1. Insufficient cylinder compression pressure
The main reasons for insufficient cylinder compression pressure are: serious wear of piston ring (serious wear of piston ring will cause serious blue smoke of diesel engine, which will not be described in this paper), small compression ratio (too large clearance of piston crown or too deep recess of valve seat ring), or lax valve sealing, etc.
a. Piston crown clearance is too large
If the piston crown clearance is not checked and adjusted in strict accordance with the requirements when assembling the diesel engine, or the piston crown clearance is not adjusted properly, the compression ratio of the diesel engine will be directly affected, and then the cylinder compression pressure will be affected. As the compression ratio becomes smaller, the compression pressure and temperature of the cylinder will be reduced, and the fuel combustion conditions will become worse. The fuel combustion is incomplete and insufficient The machine is seriously emitting black smoke.
Ensuring the correct piston crown clearance is one of the important events that must be strictly achieved when assembling the diesel engine. When assembling the diesel engine, the piston crown clearance must be adjusted within the tolerance range required by the technical specifications. Generally, as long as it is installed correctly, the piston crown clearance will not change in the process of use.
b. The valve seal is not tight
Serious deformation or wear of valve sealing belt will lead to loose valve sealing, directly reduce cylinder compression pressure and temperature, incomplete and insufficient fuel combustion, and serious black smoke of diesel engine.
c. The valve seat ring is too deeply recessed
The valve seat ring has been subjected to high combustion temperature and strong impact of the valve for a long time. In addition, the aluminum alloy property of the bottom hole of the valve seat ring will gradually increase the concave of the valve seat ring, increase the size between the valve plane and the bottom surface of the cylinder head, correspondingly increase the volume of the combustion chamber and reduce the compression ratio of the diesel engine, so as to reduce the compression pressure and temperature of the cylinder, resulting in incomplete fuel combustion . insufficient, and the diesel engine emits serious black smoke.
When the cylinder compression pressure is insufficient, in addition to making the diesel engine emit black smoke, there are the following phenomena:
The power of the diesel engine is insufficient during operation, and the acceleration of the diesel engine is weak (the acceleration performance is too poor) Fuel consumption increases. If the above problems or phenomena occur during the use of the diesel engine, a special cylinder pressure check gauge can be used to measure the cylinder compression pressure. The cylinder compression pressure measuring device is generally installed in the injector hole, tested cylinder by cylinder, and then compared with the standard value to confirm whether it is too low.
Troubleshooting: if the cylinder compression pressure is measured and it is confirmed that the black smoke of diesel engine is caused by low cylinder compression pressure, it is necessary to check the piston crown clearance, the concave depth of valve seat ring and the sealing between valve and valve seat ring. The specific methods are as follows:
Loosen the cylinder head bolt, remove the cylinder head, put lead wire on the top of the piston, then install the cylinder head, tighten the cylinder head bolt as required, and then loosen the cylinder head bolt. After removing the cylinder head, measure the thickness of lead wire. If the measured value is within the range of technical requirements, it means that the piston crown clearance is correct. Otherwise, it means that the piston crown clearance is incorrect and needs to be adjusted (the thickness of cylinder gasket is mainly selected according to the measured value).
After taking out the cylinder head, carefully observe and measure the distance between the large head plane of the valve and the bottom surface of the cylinder head. If the measured value is greater than the value required by the technical requirements, it indicates that the valve seat ring is too deep and needs to be repaired. The repair method is to replace the valve seat ring and all valves and grind the valves again. Please refer to the relevant technical requirements for the specific requirements of the valve seat ring.
If the concave depth of the valve seat ring is qualified, carefully check the sealing belt between the valve and the valve seat ring. Generally, after long-term use, the sealing belt between the valve and the valve seat ring will be greatly worn and deformed and need to be repaired. The specific methods are: grinding the sealing belt of the valve seat ring, replacing the valve and regrinding the valve.
2. Incorrect valve clearance
Incorrect valve clearance affects the valve timing of the diesel engine, that is, the valve is opened when it should be opened and closed when it should be closed, which directly affects the air intake of the diesel engine, reduces the excess air coefficient of the diesel engine, resulting in excessive diesel oil-gas mixture, incomplete and insufficient fuel combustion and black smoke of the diesel engine.
Incorrect valve clearance not only causes black smoke from the diesel engine, but also the following phenomena:
The diesel engine has insufficient power, the diesel engine may have difficulty starting, and there may be strong metal collision sound
The basic method to confirm whether the valve clearance is correct is to open the valve cover and check the valve clearance with hand feeling or feeler gauge.
Troubleshooting: readjust the valve clearance as required.
