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M.E.K (JULY;1994) Q.6

(Q) In super charging engine. (H.O)

(a)The problem connected with liner wear.

(b) The various means adopted to minize the wear rate.

(A) The main causes of cylinder liner wear are as follow1. Normal frictional wear.

Caused by metal to metal contact under boundary lubrication due to inadequate

load carrying properties, too low viscosity and an inadequate oil supply.

2. Abrasive wear 

Caused by hard foreign matters coming with induced air or by the products of 

wear which are themselves abrasive or by hard carbon caused by poor combustion and

other material which breaks away from the piston or cylinder surfaces. Ash forming

constituents present either fuel oil or lub oil. In a trunk piston engine it is equally

important to ensure adequate filteration or centrifuging of the circulating oil to remove

all foreign matter which score not only the cylinder but also the bearing as well.

3. Corrosive wear Corrosive wear is predominant with engine burning heavy oil. It is caused by

formation of sulphuric acid within the cylinder. The poor quality residual fuel having

higher sulphur content about 4.5% on weight has greatly the risk of cylinder liner 

corrosion.

The sulphur having first burnt to sulphurdioxide, which then combined with

additional oxygen convert to sulphurtrioxide (SO3) by helping from catalysts action of 

vanadium pentoxide (V2O5 ) and ferrous oxide (F2O3) .The hydrogen an the fuel burns

to form a dry water vapour. These two combined to form sulphuric acid and the

cylinder surface if the temperature is below dew point. Fortunately a relatively a small

 portion (about 0.1%) of the sulphur in fuel is normally converted to sulphuric acid, the

remainder of the sulphur oxide passing out of the cylinder with the exhaust gases.

There are many additional factors which influence liner wear.

4. Unsuitable quality of liner material.

5. Piston and ring material.

6. Scavenge temperature too low, resulting excessive condensed water entering

the cylinder.

7. Distortion of piton and liner due to thermal and mechanical stresses.

8. Poor combustion causes deposit and degrading of the lub-oil.

9. Poor design are insufficient or too great piston ring clearances.

10. Poor piston cooling causing excessive ring zone temp.

11. Inproper running-in.12. Over loading of engine.

13. Under piton deposit increasing ring zone temp.

14. Incorrect T.B.N of cylinder oil to neutralise acid formation of using fuel oil.

Oil used for cylinder lubrication must have the following properties to reduce

wear.

(a). It must reduce sliding friction between ring and liner to a minimum.

(b). It must posses adequate viscosity at high working temp.

(c). It must form an effective seal.

(d). It must burn clearly leaving as little deposit as possible.

(e). It must effectively neutralise the corrosive effect of mineral acid forming

during combustion.70 mg KOH/gm for slow speed cross head type engine using H.F.O .

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M.E.K (JULY;1994) Q.6

30 mg KOH/gm for trunk piston engine using D.O.

To minimise the liner wear rate

Chromium plated liner can reduce the cylinder liner wear rate, but it is too costly

for large liner. The chromium plated top piston ring is cheaper than chromitum platedliner and widely used in large engine.

The liner and piston rings should be ensured an oil film through the stroke.

Frequent checking of cylinder lubricator and oil passages to cylinder must be

made.

Control of cylinder lubricating oil supply in tropical climate and cold climate

must be adjusted.

Jacket temperature should always be kept as high as practicable in order to avoid

cool condition of inner liner wall, which would lead to corrosion.

Engine running with reduced speed for prolong period should be avoided.

Before starting, prelubrication of liner is made by hand crank of lubricator while

engine is turned by turning gear.Regular maintenance of engine unit must be made.

Fuel oil must be at proper temperature, viscosity and purified efficiently.

Max: allowance wear 0.5 % for M.C.E

1% OF Cylinder liner diameter for large bore engine.

Cylinder oil consumption for single acting.

4 stroke 1.07~ 1.6 gm/KW.hr  

2 stroke(uniflow) 0.54 gm/KW.hr 

2 stroke(loop & cross)0.8 ~ 0.9 gm/KW.hr 

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