The fuel system is an important part of the diesel engine, and its technical status directly affects the working performance of the diesel engine. The technical performance of the fuel system gradually deteriorates due to the wear and adjustment of parts and improper use of the diesel engine during use, and some failures often occur, making the diesel engine unable to work normally. Below we briefly analyze the causes of common faults in the diesel engine fuel system to help users pay attention to prevention during use.
1 The oil path is not smooth
Diesel engine fuel system oil path is not smooth, generally caused by air in the oil path forming air resistance. The engine has troubles such as difficulty in starting, slow acceleration, etc., and it will automatically turn off in severe cases. When the oil pipe is blocked by aging, deformation and impurities, the cross-sectional area of the passage is reduced, or the filter screen of the diesel filter and the diesel core are blocked, which will cause insufficient fuel supply and reduce the engine power or start difficulty.
This kind of fault inspection and elimination can be done on site. Pump the oil to a certain pressure with a hand oil pump, and loosen the air screw. If there is air bubbles overflowing and the air is not exhausted, it means that the oil circuit is air entering; if there is no air bubbles but the diesel oil overflows weakly from the bleed screw, it means the oil circuit is blocked. Blocked. Normally, the air screw is slightly loosened, and a column of oil is sprayed out with a certain pressure immediately. The troubleshooting method is to find out the damaged or aging gaskets, joints or oil pipes and replace them.
2 Failure of fuel injection pump and injector
2.1 The oil supply of the high-pressure oil pump is too large or too small
If the oil supply of the high-pressure oil pump is not adjusted properly or the parts are worn out, the oil supply will be too large or too small. When the fuel supply is too small, it is difficult to start, the power is insufficient, and the speed drops; when the fuel supply is too large, the diesel engine speeds too high and emits black smoke, and there may even be "traveling" and "speeding" phenomena. At this time, the oil supply of the high-pressure oil pump should be re-adjusted to make the optimal oil supply meet the requirements.
The fuel supply of the fuel injection pump is too large, which is mainly caused by adjustment errors, such as the adjustment of the maximum oil volume adjustment nut, or the improper adjustment of the control arm limit screw. The fuel supply of the fuel injection pump is too small. The main reason is that the plunger and coupling parts are severely worn. At this time, new coupling parts should be replaced; the spring force of the delivery valve is reduced or even broken, so that the delivery valve is not closed tightly or the sealing cone of the delivery valve It is cushioned by dirt, causing oil leakage, and the oil supply is reduced.
2.2 Fuel supply advance angle is too large or too small
The fuel supply advance angle of the diesel engine fuel injection pump is too large or too small, which makes it difficult to start the diesel engine. In contrast, it is more difficult to start the diesel engine if the fuel supply angle is too small. If the fuel supply advance angle is too large, it first manifests as the engine oil temperature is too high, accompanied by higher water temperature; if the fuel supply angle is too small, the first manifestation is the water temperature is too high, accompanied by the exhaust temperature is too high, and the engine oil temperature rises. High is not obvious.
The fuel supply angle adjustment method, take a single-cylinder diesel engine as an example: (1) Remove the high-pressure fuel pipe from one end of the fuel injector, and turn it at a certain angle so that the spherical oil hole of the fuel pipe joint faces upward. Put the throttle at the maximum fuel supply position. (2) Slowly shake the crankshaft, observe the oil level of the high-pressure oil pipe joints, and stop rotating the crankshaft when the oil level just starts to emerge. (3) Observe the mark of the start of fuel supply on the flywheel. If it is exactly aligned with the mark engraved line on the water tank, the fuel supply time meets the requirements. (4) If the fuel supply start mark on the flywheel has exceeded the mark engraved line on the water tank, and the oil level has not yet risen, it means that the fuel supply time is too late (the fuel supply advance angle is small). At this time, the adjusting gasket should be removed to make the high-pressure pump body move backward. (5) If the oil level of the high-pressure pipe has risen, but the mark on the flywheel for the start of fuel supply has not been aligned with the mark on the water tank (not yet reached), it means that the fuel supply time is too early (the fuel supply advance angle is large). At this time, gaskets should be added to move the pump body forward. In general, every time the 0.2 mm thick gasket is changed, the oil supply angle can be changed by 3°, that is, an increase of 0. For a gasket with a thickness of 2 mm, the oil supply angle lags behind by 3°; each decrease is 0. With a 2 mm thick gasket, the oil supply angle is advanced by 3°.
2.3 The delivery valve is stuck
When the delivery valve is stuck in the closed position and the delivery valve cannot be lifted, the high-pressure oil pump cannot supply oil; when the delivery valve is stuck in the open position, the delivery valve cannot be closed. When the nut of the high-pressure oil pipe joint at one end of the high-pressure oil pump is loosened, the diesel will automatically flow out continuously. In either case, the diesel engine cannot start. Machines in operation will also stop. The main reason for the oil outlet valve stuck is that the diesel oil is not clean, the high pressure oil pump and the oil outlet valve are dirty. At this time, you should replace the clean diesel oil and clean the parts, especially the oil outlet valve and grind the oil outlet valve assembly. .
2.4 The injection pressure of the fuel injector is too large or too small
If the fuel injector adjustment screw is screwed too tightly, the fuel injection pressure will be too high. At this time, the diesel engine will knock the cylinder, and the low speed will be more obvious and cause difficulty in starting and power drop. If the adjusting screw is too loose, or the wear gap of the needle valve of the injector is increased, the injection pressure will be reduced, resulting in poor atomization, there will be no crisp knocking sound during fuel injection, difficulty in starting, and power drop. . When the above situation occurs, the pressure should be adjusted to the standard value on the fuel injection pressure test bench. If the parts are severely worn, they should be replaced.
2.5 The needle cutting of the injector is bitten to death
When the needle valve burns to death in the open state (that is, fuel injection), there will be a metal knocking sound with no rhythm in the working cylinder. When the needle valve burns to death in the closed state (that is, without fuel injection), the cylinder will not work. Therefore, the temperature of the injector and exhaust pipe in this cylinder position is lower than that of other cylinders. The local heating of the fuel injector is the main reason that the needle valve burns to death in the needle valve body. The fuel injector may not be completely scrapped after being burned out. After the needle valve is drawn out, it can still be used after being properly ground with clean engine oil. However, at this time, the premise should be that the needle valve does not turn blue, otherwise it means that the needle valve has been annealed and should be replaced with a new one.
3 Speed governing system failure
The main fault of the speed control system is "traveling", that is, the diesel engine's rotating speed is unstable, commonly known as "gasp", the rhythmic sound of "snoring, snoring" can be heard, and the rotating speed is fluctuatingly high and low. The reason for "traveling" should be inspected mainly from two aspects: the speed control system and the fuel system. The main reason for the speed control system is that the governor is inflexible, has high friction, or the governor has a large clearance. For example: the speed control lever is up and down, not in the middle position; the upper and lower clearance of the speed control lever is too large or too small; the height of the two arc surfaces of the speed control lever is inconsistent or wears more; the inclined surface of the speed control slide is different in the center The shaft degree is out of tolerance, causing partial wear of the steel ball and the sliding plate; the pump body of the high-pressure oil pump collides with the speed control lever, and the friction is large; the surface of the speed control gear is not flat, which makes the steel ball move more resistant, and so on. When the friction resistance is too large, reduce the friction resistance according to the specific situation; when the clearance is too large, reduce the clearance to eliminate "traveling". For example, when the two arc surfaces of the speed control lever are worn out, adding gaskets to the speed control slide plate is an effective measure to eliminate "traveling".