The Cylinder Liner

The Cylinder Liner
(Diesel Engines)
Source: MAN B&W
Cylinder Liner
• The function of cylinder liner is to form part of
the combustion chamber which is
compression and combustion of fuel/air
mixture take place
• The cylinder liner forms the cylindrical space
in which the piston reciprocates. The reasons
for manufacturing the liner separately from
the cylinder block (jacket) in which it is
located are as follows;
•The liner can be manufactured using a superior material to the
cylinder block. While the cylinder block is made from a grey cast
iron, the liner is manufactured from a cast iron alloyed with
chromium, vanadium and molybdenum. (cast iron contains graphite,
a lubricant. The alloying elements help resist corrosion and improve
the wear resistance at high temperatures.)
•The cylinder liner will wear with use, and therefore may have to be
replaced. The cylinder jacket lasts the life of the engine.
•At working temperature, the liner is a lot hotter than the jacket. The
liner will expand more and is free to expand diametrically and
lengthwise. If they were cast as one piece, then unacceptable thermal
stresses would be set up, causing fracture of the material.
•Less risk of defects. The more complex the casting, the more
difficult to produce a homogenous casting with low residual stresses.
Cylinder Liner - Types
• Wet liners – usually used in medium
and slow speed engines and normally
cooling by water
• Dry liner – used for small engine like life
boat engine etc which is the engine
block built with fins and the cooling
agent will be an air
3 –PIECES LINER (DOXFORD’P’)
COOLING WATER OUT
EXHAUST PORTS
EXHAUST BELT
UPPER LUBRICATION
COOPER RING
STEEL SHRUNK RING
UPPER LINER
UPPER LINER
VALVE POCKET
COMBUSTION BELT
COMBUSTION BELT
COOLING WATER IN
LOWER LUBRICATION
LOWER LINER
SCAVENGE PORTS
TRIPARTITE (3 PARTS) CYLINDER LINER AND JACKET (DOXFORD ‘P’TYPE
CYLINDER OIL SUPPLY
GROUND FACE
COOLING WATER OUT
TO COVER
CYLINDER LUBRICATION OIL 8 POINTS
JACKET
UPPER COOLED PART
COOLING WATER IN
ABESTOS PACKING
Copper ring
TELL TALE LEAK OFF
EXHAUST PORTS
SCAVENGE PORTS
CYLINDER LUBRICATION OIL 2 POINTS
SOME COOLING OUT
WAVE JOINT
SUPPLEMENTARY
CYLINDER OIL SUPPLY
LOWER
UNCOOLED
PART BOLTED
TO JACKET
MAN KZ LINER (2
PIECES)
RND SULZER (ONE PIECE) HYPERBOLIC COOLING
PASSAGES
C/W OUT TO CYL HEAD
THICK COLLAR
COMBUSTION SPACE ABOVE
JACKET
GROUND FACE
CYLINDER OIL SUPPLY
ANGLED C/W
DRILLINGS
FREE
THERMAL
EXPANSION
JACKET
DRILLING PASSES CLOSE TO
LINER SURFACE
LEAK OFF LINE /
TELL TALE HOLE
EXHAUST PORTS
SCAVENGE PORTS
LEAK OFF LINE /
TELL TALE HOLE
SECOND ADDITIONAL
CYLINDER OIL SUPPLY
C/W INLET
RUBBER RINGS
LEAK OFF LINE /
TELL TALE HOLE
PLUG
BORE COOLING
VIEW
Stresses on liners
• Mechanical stress – pressure
• Thermal stress - temperature
Mechanical stress
• In supercharged engines, maximum
firing pressure is about 90 – 100 Bar
(non supercharged is about 75-85 Bar).
• This pressure produces circumferential
(hoop) stress and longitudinal stress,
but hoop stress is twice longitudinal
stress so only hoop stress is considered
where:
CYLINDER HEAD
• HOOP STRESS,
h
=PxD
2t
DUE
WHERE, P = GAS PRESSURE CRACK
TO HOOP
STRESS
D = LINER DIAMETER
t = LINER THICKNESS
• Thus hoop stress will increase if bore
size and firing pressure increase
THERMAL STRESS
• Resistance to heat flow through liner
metal produces a temperature gradient
across liner hence, the inner wall
expands more relative to outer wall,
where:
thermal stress, T = T
where T is temperature gradient
Liner-Stresses
• Thicker liner will increase temperature
gradient hence thermal stress but on
the other hand, thicker liner have good
resistance to mechanical stress. Thus,
liner design becomes complex ,
• Also, inner liner surface temperature
should be sufficiently low to retain oil
film and high enough to avoid acid-dew
(sulphur)
Estimated temperature in liner
- Next to liner wall
500oC
- On liner wall 140oC
due to oil film, carbon
deposits and stagnant
- Outer liner wall 75oC
due to thickness of liner
wall and cooling water
- Lower part 40oC due
to expansion
Cylinder cover
1650 oC
500 oC
Cylinder
jacket
140 oC
Piston
75 oC
Cooling
water
space
Cylinder
liner
40 oC
Combination of stresses
(plain liner)
THERMAL STRESS
OPTIMUM
METAL
THICKNESS
HOOP or MECHANICAL STRESS
METAL THICKNESS
Liner-temperatures
• The Liner will get tend to get very hot
during engine operation as the heat
energy from the burning fuel is
transferred to the cylinder wall. So that
the temperature can be kept within
acceptable limits the liner is cooled.
Liner-Temperatures & Cooling
• Cylinder liners from older lower
powered engines had a uniform wall
thickness and the cooling was achieved
by circulating cooling water through a
space formed between liner and jacket.
The cooling water space was sealed
from the scavenge space using 'O' rings
and a telltale passage between the 'O'
rings led to the outside of the cylinder
block to show a leakage.
• To increase the power of the engine for a
given number of cylinders, either the
efficiency of the engine must be increased or
more fuel must be burnt per cycle. To burn
more fuel, the volume of the combustion
space must be increased, and the mass of air
for combustion must be increased. Because
of the resulting higher pressures in the
cylinder from the combustion of this greater
mass of fuel, and the larger diameters, the
liner must be made thicker at the top to
accommodate the higher hoop stresses, and
prevent cracking of the material.
Liner-Temperatures
• If the thickness of the material is
increased, then it stands to reason that
the working surface of the liner is going
to increase in temperature because the
cooling water is now further away.
Increased surface temperature means
that the material strength is reduced,
and the oil film burnt away, resulting in
excessive wear and increased thermal
stressing.
Liner-Temperatures
• The solution is to bring the cooling
water closer to the liner wall, and one
method of doing this without
compromising the strength of the liner is
to use tangential bore cooling.
TANGENTIAL BORE COOLING
TANGENTIAL BORE
COOLING
• Holes are bored from the underside of
the flange formed by the increase in
liner diameter. The holes are bored
upwards and at an angle so that
they approach the internal surface of
the liner at a tangent. Holes are then
bored radially around the top of the liner
so that they join with the tangentially
bored holes.
Liner-Bore Cooling
• On some large bore, long stroke
engines it was found that the
undercooling further down the liner was
taking place. Why is this a problem?
Well, the hydrogen in the fuel combines
with the oxygen and burns to form
water. Normally this is in the form of
steam, but if it is cooled it will condense
on the liner surface and wash away the
lube oil film. Fuels also contain sulphur.
Liner-Cooling
• This burns in the oxygen and the products
combine with the water to form sulphuric acid.
If this condenses on the liner surface (below
140º) then corrosion can take place.
• Once the oil film has been destroyed then
wear will take place at an alarming rate. One
solution was to insulate the outside of the
liner so that there was a reduction in the
cooling effect. On The latest engines the liner
is only cooled at the very top.
Cylinder liner-Loads
• The inside surface is subjected to the rubbing
action of the piston rings as the piston is
moving reciprocate in the bore of liner.
• Subjected to a very high combustion pressure
and temperature, particularly at upper end.
• Takes the side thrust of the piston caused by
the connecting rod acting at an angle
Liner-Lubrication
• The oil is of a high alkalinity which
combats the acid attack from the
sulphur in the fuel. The latest engines
time the injection of oil using a computer
which has inputs from the crankshaft
position, engine load and engine speed.
The correct quantity of oil can be
injected by opening valves from a
pressurized system, just as the piston
ring pack is passing the injection point.
4 stroke Cylinder Liner
• The cylinder liner is cast separately
from the main cylinder frame for the
same reasons as given for the 2 stroke
engine which are:
• Modern liners employ bore cooling at the top
of the liner where the pressure stress is high
and therefore the liner wall thickness has to
be increased. This brings the cooling water
close to the liner surface to keep the liner wall
temperature within acceptable limits so that
there is not a breakdown in lubrication or
excessive thermal stressing.
• Although the liner is splash lubricated from
the revolving crankshaft, cylinder lubricators
may be provided on the larger engines.
4S Liners
• On the example shown, the lubricator
drillings are bored from the bottom of
the liner circumferentially around the
liner wall. Another set of holes are
drilled to meet up with these vertically
bored holes at the point where the oil is
required at the liner surface.
Other engines may utilise axial drillings as in a two stroke engine.
Sulzer ZA40 Liner (vee engine; The straight engine is similar)
Cylinder Liners-Cooling Water
• Where the cooling water space is
formed between the engine frame and
the jacket, there is a danger that water
could leak down and contaminate the
crankcase if the sealing O rings were to
fail. As a warning, "tell tale" holes are
led from between the O rings to the
outside of the engine.
MAN-B&W L58/64 Liner
Cylinder Liners-Cooling Water
• Modern engines tend not to use this
space for cooling water. Instead a
separate water jacket is mounted above
the cylinder frame. This stops any risk
of leakage of water from the cooling
space into the crankcase (or oil into the
cooling water space), and provides the
cooling at the hottest part of the cylinder
liner.
Cylinder Liner-AP Ring
• Note that the liner opposite is fitted with a
fireband. This is sometimes known as an
antipolishing ring.
• It is slightly smaller in diameter than the liner,
and its purpose is to remove the carbon
which builds up on the piston above the top
ring. If this carbon is allowed to build up it will
eventually rub against the liner wall, polishing
it and destroying its oil retention properties.
Liner-Materials
• Cast iron is used for the following reason:
- Castibility is good for intricate shapes
- Good wear resistance due to large surface
of irregular shaped graphite flakes and semiporous surface to retain oil
- Good thermal conductivity
- Good internal damping properties (vibration)
- Cost less relatively
MATERIAL
• Nodular or spheroidal cast iron is used for
the following reason:
- tougher
- More resistance to crack formation (less
stress raising matrix)
- Less self lubrication properties
* For higher power, shock loading due to combustion pressure
MATERIAL
• Alloy element
- Specify alloying elements namely
nickel, chromium, copper or
molybdenum – wear resistance to
corrosion
MATERIAL
• For large bore cylinder liners
generally the cast iron contains:
Carbon - 3.00%
Silicon 0.70%
Manganese - 1.00%
Sulphur 0.10%
Phosphorus - 0.25% Vanadium 0.15%
Manufacture
• Two methods
- Sand casting
- Centrifugal casting
Liners-Manufacture
• After casting, liners are rough- machined and
hydraulically pressure tested approximately 7
Bar
• Ports are formed in casting (old
practice),however nowadays they are
marked, drilled shaped and machined finish
• Then outside and inside surface is finalmachined, sometime inside surface is honed
to improved surface finish approximately
(3.5m) or surface treatment is given
Surface finish treatment
• Normally used an electrolytic deposition
of hard chrome sometime nickel
• Chrome layer is approximately 0.2 to
1.0 mm
• Chrome surface must be porous for oil
retention and this can be achieved by
etching with acid or a patented
“porus-krome”
Advantages:
• Hard surface and improve wearresistance, corrosion resistance,
uniform surface finish
Disadvantages
• Expansive since reduction in wear rate
cannot offset cost, plating can peel-off,
must use only with cast iron piston
rings, running in action may be delayed
,leading to rings collapse or scoring of
liner
Sand casting
• Better wearing properties due to better
grain flow produced in cast material
• Better graphitisation, thus lubricating
properties, due to slow cooling rate
• Normally used for large, slow speed
engines
Centrifugal casting
•
•
•
•
Stronger liner
Homogeneous in structure
Poor wearing quality (fast cooling rate)
Normally used for medium and high
speed engine
Porosity manufactured
• The plated cylinder liner is immersed
into a special bath and the current (for
electroplating) is reversed. This forms
minute pits and channels in the
chromium plating
• After plating, liner is ground or honed.
Then it is replaced in the bath together
with a screen attached to its surface.
The current is then reversed and smallhemispherical cavities are produced
Liner fault - crack
1 Crack across liner flange due to uneven or excessive
2
3
4
5
6
tightening of cylinder head studs
Hoop stress crack due to poor liner support
Circumferential crack along wear ridge due to stress
concentration or more likely new rings hitting the
ridge
Star or crazy cracking caused by flame impingement
Star cracks around lubricator quill due to water
leakage
Cracks across port bars due to overloading, poor
cooling, scavenge fire, poor fitting of rubbing sealing
ring etc
4
1
3
2
5
6
Cylinder liner wear
There are three main cause of
damage to
the liner material;
• Abrasion-caused
by
solid
particles breaking through the
lubricant film
• Corrosion-caused
by
the
acidic products of combustion
• Friction or scuffing-Break
down of the lubricating oil film
leading to metal to metal
contact
Abrasion
• Hard particles combined with cylinder
lubricant to form a light abrasive paste
causing liner wear
• In crosshead engine, cylinder lubricant
is limited and thus flushing of abrasive
paste is not effective compared to trunk
engine having a good flushing action.
Thus in crosshead engine, abrasive
wear is the major contributor for liner
wear.
Liner Wear
• Source of hard particles can originate
from
- Air borne dirt,
- Ash in fuel,
- Carbon from combustion
- Piston rings wear
Air borne dirt
• Dirty air filter
• Dirty scavenge ports which is should be
keep degree of dirtiness to minimum
• Scavenge manifold dirt
Ash in fuel
• Fuel consists of vanadium, sodium silica
and scale (iron rust) which cannot be
avoided, however it can be reduced by
effective centrifugal separation
Carbon from combustion
• Combustion can never be perfect to
form a hard carbon particles
• Means that if bad combustion occurs,
more carbon will be produced even
abrasive matter
• Therefore keep purification and
combustion good apart from injection
and pump timing even fuel temperature
to be maintained.
Piston rings wear
• Produces wear dust from rubbing and
this increases wear of both liner and
rings itself
• Therefore should used good quality ring
material and lubrication apart from good
fitting
Corrosion
• Marine fuel contain sulphur to form
sulphur dioxide and sulphur trioxide
when the fuel burns as shown:
SO2 + H2O --------- SULPHUROUS ACID
SO3 + H2O --------- SULPHURIC ACID
UNBURNED FUEL (SULPHUR) + UNPERFECT COMBUSTION (O2 + H2O) -------- SULPHURIC ACID
RELATION BETWEEN H2SO4 DEWPOINT
TEMPERATURE & FUEL SULPHUR CONTENT AT
DIFFERENT PRESSURES
H2SO4 dewpoint temperature oC)
180
40
160
150
140
1
130
120
110
1.0
2.0
Sulphur in fuel %wt
3.0.
Pressure (bar)
80
170
Liner wear
• The dew point of the above acid is
around 110oC to 180oC depending
upon concentration, hence acid is
always present due to liner temperature
around that boundary
• Thus to combat or reduces this type of
wear, the following should be made:
Remedies of corrosion
• Used alkaline oil for cylinder lubrication
• Control condensation in air cooler
• Keep cooling water temperature in
jacket as high as practicable
• Keep quantity of starting air minimum
Note: to protect waste heat system from
corrosion, by pass such system when
engine is on light load
Scuffing or friction
• This is occur when lubricant failed to
separate rings and liner surfaces
efficiently and subsequent contact
caused microwelding or microseizure.
• Reasons why these can occur on the
liner surfaces:
Liner Wear-Scuffing
• Too smooth liner surface resulting in too
little lube oil retention
• Water on the liner surface repelling oil
film
• Blow past and thus removing oil film
• Poor or inadequate oil distribution
around the liner surfaces
• Deposit on the piston absorbed oil film
Liner wear pattern
• Maximum normal liner wear occurs at top of
the liner, in port-starboard direction and
around scavenge and exhaust ports
• The reason for the above matter are as
follow;
– High temperature region reduces oil viscosity and
thus oil thickness
– High gas pressure increases ring loading causing
penetration of oil film
– Slow movement of piston results in ‘oil wedge’ to
breakedown (reversal of piston movement)
– Movement of ship maximum in port- starboard
direction than forward-aft direction (thus causing
more wear here)
– High temperature makes oil film less resistance to
acid penetration (acid more active when hot)
– Tiny particles of carbonaceous matter are formed
by combustion process, some are abrasive, but
some accumulates in grooves around ring leading
to wear promoting condition
– At higher temperature, cast iron has less
resistance to wear
– At scavenge and exhaust ports bars, oil film will be
blown-off when topmost ring opens to the ports
– Also due to the ports opening, relative pressure on
ports bars increased resulting in increase wear
another form of liner wear pattern is called
cloverleafing
CLOVERLEAFING
• Alkali in cylinder oil is used to neutralize acid.
• For fuel with 4-5% sulphur -cylinder oil with TBN
(Total Base Number) of 70
• For fuel with 1% sulphur, used cylinder oil TBN of
20 or 30
• To obtained perfect distribution of cylinder oil is
difficult so the surfaces get either more alkalinity
or less depending on the position from cylinder
lubrications quill and the TBN used
CLOVERLEAFING
Lube oil
Lube oil
Wear due to exhausted
alkalinity before
cylinder oil spreads
across liner surfaces
Lube oil
Wear due to
excessive alkalinity
in cylinder oil
Measured by
profilograph
Lube oil
an instrument
Liner wear-TBN
• If TBN use is more, surfaces near quills
will get excessive alkalinity leading to
hard calcium compounds formed.
• Alkaline compounds are burnt and
formed heavy deposits which caused
abrasive wear.
• Surfaces further from quills will have
alkali neutralized by then and thus
minimum wear is experienced
Liner Wear-TBN
• If TBN used is less, surfaces near quills
will have minimum wear but surfaces
furthest from quills will be starved of
alkaline compounds when reaches
there.
• This will lead to acidic corrosion (since
insufficient alkalis to neutralize acid)
and thus experienced maximum wear.
• If insufficient oil used, the effect will be
exchanged (TBN)
MICROSEIZURE – OIL FILM
LINER
WALL
LINER
WALL
LINER
WALL
RING
RING
RING
Asperities meet
Frictional heat and
welding
Tearing out,
cooling, hardening
OIL - WEDGE
OIL
FILM
LINER
WALL
PISTON
SKIRT
PISTON
SKIRT
LINER
WALL
OIL –
WEDGE
OIL
FILM
(1:150
TAPPER)
WEAR RATE
TEMPLETE
Cyl No
Date
Date fitted
Date of last
gauging
C
Total hours
Hours since
last gauging
D
Position
A
B
LINER
Forward and After
TOP RING
POSITION
Port and Starboard
A
WEAR
B
E
C
D
E
F
EXHAUST
PORT
F
G
H
SCAVENGE
PORT
Max wear
G
Mean Max Wear
Wear rate since new
Wear rate since last gauging
Remarks
H
LINER WEAR RECORD SHEET
RESULTS
Liner wear-Analysis
• Wear rates vary, but as a general rule, for a
large bore engine a wear rate of 0.05 0.1mm/1000 hours is acceptable. The liner
should be replaced as the wear approaches
0.8 - 1% of liner diameter. The liner is gauged
at regular intervals to ascertain the wear rate.
• It has been known for ships to go for scrap
after 20 + years of operation with some of the
original liners in the engine.
• The wear rate for a medium speed liner
should be below 0.015mm/1000hrs.
Gauging a Liner
Wear rate
• It is related to time in order to put these
figures into useful form of comparison,
in the form of diameter increase per
thousand running hours. Thus :• Wear rate since last recorded
measurement
= Increase in O since last recordX 1000
Running horus since last record
= mm/1000 hrs
Liner Wear-Analysis
• Wear rate since new :
Total increase in O
=
X 1000
Total running hours since new
= mm/1000 hrs
Maxi. Liner wear rate mm/1000
MAXIMUM CYLINDER LINER WEAR
RATE PER RUNNING HOURS
0.4
0.3
WEAR RATE INCREASES
DUE TO WORN RINGS
AND LINERS
0.2
GRAUDALWEAR
STARTS
0.1
RUNNING-IN
PERIOD
2
4
6
8
10
12
14
ENGINE RUNNING HOURS x 1000
16
18
20
Causes of excessive wear
• Improper running in – smoothing and geometry
• Misalignment of piston or distortion of cylinder – thermal stress and
uneven tightening
• Inadequate oil supply or unsatisfactory oil supply
• Lube oil too low in viscosity or too low in alkalinity
• Incorrect piston ring clearances
• Unstable cylinder liner material – phosphorous / silicon
• Contamination of lube oil by extraneous abrasive material – 4stroke
engine
• Cylinder wall temperature too high or too low – oil film breakdown or
corrosive wear
• Overloading of engine – overheated,distorted and lube oil destroyed
• Scavenge air temperature too low – wash oil film, form acid, rusting
• Inefficient combustion – carbon
• Use of low sulphur fuel (less than 1% sulphur) in conjuntion with high
alkaline cylinder oil and vise versa
DETAIL of SEALING RINGS
• Depth of groove = 0.7 to 0.8d where “d” is diameter
of rings section. This is because the sealing effect
is best when ring is in deformed state.
• Rubber ring cross-sectional area is 75 to 90% of
grooves area. (due to rubber being flexible but
incompressible)
• Di (inside Ø of rubber rings) is 2% less than DG
(diameter of the bottom of groove) – for
prestressing effect when fitted in liner.
• Sealing parts smooth and guiding edges tapered
and rounded. Rubber rings and sealing parts
applied with tallow or soft soap.
DG
Di = 0.98 DG
Di
0.7 to 0.8d
d
Cylinder liner lubrication
Cylinder lubrication
•Because the cylinder is separate from the
crankcase there is no splash lubrication as on a
trunk piston engine. Oil is supplied through
drillings in the liner. Grooves machined in the
liner from the injection points spread the oil
circumferentially around the liner and the piston
rings assist in spreading the oil up and down the
length of the liner.
DISTRIBUTOR
REGULATING VALVE
CYLINDER OIL PUMP
CYLINDER OIL SUPPLY
DISTRIBUTOR
LUBRICATOR QUILLS
PURPOSE CYLINDER
LUBRICATION
• Reduce friction between liner and ring – scuffing
• Assist in sealing of combustion gas – blowpast,burnt oil film etc
• Insulate liner against high gas temperature –
viscosity and fluidity
• Guard against corrosive attack – as above
• Neutralizing combustion acid – TBN and rate of
reaction
• Removing carbon or oxidation deposits – in ring
zones and ports
DOXFORD ‘J’ CYL LUB. SYSTEM
LUBRICATOR QUILL OR
INJECTOR
CYLINDER
LINER
HYDRAULIC
PLUNGER ROTATING
RATCHET
TO CYLINDER
LUBRICATOR
QUILLS
DISCHARGE FLOW
INDICATOR AND
ALARM
OIL PULSE TO
OPERATE RATCHET
MECHANISM
SUCTION FLOW
INDICATOR
ROTATING DISTRIBUTOR
FROM TANK
FILTER
CAMSHAFT
SPRING RETURN PLUNGER WITH
SPILL PORT
FORK LEVER
INJECTOR BARREL WITH HELICAL
SLOT
ROLLER
ACTUATOR BARREL
WITH PORTS
TO LUBRICATOR
QUILL
NON-RETURN
VALVE
TYPICAL LUBRICATOR
BUBLER GAUGE
WIRE
NUT
FILLING
FILTER
SIGHT GLASS
FILLED WITH
FLUID
AIR VENT
SCREW
NUT
QUANTITY
REGULATES
DUAL DELIVERY
VALVE
DIFFERENT
PUMP
LUNGER
MOVING
PLUNGER
WITHOUT
CAMSHAFT
TURNING
GAUGE
GLASS
CAM (POSITION
ADJUSTABLE)
CAMSHAFT
OIL IN
FLUSHING
TRIGGER
DUAL SUCTION
VALVE
JOINT PACKING
NON-RETURN
VALVE
OIL INLET
CYLINDER
JACKET
FILLING PIN
GROUN FACE JOINT
OR COPPER GASKET
COOLING
WATER
SPACE
COOLING
WATER
SPACE
CYLINDER
LINER
RUBBER PACKING
TYPICAL QUILL FOR LUBRICATOR (OLD TYPE)
SULZER RND - M
CYLINDER LUBRICATION
(ACCUMULATOR SYSTEM
NON-RETURN
VALVE
CYLINDER
LINER
LUBRICATOR
QUILL
ACCUMULATOR
FLOW CONTROLLER
OIL QUANTITY ADJUSTING LEVER
AUTOMATIC LOAD
DEPENDENT FEED
RATE REGULATION
ECENTRIC EXCENTRE
DRIVE
CAMSHAFT
CYLINDER LUBRICATING PUMP
JOINT PACKING
NON-RETURN VALVE
ACCUMULATOR PISTON &
DIAPHRAGM
CYLINDER
JACKET
UPWARD SLANTING
BORE
SLEEVE
ACCUMULATOR
PISTON &
RINGS
OIL INLET
FILLING PIN
COOLING
WATER
SPACE
GROUND FACE
JOINT
CYLINDER
LINER
SEALING RING
NEW TYPE SULZER RND-M LUBRICATOR QUILL
ACCUMULATOR operation
• Through pipe oil is supplied by the cylinder
lubricating pump (at about every 10 – 15
engine turns)into space under piston and
diaphragm.
• The accumulator piston which is sealed off by
a diaphragm is against the force of the spring
pushed upwards.
• Through this a pressure builds up in the
system which is higher than the scavenge air
pressure of the engine
• If the pressure at the delivery point drops
below the accumulating pressure, the oil will
then flow through the upward slanting bore
into the cylinder.
• As soon as the pressure at the lubricating
point on the cylinder higher than the
accumulating pressure, the lubrication is
stopped (non- return valve closes)
• At which moment, in relation to the piston
position respectively the pressure ratio, the
lubrication is carried out as shown in
schematic illustration below:-
QUILL PRESSURE
FLUCTUATION
1
2
3
4
CYLINDER LINER
PISTON
LUBRICATING QUILL
PRESSURE (BAR)
40
30
4
20
COMPRESSION
EXPANSION
1
10
Oil pressure in accumulator
6
0
BDC
90o
2
3
TDC
CRANK ANGLE
5
270o
BDC
• In the range of BDC, between the position 5 +
6 and in the range of TDC, between the
position 2 + 3 the pressure in the accumulator
is higher than the pressure at the lubricating
point. Consequently the oil flows in the said
range to the cylinder liner running surface.
• So the running surface is lubricated twice per
one engine turn.
• Between positions 6 + 2 as well as 3 + 5 the
pressure is higher at the lubricating point than
in the lubricating quill. The oil supply to the
cylinder liner is stopped (non –return valve
closes)
• Cylinder oil feed rates
– Uniflow scavenge
– Loop / Cross scavenge
– Trunk engine
-
0.54g/kWh
0.8 - 0.9g/kWh
1.0 - 1.6 g/kWh
POSITION OF CYLINDER
LUBRICATORS
• Not to be near the ports – oil can be scraped
and blown away
• Not to be situated too near the high
temperature zone or the oil will burn easily
• There should be sufficient points to ensure as
even and as complete a coverage as possible
• Oil is injected between 1st and 2nd rings at the
outer end of stroke (upper piston) also oil is
injected between 1st and 2nd rings during early
part of compression stroke (lower piston)
MULTILEVEL LUBRICATION
SULZER RTA 52/62/72/76/84/84M
Oil refreshing rate
near TDC
A
B
C
C
B+C
A
B
A
B+C
Multilevel
lubrication
V ring
Hmin
Oil film thickness
C
Hmin
Difficulty on achieving
• Piston direction changes every stroke
• In 2-stroke engine, no non-working stroke
available for oil film to reform
• In diaphragm engine, no oil is returned, therefore
supply is limited to control consumption and no
cooling effect.
• Piston and ring distorted due to gas pressure and
temperature
• All fuel contain abrasive contaminants
• Liner temperature varies causing change in
viscosity
Difficulty in Timing
• Piston speed may be high (approximately 2o of crank angle only)slow movement will destroy oil wedge
• Only very small quantity of oil being pumped
• Gas pressure resists delivery charge
• Cylinder oil viscosity changes due to temperature even will
impede (prevent) oil formation
• A long, small bore pipe is needed to connect pump and
quill(delivery lag)
• Carbon deposit may foul the quill
• A non-return valve is needed in quill which may become sluggish
• Delay between pumping and delivery may represent up to 30o of
crank movement
• Oil groove in liner may be filled with carbon deposits
Gauging a cylinder liner
Liner Gauging
• Gauging a liner is carried out for two reasons:
To establish the wear rate of the liner, and to
predict if and when the liner will require
changing.
• Although on a 2 stroke engine the condition
of the liner can be established by inspection
through the scavenge ports (evidence of
blowby, scuffing etc.), the liner is gauged
during the routine unit overhaul (15000 hrs),
or if the unit has to be opened up for any
reason
Source: www.marinediesels.info
Liner Gauging
• Because of the action of the piston rings, the
varying gas pressure and temperature in the
cylinder, the wear will not be even down the
length of the liner. Consider the piston just
beginning the power stroke. The gas
pressure pushing the piston rings against the
liner wall is at its highest; The liner surface
temperature up at this part of the liner is
about 200°C, so the viscosity of the
lubricating oil is low. The relative speed of the
piston is low, and so the lubrication is only
boundary.
Liner Gauging
• Because of these factors wear at the top of a
liner increases to a maximum a few
centimetres below the position of the top ring
at TDC, and then decreases as the ring
pressure and liner wall temperature
decreases and the piston speed increases
building up a hydrodynamic film between liner
and ring surfaces. Then as the piston slows
down and the rings pass over the port bars,
the wear will increase due to boundary
lubrication, a reduction in surface area, and
oil being blown out into the scavenge space.
Liner Gauging
• A liner is gauged by measuring the diameter
of the liner at fixed points down its length. It is
measured from port to stbd (athwartships)
and fwd to aft. An internal micrometer is used
because of its accuracy (within 0.01mm). To
ensure that the liner is always measured in
the same place, so that accurate
comparisons may be made, a flat bar is hung
down the side of the liner with holes drilled
through where the measurements are to be
taken.
Gauging a liner on a large bore RTA engine.
Source: www.marinediesels.info
Liner Gauging
• Measurements are taken at more frequent
intervals at the top of the liner where wear
rate is expected to be highest.
• To ensure accuracy, the micrometer gauge is
checked against a standard, and the liner and
micrometer should be at ambient
temperature. If the temperature is higher then
a correction factor can be applied. To ensure
micrometer and liner are at the same
temperature, lay the micrometer on the
entablature for a few minutes before starting.
Liner Gauging
• The readings can be recorded in tabular
form, and from the data obtained the
wear rate/1000 hours can be calculated.
Wear rate varies, but on a large 2 stroke
crosshead engine ideally should be
about 0.05mm/1000 hours. On a
medium speed trunk piston engine
where the procedure for gauging is
similar, the wear rate is around
0.015mm/1000 hours.
Cylinder Number: 1
Nominal Dia: 840mm
Total Running hours:
60000
Running hours since last calibration:
15000
Gauging
point
P-S
F-A
Wear rate
(average)
P-S
Wear rate
(average)
F-A
last
calib.
P-S
wear
rate
P-S
last
calib.
F-A
wear
rate
F-A
1
841.2
841.26
0.02
0.021
840.95
0.017
841
0.017
2
841.38
841.44
0.023
0.024
841.1
0.019
841.17
0.018
Etc
Figures are for illustration only.
Manufacturers quote max wear for a cylinder liner at about 0.8%
of original diameter. If the wear rate is kept to a minimum, then
the liner may last the life of the engine.
Replacing cylinder liner
Diesel Engine
The photograph above shows clearly the evidence
of the leaking liner. The cooling water has
evaporated leaving white deposits of the cooling
water treatment chemical
• The oil mist detector had activated during a
day at sea and the engine had shut down
automatically due to high oil mist content in
the crankcase. After a period of about 30
minutes the crankcase doors were removed
and the crankcase partitions inspected. The
reason for the activation was not an
overheated bearing, but water vapour due to
the failure of a cylinder liner lower “O” ring
seal on one cylinder that was allowing cooling
water from the jacket cooling space into the
crankcase. This meant that the whole running
gear for that cylinder was required to be
removed for replacement of the liner.
Liner Replacement
• The engine was isolated from main cooling
water systems and drained, the compressed
air system was isolated, the pre-lubrication
pump was stopped, and the turning gear
engaged. The expansion tank levels were
monitored during maintenance in case a
valve was passing on the engine, and the
engine refilling with water. The drain for the
engine was kept open and monitored closely
for signs of leakage.
Liner Replacement
• The cylinder head and the piston were
removed. The cylinder lubrication pipes
at the bottom of the cylinder liner were
disconnected by undoing and removing
the banjo bolts. The bolt securing the
centering piece which locates the liner
in the correct position in the cylinder
bore is removed.
Liner Replacement
• The liner must be jacked off its seating
using a hydraulic jack. In the case of the
ZA40 the jacking device is bolted to the
crankpin bearing. (Left in place when
removing the con rod, which is normally
bolted to the bearing by means of a
marine palm
After attaching the jacking device to the bottom end bearing the
bearing was turned through 90° and the crankpin turned to
TDC. The hydraulic pump connected to the jacks was operated
so that the jack locates in the bottom of the liner. The liner was
then jacked upwards until the liner moved off its seat. (the jack
has only a 54mm lift).
The liner lifting tool was
then bolted on to the top of
the cylinder liner and hooked
up to the engine room crane.
The liner was then carefully
removed from the engine
(mass of liner 450kg).
Liner Replacement
 The new assemblies were inspected prior to
fitting.
 While the liner was removed from the engine,
the jacket cooling space around the liner was
inspected for overall condition that can
indicate the effectiveness of the cooling water
treatment.
 The guiding bores in the entablature and O
ring seating were cleaned and examined for
evidence of corrosion /erosion and the
landing face for the cylinder liner was cleaned
and examined.
Fig: View looking down through engine frame with cylinder liner
removed.
Note: Although this is a ZA40 engine it is not the one being
described. This is a Vee engine: You can see the side by side
bottom end arrangement.
 The new liner was cleaned,
inspected and gauged to ensure
it was within limits specified by
Wartsila.
 Landing and sealing faces were
inspected to ensure they were
free from damage.
 Lubrication drillings were blown
through with compressed air to
ensure they were clear.
 The lifting gear was attached
and the liner tried in the
entablature without O rings to
ensure that it fitted without
binding.
Liner Replacement
 The liner was withdrawn and heat resistant Viton O
rings fitted which were well lubricated with engine oil.
 The landing face was smeared with a sealing
compound.
 The liner was fitted into the engine ensuring that the
centering piece was correctly lined up.
 Once the liner was in position the centering piece
location bolt was fitted and the cylinder lubricators
connected and checked by operating the pumps by
hand and ensuring that oil issued from the lubrication
points.
 The Liner was gauged and the readings recorded.
 The running gear was reassembled, fitting new piston
rings.
 Once the cylinder running gear was all in place, the
engine was refilled with water, and the crankcase
checked to ensure no leakage was occurring.
 The engine was then prepared for running. All equipment
used was accounted for and the crankcase was checked
clear of tools, rags and personnel. The cylinder
lubricators were wound 15 times to ensure lubrication of
the piston and liners, and the engine was turned a
minimum of 2 revolutions with the turning gear to check
for correct operation of the running gear, the running
gear is observed through the crankcase doors and the
rocker cover.
 The ammeter on the turning gear panel is monitored so
that if a partial seizure was to occur, the current drawn by
the motor would have increased, indicating a problem.
 The engine crankcase was monitored for water leakage
from the liners during the warming through procedure.
 The lubricating oil, which had been circulating through the
purifier was checked for water content, and the oil pumps
switched on and oil flow through the bearings checked.
 Once the engine was ready for starting the normal
routine for checking the engine was followed:
- After a very short run (30 seconds) the engine was
stopped and the bottom end bearing on the overhauled
unit checked.
- The engine was then run for increasing intervals
of time; 2, 10, 30 minutes, checking the bearing in
between.
 Finally the load on the engine was slowly increased
and the unit run in as per manufacturers instructions;
reduced load and increased cylinder lubrication whilst
the rings bedded into the liner.
References:
1. www.marinediesels.info
2. The Running and Maintenance of Marine Machinery
– Cowley
3. Reeds Marine Engineering Series, Vol. 12 – Motor
Engineering Knowledge for Marine Engineers
4. Lamb’s Question and Answers on Marine Diesel
Engines – S. Christensen
5. Principles and Practice of Marine Diesel Engines –
Sanyal
6. www.dieselduck.info (Martin’s Marine Engineering
Page)