A diesel engine is an engine that burns diesel fuel to release energy. It was invented in 1892 by the German inventor Rudolf Diesel. In honor of this inventor, diesel fuel takes its name from his surname Diesel, and the diesel engine is also known as the Diesel engine. 

 Advantages and Disadvantages of Diesel Engines 

Advantages: high torque and good fuel economy. Each operating cycle of a diesel engine also includes the four strokes of intake, compression, power and exhaust. However, because the fuel used in a diesel engine is diesel, its viscosity is higher than gasoline, it evaporates less easily, and its auto-ignition temperature is lower than gasoline. Therefore, the formation of the combustible mixture and the ignition method are different from those of a gasoline engine. The main difference is that the mixture in the diesel engine cylinder is compression-ignited rather than spark-ignited.

When a diesel engine is operating, only air enters the cylinder. By the end of the compression stroke, the air temperature in the cylinder can reach 500-700℃ and the pressure can reach 40-50 atmospheres. As the piston approaches top dead center, the high-pressure pump injects diesel fuel into the cylinder at high pressure. The diesel forms fine droplets, mixes with the high-pressure, high-temperature air, and self-ignites. The mixture expands violently, generating force that pushes the piston downward to do work. At this point, the temperature can reach 1900-2000℃ and the pressure can reach 60-100 atmospheres. The resulting torque is very high, which is why diesel engines are widely used in large diesel vehicles. 

Disadvantages: because operating pressures are high, related components must have higher structural strength and rigidity, so diesel engines are comparatively heavy and large in size; the fuel injection pump and injectors require high manufacturing precision, so costs are relatively high; in addition, diesel engines run more roughly, with higher vibration and noise; diesel fuel does not evaporate easily, making cold starting difficult in winter. 

 Diesel Engine Classification 

 1. By operating cycle, diesel engines can be divided into four-stroke and two-stroke engines; 

 2. By cooling method, diesel engines can be divided into water-cooled and air-cooled engines; 

 3. By intake method, diesel engines can be divided into turbocharged and non-turbocharged (naturally aspirated) engines; 

 4. By combustion chamber, diesel engines can be divided into direct-injection, swirl-chamber and pre-combustion-chamber engines; 

 5. By number of cylinders, diesel engines can be divided into single-cylinder and multi-cylinder engines 

 6. By application, diesel engines can be divided into marine diesel engines, locomotive diesel engines, automotive diesel engines, generator-set diesel engines, agricultural diesel engines, construction machinery diesel engines, and more. Automotive diesel engines are mostly arranged in inline and V configurations; 

 7. By arrangement, diesel engines can be divided into inline diesel engines, V-type diesel engines, horizontally opposed diesel engines, radial diesel engines, W-type diesel engines, and more; 

 8. By mean piston speed, diesel engines can be classified as low-speed diesel engines, cm<6M/S, medium-speed diesel engines cm=6-9m/s, and high-speed diesel engines cm=9-13m/s.

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