What is a Diesel Engine?

by MOU YONG HONG on December 01, 2021

A diesel engine is an engine that burns diesel oil to obtain energy and releases it. It was invented by German inventor Rudolf Diesel in 1892. To commemorate this inventor, diesel is represented by his surname Diesel, and diesel engines are also called Diesel engine.

Working principle of diesel engine

The working process of a diesel engine is actually the same as that of a gasoline engine. Each working cycle also undergoes four strokes of intake, compression, work, and exhaust.

The diesel engine is in the intake stroke

Pure air is inhaled. At the end of the compression stroke, the diesel oil is increased to over 10MPa through the fuel injection pump, injected into the cylinder through the fuel injector, and mixed with the compressed high-temperature air in a short 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 3.5-4.5 MPa at the end of compression, while the temperature is as high as 750-1000 K (while the mixed gas pressure of gasoline engine at this time will be 0.6-1.2 MPa, The temperature reaches 600-700K), which greatly exceeds the auto-ignition temperature of diesel. Therefore, after the diesel is injected into the cylinder, it will immediately self-ignite and burn after being mixed with air in a short time. The air pressure in the cylinder rises rapidly to 6-9MPa, and the temperature also rises to 2000-2500K. Driven by the 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 fuel 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 by means of a high-pressure fuel pump. This kind of fuel supply mode changes with the engine speed and cannot achieve the best fuel supply 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 is connected to the public fuel supply through its own high-pressure fuel pipe. The pipes are connected, and the common fuel supply pipe plays a role in hydraulic pressure accumulation for the fuel injector. When working, the high-pressure fuel pump delivers fuel to the public fuel supply pipe at high pressure. The high-pressure fuel pump, pressure sensor, and ECU work together in a closed-loop to accurately control the oil pressure in the public fuel supply pipe, completely changing the fuel supply pressure with the engine speed. phenomenon. Its main characteristics are as follows:

1. Fuel injection timing is completely separated from fuel metering, and fuel injection pressure and fuel injection process are controlled by ECU in time;

2. The fuel injection pressure, start point, and duration of fuel injection can be adjusted according to the working conditions of the engine, so as to pursue the best control point of fuel injection;

3. High fuel injection pressure can be achieved, and diesel pre-injection can be achieved.

Advantages of diesel engines

The advantages of diesel engines are large torque and good economic performance. Each working cycle of a diesel engine also undergoes four strokes: intake, compression, work, and exhaust. However, because the fuel used in diesel engines is diesel, its viscosity is higher than gasoline, and it is not easy to evaporate, and its spontaneous combustion temperature is lower than gasoline. Therefore, the formation and ignition of the combustible mixture are different from gasoline engines. The main difference is that the mixture in the cylinder of a diesel engine is compression-ignited rather than ignited. When a diesel engine is working, air enters the cylinder. When the air in the cylinder is compressed to the end, 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 high-pressure pump on the engine injects diesel into the cylinder at high pressure. The diesel forms fine oil particles, which are mixed with high-pressure and high-temperature air. The diesel mixture burns by itself and expands violently, generating explosive force, pushing the piston down to do work. At this time, the temperature can reach 1900-2000℃, the pressure can reach 60-100 atmospheres, and the torque produced is very large, so diesel engines are widely used in large diesel vehicles.

Disadvantages of diesel engine

The speed is lower than that of gasoline engines (generally 1800-3000R/MIN), high quality, high manufacturing and maintenance costs, high noise, and difficult starting. In addition, diesel vehicles often run on highways. When the vehicle runs for a long time, the engine temperature and pressure are high, and more soot and carbon deposits are generated in the cylinder. The engine oil is also prone to oxidation to produce gums. Therefore, diesel engine oil requires a good high temperature. Purity. However, the shortcomings of diesel engines are being overcome. With the improvement of diesel engine speed indicators, quality indicators, noise indicators, etc., and diesel engines emit much less harmful gases than gasoline engines (especially less CO), they are used in small and medium-sized cars. The trend of diesel engines is becoming more and more obvious. It belongs to compression ignition. The fuel relies on the heat generated by the compression of air in the cylinder to ignite, that is, air compression will increase the temperature. When the temperature of the compressed air is higher than the ignition point of diesel, diesel will burn.

This article mainly introduces the definition, working principle, and advantages and disadvantages of diesel engine. If you want to know more about diesel engine, please contact me.


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