Marine Engineering Study Materials

The following engine/turbocharger arrangement will be detailed: Six cylinder main engine, utilising a constant pressure turbocharger arrangement with two turbochargers. The turbochargers use ball/roller bearings, externally fitted.

• The damaged turbocharger needs to be isolated from the air, exhaust and water sides. The exhaust inlet to the turbocharger can be isolated by the fitting of a spade in the pipeline between the exhaust gas manifold and the turbocharger inlet.
• The air side can not be isolated as the auxiliary blower takes its suction via the air filter, thus air isolation of the turbocharger relies on the non return valve fitted at the inlet to the scavenge air manifold.
• As there is no longer any gas flow through the turbocharger, then the water cooling can be isolated by closing the inlet and outlet valves.
• The oil in the bearings can also be drained, and the rotor locking plates fitted to prevent any possible rotation of the defective turbocharger rotor. The rotor can be left in place until replacement parts are obtained and fitted.
• If the engine was operated at lower powers then the auxiliary blowers may be operated. The electrical load on the auxiliary blowers would need to be monitored if they were operated, to prevent any overheating of the motor.

The factors which may limit operation of main engine without turbocharger are the following:

When one of the two turbochargers is isolated, this will reduce the possible air input to the engine, and hence full engine power can not be developed. The following factors need to be considered when operating the engine:

• Exhaust temperatures: These will rise with the reduction in air delivery. The engine manual would be consulted as to the maximum limit, and this will be around 500 degrees.
• Exhaust smoke levels: These will also rise, and excessive smoke will cause fouling of the turbocharger and exhaust gas boiler.
• Maximum engine power: This will be limited due to the factors stated above, and this will probably be approximately 50% power with the loss of one of the two turbochargers.
• Acceleration of the engine: When the engine load is increased then the time taken to increase the load would need to be extended to prevent excessive thermal load.
• Speed of the remaining turbocharger: When the engine load is reduced this will also reduce the gas energy, which should ensure that the speed of the working turbocharger would not be excessive, but the engineering staff should also monitor this.

Hence the engine power would be reduced in consideration with all the above factors.