Answer MEP Question 65

Q. During normal engine operation, a turbocharger rapidly loses speed and the speed reduction is accompanied by appreciable noise - 

A. State with reasons the possible causes. 

B. Explain in detail how the engine might be safely operated if the damage caused by this incident is such that the turbocharger cannot function. 

C. State with reasons the factors which may limit engine operating speed with the turbocharger out of action.

A. State with reasons the possible causes; 

- The two factors of loud noise and rapid speed reduction indicates that; 

1. Rotational friction has dramatically increased, or 

2. The rotor is in contact with the stator which could be due to bearing failure. This would cause the bearing friction to be increased and affect the rotor clearances, causing the rotor to contact the stator. or Mechanical damage to the rotor. 

- Should a component from the combustion chamber be admitted to the exhaust side of the rotor, this will cause an imbalance in the rotor, leading to possible bearing failure or damage of water coolant casing. This will admit water to the gas inlet and cause a reduction in the rotor speed. 

B. Explain in detail how the engine might be safely operated if the damage caused by this incident is such that the turbocharger cannot function; 

1. Engines with one turbocharger (Engines with exhaust by-pass)

a. Stop the engine.

b. Lock the turbocharger rotor.

c. Remove the blanking plate from the exhaust by-pass pipe.

d. Remove the compensator between the compressor outlet and the scavenge air duct. This reduces the suction resistance.

e. Run engine with 15% of MCR load and 53% speed.

2. Engines with one turbocharger (Engine without exhaust by-pass)

a Stop the engine.

b Remove the rotor and nozzle ring of the turbocharge.

c Insert blanking plates.

d Remove the compensator between the compressor outlet and the scavenge air duct. This reduces the suction resistance.

e Run engine with 15% of MCR load and 53% speed.

3. Engines with two or more turbochargers

a. Stop the engine.

b. Lock the rotor of the defective turbocharger.

c. Insert orifice plates in the compressor outlet and the turbine inlet. (A small air flow is required to cool the impeller, and a small gas flow is desirable to prevent corrosion)

d. Run engine with 20% of MCR load and 58% speed.

Points to consider regarding the continued operation

a. Adequate air supply for the amount of fuel injected. Adequate flow path for exhaust gas produced.

b. Adequate cooling of idle casing.

c. Isolation of air/gas/lubricating spaces in the event of no sealing air available.

          d. Securing of damaged parts to limit further damage.

- The electrical load on the auxiliary blowers would need to be monitored if they were operated, to prevent any overheating of the motor. 

Please follow Turbocharger out of service to read all the possibilities to operated a failed turbocharger

C. State with reasons the factors which may limit engine operating speed with the turbocharger out of operation. 

The exact power limits allowable with a defective turbocharger will depend on the actual configuration of the system and on how many turbochargers remain in use. The actual operating temperatures should be taken into consideration and normal values should not be exceeded. The condition of the exhaust should be monitored to ensure that adequate combustion air is being supplied. (Dark smoke) Allowance to be made for the rate of change of air supply during acceleration periods. Remaining turbochargers to be carefully monitored for abnormal operation due to altered gas flow Auxiliary air supply to be used where possible, but this may be affected by remaining turbochargers.

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