Several misunderstandings of starting and stopping of diesel engine

1. Common incorrect startup method

(1) Put the throttle at the maximum position during start-up. For a diesel engine equipped with a full-scale speed governor, when the throttle is increased to a certain position during start-up, the fuel supply of the fuel injection pump has reached its maximum. Even if you continue to increase the throttle, the fuel supply of the fuel injection pump will not increase any more, and the preload of the governor spring will continue to increase, causing the speed of the diesel engine to increase sharply after it starts. However, the temperature of the newly started diesel engine is generally relatively low, and the lubrication conditions of each friction surface are relatively poor. Therefore, the diesel engine enters into high-speed operation as soon as it is started, which inevitably increases the wear of each pair of movements, and even causes major failures such as burning of the welding shaft. Therefore, when starting the diesel engine, the throttle should be placed at 2/3 of the positioning plate (this position is the maximum fuel supply of the fuel injection pump). It is not necessary to increase the throttle to the end so as to avoid excessively high speed after the diesel engine starts. If the technical condition of the diesel engine is poor, the throttle may be further enlarged, but it should not exceed 4/5 of the positioning plate.

(2) Preheating the air with open flame during start-up In winter, the diesel engine is difficult to start. Some operators remove the air cleaner cover and ignite a group of tarpaulin at the intake nozzle to increase the air temperature entering the cylinder. Although this approach helps the start-up of diesel engines, it can also create some hazards. The main hazards are: 1 preheat the air with an open flame, the air entering the cylinder is not filtered (dry centrifugal filtration) or is not filtered at all (some pilots ignite at the inlet of the cylinder head) so that the air contains impurities. Air directly into the cylinder, exacerbated the wear of cylinder liners, pistons, piston rings and valves, valve seats and other mechanical parts. In addition, the thick smoke from the open fire enters the cylinder and easily forms carbon deposits. 2 If the air filter is disassembled every time it is started, it may cause the air intake pipe to be closed tightly, resulting in air leakage, and some air will enter the air cylinder without being filtered, which is extremely unfavorable to the operation of the engine. 3 The start of open fire is not conducive to safety, especially some old locomotives. The leakage of fuel oil is serious and can easily cause fire. Starting at a low temperature, the diesel engine can be preheated and heated by adding hot water to the cooling system and baking the oil pan with an understated fire.

(3) After starting the slope starting diesel engine, there is a problem (the battery is not fully charged, the starting machine or the starting circuit is malfunctioning, etc.). Some operators do not repair it in time. Instead, they take the method of allowing the slope of the vehicle to slide. The wheel drive engine rotates to start the diesel engine. Little do they know that often take a slope start, the bad many. The main hazards are: 1 The diesel engine has no preheating process. If the diesel engine is not warmed up for a long time, the lubricant on each friction surface has been lost and the oil film has been seriously damaged. The diesel engine suddenly runs at a high speed, but the lubricant cannot be sent to all friction surfaces in time. The wear of the parts. 2 When starting the sloping ramp, due to the excessive engagement of the clutch, it is easy to damage the transmission components such as the clutch and the transmission by excessive impact load. 3 After the diesel engine is started, the emergency brake must be applied. This will affect the service life of the brakes and components of the traveling mechanism, especially the tire wear. Moreover, the higher the speed after starting, the more prone to accidents.

(4) When a tractor pulls and starts to pull and starts, the front vehicle usually hangs the low speed gear, and the rear vehicle hangs the high speed gear (the speed of the diesel engine starts to move at a low speed). The diesel engine is started by driving the diesel engine through the drive wheel and through the transmission mechanism. The hazards of this starting method are as follows: 1 As the locomotive started by dragging hangs the high gear, once it is started, it is bound to rush forward, easily colliding with the preceding vehicle, and causing an accident. 2 As the locomotive lubricating oil viscous initiating resistance is large, especially in the cold season, the driving wheels tend to slip, causing serious tire wear. In this start-up process, the clutch has to be disengaged many times and combined, resulting in damage or severe wear of the clutch components. 3 If the engine is not started for a long time, it will cause a large amount of diesel oil to enter the cylinder, scour and damage the lubricating oil film on the cylinder wall, and aggravate the wear of the cylinder liner, piston ring and piston. At the same time, diesel oil infiltrating into the crankcase will dilute the lubricant and reduce the lubrication quality of the lubrication system.

(5) Start the diesel engine without cooling water The start-up method is particularly harmful to the engine. Because the engine is in an explosion, the temperature in the cylinder can be as high as 2000°C, which means that the temperature not only cannot be reflected on the water temperature gauge, but also by hand. Touching the cylinder block is also not felt. It can be inferred that the temperature of the walls of the combustion chamber will rise immediately after the engine starts to fire (approximately 500°C-600°C or more). At this point, cold water is added to the engine, the wall of the combustion chamber suddenly shrinks, and the cylinder head is easily damaged (mostly fractures between the two cylinders of the same cylinder) and the cylinder liner (breakage occurs below the shoulder of the cylinder sleeve).

(6) Adding oil to start the diesel engine Before starting, add a small amount of oil from the intake pipe to improve the sealing performance of the in-cylinder components, which will help the diesel engine start. For heavily worn diesel engines, this startup method can work for a while, but the negative effect is also obvious. If this method is often used to start, easy to make the piston ring cementation and stuck in the ring groove, the cylinder will be a large number of carbon deposition. The correct way to deal with this problem is to timely repair or replace worn-out parts in the cylinder to restore the cylinder's good sealing performance.

Currently, there is a starting fuel with a lower autoignition point on the market. It is made of 70% ether, 27% 200# (or aviation kerosene), and 3% engine oil. Its auto-ignition temperature is 191°C. When starting, draw about 10mL of starter fuel with a needle and inject it into the intake manifold. Then follow the normal start-up method to allow the diesel engine to fire. However, this kind of start-up method should pay special attention to safety, because the start-up fuel has a low self-ignition point, is easy to evaporate and evaporate, and can easily cause fire. Therefore, the start-up fuel should be stored in a closed container, stored at a low temperature, and kept away from the fire source. When using starter fuel, do not add too much to each injection; do not add starter fuel to the diesel tank to prevent gas blockage or fire.

2. Common incorrect flameout method

(1) A flameout method in which the decompression mechanism is switched off without closing the throttle (or with the throttle closed but the diesel engine still running) and the decompression lever is brought to the decompression position. Its harm is: 1 can easily cause the valve to collide with the piston. If the adjustment of the decompression mechanism is inaccurate or unexpected, the valve opening during decompression is too large. In the process of decompression and flameout, the piston continues to move up and down due to the inertia of the flywheel, crankshaft, and other mechanical components. When the piston moves to top dead center, it can easily collide with the valve head, resulting in serious accidents such as valve rod bending and piston top breaking. 2 Cylinder is prone to carbon deposition. Decompression extinction, the cylinder's compression stroke can not produce high pressure and high temperature, and at this time the injector is still injecting oil into the cylinder, fuel can not be burned and remain in the cylinder. At the next start-up, after the diesel engine caught fire, not only was the sound rough, but it also produced carbon deposits because it could not be completely burned. At the same time, some of the residual diesel penetrated into the crankcase, destroying the normal lubrication of the engine.

(2) Turn off the flame and suffocate the flames by shutting down the air intake nozzle, that is, use hand or yarn to tighten the intake pipe, cut off the air source of the cylinder, and turn off the engine. This method is often used, a filter of the air filter will lose its function due to loose connection with the central air intake pipe, which will increase the burden of secondary filtration and tertiary filtration and even cause large dust and dust to directly enter the cylinder. At the same time, dust and dirt adhered to the hand or the yarn bundle will be sucked into the cylinder immediately before the sudden death, which will aggravate the wear of the cylinder components.

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