2. Advantages Of Increased Scavenge Pressure:
• Increased power for similar sized engines
• Reduced SFOC : ‑ Mechanical, scavenge and thermal
efficiencies are improved due to less cylinders, greater air
supply and use of exhaust gases respectively.
• Cheaper engine: ‑ Smaller for required output power.
• Thermal load reduced: ‑ due to less exacting cylinder
conditions
Class 2 TurboChargers
3. Advantages Of Turbo-charger
• Smaller and lighter than mechanical blower
• Less moving parts
• No drive required from engine
• Can easily deliver the large quantities of air required
• Increases thermal efficiency.
Class 2 TurboChargers
11. Radial ~ Axial Turbines
Advantages Disadvantages
• Larger pressure ratios • Difficult to cast with high
obtainable temp materials
• Greater blade tip velocity • If the turbine is damaged
attainable then the whole rotor
• Smaller requires replacement
• Reduced mass of rotor
produces better transient
• Response to load changes
Class 2 TurboChargers
26. TURBO CHARGER BEARINGS
Outside Bearing Location. Centrally Located Bearings.
• Good accessibility to bearings for • With plain bearings on main
engine lub oil system no FW
overhaul cooling is required as bearings
• Bearings in cooler region cooled by oil flow
• Oil reservoirs can be in castings • Reduced shaft mass gives better
• Greater overall turbine length transient response
• Easier to manually clean turbine
• Larger shaft diameter required to and impeller
keep the longer shaft sufficiently • Larger diameter at bearing
stiff, and this will increase rotor produces a larger friction loss
mass • Shaft balance needs to be good as
• Inlet passages of air/gas more whirl can be produced about
restrictive. centre bearing unit
• Bearing replacement a major job,
requiring impeller and rotor
removal
Class 2 TurboChargers
27. TURBO CHARGER BEARINGS
Rolling contact bearings Plain bearings
• Much lower friction than • Cheaper than roller bearings
plain bearings • Less susceptible to dirt than
• Need for dampening springs roller, main engine circ oil
to reduce vibration damage often used
of bearings, and to provide • Larger clearances required
flexible mounts for bearings in turbine for axial thrust
• Bearings can be damaged and radial tip clearances
whilst static (brinelling) • Less prone to complete
• Allows much smaller tip failure
clearances to be used
• Separate oil reservoir and
pump usual.
Class 2 TurboChargers
28. TURBO CHARGER VIBRATION
Gradual increase in vibration Sudden increase in vibration
could be due to: could be due to:
• Worn damping springs in • Washing removing only part
roller bearings of the rotor dirt
• Ineffective mounting bolts • Blade damage from
• Uneven fouling mechanical item striking
• Failure of damping wire rotor blades
• Bearing failure
Vibration after overhaul • Water striking rotor from
could be due to: casing leak
• Incomplete cleaning
• Misalignment of rotating
parts
Class 2 TurboChargers
29. RUNNING WITH DAMAGE
• Damaged Rotor Damaged Casing
• lock rotor – pulse system lock both • Blank off cooling flow to affected
ends as full gas flow must still pass casing
through turbine • Remove covers and direct
• Insert blanks – air side only for pulse scavenge air or air from vent fan
system, both sides for constant into open casing to assist in
pressure system. Blanks must have cooling
orifice to allow air flow to • Monitor oil temperature and
compressor for cooling and sealing, adjust load / rpm to ensure that
to allow gas flow to prevent cold end temperature does not go above
corrosion 90°C
• Run at reduced load/revs using
exhaust temps as load limiter (never
above 500°C). The following is used
as a guide by MAN B & W
(constant pressure T/C)
CUT OUT % POWER % M/E REVS
1 of 1 T/C 15 53
1 of 2 T/C 50 70
1 of 3 T/C 66 87
Class 2 TurboChargers
30. TURBOCHARGER REDUCED AIR
DELIVERY
• Drop in ambient pressure
• Reduction in engine load
• Change in fuel quality
• Change in engine timing
• Fouling of air intake filter
• Fouling of inducer/diffuser
• Fouling of air side of charger air
cooler
• Fouling of exhaust ports and
pipework
• Fouling of protection grid
• Fouling of nozzle ring, turbine
blades
• Fouling of exhaust gas boiler
• Fouling of silencer
• Mechanical damage to rotor
• Casing or piping leaks
Class 2 TurboChargers
31. Reasons For Turbo Charger Surging
• Rapid Change In Load
– Fluctuations due to rough weather, will cause variations in air mass flow rate due to
change in engine speed.
• Insufficient Supply Of Fuel
– This can cause the engine speed to vary due to fuel starvation. Produces similar result as
above.
• Fault In Fuel System
– Due to incorrect settings, timing of fuel pumps, or sticking fuel pump barrels, etc, result
in different combustion conditions for individual cylinders. This can lead to variation in
turbocharger speeds and air mass flow rates (pulse system).
• Restriction Of Scavenge Passages
– Blockage of air filters, will cause pressure ratio across compressor to increase and reduce
airflow rates. Operating line of turbocharger moves closer to the surge line.
• Narrowed Exhaust Gas Passages (After Turbo)
– An extreme increase in resistance of the exhaust gas discharge passage will result in the
reduction of airflow through the compressor.
• Engine Operation At Overload
– If the engine speed is maintained constant after fouling of the hull or damage to the
propeller turbocharger speed will increase without an increase in air mass flow.
Reduction in surge margin.
• Failure Of Turbine Blade, Nozzle Or Diffuser
– Fouling or damage to the above will result in increased resistance to gas flow and reduce
airflow into the engine.
Class 2 TurboChargers
32. PULSE SYSTEM CONSTANT PRESSURE
Advantages: SYSTEM
• T/C responds rapidly to load Advantages:
changes • Higher turbine efficiencies at
• No auxiliary blowers needed for steady loads
low loads • Simple pipework
• High energy input to turbine • Good performance at high loads
Disadvantages: Disadvantages:
• Exhaust pipework more complex • Requires auxiliary blowers to
• Turbine efficiency reduces at assist at low loads
higher loads due to operating with • Poor turbine response to load
fluctuating gas flow changes
• Pressure pulses can influence • Large space taken up by exhaust
blow down from adjacent receiver
cylinders
• Turbocharging dictates engine
timing
Class 2 TurboChargers
33. Fouling can be due to: This fouling is identified by:
2. The high temperatures of • rising scavenge air
the inlet air, which will temperatures (1, 2, & 3)
cause the salts in the sea • rising SW differential
water to come out of pressure (1, 2 & 3)
solution, form a hard scale • falling sea water
and reducing heat transfer temperature differential (1)
3. Debris in the water causing • rising sea water temperature
a blockage at the inlet to differential (2 & 3)
the tubes, reducing sea
water flow
4. Organisms (molluscs)
growing in the tubes
restricting coolant flow.
Class 2 TurboChargers
34. SCAVENGE FIRES
Contributing factors. Signs of scavenge fire.
• Inadequate draining of the • High temperature of exhaust
scavenge spaces. and scavenge system.
• Poor combustion. • Rough running of engine
• Faulty injectors or fuel and possible surging of
timing. turbochargers.
• Worn liners. • Smoky exhaust.
• Worn or damaged piston • Flames, smoke and sparks at
rings. scavenge drains.
• Exhaust system back • Failing engine speed.
pressure.
• Defective piston rod glands.
• Too little or too much
cylinder lubrication.
Class 2 TurboChargers
35. SCAVENGE FIRES
Avoidance. Action if Fire Occurs.
• Regular draining of the • Two different approaches.
scavenge spaces. • Slow down, shut fuel off
• Correct cylinder lubrication affected unit, increase
(spaces just damp). cylinder lubrication,
• Regular maintenance of continue until fire burns out.
cylinders, fuel injection (Sulzer recommendation)
equipment, etc. • Cut off fuel to affected unit
and slow down, ask bridge
for permission to stop.
Apply extinguishing
medium. Allow to cool
down then open up, clean
and inspect for damage.
(B&W ‑ also check tie rods)
Class 2 TurboChargers
