What is the reason for the loud noise and vibration of diesel engines?

The reason for the loud vibration and loud noise is due to the difference between diesel and gasoline. In order to ignite diesel, the current technology is to increase the compression ratio of the engine, so the compression ratio of diesel engines is very high, generally around 20.

However, an excessively high compression ratio greatly reduces the smoothness of the engine's operation. The sudden complete combustion will cause the gas in the cylinder to rapidly expand, so that the piston will have a rapid downward force. Due to the running inertia of the engine, the piston cannot move downward smoothly, which will cause cylinder knocking, that is, the piston skirt collides with the cylinder wall. This is one of the important reasons why diesel engines have greater noise and vibration than gasoline engines. one.

The vibration is particularly strong, which may be caused by problems such as low technical content of the engine itself, or its relatively long service life, as well as abnormal oil supply system, unclean fuel injector, dirty throttle valve, etc. of.

In a diesel engine, since the fuel itself relies on compression ignition, which is the same working condition as when compression ignition knock occurs in a gasoline engine, a lot of noise will inevitably be produced. In addition to the greater noise caused by the difference in combustion in the cylinder, other mechanisms of the diesel engine also produce greater noise, such as the fuel pump of the diesel engine. Different from gasoline engines, during the compression stroke, gasoline engines compress a mixture of oil and gas, while diesel engines compress pure air.

Extended information:

Diesel engine features:

1. The advantages of diesel engines are large torque and good economic performance. The working process of diesel engines has many similarities with gasoline engines. Each working cycle also undergoes the 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 and it is not easy to evaporate, but its auto-ignition temperature is lower than that of gasoline. Therefore, the formation and ignition method of the combustible mixture are different from those of gasoline engines.

2. The main difference is that the mixture in the cylinder 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, the temperature can reach 500-700°C and the pressure can reach 40-50 atmospheres.

3. When the piston is close to top dead center, the fuel injection nozzle of the fuel supply system injects fuel into the cylinder combustion chamber with extremely high pressure in a very short time. The diesel fuel forms fine oil particles, which interact with the high pressure and high temperature The air is mixed, and the combustible mixture burns on its own, expands violently to produce explosive force, and pushes the piston downward to perform work. At this time, the temperature can reach 1900-2000°C, the pressure can reach 60-100 atmospheres, and the torque generated is very large, so diesel engines are widely used. Applied to large diesel equipment.

4. Characteristics of traditional diesel engines: better 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. At this time, diesel and diesel are injected The spray mixes with air and ignites itself. Therefore, diesel engines do not require an ignition system.

5. At the same time, the fuel supply system of diesel engines is relatively simple, so the reliability of diesel engines is better than that of gasoline engines. Since it is not subject to knocking restrictions and the need for diesel spontaneous combustion, the compression ratio of diesel engines is very high. Thermal efficiency and economy are better than gasoline engines. At the same time, under the same power, diesel engines have large torque and low speed at maximum power, making them suitable for use in trucks.

6. 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 bulky and large in size; the fuel injection pump and nozzle of the diesel engine require high manufacturing precision, so The cost is higher.

7. In addition, the diesel engine works rough and vibrates and makes loud noises; diesel is not easy to evaporate, and it is difficult to start when the car 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 rarely favored by cars because they are relatively bulky, have lower power per liter than gasoline engines (lower speed), higher noise and vibration, and serious soot and particulate (PM) emissions.

8. Especially with the new development of small high-speed diesel engines, a number of advanced technologies, such as electronically controlled direct injection, direct injection, turbocharging, intercooling and other technologies, have been applied to small diesel engines. Application, the shortcomings of the original diesel engine have been better solved, and the advantages of the diesel engine in terms of energy saving and CO2 emissions cannot be replaced by all heat engines, including gasoline engines, and it has become a "green engine".

Reference: Baidu Encyclopedia Diesel Engine