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The reason why diesel engines emit black smoke

Publisher: DTS     Release time:2018-11-16

After the wear valve, piston ring and cylinder liner of the piston ring and cylinder liner are worn, the compression pressure is insufficient and the oil is on the combustion chamber, so that the normal proportion of the mixture at the end of the compression stroke changes, the fuel is in the absence. combustion under oxygen conditions, the combustion process is prone to coke formation and the exhaust gas forms a large amount of black smoke.

The shape of the combustion chamber changes. the shape of the combustion chamber due to the manufacturing quality and long-term usage resulting in a decline in the technical condition. And the compression residual seam is too large, too small, and the piston position is wrongly installed, the shape and volume of the combustion chamber will be changed, thereby affecting the mixing of fuel and air. The quality makes the fuel burning conditions worse.

Injector dynamometer diesel engine exhaust smoke is closely related to fuel atomization quality. In the diesel fuel injection process, the injection pressure drops and the atomization quality is poor at each end of the injection, so that the droplet diameter ratio is mainly The oil droplets in the spraying stage are 4-5 times larger (the volume is increased by about 100 times), and the evaporation and burning time of these oil droplets is short, the concentration of surrounding oxygen is low, and soot is easily generated. The injector is not atomized, poorly atomized or dripped, so that the fuel cannot be sufficiently mixed with the air in the cylinder and cannot be completely burned. The phenomenon of black smoke caused by poor injector operation is more obvious when the diesel engine runs at low speed, because the intake vortex in the cylinder is weak at low speed, the possibility of oil droplets or oil bundles being dispersed by the airflow is reduced and the waiting time is longer. it is easier to form carbon black discharge.

The oil supply is too large so that the amount of oil entering the cylinder is increased, resulting in less oil and less fuel combustion. In addition, excessive workload, poor fuel quality, and low operating temperatures can cause exhaust fumes. The pyrolysis reaction of the fuel in the diesel engine is unavoidable, especially in the diesel engine with space mixing combustion. Because the high temperature gas surrounds the liquid oil droplets, the conditions favorable to the cracking reaction are generated, so a large amount of carbon is generated in the initial stage of combustion. When the diesel engine is in normal combustion, a large amount of carbon particles formed at the initial stage of combustion can be substantially burned before the exhaust valve is opened, and the exhaust gas is substantially smokeless. However, under certain unfavorable conditions, the carbon particles cannot be burned in time but instead are agglomerated and adsorbed, forming larger soot particles or flocs in the cylinder and during the exhausting process, causing the exhaust to emit black smoke.

Improper adjustment of fuel supply advance angle (1) The fuel supply advance-angle is too large, and the fuel is injected into the combustion chamber prematurely. Because the pressure inside the cylinder is lower, the fuel cannot be burned. When the piston is up, the cylinder reaches a certain pressure. And the temperature, the combustible mixture burns. In the direct injection diesel engine, when the other parameters are constant, increasing the injection advance angle can reduce the exhaust smoke. Because increasing the fuel injection advance angle will lengthen the retardation period so that the amount of oil injected into the cylinder before the fire increases, the premixing amount increases, the premixed gas increases, the burning speed is accelerated, and the combustion can be terminated earlier, thereby making the main combustion The formation of carbon particles has a higher temperature and a longer residence time at high temperatures, which is beneficial to the disappearance of carbon particle oxidation. However, premature fuel injection increases the amount of premixed fuel, making the diesel engine work rough, increasing combustion noise, causing large mechanical loads and more black smoke emissions.


(2) The fuel supply advance-angle is too small, the fuel injected into the cylinder is too late and some of the fuel is not separated or formed into a combustible mixture so that some of the fuel in the exhaust pipe is decomposed and burned by the high temperature. The black smoke is discharged along with the exhaust gas.

How to do if the diesel engine emits black smoke? 


1. First check whether the advance angle is too large or too small according to the instructions.

2. Check or readjust the pressure range of the fuel injection pump according to the pressure demand of the fuel injection pump.

3. Check if the injector has poor atomization, jamming or dripping. If it is confirmed, it is good to replace the injector or injector directly.

4.The fuel injection pump should not be adjusted as much as possible.

5. Check that the valve clearance according to the instructions.

6. Unblock or improve the intake pipe.

7. Never use inferior diesel. Although the engine has several layers of filtering devices, it will inevitably cause problems for a long time.




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