Q4. A. Discuss the nature of the forces to which a main engine crankshaft is subjected in normal service and explain how the resulting stress are maintained at a safe limit by design and efficient maintenance respectively.
B. Indicate the circumstances under which the crankshaft may--
i. over stressed; ii. Become defective without being over stressed.
Q2. With reference to four stroke diesel engine emission control:
(a) Describe how the Miller Cycle operates to control NOx emissions;
(b) Describe, with reasons, the modifications needed for a medium speed engine to operate on the Miller Cycle;
(c) give the advantages and disadvantages of closed against open scrubber systems.
Q3. Describe the developments that have taken place in the design of bearings of slow speed marine diesel engines, including geometry and material, focusing on the reasons for such changes.
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.
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.
Q6. Discuss the key factors considered when the power density of 2 stroke diesel engines is being increased.
a) Explain how T/C performance curves are matched to the propulsion engine requirements?
b) Explain how the engine performance is matched to the propulsion power?
c) Explain the influence of the calculation of the intermediate shafting system for a given power of the engine and propeller diameter?
Q9. If a main engine piston seizes in its liner at sea and it is not possible to replace the unit, explain, in detail, what provisions are made in the engine, to enable the ship to reach port?
Q8. With reference to main boiler super heater arrangements:
A. Compare the advantages and disadvantages of contra flow with parallel flow design.
B. Describe how the element tube banks are supported yet allow for expansion.
C. Describe how boiler carryover affects super heater effectiveness and condition.
Q2. A. Explain the term Variable Injection Timing (VIT) when applied to fuel pumps and state why a change in timing of fuel injection may be required.;
B. Describe, with the aid of sketches a VIT fuel pump and explain how the change in timing is achieved whilst the pump is in operation
C. Explain how it may be determined that individual fuel pumps are injecting the correct quantity of fuel with the correct timing at a particular pump setting.
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