Abstract: Diesel generators are a reliable guarantee for production electricity, and their safe and effective operation is crucial for ensuring platform production. High water temperature in diesel generators is one of the most common faults, which, if not dealt with in a timely manner, can extend to major equipment failures, affecting production and causing incalculable economic losses. The temperature during the operation of diesel generators, whether it is oil temperature or coolant temperature, must be within a normal range. For diesel generators, the optimal operating range for oil temperature should be 90 ° to 105 °, and the optimal temperature for coolant should be within the range of 85 ° to 90 °. If the temperature of the diesel generator exceeds the above range or even higher during operation, it is considered overheated operation. Overheating operation poses significant risks to diesel generators and should be promptly eliminated. Otherwise, high water temperature usually causes boiling of the coolant inside the radiator, a decrease in power, a decrease in lubricating oil viscosity, increased friction between components, and even serious malfunctions such as cylinder pulling and cylinder gasket burning.
1、 Introduction to Cooling System
In diesel generators, about 30% to 33% of the heat released by fuel combustion needs to be dispersed to the outside world through components such as cylinders, cylinder heads, and pistons. In order to dissipate this heat, a sufficient amount of cooling medium needs to be forced to continuously flow through the heated components, ensuring the normal and stable temperature of these heated components through cooling. Therefore, cooling systems are installed in most diesel generators to ensure sufficient and continuous flow of cooling medium and appropriate temperature of cooling medium.
1. The role and method of cooling
From the perspective of energy utilization, cooling of diesel generators is an energy loss that should be avoided, but it is necessary to ensure the normal operation of diesel generators. The cooling of diesel generators has the following functions: firstly, cooling can maintain the working temperature of the heated parts within the allowable limit of the material, thereby ensuring sufficient strength of the heated parts under high temperature conditions; Secondly, cooling can ensure an appropriate temperature difference between the inner and outer walls of the heated parts, reducing the thermal stress of the heated parts; In addition, cooling can also ensure the appropriate clearance between moving parts such as the piston and cylinder liner, and the normal working state of the oil film on the working surface of the cylinder wall. These cooling effects are achieved through the cooling system. In management, both aspects of diesel generator cooling should be taken into consideration, neither allowing the diesel generator to become supercooled due to excessive cooling nor overheating due to lack of cooling. In modern times, starting from minimizing cooling losses to fully utilize combustion energy, research on adiabatic engines is being carried out both domestically and internationally, and a number of high-temperature resistant materials, such as ceramic materials, have been developed accordingly.
At present, there are two cooling methods for diesel generators: forced liquid cooling and air cooling. The vast majority of diesel generators use the former.
2. Cooling medium
In the forced liquid cooling system of diesel generators, there are usually three types of coolants: fresh water, coolant, and lubricating oil. Freshwater has stable water quality, good heat transfer effect, and can be used for water treatment to solve its corrosion and scaling defects, making it an ideal cooling medium widely used at present. The requirements for fresh water quality of diesel generators are generally free of impurities in fresh water or distilled water. If it is fresh water, the total hardness should not exceed 10 (German degrees), the pH value should be 6.5-8, and the chloride content should not exceed 50 × 10-6. When using distilled water or completely deionized water generated by ion exchangers as cooling fresh water, special attention must be paid to water treatment of the fresh water and regular testing must be conducted to ensure that the concentration of the water treatment agent reaches the specified range. Otherwise, the corrosion caused by insufficient concentration is more severe than using ordinary hard water (due to the lack of protection from lime film sediment formed by ordinary hard water). The water quality of the coolant is difficult to control and its corrosion and scaling problems are prominent. To reduce corrosion and scaling, the outlet temperature of the coolant should not exceed 45 ℃. Therefore, it is currently rare to use coolant directly to cool diesel generators; The specific heat of lubricating oil is small, the heat transfer effect is poor, and high-temperature conditions are prone to coking in the cooling chamber. However, it does not pose a risk of contaminating the crankcase oil due to leakage, making it suitable as a cooling medium for pistons.
3. Composition and equipment of cooling system
Due to different working conditions of the heated parts, the required coolant temperature, pressure, and basic composition also vary. Therefore, the cooling system of each heated component is usually composed of several separate systems. It is generally divided into three closed freshwater cooling systems: cylinder liner and cylinder head, piston, and fuel injector.
The fresh water from the outlet of the cylinder liner cooling water pump enters the lower part of each cylinder liner through the main inlet pipe of the cylinder liner water, and is cooled along the route from cylinder liner to cylinder head to turbocharger. After the outlet pipes of each cylinder are combined, they are cooled by the water generator and fresh water cooler along the way, and then re enter the inlet of the cylinder liner cooling water pump; The other way enters the fresh water expansion tank. A balance pipe is installed between the fresh water expansion tank and the cylinder liner cooling water pump to replenish water to the system and maintain the suction pressure of the cooling water pump.
There is a temperature sensor in the system that detects changes in the outlet temperature of the cooling water and controls its inlet temperature through a thermal control valve. The maximum water temperature should generally not exceed 90-95 ℃, otherwise the water temperature sensor will transmit a signal to the controller, causing a diesel engine overheating alarm and instructing the equipment to stop.
There are two cooling methods for diesel generators: integrated and split. It should be noted that in the split type intercooling system, some models may have a cooling area of the intercooler heat exchanger that is larger than that of the cylinder liner water heat exchanger, and the manufacturer’s service engineers often make mistakes. Because it feels like the cylinder liner water needs to exchange much more heat, but due to the small temperature difference in intercooling cooling and low heat exchange efficiency, a larger cooling area is required. When installing a new machine, it is necessary to confirm with the manufacturer to avoid rework affecting the progress. The outlet water temperature of the cooler should generally not exceed 54 degrees. Excessive temperature can generate a compound that adsorbs on the surface of the cooler, affecting the cooling effect of the heat exchanger.
2、 Diagnosis and treatment of high water temperature faults
1. Low coolant level or improper selection
The first and easiest thing to check is the coolant level. Don’t be superstitious about low liquid level alarm switches, sometimes clogged fine water pipes of the level switches can mislead inspectors. Moreover, after parking at high water temperatures, it is necessary to wait for the water temperature to drop before replenishing water, otherwise it may cause major equipment accidents such as cylinder head cracking.
engine specific coolant physical object. Regularly check the coolant level in the radiator and expansion tank, and replenish it in a timely manner when the liquid level is low. Because if there is a lack of coolant in the cooling system of a diesel generator, it will affect the heat dissipation effect of the diesel generator and cause high temperatures.
2. Blocked cooler or radiator (air-cooled)
The blockage of the radiator may be caused by dust or other dirt, or it may be due to bent or broken fins that restrict air flow. When cleaning with high-pressure air or water, be careful not to bend the cooling fins, especially the intercooler cooling fins. Sometimes, if the cooler is used for too long, a layer of compound will adsorb on the surface of the cooler, affecting the heat exchange effect and causing high water temperature. To determine the effectiveness of the cooler, a temperature measuring gun can be used to measure the temperature difference between the inlet and outlet water of the heat exchanger and the inlet and outlet water temperature of the engine. Based on the parameters provided by the manufacturer, it can be determined whether the cooler effect is poor or there is a problem with the cooling cycle.
3. Damaged air deflector and cover (air-cooled)
The air-cooled diesel generator also needs to check if the air deflector and cover are damaged, as damage can cause hot air to circulate to the air inlet, affecting the cooling effect. The air outlet should generally be 1.1-1.2 times the area of the cooler, depending on the length of the air duct and the shape of the grille, but not less than the area of the cooler. The direction of the fan blades is different, and there are also differences in the installation of the cover. When installing a new machine, attention should be paid.
4. Fan damage or belt damage or looseness
Regularly check if the fan belt of the diesel generator is loose and if the fan shape is abnormal. Because the fan belt is too loose, it is easy to cause a decrease in fan speed, resulting in the radiator not being able to exert its due heat dissipation capacity, leading to high temperature of the diesel generator.
The tension of the belt needs to be adjusted appropriately. While loosening it may not be good, being too tight can reduce the service life of the support belt and bearings. If the belt breaks during operation, it may wrap around the fan and damage the cooler. Similar faults have occurred in the use of the belt by some customers. In addition, fan deformation can also cause the heat dissipation capacity of the radiator to not be fully utilized.
5. Thermostat failure
Physical appearance of the thermostat. The failure of the thermostat can be preliminarily judged by measuring the temperature difference between the inlet and outlet water temperatures of the water tank and the water pump inlet and outlet heat exchanger using a temperature measuring gun. Further inspection requires disassembling the thermostat, boiling it with water, measuring the opening temperature, fully open temperature, and fully open degree to determine the quality of the thermostat. requires a 6000H inspection, but usually it is directly replaced during top or upper and lower major repairs, and no inspection is conducted if there are no faults in the middle. But if the thermostat is damaged during use, it is necessary to check whether the cooling water pump fan blades are damaged and whether there is any residual thermostat in the water tank to avoid further damage to the water pump.
6. Water pump damaged
This possibility is relatively small. The impeller may be damaged or detached, and it can be determined whether to disassemble and inspect it through a comprehensive judgment of a temperature measuring gun and pressure gauge, and it needs to be distinguished from the phenomenon of air intake in the system. There is a discharge outlet at the bottom of the water pump, and dripping water here indicates that the water seal has failed. Some machines may enter the system through this, affecting circulation and causing high water temperature. But if there are a few drops of leakage in one minute when replacing the water pump, it can be left untreated and observed for use. Some parts will no longer leak after running in for a period of time.
7. There is air in the cooling system
Air in the system can affect the flow of water, and in severe cases, it can cause the water pump to fail and the system to stop flowing. Even some engines have experienced continuous overflow of water from the water tank during operation, low level alarm during parking, and misjudgment by the manufacturer’s service provider, thinking that combustion gas from a certain cylinder had leaked into the cooling system. They replaced all 16 cylinder cylinder gaskets, but the malfunction still persisted during operation. After we arrived at the site, we started to exhaust from the highest point of the engine. After the exhaust was completed, the engine ran normally. Therefore, when dealing with faults, it is necessary to be certain that similar phenomena have been eliminated before making major repairs.
8. Damaged oil cooler causing coolant leakage
(1) Fault phenomenon
A generator set in a certain unit was found to have water continuously dripping outward from the edge of the lubricating oil dipstick hole during pre startup inspection, leaving little coolant in the radiator.
(2) Fault finding and analysis
After investigation, it is known that before the diesel generator set malfunctioned, no abnormal phenomena were found during construction on the construction site. The coolant leaked into the oil pan after the diesel generator was shut down. The main causes of this malfunction are oil cooler leakage or damage to the cylinder liner sealing water chamber. So first, a pressure test was conducted on the oil cooler, which involved removing the coolant from the oil cooler and the inlet and outlet connecting pipes of the lubricating oil. Then, the coolant outlet was blocked, and a certain pressure of water was introduced at the coolant inlet. As a result, it was found that water flowed out of the lubricating oil port, indicating that the water leakage fault was inside the oil cooler. The coolant leakage fault was caused by the welding of the cooler core, and it may have occurred during the shutdown of the diesel generator. Therefore, when the diesel generator set finished working, there were no abnormal phenomena. But when the diesel generator is turned off, the lubricating oil pressure approaches zero, and the radiator has a certain height. At this time, the coolant pressure is greater than the lubricating oil pressure, and the coolant will flow into the oil pan from the opening of the cooler core, causing water to drip outward from the edge of the oil dipstick hole.
(3) Troubleshooting
Disassemble the oil cooler and locate the location of the open weld. After re welding, the fault was resolved.
9. Cylinder liner leakage causing high coolant temperature
(1) Fault phenomenon
A B series diesel generator. During the overhaul at the repair shop, the piston, piston rings, bearing shells and other components were replaced, the cylinder head plane was ground, and the cylinder liner was replaced. After the major overhaul, no abnormalities were found during the running in process in the factory, but after being delivered to the machine owner for use, a fault of high coolant temperature occurred. According to the operator’s feedback, after reaching normal operating temperature, the coolant temperature will reach 100 ℃ after running for 3-5 kilometers. If it is parked for a period of time and continues to operate after the water temperature drops, it will rise again to 100 ℃ in a very short period of time. The diesel generator has no abnormal noise, and there is no water seeping out of the cylinder block.
(2) Fault finding and analysis
The diesel generator has no abnormal noise, and the smoke from the exhaust pipe is basically normal. It can be judged that the clearance between the valve, valve and guide rod is basically normal. Firstly, measure the cylinder pressure with a compression pressure gauge, and then conduct a basic inspection of the cooling system. No water leakage or seepage was found, and the cooling liquid level in the radiator also meets the regulations. When checking the operation of the water pump after starting, no abnormalities were found, and there was no obvious temperature difference between the upper and lower chambers of the radiator. However, a small amount of bubbles were found, so it was suspected that the cylinder gasket was damaged. Therefore, after removing the cylinder head and inspecting the cylinder gasket, no obvious burning phenomenon was found. After careful observation, it was found that there was a damage at the top of the cylinder liner that was higher than the upper plane of the cylinder block. When installing the cylinder gasket, the piston hole was precisely placed on the outer circle of the damaged area, and the cylinder gasket was flush with the upper plane of the damaged port. From this, it can be inferred that the poor sealing of the cylinder gasket caused high-pressure gas to enter the water channel, resulting in excessively high coolant temperature.
(3) Troubleshooting
After replacing the cylinder liner and tightening the cylinder head bolts according to the specified torque, there was no phenomenon of high coolant temperature again.
10. Long term overload operation
Long term overload operation of diesel generators can increase their fuel consumption and thermal load, resulting in high water temperature. To this end, diesel generators should be avoided from long-term overload operation.
11. Engine cylinder pulling
Engine cylinder pulling generates a large amount of heat, causing an increase in oil temperature and cylinder liner water temperature. When the cylinder is pulled severely, white smoke will be emitted from the ventilation port of the crankcase, but slight pulling can only show a high water temperature, and there is no significant change in the ventilation of the crankcase. If the change in oil temperature is no longer observed, it is difficult to determine. When the water temperature is abnormally high, it can be used as a possibility to open the crankcase door, inspect the surface of the cylinder liner, timely detect problems, and avoid serious cylinder pulling accidents. During the inspection, it is necessary to check the air outlet of the crankcase every shift. If there is white smoke or a significant increase in air outlet, it must be stopped for inspection. If there is no abnormality in the cylinder liner, it is necessary to consider whether there is poor bearing lubrication causing high oil temperature. Similarly, an increase in air outlet will be found in the crankcase. It is necessary to identify the cause and handle it before operating the machine to avoid major equipment accidents.
The above are several possible reasons, which can be judged from simple to complex, combined with other possible fault phenomena, to identify the cause. When testing a new car or undergoing major repairs, it is necessary to measure and record the water temperature at the inlet and outlet of the cooler, the inlet and outlet of the machine, and the temperature of each lubrication point under various load conditions, so as to facilitate the comparison of parameters and timely investigation of abnormal points in case of machine abnormalities. If it cannot be easily handled, you can measure several more temperature points and use the following theoretical analysis to find the cause of the fault.
3、 High temperature hazards and preventive measures
If the diesel generator is in a “dry burning” state, that is, operating without cooling water, any cooling method of pouring cooling water into the radiator is basically ineffective, and the diesel generator cannot dissipate heat during operation. Firstly, in the running state, the oil filling port should be opened and lubricating oil should be quickly added. This is because in a completely dehydrated state, the lubricating oil of the diesel generator will evaporate at a large amount of high temperature and must be quickly replenished. After adding lubricating oil, the engine must be turned off, and any method should be taken to turn off the diesel generator and cut off the oil. Simultaneously operate the starter and passively operate the diesel generator, continuously running for 10 seconds with a 5-second interval to maintain this frequency. It is better to damage a starter engine than to protect the diesel generator, in order to minimize serious accidents such as sticking or pulling the cylinder. Therefore, preventive measures need to be taken for the cooling system.
1. Adjusting the working parameters of the cooling system
(1) The outlet pressure of the cooling water pump should be adjusted within the normal working range. Usually, the fresh water pressure should be higher than the coolant pressure to prevent the coolant from leaking into the fresh water and causing it to deteriorate when the cooler leaks.
(2) The fresh water temperature should be adjusted to the normal operating range according to the instructions. Do not let the outlet temperature of fresh water be too low (causing increased heat loss, thermal stress, low-temperature corrosion) or too high (causing evaporation of the lubricating oil film on the cylinder wall, intensified wear of the cylinder wall, vaporization in the cooling chamber, and rapid aging of the cylinder liner sealing ring). For medium to high speed diesel engines, the outlet temperature can generally be controlled between 70 ℃ and 80 ℃ (without burning sulfur-containing heavy oil), and for low-speed engines, it can be controlled between 60 ℃ and 70 ℃; The temperature difference between import and export shall not exceed 12 ℃. It is generally advisable to approach the allowable upper limit for the outlet temperature of fresh water.
(3) The outlet temperature of the coolant should not exceed 50 ℃ to prevent salt analysis from depositing and affecting heat transfer.
(4) During operation, the bypass valve on the coolant pipe can be used to adjust the amount of coolant entering the fresh water cooler, or the bypass valve on the fresh water pipe can be used to adjust the amount of fresh water entering the fresh water cooler or the coolant temperature. Modern newly built ships are often equipped with automatic temperature control devices for fresh water and lubricating oil, and their regulating valves are mostly installed in the pipelines of fresh water and lubricating oil to control the amount of fresh water and lubricating oil entering the cooler.
(5) Check the flow of cooling water in each cylinder. If it is necessary to adjust the cooling water flow, the outlet valve of the cooling water pump should be adjusted, and the adjustment speed should be as slow as possible. The inlet valve of the cooling water pump should always be in the fully open position.
(6) When the pressure fluctuation of the cylinder cooling water is found and the adjustment is ineffective, it is usually caused by the presence of gas in the system. The cause should be identified and eliminated as soon as possible.
2. Perform regular inspections
(1) Regularly check the water level changes in the expansion water tank and fresh water circulation cabinet. If the water level drops too quickly, the cause should be quickly identified and eliminated.
(2) Regularly check the coolant level, water pipes, water pumps, etc. of the diesel generator system, and promptly identify and remove faults such as scale and blockage.
(3) Check if the coolant filter and coolant valve are blocked by debris. When sailing in cold regions, it is necessary to strengthen the management of the coolant pipeline system to prevent the underwater valve from being stuck by ice, and to ensure the temperature of the coolant entering the cooler (25 ℃).
(4) It is best to check the quality of the cooling water once a week. The concentration of water treatment additives (such as corrosion inhibitors) should be within the specified range in their instructions, with a pH value (7-10 at 20 ℃) and chloride concentration (not exceeding 50ppm). The changes in these indicators can roughly determine the working status of the cooling system. If the concentration of chloride increases, it indicates that coolant has leaked in; A decrease in pH value indicates exhaust leakage.
(5) During operation, it is necessary to check whether the ventilation system is smooth, allowing sufficient air flow to the diesel generator, greatly improving its heat dissipation capacity and reducing the risk of high temperatures.
Summary:
Reasonable preventive measures and solutions for the high temperature phenomenon of diesel generators are necessary to reduce the risk of unsmooth operation of diesel generators, ensure the normal production efficiency and service life of diesel generators. The environment of diesel generators can be improved in multiple ways, the quality of diesel generator components can be improved, and maintenance measures can be taken to reduce the risk of high temperature phenomena, thereby better protecting and utilizing diesel generator sets. High water temperature faults in diesel generators are common, but as long as they are detected in a timely manner, they generally do not cause significant damage to the diesel generator set. Try not to shut down the machine urgently after discovery, do not rush to replenish water, and wait for the load to be unloaded before shutting down. The above is based on the training materials of the generator set manufacturer and the experience of on-site service. I hope we can work together to maintain the power generation equipment in the future.
Post time: Mar-07-2024