How to start the diesel generator at low temperature

How to start the diesel generator at low temperature

One of the diesel engine application standards: When the temperature is not lower than 5°C, the engine can be started smoothly without preheating measures. The actual situation is often in many cases the temperature is lower than 5 °C, which requires the use of certain preheating means to start the engine.

1. Conditions for low temperature starting engines

When the temperature is below -10°C, the cold start of the diesel engine has certain difficulties; when the temperature drops below -40°C, some low temperature start-up measures are not used, and it is impossible to start at all. The necessary conditions for diesel engines to start at low temperatures in winter are as follows:

1) must reach a certain starting speed

The starting speed of the diesel engine is generally greater than 100r/min, and the low temperature start is mainly affected by the starting resistance. The crankshaft rotation resistance at the start includes the reaction force of the compressed air in the cylinder, the inertia force of the moving parts, and the frictional resistance of each friction system.

2) The air cylinder mixture should have enough pressure

There are several compression ratios that are high, and the general general-purpose model has a compression ratio of about 14-22. At the end of the compression stroke, the pressure of the combustion chamber mixture should reach 3-5 MPa.

3) In-cylinder gas mixture should have sufficient temperature

At the end of the compression stroke, the in-cylinder gas mixture has enough problems. When the general diesel engine requires the end of the compression stroke, the problem in the cylinder should reach above 400°C.

4) The oxygen content in the compressed air should meet the standard

There must be enough air to enter the cylinder so that the oxygen content in the compressed air is sufficient, and combustion can be achieved only after the mixture is formed in the cylinder.

2. Reasons for difficulty in starting at low temperatures

1) Increased frictional resistance

The rotation resistance torque and the starting rotation speed of the diesel engine crankshaft are mainly affected by the viscosity of the engine oil at low temperatures. As the outside temperature decreases, the viscosity of the oil increases or even condenses, the fluidity is poor, the resistance between the friction pairs increases, and the rotation resistance torque of the crankshaft is increased, so that the starting rotation speed of the diesel engine is reduced. At the end of the compression, if the compressed air in the cylinder does not reach the pressure and temperature required for diesel combustion, the diesel engine is difficult to start.

2) Startup power increase

The greater the oil viscosity grade selected for the diesel engine, the greater the power required to start the diesel engine. For example, when a diesel engine is at a temperature of -23.3°C, SAE10W engine oil requires only 3.7kW of starting power, and SAE20W engine oil requires 7.4KW of starting power, while SAE30W engine oil startup power actually increases to 11.8KW.

3) Increase in viscosity and density of diesel fuel

With the decrease of the outside temperature, the viscosity and density of diesel oil increase, and the surface tension increases. It was determined that when the temperature dropped from 40°C to -10°C, the viscosity of diesel increased by 83% and the density increased by 8%. As a result, the fluidity of the diesel fuel is deteriorated, the atomization is poor, the ignition lag period is prolonged, and the starting of the diesel engine is difficult.

4) The output power of the battery decreases

The battery's good working temperature is in the range of 10°C to 40°C. Under low temperature conditions, the battery electromotive force does not change much, that is, when the ambient temperature changes greatly, the single cell voltage of the battery does not drop much. However, as the temperature decreases, the viscosity of the electrolyte of the battery increases, the permeation capacity to the plate decreases, and the internal resistance increases. In order to prevent the electrolyte from freezing, the lower the boundary temperature, the greater the need to increase the electrolytic density. At the same time, when the diesel engine is started, the discharge current of the battery is very large, and the voltage and capacity of the battery terminal are significantly reduced. When the battery output capacity is -30°C, it is only about 34% of the rated output. When the diesel engine starts at a low temperature, a relatively large starting power is required. However, the low temperature causes the output power of the battery to decrease. The inability to drive the starter to drive the diesel engine to rotate or not to reach a low start speed will cause the diesel engine to be difficult to operate with fire.

3. Technical measures for cold start

1) Use low-temperature special battery

Advantages of this type of battery: The use of unit spiral winding technology, the gap between the plates is extremely small; the use of solid acid, and can be adsorbed by the glass fiber mesh; the structure is tight, the plate area is much higher than the area of ​​ordinary flat battery At low temperature, there is no freezing phenomenon of liquid acid, and it can work normally under the environment of -40°C; the cold start power, charging speed and other indicators have obvious advantages over ordinary batteries.

2) Strengthen the maintenance of ordinary batteries

When using common batteries in cold seasons, some technical measures should be taken to ensure that the batteries are normally charged under low temperature conditions and have sufficient current output, so as to improve the low temperature start-up performance of diesel engines and prolong the service life of the batteries.

The method of heat preservation of the storage battery is to make a suitable wooden double-layer insulation box, and heat insulation materials such as wool and sawdust are filled in the sandwich, and the battery is firmly placed in the box, so that the density of the electrolyte can be reduced, and the storage capacity of the battery can be increased. Electricity.

When the density of the electrolyte is adjusted, if the loss of electricity occurs, the density will decrease, and the loss of the battery will not only make it difficult to start but also cause cracking. The electrolyte density can be appropriately increased (0.03 to 0.06 g/cm3 greater than the summer density). The density of the charged battery electrolyte should be 1.28 g/cm3.

Appropriately increase the generator regulator limit voltage and charging current due to battery discharge at low temperatures increase, so we must increase the generator charge. In winter cold conditions, the limit voltage of the regulator is more than 0.6V higher than summer.

When the battery is placed in the house and it encounters severe cold weather, the battery can be unloaded and kept warm in the house. The battery is then installed the next day. Although this is somewhat troublesome, it can effectively maintain the temperature of the battery and guarantee its working ability.

3) Regular maintenance starter

Diesel engine start-up is difficult in winter and the number of starter machines is frequently used. If the starter power is insufficient, diesel engine start-up difficulty will be further increased. Therefore, the starter should be regularly maintained to keep all parts of the starter clean and dry. In particular, there should be good contact between the brush and the commutator.

4) Select suitable diesel

Under possible conditions, diesel with low freezing point and good flow properties should be used. The principle of choice for diesel fuel is that the freezing point is about 5°C lower than the ambient temperature. For example, when the temperature is -5 °C, you must choose -10 diesel. The available diesel grades for winter in China are Nos.-10, -20, -35 and so on. Once the diesel fuel in the fuel system solidifies, it cannot be baked with an open flame, but it must be heated with hot water or hot steam to prevent a fire accident.

5) Choose low-temperature performance oil

This kind of oil has low viscosity at low temperature, and it is well lubricated between friction pairs at start-up, and the starting resistance is small. The single-stage oil has a narrow operating temperature range, and the multi-stage oil can work in a wide temperature range. Generally, it is possible to select a multigrade oil with a viscosity grade of SAE5W-40 or SAE10W-40. In certain cold areas, special anti-freeze engine oil should also be used.

6) Choose reliable antifreeze

Where conditions permit, the diesel engine coolant should be made of reliable antifreeze as much as possible. The freezing point of the antifreeze should be about 5°C lower than the ambient temperature.

7) Antifreeze measures for cooling water

For diesel engines using demineralized water as cooling fluid, open-air parking should be avoided as long as possible to prevent freezing tank accidents. If it must be parked in the open air for a long time, it should be idling for 5 to 10 minutes before parking. When the water temperature drops to 40°C, it will be turned off and discharged. When the water is drained, the radiator cover, the body drain switch, and the water radiator drain switch should all be opened together. After the water is not flowing, you should use the crank to shake the diesel engine for several weeks or use a starter to drag the remaining cooling water to avoid freezing the pump impeller.

8) Insulation for open-air use

When the diesel engine is used in open air in winter, insulation measures shall be taken. For example, the radiator cover is equipped with a cotton or felt insulation cover, and a layer of glass fiber is sealed under the oil pan. This kind of heat preservation method can make the temperature in the diesel engine cover be kept at 20-35°C when the machine is working under the temperature of about -30°C. After shutting down, the cooling rate of the main parts of the diesel engine is also nearly 6 times lower than that without the insulating sleeve.

4, the specific method of low temperature start

1) Hot water pre-heating method

This method is applicable to units that use softened hot water as a cooling fluid and soften hot water. The specific approach is: first add 40 ~ 50 ° warm water to the cooling system (to prevent the proliferation of boiling water to make the water radiator core tube, cylinder head burst), and then continuously heated water (let water out of the cylinder), and gradually increase The water temperature is warmed up. When the temperature of the outflowing water is high, close the drain switch again.

2) Steam preheating method

That is to say, the steam enters the cooling system through the pipeline from the water pipe of the water radiator, or directly enters the diesel water jacket, and the diesel engine block is preheated with steam. This method is suitable when using demineralized water as a cooling fluid.

3) Adopting a forced circulation type fuel heater

The method uses random diesel oil to pump the coolant in the diesel engine cooling system through the pump attached to the fuel heater. After being radiated and heated by the heater, it is recycled into the diesel engine cylinder. At this time, the cylinder, piston, piston ring and other friction pairs are The temperature increases. This method can heat the cylinder block of the diesel engine to about 40-50°C. When the engine oil of the diesel engine is heated, the viscosity decreases, and the lubrication conditions of the diesel engine are improved.

4) Install a spiral resistance heater in the intake pipe

This kind of device is powered by the battery. Before starting, the power supply is turned on for 10-30S to make the spiral resistor heat up, so as to heat the air entering the cylinder and increase the temperature of the gas in the cylinder when the compression is finished.

5) Hot flush the intake manifold with hot water

That is, after hot flushing the intake manifold with hot water, the air entering the cylinder is preheated to increase the temperature of the compressed air at the end of compression, which facilitates the ignition of diesel fuel.

6) Screw resistor installed in oil pan

The resistor heats the oil in the oil pan, reduces the viscosity of the oil and reduces the starting resistance. When using this method, the heating time should be controlled to avoid the oil aging and deterioration due to too long heating time and high oil temperature.

7) Start with flame preheater

The flame preheating device is composed of an electronic controller, a solenoid valve, a temperature sensor, a flame glow plug (installed in the intake pipe), a fuel pipe, and a wire. The device's low operating temperature is -40°. Its working process is: Before the start, the flame glow plug is turned on. After ten seconds, the flame glow plug is heated to 900°C, which is enough to ignite the diesel. Start the machine, the solenoid valve automatically opens the oil circuit, and the oil pump pumps out the diesel fuel. The oil is supplied to the flame glow plug through the fuel pipe through the solenoid valve, and the flame is warmed up to start.

8) Start with cold start fluid

This method is to inject a certain percentage of low temperature starter fluid into the diesel intake manifold before starting. The ether flash point in the low-temperature start-up fluid is low, and the ignition point of the ether is only about 57°C under the pressure of 3.25MPa, so the diesel engine does not need to meet the requirement of low start-up speed, and the ignition can be started. Practice has proved that using a low temperature starter fluid can ensure that the diesel engine starts quickly when the temperature is -45°C.

5. Low temperature startup considerations

1) Control start time

When the engine is started at a low temperature, the starter continuously drives the diesel engine to rotate normally and cannot exceed 10S. If the engine cannot be ignited for three consecutive times, it should be suspended for 2 to 3 minutes before starting. If you still cannot start the ignition 2 or 3 times before starting, check whether there is air or blockage in the oil circuit and if the air filter is clogged. If you keep on starting, the battery will be over-discharged and it will cause aging of the plate.

2) Various starting methods should be used reasonably

In order to achieve a good start effect, the above-mentioned several startup methods are often used simultaneously. However, the low-temperature start-up assist start and intake flame preheating, the low-temperature low temperature start-up assist start and the intake spiral resistance heating cannot be used at the same time, otherwise the flame will ignite the start-up fluid mixture and cause explosion, causing serious consequences.

3) The use of low temperature starter should pay attention to safety

The cryogenic priming fluid container should be installed in a cool and ventilated place, away from high temperature heat sources, and close to open flames to prevent explosions and injuries. The low-temperature starter fluid is flammable and has anesthetic effect. It should be sealed and stored. It should be kept in a cool, ventilated warehouse with low temperature. It cannot be stored in the open air. Attention should be paid to personal safety during storage. Do not add the low-temperature starter fluid to the tank to avoid gas resistance.

4) The fuel heater should be selected correctly

When an external forced circulation type fuel heater is used, gasoline cannot be used as fuel. Appropriate brands of light diesel oil (or kerosene) should be selected according to the ambient temperature of the machine. When using diesel of the same brand as the diesel engine, the use environment should be guaranteed. At temperatures, diesel oil does not freeze or wax, preventing the supply circuit from becoming clogged.

5) Start with less trailers

Try not to start the diesel engine by using the method of starting the trailer. Because the diesel engine is not preheated, the viscosity of the oil is large. The start of the trailer will cause the parts to be abraded due to poor lubrication.

6) Run at low speed after startup and check exhaust gas

In the initial period after the ignition of the diesel engine, do not increase the high-speed operation of the throttle, otherwise it may easily lead to accidents such as pulling the cylinder, burning the shaft, and holding the tile.

After the diesel engine is started, it should be idling for 2 to 3 minutes, and then gradually added to the "warm speed" at medium speed. When the temperature of the coolant reaches above 60°C, check the oil pressure, water temperature, and indicator light on the instrument panel. In particular, the oil pressure should be in the range of 0.15 to 0.50 MPa. In the absence of any abnormal sound and normal operation of the diesel engine, gradually increase the load to operate.

In general cold start, the exhaust pipe will emit a white smoke. As the diesel engine temperature increases, white smoke should gradually disappear.

For the low-temperature start-up of diesel generators at high altitudes, the power correction problem must also be considered due to the relatively low atmospheric pressure.