The SulZER 6RTA-84T-D host control system has three major optimization functions:
(1) Electronic controlled VIT+FQS (variable fuel injection timing and preset fuel injection advance angle based on fuel quality).
(2) Electronic controlled VEC (variable exhaust valve closing timing).
(3) The cooling water flow rate of the cylinder liner is automatically adjusted according to the load size.
Marine personnel should have a thorough understanding of their working principles in management, otherwise they may feel complex when faults occur.
This article describes the cause analysis and solution process of a malfunction in the main engine of a 300000 ton Very Large Ore Carrier (VLOC) SULZER 6RTA-84T-D type ore carrier, which was unable to accelerate.
Fault phenomenon
A certain VLOC set sail from Kemen Port in Fuzhou, and after departure, the cockpit controlled the main engine to accelerate cautiously and slowly.
Unlike ordinary small ships, the acceleration process from the speed inside the port to the speed at sea requires a longer time.
In addition to the control of the acceleration process load limit program set by the host remote control system, according to the instructions, in order to prevent wear and tear of the piston and cylinder liner due to rapid load changes, the throttle is manually controlled to slowly accelerate from the full AHEAD to the full AT SEA of the motorized vehicle, which takes nearly 2 hours.
But this time it's different. After more than 2 hours, the main engine still hasn't reached the engine speed (i.e. sea speed), and the throttle is constantly limited by the scavenging pressure.
Record the load indicator, exhaust temperature of each cylinder, VIT angle and VEC indicator, turbine speed and its front and rear exhaust temperature and scavenging pressure, and compare them with the records during the sea trial. It is found that at similar speeds and throttle openings, the turbine speed and scavenging pressure decrease, the fuel injection advance angle increases, and the VEC reading also increases.
Fault cause analysis
When analyzing the cause of the malfunction, first suspect that there is a problem with the scavenging system.
But whether it is the turbine filter or the intercooler, the oil pressure difference display of both shows that they are in a good state.
The impeller at the compressor end of the turbine is often washed with water, and although the exhaust end worm gear and nozzle ring have not been dry cleaned, they are washed with water every time sailing at low speeds.
In addition, the operating conditions of the host remained normal until it arrived at Kemen Port.
To avoid subjective judgment errors, the turbine compressor end impeller, exhaust gas end worm gear, and nozzle ring were flushed again, but the expected results were not achieved.
Therefore, there is no problem with the scavenging system.
During the maiden voyage, there was a malfunction in the VIT+FQS control unit of the main engine. This time, a related circuit board in the function optimization box was replaced at Kemen Port. We are considering whether it is related to the newly installed circuit board.
After the installation of the new circuit board, various parameter settings have been checked and compared.
When the host cannot accelerate, there are no abnormal alarms in the remote control system and function optimization box of the host.
Due to the observation of an increase in the VIT angle, the VIT+FQS control unit and VEC control unit were turned off using the "USER PARKER" function, and the VIT was fixed in the 0 position using a special tool.
At this point, the load indicator of the main engine increases, the turbine speed and scavenging pressure gradually increase, and the main engine speed also gradually accelerates.
After shutting down the VIT+FQS control unit and VEC control unit, the host resumed normal acceleration.
It is believed that there may be a problem with the newly installed circuit board and a report should be made to the maintenance supervisor, hoping that the service engineer can board the ship again for inspection.
The operation of the host with a functional optimization mechanism but unable to achieve VIT+FQS functions means that the fuel that could have been saved cannot be saved, and incomplete combustion can easily cause dirty exhaust channels.
Considering that the VIT control unit has no faults and the parameter settings are correct, and the host cannot accelerate, the author believes that the cause of the fault is not clear.
By consulting information, the cause of the malfunction was identified as related to the throttle lever system and the VIT locator. However, the throttle lever system has been lubricated with oil, and no issues were found with the VIT locator.
After the ship arrived in Singapore, the service engineer boarded the ship to inspect the functions of the VIT+FQS control unit and did not find any abnormalities. They only pointed out that the control range set by the VIT+FQS control unit may be too large, stating that the control range for the same type of engine they serve is usually set at -3 ·～+3 ··, while for this ship, it is -6 ·～+6 ··. It is recommended to consult the diesel engine manufacturer whether to change this setting.
The inspection results are expected, but due to the fact that the VIT control is not too large in this range and the host has been running normally before, this suggestion may not be adopted.
Perform a detailed inspection of the throttle lever system again to identify the true cause of the problem.
The SULZER 6RTA-84T-D main engine of the ship adopts the NABTESCOMG-800 electronic speed control system, and the speed signal comes from the speed probe of the camshaft transmission gearbox.
The governor consists of three parts: MCG-402 control unit, ADU-500A actuator drive unit (power amplifier), and EAR-500 actuator.
The EAR-500 actuator is the final component of the governor control, which directly adjusts the throttle opening of the main engine according to the speed command given by the governor.
The governor is set with a scavenging pressure limit and a torque limit, that is, the input signal of the governor is scavenging pressure, speed, and vehicle command, and the output signal is the throttle opening controlled by the actuator.
In Figure 1, the output shaft 1 of the electronic speed regulator actuator 22 is connected to the intermediate adjustment shaft 4 through cylinder 2 and its transmission rod 3.
The intermediate shaft 4 is connected to the corner handle 7 (conversion rod) through rod 5 and horizontal crossbar 6.
Corner handle 7 is connected to vertical rod 8, which is connected to corner handle 16 (used for VIT conversion rod). Its pivot is fixed on the regulating rod 12 of the high-pressure oil pump suction valve, and the other end is connected to the regulating rod 17 of the high-pressure oil pump overflow valve through rod 14.
It is known that the angle handle 7 and angle handle 16 are special components used to convert rotary motion into linear motion or linear motion into rotary motion, while the actuator controlled by VIT - locator 20 is connected to the high-pressure oil pump suction valve regulating rod 12 through its own piston rod and connecting belt 21.
According to different programs, corresponding to the scavenging pressure and speed, two angle signals are generated. These two angle signals are superimposed with the preset FQS angle signal (adjustable), converted into a pneumatic piston stroke signal, compared with the feedback signal, and then output is the control signal of the locator solenoid valve.
The actuator controls the extension and contraction of the locator piston through four solenoid valves, and the position signal is fed back to the electronic regulator by the piston stroke sensor to adjust the fuel injection timing.
When the piston stroke of the locator does not meet the program requirements, it continues to expand and contract under the control of compressed air through the on-off of four solenoid valves, until the feedback signal is consistent with the control signal.
If there is a malfunction, such as a broken solenoid valve or a stuck piston, which cannot achieve final control, a fault alarm will be given:
VIT position error or solenoid valve disconnection.
At this point, the remote control system will slow down the main engine to a certain value (set at 64.9 r/min for this ship) through the set control program, and make the SPEED REDUCEDBY VIT+FQS Control FAILUER indicator light on.
Solution measures
Analyze the action process and interaction between the throttle lever system and the VIT+FQS control unit during the acceleration process of the ship from the full AHEAD speed in the port to the full speed at sea.
When the governor provides an acceleration signal, its actuator raises the vertical rod 8 through the throttle lever system, and the angle handle 16 rotates counterclockwise around its pivot, driving the relief valve adjustment rod to rotate in the same direction, resulting in an increase in fuel injection volume;
At this point, a sharp angle is formed between the vertical rod 8 and the angle handle 16. When it rises and pulls the angle handle, a torque is applied through the pivot to the suction valve adjustment rod 12, causing it to rotate counterclockwise.
In fact, the curve of the VIT+FQS control unit varies from machine to machine based on the changes in scavenging and speed data. The curve set during the main engine bench test of this ship may differ from Figure 3, but the purpose is the same: to change the timing advance angle of fuel injection under partial load, so that the maximum explosive pressure is close to the pressure at maximum continuous power, thereby saving fuel.
At low loads, a sharp angle is formed between the vertical rod 8 and the angle handle 16. Although the torque generated is offset by the action of the VIT locator, a greater interaction force is generated between the angle handle 16 and its pivot, which requires the rotation of the angle handle to overcome greater frictional resistance (especially in the absence of lubrication in the bearings). In severe cases, it will prevent the angle handle from rotating around the pivot.
The reason why the host in this article cannot increase speed is due to this.
The bearing of the angle handle 16 is equipped with a dedicated oil nozzle, but the chief engineer did not inject oil into this nozzle during the maintenance of the throttle lever system, resulting in this malfunction.
The limitation of the scavenging pressure is also due to the fact that as the ship speed increases, the main engine speed has stabilized under the throttle opening, and the auxiliary blower automatically stops. The increase in scavenging pressure lags behind the increase in main engine speed, and the VIT is adjusted to a larger position, resulting in a higher maximum burst pressure and lower exhaust temperature, and lower turbine speed. Therefore, the scavenging pressure remains low, limiting the increase in throttle opening. After oil lubrication, the fault is eliminated.
Conclusion
The fault phenomenon in this article is very unique, and the only cause of the fault is inadequate lubrication with grease.
If this fault is not detected and not lubricated, long-term insufficient lubrication will cause bearing wear, resulting in a gap between it and the pivot shaft. The speed control performance of the main engine remote control system and the operating conditions of the main engine will be seriously affected.
This fully demonstrates the importance of comprehensive lubrication and maintenance of the throttle lever system.
Therefore, lessons should be learned, and the manual should be consulted regularly to fully understand the working principle of the equipment. Diligent observation, thinking, and summarization should be made to guide daily management work.
