Fuel injector

Image Credit: www.riceweightloss.com

Older loop scavenged engines may have a single injector mounted centrally in the cylinder head. Because the exhaust valve is in the centre of the cylinder head on modern uniflow scavenged engines the fuel valves (2 or 3) are arranged around the periphery of the head.
The pressure at which the injector operates can be adjusted by adjusting the loading on the spring. The pressure at which the injectors operate vary depending on the engine, but can be as high as 540bar.

OPERATION

– Fuel injectors achieve this by making use of a spring loaded needle valve.
– The fuel under pressure from the fuel pump is fed down the injector body to a chamber in the nozzle just above where the needle valve is held hard against its seat by a strong spring.
– As the fuel pump plunger rises in the barrel, pressure builds up in the chamber, acting on the underside of the needle as shown. When this force overcomes the downward force exerted by the spring, the needle valve starts to open.
– The fuel now acts on the seating area of the valve, and increases the lift.
– As this happens fuel flows into the space under the needle and is forced through the small holes in the nozzle where it emerges as an “atomised spray”.

Image Credit: www.marinediesels.co.uk

At the end of delivery, the pressure drops sharply and the spring closes the needle valve smartly.

ATOMIZATION

It is the break-up of the fuel change into a very small particles when it is injected into the cylinder
Proper atomization facilitates the starting of the burning and ensures that each minute particle of fuel is surrounded by oxygen particles which it can combine

Image Credit: www.marineinsight.com

PENETRATION

It refers to the distance that the fuel particles travel or penetrate into combustion chamber

TURBULENCE or SWIRL

– It refers to the aim movement pattern within the combustion chamber at the end of compression.
The spray pattern of the fuel is cone-shaped.

– These occurs when there is an excess velocity of fuel spray during injection, causing contact with metallic engine parts and one result is flame burning

INJECTOR NOZZLE:

The body of a fuel injector valve is normally flanged at the upper end and the lower end is threaded to accommodate the nozzle body and nozzle cap nut
The nozzle body contains four holes. One is for the fuel inlet and another for the fuel priming valve, these two holes are connected through a common space within the fuel nozzle or by annular space

Image Credit: DieselNet

The valve needle which has been lapped into a very accurately machine guide into the nozzle body, is held on the conical seat immediately above the atomization holes
Slightly clearance between needle and nozzle body to allow for temperature changes when working with heated fuel.

COOLING OF FUEL INJECTION VALVE:

Some injectors have internal cooling passages in them extending into the nozzle through which cooling water is circulated. This is to prevent overheating and burning of the nozzle tip.
Injectors on modern 2 stroke crosshead engines do not have internal water cooling passages. They are cooled by a combination of the intensive bore cooling in the cylinder head being close to the valve pockets and by the fuel which is recirculated through the injector when the follower is on the base of the cam or when the engine is stopped.

As well as cooling the injector, recirculating the fuel when the engine is stopped keeps the fuel at the correct viscosity for injection by preventing it from cooling down.
The animation opposite shows the principle on which one system operates.
Fuel injectors must be kept in good condition to maintain optimum efficiency, and to prevent conditions arising which could lead to damage within the cylinder. Injectors should be changed in line with manufacturers recommendations, overhauled and tested. Springs can weaken with repeated operation leading to the injector opening at a lower pressure than designed. The needle valve and seat can wear which together with worn nozzle holes will lead to incorrect atomisation and dribbling

FAULTS OF FUEL INJECTORS:

1. Over heating OR under cooling:
If cooling of the injector is reduced, either by fuel valve cooling system or poor heat transfer to the cylinder head, then the working temperature of the injector will rise. This can cause:-
– Softening of the needle and seat which increases the possibility of nozzle leakage and/or,
– Fuel to expand/boil out of the fuel sac, leading to carbon trumpet formation, and increased levels of HC and smoke in the exhaust gases.

2. Over cooling:
More common on older vessels with separate fuel valve water cooling systems. When the injector is over cooled, the tip of the injector falls below the condensation temperature and acid corrosion due to the sulphur in the fuel oil occurs. This can severely corrode the injector tip, causing the spray pattern to be affected.

3. leakage from Nozzle:
This fault will produce carbon trumpets as the dribble of fuel burns close to the tip and the carbon deposits remain. The formation of the trumpets will have a progressive affect by influencing the spray pattern of the fuel, and this can be detected in the increased exhaust gas temps and smoke levels.
Nozzle leakage can sometimes be identified by a seat defect(the seat is no longer narrow in appearance, and is caused by):-
– Insufficient cooling,
– Dirt within the fuel damaging/abrading the seating area,
– Excessive needle valve hammering, due to excessive time in service, excessive needle lift or spring force.

4. Weak spring:
This will cause the injector to open and close at a lower pressure. Thus the size of the fuel droplets will increase during these injection periods.
Increased droplet size at the start of combustion will decrease the maximum cylinder pressure (late combustion), whilst increased droplet size at the end of combustion will increase the exhaust temperature and smoke (afterburning).
Causes of a weak spring are usually metal fatigue, due to an excessive number of operations.

5. Slack needle:
Slight leakage between the needle valve and its body is required to provide lubrication of the moving parts. However excess leakage due to a slack needle will allow a greater quantity, and larger size of fuel particle to pass between the valve and body.
The quantity of leakage should not influence injector performance unless excessive, but dirt particles between the needle and body can increase friction and make the needle action sluggish.
The cause of a slack needle is usually poor filtration of the fuel causing wear between needle and body.

6. Poor atomisation:
This will increase the size of the fuel droplets, which will increase the time required for combustion. Thus engine noise, exhaust smoke, exhaust temperatures, etc will increase. Poor atomisation can be caused by low injection pressure (fuel pump wear), high fuel viscosity and nozzle hole obstruction such as carbon trumpets.

7. Poor penetration
This will reduce the mixing which occurs between the fuel and air, and will increase the over-rich areas in the centre area of the cylinder. Thus only following combustion in the centre area will the expanding gases move the fuel charge into the air rich outer ring of the cylinder where the greatest mass of air is present.
This will increase the time required for combustion as the fuel/air mixture is not correct in many areas, and hence afterburning, exhaust temps, and smoke will increase.
Causes of poor penetration is reduced injection pressure, and nozzle hole blockage such as trumpets or sac deposits.

8. Over penetration
This will occur when the air density within the cylinder is reduced, or with over-size holes. The liquid stream travels too far into the cylinder, so that a high level of liquid impingement on the liner wall takes place. This will remove the liner lubrication, and once burning will greatly increase the liner wall temperature, and its thermal stress.
If this over penetration is caused by prolonged low power operations, then “slow speed” nozzles should be fitted.

Slow steaming nozzles can be used when regular and prolonged engine operation is required between 20-50% power.
The nozzle hole diameter is reduced to
i. Reduce the penetration that will occur into the less dense cylinder air
ii. Keep the atomisation level and injection pressure sufficient, as mass flow rate is reduced.

If the engine is operated for long period on low levels of power/speed with `normal’ size injector nozzles, then the atomisation will reduce, thus engine noise, mechanical loading, exhaust smoke, exhaust temps, and fuel consumption will increase.

EFFECT OF FAULTY FUEL INJECTORS:

1. Greatly enlarged holes cause overheating, perhaps burning of piston upper surface, also cause carbon deposits in the piston cooling space, if oil cooled. It may also cause increased cylinder and piston ring wear

2. If the holes are chocked, the fuel sprays will be effected to the extent that imperfect combustion will result. This in turn may reduce the power output quite considerably and bring about all the mechanical troubles usually associated with after burning.
3. If the injectors leaky or spring is damaged, burning of piston upper surface, also cause carbon deposits in the piston cooling space, if oil cooled. It may also cause increased cylinder and piston ring wear and can lead to scavenge fire.

INDICATION OF FAULTS:

1. Early injection is usually evidenced by knocking in the cylinder. On the power diagram the maximum pressure will be considerably in excess. Exhaust temperature will be low.

2. Leaky valve can be detected through indicator diagram, which show reduced combustion pressure. This will be some reduction in power output, increasing in exhaust temperature about 10oC and smoky gases. Chocking of atomizer and exhaust ports. Surging in turbo-blower are also some of the indication

3. After burning will cause higher exhaust temperature and pressure. The maximum height of both the power and draw diagram would be reduced. Other indications are smoky exhaust, possible fires in uptake, fouling of exhaust system, surging of turbo-blower

4. Choked fuel injectors – combustion efficiency of an engine depends on fuel atomization, shape and direction of the fuel sprays. So the holes should be clear and clean. First outward indication of accumulation of carbon deposits will be increase in the exhaust temperature due to fuel not mixing properly with the air, consequently not burning completely in the allocated time. Power output is reduced and the exhaust is smoky.

MAINTENANCE

• Fuel injectors must be kept in good condition to maintain optimum efficiency, and to prevent conditions arising which could lead to damage within the cylinder.
• Injectors should be changed in line with manufacturers recommendations, overhauled and tested.
• Springs can weaken with repeated operation leading to the injector opening at a lower pressure than designed.
• The needle valve and seat can wear which together with worn nozzle holes will lead to incorrect atomization and dribbling.
• Proper cooling should be made during operation. Cooling passages to be cleaned during overhaul.
• Proper grade of fuel oil should be used and it should be used after proper purification to prevent atomized holes become enlarged, conical and oval due to abrasive materials.
• The valve body and valve needle should always be considered as a unit, not as two separate pieces and they should be renewed together.
• The holes should be cleaned and cleared properly without damaging by blown with compressed air.
• The valve needle must be perfectly fluid tight when in the closed position and must open and close smartly.
• The cam operating the fuel valves or the fuel pump, as the case may be, should effect opening and closing in the shortest time practicable.

References:

1. www.marineengineering.co.uk
2. The Running and Maintenance of Marine Machinery – Cowley
3. Reeds Marine Engineering Series, Vol. 12 – Motor Engineering Knowledge for Marine Engineers
4. Lamb’s Question and Answers on Marine Diesel Engines – S. Christensen
5. Principles and Practice of Marine Diesel Engines – Sanyal

Written by Mohammud Hanif Dewan, IEng, IMarEng, MIMarEST, MRINA

Moror and MEP questions and answers

How does emergency alarm ring?

Ans:    Continuous ringing of bell. Emergency situation is explained at the muster situation. Pattern of Emergency signal is indicated on Muster list

Q. Explain the Fire Tube and Water Tube Boiler.

Fire Tube Type: Due to simple design of the tubes effective heat transfer takes place, but periodical cleaning/maintenance is slightly difficult. Soot blowing is not effective for regular cleaning. Used with low pressure boiler

 Water Tube type: In comparison to fire tube type heat transfer is not so so effective. Gas side cleaning is easier, sometimes fixed water spray design is used for cleaning.  Soot blowing is effective , used with medium – high pressure boiler

Q. What is Ogee ring?

Ans:    Connects the bottom of the furnace to the boiler shell plating.

 Q. How the boiler Gas side is cleaned during operation?

  Ans:   

i. By means of steam, soot blowing

ii. By injecting soot remover powder (chemical) to the system.

Sketch a gauge glass and explain blow down procedure.

 Ans:    a) Close steam and water cock, open drain cock, nothing should come out the cocks are not leaking.

1. Open and close steam cock to check cock is clear.
2. Open and close water cock to check cock is clear.
3. Close the drain
4. Now open water cock, water should gradually rise up the top of gage glass.
5. Open the steam cock, the water should fall to the level of the water in the boiler.

 What is the consequence of low water level? What is your immediate action?

Ans:   Boiler running without water will cause overheating the tubes, tube plates and shell, that will lead the boiler to face thermal over stress damage, crack or rupture to the tube, tube plates, shell plates.

However, low water level alarm should be activated and boiler firing will shutdown. If the boiler water level found minimum at the water cock level it is safe to put feed water in the boiler. If the level is below this line care has to be exercised not to thermally stress boiler while putting water into boiler.

 What is the consequence of high water level? What is your action?

 Ans:  This will cause priming of the boiler, loss of heat from the heaters, possibly loss of steam pressure.

As per as possible steam heating to be minimized temporarily, carry out partial blow down to normal level. Then introduce normal heating again.

 What is the purpose of treating boiler water?

 Ans:  

a) Prevent scale formation

b) Prevent corrosion

c) Control of sludge formation and prevent carry over to the system

d) Prevent entry of foreign matters to the boiler.

 What type of chemicals are used to treat low pressure boilers?

            Ans:   

Lime Ca(OH)2  and soda ash are used Na2CO3 are used to deal with calcium and magnesium compounds in the boiler water.

 MgCl2 + Ca(OH)2                      Mg(OH)2 + CaCl2

 CaCl2  + Na2CO3                       CaCO3 + 2 NaCl

 What is the problem if boiler water contaminated with oil?

Ans:   

i) Create layer on the boiler plates, tubes etc and reduces heat transfer and thermal stresses are induced.

ii) initiates corrosion

With regard to capacity state the regulation for steering gear?

             Ans:    A vessel at deepest draught and at maximum service speed should be able to move rudder angel from 350 one side and to 350 other side. It should be capable to move 350 ­ one side to 300 other side within 28 seconds.

The auxiliary steering gear should be able to move from 150  ­one side to 150  other side at half service speed or 7 knots whichever is greater in 60 seconds.

Describe steering gears routine checks before departure and arrival ports.

Ans:        

I) After prolonged use of auto pilot check remote/manual steering on arrival.

ii) Check both steering gear power unit on arrival, run simultaneously on maneuvering channel.

On departure from port within 12 hours:

• Check main and auxiliary steering gear
• Remote control system for steering gear
• Steering position on navigation Bridge
• Emergency power supply
• check compass rudder angel position
• Alarms
• Auto isolation arrangements

 How often the emergency steering drill is carried out? How you used to carry out in      your last ship?

Ans: Every three months.

Controlling the pumps in either direction by means of manual push buttons from steering gear room locally.

What is the function of by pass valve and relief valves?

Ans: By pass valve are used to open circuit any particular unit.

 Relief valves are given to relief over pressure, especially during rough sea undue movements of rudder created extra oil pressure which is relieved by them to avoid any rupture, leakage, damage.

 Care and management of pumping systems:

Candidates should remain aware of various pumps working principle.

Q:    Classify pumps.

 Ans: i) Positive displacement pumps e.g. reciprocating, screw, gear etc.

ii) Rotor dynamic e.g. Centrifugal, 

 Q: A centrifugal pump not taking suction, what action you are going to take?

Ans:

• Check valves open
• Suction live have crack/leakage
• Air Ingress to check, primer to check
• Suction line jointing to check
• check suction filter clogged
• should the above not complying check the wear ring clearance excessive
• may be the impeller securing arrangement detached.

Q:    Why positive displacement pumps require relief valves?

Ans: with the pumping action, pumping rate is same but if the delivery is obstructed the pressure will be built up gradually, which will damage line, casing etc. To protect from above relief valves are required to be fitted.

Q:    What type of pump is used for Oily Water SWeparator? Is centrifugal pump is suitable for the above?

 Ans: positive displacement pumps e.g. rotor line screw, reciprocating and gear pumps are used for the above. Centrifugal pumps are not suitable for above because they produce large quantities of small oil droplets.

 Q:    How the tubular coolers thermal expansion is allowed?

Ans:  i) By means of expansion piece

ii) by means of free end arrangements

Q:    What for “bilge injection” v/v is used? What is relevant regulation?

Ans:  Bilge injection valve is used for in case of serious flooding in the machinery space. Diameter of the valve should be 2/3rd of the diameter of main sea inlet, valve spindle should be clear of engine platform.

What is the function of oil sensing probe in OWS?

Ans: The Capacitance probe in 1st stage senses and causes the solenoid to be energized through control switch. Hence control air access to the diaphragm controlled piston valve to drain oil to bilge oil tank.

Q:    what is the function of coalesce filter ?

Ans:  Removes fine solids up to certain extent. Small drops of oil coalesce to form larger drops. These rise up to oil collecting space.

Q:    How to ensure no accidental discharge O/B will take place from O.W separator?

Ans: i) 15 PPM alarm monitor will activate  and discharge P/P will stop automatically.

ii) Three way valve will activate on reaching effluent content 15 PPM, will divert the flow to bilge water tank instead of O/B.

 Construction, maintenance and operation of fire fighting equipment, fire    detection and prevention:

 Candidate should know the basic principle operation of portable extinguishers, fixed fire fighting  installations and fire detector sensors.

Q:    With regard to capacity state the regulation for emergency fire p/p.

Ans:  Capacity should be at least 40% of fire pumps but not less than 25m3/hour. To

supply 2 jets 13 mm dia with a horizontal throw of 13 m.

Q:     How does smoke detector works? How do you test it ?

Ans:  smoke is sensed by the photo electric call, this signal is transmitted to trigger the

alarm. It can be tested by    (i) Smoke (ii) Spray can

Q:     How does sprinkler system work? Where is it used ?

Ans:  Sprinkler heads are fitted with quartzoid bulb. Heat expands the liquid and

shatters the bulb. Water strikes a deflector to ensure a cover of floor area of 12m2. On dropping system pressure sprinkler P/P starts automatically.

Used for accommodation, alleyways of passenger ships and some cargo spaces.

Q:     What is international shore connection?

Ans:  It is to be provided to enable water to be supplied from another ship or from shore

to the fire main.

PCD 132 mm, Outer dia of flange 178 mm, Bore (inner dia of flange) 64 mm.

4 bolts are required of 16 mm dia and 50 mm length.

Q:     With regard to CO2 total flooding state the regulation?

Ans:  85%of the gas must be released within two minutes. The quantity of gas carried

1. must be sufficient to give a free gas volume equal to 40% of the volume of the space except where the horizontal casing area is less than 40% of the general area of the space.
2. Must give a free gas volume equal to 35% of the entire space whichever is greater.

Q:     How the CO2 total flooding system is maintained?

Ans:  CO2  room visual inspection is carried out regularly (say weekly), CO2  alarm checked on monthly basis and servicing and others checking of the system is carried out annually by authorized work shop.

Modern vessels maintain routine check lists of weekly, monthly, quarterly, 6 monthly and annually.

Q:     What is fireman outfit?

Ans: 

a) A safety lamp

b) A fireman’s axe

c) A breathing apparatus or ii. Smoke helmet,  or  A smoke mask.

Q:     Before wearing a BA set, what would you check?

Ans: 

i) Pressure normal; 140-210 bar

ii) Test alarm whistle working

iii) Check mask “seals”, not leaking

Alarm comes when air contents are brought about 80%.

 Q:    State the procedure of CO2   flooding

Ans:  On completion of assessment , permission granted by Master in consulting with chief engineer to carry out flooding:

• personnel counted
• all openings sealed including flaps, ducts for ventilation
• shut down all fans, blowers, pumps, purifiers, motors by remote stop device
• shut down fuel supply by quick closing valve operation
• follow operating instruction for operating pilot cylinder for gang release and there after the master valve
• use boundary cooling and observe fire and rescue procedure.

 Q:     what are the safety incorporated in co2 system? How it works?

Ans:  1) relief v/v on manifold, rupture dick for cylinders

11) interlock for fan, pump and  purifiers stop

111) audio-visual alarm while operating lever box is opened.

iv) overriding procedure for releasing, if pilot release fails

co2 cylinders are stored to maintain temp below 55ºc and at 52 bar. If pressure rise above 177 bar at temp 63ºc or above, rupture disk on cylinders opens. This gas is released through safety v/v on manifold.

 When the co2 cyl require recharging? How the content be checked?

Ans:  

Re-charge when weight reduce by 10%

• check by weighting, or radio active level indicator or ultrasonic gauging.

 Codes of safety working practices:

Candidates should be familiar with a book “code of safe working practices” available on board

vessels. It is important to identify safeties to encounter hazards.

Q:     What precaution should be taken while entering a enclosed space?

Ans:  To be complied with company check lists but in the general it will cover followings:

1. Assessment of atmosphere
2. Ventilation
3. Illumination (safety)
4. Permit to work
5. Self contained B/A set stand by
6. Ladder required as appropriate
7. Man standby at entry position
8. Communication should be established

 Q:     What precaution should be taken before decarbonizing a M/E unit?

Ans:  Company policies are relevant. In general they are

1. Immobilization granted
2. Turning gear engaged
3. Starting air valve shut off
4. System, staring air line vented
5. Starting air distributor inlet valve shut
6. Appropriate notices given
7. Fuel, cooling etc relevant valves in appropriate position
8. Over head crane tested.

 Methods of manicuring, including bridge control Systems and Variable pitch propellers.

Bridge Control Procedures:

Engine should be tested from ECR first to ensure safe operation. If satisfactory, control is change over to bridge and engine tested ahead and astern, telegraphic printer checked working Properly.

 Bridge alarm panel checked, in order. During maneuvering speed program may be cancelled, while at full away condition load up program should remain on to speed up gradually. Maximum rpm can be limited from ECR.

Variable pitch Propellers:

 While testing engine/vessel ahead and astern movements, only propeller pitches are adjusted to get desired movements. Engine need not to stop for ahead/astern moves. Engine  clutch/declutch mechanism can be utilized as appropriate.  Hydro oil level, pressure, and pumps should be checked.

Pitch control  – tried out from bridge/control room as well from local control.

Emergency Control:

Q:    With respect to M/E , what is emergency control?

Ans: Should M/E remote operation is not working, it may be operated from emergency / local control stand which will cover following:

1. Manual Fuel Control
2. Manual Air control
3. Manual Reversing

Q:    What action you are going to take in the event of a black out/M/E failure?

Ans:

1. Inform bridge/chief engineer
2. Engineers alarm may be raised for additional help
3. Emergency lighting/emergency generator will be active
4. identify the problem, preferably start other generator which was not in service and restore power.
5. Run appropriate cooling P/Ps, reset all needful breakers, start all other plants
6. Prepare M/E and restore same after informing bridge
7. Check all Standby machineries and emergency equipments at ready mode.

Working principle and constructional details of a compressor, air receivers, and associated equipment:

Candidates should have understand the efficacy of inter coolers, P-V diagrams gain in efficiency.

Q:    What is the working principle of a main air compressor?

Ans: Reciprocating motions are used to in conjunction with spring loaded non -return suction and delivery valves to achieve compressed air. Intercoolers are used to acquire gain in efficiency.

Q:    Describe the construction of a main air compressor you used in our last ship.

Ans: It was a in line reciprocating  2 stage compressor. 1st stage piston relatively larger and 2nd stage piston smaller in comparison, materials respectively aluminum and cast iron. Both stages were having spring loaded suction and  discharge non-return valves. Inter stage cooler and after coolers were there.

 Q:    Other than in line, what different type of compressor is used?

Ans: Tandem type compressor are the other type commonly used. 1st stage piston relatively larger, 2nd stage piston exists on top of above relatively of smaller size.

Q:    Why the bumping clearance is important?

Ans: Bumping clearance should be optimum. The more clearance volume increase, volumetric efficiency and hence capacity decreases.

Q:    How do you take bumping clearance?

Ans: Remove suction or disch valve assy from the unit, place a small ball of lead wire on the piston edge. Then rotate the flywheel by hand and to take the piston at TDC. Remove and measure the thickness of lead wire ball.

Q:    What is function of intercooler and after cooler?

Ans:

Intercooler:         i) Decreases air temp

ii) Reduces work done

iii) Maintains safe lubrications

iv) Increase compressor efficiency

After-cooler:        i) Separate oil and water from compressed air

ii) Reduces air temperature before the filling receiver

Q:    What mounted safeties are incorporated with a main air compressor?

Ans: i) Relief valves are fitted at the discharge of each stage

ii) incorporated discharge non return valve

iii) Bursting discharges are fitted with intercoolers to protect from over pressure due to tube leakage

iv) Un-loader/drain valves

Q:    What safeties are incorporated for compressor protection?

Ans:

i) Low pressure alarm, stop for lube oil

ii) Jacket high temperature/air discharge high temperature, alarm, stop.

Q:    Describe the special features for main air receivers?

Ans:

i) Manhole door elliptical, for the ease of opening and consider strength of the pressure vessel

ii) Circumferential and longitudinal welding seams are existing.

iii) Relief valve fitted (if isolated from relief valve, fitted with fusible plug, melting point 1500 C.)

iv) Drain valve, pressure gauge

v )  Pressure switch for cut in /cut off air compressor auto running.

Operations, Testing Power, the running adjustment to maintain performance:

 Candidates should know how to use indicator machine, taking power cards, draw cards etc and

know how to measure engine power.

Q:    If an individual unit of M/E shows high exht temp, what should you do ?

Ans: i) If the parameter goes beyond limit, that case engine power/rpm may have to be reduced informing bridge and chief engineer. Need to find out fault.

ii) check the funnel smoke and check the pyrometer is correct, fuel rack in order.

iii) Fuel injection equipment, – fuel valve, fuel P/P may be faulty. Take power card to understand fuel injection, all units peak pressure may be compared

iv) Compression pressure can be checked from above, to have an idea about liner wear/piston rings.

v) Exhaust valve operation can be checked visually (through glass) or light spring card can be taken to ensure the problem with exhaust valve or not.

vi) check particular unit scavenge drain line

vii) Should all above are in order, consider mistiming for late injection or mistiming of  early opening.

Q:    M/E all units exhaust temps are high what could be the reason?

Ans:

Consider it is a common problem for all, hence it can be of followings:

1. Faulty governor or fuel linkage
2. Fuel quality to be assessed
3. Problem with T/C, scavenging not enough
4. T/C Air filter dirty
5. Scav. Air temperature high
6. Residual temperature low, responsible for incorrect injection
7. check fuel load, if the vessel at shallow water
8. Ships hull fouled
9. in worst case due bad quality fuel injection equipment may be worn.

Q:    How do you calculate POWER in a conventional method?

Ans:    – take power card (in-phase diagram)

Where: PmLAN   in KW = POWER  ……………… (1)

Pm = MEAN EFFECTIVE PRESSURE  , L= STROKE LENGTH,  A= AREA OF PISTON ,  N= REVS NO.

Calculate area of the diagram by using planimeter, check length of diagram

Calculate the mean height of diagram, which is n = area (mm²)/ length(mm)

Now the MEP= h (mean height, mm) x spring scale (bar/mm)

i.e  MEP found in bar   or, MEP is (barx10²) kN/m²

from (1) we get power= PmLAN   kW for one cylinder. For total engine, the result of other cylinders to be accounted for.

 Q:    What was the main Engine Type in your last ship? How did you calculate engine power?

Ans: Engine Type SULZER5RTA48T

Power of first estimation was P1(KW) can be read from the graph read by (Fn-F0)×N from

Where              Fn = Load indicator pos

F0 = 1.22 (mean), pos of load indicate pos corresponding to FO P/P idle stroke

N  =  Engine speed (rpm)

r                   Hu

Effective Power    N =     P1×—————-×————- KW

818.70           42.50

r = Specific gravity of FO at engine inlet temp

r`= 8.18.7 kg/m3  FO used during trial (at engine inlet temperature)

Hu= Lower catorific value of fuel oil

Hu`= 42.50MJ/Kg (lower cal. Value of DO used during trial)

Safe and efficient operation and maintenance of marine diesel Engine

candidates should remain aware of the working principles of various main and auxiliary machineries. Should know how to decarb a particular 2 stroke/4 stroke  engine unit and relevant inspections. To be familiar with operation recommended by the manufacturer, specially while during operation with defective components.

 What is the indication of black/blue smoke?

Ans: Black smoke indicate incorrect /incomplete combustion. Blue smoke indicates       burning of LO with the combustion. Smoke should be clear.

What are the causes of scavenge fire?

Ans:

i) Blow past through liner and piston rings

ii) Due to incorrect fuel injection

iii) Due to lack of cooling, breaking of Cylinder LO film

iv) Excessive cylinder lubrication give undue fuel and cylinder film breakage will cause hot gas to blow by, consequence scavenge fire.

  What action you are going to take with above?

Ans:

i) Inform bridge/chief engineer officer

ii) Slow down engine to extinguish fire

iii) Scavenge drain can be checked carefully

iv) shut off fuel to the particular unit

v) Increase cyl lubrication to give adequate sealing

vi) check funnel, scav drain, scav temp if satisfactorily return to normal with appropriate rpm.

vii) if above are not successful, not extinguished, stop engine, engage turning gear, mask T/C air filter, use fixed CO2 / steam to extinguish.

viii) On completion, inspect, rectify the fault then start engine.

Candidates to know starting air explosion and c/case explosion, causes, remedy and action.

 What inspection is carried out on piston ring?

Ans:                                        

i) Axial clearance .

ii) Butt clearance

iii) Ring thickness

iv) Radial thickness

v) ring tension

What inspection should carry out with cylinder liners?

Ans:     

i) Check the ridge on top, remove by grinding if any

1. ii) check for crack, oilyness

iii) Check lubricators, condition of retaining Cylinder LO

iv) Check for wear (gauging), ovaliti

v) Scuffing

vi) Abrasive wear

vii) Corrosion

What is thrust block?

Ans: This makes use of the engine bedplate and seatings to distribute the propeller thrust to the ships structure.

What is the function of flywheel?

Ans: i) Store energy while acceleration and releases  while deceleration, smooths out fluctuation of engine speed.

1. ii) Turns the engine for maintenance

iii) Used as pointer of engine position

 What are the TBN values for C/C oil of cross head engines and trunk piston engine?

Ans: Engine using residual fuel, C/C oil to be alkaline.

For X-head engine 10-15 TBN

For trunk piston engines up to 40 TBN

What is microbial degradation?

Ans: It is a infection of C/Case oil by micro organism. This live by consuming hydrocarbons in the base oil together with nitrogen, sulpher and phosphorus from additives. Cooling water etc. leakage are responsible for depleting the above situation.

Safeties during working shipboard electrical system:

 Electrical shock and fire can cause loss of life and damage to the equipment, hence in general

following should be complied :

1. To be familiar with ship electrical equipment and diagram.
2. Operate as makers instructions
3. Maintain as per makers instruction
4. Guards, covers, doors etc securely tightened
5. While shutting off the power, inform duty officer/engineer of the watch
6. While maintenance being done, remove fuse etc.
7. Before working with the equipment confirm circuit is dead.
8. Do not leave live conductors or rotating parts exposed
9. Avoid overloading equipment
10. Use appropriate warning notices

 What are the conditions of electric shock?

 Ans     :             

• Minimum 15 mA AC or DC current is enough to cause an electric shock. Circuit may be from hand to hand or hand to foot. Shock current is related to the applied voltage and body resistance. Unfortunately if the applied voltage goes up, body resistance goes down, that means shock current is further increased.

What are the safety of the panel boards?

Ans:            

•  Guarded
• Insulated barriers
• Some panel board cannot be opened unless the  breaker is off
• Adjacent floor covered by insulated mats.

During a watch you find low insulation resistance alarm, what is your action?

Ans:     Inform chief engineer officer and electrical engineer officer. Meanwhile take following actions to find  detect the faulty equipment.

• Isolate/change the running motor and check megger
• If not found, check galley, laundry equipments
• Deck crane electrical motor
• Fwd/aft electrical equipments

After the faulty equipment is isolated, insulation indicator will restore back to normal.

How do you check insulation resistance?

Ans:   

i) Phase to phase

ii) Phase to earth.

In dry dock while connecting shore electrical power, what will you check?

Ans:    i) Check supplied voltage 

ii) Frequency

iii) Phase sequence ( specially check at least one E/R exhaust fan that it is rotating in normal direction).

iv) If shore supply is earthed neutral, the ships body has to be earthed.

v) Check the capacity of the circuit breaker.

What is the sequence method synchronizing ? if synchroscope and light methods are out of order how do you  parallel generator?

Ans:    Two lights bright and one light goes out (dark), synchronizing method is sequence method.

Same phase of the bus bar and incoming generator are connected across a 500 V voltmeter. When voltmeter indicates 0 to maximum slowly and when voltmeter shows at zero, breaker to be closed. This is the point where they are in correct phase sequence.