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1. Assume you are a Chief Engineer of a large container vessel and your company’s technical manager asked you to carry out inspection for cracking in bed plate transverse girder of your main propulsion engine due to sister ship of the same fleet has experienced cracking in bed plate transverse girder.

a) Describe the investigation that should be carried out for possible cracks, using sketch to show where the cracks are most likely to occur.

Here we are describing the possible reasons of the crack occurs in the bed plate of a large vessel after doing a complete survey on this topic we have come to know the exact properties of the bed plate of that particular vessel and the possible cracks on it also their reasons.

For the bed plate we can say, it is the lower most part of a marine engine which hold the entire engine above it and related accessories of a marine engine along with it. This part is basically made of some kind of structural steel parts. In small marine engines it is actually made of structural steel parts with welded joints and in case of larger engines this is made of pre casted structural steel body as a whole unit without any welded joint on it. The possible cracks can be found in some areas like at the portions of the perpendicular joint portions of the bed plate. Another fatigue can be found on the fillet joints on the bed plate. Some time due to unbalanced position of the crankshaft the crack can be found at the bottom part of the main bearing of the engine. The reasons behind this kind of cracks are, for a welded joint a dissimilar material is incorporated with the main material due to this the internal property of the material does not match with it and stress concentration increases and the yield point comes early enough. For some another cases due to extensive heat generation at the time of welding the material molecular bond structures deforms and this parts are basically unable to sustain the load accordingly it shows failure in terms of fatigue. The crack at the bottom of the main bearing is just due to the unbalanced condition of the crankshaft on the main bearing. A sketch is shown below to understand this kind of condition.

b. Explain possible reason for these cracks.

The main reasons behind this kind of fatigue are stated below,

• At the time of welding some kind we know a high temperature gradient is experienced at the surrounding position which makes a change in the material property at its surrounding. At this condition the change in material property plays a role for such kind of fatigue or crack.
• For the fillet joints position if we can observe a crack on it then the main reason is the capability of the filet joint. Some time it may happen that the fillets are attached at some position but they are unable to sustain such loads. For that reason, if we attach such fillets without calculating the stress concentration there we may face some cracks on this part.
• The fatigue at the bottom part of the main bearing is due to the unbalanced condition of the crankshaft. If the crankshaft is attached with the engine without proper dynamic balancing, then it may exert a huge variation of load flow at the main bearing parts which can result such kind of fatigue at the bottom part of the main bearing of the bed plate.
• Not only these are the reasons for such cracks on the bed plate along with them some another basic reasons are sudden loading on the engine, excessive vibration, lack of damping arrangement and all.

2. With reference to Crankcase diaphragm glands (Stuffing Box):

a. Explain why effectiveness deteriorates in service.

The usage of stuffing box is to prevent the passing of the lubricating oils from the crank case to the air gap it also prevents the leakage of air from the air space to the crank case. At the service condition the effectiveness of the stuffing box deteriorates with a great extend. The most common reason for this kind of situation is the abrasion. It is a general phenomenon seen in all kind of diesel engine. The cylinder oil and the carbon generated at the time of combustion attached with each other and after a long time of running condition it makes a tar type material and it is being collected at the joint position of the piston rod and packing which makes deterioration on its effectiveness.

b. Describe the procedure for renewal of parts so that efficiency is restored.

The procedures for the renewal of the condition so that the efficiency can be increased for this particular part is stated in the paragraph below. All the parts along with the diaphragm gland are needed to be check carefully for a clear observation to decide the usability of the part or the need of replacement of it. The garter spring into the stuffing box with an extensive elongation after its permissible value need to be replacing with a new one. This kind of parameters are taken from the above study has been done and such kind of renewal process can be followed up for a better outcome in terms of the efficiency of the marine engine.

c. Describe how effectiveness is restored if spares are unavailable on board due to current epidemic COVID 19 and will be delayed supply up to 4 months or more. What would you do as chief engineer because You must run Engine in optimum condition.

As a chief engineer it is important to make a complete running condition of the vessel at any circumstances. Since, the current scenario is kind of this everything is closed for the unwanted situation arising due to the effect of COVID 19. It may happen at this condition we are not getting the spare parts in our hand for the repairing task but we need to make a running condition then we need to follow the points stated below.

• For the packing element we can perform a filing on the metal piece into it to provide a clearance between the end faces at the time of assembling it tightly.
• For the garter spring provided into it elongated can be reduced by reducing its length and providing a tension.
• For both the upper section and the lower section of the stuffing box we need to make a rubbing and filing on them for getting a knife edge surface that will not allow any kind of leakage on the engine.
• Since, we need to find an option to get a running condition with the help of existing spare parts we should follow the points stated above for a healthy operation of the marine engine.

d. Explain the function of Sealing and scrapper rings. Sketch complete stuffing box drawing to identify the location of above rings.

In the marine engine all the rings available on the piston have the same working just like any other internal combustion engine. Basically there the upper most rings is the compression ring which does not allow the entry of lubricating oil to enter into the combustion chamber. Eventually it also makes a separation so that the combustion gas does not enter into the engine crank case.

For the scrapper ring it is the oil controlled ring of any marine engine. The lubrication required between the cylinder liner and the piston due to the to and fro motion of the piston. This lubrication is provided by the scrapper ring or oil ring. The basic work of this ring is to make a layer of lubrication oil on the inner surface of the cylinder liner and come back with the oil at the time of returning of the piston. The name scrapper ring comes from the scrapping mechanism of its.

3.With reference to the Marine slow speed engine cylinder head exhaust valves:

a. Discuss with reason, the indication of valve burns out and what will be the causes for above valve burn out.

The general symptoms are stated below and the reasons are also given in this part.

• A routine emission test is performed for checking purpose will fail if the exhaust valves are burnt. At the time of emission test we can observe vapor of diesel on the exhaust gas for the combustion leakage through the burnt portion of the valves.
• A problem at the time of starting of the engine is a common symptom of the burnt valve. For proper combustion at the combustion chamber a complete air lock condition is needed that means a proper sealing. If there is any burnt part on the exhaust valve that will cause a leakage.
• When the combustion takes place the thrust is imposed on the piston surface and it goes down and a complete cycle is being achieved there. At that time a leakage condition on the valve we may face a decrement in thrust on the piston. That means a complete work done is not happening in the engine so it will have termed as a power loss on the engine.
• Since the exhaust valves are there also for providing a complete sealing in the combustion chamber if there is a burnt part on the exhaust valve it may cause a leakage on the combustion chamber. It will cause an extensive amount of misfiring on different strokes of the engine.

The reasons of this kind of burning on the exhaust valves are,

1. An extensive overloading on the engine is one of the most significant reasons behind burning of the exhaust valve.
2. A failure fuel injector may be the reason of the burnt exhaust valve because a improper fuel injection makes different types of combustion in the combustion chamber.
3. If there is a gap between the valve and the combustion chamber then from the leakage position the combustion takes place a burning at the valve may occur.
4. Some time an insufficient cooling may be the reason of burning of the exhaust valve of marine engine.
5. Hot corrosion is an important topic for burning of exhaust valve, if there is an impurity in the fuel then corrosion takes place at the edges of the exhaust valve.

b. Assume you are the chief engineer of the vessel and what is your best practice to minimize above valve failure situations.

As a chief engineer there we need to follow some steps to reduce the chance of burning the exhaust valve in marine engine.

• We should check the loading on the engine may not exceed thoroughly to reduce the chance of high heat generation on the combustion chamber.
• Since, we know the poor combustion is an important reason for such kind of valve burnt out so we need to check the compression on the combustion chamber and the deliveries of the fuel injectors regularly.
• A polishing is required at the joint position of the valve and the combustion chamber to prevent the uneven surface finish.
• The cooling system is to be proper so that extensive heat is not generated at the combustion chamber of the engine.
• For every refueling we need to check the fuel quality for the observation of any unwanted material in it which may be the reason of corrosion on the exhaust valve.

There is some advance technique are there for preventing this issue like bore cooling mechanism, valve rotation mechanism and all.

c. Critically analyze why variable exhaust valve closing can be advantageous in the operation of large slow speed main Engines and Discuss any mechanism for variable exhaust timing you know which are employed in current marine slow speed diesel engines.

1. Proper combustion can take place at the time of combustion on the cylinder head.
2. A proper compression can take place if we can vary the valve timing in terms of closing them or opening them.
3. We can also be able to get an economic response from the engine performance.
4. If we can close the valve in a pre-compression mode, then we will be able to reduce the loss of fuel in terms of fuel vapor.
5. One most advantage is that, we can also reduce the chance of burning of exhaust valve.

There are various ways can be implement on variable valve control in marine engine. The methods of variable valve control are cam switching, cam phasing, oscillating cam, eccentric cam drive, two shaft combined cam lobe profile, coaxial two shaft combined cam lobe profile, helical camshaft, cam less engine and hydraulic system. These methods can control the exhaust valve by opening them in exact time and controlling their opening for pre compression mode for a proper combustion.

4.

a. Describe the precautions and procedure for taking Crank shaft deflection in large slow speed main engine.

Crank shaft deflection is one of the worst problems in the marine engine basically happens on large engines. The uneven loading is one of the most important reasons for such kind of deflection on crank shaft. A misalignment in the main bearing of the crankshaft also a reason of deflection in the crank shaft. Now the question comes into our mind how we can get to know there is a misalignment. If the temperature of the main bearing is much higher than the general condition then it is the indication of deflection of the crank shaft of the marine engine. The reasons are,

1. Damaged main bearing
2. Excessive engine vibration due to improper fittings and lack of damping arrangement
3. Cracking at just below the main bearing on the bed plate
4. Corrosion on the engine parts
5. Internal effects from the time of manufacturing
6. Improper lubrication in the crankshaft

Here we are stating the general precautions and the safety measures are to be taken for checking of the crankshaft deflection. Along with wit we are also discussing the procedure by which we can check if there is a deflection in the crankshaft or not.

The measuring instrument used for checking of crank shaft deflection is dial gauge. We can attach it between the adjacent webs of the crank shaft. It can readout the spread of the different webs in the crank shaft in different angular positions.

First we need to place a dial gauge axially in the crank just on the opposite of the crank pin and mark that position for correct positioning and also punch that position. Set the dial gauge to zero at the BDC of the crank. Then we just need to take the readings from the dial gauge for different positions like top, cam shaft side, near bottom and all the possible readings. And perform this kind of procedure for both of the webs in the crank shaft to ensure all of them are providing a same result if there are some differences in the values between different webs than indicates the deflection in the crank shaft.

The safety precautions are to be taken into consideration before performing this kind of checkup in marine engine,

1. First we need the engine in off condition.
2. The starting mechanism is to be blocked properly.
3. All the air supply valves are to be stopped in the engine.
4. Engine cooling pump should be in off state.
5. The engine should be left for a long time to cool it properly.
6. Before entering we need to engage the turning gear.
7. For getting a vacant space in the crank case we need to off the entire lubrication pump.
8. Before entering in the crank case for ventilation we need to make it open for a long time.
9. The person entering must have proper shoes and adequate amount of light, leather gloves, eye protection glasses are also necessary for this measurements.

We need to follow these safety precautions for measuring the crankshaft deflection.

b. Describe the action that should be taken if the current reading deviates significantly from the previous readings.

Here we are discussing about the actions should be taken for the deviation in the result at the time of measuring the deflection in the crankshaft. The deviation shows the deflection is there in the crankshaft. So, what kind of action should be taken for this kind of situations is discussed in this part.

For this kind of unwanted situation, the best thing is to replace the crankshaft, but it is not a better option for this kind of damage and it is very costly too. So, the things we need to do for such kind of damage is.

Change all the journal bearings, main bearings and connecting rod bearings also connected to the crank shaft. If there is any kind of play in between the bearings then try to remove this play with the help of packing materials and material addition at that place and finishing. These are two possible ways to get a better running condition without replacement with a new one.

5.

a. Assume you are the newly signed- on Chief Engineer officer to your vessel and as part of your company policy you must carry out detailed Piston/Liner inspection via Cylinder scavenge ports to evaluate your engine condition to attach new chief engineer taking over report. Make detail report which could present to your technical manager explaining the key area of inspection with at least four possible defects which you found during your inspection with possible causes and your suggestions which should be taken to prevent their re-occurrence.

Here in this part as the problem statement is given, we need to perform a throughout investigation from the spaces of the cylinder liner. The main reason behind this kind of survey is to check the condition of the piston and the cylinder of the marine engine. The basic outcome for such kind of investigation is to become familiar with the different kind of defects on the cylinder liner and piston.

Part	Damage	Causes	Suggestion
Piston	Piston surface uneven	Due to the presence of hard carbon coating on the piston.	The surface is to be cleaned and polished properly.
	Oxidation surface	Due to presence of moisture in fuel oxidation may occur.	Fuel quality should be checked before refueling.
	Scratches on external surface	Due to improper lubrication on the piston and cylinder liner assembly.	The oil rings on the piston is to be checked and replaced with new one.
	Play on the connecting pin	For poor quality of connecting pin and uneven loading.	The connecting pin bushing and pin is to be replaced or packing needed between the bushing
Cylinder liner	Rusted surface	Due to extensive moisture in the weather we may observe rusted cylinder liner surface.	A regular oiling is required for such kind of rusted surface.
	Scratched inner surface	Improper lubrication in the cylinder piston assembly such scratches are there.	The piston rings are to be checked if there is some defects those need to be replace with new one.
	Damaged hair lining hatching	Due to extensive friction between cylinder liner and piston for damaged piston ring.	The hatched lining is important otherwise lubrication will not be there so proper lubrication is required.
	Groove in inner surface	Due to completely damaged piston ring and extensive friction.	We need to replace the piston rings with new one otherwise no option is available without changing the cylinder liner.

 

We have discussed the related findings with their reason and following suggestions required for preventing this kind of unwanted situations.

b. With reference to a Piston which has been removed from a liner of a main Engine. Assume you are the in-charge engineer of decarb job and how do you assume whether piston and liner suitable for further use.

As the problem statement given in this part we have to check the cylinder liner and the piston to get a clear view about the reusability of the piston and the cylinder. For this purpose, we can follow these conditions of piston and cylinder liner,

For the piston,

• For deposition of hard carbon layer those are to be clean and after polishing it can be reuse again.
• For extensive amount of scratches, after replacing the piston rings we can use it again.
• For a large gap between the piston rod hole and the connecting pin we can change the friction bearing or insert some kind of packing in the gap and reuse it.
• For the cylinder liner,
• For a rusted external surface of the cylinder liner we can coat them with lubricating oil so that moisture will not be able to attach this surface.
• On the inner wall if we found a few amount of scratches then we can use this cylinder liner by changing the piston ring.

If a huge amount of groove cutting is there on the inside wall of the cylinder liner, then we can bore the cylinder liner and can use an over sized piston and reuse it.

6.

a. Describe with the aid of a sketch, the cam shaft chain drive for a large slow speed two Stroke engine, incorporate with chain tightening wheel and primary and secondary Moment compensators.

Here we are describing the detail discussion on the crank shaft and cam shaft chain drive with its chain tightening arrangement. The basic concept is to transfer the rotating motion of the prime mover of the engine to the any other part. To get such kind of motion we need an efficient method. Among all the efficient methods the chain drive is the most prominent and efficient one compared to any other drives like gear drive and belt drive. The reason behind its most efficiency due to its slip less condition. Among all the different methods to transfer rotating movement there is less amount of slip in chain drive. That will provide a complete efficient outcome at the crankshaft and camshaft of the marine engine.

The figure attached below states the entire mechanism of the rotating parts and the chain drive arrangement.

b. Explain how chain slackness is caused and it effect on engine operation.

In a complete chain drive the arrangement is chain and gear assembly. In this kind of assembly if proper lubrication is not there then an extensive friction will be experienced in the entire system. For such kind of friction, the gap between the chain links will increase and the chain slackness is being observed on the entire chain drive.

The chain slackness is a worst condition for a chain drive. If the slackness is higher in a chain drive then we can experience a more friction as well. For such condition we will experience a vibration on the chain like a two and fro motion on the chain on its axis. So, we can face a condition like the chain links will jump above the teeth of the gear. So a breakage on the chain can be occurring.

c. What is the vibration excitation sources in Propulsion engines other than external unbalanced moment and Explain with suitable drawing counter measuring devices fitted for above.

Here in this part we have been asked to find out the sources of excitation of vibration of the marine engine. We have discussed all the possible reasons of vibration on the marine engine in this section. The main reasons are propeller fluctuating loads, diesel engine excitation, shaft alignment errors, manufacturing defects in gearing system and all.

For propeller fluctuating loads, at all the time the loads are not uniform in nature. So if the loads are kind of non uniform then we can experience some vibration on the main engine.

The moving parts of the engine are the most effective parts causing the most vibration on marine engine. There are various rotating and moving parts are available in the engine and for a very few amount of asymmetric fitting we can experience some vibrations on the marine engine.

Shaft alignment error is also one of the most important reasons for vibration. If there is any kind of off-centered shaft is there that also provide a vibration.

A manufacturing defect on the mechanical part of the gear box of the marine engine is also responsible for some excessive vibration. If the teethes of the gear in the chain drive are not properly made then the chain will not fitted on the gear and in running condition it will cause a vibration.

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