Turbocharger L & M, surging, how to minimise & sealing arrangment

L & M 

K = It is the distance between the compressor end cover mounting face and shaft end .Mark it as K.

Pull the rotor shaft towards the compressor side until the impeller comes in contact with the insert and determine K2.

Impeller clearance L = K – K2

 

Thrust the rotor shaft towards the turbine side until the turbine disc and nozzle ring comes in contact with each other and measure K1

Disc clearance M = K1 – K

 

The above measured clearance is very important as this will determine the proper functioning of the labyrinth seal between the impeller and exhaust shield and also the alignment of the shaft.

 

K 

To ensure that rotating impeller does not to touch the stationary blower casing cover in case of thrust bearing worn out.

 

Shroud ring 

The area around the turbine is always in contact with highly corrosive exhaust gases. 

shroud ring protects the turbine inner casing, can be easily replaced.

Turbocharger surging 

• It is the back flow of air from discharge to suction and it is characterized by noise and vibration of turbocharger.

Causes of turbocharger surging

Exhaust System

1. Uneven load
2. ME load too high
3. Exhaust valve defective
4. Damage T/C flaps

Fuel

1. Defective injector
2. Defective suction valve
3. Pressure too low, fuel Pump leaking, cir pump/supply pump pressure low
4. Air lock

Scavenge

1. Air cooler dirty
2. Scavenge port chock
3. Too high Scavenge temp
4. EGE dirty/fouled

Turbocharger

1. Air filter dirty
2. Nozzle ring dirty
3. Silencer dirty
4. Blower side dirty
5. Turbine Side dirty
6. Fans not running
7. Load reduction too fast
8. Bearing failure
9. Heavy Weather
10. Scavenge Fire

Action to be taken

1. Inform bridge to reduce rpm
2. Monitor all parameters
3. Conduct Blower side waster washing
4. Turbine side grit washing
5. Change Air filter
6. Check fuel system
7. Reduce engine load

Differences between sleeve and roller bearing

 

Sleeve bearing advantages

Cheap in design

Indefinite life

Not prone to vibration

Load is disperse to the side

Low running cost

 

Disadvantages

Prone to oil contamination

Poor performance at low load

Sensitive to lub oil failure

High friction at low load

 

Roller bearing advantages

Low load good performance

Low friction at low and high load

Not affected by lub oil contamination 

Does not need special oil

 

Disadvantages

High running cost

More prone to damages

Sensitive to vibration and fatigue

 

Actions in case surging 

 

1. Inform bridge to slow down , reduce rom
2. Monitor all parameters
3. Conduct blower side water wash
4. Turbine side grit wash
5. Change air filter, check fuel system, reduce load

How is sealing achieve 

1. The labyrinth seal on turbine side of turbocharger prevent gas contaminating with bearing lub oil supply
2. The seals consist of series of fine turns opposite to the steps on casing
3. It provide a narrow space which exhaust gas leaks 
4. As gas passes through, it is subjected to throttling, pressure energy convert to kinetic energy.
5. Kinetic energy dissipate, as it passes down the gland 
6. Sealing air is bled from compressor end to mid turbine gland which expands in both direction.

Air tightness between diffuser ring casing and impeller back

1. Space between the casing and impeller back pressurized from impeller discharge,
2. Air will attempt to access the exhaust gas passage,
3. Grooves machine behind regulate the leak.