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Radial Turbocharger
1 turbine rotor with shaft
2 compressor wheel
3 bearing casing
4 plain bearing
5 gas admission casing
6 nozzle ring
7 gas outlet diffusor
8 gas outlet casing
9 compressor casing
10 diffusor
11 silencer

Turbocharging 1 2

Flow through radial turbocharger Axial Turbocharger

8 3
10 7
6
5
2 1
4

1 turbine rotor with shaft 6 nozzle ring

2 compressor wheel 7 gas outlet diffusor
3 bearing casing 8 compressor casing
4 plain bearing 9 diffusor
5 gas admission casing 10 silencer

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Flow through axial turbocharger

More power and torque by supercharging

Engine power = cylinder capacity x speed x average cylinder pressure

Design of engine Supercharging

=> Increasing power of engine by same engine size

Torque = cylinder capacity x average cylinder pressure

Design of engine Supercharging

=> Increasing torque of engine by same cylinder capacity

PM Jul 2015 8

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Axial Turbocharger Rotor

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Construction & Operation of Exhaust Gas T/C

Turbocharger

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Turbo Charger Operation Turbo Charger Construction

The turbocharger consists of a single stage impulse • The turbine casing is of cast iron.
turbine connected to a centrifugal impeller via a shaft.
Some casings are water cooled which
The turbine is driven by the engine exhaust gas, complicates the casting.
which enters via the gas inlet casing. The gas expands • Water cooled casings are necessary
through a nozzle ring where the pressure energy of for turbochargers with ball and roller
the gas is converted to kinetic energy. This high
velocity gas is directed onto the turbine blades where
bearings with their own integral LO
it drives the turbine wheel, and thus the compressor at supply (to keep the LO cool).
high speeds (10 -15000 rpm). The exhaust gas then • Modern turbochargers with
passes through the outlet casing to the exhaust externally lubricated journal bearings
uptakes.
have uncooled casings. This leads to
On the air side air is drawn in through filters, and greater overall efficiency as less heat
enters the compressor wheel axially where it is energy is rejected to cooling water
accelerated to high velocity. The air exits the impeller and is available for the exhaust gas
radially and passes through a diffuser, where some of boiler.
the kinetic energy gets converted to pressure energy.
The air passes to the volute casing where a further
energy conversion takes place. The air is cooled
before passing to the engine inlet manifold or
scavenge air receiver. 13 14

Turbocharger Nozzle Ring

Nozzle Ring
Nozzle Ring »Extended
• In the steady-flow gas turbine, life time«
 New designed cast iron nozzle ring with
exhaust gases are delivered to
extended life time
the turbine with high-pressure
energy but small kinetic energy.  New blade profile for higher efficiency
Nozzle

• Most of this pressure energy is

converted into kinetic energy
by expansion in the single row
of fixed-nozzle vanes, where
the gases are accelerated to a
high velocity with a large swirl
component.

15 <16 >

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Benefits of Variable Turbine Area

 VTA cuts fuel consumption

 Up to 4 g/kWh lower SFC
 Lower soot and smoke emission
 Lower CO2 emissions
 Lower particle emissions
MAN VTA TURBOCHARGER

Microprocessor controlled positional

motor used to actuate the adjustable
nozzle ring vanes.

VTA Turbocharger Nozzle Ring

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How Turbine works

Turbine Axial flow of gas

• The high-velocity swirling gases

impinge on the rotating blade
row, which absorbs most of the Turbine Change of radial
tangential momentum, and momentum drives rotor
rejects the gases with low swirl round
or tangential momentum.

• Power is generated according

to the rate of change of
tangential momentum and is
proportional to the mass-flow,
the blade speed, and the
change in tangential velocity.

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Rotor motion. 20

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Turbine Disc Blowdown of Exhaust Gas

Gives Energy to Drive T/C

<21 >

Ideal Work Actual Work

• The area ABEO represents the • Actual work done in the
energy in the gas at mean turbine is not adiabatic
turbine inlet pressure P1
• Actual work is area ABGD.
• The area BCFE represents the
Efficiency of turbine = Actual work done
conversion of. energy in Ideal work done
expansion from P1 to P2

• The area CDOF the energy in • In practice the turbine

the gas at the turbine exhaust efficiency is lower because
pressure P2 of
– Friction loss
• The work done is given, by area
ABCD, which equals ABEO + – Gas leakage
BCFE - CDOF – Windage

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Friction & Clearance

• The turbine nozzle and blade
friction is caused by
combustion and cylinder oil
deposits and corrosion. This
increases the surface
roughness of blades.

• Regular cleaning of turbine by

water washing and dry
cleaning, maintains the
efficiency.

• The blade running clearances

must be kept as small as
possible in order to limit the
gas leakage, maximise the
exhaust gas through the blades
to perform useful work.

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Influence of Wear on Turbine Blades & Shroud Ring

Shroud Ring

Turbine Blade

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Turbine Blades Attachment

• Roots Fir Tree shape - Less stress concentration at junction

• Machining tolerances fine

• Loose fitting - Provide damping with less vibration

• Segmented binding wire near tip of turbine blade loose

fitted - prevents vibration and failure

29 30

Development of Turbine Blades

Turbine Blades
Development steps in turbine balde design
New turbine blade: Wide-chord design without damping wire »More
also for four-stroke applications efficiency«

31 <32 >
New design

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Advantages of plain bearings in

Principle systems of bearing arrangements
comparison with roller bearings

low
Inboard plain bearings insensitive to running noise ideal damping
imbalances behaviour

lubrication by
significantly the engine lube
plain bearings oil system
higher lifetime
(min.25,000) feasible

Outboard roller bearings

insensitive to no necessity for

vibrations vibration control
no need for
spring packages

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Advantages of inboard bearing arrangement Advantages of uncooled hot gas casings

in comparison with outboard bearings in comparison with water cooled casings
short bearing no extraction
short and rigid distance exact rotor of energy higher turbine outlet
lower casing
rotor shape alignment temperature usable
weight
for recovery

usage of
light rotor uncooled no corrosion in
inboard bearing hot gas single walled uncooled hot
design, low heavy fuel
arrangement casings casings gas casings
rotating masses operation
feasible

better good access no cleaning or

no wall temperatures
acceleration undistorted, axial gas to all bladed decalcifying of no additional
below the dew - point
behaviour admission to turbine components water spaces water
and compressor connections

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Thrust Bearing
Bearings

Floating journal bearing bushes

for ideal damping behaviour

High performance thrust bearing

with minimised mechanical losses

Floating thrust bearing disk

37 <38 >

Plain bearing lube Oil system Labyrinth Seals

Principle

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Labyrinth Seals Blower

• Labyrinth seals are fitted to the shaft
and casing to prevent the leakage of
exhaust gas into the turbine end • In actual uncooled
bearing, or to prevent oil being compressor the
drawn into the compressor. compression is=|
• To assist in the sealing effect, air from
the compressor volute casing is led • Friction
into a space within the gland. • Shock
• A vent to atmosphere at the end of • Eddy
the labyrinth gives a guide to the
efficiency of the turbine end gland.
• Discolouring of the oil on a rotor • This actual compression
fitted with a roller bearing will also results in conversion of
indicate a failure in the turbine end
gland.
some work to heat.
• A labyrinth arrangement is also fitted
to the back of the compressor
impeller to restrict the leakage of air
to the gas side 41 42

How Blower Works

Turbocharger & Engine Matching
• Affects air flow through the engine
• Affects scavenge efficiency
• Impacts Engine Performance

The turbine extracts energy from the engine

exhaust, and matches the energy needed to
power the compressor.

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Turbo-blower & Engine Matching

Turbocharger & Engine Matching
Important Parameters:
Engine Operating point should

• Air flow rate through compressor be close to optimum efficiency

If mis-matched, charge air pressure

• Pressure ratio will be either low or high.

Correction is made by changing

• Compressor speed
turbine capacity or blower diffuser

• Surge line
• Engine air flow load line

Blower Capacity

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Turbo-blower & Engine Matching T/C OPEEATIONAL PROBLEMS

 High exh temp
• The correct matching of a turboblower to an engine is extremely
important  Low charge air pressure
• With correct matching, the engine operating point should be  High charge air pressure
close to optimum efficiency as shown in blower characteristic
 Low T/C RPM
curve
• If the matching is incorrect, turboblower will supply charge air  High T/C RPM
- either @too low pressure  High L.O. Temp
- or @too high pressure
 Loss of L.O.
• Mismatching can usually be corrected by change of
- turbine capacity  High noise level
- blower diffuser  Vibration
 Surging
RB Nov 2004 47

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Turbocharger Surging
S
 Surging is a phenomenon that affects centrifugal compressor when
mass flow rate of air falls below a suitable level of a given pressure
U
ratio R
 It is a phenomenon caused due to periodical breakdown of air
delivery from blower
G
 Surging is caused by cyclic back flow of air into compressor when I
there is high resistance to air flow
N
 It is identified by irregular howling noise from the turbocharger
G
 Surging is undesirable as it interferes with combustion
Surge line 1 is the pressure limit of the compressor. Above that pressure at a given mass flow, air will
allempt to flow back through the rotating impeller causing the heavy vibration and consequent noise
 More importantly, Surging increases the possibility of thrust bearing called barking (surging).

failure Engine operating line 2 is the charge air demand line of the engine, i.e. the pressure mass flow
relationship at different rpm.

SURGING OF TURBOCHARGER Turbocharger Surging

• Surging is a common hazard which can be

initiated by many events

• Surging causes shifting of the turbocharger

operating point towards the surge line

RB Nov 2004 52

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Symptoms of surging Causes of Surging

• Insufficient Engine room ventilation
• Clogging of TC intake silencer
• Howling Noise
• Dirty blower
• Rapid surge in scavenge air pressure • Dirty scavenge air cooler
• Gulping of air by blower • Clogging of gas inlet protection grid
• Dirty nozzle ring/turbine
• Repeated irregular violent thud from air intake to blower • Wear of TC components (nozzle ring, turbine blades, shroud ring)
• Alternate Suck-in & push-out at blower intake • Power imbalance between cylinders
• Unit cut-out & engine running above 40-50% load
• Fluctuating T/C RPM
• Engine racing
• Fluctuating Engine RPM • Faulty injection/misfiring
• High Exhaust Temperature • Increased back pressure due to dirty EGE/silencer
• Hull fouling - causing the engine to run at torque rich condition
• Black Smoke • Mismatching engine & T/C

Consequences of Surging Flow Path of Air & Exhaust Gas

• Vibration
• Bearing Damage
• Turbine blade damage
• Rotor damage

Immediate Action:
Reduce Engine RPM until surging stops or faults rectified

Prevention Against Surging

• Careful attention to engine maintenance and
• TC cleaning 55 56

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WHAT PARAMTERS ARE NECESSARY TO

MONITOR THE PERFORMANCE? Scavenge Pressure vs Engine Power

1.8
1.6
1.4
1.2

Pscav (Bar)
1.0
0.8
0.6
0.4
0.2
0
8000 10000 12000 14000 16000 BHP

● Fouled air filter

● Fouled air cooler
● Turbocharger condition

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Diff Press Across Air Filter vs Scavenge Pressure Diff Temp Across Air Cooler vs Scavenge Pressure
(Temp Air Out – Temp Water In)

10 10
∆Pc(air-filterr) (mmWC)

∆T(air-water) (oC)

8 8

6 6

4 4

2 2

0 0
0.5 1.0 1.5 2.0 0.5 1.0 1.5 2.0
Scavenge Air Pressure (Bar) Scavenge Air Pressure (Bar)

● Fouling of air side & or fouling of water side

Filter elements must be cleaned if pressure drop is 50% higher
than testbed value ● Heat transmission is reduced by an oily film on tubes and fins
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Diff Press Across Air Cooler vs Scavenge Pressure

Turbocharger Maintenance

 T/C Cleaning
10
∆Pc(air-cooler) (mmWC)

8  Water washing – blower side

6
 Water washing – turbine side
4

2
 Dry cleaning – turbine side
0
0.5 1.0 1.5 2.0  T/C Overhauling
Scavenge Air Pressure (Bar)

 Air Cooler Cleaning

Air cooler must be cleaned if pressure drop is 50% higher
than test bed value
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Turbocharger Maintenance Turbocharger Maintenance

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Charge air cooler & Water Separator

CHARGE AIR COOLER

 to remove heat
Cooling water
 to remove moisture

 increase air density Cooling water

 lower thermal load

Turbine Blower

Air cooler grid type water separator

Exh Gas
Receiver

Air Cooler

Water Separator
Scavenge Air Receiver
Non-return valves

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Aux Blower

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Exh Gas TC

Turbocharger Abnormal Operation

If heavy vibrations, bearing failure, or other troubles occur in a turbocharger,
preliminary measures can be taken if the ship must be instantly
manoeuvrable, but the damaged turbocharger cannot run even at
Exh Gas
reduced load:
Receiver

Air Cooler
Turbochargers out of operation for short period
Engines with one turbocharger & without exhaust bypass:
Water Separator

Aux Blower
1.Stop the engine

2.Interrupt LO supply for external lubrication

3. Lock the rotor

4. Put Aux blower in operation

5. Load restriction to be followed according to the manual

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Turbocharger Abnormal Operation Turbocharger Abnormal Operation

Turbochargers out of Operation for a long period

Engines with one turbocharger & with exhaust bypass:
Engines with one turbocharger & without exhaust bypass: 1.Stop the engine

1.Stop the engine 2.Interrupt LO supply for external lubrication system

2.Interrupt LO supply for external lubrication system 3. Lock the rotor

3. Remove the rotor assembly 4.Open covers E on air receiver & F on Aux blower

4. Blank off the gas casing at the rotor space 5.Remove blind flange G

5. Put Aux blower in operation 6. Put Aux blower in operation

6. Load restriction to be followed according to the manual 7. Load restriction to be followed according to the manual

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Turbocharger Abnormal Operation

Engines with two or more turbocharger:

Countermeasures on defective TC:

• Remove expansion piece between TC

and exhaust manifold

• Fit blank flange A&B

• Fit blank flange D at blower air outlet

• Shut off TC cooling system

• Interrupt lube oil supply for external LO system

• Block rotor of defective TC

• Load restriction to be followed

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