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Q7. With respect to large two stroke crosshead main engines;

A. Sketch and describe a crosshead designed to prevent or minimize bearing edge loading.

B. State how the arrangement describe a achieves its purpose.

C. What would be an acceptable range of bearing clearance for the top end bearing and bottom end bearings of a large two-stroke marine diesel engine.

Q5. With regards to modern 4-stroke diesel engine explain the following. a) The function of protection ring installed on the upper part of liner. b) The moderation in fuel injection drive system compared to conventional 4-stroke engine. c) Staggering of layout for multi hole nozzles. d) Effect of swirl and squish during the combustion process and how swirl and squish is generated.

Q9. With respect to the refrigeration system on board vessels, answer the following
a) Why are some TEVs fitted with an external equalising connection?

b) What is the purpose of a back pressure valve. what will the effect if it leaks?

c)How does an electronic TEV function.

Q6. Electronically controlled marine diesel engines are said to provide advantages over the traditional engines in the following areas

a) Improved fuel economy

b) Emission control

c)Engine response during manoeuvring, especially crash movements.

Explain how these are achieved.

Q3. With reference to main Thrust bearing of the pivoting pad type, explain with sketches where necessary

a) The principle of operation of the bearing

b) The critical clearances and why they are critical?

c) How these clearances are adjusted

d) Why such bearings sometime overheat although the clearances are adequate?

e) How is the lubrication film between faces of collar and thrust pad maintained?

Q6. It is common practice to plot in a graphical form the wear of a cylinder liner against the number of hours it has been in operation. When this is done it is often noticed that some scatter exists between the plotted points after a few wear figures have been recorded.

What is the reason for the scatter and how can the wear rate be shown in a more acceptable form? How would you forecast the length of life for a cylinder liner? (16)

Q7. (a) Describe, with the aid of a sketch, an external system for reducing engine NOx emissions, explaining the chemistry of the process (6)

(b) Explain why Urea is used in the Selective Catalytic Reduction process instead of ammonia. (5)

(c) Explain why the exhaust gas quality must be monitored before and after the Selective Catalytic Reduction unit, stating how such monitoring influences operation of the SCR unit (5)

Q7. A. Explain how static and dynamic imbalance of crankshafts can be overcome. B. Discuss the methods employed to obtain primary, reciprocating balance in an engine and plain why they are not completely successful. C. Describe engine additions which may be fitted to overcome problems resulting from primary or secondary imbalance.

Q9. a) Define the following conditions relating to lubricating oil

(i) Oxidation

(ii) Emulsification

(iii) Acidity (6)

b) Explain how each of the conditions in Q9 (a) is controlled by maintenance (5)

c) Suggest possible consequences if the conditions in Q9 (a) change and no corrective action is taken (5)