . Therefore, diesel engines do not need an ignition system. At the same time, the oil supply system of the diesel engine is relatively simple, so the reliability of the diesel engine is better than that of the gasoline engine. Diesel engines have a high compression ratio due to the freedom from deflagration and the need for diesel spontaneous combustion. The thermal efficiency and economy are better than those of the gasoline engine. At the same time, under the condition of the same power, the diesel engine has large torque and low speed at the maximum power, which is suitable for the use of trucks.

However, due to the high working pressure of the diesel engine, the relevant parts are required to have high structural strength and rigidity, so the diesel engine is relatively heavy and bulky; the fuel injection pump and nozzle of the diesel engine require high manufacturing precision, so the cost is high; in addition, the diesel engine works rough , Vibration and noise are large; diesel is not easy to evaporate, and it is difficult to start the car when it is cold in winter. Due to the above characteristics, diesel engines were generally used in large and medium-sized trucks in the past. Traditionally, diesel engines have been seldom favored by cars due to their heavy weight, lower power per liter index than gasoline engines (lower speed), higher noise and vibration, and serious soot and particulate (PM) emissions. Especially with the new development of small high-speed diesel engines, a number of advanced technologies, such as electronically controlled direct injection, common rail, turbocharging, intercooling and other technologies, have been applied to small diesel engines, so that the shortcomings of the original diesel engines have been improved. The advantages of diesel engines in energy saving and CO2 emissions cannot be replaced by all heat engines, including gasoline engines, and become "green engines".