Marine Engineering Study Materials

When operating at steady speed, turbocharger vibrations could occur when:

• Rotor imbalance due to rotor damage from an object displaced from the cylinder, such as a broken piston ring or exhaust valve
• Imbalance of the rotor from breaking of the lacing or binding wire
• Bearing failure, which would reduce the support of the rotor
• Slack foundation mounting of the turbocharger casing
• Rotor imbalance following inadequate in-service cleaning
• Surging of the turbocharger, when the unit is operated close to the surge line possibly due to a fouled hull
• Vibration transmitted to the turbocharger unit from an adjacent machinery unit.

Turbocharger vibrations can minimized by the following:

• Fitting of a protective grid between the engine and the turbocharger, and regular overhaul of the exhaust valve/piston rings
• Regular changing of the lacing wire at the inspection stage
• Regular changing of the bearings and the sump oil
• Regular checks of the foundation bolts

When a pulse system turbocharger is damaged and cannot be used, then the following cause of action could be used:

1. Stop engine
2. Remove bearing end covers and fit rotor locking devices at both ends
3. Close in the compressor outlet to ensure that scavenge air does not leak out, but at the same time prevent rotor warping
4. Maintain freshwater circulation
5. When the engine is operating, then the engine power must be reduced to avoid thermal overload of the engine. The amount of engine power that can be developed could be limited by one of the following: Excess exhaust gas temperatures, Excess exhaust smoke, Engine vibration, Excess speed of the remaining turbocharger.
6. The time taken for engine speed up would be extended and thus manual engine speed up should be used.

Turbocharger Maintenance

Regular maintenance must be carried out to prevent unwanted turbocharger vibrations.

The gas side of turbocharger refers to the nozzle ring and turbine blading. The fall off in performance of these components would be mainly due to fouling, which would also cause the inlet gas temperature and pressure to rise, and hence these should be monitored.

The compressor performance would be reduced by fouling of the compressor wheel and diffuser. This fouling would also cause the delivery pressure to fall, whilst the turbocharger was maintaining a stable speed and all other parameters were normal. Hence the delivery pressure of the compressor would be monitored.

The suction filter performance would reduce when fouling is present. This would be monitored by measuring the pressure drop across the filter. The after cooler performance would reduce when fouling is present. This would be monitored by measuring the air pressure drop across the cooler, and the temperature of the cooling water.

The performance of the turbine is maintained by regular in-service cleaning, supplemented by manual cleaning of the turbocharger on a yearly operational running hour routine. The in-service cleaning can be carried out using either dry cleaning involving dry particle cleaning, and/or water washing of the turbocharger using warm water and air blast (only when the engine and turbocharger speed has been reduced). The inservice cleaning should be carried out twice weekly, or at any stage the performance of the turbine indicates a high rate of fouling.

The performance of the compressor is maintained by regular in-service cleaning, supplemented by manual cleaning of the compressor and diffuser on a yearly operational running hour routine. The in-service cleaning can be carried out using a small quantity of warm water injected into the turbocharger suction housing at full turbocharger speed. This cleaning can be carried out twice weekly.