JNE 316 Advance Marine Engineering Knowledge
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Q1) 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 according to the problem statement we have to perform an investigation based on the possibilities of the crack on the bed plate of the engine we have taken into consideration for this case study. Along with a general sketch we have to define the location of the crack on the base plate.
The bed plate is basically the lower most part of a marine engine which holds the entire engine on it above the engine room floor. This structural part of an engine is basically made of selected by some kind of alloy with different parameters for different loading conditions. In case of normal sized engine, the bed plate is made by structural steel and by welded joints and some nut and bolts joints as we have shown below in sketches. But in case of much heavier engines the bed plate is a complete casted body, there is not any kind of joints are provided on it for better load carrying capacity. We have investigated these issues on the bed plate of the marine engine and we found some fatigue or cracks on it. As the problem statement given to us it is necessary to find out the location or the perfect position of the cracks then only we can get a clear over view of the reason behind this kind of fatigues. We have got fatigue or crack on three positions on the bed plate one is on the joining part of two steel on perpendicular manner, second one is at the jointing position of the fillet on it and lastly the third one is at just below at the main bearing position of the engine. A free hand sketch is provided below to show the exact locations of the crack positions.
b) Explain possible reason for these cracks.
Here we have to discuss about the different reason behind this kind of fatigue on the bed plate of a marine engine. Since, it is a very common topic for several cases that is why we are taken this thing into consideration. Generally, the basic reason of any failure occurs on structural items is the loading. But here along with the loading also some internal matters come into role for this kind of damage on the engine bed plate.
- The reason behind the first crack we have observed on the bed plate is due to the welding problems at the joint positions. At the time of welding there a huge temperature gradient occurs to the surrounding members of the bed plate but due to this kind of temperature gradient, a change in the internal property of the steel in terms of their molecular structure can change and that may be the reason of the crack. Even this is a very common and effective reason of such kind of failure or cracks.
- The second fatigue or crack was observed at the joint position of the fillet joints at the lower most position. The fillet is the part used in any structural component for a better holding and to increase the load carrying capacity of the bed plate. For here also the intention was same but the fatigue was found due to a misconception on that. Before attaching any fillet plate, we need to calculate the local stress on that position if it is not checked and the fillet plate joint arbitrarily at that time fatigue/ crack may occur. Definitely here also the reason is same. Another one reason may be the welding internal defects on that part. Sometime various kind of impurity attached with some welding material and that plays an important role for such kind of structural failure.
- The third and last one fatigue/ crack were found at the lower position of the main bearing. The main reason is that; we can see the engine is a direct propulsion engine so there is a much more pressure or load exerted at the crankshaft of the engine compared to electric propulsion engine. In this kind of condition is there is a kind of situation occurs like the engine is set up with a different angle from the specified one on the bed of the floor then the dynamic balancing of the crank may hamper and that exerts a non-uniform loading on the main bearing position which also may be the reason for that particular crack we have found on the bed plate.
- Along with this all there are also some another reasons are available for this kind of crack this are loose fitting, lack of damping mechanism, sudden loading, rusted body parts and also lack of maintenance.
Q2) With reference to Crankcase diaphragm glands (Stuffing Box),
a) Explain why effectiveness deteriorates in service.
Stuffing box is basically a sealing gland used in various aspects for leakage in various parts where there is some lubricating oil is there. The basic two function of this device is to act like a sealing material and to keep the system leak proof and operational in cool condition. Since, the marine engines are diesel engine and in such kind of diesel engine can be seen in the bore at the bottom of the scavenge air box. The need of this part is to prevent the entry 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 running or 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 deposited carbon mixed with each other and attached with the piston rod of the engine and it gets collected at the joint of the piston rod and its packing element. At that position after a long time the carbon tar makes a solid hard substance which causes the abrasion. This is the main reason behind deteriorate of the effectiveness of the stuffing box.
b) Describe the procedure for renewal of parts so that efficiency is restored.
In this part we are going to make a possible way to find out a solution for the renewal of the stuffing box so that its efficiency restored.
The procedures of renewal of the different parts are stated below. All the parts along with the diaphragm gland also dismantled and need to be checked carefully for a clear observation so that we can decide we can use it or a replacement is required. Mainly the packing elements are considered such kind of renewal works. The garter spring into the stuffing box if elongated after its permissible value at that time also the renewal is required. 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 of that kind of marine engine room if a maintenance work is going on then we need to be much more careful about the current unfortunate scenario also. Not only for this COVID 19 scenario at this present condition there might be some kind of situation may happen that we don’t get the spare parts so for this time also if we need to maintain the effectiveness of the stuffing box then we can follow these things,
- 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 can be increased 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 on them so that a clearance will be there and the leakage may not occur.
Basically in general terms when such kind of situation arises we are not getting the spare parts for the some uncertain condition but we have to get a running condition at that time as a chief engineer of the vessel we just need to find out the possible ways to get a repaired parts so that somehow it will not effect on the running behavior.
d) Explain the function of Sealing and scrapper rings. Sketch complete stuffing box drawing to identify the location of above rings.
For the marine engine either it is a low speed or high speed engine the purpose of the piston rings are almost same for both cases. The sealing is basically the compression ring or pressure ring of the piston. It provides the sealing of the combustion gas to come into the cylinder by crossing the piston. It is the top most ring of a piston. The extra oil left on the cylinder liner helps this ring for proper lubrication.
The scrapper ring is the oil controlled ring of a marine engine. For the two and fro motion of the piston into the cylinder liner a proper lubrication is required throughout the cylinder liner that lubrication is provided by the oil ring. The name is scrapper ring because of it scrap the oil to the cylinder liner inner wall and returns the oil into the crank case. Throughout the scrapper ring there are some cuts or holes are there to return the excess oil in the crankcase.
So generally we can say in fewer words that the sealing is the ring which provides the sealing from the combustion chamber to the lower portion of the cylinder. The scrapper ring is the ring of an engine that provides an ample amount of lubrication throughout the liner wall.
Q3) 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.
Here we are discussing the indication of the burn out exhaust valve in marine engine. These are the very basic outer symptoms of the engine we can see if the exhaust valves are burnt.
- Misfiring and a rough running can be observed if the exhaust valves are burnt in the marine engine. Since, the exhaust valves are providing a ceiling on the cylinder head at the time of combustion at that time a high pressure is there in the combustion chamber and a burnt valve is there that means it is not completely sealed combustion chamber. For that time at the running condition the combustion occurs on the combustion chamber as well is in the exhaust pipe also so a misfiring sound comes from the engine.
- Starting problem is also one of the most seen symptoms of the valve burnt out. For proper combustion at the combustion chamber a complete vacuumed condition is needed that means a proper sealing must be there in the combustion chamber. If there is any burnt part on the exhaust valve that implies a leakage on it so proper combustion is not takes place at that place so a staring problem can be experienced in this condition.
- Power loss is one of the most important factor can be experienced in the marine engine for burnt valve. 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. But if there is a leak in the combustion chamber then with giving the thrust on the piston head it goes away through the leakage portion. That means a complete work done is not happening in the engine so in general a power loss can be experienced for this kind of issue.
- The routine emission test can be failed also if there is a burnt exhaust valve. At the time of emission test we can feel some vapor of diesel on the exhaust gas for the combustion leakage through the burnt portion of the valves. Along with this a high temperature can also be experienced in the emission test.
These are the basic symptoms we can experience if there is any burnt exhaust valve in the marine engine.
The reasons of this kind of burning on the exhaust valves are,
- A continuous overloading on the engine is one of the main reasons of burning of the exhaust valve because a continuous overload means a high temperature at the combustion chamber continuously.
- For some cases we can see a poor combustion due to improper injection of some kind of fuel and some impurities in fuel can be the reason of the burning of the exhaust valve.
- If the closing position of the valve is not properly sealed, then from the leakage position the combustion takes place a burning at the valve may occur.
- Sometime an insufficient cooling may be the reason of burning of the exhaust valve of marine engine.
- Hot corrosion is also plays an important role on the context of burning of exhaust valve if there is an impurity in the fuel then corrosion takes place and burning may occur.
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 might be check that, the loading on the engine may not exceeded thoroughly and a preferable loading takes place in the engine so that high heating in the combustion chamber may not takes place.
- Since, poor combustion is one of the most important topics for burning of exhaust valve so we need to check the compression with a routine checkup and the deliveries of the fuel by the fuel injectors are to be proper then this kind of burning on exhaust valve can be reduced.
- To make a proper closing at the position of exhaust valve flange we need to polish the exhaust valve by routine checkup so the corrosion may not be there in the valve.
- The cooling mechanism of the engine is to be check so that it does not fail at any cost otherwise this kind of failure may occur in the exhaust valve.
- Before refueling we need to check the quality of the fuel (vanadium and sodium) to ensure any corrosive element is there in the fuel or not. And to make sure the proper combustion for that particular fuel we have.
Some other kind of advance design can also be implemented in it to get rid of this kind of issues. Like, bore cooling mechanism, valve rotation mechanism, heat and corrosion proof material usage and all.
c) Critically analyses 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.
One of the most important ways for better performance of a marine engine is the variable exhaust valve closing. It has some advantages on marine engine for their better performance and to make the engine economically strong enough it is the only one way. The advantages are,
- Proper combustion can take place at the time of combustion on the cylinder head.
- A proper compression can take place if we can vary the valve timing in terms of closing them or opening them.
- We can also be able to get an economic response from the engine performance.
- 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.
- One most advantage is that, we can also reduce the chance of burning of exhaust valve.
Here we are discussing the timing of the variable exhaust valve control method applied in some current engines. There are so many ways by which we can implement the variable valve control in the marine engine. The methods of variable valve control methods are cam switching, cam phasing, oscillating cam, eccentric cam drive, three dimensional cam lobe, two shaft combined cam lobe profile, coaxial two shaft combined cam lobe profile, helical camshaft, cam less engine and hydraulic system. With the help of these methods we can control the exhaust valve controlling by opening them in proper timing and controlling their opening for pre compression mode to get a proper compression and proper combustion. In many of the low rpm marine engines presently this kind of mechanisms are implemented with the help of some methods stated above.
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. The reason behind the crankshaft deflection is due to the different kind of non-symmetric loading on the engine parts like the pistons. Some kind of misalignment in the main bearing of the crankshaft also is the reason of deflection in the crank shaft. Now the question comes into our mind how we can get a symptom that there is a misalignment in the crank shaft. The only two best methods are the sound of the engine should be check and the main friction bearing temperature should be check so that we can understand there is any kind of friction happening or not. 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 for such kind of misalignment are,
- Main bearing damage
- Loose engine foundation and lack of damping equipment’s
- Bed plate crack at the position of main bearing
- Corrosion effects on the structure
- Manufacturing defects in the crank shaft
- Lack of lubrication
Here we are describing the precautions and the procedures are to be taken into consideration if we need to check the deflection in the crank shaft. Since, it is heavy machinery we are checking then the precaution is the most important thing we need to consider first. But first we are discussing the procedures to check the crank shaft deflection,
The equipment used in the marine engine for checking of crank shaft deflection is dial gauge. It is fitted between the adjacent webs of the crank shaft. The dial gauge measures the spread of the different webs in the crank shaft in different angular positions.
The procedure is, to place a dial gauge axially in the crank throw 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 bottom dead center 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,
- First we need to stop the engine.
- Blocking of the starting mechanism is necessary.
- Shutting of the air supply in the engine is also an important task.
- We need to stop the engine cooling pump.
- The engine should be left for a long time to get a cooling.
- Turning gear of the engine must be engaged.
- We need to stop the lubrication oil pump to get a vacant space into the crank case.
- Opening the crank case for a long time before entering into it for ventilation purpose is required.
- The person entering must have proper shoes and adequate amount of light is also necessary for this measurements.
These are to be follow at the time of measuring the deflection in the crank shaft.
b) Describe the action that should be taken if the current reading deviates significantly from the previous readings.
Here in this problem statement we are discussing about the actions should be taken for the deviation in the result. The deviation in the result means the deflection is there in the crankshaft. So what we need to follow or what kind of action should be taken for this scenario is discussed here.
Since, we have assumed that the current reading is significantly deviated the initial reading from the previous one. For this kind of damage, the best thing is to replace the crankshaft with a new one, 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 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. Along with these, at the running condition also we have to be very much careful so that continuous over loading is not there in the engine because a continuous over loading may cause an excessive damage on the crankshaft.
Here the points stated in the above paragraph are the best options for such kind of condition.
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.
|Piston||Un even surface finishing of the piston||The reason behind it is the attachments of hard carbon layer on it which is very hard||The surface is to be cleaned and polished properly so that efficiency increases.|
|Oxidation of the material||Due to improper fuel at the time of burning carbon dioxide and Sulphur dioxide makes a oxidation layer on it||Check the fuel quality before refueling to ensure the less amount of impurity.|
|Scratches on the external surface||For a extensive amount of friction with the cylinder liner there are so many scratches on it the main reason is the improper behavior of piston rings||The piston rings are to be change so that the piston may not get touched with the cylinder liner and to get proper lubrication on liner wall|
|Play on the connecting pin||For poor quality of connecting pin bushing there is a play on the attachment of the connecting rod and the piston||Only one option is there to get rid of this, it is to change the connecting pin and bushing at the attachment|
|Cylinder liner||Rusted outer surface||Due to salted moisture and lack of lubricating oil the outer surface is completely rusted||A regular maintenance in terms of oiling on them is required for reducing rust|
|Scratches in the inner surface||For the friction of the piston with the inner wall there was so much scratches on the inner wall of the cylinder liner||To get rid of this kind of issue we need to change the piston rings as soon as possible so that the friction may not occur with the cylinder liner|
|Hair lining hatching damaged||Due to friction of the piston with the cylinder liner inner wall the hatched line was completely damaged||The hatched lining is important for the lubrication oil to be comes down to the crank case. For this there is not any option rather than replacing it with a new one|
|Groove cutting inner surface||Due to damaged piston ring there is a cutting line into the inner wall of the cylinder liner||For such kind of damage we need to first change the piston rings otherwise there is not any other option to prevent it|
On the above table we have discussed the damaged part and the reason behind it. Along with this we also discussed the ways to prevent them so that we may not face such kind of issues any more.
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.
Now according to the problem statement we have dismantled the piston and the cylinder liner and we have to observe it and after observation we need to suggest if they are usable or not. To get the result if the piston and the cylinder liner are usable or not we have to consider some parameters. If we can see those parameters are in safe limit for the using, then obviously they are usable. Those things are stated below,
For the piston,
- If there are hard carbon layer on the top side, then they can be removed by polishing and can be easily used. But if there is an extensive oxidation occurs on its top surface it is difficult to use it again.
- If there are so many scratches on the external surface of the piston, then also it can be use if we change the piston rings.
- If there is a huge amount of play between the connecting pin and piston body for loose bushing, then there is no option for reuse of the piston. But in some cases we can use packing on them so that it fits tightly.
For the cylinder liner,
- If the external surface of the cylinder liner is damaged, then also for a long time by applying oil coating we can use it.
- If the scratches at the inner wall of the cylinder liner are not that much prominent then by replacing the piston rings, we can re-use the cylinder liner.
- For some cases if there are huge amount of metal cutting is being done in the inner wall of the cylinder liner then for some cases a new boring and over size piston can be used for the worst case only, otherwise it needs to be replaced.
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.
In this part we are describing the detail discussion on the crank shaft and cam shaft chain drive with its chain tightening arrangement. The requirement is to transfer the rotating motion of the prime mover of the engine that is the crankshaft to the any other part. Here in this discussion the rotating motion is transferred at the cam shaft of the engine. 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 most one useful feature of chain drive is, it is completely slip less just like the gear drive but more efficient because same effect can be experienced like gear drive with a lesser weight. Along with this the chain drive is preferred than belt drive because belt drive have some slips.
Here we need to rotate the cam shaft from the rotation of the crank shaft. The methodology is stated below with the help of free hand drawings.
b) Explain how chain slackness is caused and it effect on engine operation.
When the chain moves on the chain gears at that time if we do not provide proper lubrication then a friction is being experienced on the connection of gear and chain. For extensive friction the links between the chains makes its gaping larger. Since the gaping increases therefore the length of the chain increases and hence the slack can be experienced.
The effect of the chain slack is kind of slipping of the chain on the gear. The rotational speed of the chain gears also can be decreased due to extensive slackness on the chain. If the slackness is very much higher at that time we may experience more friction and that can cause a fatigue on the chain and accident may occur.
c) What is the vibration excitation sources in Propulsion engines other than external unbalanced moment and Explain with suitable drawings counter measuring devices fitted for above.
The main excitation methodologies for vibration on marine engine are described here in this part. The problem statement is to determine the various aspects or reasons of vibration. 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 centered shaft is there that also provide a vibration.
The manufacturing defect on the gearing system plays an important role on the vibration phenomenon of the marine engine. If the teeth of the larger sized gears are not prominent and have some defects, then we can feel some vibration on the machine or in the gear box. Hence the vibration on the gear box is transferred to the main engine. Some figures are stated below.
Eyres, D. J. and Bruce, G.J. (2012). Ship Construction, Butterwirth- Heinemann.
Aeberli, K. (2007). New High-Economy Engines for Panamax Containerships and Large Tankers. Winterthur, Switzerland.
MAN Diesel, (2009). Improved Efficiency and Reduce CO2, Man diesel, Denmark.
Wartsila, (2012), Wartsila Pulse Lubricating System.
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Essays, BookMy. (November 2018). JNE 316 Advance Marine Engineering Knowledge. Retrieved from https://www.samples.bookmyessay.com/jne-316-advance-marine-engineering-knowledge/
Essays, Bookmy. (November 2018). JNE 316 Advance Marine Engineering Knowledge. Retrieved from https://www.samples.bookmyessay.com/jne-316-advance-marine-engineering-knowledge/
All Answers ltd, 'JNE 316 Advance Marine Engineering Knowledge' (Bookmyessays.com, September 2019) https://www.samples.bookmyessay.com/jne-316-advance-marine-engineering-knowledge/ accessed Friday 10th July 2020