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ENGINNEERING KNOWLEDGE MOTOR (MA 3016)
Learning Outcomes Discuss materials used for liners Explain heat transfer and strength of liner Explain how Sealing in liner achieved Discuss how expansion on liner is accommodated Describe wear and wear rate on liner
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Learning Outcomes Sketch and describe a modern liner Discuss surface treatment of liner Describe procedure in renewal of liner Discuss running-in of liner
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Form part of combustion chamber Forms cylindrical space in which piston reciprocates
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Cylinder LinerIntroduction Cylinder block is made from grey cast iron Liner is manufactured from cast iron alloyed with chromium, vanadium and molybdenum. Alloying elements help resist corrosion and improve wear resistance at high temperatures Liner will wear with use, and therefore may have to be replaced Cylinder jacket lasts the life of engine.
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Cylinder LinerIntroduction At working temperature, liner is a lot hotter than the jacket Liner will expand more and is free to expand diametrically and lengthwise. If liners were cast as one piece, then unacceptable thermal stresses would be set up Complex casting, difficult to produce a homogenous casting
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Wet liners medium and slow speed engines cooling by water Dry liner small engine cooling by air e.g life boat engine
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3 PIECES LINER (DOXFORDP)
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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 PTYPECyliner Liner 5/26/2011 9
CYLINDER OIL SUPPLY GROUND FACE
COOLING WATER OUT TO COVER CYLINDER LUBRICATION OIL 8 POINTS
JACKET
COOLING WATER IN TELL TALE LEAK OFF
UPPER COOLED PARTABESTOS PACKING Copper ring 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)Cyliner Liner 5/26/2011 10
RND SULZER (ONE PIECE) HYPERBOLIC COOLING PASSAGESC/W OUT TO CYL HEAD THICK COLLAR COMBUSTION SPACE ABOVE JACKET
GROUND FACE
CYLINDER OIL SUPPLY
ANGLED C/W DRILLINGS
JACKET
FREE THERMAL EXPANSIONDRILLING 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
BORE COOLING VIEW
C/W INLET LEAK OFF LINE / TELL TALE HOLE PLUG
RUBBER RINGS
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Mechanical stress pressure Thermal stress - temperature
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Supercharged engines, maximum firing pressure is about 90 100 Bar or more Non- supercharged is about 75-85 Bar This pressure produces circumferential (hoop) stress and longitudinal stress Hoop stress is twice longitudinal stress so only hoop stress is considered
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HOOP STRESS
h
=PxD 2t
CYLINDER HEAD
WHERE, P = GAS PRESSURE D = LINER DIAMETER t = LINER THICKNESS Thus hoop stress will increase if bore size and firing pressure increaseCyliner Liner
CRACK DUE TO HOOP STRESS
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Resistance to heat flow through liner metal produces a temperature gradient across liner Liner wall expands more relative to outer wall, where: thermal stress, T = T where T is temperature gradient
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Thicker liner will increase temperature gradient hence thermal stress Thicker liner have good resistance to mechanical stress. Liner design becomes complex Inner liner surface temperature should be sufficiently low to retain oil film and high enough to avoid acid-dew (sulphur)
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Next to liner wall 500oC On liner wall 140oC due to oil film, carbon deposits Outer liner wall 75oC due to thickness of liner wall and cooling water Lower part 40oC due to expansion
Cylinder covero 1650 oC 500 C
Piston
Cylinder 140 oC jacket 75 oC Cooling water space
Cylinder liner
Cyliner Liner
40 oC
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THERMAL STRESS
OPTIMUM METAL THICKNESS HOOP or MECHANICAL STRESS
METAL THICKNESSCyliner Liner 5/26/2011 18
Older lower powered engines had a uniform wall thickness Cooling was achieved by circulating cooling water through space between liner and jacket. Cooling water space was sealed from scavenge space using 'O' rings Telltale passage between 'O' rings led to outside of cylinder block to show a leakage.
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Tell-tale passage
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To bring cooling water closer to the liner wall, without compromising strength tangential bore cooling is used.
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TANGENTIAL BORE COOLING
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Holes are bored from underside of flange formed by increase in liner diameter Holes are bored upwards and at an angle so that they approach internal surface of liner at a tangent. Holes are then bored radially around top of liner so that they join with tangentially bored holes.Cyliner Liner 5/26/2011 23
One piece liner & Tangential Drilling for C.WCyliner Liner 5/26/2011 24
In some long stroke engines undercooling further down the liner was taking place. Condensation of water vapour on liner surface wash away lube oil film. Condensation of sulphuric acid vapour into acid contribute corrosion
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Insulating tube minimize condensation of vapour
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Sulphuric acid if this condenses on liner surface corrosion can take place. Once oil film has been destroyed then wear will take place at an alarming rate Insulate outside of liner so that there was a reduction in cooling effect. Latest engines liner is only cooled at the very top.
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Inside surface is subjected to rubbing action of piston rings Subjected to high combustion pressure and temperature at upper end. Takes side thrust of piston caused by the connecting rod angularity
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Modern liners employ bore cooling at the top Pressure stress is high and liner wall thickness has to be increased. This brings cooling water close to liner surface to keep liner wall temperature Efficient cooling lead to no breakdown in lubrication or excessive thermal stressing. Although liner is splash lubricated cylinder lubricators may be used on larger enginesCyliner Liner 5/26/2011 29
Cooling water space is formed between engine frame and jacket Danger is water could leak down and contaminate crankcase if O rings failed As a warning, "tell tale" holes are led between O rings to outside of engine.Cyliner Liner 5/26/2011 30
MAN-B&W L58/64 Liner
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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 crankcase Provides the cooling at the hottest part of the cylinder liner.Cyliner Liner 5/26/2011 32
Liner is fitted with a fireband also known as an anti-polishing ring. It is slightly smaller in diameter than liner Purpose is to remove carbon which builds up on piston above top ring. If carbon is build up it will rub against liner wall, polishing it and destroying its oil retention properties.Cyliner Liner 5/26/2011 33
Grey Cast iron is used because Castibility is good for intricate shapes Good wear resistance large surface of irregular shaped graphite flakes and semiporous surface to retain oil Good thermal conductivity Good internal vibration damping properties Cost less relativelyCyliner Liner 5/26/2011 34
Liner Materials Nodular or spheroidal cast iron is Tougher More resistance to crack formation (less stress raising matrix) Less self lubrication properties * For higher power, shock loading due to combustion pressure
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Alloy Element Nickel Chromium Copper or molybdenum wear resistance to corrosion
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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%Cyliner Liner 5/26/2011 37
Two methods
Sand casting Centrifugal casting
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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
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Stronger liner Homogeneous in structure Poor wearing quality (fast cooling rate) Normally used for medium and high speed engine
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After casting, liners are rough- machined and hydraulically pressure tested ~ 7 Bar Ports are formed in casting - old practice 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 ~ 3.5m or surface treatment
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Normally used an electrolytic deposition of hard chrome sometime nickel Chrome layer is ~ 0.2 to 1.0 mm Chrome surface must be porous for oil retention This can be achieved by etching with acid or a patented porus-krome
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Advantages Hard surface and improve wear-resistance, corrosion resistance, uniform surface finish Disadvantages Expensive 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 linerCyliner Liner 5/26/2011 43
Plated liner is immersed into a special bath and current (for electroplating) is reversed This forms minute pits and channels in the chromium plating After plating, liner is ground or honed It is then replaced in the bath together with a screen attached to its surface. The current is then reversed and smallhemispherical cavities are producedCyliner Liner 5/26/2011 44
1. Crack across liner flange due to uneven or excessive tightening of cylinder head studs 2. Hoop stress crack due to poor liner support 3. Circumferential crack along wear ridge due to SCR or new rings hitting the ridge 4. Star or crazy cracking caused by flame impingement 5. Star cracks around lubricator quill due to water leakage 6. Cracks across port bars due to overloading, poor cooling, scavenge fire, poor fitting of rubbing sealing ring etcCyliner Liner 5/26/2011 45
1 2
4 3
5
Liner Fault - Crack
6
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Three main causes of damage/wear to the liner material; Abrasion - caused by solid particles breaking through the lubricant film Corrosion caused by acidic products of combustion Friction or scuffing - Break down of lubricating oil film leading to metal to metal contact Note: Normal and abnormal wearCyliner Liner 5/26/2011 47
Hard particles combined with cylinder lubricant to form 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 Thus in crosshead engine, abrasive wear is the major contributor for liner wear.
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Source of hard particles can originate from Air borne dirt, Ash in fuel, Carbon from combustion Piston rings wearCyliner Liner 5/26/2011 49
Dirty air filter Dirty scavenge ports Scavenge manifold dirt
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Fuel consists of vanadium, sodium silica and scale (iron rust) It can be reduced by effective centrifugal separation
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Difficult to achieve perfect or complete combustion Bad combustion results in more carbon produced as abrasive particles To minimise carbon in cylinder: Efficient oil purification Good combustion Correct injection and pump timing Maintain correct fuel temperatureCyliner Liner 5/26/2011 52
Produces wear dust from rubbing Increases wear of both liner and rings Use good quality ring material and lubrication
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Marine fuel contain sulphur After combustion sulphur dioxide and sulphur trioxide
SO2 + H2O --------- SULPHUROUS ACID SO3 + H2O --------- SULPHURIC ACID UNBURNED FUEL (SULPHUR) + UNPERFECT COMBUSTION (O2 + H2O) ------- SULPHURIC ACIDCyliner Liner 5/26/2011 54
RELATION BETWEEN H2SO4 DEWPOINT TEMPERATURE & FUEL SULPHUR CONTENT AT DIFFERENT PRESSURES
180
H2SO4 dewpoint temperature oC)
170
80
160
150
140 1
130
120
110
1.0
Sulphur in fuel %wt
2.0
3.0. Cyliner Liner 5/26/2011 55
Pressure (bar)
40
Dew point of sulphuric acid is around 110oC to 180oC depending upon : Pressure in cylinder Sulphur concentration
Acid is present especially during slow steaming - temperature around that boundary
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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 loadCyliner Liner 5/26/2011 57
Occur when lubricant failed to separate rings and liner surfaces Subsequent contact caused microwelding or micro-seizure.
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Too smooth liner surface resulting in too little lube oil retention Water on 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 filmCyliner Liner 5/26/2011 59
Maximum normal liner wear occurs at top of the liner, in port-starboard direction and around scavenge and exhaust ports Reason for above wear pattern: 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 break-down (reversal of piston movement)Cyliner Liner 5/26/2011 60
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 Surfaces get either more alkalinity or less depending on position from cylinder lubrications quill and TBN usedCyliner Liner 5/26/2011 61
CLOVERLEAFING
Lube oil
Wear due to exhausted alkalinity before cylinder oil spreads across liner surfaces
Lube oil
Lube oil
Wear due to excessive alkalinity in cylinder oilLube oil
Measured by profilograph an instrument
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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 experiencedCyliner Liner 5/26/2011 63
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)Cyliner Liner 5/26/2011 64
MICROSEIZURE OIL FILMLINER WALL LINER WALL LINER WALL
RING
RING RING
Asperities meet Frictional heat and weldingCyliner Liner
Tearing out, cooling, hardening5/26/2011 65
OIL - WEDGEOIL FILM
LINER WALL PISTON SKIRT LINER WALL
PISTON SKIRT
OIL WEDGE OIL FILM (1:150 TAPPER)
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Gauging a Liner
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Gauging a liner on a large bore RTA engine.
Liner Wear Pattern
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. Liner should be replaced as the wear approaches 0.8 - 1% of liner diameter. Liner is gauged at regular intervals. The wear rate for a medium speed liner should be below 0.015mm/1000hrs.Cyliner Liner 5/26/2011 70
WEAR RATETEMPLETE Cyl No A B C D Date fitted Total hours Position A B E C D E F EXHAUST PORT SCAVENGE PORT G F G H Max wear Mean Max Wear Wear rate since new Wear rate since last gauging Remarks H Date Date of last gauging Hours since last gauging Forward and After Port and StarboardTOP RING POSITION
LINER
WEAR
LINER WEAR RECORD SHEETCyliner Liner
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RESULTS
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Related to time in order to put these figures into useful form of comparison Form of diameter increase per thousand running hours. Thus :Wear rate since last recorded measurement Increase in O since last record
Running hours since last record = = mm/1000 hrsCyliner Liner 5/26/2011 72
X 1000
Wear rate since new : Total increase in O (diameter)=
Total running hours since new= mm/1000 hrs
X 1000
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Discuss Overhauling of liner Liner Disassembly
Safety Procedures Tools required Spare parts Work plan Measurements to take
Liner Assembly
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Max. Liner wear rate mm/10000.4
MAXIMUM CYLINDER LINER WEAR RATE PER RUNNING HOURS
0.3
0.2
0.1
GRAUDAL WEAR STARTS
WEAR RATE INCREASES DUE TO WORN RINGS AND LINERS
RUNNING-IN PERIOD2 4 6 8 10 12 14 16 18 205/26/2011 75 ENGINE RUNNING HOURS x 1000
Cyliner Liner
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 versaCyliner Liner 5/26/2011 76
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 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.Cyliner Liner 5/26/2011 77
DG Di = 0.98 DG Di 0.7 to 0.8d d
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Oil is of high alkalinity which combats acid attack from sulphur in fuel. Injection of oil is timed using inputs from crankshaft position, load and speed. Correct quantity oil injected by opening valves from pressurized system, as piston ring pack passing injection point.
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Sulzer ZA40 Liner (4 Stroke Vee Engine; Straight engine is similar)Lubricator drillings are bored from bottom circumferentially around 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.
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Summary Discuss materials used for liners Explain heat transfer and strength of liner Explain how Sealing in liner achieved Discuss how expansion on liner is accommodated Describe wear and wear rate on liner
BEDPLATES
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Summary Sketch and describe a modern liner Discuss surface treatment of liner Describe procedure in renewal of liner Discuss running-in of liner
BEDPLATES
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Exercises Explain the causes of liner wear Explain the meaning of wear rate of liner Sketch and describe procedure in renewal of liner Discuss running-in of liner Discuss the causes of excessive wear on linerBEDPLATES 5/26/2011 83