Why is it difficult to start a diesel engine in winter?

The common faults of diesel engine fuel system include difficult starting, insufficient power, unstable operation, abnormal exhaust smoke color, out of control and so on. 1. Starting difficulty 1) Phenomenon: the diesel engine has no starting signs, or it can't be started although it has starting signs; When starting, the exhaust pipe smokes little or no smoke; The exhaust pipe emits white smoke when starting. 2) Reason: (1) There is no oil in the fuel tank or the fuel tank switch is not turned on; (2) The vent hole of the fuel tank cover is blocked; (3) The tubing is blocked, broken or the pipe joint leaks oil; (4) There is air or water in the oil circuit or water in the cylinder; (5) The diesel filter is blocked or unsealed; (6) The pressure-limiting relief valve of low-pressure oil circuit is not tightly sealed, the spring is too weak, and the spring is broken or out of balance, resulting in low oil pressure; (7) The oil transfer pump is not working normally or the oil inlet screen is blocked; (8) The quantity of diesel oil used is wrong or the quality of diesel oil is poor; (9) The plunger of the fuel injection pump does not return due to the fracture of the return spring or excessive wear of the plunger coupler; (1O) The adjustable fork on the oil supply pull rod or the adjustable sector teeth on the plunger sleeve are loose; (1 1) The coupling of the oil outlet valve is not closed properly or the spring is broken; (12) The high-pressure oil pipe is broken or the joint is loose; (13) The oil supply time is too early or too late or the adjustable part of the coupling is loose; (14) The injection pressure of the injector is too low, because the needle valve coupling is excessively worn, the lower cone of the needle valve is not tightly sealed with the valve seat, and the injector spring is broken or improperly adjusted. (15) The needle valve of the injector is stuck and cannot be closed or opened; (16) The nozzle of the fuel injector is blocked or poorly injected; (17) Insufficient cylinder compression pressure or serious air filter blockage; (18) The startup speed is too low or the startup preheating degree is not enough; (19) The fuel supply rod of the fuel injection pump is stuck in the parking position or the starting fuel supply adjustment is insufficient. 3) Diagnosis method: The necessary conditions for the smooth start of diesel engine are: sufficient starting speed, high cylinder compression pressure, sufficient air and fuel, good preheating of combustion chamber, and necessary preheating and insulation of cooling system, lubricating system and even oil supply system in winter. When the ambient temperature is higher than 5℃, the diesel engine should generally be able to start smoothly within 5 s, and it is normal to start several times. If it doesn't catch fire after repeated starting, it should be considered as starting difficulty. At this time, we must first check whether the necessary conditions for starting can be met, and if they are not met, they will be met (except the compression pressure of the cylinder), and pay attention to the smoke exhaust of the exhaust pipe during starting, and then diagnose according to the following methods. (1) If the exhaust pipe does not smoke when starting, the fuel injection pump will not supply oil. According to the following method, if air is discharged from the air bleed screw first, and then the oil flow is normal, it means that there is air in the low-pressure oil circuit that hinders the fuel flow. The air in the low-pressure oil circuit should be removed immediately. When removing air, the fuel tank should be filled with oil first. When the oil circuit is well sealed, first operate the hand pump to supply oil, then loosen the deflation screw on the diesel filter to expel air until the fuel flowing out of the deflation screw hole does not contain bubbles, and then tighten the deflation screw when the fuel overflows. In the same way as above, loosen the two deflation screws at the upper part of the fuel injection pump first, and then tighten them after the air in the low-pressure oil chamber of the fuel injection pump is exhausted. When the weather is too cold, if there is water in the diesel oil, it will freeze, or because the diesel oil number is improperly selected and the viscosity is too high to flow, the fuel injection pump will not supply oil. In this case, we should try to heat the whole fuel supply system, and then unscrew the oil drain plugs of the fuel tank and diesel filter to drain water and dirt, and drain the water in the low-pressure oil circuit like air until there is no water drop in the fuel flowing out of the exhaust screw of the fuel injection pump. If the diesel brand used does not meet the requirements, it should be replaced. The specification of light diesel oil in China (GB252-64) is named according to the freezing point. There are five grades:+10, 0,-10, -20, -35. Numbers indicate the freezing point temperature of diesel oil. Such as -20 diesel oil, indicating that its freezing point is -20℃. When choosing diesel oil, it should be carried out according to different seasons and local temperature conditions. In general, the freezing point of diesel oil should be 3-5℃ lower than the local seasonal minimum temperature. If the freezing point of diesel oil is higher than the local seasonal minimum temperature, it will not only make the fluidity of diesel oil worse, affect the normal oil supply, but also make the diesel engine work rudely because of poor atomization performance.

(2) If the exhaust pipe emits white smoke or gray smoke when starting, it is still not easy to catch fire. Diagnose and check whether there is water in diesel oil according to the following methods. Check and remove the water in the low-pressure oil circuit in the same way as above. When checking and removing the water in the high-pressure oil circuit, you can remove the side cover of the fuel injection pump and unscrew the pipe joint between the high-pressure oil pipe and the fuel injector, so that the fuel supply pull rod is at the maximum fuel supply position. While pumping oil by hand, pry the plunger of the fuel injection pump up and down with a special tool or a large screwdriver. If the loose pipe joint flows out of water or water drops are mixed in the fuel, it means that there is water in the high-pressure oil circuit. Continue to pry until the pure fuel flows out and tighten the pipe joint when the fuel overflows. Drain the water in the high-pressure oil pipe in turn, or use this method to remove the air in the high-pressure oil pipe. Check the starting oil supply. The starting oil supply of diesel engine is often equal to or greater than the rated oil supply. Some models, such as none. The type II fuel injection pump used in the Yellow River JN1106 even requires that the starting oil supply be increased by about 50% compared with the rated oil supply. During inspection, the accelerator pedal should be stepped to the bottom, the control arm of the fuel injection pump should lean against the high-speed limit screw, and then observe or measure whether the fuel supply pull rod can be in the limit position in the fuel supply direction. For example, in paragraph. In the second fuel injection pump, when the accelerator pedal is stepped to the bottom when the engine is at rest, the fuel supply rod moves a certain distance from the rated fuel supply position to the fuel supply direction under the action of the governor idle spring, the speed regulating spring and the starting spring, so as to ensure the increase of the fuel supply for starting, thus making the starting smoothly. However, if the oil supply is adjusted too much, or too much oil is accumulated in the combustion chamber due to repeated starting failures, it will be difficult for the diesel engine to start. Check the injection quality of the fuel injector. Remove the injectors of each cylinder in turn and reconnect them to the corresponding high-pressure oil pipes. Place the fuel supply rod at the maximum fuel supply position, pry the plunger of the corresponding fuel injection pump cylinder with a special tool or a large screwdriver, and observe the spray situation. A good oil mist bundle, the oil mist must be very uniform and delicate, without obvious oil drops and oil flows, and without the phenomenon of different shades. Moreover, the oil cut-off is crisp, the cone angle and direction of the oil mist are normal, there is no oil dripping phenomenon before and after injection, and the vicinity of the injection hole for multiple injections is dry or slightly wet. If the spray quality of the fuel injectors can't meet the above requirements, and the difference is far, or the spray holes of individual fuel injectors are blocked, it is difficult to start the engine. 2. Insufficient power (1) phenomenon: when the car is driving, the power is insufficient, the acceleration is invalid, and the speed cannot be increased to the due range. 2) Reason: (1) 2-17 of the above "startup difficulty"; (2) Insufficient heat preservation measures in winter lead to low working temperature of the engine; (3) Inaccurate valve timing; (4) The oil supply pull rod or the moving parts of the governor are stuck, and the speed regulating spring is broken, resulting in the oil supply pull rod not reaching the rated oil supply position; (5) The governor is not properly adjusted, which causes it to work prematurely at high speed, so that the engine cannot reach the rated speed; (6) The rated oil supply is adjusted too low or too high; (7) Individual cylinders do not work or work badly; (8) There is too much oil in the oil pool or oil on the cylinder. 3) Diagnosis method: When the engine is unstable, the cylinder that does not work or works badly can be found by the single cylinder fuel cut-off method. At this time, the engine should be set to run at idle speed, and the high-pressure oil pipe joints of each cylinder should be loosened with a wrench to make diesel oil leak. If there is no obvious change in the engine operation after the single cylinder is cut off, it means that the cylinder does not work; If the operation changes little, the cylinder is not working well. For cylinders that are not working or working abnormally, in-depth diagnosis should be carried out until the cause of the failure is found out.