1. Insufficient cylinder compression pressure
The main reasons for the insufficient compression pressure of the cylinder are: severe wear of the piston ring (severe wear of the piston ring will cause the diesel engine to emit blue smoke, which is not described in this article), and the compression ratio is too small (the piston crown gap is too large or the valve seat ring is recessed too deep ) Or the valve is not tightly sealed.
A, the piston crown clearance is too large
If the diesel engine is assembled, the piston crown clearance is not strictly checked and adjusted according to the requirements, or if the piston crown clearance is too large when adjusted improperly, it will directly affect the compression ratio of the diesel engine and thus the cylinder compression pressure. As the compression ratio becomes smaller, the compression pressure and temperature of the cylinder are reduced, and the fuel combustion conditions become worse. The fuel combustion is incomplete and insufficient, and the diesel engine emits black smoke seriously.
Ensure that the piston crown clearance is correct is one of the important events that must be strictly done 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. Under normal circumstances, as long as the installation is correct, the piston crown clearance will not change during use.
B, the valve is not tightly sealed
Severe deformation or wear of the valve sealing belt will lead to inadequate valve sealing, directly reduce the compression pressure and temperature of the cylinder, make the fuel combustion incomplete and incomplete, and cause the diesel engine to emit black smoke.
C. The valve seat is recessed too deep
The valve seat ring has withstood the high temperature of combustion and the strong impact of the valve for a long time. In addition, the aluminum alloy nature of the bottom hole of the valve seat ring will gradually increase the recess of the valve seat ring, so that the size between the valve plane and the bottom surface of the cylinder head will increase relatively, correspondingly increase The volume of the combustion chamber is reduced, and the compression ratio of the diesel engine is reduced, thereby reducing the compression pressure and temperature of the cylinder, resulting in incomplete and insufficient fuel combustion, and the diesel engine emits black smoke.
When the compression pressure of the cylinder 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 when the diesel engine is weak (the acceleration performance is too poor). The fuel consumption increases. If the above problems or phenomena occur during the use of the diesel engine, you can use a special cylinder pressure checklist to measure the cylinder compression pressure. The cylinder compression pressure measuring device is generally installed in the injector hole, and the single-cylinder test is carried out cylinder by cylinder. Then compare with the standard value to confirm whether it is too low.
Elimination method: If the cylinder compression pressure is measured and it is confirmed that the diesel engine emits black smoke due to the low cylinder compression pressure, it is necessary to check the piston crown clearance, the recessed depth of the valve seat ring and the seal between the valve and the valve seat ring. The specific approach is:
Loosen the cylinder head bolt, remove the cylinder head, put the 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, remove the cylinder head and measure the thickness of the lead wire, if measured If the value is within the range of technical requirements, it is clear that the piston crown clearance is correct. On the contrary, it shows that the piston crown clearance is not correct and needs to be adjusted (mainly the thickness of the cylinder head is selected according to the measured value).
After removing the cylinder head, carefully observe and measure the distance between the valve head plane and the bottom surface of the cylinder head. If the measured value is greater than the technical requirements, it means that the valve seat ring is too deep and needs to be repaired. The repair method is: replace the valve seat ring and all valves, and regrind the valve. For specific requirements of valve seat ring, please refer to relevant technical requirements.
If the recessed depth of the valve seat ring is qualified, the sealing tape between the valve and the valve seat ring should be carefully checked. Under normal circumstances, after long-term use, the sealing tape between the valve and the valve seat ring will have greater wear and deformation and need to be repaired. The specific method is: twist the valve seat sealing tape, replace the valve and re-grind the valve.
2. Incorrect valve clearance
The valve clearance is incorrect, which affects the timing of the diesel engine valve. That is, the valve is opened when it is opened and closed when it is closed. It directly affects the intake air of the diesel engine and reduces the excess air coefficient of the diesel engine, causing the diesel engine oil and gas mixture to be too rich. The fuel combustion is incomplete and incomplete, and the diesel engine emits black smoke.
Incorrect valve clearance In addition to the black smoke from the diesel engine, there are the following phenomena:
Diesel engine power is insufficient Diesel engine may be difficult to start may have a 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 a hand or feeler gauge.
Elimination method: readjust the valve clearance as required.
