Function
The compression of air and the combustion of fuel/air mixture take place inside the cylinder liner, so it forms part of the combustion chamber.
Cylinder liner wear
Normal frictional wear :
Due to metal-to-metal contact with very high surface asperities under marginal lubrication condition.
Abrasive wear :
Due to presence of hard foreign particles from Air, fuel and lub oil.
Corrosive wear :
Due to H2SO4acid attack owing to products of combustion. Sulphur within a fuel. Only about 0.1% of the Sulphur in the fuel causes corrosive wear,like hot and cold corrosion, and the remainder escapes with exhaust gases.
Due to Hydrochloric acid attack because of salts in air, charge air coolerleakage, sea water in fuels and lube oils.
Causes of liner wear
(A). Improper running-in-during first few hours, 10 to 20 hours, the piston rings have to form an effective seal against the passage of destructive blow by gases. Surfaces of rings and liner slide freely against one another without the asperities welding together when engine is under load. Metallurgical changes take place on the metal surfaces during the initial running- in that a thick work hardened layer is formed, which has good anti-wear properties in subsequent operation.
(B). Misalignment of piston, or distortion of liner, preventing bedding-in of piston and liner.
(C). Inadequate oil supply or unsatisfactory arrangement of cylinder lubrication.
(D). Lube oil is too low in viscosity or too low in alkalinity (Grade of cylinder oils).
(E). Incorrect piston rings clearances.
(F). Unsuitable liner material (quality).
(G). Unsuitable piston and ring materials.
(H). Contamination of lube oil by abrasive materials.
(I). Cylinder wall temperature too high or too low.
(J). Engine overload.
(K). Scavenging air temperature too low, resulting in excessive quantities of condensed water entering the cylinder (leading to dew point corrosion).
(L). Inefficient combustion, promoting deposits formation and degradation of the lube oil.
(M). Use of low Sulphur fuel oil in conjunction with high (TBN) alkalinity lubes oil.
Causes of cylinder liner wear.
1) Improper running in.( 10 to 20 hours)
2) Misalignment of piston or distorted liner.
3) Inadequate oil supply or unsatisfactory arrangement of cylinder lubrication.
4) Cyl oil is too low in viscosity or too low in alkalinity.
5) Incorrect piston ring clearance.
6) Unsuitable liner material.
7) Contamination of cyl oil by abrasive materials.
8) Engine over load.
9) Scavenge air temperature too low.
10) Insufficient combustion.
11) Use of low sulphur fuel oil in conjunction with high alkalinity lube oil.
Types of wear
Scratching:
Small Scratch may develop in the region of ring travel due to small particles entrapped between the bore and rings. Those particles originated from the machined surfaces of the mating pair.
Scoring:
Score confined to the region of ring travel and may extend to the region swept by the piston.
Scoring being developed from Scratching and the origins is similar to Scratching.
Scuffing:
Scuffing is a condition develops in the ring travel on the thrust side of the liner and depends on the efficiency of the Lubrication, speed and Loading.
Clover leaf pattern:
Some liners wears irregular ovality patterns but some gives "Clover-Leafing" pattern of longitudinal corrosive wear at several points around the liner concentrated between the lubrication orifices.
The cause is owing to combined effects of incorrect feed rate of cylinder oils (inadequate)and acidic effect of combustion products (or low TBN lube oil). The wear concentrated between the
points of lube oil quills.
1. In actual practice, wear never takes place concentrically, and it depends on heel and trim of the ship in service, and effective guide clearance
1.In tankers and bulk carriers, where long ballast passage are made with the trim aft,
Maximum wear will be in the fore and aft plane, and especially on aft side of the liner.
WEAR RATE
1. Liner wear rate is high during the running in period after which it will come to a uniform wear rate within most of its service life.
1. Finality the wear rate increases as wear becomes excessive and rapidly due to difficulties in maintaining the rings gas tight.
3.Wear rate can be high about 0.75mm/1000 has in large slow speed engines using residual
fuel oils which contain in excess of 1.5% of Sulphur
4. Wear rate being lower about 0.02 mm/1000 hrs in medium speed engines, due to burning low Sulphur fuel oils.
5.When the Vanadium is added during manufacturing, the wear rate could be significantly reduced to 0.025mm-0.50mm/1000 hrs.
6. Maximum wear allowance of liner = 0.7% to 1% of original bore for large output engines.
WEAR PATTERN
1.Maximum liner wear is at the upper limit of the travel of the top compression rings at the top of the stroke
2. This reduces towards the lower end of the stroke but will increase in way of exhaust and scavenge ports.
Reasons for maximum wear at top of the stroke being:
(01) The gas load behind the ring is maximum
(02) It is the hottest region
(03) Viscosity of oil film is low and liable to breakdown under heavy load and high temperature
(04) Abrupt Change in direction of piston rings, at dead ends of reciprocating motion.
(05) Corrosive wear
(06) More liable to be attacked by acids.
Reason of maximum wear around the ports.
Due to leakage of hot gases past the top ring into the ports and these hot gases will tend to burn off the oil film.
How to maintain minimum liner wear ?
(01) By use of good quality cylinder oils with detergent additives of proper TBN valve.
(02) By use of corrosion resistant liner materials with some proper percentage of Vanadium,Titanium, Chromium and chrome plated liners.
(03) By maintaining good Fuel injection condition (efficient cleaning of F.O, Correct F.O temp:,Correct F.O grade)
(04) By maintaining Jacket, water temperature as high as practical to avoid dew point
condensation of acid products.
(05) By maintaining proper feed rate of cylinder oils.
Points to remember:
(1) Lubricator timing
(2) Position of quills
(3) Oil feed rate
(4) Oil refreshing rates
(5) Oil film thickness
(6) Engine load
Sign of liner crack
(01) Fluctuation of pressure and temperature of jacket C.W system
(02) F.W coming out from the scavenge drains
(03) Overload at that particular unit (high in exht: temp: and Jacket temp)
(04) Expansion tank foaming
CAUSES
(01) Due to rapid contraction of metal
(02) High difference in Jacket water (working) temperature
(03) Insufficient cooling
(04) Over tightening of cylinder head bolts
(05) Design failure
(06) After effect of immense Scavenge fire
(07) Due to loosened out foundation chocks resulting tie bolt slackening and Hoop Stresses on Cylinder liner increases
(08) Due to very high injection viscosity
Cause of cylinder liner crack.
1. Excessive thermal & mechanical load.
2. Poor material & design.
3. Piston seizure.
4. Localized scavenge fire.
6. Over or Uneven tightening of cylinder cover nut.
7. In loop & cross scavenging, high temperature gradient.
8. Water side corrosion reduce liner strength.
PREVENTION
(01) Use torque spanner
(02) Maintain C.W temp: at a level within a limit
(03) Close watch on temp: and press: of gases, Fuel oils and C.W ETC…
(04) Renew cylinder liner when worn down beyond limit about 0.7% more than original bore.
Consequence of excessive liner & piston ring wear
1) Blow pass occur & scavenge fire can occur
2) Blow pass occur & crankcase explosion can occur
3) Over heat on liner & liner crack & piston seizure & piston breakage may occur
4) Engine become unbalance & power loss
5) Turbocharger surging may occur
Removing and refitting the liner
Before removing
1) Immobilisation permit taken from port authority
2) Vessel in upright position
3) Lifting gears and tools in good working order
4) All spares are ready.
5) Persons grouped for assigned jobs.
Removing the liner
1) Drain CW from cylinder jacket
2) All lubricator quills removed
3) Cylinder cover, piston and stuffing box removed in usual way
4) Cover the piston rod stuffing box seating with special cover
5) If liner is to be reused, liner wear should be measured and recorded
6) Position of liner, relative to cylinder jacket, properly marked
7) CW outlet pieces to cylinder cover removed
8) Attach the liner withdrawing tool as per instruction, and tighten the upper nut until liner
comes in contact with upper supporting bar [strong back bar]
9) With overhead crane and sling arrangement, liner is drawn out
Before refitting
01) If old liner is to be reused, clean thoroughly
02) Landing surface of quills checked for damage and carbon deposits on oil holes cleaned.
03) Rubber sealing ring groves, cleaned with old round file until to bare metal
04) Surface inside jacket, coated with anti-corrosive paint, and sitting surfaces cleaned.
05) Sharp edges inside jacket, chamfered slightly to prevent cutting rubber sealing rings.
06) If new liner is to be fitted, gauged before fitting
07) New liner is to be lowered down into position, without sealing rings fitted, to ensure it is correct size. Liner should not only drop freely by its own weight, but there should be slight radial clearance between liner and jacket to allow for expansion.
08) Radial clearance at lower end, < 0.2 mm for 750 bore liner
09) Radial clearance at top, < 0.001 mm/mm of liner bore.
10) Rubber sealing rings should grip firmly around liner, and a 10% stretch would be adequate
11) If there is no original reference mark on liner, quills should be fitted and mark the correct position of liner relative to cylinder jacket.
12) Remove the liner again and sealing rings fitted.
Refitting liner
1) Soft soap or similar lubricant to be applied to rubber sealing rings for easy fitting
2) Fit in correct position as per instruction
3) New liner re-gauged after final landing to check any distortion and recorded
4) Refit quills and test lubrication. All parts refitted in usual way
5) Fill cylinder jacket and check water-tightness under pressure.
Running in During the first 10~20 hours
1) Cylinder oil feed rate at maximum
2) Engine load reduced
3) Reduce oil feed rate to normal and increase the load stepwise
4) Liner checked from inspection door and scavenge space, at first opportunity
Fitting cylinder liner
1) Clean close fitting parts, L.O fittings, rubber sealing ring grooves.
2) Clean inside the jacket and coated with anti corrosive paint.
3) Chamfered slightly sharp edges inside the jacket.
4) Soft soap or similar lubricant apply to rubber ring and fitting surfaces.
5) For new liner first lowered into position without fitting rubber ring to check the fitting clearance and fitting of cylinder lubricator.