gme 2011 ekm

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Contents

1.

1. ................................................................................................................................................................... 1

Question Sr 1 2011. Sr 6 2008, ...................................................................................................................... 4

Explain why it is necessary to heat heavy oil before burning it in the Cylinder Of an internal combustion

engine. .......................................................................................................................................................... 4

Describe the effect on engine condition and performance due to excessive heating of fuel oil. ................ 4

Precaution during maneuvering on heavy oil. .............................................................................................. 4

2011. Sr 6 2008, Sr 4 2006 ............................................................................................................................ 6

Describe ANY Arrangement used in connection with an IC engine for the recovery of heat from exhaust

gases.............................................................................................................................................................. 6

State the temp of the gas at the cylinder exhaust passage and entering and leaving the equipment

described Turbo Charging ............................................................................................................................. 6

Qb- Describe ways of using energy from the main engine other than for main propulsion ........................ 6

Sketch and describe a fuel injector for a diesel engine. ............................................................................... 8

State four parameter that indicate fuel injectors require immediate overhaul. ......................................... 8

Answer. ......................................................................................................................................................... 8

Question Sr 6, 4 2009, 2006 ........................................................................................................................ 12

What are the causes for crankcase explosion? ........................................................................................... 12

What action can be taken by the watch keeper when the vessel is in port to minimize their occurrence?

.................................................................................................................................................................... 12

Describe with the aid of sketches any mechanical devices designed to limit the violence of such an

explosion should it occur ............................................................................................................................ 12

Question Sr 4 2008, sr 4 2006 ..................................................................................................................... 16

State with reason the effect of the following ............................................................................................. 16

Increase fuel to the engine ......................................................................................................................... 16

Open exhaust gas boiler bypass.................................................................................................................. 16

Clean filter ................................................................................................................................................... 16

Reduced coolant flow through air cooler ................................................................................................... 16

Question Sr 4 2008, Sr 4 2006 ..................................................................................................................... 17

With reference to the scavenge spaces of main engines, give reasons for the following faults: .............. 17

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(a) Lubricating oil accumulation. ................................................................................................................ 17

(b) Scavenge fires. ...................................................................................................................................... 17

(c) Water accumulation.............................................................................................................................. 17

(d) High air temperature. ........................................................................... ................................................ 17

Question Sr 6 2009, Serial 11, 10 2008 ....................................................................................................... 20

Discuss the properties required by L.O for use in; ...................................................................................... 20

Auxiliary diesel engines, .............................................................................................................................. 20

Stern tube bearings, .................................................................................................................................... 20

Refrigeration compressors .......................................................................................................................... 20

Give reason for the differing properties of the oils recommended for these three purposes. ................. 20

Question ...................................................................................................................................................... 24

Describe the action you as watch keeper would take and outline possible reasons for failure in both thefollowing cases:- .......................................................................................................................................... 24

(a) The auxiliary diesel engine fails to turn on starting air,........................................................................ 24

(b) The engine turn on starting air but fails to fire. .................................................................................... 24

Question Sr 12 2010 .................................................................................................................................... 26

Describe the process of replacing the cylinder liner in an auxiliary engine. How is water tightness

ensured and what precautions are taken before commissioning the engine? .......................................... 26

Question Sr 2 2009 ...................................................................................................................................... 28

Describe the procedure for taking M\E crankshaft deflection, explaining all precaution that must beobserved. .................................................................................................................................................... 28

Explain what deflection reading actually mean and suggest the action which must be taken should

readings be outside values recommended by the engine manufacturer? ................................................. 28

Explain what deflection reading actually mean and suggest the action which must be taken should

readings be outside values recommended by the engine manufacturer? ................................................. 30

Question Sr 11 2010 A) i) Describe, with the aid of a sketch, a hydraulically operated main engine

exhaust valve; ............................................................................................................................................. 33

ii) Explain the operation of this valve, stating how the design allows for expansion of the valve stem and

ensures that the valve closes. ..................................................................................................................... 33

b) State the materials used for exhaust valves, seats, and cages. .................................... .......................... 33

Question Sr 6 2009, ..................................................................................................................................... 36

Sketch and describe a device employed for continuous monitoring of the viscosity of heavy fuel oil being

supplied to a main engine. .......................................................................................................................... 36

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Answer. ....................................................................................................................................................... 36

13.Question Sr 6 2009, Sr 11 2005 .............................................................................................................. 38

With reference to a 2 stroke slow speed main propulsion engine air starting system ................... ........... 38

State, with reasons, Three safety features incorporated in an air starting system.................................... 38

State with reason why an engine may fail to turnover on air. ................................................................... 38

Explain how the cause of an engine failing to turn over on air may be determined. ................................ 38

14.Question April 2010.Sr No 8 2005 ......................................................................................................... 42

With reference to auxiliary engine fuel pumps: ......................................................................................... 42

a) Explain how a fuel pump, may be checked for accuracy of injection timing; ........................................ 42

b) Describe how fuel pump timing may be adjusted after overhaul; ..................................... .................... 42

c) Explain the circumstances in which it is considered necessary to replace a fuel pump. ........................ 42

15.Question April 2010. .............................................................................................................................. 46

Select the correct statement and explain ................................................................................................... 46

An explosion in the high pressure air pipe line can be due to .................................................................... 46

Cylinder air starting valve not opening ....................................................................................................... 46

Cylinder air starting valve leaking ............................................................................................................... 46

Wrong timing of opening of air starting valve. ........................................................................................... 46

Question Sr 7 2007, ..................................................................................................................................... 48

a) Describe, with the aid of a sketch, a piston for a large slow speed crosshead engine. ......................... 48

Qb- State, with reasons, the materials used for different parts of the piston described above including

ring material. ............................................................................................................................................... 48

Qc- Compare the relative merits of water and oil cooling for a piston ...................................................... 48

Question Sr 2 2010, Sr 4 2007 ..................................................................................................................... 59

With reference to charge air coolers .......................................................................................................... 59

Describe with the aid of a sketch, a charge air cooler; ............................................................................... 59

Describe the procedure for cleaning both air and watersides of a charge air cooler; ............................... 59

State the importance of maintaining correct charge air temperature. ...................................................... 59

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Question Sr 1 2011. Sr 6 2008,

Explain why it is necessary to heat heavy oil before burning it in the

Cylinder Of an internal combustion engine.

Describe the effect on engine condition and performance due to

excessive heating of fuel oil.

Precaution during maneuvering on heavy oil.

Explain why it is necessary to heat heavy oil before burning it in the Cylinder Of

an internal combustion engine.

Heating is required in order to reduce the viscosity at the injectors to

approximately that of diesel oil. This ensures good atomisation and brings the

temperature of the fuel closer to the ignition point.

Heating the fuel helps separate solid and liquid contaminants in tanks and incentrifuges, and allows it to flow readily from the tanks to fuel manifold where

the final heating for injection takes place.

Describe the effect on engine condition and performance due to excessive

heating of fuel oil.

Too high a temperature has adverse effects by reducing penetration and causingdeposits to be left on nozzle tip affecting atomisation.

The most significant problem, however, is the fouling of fuel injectors, exhaust

ports and passages and the turbocharger gas side due to failure to burn the fuel

completely.

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Other problems arise from these heavier fuels are engine knocking, after burning,

uneven burning, variations in ignition delay, and a steeper ignition pressure

gradient. These factors contribute to increased fatigue of engine components,

excessive thermal loading, increased exhaust emissions, and critical piston ring

and liner wear. The long-term effects on the engine are a significant increase in

fuel consumption and component damage. The greatest fouling and deposit

build-up will occur when the engine is operated at reduced or very low loads.

Precaution during maneuvering on heavy oil.

Inform wheel house that engine is maneuvering on heavy oil [possibility of

missing kick, starting is sluggish]

Viscosity of oil and temperature to be properly maintained.

Make sure boiler is running

Service tank to be drained to avoid vapour lock due to water entry.

Tracing steam has to be kept on.

Fuel valve should be on recirculation.

Longer stoppage should be avoided, give intermittent kick.

Compression temperature is higher, by keeping JCW at high level.Question Sr 1

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2011. Sr 6 2008, Sr 4 2006

Describe ANY Arrangement used in connection with an IC engine for the

recovery of heat from exhaust gases

State the temp of the gas at the cylinder exhaust passage and entering

and leaving the equipment described Turbo Charging

Qb- Describe ways of using energy from the main engine other than for

main propulsion

Exhaust Gas Economiser

Fresh Water Generator

Turbo charging uses energy in the exhaust gas, including heat energy, to drive a

turbine wheel which in turn drives a compressor to pressurize the air used in

scavenging the engine cylinders and to provide the mass of oxygen required for

the following combustion cycle.

The efficiency of the process can easily be seen by noting the drop in temperature

of the exhaust gas across the turbine. About 35% of the energy supplied by the

fuel is lost in the exhaust gas, turbo charging reclaims 7% and has helped in

boosting the efficiency of the modern diesel engine to around 50%.

The exhaust gas economiser is situated in the uptake and is a heat exchanger

which consists of a row of tube banks circulated by feedwater over which the

exhaust gases flow.

The tube banks can be arranged to provide feed heating, steam generation and

superheating.

A boiler drum is necessary for steam separation to take place, and it is normal to

use the drum of an auxiliary boiler.

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Provision is made for by passing the economiser by the use of dampers during

stand by and for steam production control, and the system will also be fitted with

a method of dumping excess steam to a condenser and a safety valve.

Although designers have attempted to regain a maximum amount of waste heatby this method, care must be taken not to reduce the velocity of the exhaust gas

by too much (soot deposits and risk of fire) or to cool the gas below its dew point

of approx 140° (acid corrosion)

The fresh water generator uses the heat energy carried away in the jacket cooling

water.

The cooling water leaves the engine at approximately 78 - 80°.

The Fresh water generator, which can be either a flash or boiling evaporator,

operates under a vacuum where the water supplied boils at about 60°. The

cooling water treatment used in the jacket water must benon toxic in case of

contamination of the raw water being supplied for evaporation.

Qb- Describe ways of using energy from the main engine other than for main

propulsion

Ans-

Power from the engine can be utilised to drive a shaft alternator.

This can be a constant speed device often driven through a speed up gear box and

clutch arrangement, or a variable speed device as used in modern 2 stroke slow

speed engines which employs thyrister controls to maintain voltage and

frequency.

Usually they cannot be run load sharing with the auxiliary generators except

during synchronisation.

Power is also used to drive engine driven pumps.

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Some engines have Lube oil and cooling water pumps driven from the main

engine.

Electrical standby pumps are usually fitted which can run instead of the engine

driven pumps, if not, a lube oil booster pump must be fitted for start up and shutdown.

Most engines utilising cylinder lubrication will have engine driven cylinder LO

pumps.

Before turbo charging became popular, two stroke engines were fitted with

engine driven Rootes Blowers or reciprocating scavenge pumps which were

methods of supplying low

Pressure high volume compressed air 2 stroke crosshead engines used to (and

some still do) utilize under piston scavenging where the underside of the piston is

used to boost the pressure of the scavenge air.Question Sr 6 2009, Sept 2006

Sketch and describe a fuel injector for a diesel engine.

State four parameter that indicate fuel injectors require immediate

overhaul.

Answer.

1. Fuel inlet pipe connection. 2. Valve head. 3. Union nut. 4. Valve body. 5. Thrust

spindle. 6. Thrust foot. 7. Spindle guide. 8. Nozzle tip. 9. Spindle. 10. Circulation

spring. 11. Thrust spring. 12. Outlet pipe connection for recirculation

The fuel valve consists of a valve head, union nut, valve body, and nozzle. Fitted

within the valve body are non ¬return valve with a combined slide/-valve, thrust

spindle with thrust spring, thrust foot, and spindle guide.

When the fuel valve is fitted in the cylinder cover, the valve parts are tightened

together by the pressure from the nuts being transmitted through valve head,

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non-return valve, thrust spindle, spindle guide and nozzle to the valve body,

which is pressed into the tapered bore in the cylinder cover. The union nut keeps

valve head and valve body together during dismantling of the fuel valve.

The spindle guide consists of spindle guide, thrust piece and spindle with cut-off slide. The spindle guide is assembled with a press fit.

The spindle is pressed against the tapered valve seat of spindle guide by the

action of the thrust spring, the spring pressure being transmitted through the

slotted thrust foot. The thrust spring determines the opening pressure of the

valve.

Optionally, an extra disc can be inserted to raise the opening pressure by 30 bar.

The non-return valve consists of hous¬ing, thrust piece, slide and spring. The non¬

return valve is assembled with a press fit.

The slide is pressed by the spring against the tapered valve seat inside the non-

return valve. In this position the head of the slide uncovers a small bore arranged

for circula¬tion purposes in thrust piece.

The operation of the fuel valve is as follows:

The electrical, fuel oil circulating pump circu¬lates preheated oil through the fuel

pump and fuel valve. In the fuel valve the oil pas¬ses through the central bore of

the valve head and continues to the thrust piece of the non-return valve, leaving

through the circulation bore of the latter. Thence the oil is passed through the

interior of the valve body to an outlet pipe on the side of the valve head.

The space round the tapered valve seat of the spindle is also filled with oil, but

the cir¬culating pump, pressure is insufficient to overcome the force of the spring

and lift the spindle.

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If, for some reason, valve spindle should not close during engine standstill, then

the closed spindle in the non-return valve will prevent the circulating pump from

pressing oil through the nozzle, and thus obviate the risk of the engine cylinder

being filled with oil.

When, at the beginning of the delivery stroke, the pressure has risen to about 10

bar, the force of the spring in the non-return valve will be overcome and spindle

pressed back against the shoulder of thrust piece.

When the spindle in the non-return valve is pressed upwards, the circulation bore

of the thrust piece is closed, and the oil passes the seat of the spindle and enters

the space round valve spindle seat in spindle guide. When the pressure has risen

to the preset opening value of the fuel valve, the spindle is lifted, and oil is forced

through the nozzle into the engine cylinder.

At the termination of the delivery stroke, first the valve spindle and then the

spindle in the non-return valve will be pressed against their respective seats, theinjection of fuel stops, and oil is again circulated through the valve.

State four parameter that indicate fuel injectors require immediate overhaul.

Repeated operation of the fuel injector will lead to weakening of the spring this

will allow the injector to open early, and at a lower pressure correct atomisation

and penetration into the combustion space will not occur as there is not sufficient

pressure energy for conversion in the atomisation holes. Repeated operation will

lead to erosion and enlarging of the atomization holes, accelerated by using fuel

contaminated with water or catalytic fines.

The holes will be of the wrong shape and size to allow efficient atomisation.

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Wear of the needle and nozzle seating will allow dribbling to take place, again

interfering with the pressure rise required to allow correct atomisation to take

place.

The first signs of defective atomisation may be noticing a drop in power from the

engine.

The colour of the exhaust from the funnel will darken indicating poor combustion.

Because atomisation and penetration is not correct and the fuel droplets larger

than they should be, afterburning may occur causing higher than normal exhaust

temperatures.

If allowed to continue over a period of time, fouling of the turbocharger will

occur, leading to a drop off in performance.

If defective fuel injection is suspected, then an out of phase card can be used to

show faults with the fuel injection. If confirmed, the injector should be changed as

soon as possible.

[Exhaust temp will be higher compared to other unit

Black smoke due to improper combustion

Sparking in funnel

Loss of power

R.P.M. fluctuate due to imbalanced engine

J.C.W. P.C.W. temp will increase due to after burning

Consequently, the unbalanced operation of the engine must be detected by the

sound and revolutions of the engine.

Reduce load cut off unit with excessive leak

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Stop engine and replace valve]

Question Sr 6, 4 2009, 2006

What are the causes for crankcase explosion?

What action can be taken by the watch keeper when the vessel is in port

to minimize their occurrence?

Describe with the aid of sketches any mechanical devices designed to

limit the violence of such an explosion should it occur

For an explosion to occur there must be oxygen, fuel, and a source of ignition.

The oxygen will be present in the air in the crankcase, the lubricating oil is the

fuel, and the source of ignition is usually an overheated bearing (although it can

also be anywhere two metals are rubbing together, or blow by on a trunk piston

engine)

The mixture of oil and air must be in an ratio that is within the range of inflammability; the splashing of the lubricating oil inside the crankcase breaks it

up into droplets or globules of widely varying size distributed in varying density

throughout the crank chamber.

The overall mixture strength is usually very weak and will not support

combustion.

However, if a hot spot exists, some oil will come into contact with it and will be

vaporized, circulate to cooler parts of the crankcase and there condense to form a

white mist of finely divided oil particles well mixed with air.

This mist is combustible within certain concentrations.

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If the mist should now circulate back to the hot spot in such concentrations, it will

be ignited and a primary or minor crankcase explosion will occur.

This explosion causes a flame front and pressure wave to accelerate through the

crankcase, vaporizing further oil droplets in its path.

The pressure shockwave may build up sufficiently by the time it reaches the

crankcase casing to rupture crankcase doors or panels, unless otherwise relieved.

If the pressure wave reaches an opening through which it can escape to the

atmosphere a suction pulse of lower magnitude but greater duration immediately

follows the pressure pulse.

This suction pulse can be responsible for drawing in a charge of fresh air to take

the place of that which has been burned by the initial explosion.

A secondary explosion or major explosion of such intensity as to cause

widespread damage then follows.

Fires are a distinct possibility as the secondary explosion will cause a fireball to

engulf the engine room. Engine room plates can be blown off, doors blown off.

Engine damage may be considerable. Damage to crankcase and doors and

running gear. Personnel if in the engine room will be injured or killed.

Before commencing of voyage

Lube oil pump should be started well in advance

Check sump sounding

Turn lubricator, increases lubrication for cylinder liners

Turn engine on turning gear observe motor amperes

Blow through engine on air

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Purifier to be kept running in port to remove water content

Ensure S.W. pump are running satisfactorily to cool lube oil

Check operation of standby pump and other pumps

Ensure that lube oil pressure is correct

Switch on O.M.D. if it is switched off

Precaution after finish with engine

All pumps including L.O. pumps are kept running

Lube oil camshaft, lube oil J.C.W. pump is kept running for atleast 2 hrs after finish

wuith engine auxiliary blowers stopped

Do not open crankcase doors for a minimum of 2hrs unit engine is completely

cooled down

When inspecting the crankcase.

Pay careful attention to all bearing, looking for evidence of sqeezed out white

metal, wiping etc.

Check all fastening devices.

Check for evidence of metal to metal contact (e.g. chain case and stuffing boxes,

liners for scuffing on trunk piston engines)

Check LO filters regularly for evidence of white metal.

Clean lenses on oil mist detectors regularly, calibrate and test. (every day)

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When a crankcase explosion occurs, flame speeds may reach 300mls with a

substantial rise in crankcase pressure. If this pressure is not relieved it can reach

several bar and result in the blowing off of the crankcase doors. This then allows alarge amount of air to be drawn in to the crankcase to fill the vacuum caused by

the so called primary explosion. The result is a high risk of a devastating

secondary explosion which can cause extensive damage, fire and fatalities.

To prevent this sequence of events, the explosion relief door prevents an

excessive pressure rise, and because it is a non return valve, stops air being drawn

back into the crankcase after the pressure has been relieved.

The explosion relief door is designed to limit crankcase pressure to 1.3bar. it

should be fully open at a crankcase pressure of 0.2bar. The flame trap dissipates

heat and prevents the flame trap from the explosion entering the machinery

space where they could cause injury to personnel and start an external fire.

Because it is a non return valve, the explosion relief door stops air being drawn

back into the crankcase after the pressure has been relived, thus preventing a

secondary explosion.

The spring loaded valve is of aluminum for low inertia. A non stick heat resisting

rubber O ring ensures positive sealing. The valve is designed to be fully open at a

crankcase pressure of 0.2bar.

A dome shaped flame trap of oil soaked wire gauze in Side the crankcase With a

free area equal of above that of the valve opening area is designed to dissipate

the heat from the explosion. A deflector shield secures the valve spring and

directs any gas emitted in a downward arc of 1200 where the damage caused will

be minimal.

Fitted to engines with bore of 200mm and above with a crankcase volume of

O.6m3 and above (one door at either end of crankcase). Engines with bore of

300mm and above.must have a door fitted to each crank throw compartment.

Free area of valve a min of 45cm2 and 115cm2 per.m3 of crankcase volume.

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Question Sr 4 2008, sr 4 2006

State with reason the effect of the following

Increase fuel to the engine

Open exhaust gas boiler bypass

Clean filter

Reduced coolant flow through air cooler

Answer

Increase fuel to the engine

Charge air pressure will increase because when more fuel is burnt in engine more

quantity of heat is available in exhaust ‘this heat is converted to K.E.

Hence turbocharger speed will increase and will suck more air

Open exhaust gas boiler bypass

Back pressure on turbocharger reduces by opening back pressure valve on

economizer finned tube

Finned tube give resistance to flow therefore back pressure increases

T\C outlet pressure increases

T\C. speed is reduced

Scavenge air pressure reduces

With economizer by pass open free flow of gas there fore less resistance hence

T\C. speed increases

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Clean filter

Air entry is unrestricted hence more air is sucked by blowers and given to engine

Pr drop reduces. Pr drop should not be more than 50mmwg

Charge air pressure increases

Reduced coolant flow through air cooler

Charge air pressure will drop because vol efficiency of T\C. reduces

Cooling efficiency of air cooler reduces and due to that voleffic of blower reduces

Air is not sufficiently cooled

Density of air decreases

Quantity of air supplied is reduced hencecharge air pressure will drop

Question Sr 4 2008, Sr 4 2006

With reference to the scavenge spaces of main engines, give reasons for

the following faults:

(a) Lubricating oil accumulation.

(b) Scavenge fires.

(c) Water accumulation.

(d) High air temperature.

Answer

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(a) Lubricating oil accumulation.

Leaky sealing rings in the piston rod gland as well as blocked drain pipes from the

piston underside will lead to an accumulation of system and cylinder lubricating

oil

Worn, sticking or broken piston rings.

Worn cylinder liner.

Individual cylinder lubricating quills are not working.

Damage to the running surface of the cylinder liners.

If one or more of these operating conditions prevail, residues, mainly consisting of

incompletely burned fuel and cylinder lubricating oil, will accumulate

(b) Scavenge fires.

With blow-by, hot combustion gases and sparks which have bypassed the piston

rings between piston and cylinder liner running surface, enter the space on the

piston underside.

In the same way backflow at the B.D.C. of the piston (gas pressure higher than

scavenge air pressure) can cause increased contamination.

Leaky sealing rings in the piston rod gland as well as blocked drain pipes from the

piston underside will lead to an accumulation of system and cylinder lubricating

oil and therefore to a major fire risk.

Worn, sticking or broken piston rings.

Excessive butt clearance

piston rings seized in liner.

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Fuel injector dripping

Incorrect fuel injection timing

(c) Water accumulation.

Cylinder liner cracked

Air cooler leaking

After cooler drain separator is chocked there fore condensate warter gets carried

away

Cylinder liner ‘o’ ring leaking

Water cooled piston seal leaking

(d) High air temperature.

Air cooler dirty

Air side fouled

Due to deposits dirt dust heat transfer efficiency is reduced and temp are higher

Hence pr difference across cooler will increase and at the same time temp

difference across air cooler reduces

Water side fouled

Circulation of water is less due to formation of scale, mud accumulation sea weed

blocking passages; partition plate is holed or corroded

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Question Sr 6 2009, Serial 11, 10 2008

Discuss the properties required by L.O for use in;

Auxiliary diesel engines,

Stern tube bearings,

Refrigeration compressors

Give reason for the differing properties of the oils recommended for

these three purposes.

Answer.

The crankcase oil in a trunk-piston engine is continuously exposed to combustion

products as the impurities which mix with the cylinder lubricating oil, work down

past the piston rings and contaminate the crankcase oil.

The impurities which contaminate the crankcase oil are

(i) Incombustible elements of fuel oil,

(ii) Carbon particles,

(iii) Dust from the suction and scavenge air,

(iv) Minute metal particle from either the cylinder wall or piston rings,

(v) Products of incomplete combustion of the air-fuel mixture and

(vi) Sulphuric acid due to high sulphur content in the fuel.

Condensed water vapour or water from cooling system may also find access to

crankcase.

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Unburnt fuel dilution of lubricating oil is also to be taken into considerations along

with high temperature oxidation of lube oil.

So the lubricating oil in the crankcase of a trunk-piston engine must have high

detergency and dispersivity property.

The additives are to be added to break the insoluble particles in one colloidal part

so that they remain in suspension. Anti-oxidation property to be imparted by

adding additives to combat high temperature oxidation.

The Base Number i.e. alkalinity reserve must also be kept high in crankcase

lubricating oil in trunk-piston engines in order to neutralize the sulphuric acid to

prevent corrosion.

Thus crankcase lube oil for a trunk-piston type engine must have good properties

of alkalinity, detergency, dispersancy and oxidation stability

Stern tube lubricant

To perform satisfactorily, however, the lubricant must have the correct viscosity

to flow properly under gravity head without excessive rapid flow that would

result in high consumption; must minimize wear under the heavy loads

encountered in the bearings; must protect the bearings and other components

from corrosion and must emulsify with any seawater that passes the seals in

order to maintain lubricating characteristics and minimize corrosion.

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Water based stern tube lubricants having the advantages of oil but with a more

eco-friendly face.

These lubricants must have an adequate viscosity, resistance to sea water

contamination as well as biodegradability.

They typically have a water content greater than 90% and are highly soluble.

Friction is reduced in comparison to equivalent mineral oil/white metal bearing.

Other benefits include increased heat transfer rates and better protection against

galvanic corrosion of dissimilar metals found in the shaft/prop arrangement. The

fluid has no measurable flash point.

Refrigerating machinery

It should be free from moisture to prevent corrosion and freezing @ expansion

valve. Oil kept in open has a tendency to absorb moisture from the atmosphere,

so use oil from sealed can.

Low pour point (-32degC) to remain fluid with good lubricating properties @ the

lowest temperature in the system. Pour point depressant additives help to lower

the pour point.

Wax free to prevent formation of solid and thickening of oil. Wax deposits on

regulating valve interfere with operation.

Easily separable from refrigerant to return oil carried over from compressor back

to c\case. Oil carried over the circuit could congeal on the evaporator coils, so

drastically reducing heat transfer rate.

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High flash point to prevent vaporisation @ compressor point.

No reaction with refrigerant and metal construction.

Flurogenated ref in liquid form being miscible with L.O has a thinning effect. High

viscosity

Properties ideal for gear case

High film strength to prevent metal to metal contact. Hence, high viscosity

adhesive to resist sliding and centrifugal forces

Corrosion protection

Cooling

Reduces friction

Good low tempo viscosity

Good high tempo viscosity

The thicker the oil film the greater the cushioning against shocks.

Also less tendency for pit formation by hydraulic action in cracks,

Sound damping properties with cushioning effects

Antifoam properties

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Question

Describe the action you as watch keeper would take and outline possible

reasons for failure in both the following cases:-

(a) The auxiliary diesel engine fails to turn on starting air,

(b) The engine turn on starting air but fails to fire.

ENGINE REFUSES TO START ON AIR.

CAUSES.

1. Starting air valve not opening.

2. Master air valve not open sufficiently.

3. Faulty setting of valve gear.

4. Leaky st1rtillg air valve.

WHERE TO LOOK.

Starting air valve.

Master air valve.

Valve gear.

Feel all starting air valve, pipe and listen for leak.

REMEDY.

Test opening of the valve.

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Test amount of opening.

Check setting of valve gear. Also roller and cam clearance.

Regrind starting air valve as soon as possible.

ENGINE START ON AIR, BUT REFUSE TO PICK UP FIRING.

CAUSES.

1- Valve open.

2. Fuel system air locked.

3. Filter choked.

4 Fuel injector filter choked.

5. Fuel pump incorrectly set.

6. Fuel oil too thick.

7. Level of oil in service tank too low.

WHERE TO LOOK.

1- Inlet or exhaust valve.

2- Fuel pipes.

3- Fuel filter.

4- Fuel injector.

5- Fuel pump timing gear.

6- In cold weather.

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7- SERVICE TANK GAUGE.

REMEDY.

1- Examine valves and free. If seating properly valve face may be defective.

2- Prime fuel pumps and test.

3- Turn on No.2 filter and clean No. 1 at once. Remove filter,

4- Fit spare and clean return to store.

5- Reset fuel pump.

6- Circulate fuel system with hot oil or oil of lower viscosity.

7- Refill service tank and prime fuel pump.

Question Sr 12 2010

Describe the process of replacing the cylinder liner in an auxiliary

engine. How is water tightness ensured and what precautions are taken

before commissioning the engine?

The following describes the removal of a sulzer ZA40 cylinder liner.

All lifting equipment is examined to ensure it is in certification and free fromdefects.

The cooling water will have been drained from the jacket prior to removal of the

cylinder head and piston.

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Assuming the piston and con rod withdrawn, leaving bottom end bearing in

engine.

Cylinder lubricators are disconnected.

The bolt securing the centering piece, which locates the liner in the correct

position in the cylinder, bore is removed.

The liner must be jacked off its seating using a hydraulic jack.

In case of ZA 40 the jacking device is bolted to the crankpin bearing and the

crankpin turned to TDC.

The hydraulic pump connected to the jack locates in the bottom of the liner.

The liner is jacked upwards until the liner moved off its seat.

The liner-lifting tool is bolted on to the top of the cylinder liner and hooked up to

the E\R crane; the liner is then carefully removed from the engine.

The J.C.W. space around the liner is inspected for overall condition that can

indicate the effectiveness of the cooling water treatment.

The guiding bores in the entablature and O-ring seating are cleaned and examined

for evidence of corrosion\erosion and the landing face for the cylinder liner is

cleaned and examined.

The new liner is cleaned, inspected and gauged to ensure it is within limits

specified by wartsila.

Landing and sealing faces are inspected to ensure they are free from damage.

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Lubrication drillings are blown through with compressed air to ensure they are

clear, the lifting gear is attached and the liner is tried in the entablature with out

O-rings to ensure that it fits without binding.

Question Sr 2 2009

Describe the procedure for taking M\E crankshaft deflection, explaining

all precaution that must be observed.

Explain what deflection reading actually mean and suggest the action

which must be taken should readings be outside values recommended

by the engine manufacturer?

Answer-

Safety precautions to be observed when taking crankshaft deflection are as

follow;

Carry out a risk assessment procedure, most companies now have this preloaded

on a computer in the form of a checklist, it will include;

Permission granted to immobilize engine.

Starting air shut off and locked off.

Open the indicator cocks.

Engine cooled down sufficiently to allow LO pumps to be shut down.

On large engines where it is possible to climb inside the crankcase or to put head

and shoulder inside while working, it should be treated as an enclosed space, and

a permit to work is required.

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Ensure that no one else is working elsewhere on the engine (e.g. cleaning the

scavenge space).

Check that no one is working in the vicinity of the shafting system, and that the

bridge has confirmed that it is OK to turn the engine.

If deflection is being taken after working on the engine ensure that all tools and

lifting gear are removed from the engine.

Only person in charge of operation is to operate the turning gear.

Deflection is taken by placing a dial indicator or a remote reading gauge into a

pop marked position between the two crank webs of a crankshaft throw.

When the crank throw is at BDC the con rod will be in way of where the dial

indicator should fit, for this reason a deflection cannot be taken at BDC.

Instead the crankshaft is turned until it is just past BDC and the dial indicator

fitted.

The position is adjusted to read zero,

The engine is then turned, and the gauge reading taken when the engine is 90deg

before TDC, TDC, 90deg after TDC and then lastly just before BDC.

This procedure is carried out on every unit and recorded

The two reading taken either side of BDC are averaged to give the reading at BDC.

It is normal practice to turn the engine to just after the gauge position and then

reverse the turning gear to negate the lifting effect of turning gear.

It is important that the crankshaft journals are sitting on the bottom end bearing

shells when taking the readings; this can be checked using feeler gauges.

The reading are recorded on a chart as shown

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UNIT NO 1 2 3 4 5 6

(A) BDC (1).

(B) PORT.

© TDC.

(D) STBD.

(E) BDC (2).

(F) A\2 + E\2.

C – F.

B – D.

The vertical deflection is the reading at TDC minus the average of the two BDC

readings; the horizontal deflection is the port reading minus the stbd reading.

Question

Explain what deflection reading actually mean and suggest the action

which must be taken should readings be outside values recommended

by the engine manufacturer?

Ans-

If a crank throw is supported between 2 bearings of equal height, then the weight

of the running gear will open and close the crank webs.

Therefore if the bearings are of equal height and perfectly aligned, the crank webs

will open and close as the engine is turned.

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When the engine is first installed in the ship and the ship is afloat, the alignment

of the bearings is checked and a set of deflection readings taken, these are

recorded in the engine documentation.

If the bearing are out of alignment either horizontally or vertically, then thesedeflections will alter as the crank shaft bends to sit down in the bearings, if this

bending becomes excessive (indicated by excessive deflections) then operating

the engine may overstress the crankshaft leading to fatigue failure.

By comparing the deflections obtained with the original readings, it can be

determined whether this bending is within acceptable limits.

If the deflections are found to be outside the laid down parameters, then the first

thing to do is to check that the reading taken were correct by re taking them.

If the reading has been taken after work on the main bearings (i.e. fitting new

bearings), then the job must be re- examined; perhaps the wrong type of shell has

been fitted.

The most obvious cause of excessive deflections is uneven bearing wear down,

however, incorrect cargo loading, differential hull temperature, collision,

grounding and fretted chocks can all cause distortion of the engine bedplate and

thus bearing misalignment.

If the deflections are excessive, then ensure the cause is not one of the easily

rectifiable causes (i.e. incorrect loading of cargo).

Next, the bearing wear down must be checked, and if found to be uneven,

rectified.

If these are OK then it may be due to one or more severe reasons, it is at this

point that consultation with engine builder, and superintendence may berequired.

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It may be possible to operate the engine at reduced load until the cause can be

more fully analyzed and steps to rectify the problem investigated.With reference

to exhaust valves for large slow speed engines;

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Question Sr 11 2010A) i) Describe, with the aid of a sketch, a

hydraulically operated main engine exhaust valve;

ii) Explain the operation of this valve, stating how the design allows for

expansion of the valve stem and ensures that the valve closes.

b) State the materials used for exhaust valves, seats, and cages.

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The sketch shows a hydraulically operated exhaust valve as fitted to a large slow

speed engine. The main parts of the valve casing are of cast iron and water cooled,

there being no particular strength requirement for this part. The water-cooled cast

iron exhaust valve cage with replaceable seat is located in the center of the cylinder

head. This allows for removal from the cylinder head, giving ease of maintenance.

The valve is circulated with cooling water from the main engine jacket water-

cooling system; this reduces the thermal stress and prolongs the valve life. It is the

seat area, which is subject to high temperatures and wear, hence the use of better

materials. The seat is detachable in order to allow removable for machining and

replacement. Large exhaust valves are provided with detachable seats made form

molybdenum steel. The exhaust valve spindle which is designed to open inwards

into the engine is located in a replaceable air cooled lubricated valve guide pressed

into the valve cage. A valve spinner is fitted to the spindle, which rotates the

exhaust valve as the gas passes through it. , This gives even temperature

distribution and wear, also prevents the build up of deposits. With modern fuels,

vanadium and other deposits can build up on valve faces leading to damage. These

deposits can be hammered into the seating faces. If the valve is rotated and reseats

in a different place then the same damage does not occur. Rotating the valve also

prevents localized overheating due to a faulty atomizer. If the valve is set spinning

and is still rotating as it reseats a light grinding action takes place. This removes

deposits and ensures a good seal. Spinners on the valve stem upon which the

escaping exhaust gas acts induce such rotation. To allow for this effect the

frictional effect of the springs and valve/cover must be removed. The removal of

springs means that a closing force by some other means is required. Air springing

can be used. This consists of a piston fitted to the valve stem below the hydraulic

unit. As the valve opens air below the piston is compressed and this compression

provides the upward force of closing the valve. The space above the piston is

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vented to atmosphere and the pressure below the piston maintained at 7 bar from

an air supply via a non-return valve. Ensuring positive closing of the valve. The

hydraulic operating piston mounted on the top of the spindle closes into a damping

pin. The adjustable clearance between the bottom of the damping pin and the top of

the piston allows for expansion. Thermal expansion is accounted for by allowing

the oil to escape at a relief valve on the pump unit. The opening face is always

axial.

A hydraulic pump operated by the exhaust cam supplies the hydraulic oil to

operate the valve. A small permanent vent ensures the air is excluded from the

system. The leak off of oil is returned to the air spring cylinder for lubrication and

is then drained away. The hydraulic pump is supplied with a make up supply via a

non-return valve and a relief valve. . (Oil loss is made up at the pump unit from the

cam lube oil supply system)

ii) The valve is operated by means of hydraulic system, a high pressure pump

driven from the main engine camshaft as the cam rotates in time with the cam shaft

it lifts the plunger on the hydraulic pump and delivers oil at a pressure of around

150 BAR via double skinned high pressure pipe (The hydraulic pipe must be

sheathed to avoid the risk of fire in the event of pipe failure.) to a piston situated on

top of the valve spindle, Oil displaced by the pump plunger displaces the exhaust

valve operating piston, moving it and the exhaust valve spindle downwards against

the air spring pressure and opening the exhaust valve. Allowing exhaust gas to be

blown out, as it passes the vanes, rotating the exhaust valve when the cam

operating the H.P pump has passed its travel, the pressure will drop rapidly, the

valve will now close with the aid of compressed air. This air is supplied from the

main engine starting system via a reducing valve that reduces the compressed air

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pressure to around 7 BAR. As the operating piston enters the damping pin, the

closing is slowed down, thus preventing hammering of the valve.

(An additional advantage with this system is that when the engine is stopped the

valves will all close after a short delay. This prevents the flow of cool scavenged

air through units, which with a rocker system would otherwise be open. Preventing

this allows all cylinders to be equally warm and stops the rotation of the turbo

blower, which can occur.)

b) Materials used for valves, seats and the cage are as follows;

The exhaust valve spindle is either manufactured from heat resisting alloy steel

With a layer of satellite welded onto the seating face or the valve head is made

from nimonic alloy, which is friction, welded to an alloy steel spindle

The valve seats are manufactured from surface hardened molybdenum steel.

The exhaust valve cage is of pearlite grey cast iron or in some case cast steel.

Question Sr 6 2009,

Sketch and describe a device employed for continuous monitoring of the

viscosity of heavy fuel oil being supplied to a main engine.

Answer.

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The sketch shows the operating principle of a viscose’s, a device to measure and

control the viscosity of heavy fuel oil.

The sensor is suspended in the oil being measured by screwing the device into a

tapped hole in a stub pipe.

The system uses the principle that the damping of a vibration signal is proportional

to the square root of the viscosity. Not affected by vibrations or pressure and flow

fluctuations.

No moving parts to wear out.

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The sensor comprises of a stainless steel pendulum attached to a base plate via a

torsion tube.

Two piezo elements are driven by an alternating signal causing the pendulum to

vibrate.

A second set of elements sense the torsional vibration via a feedback, and a

processor measures the phase difference between the transmitted and received

signals.

This phase difference is processed which results in a value proportional to the

square root of the fuel oil’s viscosity.

13.QuestionSr 6 2009, Sr 11 2005

With reference to a 2 stroke slow speed main propulsion engine air

starting system

State, with reasons, Three safety features incorporated in an air starting

system.

State with reason why an engine may fail to turnover on air.

Explain how the cause of an engine failing to turn over on air may be

determined.

Answer

Lloyd’s regulations state:

“The starting air piping air system is to be protected against the effects of

explosions by providing an isolating non return valve or equivalent at the starting

air supply to each engine."

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This is to prevent a pressure wave/flame front going back to the main air receivers,

where a catastrophic explosion may take place (ref. M474 Cape Town Castle)

"In direct reversing engines bursting discs or flame arrestors are to be fitted at the

starting air cylinders on each cylinder"

This is to prevent flame from combustion in the cylinder, due perhaps to fuel

leakage into the cylinder, traveling back into the air start line when starting air is

being admitted to the cylinder.

In addition to this some large slow speed engines are fitted with a pressure relief

valve midway down the air start manifold to vent an excess of pressure.

Non-Return Valve

This may be incorporated into the automatic valve. As implied it will close when

the pressure in the air start manifold exceeds the pressure in the air start valve.

It is to prevent an explosion in the air start line, due perhaps to an air start valve

jamming open whilst the engine is firing, going back to the air start bottle.

Relief Valves

Simple spring-loaded relief valve. To relieve an excess of pressure in the air start

manifold. Should be regularly overhauled, set and tested.

Flame Traps

One per cylinder adjacent to air start valve on a reversing engine. On a non-

reversing engine such as an auxiliary engine only one need be fitted between the

air start manifold and the automatic valve.

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To prevent flame from cylinder reaching air start line and possibly igniting any oil

present if the air start valve sticks open. Bursting disks can be fitted in lieu of relief

valves.

(b) State with reason why an engine may fail to turnover on air.

Main Air Start valve closed: - operator error.

Turning gear engaged, or if disengaged, the air operated interlock switch my not be

venting.

If a CPP is part of the installation the pitch may not be set to. Zero (an interlock)

On a reversing engine, the camshaft may not be in the correct position for the

direction required.

The air start pilot valve for the particular unit receiving air may be sticking shut;

the engine will therefore have a "dead spot"

The engine is not receiving the start signal from the bridge or control room

Explain how the cause of an engine failing to turn over on air may be determined.

Always check the simplest cause first. When preparing an engine for sea, it is usual

to blow the engine over using compressed air before shutting the cocks. It is here

that the problem may manifest itself. Check that the isolators on the correct air

receivers are open and that the automatic valve is in the automatic position. Check

that the turning gear is out and that no interlock warning lights are showing. On a

unidirectional engine fitted with a CPP check that the pitch is at zero. On a

reversing engine check that the camshaft is in the correct position for the direction

required. Now the engine should turn when the automatic valve is operated by

hand. If not then the fault will probably be with the pilot valve for a particular unit.

It is not unknown, because of moisture in the air for these to corrode and stick.

Note the position of the flywheel (mark with chalk), turn the engine so another

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piston has just come over TDC, disengage turning gear and try again. If the engine

now turns when operating the automatic valve manually, try again from the control

room.

If the engine will start locally, but not from the control room or the bridge, then the

fault must lie with the air signal to the automatic valve. The investigation from

here must follow a logical series of steps with the help of the manual and the air

start drawings

Engine systems vary, but basically a pneumatic or solenoid valve allows an air

signal to operate the main automatic valve. At the same time an air signal allows

air to the air start distributor, which will allow the cylinder valves to open in the

correct sequence. Before the air signal can reach either of these devices, switches,

either electrical or pneumatic relays, must confirm that the previously mentioned

interlocks are clear and that the camshaft is in the correct position.

Some engine builders include a faultfinding system, which involves checking the

air start relays, which are all together in a box by the engine side local controls. An

indicator will show which relay valves are open and these are checked off against

the faultfinding list.

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14.Question April 2010.Sr No 8 2005

With reference to auxiliary engine fuel pumps:

a) Explain how a fuel pump, may be checked for accuracy of injection

timing;

b) Describe how fuel pump timing may be adjusted after overhaul;

c) Explain the circumstances in which it is considered necessary to

replace a fuel pump.

Answer-

Depth gauge\micrometer

With a jerk type fuel pump, injection starts when the top edge of the plunger cuts

off the spill ports as the plunger is moving upwards on the delivery stroke.

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To check the accuracy of the start of injection, the engine crank angle for the start

of injection must correspond to the manufacturers setting when the plunger is at

this point.

On some pumps it is possible, after isolating the fuel and draining the pump, to

remove erosion plugs and sight through the spill ports while turning the engine.

At the point where the edge of the plunger is seen to cover the top of the spill port,

the crank angle for that particular unit is noted and compared with the

manufacturer’s recommendation.

Small pumps mounted in a block can be set using spill timing, where the HP

delivery pipe is exchanged for a U pipe led to a receptacle.

With the rack turned to maximum and the fuel open to the pump (delivery valve

removed) the engine is turned until the flow of fuel into the receptacle is cut off by

the plunger (start of injection).

Larger pumps can use compressed air to establish when the plunger has cut off the

spill ports.

On other pumps it may be necessary to remove the top cover of the pump and

delivery valve and measure the distance from the top of the barrel to the top of the

plunger.

The manufacturer will give the correct distance at which the plunger has covered

the spill ports.

Alternatively the distance to the top of the plunger when the unit is on TDC may

be given.

b) Describe how fuel pump timing may be adjusted after overhaul;

Once the pump has been bolted down on the engine, and the fuel quantity rack

connected to the fuel control shaft, remove the erosion plugs, adjust the rack to the

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zero position and by sighting through the spill ports ensure that the no load groove

is lined up.

The timing must be checked. The method of doing this will vary from engine to

engine, but basically entails ensuring that the top edge of the plunger covers the

spill ports at the crank angle specified by the engine manufacturer. The distance

between the top of the barrel and the top edge of the spill ports is known, so once

the engine has been turned to the correct position, a measurement using a depth

gauge can be made from the top of the barrel to the top of the plunger.

(Measurement A) To enable this measurement to be taken will entail removing the

delivery valve and/or plugs in the top of the pump assembly. Adding or removing

shims from under the pump body or between the cam follower and plunger, or by

adjustment of the VIT rack makes adjustment.

A fuel setting is then put on the pump. This will vary from manufacturer to

manufacturer, but will be about 80%. The engine is turned ahead until the edge of

the helix on the fuel pump plunger just cuts the spill port. The distance between the

top of the plunger and the top of the barrel is again measured (measurement B).

The effective stroke is then defined as A . B.

It is also normal to check the idle stroke, which is the distance, moved by the

plunder before the spill ports are closed by the edge of the plunger. This is done by

turning the engine so that the follower is on the base circle of the cam and

measuring the distance from the top of the plunger to the top of the barrel

(measurement C) The idle stroke is C- A.

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If the engine is turned so that the follower is on the peak of the earn and the

distance between top of plunger and top of barrel again measured (measurement D)

then actual stroke is C - D. This is none adjustable and fixed by the lift of the cam.

On some engines the top of the pump and delivery valve is removed and replaced

with the setting jig, which allows air to flow via a nozzle to the top of the plunger.

A dial indicator to measure the plunger stroke is fitted to the top of the plunger.

The rack is set to the maximum position. The engine is turned until maximum air

pressure is reached on the setting gauge. The engine is turned back and then ahead

until the pressure on the setting gauge is half the maximum pressure. This shows

the top edge of the plunger has just covered the spill ports. The Dial indicator is set

to zero. The engine is now turned ahead and the pressure gauge observed. It should

reach maximum pressure and then fall back to half pressure just as the edge of the

helix is about to uncover the spill ports. The dial indicator is read at this point

which will give the effective stroke of the plunger. Adjustment of the rack position

is by adjustment of a clamp ring around the rack.

After these measurements have been checked and adjusted as necessary, replace

the erosion plugs and other components removed and secure with locking wire as

required.

Explain the circumstance in which it is considered necessary to replace a fuel

pump

After prolonged operation the jerk type fuel pump will wear on the top edge of the

plunger, on the edge of the helix and the edge of the spill ports, this is due to

erosion by the high-pressure fuel as it spills back.

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The result of this will be late start of injection.

The timing of the fuel pump may be advanced to compensate for the lateness of

injection and small adjustment to the individual fuel rack may be possible to

compensate for late end of injection, ensuring that the pump is still zeroed when

the engine is stopped.

Abrasive particles in the fuel due to poor filtration\purification (esp. catalytic fines)

will cause scoring of the plunger allowing fuel to leak back to the suction side.

The pump will take longer to build up to injection pressure, retarding the injection

timing and delivering less fuel.

When either of these situations has reached the point beyond which adjustment can

adequately compensate for wear, the fuel pump must be changed.

This point can be established by inspection and comparison of the out of phase

diagram for the particular cylinder, or by comparing peak pressure together with

fuel rack setting and exhaust temperatures with previous readings and other units.

15.Question April 2010.

Select the correct statement and explain

An explosion in the high pressure air pipe line can be due to

Cylinder air starting valve not opening

Cylinder air starting valve leaking

Wrong timing of opening of air starting valve.

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Cylinder air starting valve not opening

False because if valve is not opening at all hot gases of combustion cannot enter

the high pressure air pipe, hence explosion cannot take place.

Correct answer is Cylinder air starting valve leaking

Should a cylinder air start valve leak during operation un-burned fuel and cylinder

oil may enter the manifold

This oil along with oil film already present will carbonize with further heating to

form incandescent carbon (glowing flakes).

If starting air is now applied while it is hot an explosion may occur causing flames

to pass along the air pipe.

Wrong timing of opening of air starting valve.

There is every possibility that valve will open at wrong crank angle and during this

if firing of fuel takes places and combustion gases enter high pressure air line and

causes explosion quite possible in sulzer engine because both air and fuel are given

at same time

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Question Sr 7 2007,

a) Describe, with the aid of a sketch, a piston for a large slow speed

crosshead engine.

Qb- State, with reasons, the materials used for different parts of the

piston described above including ring material.

Qc- Compare the relative merits of water and oil cooling for a piston

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The working piston consists basically of:

Piston crown 1,

Piston skirt 3,

Piston rod 5,

The oil cooling components and piston rings 2.

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Piston crown and piston rod are joined by ten elastic bolts 9.

Piston skirt 3 is directly screw fastened to the piston rod 5.

Piston rod 5 is fastened to crosshead pin 8 in a particular position.

A compression shim 7 is fitted between them, its thickness being adapted to the

compression ratio.

All piston rings have to be fitted with the marking TOP' upwards.

Piston cooling

The piston crown 1 is cooled by bearing lubricating oil. The piston cooling oil 'KO'

is fed from crosshead pin 8 into the two inlet slots 'EN'. From here it flows outside

the oil pipe 6 (arranged in the piston rod 5) till spray plate 4.

The cooling oil is sprayed into the cooling bores of the piston crown through

nozzles in the spray plate.

From there the oil 'OR' flows through oil pipe 6 into the crosshead pin from where

it emerges sideways.

The circulation of coolant (oil) ensures a lower working temperature of the ring

groove zone and thus reduces tendency for thermal distortion.

The piston is cooled by circulation of lubricating oil treated with a rust and

corrosion inhibitor.

Oil is forced through telescopic pipe via the crosshead and piston rod to an annular

space around the ring groove.

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The discharge ports are so made that a circulatory motion is created in the space.

The flow moves along the walls of the convex contour of the crown, thus ensuring

a high velocity flow of coolant past the surface under the influence of high

temperature.

Cooling of piston is very efficient and a temperature of 110 deg C at the ring zone

is claimed the supply of oil is effected through a separate piston cooling line.

The return is collected at a collector where flow and temperature indicators are

provided.

The crosshead is of forged steel and is provided with steel cast guide shoes with

white metal on the running surfaces.

A bracket for oil inlet from the telescopic pipe and a bracket for oil outlet to slit

pipe are mounted on the crosshead.

The materials used for different parts of the piston

Piston crown; - Chrome molybdenum steel.

Maintain strength and resists corrosive \ erosion at high temperature. As previously

stated, this piston has a layer of inconel welded to the hottest part of the crown.

Skirt; - Cast iron.

Cast iron contains graphite, a lubricant.

In theory the skirt should not touch the liner, in practice it does.

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Cast iron has good retention qualities, and its rate of expansion is the same as the

liner in which it runs, allowing minimal clearances.

Rings; - Rings are harder than the liner in which they run, to give them a

reasonable life.

Pearlitic grey cast iron containing molybdenum, chromium, vanadium titanium,

nickel, and copper.

PISTON COOLING MEDIUMS

Choices -Either water, preferably distilled, or oil.

Distilled Water

Advantages

- High specific heat capacity.

- High available temperature rise. (14o)

- Relatively small capacity required.- Generally lower piston temperatures possible.

Disadvantages

- Risk of crankcase leakage.

- Corrosion and scale treatment required.

- Complex gland system required.

- Closed telescopics to and from piston.

- Usually requires air cushioning system.

- Usually separate from main cooling system so extra pumps,

coolers, etc. required.

Oil

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Advantages

- Crankcase leakage not a problem.

- Simpler glands possible.

- Can be combined with main L.O. system.

- Telescopics or swinging links to crosshead only.- No corrosion or scale problems.

Disadvantages

- Relatively low specific heat capacity, (½ that for water)

- Temperature limited due to risk of coking.

- Increased L.O. system size to al

Question April 2010.

Describe, with the aid of a sketch, the air start valve for a large slow speed diesel

engine

Answer-

The Air Start Valve shown is from a slow speed MAN-B&W two stroke engine.

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Fitted into the cylinder head, it is opened by control air from the starting air

distributor.

Materials

The body of the valve could be of mild steel, the spindle of high tensile or stainless

steel, and the valve and seat could have the contact faces stellited or hardened.

How it works

Main starting air at about 30 bar from the manifold enters the chamber above the

valve via the circumferential ports in the valve body.

The air pressure will not open the valve because a spring is holding the valve shut,

an the area of the balance piston is the same as that of the valve lid so the valve is

pneumatically balanced.

When the valve is required to open, air at 30 bar from the air start distributor enters

the the top of the valve body and acts on a piston.

This force overcomes the spring force holding the valve shut, and the valve opens.

When the air signal from the air start distributor is vented, the spring closes the

valve.

When the start sequence is finished the main air start pressure is vented through

holes in the main start air manifold.

State with why a leaking cylinder air valve should receive immediate attention.

Whilst the engine is running, the hot gases produced as the fuel burns in the

cylinder (at above 1200;C) leak past a valve which has not re-seated correctly. The

branch pipe to the air start manifold heats up to red heat. If the engine is stopped

and restarted before the pipe has time to cool, any oil vapour in the air can be

ignited and an explosion can result if the mixture of oil/air is correct.

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Fuel leaking into the cylinder whilst the engine is stopped.

When the engine then undergoes a start sequence, and builds up speed, the fuel

which has leaked into the cylinder vaporises and the heat from the compression of

the air in the cylinder, as the piston rises, ignites the fuel. When the air start valve

opens as the piston comes over TDC, the pressure in the cylinder is higher than the

air start pressure, and the burning combustion gases pass to the air start manifold,

igniting the oil entrained in the air.

Question Sremergy 2007-2008

With reference to engine inlet and exhaust valves:

(a) State why tappet clearance is essential and why it must be periodically

checked.

(b) List with reasons the likely consequences of excessive and insufficient tappet

clearance.

(c) State how carbon build-up can occur during engine running and indicate the

possible effects on cylinder performance.

ANSWER

As the engine comes up to working temperature the valves, because of the higher

temperatures in the cylinder will expand at a greater rate than the cylinder head and

rocker gear. This is especially applicable to the exhaust valves. If no clearance

were provided then the valve would expand downwards into the cylinder,

preventing the valve from closing.

Insufficient clearance:

The valve will open early and close late. It may well not close properly as

described above. This would lead to a drop in compression pressure, poor

combustion, and lack of power. Afterburning would lead to excessive cylinder and

ring wear as the lube oil was burnt/washed off the liner walls Burning gases would

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pass across the face of the valve causing overheating and erosion commonly

known as burning. In the case of inlet valves, fouling of the air inlet manifold

would result. Fouling of the turbocharger and exhaust gas economiser would result

from unburnt fuel passing across the exhaust valve. In the worst-case scenario, the

overheating of the exhaust valve could cause a piece to break off, causing damage

to nozzle ring and blading.

Excessive clearance:

The valve will open late and close early, hammering of the tappet faces will cause

damage, closing off any lubrication holes leading to excessive wear and possible

failure at the valve stem head.

Vanadium slag deposits which form on the seats when burning residual fuels

The slag forms due to the combustion of vanadium and the solidification

temperature of the slag is reduced in the presence of sodium, a critical ratio of 3:1

vanadium to sodium giving the lowest solidification temperature. It is extremely

difficult to avoid vanadium in modern residual fuels and the engine designer must

take steps to minimise the problem, including cooling of the seat area and the use

of resistant materials. Whether exhaust valves are in cages or fitted directly into the

cylinder cover, the seat area is cooled by water circulating in passageways close to

the seat. The reduction in seat temperature means the molten slag is less likely to

stick.

It is very important to keep the valve seat temperatures below 450°C.

Deposit on seating faces prevent the valve from closing and allow blow by which

will lead to wire drawing and burning out of the valve and seat.

Hammering of the valve seat due to products of combustion being trapped between

the valve and seat

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Question Sr 6 2009

Make a diagrammatic sketch of a jacket cooling water system as applied to a group of medium speed auxiliary diesel

engine.

Indicate the temperature and pressure in the system.

Describe in particular the flow of water from entry to the engine to the outlet from the engine and sketch the more

important joints in the system.

Jacket cooling water common for main engine and generator sets

Pressure MPa (kgf/cm2}

Cooling water Jacket line (jacket inlet) 0.25-0.35 (2.5-3.5) Consider static and dynamic

pressure due to tank head and pipe resistance

Cooler line (cooler inlet) 0.1-0.2 (1-2)

Temperature °C

Jacket line (fresh water) Engine inlet 65-70 80

Engine outlet 70-75 85 (90)

Cooler line Engine inlet 32

Medium Unit Location Function Setting Time delay

High Temperature Cooling Water Pressure Engine Inlet Alarm 3.5 bar 0 sec

Slow Down 3.0 bar 20 sec

Shut Down 3.0 bar 60 sec

Temperature Engine Outlet Alarm 95°C Osec

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Slow Down 97°C 20 sec

Shut Down 97°C 60 sec

Low Temperature Cooling Water Pressure Pump Outlet Alarm 2.0 bar 0 sec

Temperature CAC Inlet Alarm 25°C 60 sec

CAC Outlet Alarm 55°C 60 sec

Central Fresh Water Cooling System

Cooling Water System

All cooling water requirements for the generator engines are provided by water from the low temperature fresh

water central cooling system.The engine is cooled by a closed circuit cooling water system divided into a high temperature circuit (HT) and a low

temperature circuit (LT).

The air cooler and lubricating oil cooler are supplied in series from the central cooling and this forms the LT circuit.

Water circulates around the LT system which has a temperature control valve thus maintaining the temperature in

the LT circuit independent of the load on the engine.

Circulation is part of the LT central cooling system.

The alternators are also cooled directly from the central cooling system.

The engine driven cooling water pump draws water from the outlet of the LT system and circulates the HT circuit

which cools the cylinders and cylinder heads.

The jacket HT cooling water pump discharges through the engine jacket and cylinder head cooling water spaces andthen to a thermostatically operated valve, set at 80°C.

If the temperature of the cooling water leaving the engine is below the normal operating temperature, the thermostat

will direct the cooling water back to the pump suction.

When the cooling water outlet temperature reaches operating temperature, the thermostat will begin to direct the

water to the central fresh water cooling system and the pump will take less suction from the recirculated generator

engine cooling water and more from the central fresh water cooling system, thus maintaining a constant jacket water

temperature.

When an engine is on standby or prepared for operation, its jacket cooling water is heated by a thermostatically

controlled preheater to approximately 60-80°C.

An electrically driven circulating water pump is used in conjunction with the electric heater; there are two pumpsone of which will be set to operate and the other on standby.

The preheater circuit has its own pipework to and from the generator engines and water flow through the generator

engine jackets is in the opposite direction to the normal engine driven pump flow.

The preheater pump circulation through the jacket cooling water system is by way of non¬return valves.

Non-return valves fitted to the system mean that the engine driven pump will take over from the preheating pump

automatically when the engine starts, thus there is no need to open or close valves.

The preheating pump will similarly take over from the engine driven pump when the engine stops.

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Question Sr 2 2010, Sr 4 2007

With reference to charge air coolers

Describe with the aid of a sketch, a charge air cooler;

Describe the procedure for cleaning both air and watersides of a charge

air cooler;

State the importance of maintaining correct charge air temperature.Answer-

The sketch illustrates a charge air cooler Surfaces and collect in the bottom of the receiver.If not drained off regularly this water may cause corrosion in the receiver as well as being entrained in the air

leaving the receiver and causing corrosion and subsequent jamming of main and pilot air valves.

The cooling water makes two passes to maximize cooling effect, the air makes a single pass to keep the pressure

drop to a minimum.

A manometer connected across the cooler give an indication of any fouling on the airside.

The moving tube plate allows for expansion, sacrificial anodes may be fitted in the water boxes to reduce corrosive

attack, especially if the cooling medium is seawater.

The flow of cooling water through the cooler is automatically controlled to keep the air inlet to the engine at

optimum temperature.

Describe the procedure for cleaning both air and watersides of a charge air cooler;

Answer-

CLEANING AIR SIDE.

On large 2 stroke cross head engine the air cooler may be cleaned by injecting an air cleaner chemical into the

charge air while the engine is running.

The chemical used is hazardous to health and thus protective clothing must be worn, and manufacturers instructions

followed.

Alternatively, a system using a chemical circulation tank, pump and built in sprays may be used when the engine is

stopped.

After circulating the chemical for a period of time as instructed, the air cooler must be rinsed using fresh water,

ensure drains from the air cooler to bilge are clear.

On a medium speed engine, the air cooler can be cleaned in situ (with the eng stopped) by blanking the air inlet and

outlet and filling with cleaning solution.

However, it will be necessary to support the air cooler, as the fastenings may not be designed to cope with the extra

weight.

However it may be easier to remove the whole cooler and place it in a bath of cleaning solution, again protective

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clothing must be worn, and suitable ventilation provided.

It is normal practice to pressure test the cooler stack when it is in the rinsing bath to check for leaking tubes.

CLEANING WATER SIDE

This is normally done in situ with the engine stopped.

After isolation and draining, the end covers on the cooling water boxes are removed and the cooler is rodded

through or blasted using a pressure lance.

In the case of the latter suitable protective clothing must be worn.

Cleaning the waterside is normally only carried out on the air coolers using seawater.

Sacrifical anodes should be inspected and replaced as necessary.

Question

State the importance of maintaining correct charge air temperature.

Answer-

It is necessary to maintain the correct charge air temperature for the following reason.

So that the correct mass of air is allowed into the cylinder for combustion of the fuel. (Higher the temperature thegreater the specific volume)

To keep the exhaust gas temperature at acceptable levels. (Will rise if air temp is too high)

To prevent water depositing on the liner surface destroying L.O. film if temp is too low

To prevent thermal shocking of liner if temp is too low

Describe how you would deal with a scavenge fire in the scavenge space of a marine diesel engine.

Explain the causes of such fire.

What measures which have to be taken to limit their occurrence.

If a scavenge fire starts two immediate objectives arise – they are to contain the fire within the scavenge space of

the engine and to prevent or minimize damage to the engine. The engine must be put to dead slow ahead and the fuelmust be taken off the cylinders affected by the fire the lubrication to these cylinders must be increased to prevent

seizure and all scavenge drains must be shut to prevent the discharge of sparks and burning oil from the drains into

the engine room. A minor fire may shortly burn out without damage, and conditions will gradually return to normal.

The affected units should be run on reduced power until inspection of the scavenge trunking and overhaul of the

cylinder and the piston can be carried out at the earliest safe opportunity. Once navigational circumstances allow it,

the engine should be stopped and the whole of the scavenge trunk examined and any oil residues found round other

cylinders removed. The actual causes of the initiation of the fire should be investigated.

If the scavenge fire is of a more major nature, if there is a risk of the fire extending or if the scavenge trunk is

adjacent to the crankcase with risk of a hot spot developing it sometimes becomes necessary to stop the engine.Normal cooling is maintained, and the turning gear engaged and operated. Fire extinguishing medium should be

applied through fittings in the scavenge trunk, these may inject carbon dioxide, dry powder or smothering steam.

The fire is then extinguished before it can spread to surfaces of the scavenge trunk where it may cause the paint to

start burning if special non inflammable paint has not been used. Boundary cooling of the scavenge trunk may be

necessary. Keep clear of scavenge relief valves, and do not open up for inspection until the engine has cooled down.

The main cause of fouling of the scavenging air space is the blow by of the products of incomplete combustion, due

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to defective fuel injector, faulty fuel pump timing, lack of scavenging air, partially choke exhaust ports, low

compression, engine operating at overload conditions, defective piston rings or badly worn cylinder liner, past the

piston and into the air space. A further result will be an accumulation of fuel residues mixed with excessive cylinder

oil in the scavenge air space. Accumulation of such mixtures can be set alight by the sparks or flame blow-by.

To prevent scavenge fires good maintenance and correct adjustment must be carried out. Scavenge trunking must be

periodically inspected and cleaned and any buildup of contamination noted and remedied. The drain pockets should

also be cleaned regularly to remove the thicker carbonized oil sludges which do not drain down so easily and which

are a common cause of choked drain pipes. Scavenge drains should be blown regularly and any passage of oil from

them noted. The piston rings must be properly maintained and lubricated adequately so that ring blow by is

prevented. At the same time one must guard against excess cylinder oil usage. With timed cylinder oil injection the

timing should be periodically checked. Scavenge ports must be kept cleared.

The piston rod packing rings and scraper rings should also be regularly adjusted so that oil is prevented from

entering the scavenge space because of butted ring segments. This may and does occur irrespective of the positivepressure difference between the scavenge trunk and the crank space.

Fuel injection equipment must be kept in good condition, timed correctly, and the mean indicated pressure in each

cylinder must also be carefully balanced so that individual cylinders are not overloaded.

If cylinder liner wear is up to maximum limits the possibility of scavenge fires will not be materially reduced until

the liners are renewed.

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