Q6. What is "virtual tappet" in the hydraulically actuated air spring return exhaust valves, and how is it set. Explain why the damage occurs to the seats of the exhaust valves due to furrowing and cutting and how an incident of "valve drop" leading to extensive damage to running gear can occur.
Q6. (a) Describe, with the aid of sketches, the procedure for cutting out and "hanging-up" an engine cylinder of a two-stroke crosshead engine in the event of complete failure of the crosshead pin such that the crosshead pin cannot be operated and no replacement is immediately available. (12)
(b) State, with reasons, the factors which may inhibit starting and limit the operating speed of the engine with a cylinder cut out. (4)
Q6. Selective catalytic Reactors (SCR) are being extensively used in marine diesel engines for the compliance of Tier-III NOx emission requirements. Explain various types of SCRs in use with particular focus on the following:-
a) High-Pressure SCRs (HPSCR) vs Low-Pressure SCRs (LPSCR)
b) SCRs with static mixers.
c) SCRs installed upstream the turbocharger(s) Vs downstream turbochargers.
Q4. a) With reference to main engine starting and reversing:
A. Define the function of air distributors. (5)
b) Give reasons why air distributors are not fitted to some large direct reversing engines. (3)
c) Briefly Discuss the potential issues with air distributors and their respective solutions. (8)
Q4. Misalignment of the main shafting between engine and propeller causes bearing overloads and shaft stress;
A. State the difficulties associated with checking shaft alignment and the reasons why results are unreliable due to external factors;
B. Explain with a simple sketch how a bearing load is assessed.
C. Explain how uneven loading could be rectified
Q5. Discuss the consequences of failure to maintain correct clearances in the case of main diesel engine crankshaft and bottom end bearings. Sketch a bottom end bearing paying particular attention to the arrangement of ensuring uninterrupted flow of oil to the top end bearing.
Q7. With reference to electronically controlled engines:
(a). Describe how fuel injection quantity and timing is adjusted.
(b). Describe how the exhaust valve timing may be varied.
(c). Describe how starting air valves are regulated.
Q3. Discuss critically the following alternative types of main propelling machinery for installation in a proposed new ship - A. 2 stroke single acting cross head type slow speed engine; B. 4 stroke single–acting with reverses / reduction gear.
Q9. a) Briefly discuss the advantages, disadvantages and working of pulse type cylinder lubrication system. (8)
b) Explain the process of calculating specific cylinder oil consumption of main engine. (8)
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