1. Fault overview. During the daily towing training of this ship, the power of the left main engine increased sharply from 35% to 60% at the highest speed (500r/min), and then two abnormal sounds of "clanging" were heard. The monitoring computer issued an "overload alarm for the left main engine, load limit alarm for the left main engine", and the speed immediately dropped to 400 r/min (set at 500r/min). The local control panel of the main engine issued a series of alarm messages such as "secondary alarm for the fuel injection module, excessive opening of the suction valve (throttle valve), failure to reach the set point of the fuel rail pressure, leakage alarm for the left main engine injector and fuel injection pump, and load limit for the left main engine". Upon checking the local operation control screen, it was found that the common rail pressure is around 870 bar, which is much lower than the pressure of around 1200 bar under this load (normal pressure of 1000-1600 bar). According to the host operation manual, after the safety valve trips, the host must urgently stop and the accumulator must release pressure in order to reset the safety valve (safety valve opening pressure of 1850 bar). After communicating with the driver's console, immediately stop and check. Upon checking the monitoring computer, it was found that the parameters of the main engine oil temperature, water temperature, cylinder exhaust temperature, bearing temperature, oil mist detection, etc. were normal without any abnormal alarms.
2, Main engine fuel system.
Figure 1 Schematic diagram of fuel system
3.Fault analysis and handling process. Regarding the fault phenomenon, the possible causes are analyzed as follows: firstly, unstable fuel supply pressure in the external fuel system; The second is the failure of the safety valve; Thirdly, there is a malfunction in the fuel injection control unit; Fourthly, the throttle valve core is stuck or the control driver is malfunctioning; The fifth issue is the wear of the plunger of the high-pressure oil pump.
1. Check if the external fuel system is functioning properly. Check if the low-pressure fuel system is normal. According to the design requirements, the outlet pressure of the fuel pump should not be lower than 8 bar (low-pressure alarm). After inspection, the outlet pressure is around 12 bar, which meets the design requirements, and there is no alarm information in the monitoring records, ruling out external low-pressure fuel system problems.
2. Check and verify if the safety valve is functioning properly. In order to further confirm the fault phenomenon, various operating parameters of the main engine were consulted to confirm that the oil temperature, water temperature, exhaust temperature of each cylinder, bearing temperature, oil mist detection and other parameters of the main engine were normal. The crankcase inspection door was opened to check the internal crankshaft connecting rod and other components of the body, and there were no obvious scratches or damage. The external fuel supply system was checked to be normal. The car was blown and started for testing. When the local speed increased from 300 r/min to 500 r/min, the throttle valve opening changed significantly at around 460 r/min. When decelerating from 400 r/min to 300 r/min, the throttle valve opening was 0% and remained unchanged, and the rail pressure fluctuated between 1200 bar and 1500 bar (set value 1200 bar). Then, the rail pressure reached above 1850 bar, and the safety valve jumped. From the actual rail pressure data, it can be confirmed that it is safe The valve is normal.
3. Check if the injection unit control module is functioning properly. If the injection unit control module or software system malfunctions, the host monitoring system will automatically sound an alarm. During the testing process, if the host exhaust temperature is normal and there are no alarms, it is inferred that the module is normal.
4. Disassemble and inspect the throttle valve. The engine speed decreases and the throttle valve opening gradually decreases, but the throttle valve opening is displayed as 0%. However, the actual rail pressure has exceeded the safety valve opening pressure, and the control of the throttle valve does not match the actual action. Therefore, it is inferred that the throttle valve may be faulty.
In order to further confirm whether the throttle valve is damaged, the throttle valve was disassembled and inspected. It was found that the appearance of the throttle valve core was intact, and the throttle valve control driver could not be detected. In order to rule out the fault of the throttle valve control driver, two throttle valve control drivers were replaced. When starting up, all parameters were normal from 300 r/min to 500 r/min locally. After 10 minutes of shutdown, the machine was restarted again and ran for 30 minutes. All parameters were normal. Therefore, it was determined that at least one throttle valve control driver was faulty. After returning to the factory for testing, it was found that one of the throttle valve control drivers was faulty. Start the engine again, notify the cab to slowly accelerate, confirm the operating condition of the engine when the load increases. When the engine load rises to 53%, the common rail pressure of the engine suddenly displays a low pressure alarm, and the common rail pressure is only about 870 bar.
5. Disassemble and inspect the high-pressure oil pump. After excluding faults in the throttle valve and injection unit, it is inferred that the cause of the instantaneous high common rail pressure is due to a malfunction in the high-pressure oil pump itself. In order to thoroughly inspect the high-pressure oil pump, the ship dismantled and inspected two high-pressure oil pumps on the left main engine while ensuring navigation safety. It was found that the plunger of the oil pump was severely worn and had obvious scratches near the cam end. After replacement, the engine was restarted and the load was slowly increased, and the main engine returned to normal.
4, Fault mechanism analysis. The malfunction of the throttle valve caused overload and a decrease in the speed of the left engine. One of the throttle valves had a small opening due to a control driver failure. As the camshafts of the two high-pressure oil pumps work alternately with a 60 ° interval, in order to ensure that the outlet rail pressure of the high-pressure oil pump is stable at a certain value, the opening of the other throttle valve is inevitably too large. When the throttle valve with a small opening is experienced, the fuel supply is insufficient and the speed decreases. Then, when the other high-pressure oil pump is working, the throttle valve opening is too large, the rail pressure fluctuates abnormally, and the speed suddenly increases and decreases. This causes the wear of the high-pressure oil pump plunger to increase when the speed increases instantly. The oil temperature used to lubricate the plunger will increase, the fuel viscosity will decrease, and the plunger will be stuck and abnormally worn. When the fault occurs, the two abnormal noises are the plunger. Caused by jamming. Due to the wear of the plunger of the high-pressure oil pump, its leakage increases. At low loads, the rail pressure can be maintained at a certain value with small fluctuations. However, as the load increases, the rail pressure automatically rises, causing an increase in the leakage of the high-pressure oil pump and abnormal fluctuations in the rail pressure. This leads to abnormal pressure relief of the safety valve and prevents the main engine from working properly. There are many reasons for the wear of the plunger of the high-pressure oil pump. Regarding the fault itself, in addition to the cause of the throttle valve failure, combined with practical installation, this article analyzes and discusses several aspects such as the quality of the plunger components, fuel quality, fuel viscosity, and external fuel supply.
1. There are certain design issues with the plunger components themselves. The inspection cycle for high-pressure oil pump plunger components is generally between 10000 and 12000 hours, while the high-pressure oil pump on this ship only used about 3000 hours before the failure. It is inferred that there may be a problem with the quality of the plunger. From the disassembled plunger, it can be seen that there is severe wear away from the working end, as shown in Figure 2. In addition, a small part of the upper part of the working face has not been coated. The plunger components equipped by the manufacturer have been improved, and all the working faces of the plunger have been coated (as shown in Figure 3).
Figure 2 High pressure oil pump worn plunger
Figure 3 Comparison of new and old high-pressure oil pump plungers (new on the left)
2. The fuel may be mixed with hard impurities, resulting in a decrease in fuel quality. The high-pressure common rail system has high requirements for fuel quality. This ship is equipped with two filter systems before the fuel enters the machine. During inspection, it was found that one of the filters itself had quality problems. The filter seal ring was defective during assembly, and there was a lack of visible residual holes at the bottom of the filter. Only a plug was used to block it, which allowed impurities remaining at the bottom of the filter seal ring to enter the engine after it was damaged, making it possible for hard impurities to exist in the fuel.
3. The fuel temperature is too high and the fuel viscosity is low. The lubrication of the high-pressure oil pump plunger of this type of engine is provided by high-pressure fuel leakage oil. The fuel related parameters defined in the main engine data are based on the 0 # diesel setting, which requires that the fuel inlet temperature should not exceed 45 ℃. However, this ship uses -10 # fuel in the north. From the actual temperature parameters detected, the fuel inlet temperature is 30 ℃, the speed is 460rpm, and the load is 54%. The temperature of the high-pressure oil pipe has already reached 50 ℃. At 50 ℃, the measured viscosity of -10 # diesel is 2.017cst, and the standard viscosity of the main engine data is not less than 1.9cst. As shown in Figure 4, the oil temperature is 54 ° C, and the viscosity has reached the critical value.
Figure 4-10 # Diesel Viscosity Variation Curve
Table 1 shows the measured parameters of the main engine during two in four operation. The internal oil temperature was estimated by measuring the oil leakage of the high-pressure oil pump. The data shows that when the load of the main engine reaches about 55%, the oil temperature has exceeded the critical value, and the viscosity of the fuel is insufficient, which accelerates the wear of the high-pressure oil pump plunger.
4. Low pressure fuel rail pressure is unstable. The host operation manual requires a low-pressure fuel rail pressure range of 11-12 bar. In practical use, it has been found that when the engine load exceeds 80%, the low-pressure fuel rail pressure fluctuates between 9.5 and 1.12 bar, and the low-pressure fuel supply pressure is insufficient, further exacerbating the working temperature of the high-pressure fuel pump.
5, Suggestions for using high-pressure oil pump. 1. Technical improvements have been made to the pipelines and fuel pumps of the low-pressure rail, increasing the fuel intake and low-pressure rail pressure to ensure that the low-pressure fuel supply meets the standards. 2. Regularly check the fuel leakage of the high-pressure fuel pump, analyze the operating status of the high-pressure fuel pump through big data, and recommend disassembling and inspecting the high-pressure fuel pump plunger every 2000 hours of operation or when the leakage increases exponentially. 3) When the engine load is high, the viscosity of -10 # diesel decreases and cannot achieve lubrication effect. Long term use will gradually lead to poor lubrication of the high-pressure oil pump plunger and gradual wear, shortening the service life. It is recommended to use 0 # diesel fuel under conditions where the external ambient temperature allows. 4) The internal leakage of oil in the high-pressure oil pump is caused by a pipeline connected from the pump body to the upper part of the throttle valve core, and then discharged into the "fuel injector and fuel pump leakage oil pipe". When there is abnormal noise or safety valve tripping in the high-pressure oil pump, the wear of the high-pressure oil pump can be determined by removing the throttle valve control driver (closing the fuel valve in advance) and observing whether there are iron filings on the upper part of the throttle valve core.