Whether the host can be operated normally and whether the working conditions are normal are undoubtedly the most concerning issues for marine engine management personnel.
The normal operation of the main engine is the basic guarantee for the safe navigation of ships entering and leaving ports and narrow waterways.
Below is a summary and brief analysis of some faults that affect the operation of the main engine encountered by the author in ship management practice, in order to provide us with reference when encountering similar problems and to have an additional approach when judging similar faults.
1, Several common faults
The most common reason for the difficulty in operating the main engine is that the suction valve of individual high-pressure oil pumps in the main engine is stuck, the needle valve of the oil head is stuck, the exhaust valve is severely eroded, and the piston is broken, causing the compression pressure to fail to meet the ignition conditions;
Another common fault is improper adjustment of the distance between the thrust flange and the sealing end face of the high-pressure oil pipe of the exhaust valve, which causes serious leakage and direct backflow of camshaft oil at the high-pressure oil pipe joint of the exhaust valve, making the exhaust valve unable to open normally. This situation usually occurs when the exhaust valve is just replaced.
There are also individual cases where the single cylinder fuel stop device is activated (some models are equipped with this device, which accidentally touches the single cylinder fuel stop handle during maintenance or cleaning work, causing it to actuate), resulting in the single cylinder not firing.
The probability of the above situations occurring is relatively high, and the reasons should be easy to determine and solve.
2, Reasons and solutions for the failure of single cylinder ignition in the main engine
1. Malfunctions caused by reversing mechanism
Single cylinder failure or even multi cylinder failure due to improper reversing.
When this situation occurs, even if the host can start up, the host speed will fluctuate dramatically, and in severe cases, it may not even cross the critical speed zone.
Main reasons and solutions:
1) One of the reasons is that the car clock handle was placed in the starting position for too short a time, resulting in some cylinders not being able to change direction. If one cylinder cannot be changed direction, it is difficult to accelerate normally.
At this point, you can communicate with the captain and place the clock handle in the parking space, which is equivalent to resetting and usually completes the direction change;
2) The second reason is that the sealing of the reversing cylinder causes severe aging, leading to air leakage, or the reversing mechanism gets stuck, which can also cause the single cylinder to fail to ignite.
Disassembling the directional valve and replacing the sealing ring can solve the problem.
To avoid this situation, it is necessary to regularly replace the sealing ring of the reversing cylinder and strengthen maintenance to keep the reversing mechanism active.
2. Reasons and solutions for faults caused by insufficient compressed air pressure of exhaust valve air spring
The insufficient compressed air pressure of the air spring causes the exhaust valve to close slowly or incompletely, resulting in single or multiple cylinders unable to ignite, causing difficulty in starting. The reasons and solutions are as follows.
Reasons and solutions:
1) The common cause of insufficient compressed air pressure in the air spring, excluding faults in the control air system, is due to aging of the exhaust valve air spring cylinder seal and severe air leakage caused by worn copper sleeves.
Temporary measures can be taken by connecting the cabin daily air hose to the main engine control air pipeline, so that the supplied air volume is greater than the leaked air volume, which can temporarily ensure the compressed air pressure of the exhaust valve air spring. This situation usually occurs on aging ships.
The long-term response measures must dismantle the exhaust valve, replace the corresponding sealing ring, copper sleeve, etc;
2) If the exhaust valve stem is severely worn, it can also cause a large amount of compressed air leakage from the air spring, and because the leakage distance is relatively short and the leakage speed is fast, it can also cause insufficient compressed air pressure in the air spring.
When renovating the exhaust valve, it is necessary to measure the diameter of the exhaust valve stem. If excessive wear is found, it should be scrapped and should not be refurbished again.
3. Malfunction caused by intake of camshaft oil system
The opening of the exhaust valve stem is performed by a hydraulic drive mechanism, so specialized camshaft oil pumps, camshaft oil tanks, etc. are installed.
The exhaust valve driver is generally equipped with a safety valve and a throttle valve, which can provide protection and reduce the opening and closing noise of the exhaust valve.
If air enters the camshaft hydraulic system, it will seriously affect the timing of the exhaust valve opening. The exhaust valve may open too slowly or not fully, causing the exhaust valve to knock or even the single cylinder to fail to ignite.
Reasons and solutions:
1) The intake of the camshaft system is generally drawn in by the camshaft oil pump from the disc or suction pipe.
A similar fault phenomenon occurred in a certain round, and after careful investigation, it was found that it was caused by a slight leakage at the residual plug of the inlet filter of the camshaft oil pump;
2) Leakage of fuel from the high-pressure fuel pump into the camshaft system can increase the viscosity of the camshaft oil, and the suction vacuum of the camshaft oil pump is too high, which can easily cause the camshaft oil system to suck air. Therefore, the oil in the camshaft oil tank should be replaced regularly.
Moreover, the condition of the high-pressure oil pump components and their sealing devices of the exhaust valve is also crucial.
In a certain round, due to the camshaft oil system being too dirty and viscous, air entered the camshaft oil system. When the air accumulated to a certain amount, it would affect the timing of the exhaust valve, and some cylinder exhaust valves would not open completely.
The main fault phenomena include individual cylinders not firing, automatic engine deceleration, combustion chamber knocking, turbine surge, etc. After replacing the camshaft oil, the fault phenomena disappeared.
To determine whether the malfunction is caused by air entering the camshaft hydraulic system, the exhaust valve opening indicator can be lowered when the malfunction occurs. It can be seen that the opening amplitude of the exhaust valve of the cylinder significantly decreases, that is, the exhaust valve cannot be fully opened.
4. Malfunctions caused by the remote control system of the host
In terms of the remote control system of the host, taking the B&W 5L50MC as an example: if the oil stop delay relief valve (25 # valve) does not work properly, it will cause the high-pressure oil pump to not supply oil in a timely manner, resulting in difficulty in starting. The cylinder in poor condition cannot reach the ignition speed, causing starting failure;
If the delay adjustment of valve 32 # is improper, the opening delay of the main starting valve is too short, and the oil and gas merging time is too short, it will also cause difficulty in starting the vehicle.
Reasons and solutions:
The malfunction of pneumatic valve components is generally caused by high water content in the air or improper adjustment of the valve components.
Therefore, valves such as 25 #, 26 #, 117 #, 32 #, 33 #, and 274 # should be regularly disassembled, inspected, and cleaned. It is best to replace the repair kit for the main remote control system every 5-8 years.
It should be noted that:
If the interior of the host control air system is dirty and the control air compressor or dryer is not functioning properly, the probability of malfunction will increase significantly.
So corresponding measures should be taken to ensure the normal operation of all valves in the remote control system, strengthen the control of air system leakage, and quickly release all air from the main control system after each vehicle is completed, in order to avoid excessive sedimentation of dirt in the system as much as possible.
5. Malfunction caused by exhaust valve air throttle pipe
Some B&W 5L50 models of ships do not have sealed air throttling pipes installed on their main engine exhaust valves, or the diameter of the throttling holes of the throttling pipes is enlarged, so that the air spring air chamber and the sealed air chamber are directly connected. The compressed air of the air spring will be released into the flue through the gap between the valve stem and the guide sleeve, causing a decrease in the compressed air pressure of the air spring and resulting in changes in the timing of the exhaust valve. Cylinders with severe leakage will not ignite, or it will be difficult to start the car when reversing (because reversing consumes more air and is not easy to start).
The failure of a single or multiple cylinders of the main engine to ignite can seriously affect the maneuverability of the main engine, thereby affecting the safety of ship navigation.
The analysis of faults can sometimes be complex, but the accumulation of experience provides a shortcut for quickly solving problems. We hope that the above experience and analysis can provide reference for industry colleagues when encountering similar problems in the future.
Regular maintenance and upkeep of mechanical and electrical equipment can prevent many malfunctions.