The abnormal sound of diesel combustion (working rough sound) refers to a rhythmic metal-like percussion sound when the engine is working.
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â— Reason analysis
When the diesel engine is in operation, the diesel fires a combustion process in the combustion chamber, that is, the combustion process. It is divided into four phases, namely the backward phase of fire, the rapid combustion phase, the slow combustion phase and the complementary combustion phase. The so-called post-ignition period refers to the fact that the diesel injection chamber is not immediately burned. It needs to be evaporated, mixed with air, oxidized and heated, and then flamed. Into the fast-burning period, the fire source is rapidly formed, the combustion rate is accelerated, and the heat is released. Faster and faster, the temperature and pressure in the cylinder rise sharply. During this period, the rotation angle of the crankshaft rotates by 1°, the rate of increase in gas pressure is generally 0.39 to 0.59 MPa, and the piston passes through the top dead center crank angle 10° to 15°. The gas pressure rises to the highest point, and then transits to the leaner period and even to the complementary period.
From the diesel engine combustion process, the piston compression is close to top dead center, and the diesel fuel is injected into the cylinder. After the ignition period, when the fuel enters the fast burning period, the fuel accumulated due to the ignition is simultaneously burned with the fuel of the investor. The speed of combustion is accelerated, the amount of heat released is faster and more, and the temperature and pressure in the cylinder rise sharply. If the rotation angle of the crankshaft rotates by 1° each time during this period and the gas pressure increase rate exceeds 0.39 to 0.59 MPa, the gas pressure increase rate is too high and the combustion gas generates a high-pressure wave. High-pressure waves of the combustion gases in the combustion chamber impact the parts that enclose the combustion gases and emit a similar metallic percussion sound, that is, the diesel combustion is abnormally sounded.
From the above, it can be seen that the fuel supply advance angle is too large (the injection time into the cylinder is too early), the fuel quality is poor, the fuel supply advance angle is too large (the injection time to the cylinder is too early), the fuel quality is poor, and the fuel supply is poor. Excessive volume, over-load operation, poor fuel atomization, etc. will all result in poor preparation conditions for combustion and prolonged post-ignition periods, leading to an increase in the rate of pressure increase during the flash-fuel period and brutal work.
When diagnosing and excluding the diagnosis, the diagnosis should be made first according to the conditions described in the symptoms. If the abnormal noise meets the rude sound of the engine initially determined in the fault phenomenon, the following checks shall be made:
Inspection and adjustment of diesel engine oil advance angle: Remove the observation window cover of the first cylinder oil tube and flywheel casing on the fuel injection pump, and then turn the flywheel to rotate. At this time, observe the injection port of the fuel injection pump (high pressure oil pump), if oil The oil level begins to rise and stops turning the flywheel. At this time, the observation window fixing mark (pointer or engraved line) indicates that the scale on the flywheel is the fuel advance angle (the optimum advance angle of the diesel engine in the unified combustion chamber is generally 25°. ~35°, the best fuel injection advance angle of the divided combustion chamber diesel engine is smaller, generally 15 ° ~ 20 °).
If the indicated injection advance angle does not comply with the technical documentation, it should be adjusted. Adjustment, some diesel engines (such as 135 diesel engine used vertical injection pump) fuel injection time adjustment is in the fuel pump drive coupling, can loosen the coupling clamping bolts, shake the flywheel to make oil advance The angle mark is aligned with the observation window fixing mark, and then the coupling clamping bolt can be tightened.
If the timing of fuel supply is directly driven by the timing gear of the engine, the fixing screw of the injection pump will be loosened and the injection pump will be swung so that the advance angle of the injection pump can meet the technical requirements. After the adjustment, the fixing screw can be tightened.
Road test: road test should choose a good road, with a low speed block to stabilize the speed driving, the accelerator pedal step in the end, so that the vehicle accelerates. At this time, if you can hear the diesel engine has a slight rough sound of work, when the sound speed disappears, the sound disappears when the fuel supply advance angle is normal; if you hear the strong sound of the diesel engine work and the vehicle speed does not disappear after the increase, then explain the oil supply time Too early, it should be readjusted. If you do not hear rough work noise when you are accelerating, and you feel that you are unable to drive, it means that the fuel supply is too late and you should readjust it.
Cummins NH-220 diesel engine fuel injection time adjustment, change the thickness of the adjusting gasket under the pin shaft cover of the roller frame, can adjust the fuel injection time, that is, increase the gasket, and the injection time is advanced. On the contrary, the gasket is reduced and the injection time is delayed.
Fuel Quality Check: Select good quality fuel.
If the fuel supply is too large, the injection pump should be removed and placed on the calibration table for verification.
When the engine load is too large, rough noise occurs and the engine load should be reduced.
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