II. STC Turbocharger Failure Cases
In recent years, a large vessel has been in long-term navigation. The diesel engine of the ship has accumulated approximately 11,000 hours of operation under high-intensity conditions.
The main propulsion engine is a PA6 series four-stroke diesel engine with 16 cylinders arranged in a V shape at 60°, featuring a bore of 280mm and a stroke of 290mm. The maximum single-cylinder explosion pressure is ≤14.5MPa, and the maximum single-cylinder exhaust temperature is ≤580℃. The maximum continuous speed is 1000r/min, and the rated power is 5184kW. It is equipped with an STC turbocharger.
Due to prolonged high-intensity use, the exhaust gas turbocharger of the PA6 diesel engine on this vessel has frequently malfunctioned, resulting in various issues such as nozzle damage, blade damage, oil seal leakage, and bearing wear.
Two particularly typical cases are noteworthy:
1. A sudden abnormal noise occurred in the B-row turbocharger of a certain diesel engine. Upon investigation, it was found that the expansion joint of the exhaust system had aged and fallen off, causing fragments to enter the turbine end and damage the nozzle ring.
2. Early one morning, while sailing at an economic speed (diesel engine speed: 660 r/min, controllable pitch propeller pitch ratio: 90%), the duty engineer heard an abnormal "buzzing" sound from the A-row turbocharger of a certain diesel engine during routine inspection. A visual inspection revealed slight shaking of the turbocharger, which was increasing in intensity. The engineering crew immediately took emergency measures, reducing the speed of the power system and disconnecting the propulsion. During this process, a slight burnt smell was emitted from the turbocharger. After shutdown and turning the engine by hand, lubricating oil was found leaking from the lower observation port of the A-row turbocharger. Subsequent disassembly and inspection revealed that the oil seal ring had failed and the sliding bearing was worn, leading to a sudden drop in lubricating oil pressure. The following section will focus on analyzing the causes and diagnosing this fault case.
III. Analysis of Fault Causes of STC Turbocharger
1. Abnormal Noises from the Turbocharger
(1) High-pitched, shrill screeching.
This is caused by a reduction in the nozzle ring area, a decrease in the diffuser flow area, and an increase in turbocharger speed (overspeed).
(2) "Buzzing" surging sound, accompanied by significant fluctuations in boost pressure and unstable operation of the diesel engine.
This is caused by blockages in the intake system, including fouling of the air cooler, intake passage, intercooler, compressor fouling, reduced valve clearance, and incorrect valve timing.
(3) "Sssss" and "Pppp" sounds.
These are mainly due to air leakage at the flange connections between the turbocharger and the pipeline. At the exhaust turbine end, there is a "Pppp" high-speed pulsating sound, while at the intake compressor end, there is a "Sssss" continuous high-speed airflow sound. Another possible cause is the rupture of the bellows.
(4) Mechanical scraping sounds from metal, accompanied by abnormal vibration of the turbocharger.
This is caused by changes in the clearance between the bearing and the shaft (either increasing or decreasing), reduced clearance between the impeller and the volute, impeller deformation, eccentric wear on the rotor journal, severe wear of the floating sleeve or thrust plate, or disruption of the rotor's dynamic balance.
(5) Abnormal vibration and noise caused by severe carbon deposits in the turbine or foreign objects falling into the supercharger, resulting in damage to the blades and nozzles.
2. Abnormal Vibration of the Turbocharger
As a high-speed rotating mechanical device, the main causes of abnormal vibration in the turbocharger include damage to rotating parts, loss of dynamic balance of the rotor, and severe surge. The cause of surge has already been analyzed.
(1) Blade Breakage.
This is mainly caused by foreign objects or fragments from broken piston rings or valves entering the impeller, overloading of the turbocharger, or resonance of the blades due to strong external airflow excitation frequency or exhaust gas pulses, leading to damage of the turbocharger.
(2) Bearing Burnout.
The main causes include insufficient lubricating oil supply, excessive bearing load, mechanical damage caused by impurities mixed into the friction pair, rotor dynamic imbalance, and shaft bending deformation, etc. These factors cause axial movement of the rotor, resulting in severe vibration of the turbocharger.
(3) Loss of Rotor Dynamic Balance.
Long-term use inevitably leads to blade wear, bearing wear, shaft deformation, etc., naturally causing the rotor to lose dynamic balance.
3. Turbocharger Oil Leakage
Turbocharger oil leakage mainly occurs due to excessive vacuum in the compressor causing oil to be drawn in (such as when the air filter or compressor is clogged), blocked return oil lines, excessive oil supply to the system, and failure of the oil seal (such as excessive wear of the oil seal ring or insufficient elasticity of the oil seal ring). Severe oil leakage can lead to the turbocharger not operating normally [5].
IV. Diagnosis and Elimination of STC Turbocharger Fault Cases
1. Fault Diagnosis and Handling Process
When a fault occurs during the operation of the turbocharger, emergency measures should be taken, a fault analysis conducted, and the fault promptly eliminated. After the fault is eliminated, necessary verification should be carried out before it can be put back into use.
The following steps should be observed:
(1) Stop the vehicle if necessary (in case of major faults, such as abnormal noises);
(2) Record and observe the fault phenomena in real time;
(3) Accurately locate the faulty part;
(4) Determine the cause of the fault;
(5) Confirm the fault phenomena;
(6) Take measures to eliminate the fault;
(7) Verify whether the fault has been eliminated.
2. Troubleshooting Methods
Based on the cause analysis in Section III, combined with the abnormal humming sound of the turbocharger, obvious surging, severe shaking, the smell of burning during deceleration, and the leakage of lubricating oil found when the observation hole was opened after shutdown.
From the above judgment, the possible causes of the fault may be the failure of the oil seal, the increase in the gap between the bearing and the shaft, the imbalance of the rotor causing axial movement and rubbing, leading to strong vibration of the turbocharger.
When troubleshooting the specific faults of the turbocharger, a preliminary analysis should first be conducted based on the appearance, fault phenomena, lubricating oil consumption, oil quality after lubrication, and diesel engine operating parameters. Then, the turbocharger should be disassembled, and all components should be inspected.
The specific steps are as follows:
(1) Check for oil leakage at the turbine end and whether the blades are damaged.
Use an industrial endoscope to observe the oil seal and the condition of the turbine blades through the inspection hole to determine if the elasticity of the oil seal ring is good and if it is worn. Obvious oil leakage marks can be found at the turbine end, and there are obvious scraping and wear marks on the turbine blades and the turbine housing. It can be determined that the oil seal has failed.
(2) Check for any foreign objects entering the turbine end.
After disassembling and inspecting the intake manifold and volute, and checking the turbine and nozzle ring, it was found that except for scratches on the impeller, there was no damage to the turbine and nozzle ring, and no foreign objects were present.
(3) Check if the fit clearance is too large.
The measurement method is as shown in the clearance measurement diagram in Figure 3. The inspection standards are: axial clearance A: 0.10 - 0.32 mm, radial clearance B: 0.47 - 0.93 mm. After measurement, it was found that the clearance between the bearing and the shaft has increased, with the radial clearance B reaching 0.97 mm, exceeding the standard range by 0.04 mm. There is radial movement of the shaft, indicating that the impeller and the volute are in contact and scraping.
(4) Disassemble and inspect the turbocharger.
During the comprehensive and thorough disassembly and inspection of the turbocharger, technicians conducted meticulous and detailed checks and tests on its internal precision components.
After careful disassembly and investigation, it was found that there were obvious signs of wear on the floating sleeve assembly and thrust plate components inside the turbocharger, which need to be replaced.
(5) Repair Plan.
After a thorough inspection and diagnosis, it was determined that the intermediate assembly set needs to be replaced. This is the most direct and effective way to eliminate the current fault.
After the replacement is completed, a comprehensive reinstallation and test run will be carried out to ensure that all components are installed correctly and the system operates stably.
After the test run, the performance was good, and the fault was successfully eliminated.
V. Preventive Countermeasures and Measures
1. Strictly Maintain and Service the Turbocharger as per Regulations
Based on practical installation experience in recent years, the following points should be noted:
Firstly, the filter element of the turbocharger's fine filter should be replaced regularly (every 100 hours) to ensure unobstructed oil flow and clean lubricating oil.
Secondly, the oil seal at the turbine end and the working condition of the turbine blades should be inspected regularly using an industrial endoscope.
Thirdly, the corrugated pipe at the turbine's gas inlet end should be disassembled regularly to check for any metal debris at the turbine inlet and any scratches or damages on the nozzle ring. Manually rotate the turbine to check for any abnormal sounds or rubbing.
2. Do a Good Job in the Operation and Management of the Turbocharger
First, monitor the working status of the turbocharger in real time, paying particular attention to changes in the turbocharger's speed, boost pressure, lubricating oil pressure, turbine inlet temperature, cooling temperature, and lubricating oil temperature, especially the lubricating oil inlet pressure of turbocharger A (B).
From the perspective of equipment design, an alarm will only occur when the lubricating oil pressure is ≤ 0.03 MPa. However, in actual use, it has been found that as long as the lubricating oil pressure is ≤ 0.07 MPa and shows a downward trend, the machine should be immediately shut down; otherwise, insufficient oil supply can cause the turbocharger bearings to burn out, or even lead to the scrapping of the entire turbocharger.
Second, when the turbocharger is in operation, strengthen the visual inspection of its appearance, judge whether the operation is stable, and listen carefully to its operation sound. If the blades are broken or the turbine is seriously carbonized, abnormal sounds will occur.
When abnormal vibration sounds or burnt smells are detected from the turbocharger, the engine should be immediately shut down and the turbocharger removed. Use an industrial endoscope to check through the observation hole whether the oil seal, turbine blades, etc. are normal.
If oil leakage from the oil seal or damage to the turbine blades is found, the main engine must be taken out of service for handling, and then repaired and tested based on the cause. If the core components such as bearings and rotors are damaged, they must be sent to the original manufacturer for repair as per regulations and undergo dynamic balance tests. It is strictly prohibited to reinstall the turbocharger without conducting dynamic balance tests.
3. Strengthen the Operation Management of Diesel Engines
Poor combustion, excessively high exhaust temperature, fuel injection faults, inadequate cooling, rapid load changes, and improper operation of diesel engines can all affect the quality of exhaust emissions, including exhaust temperature, pressure, and flow rate.
These parameters are crucial to the operational quality of the exhaust gas turbocharger.
For instance, when the load on the diesel engine increases, the exhaust temperature and flow rate also rise, causing the turbine speed to increase and the intake pressure to rise; frequent acceleration and deceleration or rapid load changes can lead to unstable operation of the turbocharger with its speed fluctuating; problems in the fuel system, intake and exhaust systems, or cooling system may deteriorate the working environment at the turbine end of the turbocharger, resulting in excessively high intake temperatures at the turbine end and reducing the turbocharger's lifespan.
Therefore, it is necessary to enhance the operation management and maintenance of marine propulsion diesel engines to maintain their good operating condition and combustion quality, ensure their reliable operation, better match the operational requirements of the turbocharger, and also operate the main engine reasonably.