What is Liner Wear?
Cylinder liner requires adequate lubrication to reduce piston ring friction and wear.The oil film not only acts as a gas seal between the liner and piston rings, but also as a corrosion inhibitor.
If the cylinder lubrication is low the oil forced into the piston ring grooves reduces ultimately it causes the liner wear .And also due to acidic corrosion the wear takes place.
The rate of cylinder sleeve wear varies over the life of liner. It is high during the initial Running-in period after which it should reduce to an almost constant rate for most of the useful life of liner. Finally the wear rate progressively increases as the wear becomes excessive.
RUNNING-IN PERIOD :
It is nothing but the time period where running of engine is by using the newly fitted piston rings and liner after the replacement / renewal done in engine overhaul or running a new engine.
so new piston rings and liner may take certain period to form a perfect gas seal .Until this time the engine is run on low load & less speed to maintain a perfect Micro-seizure taking place this is called as RUNNING-IN PERIOD.
MAXIMUM wear of liner before renewal after the overhaul is usually (0.6-0.8)% of the original bore diameter .
For TWO-STROKE engines normal wear rate is about (0.0250 to 0.050)/1000 running hours.
For FOUR-STROKE engines normal wear rate is about (0.0125 to 0.025)/1000 running hours.
Effects Of Liner Wear
- If the cylinder is operated with excessive wear ,then the RATE of WEAR Rapidly increases.
- GAS BLOW PAST may occur this removes the cylinder lubrication oil film,piston rings may distort and break. Piston movement cause the removal of liner material.
- Compression is reduced causing incorrect combustion with fouling of exhaust system.This gives rise to further problems like surging of turbo charger and loss of engine power.
- Unburned oil due to less compression may be blown into scavenge spaces giving rise to SCAVENGE FIRE.
How To MInimize Cylinder Liner Wear?
Correct Quantity and Grade of cylinder liner lubrication to be used.
- Correctly fitting piston rings.
- Correct warming through prior to starting.
- Well maintained and timed fuel injector.
- Well managed fuel storage and purification plant.
- correct cooling water and lubrication oil temperature.
- Correct scavenge air temperature.
- Engine load changes carried out gradually.
- Well maintained equipments.
Low Wear Rate Factors
- The development of high alkaline lubricating oil neutralize the acid formed during the combustion.
- The development of load dependent temperature control of cooling water which maintains the cylinder liner temperature at optimum level thus we can maintain the lube oil film in cylinder liner.
- The use of good quality cast iron with sufficient hard phase content for cylinder liner.
- Careful design of piston rings profile to maximize the lubricating oil film .
- improve in lubrication oil distribution across cylinder liner surface .This includes multi-level injection in 2’s engines and forced lubrication system in 4’s engines.
- Improve separation of condensate from scavenge air by using correct grade of dry scavenge air for combustion.
In the next article, we will talk about the types of liner wear which is found from experience.