What is diesel engine and its working principle

What is Diesel engine?

Diesel engine, the name comes from the fact that diesel engines are compression ignition engines, invented by Rudolf Diesel, diesel engine is an engine that burns diesel to obtain energy release.

Diesel engine working principle

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

The diesel engine draws in pure air during the intake stroke. Near the end of the compression stroke, Diesel fuel is raised to more than 10MPa by the injection pump, Injected into the cylinder through the injector, Mixing with compressed high temperature air in a very short time, Formation of combustible gas mixture, Due to the high compression ratio of diesel engines (typically 16-22), So the air pressure in the cylinder at the end of compression can reach 3.5-4.5MPa, At the same time the temperature is up to 750-1000K (while the gasoline engine at this time the mixture pressure will be 0.6-1.2MPa, the temperature reaches 600-700K), Greatly exceeds the auto-ignition temperature of diesel fuel. Thus diesel fuel, after being injected into the cylinder, Immediately after mixing with air in a short time, it burns on its own. The air pressure in the cylinder rises rapidly to 6-9MPa, The temperature also rises to 2000-2500K. Under the high-pressure gas, the piston moves downward and drives the crankshaft to rotate and do work, and the exhaust gas is also discharged into the atmosphere through the exhaust pipe.

  The oil supply system of a normal diesel engine is driven by the engine camshaft, Diesel fuel is delivered to each cylinder fuel chamber with the help of a high-pressure oil pump. This kind of oil supply method has to change with the change of engine speed so it can’t do the best oil supply at various speed. 

    The common rail injection fuel supply system consists of a high-pressure fuel pump, a common supply line, injectors, an electronic control unit (ECU) and some pipe pressure sensors. Each injector in the system is connected to a common supply line through its own high-pressure fuel line, The common oil supply pipe acts as a hydraulic pressure accumulator for the injectors. During operation, the high-pressure fuel pump delivers fuel at high pressure to the common fuel supply line, High-pressure oil pump, pressure sensor and ECU form a closed-loop operation, Precise control of oil pressure in the common supply lin Completely changed the phenomenon of oil supply pressure varying with engine speed. Its main characteristics are the following three aspects:

  1. Injection timing and fuel metering are completely separated, and the injection pressure and process are controlled by the ECU in a timely manner;
  2. It is possible to adjust the injection pressure, injection start point and duration of each cylinder according to the engine working condition, so as to pursue the best control point of oil injection;
  3. High injection pressure and pre-injection of diesel can be achieved.

how does a diesel engine work
Diesel engine features

The advantages of diesel engines are high torque and good economic performance. The working process of a diesel engine process and gasoline engines have many of the same, Each work cycle also goes through four strokes: intake,  compression, work, and exhaust.  However, since diesel fuel is used in diesel engines, It has a higher viscosity than gasoline,Does not evaporate easily, And its auto-ignition temperature is lower than that of gasoline, Therefore, the formation of combustible mixture and ignition method are different from gasoline engines. The main differences are, The mixture in the cylinder of a diesel engine is compression ignition, not ignition. When diesel engine works, It is air that enters the cylinder, The temperature of the air in the cylinder can reach 500-700℃ when it is compressed to the end of, Pressure can reach 40-50 atmospheres. When the piston approaches the upper stop, The injector nozzles of the fuel supply system inject fuel into the cylinder combustion chamber at very high pressure and in a very short period of time, Diesel oil forms fine oil particles and mixes with high pressure and high temperature air, The combustible mixture burns itself and expands violently to produce an explosive force that pushes the piston downward to do work, At this time the temperature can reach 1900-2000 ℃, the pressure can reach 60-100 atmospheres, The torque generated is very high, so the diesel engine is widely used in large diesel equipment. 

Difference between gasoline engine and diesel engine

1、Structure In the structure, the gasoline engine cylinder top with spark plug, And diesel engines have injectors on top of the cylinders, This is the main difference between them;

2、Ignition method gasoline engine is to gasoline as fuel, diesel engine is to diesel fuel;

3、 Different performance Diesel engines are 30% more thermally efficient compared to gasoline, Thus, in terms of energy saving and fuel cost reduction engines, The promotion of the use of diesel engine cars is of great significance;

4、The application of different models of gasoline engines because of its small size, light weight, good starting characteristics are widely used in passenger cars, cars and other small body models.And relatively large, large torque, high reliability of diesel engines are mainly used in large and medium-sized trucks

Diesel engine classification:

1、According to the use: power generation, marine, automotive, agricultural irrigation, construction machinery and other industrial supporting diesel engines.

2、By body structure form is divided into: Single-cylinder diesel engine multi-cylinder diesel engine, which is divided into inline type and V-shaped arrangement according to the different cylinder arrangement;

3、According to the cooling method is divided into: air-cooled and water-cooled;

4、By work cycle process is divided into: two-stroke and four-stroke;

5、Divided by rated speed:High speed (rated speed above 1000r/min), medium speed (rated speed in the range of 600~1000r/min) and low speed (rated speed below 600r/min),At present, the rated speed of diesel engines used in diesel generator sets is generally 1500r/min or 3000r/min;

6、According to the air intake method is divided into: self-combustion suction type and pressurized type.

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