Low temperature start-up of the hottest constructi

Low temperature start of construction machinery

whether the diesel engine can start smoothly depends on whether the diesel injected into the cylinder can quickly form a combustible mixture with the compressed air and ignite in time. Therefore, the air entering the cylinder is required to have a higher temperature and pressure after being compressed. The basic conditions for start-up should have sufficient start-up speed, high start-up speed, less gas leakage, short time for compressed air to transfer heat to the cylinder wall, less heat loss, which can improve the temperature and pressure of the air at the end of compression, good cylinder sealing, less gas leakage at start-up, which is conducive to the temperature and pressure increase of the air at the end of compression and maintain the integrity of parts and components; High; At the end of compression, the oxygen content in the mixed gas should exceed a certain concentration to ensure diesel ignition; The starting system must have enough power to ensure the starting speed and enable the starting torque to overcome the compression resistance torque and friction resistance torque

in winter in northern or western plateau areas of China, it is difficult to start construction machinery due to low ambient temperature. The main reasons are: the air temperature of the diesel engine cylinder at the end of compression cannot reach the temperature required for starting, and the compressed air pressure in the cylinder is also significantly lower than the pressure required for starting; The optimal working temperature of the battery is 20~40 ℃. With the decrease of the ambient temperature, its output capacity also decreases correspondingly, resulting in the reduction of the power of the diesel engine starting system, which is driven by the flexible transmission system; When the ambient temperature is low, the viscosity of engine oil increases, and the resistance between friction pairs increases, so that the starting speed of diesel engine decreases. At the same time, the viscosity of diesel oil increases, and the atomization quality of butter becomes poor, which prolongs the ignition lag period; The air density and oxygen content in the air decrease with the increase of altitude. The higher the altitude, the harder it is to start the diesel engine

the way to solve the difficulty of low-temperature starting of diesel engine is:

(L) choose diesel engine oil with good low-temperature performance

this kind of engine oil has low low low-temperature viscosity, good lubrication between friction pairs, and small starting resistance, which is conducive to starting. For the multi-level oil currently used, for example, the smaller the number before 15w/40w, the better the low-temperature fluidity of the engine oil. Therefore, it is recommended to use 10W or 5W engine oil at low temperature

(2) the battery with good low-temperature performance

if necessary, the battery can be insulated to ensure that it can be charged normally at low temperature and has sufficient output current, so as to improve the power of the starting system

(3) inject low-temperature starting fluid

the starting fluid has a low ignition point, which can quickly ignite when the speed of the diesel engine is low, that is, the compressed air temperature and pressure are low, so as to ignite the diesel injected into the combustion chamber to realize the start of the diesel engine. Therefore, a certain amount of starting fluid can be injected into the intake pipe before starting. Figure 1 shows a low-temperature starting device that uses ether starting fluid injection. The nozzle is installed in the intake pipe of the diesel engine. Turn the start switch key to the start position to rotate the crankshaft. At the same time, press the ether start switch to inject ether into the intake pipe and into the cylinder. Because ether can burn at a lower cylinder temperature and is a highly volatile fuel, it can also be started at a low temperature of -30 ℃. Note: the starting device can only be used when the ambient temperature is lower than 0 ℃. Press the switch for no more than 3S; Because the starting fluid is easy to burst and shock, which is unfavorable to the service life of the machine parts, the amount of starting fluid injected at one time should not be too much (generally not more than 3ml), nor should it be used frequently, nor should it be used at the same time with the electric heating device

(4) a heating device is set on the intake pipe, which heats the intake air of the diesel engine and increases the gas temperature in the cylinder at the end of compression. The common method is to use the electric energy inside or outside the machine to electrically heat the resistance wire installed in the intake pipe to improve the intake temperature

in diesel engines with swirl chamber or precombustion chamber combustion chambers, glow plugs are used to preheat the air in the combustion chamber. Figure 2 shows a closed glow plug. The central screw 2 of the glow plug is connected to the battery in parallel with wires. One end of the resistance wire 8 is welded to the central screw 2, and the other end is welded to the bottom of the high temperature resistant heating element steel sleeve 9 made of stainless steel. Before starting, use a special switch to turn on the glow plug circuit. The cathode wire 8 generates high temperature, and the heating body steel sleeve 9 soon becomes red and hot, raising the temperature of the air in the cylinder, thus increasing the temperature of the compressed air and making the diesel injected into the cylinder easy to catch fire. Power off the glow plug immediately after starting

１. Fixing nut; ２. Central screw; ３. Adhesive 4 Insulator; ５. Washer; ６. Shell; ７. Fillers

８. Resistance wire; ９. Heating element steel sleeve; 10. Spring washer; 11. Crimping washer; 12. Crimping nut

electric flame preheater is often used as an auxiliary device for cold start of medium and small power diesel engines. Mainly, but Russia is still the largest importer of extruders in China. The principle is to mix foggy diesel with air to form a flammable mixture, and burn it in contact with the glow plug to preheat the intake air. Figure 3 shows an electric flame preheater installed in the intake pipe to heat the air passing through the intake pipe. The thermal expansion valve tube 3 is made of metal material with large expansion coefficient. One end is connected with the oil inlet pipe, and the other end is connected with the ball valve rod 4 (valve core). When the preheater is not working, the ball valve 5 blocks the oil inlet, and the thermal expansion valve tube 3 is wrapped around the surface insulated resistance wire. When starting, after the preheater circuit is connected, the resistance wire heats up and heats the thermal expansion valve tube 3 to lengthen and drive the valve core down. The ball valve 5 opens, and the diesel oil flows through the thermal expansion valve tube 3 to be heated and vaporized and ejected from its inner cavity. It is ignited by the hot resistance wire into a flame and injected into the intake pipe to preheat the air for convenient starting. When the preheating switch is turned off, the circuit is cut off to cool the resistance wire, the thermal expansion valve tube 3 is cooled and contracted, the ball valve is reseated, the diesel oil is blocked to extinguish the flame, and the preheating stops

the auxiliary starting heating device of Cummins diesel engine with intercooler usually adopts grid heater, which is matched with the diesel engine. Its wiring method is shown in Figure 4. It is installed inside the intake manifold to heat the air in the intake manifold after the intercooler. Before starting, turn the key switch to the on position and start preheating. The preheating time will change according to the change of ambient temperature until the set temperature is reached (there is a waiting indicator light controlled by ECM). Attention: to avoid frequent vibration, the relay cannot be fixed on the diesel engine body

(5) heating the cooling medium

the above methods can only ensure the normal start of the diesel engine when the ambient temperature is higher than -30 ℃. The method of heating the cooling medium can make the diesel engine start normally in the environment below -40 ℃. Figure 5 shows a fuel oil heater, which can continuously heat the cooling medium in the whole circulating system

１. Protective cover; ２. Oil pump; ３. Motor; ４. Deflector; ５. Water inlet pipe; ６. Glow plugs; ７. Main combustion chamber; ８. Combustion chamber

９. Rear combustion chamber; 10. Outlet pipe; 11. Water jacket body; 12. Heat sink; 13. Atomizer; 14. Smoke exhaust outlet; 15. Combustion supporting fan; 16. Drip pipe

1７. Air inlet; 18. Oil pipeline; 19. Connector; 20. Oil inlet pipe; 21. Water temperature lever; 22. Rotary vane; 23. Overheat protector; 24. Ignition rod conveyor

the heater adopts 24V DC power supply and forms a circulating heating system with diesel engine and radiator. It can not only increase the oil temperature and decrease the oil viscosity between the cylinder and the piston and other friction pairs, but also heat the air in the intake manifold. It should be noted that the heater can only be used when the ambient temperature is lower than -15 ℃, and the heater should be turned off in time after startup

the emergency measures to improve the low-temperature ring of diesel engine. The examinee only needs to swallow one intelligent "capsule" to start the environment include: injecting oil into the intake pipe, using a pressure reducing mechanism, and even injecting hot water into the engine