Basic knowledge of marine diesel engines

1. What should the operator pay attention to when the exhaust gas turbocharger is operating?

Answer: 1. When the diesel engine is running at low speed, the operator should observe whether the turbocharger speed indicator needle fluctuates excessively. During deceleration and shutdown, the turbocharger speed should decrease smoothly. If there is no speed indicator, the operator can listen to the sound to determine if the turbocharger is operating smoothly.

2. Lubrication issues: The operator must regularly check the oil level. Because a turbocharger is a high-speed rotating machine, even a short-term oil shortage can cause bearing damage and accidents. Therefore, the oil level should be maintained at the specified level. For high-pressure lubrication systems, the oil supply and flow should also be monitored. Oil flow must not be interrupted, especially the inlet pressure and outlet temperature. These parameters should be adjusted according to the specifications of each model.

3. Regularly listen to the turbocharger to ensure it is operating smoothly.

Regardless of whether the engine is operating at partial load, full load, or overload, the operator should pay close attention to the boost pressure, speed changes, and exhaust gas temperature before the turbine. If any abnormal conditions are detected, the turbocharger and its system must be thoroughly inspected to identify and resolve the problem.

2. What maintenance and management should be performed on the exhaust gas turbocharger system on a daily basis?

Answer: 1. Before starting the engine, listen for any abnormal noises when the turbocharger rotates under the influence of starting air, and observe whether there is any resistance to rotation. If so, the cause must be carefully investigated and resolved.

2. The turbine blades are easily fouled due to direct contact with exhaust gas, especially in pulse turbochargers. Excessive and uneven deposits will disrupt the rotor's dynamic balance, causing vibration. Therefore, the rotor must be regularly inspected and cleaned. During operation, the turbine and compressor can be cleaned with water or solid plant particles to remove carbon and dust, preventing severe fouling, but this cannot replace regular inspection and cleaning of the turbocharger.

3. ... When disassembling, inspecting, and cleaning the impeller, carefully check the blades for any damage.  Replace any blades with cracks or bends. If blade replacement is difficult, temporarily remove the blade symmetrically opposite the damaged one to maintain impeller balance and prevent vibration.

4. Regularly inspect the turbine and compressor bearings. For sliding bearings, pay attention to bearing clearance and lead wear. If scoring, lead wear, or excessive clearance is found, repair or replace the bearing. For rolling bearings lubricated by oil splash or an integral oil pump, pay special attention to oil quality and level, and regularly change the lubricant. Also, check bearing wear; replace as needed (inspection intervals depend on operating speed, generally 8000 hours).

5.  Maintain the air cooler properly; ensure full airflow at the inlet and outlet. Soiling of the air cooler increases airflow resistance and reduces cooling efficiency, directly affecting engine power and thermal load. Therefore, regularly clean and blow out the cooler.

6. To prevent turbocharger surge, besides regularly cleaning the air cooler, systematically inspect the engine's scavenging and exhaust ports to remove carbon deposits and ensure proper turbine operation.

3. What maintenance should be performed on the turbocharger during a factory overhaul?

A: During a factory overhaul, the following components of the turbocharger should be inspected to meet the required standards:

1. Rotor: Carefully clean the rotor and blades with diesel fuel; remove any scratches; replace any cracked or bent blades.

2. Nozzle: Inspect the nozzle blades for cracks, paying particular attention to the blade roots. Tap the blades with a steel rod to check for abnormal sounds; repair or replace any cracked blades.

3. Seals: For metal seals, repair minor scratches and wear, and realign; replace severely worn seals.

4. Bearings: Check bearing clearance and babbitt lining. If there are any scratches, cracks, chipping, or if the clearance exceeds the wear limit, the part must be replaced.

When replacing the compressor end bearings, ensure that both end surfaces are in close contact with the rotor thrust plate and oil seal ring end surfaces. Use dye penetrant inspection; the contact area should not be less than 75%.

5. Fixed Components: These include the turbine inlet and outlet housings and the compressor casing. Inspect the inner walls of all housings for scratches and eliminate the cause. Clean carbon deposits from the exhaust housing and scale from the cooling water chamber.

6. Air Filter and Muffler: Inspect the muffler panel; repair any damage. Clean the filter screen.

7. Check the clearance between the shaft and the outer ring; if it exceeds the requirement, replace the outer ring.

4. What are some common malfunctions of exhaust gas turbochargers, and how should they be handled?

A: 1. Bearing burnout: Exhaust gas turbochargers are high-speed rotating machinery, so bearing lubrication and cooling are extremely important. Insufficient oil pressure, insufficient oil volume, or dirty oil can cause bearing burnout in a short time.

Bearing burnout is often indicated by an increase in oil outlet temperature, a decrease in turbocharger speed, and reduced boost pressure. If the thrust bearing burns out, the rotor will move axially, causing the impeller to collide with the casing, producing a metallic grinding or clanging sound.

2. Turbine blade damage: Blade damage is mostly caused by foreign objects entering the turbine, such as broken piston rings, fragments from the inner shield of the exhaust pipe expansion joint, and exhaust valve fragments. This can have serious consequences, sometimes damaging several blades at once.

If a turbocharger has the above damage, it should be addressed immediately. If possible, shut down the engine. First, use special tools to secure the damaged turbocharger rotor, but do not interrupt the lubrication oil and cooling water flow; oil pressure can be reduced. The diesel engine must also reduce its load. If shutdown is not possible, run at low speed until the turbocharger stops vibrating.

3. Low boost pressure:  The causes of low boost pressure include a decrease in the turbocharger's rotational speed and severe fouling of the compressor passages. This can lead to excessively high exhaust temperatures, potentially causing the exhaust pipe to turn red-hot. To restore normal operation, maintenance personnel should consider disassembling and cleaning the turbocharger, and then perform a cylinder head inspection and repair.

4. High boost pressure: High boost pressure, especially when accompanied by an increase in turbocharger speed, is often caused by malfunctions in the fuel injection system, severe leaks in the cylinder or valves, or blocked intake passages. These issues lead to incomplete combustion and high exhaust temperatures. Appropriate inspections and cleaning are necessary.

If the problem lies with the turbocharger itself, it is usually due to carbon buildup and fouling in the turbine passages, which reduces the flow area and increases the exhaust gas velocity. This requires disassembly, inspection, and cleaning of the turbocharger.

5. Corrosion and pitting of the turbine housing: This issue can occur on both the coolant side and the exhaust gas side. On the coolant side, it is often caused by water impact and electrochemical corrosion. Regular inspection, installation, and replacement of sacrificial zinc plates are necessary. On the exhaust gas side, it is due to low-temperature dew point corrosion caused by sulfur. To prevent dew point corrosion, maintain a sufficiently high coolant temperature. During low load operation, pay attention to coolant temperature regulation. Currently, turbochargers with waterless cooling systems are available, eliminating corrosion in the water passages.

6. Surge: Compressor surge occurs when the airflow resistance at the compressor inlet increases, causing the airflow to decrease to the surge flow rate. Severe fouling of the air filter, intake passages, and turbine exhaust passages can all cause reduced airflow and lead to surge. In this case, the turbocharger should be disassembled, inspected, cleaned, and the relevant airflow passages should be cleaned.

8. Large clearance between the blade tip and the outer ring, caused by corrosion of the outer ring; replace the outer ring.