EKM-Jul-2021 (2)

Q1. Draw an “out of phase” diagram for a large 2-stroke slow speed cycle engine. Describe in detail the part of the cycle showing on this diagram. With the help of a diagram, explain the effects of burning high and low-grade fuels (when fuel injection timing is not altered). Explain how good ignition and combustion can be obtained when using low-grade fuel.

Q2. Sketch and describe a system of control for manoeuvring a main diesel engine from the bridge and show how local control may be affected in case of breakdown of the system.

Q3. With reference to torsional vibrations in a main propulsion installation based on medium speed engines, gearbox and controllable pitch propeller: A. Explain how the vibrations may be caused; B. State the possible effects and damage that could result; C. Discuss the methods employed to minimise the potential problems associate with torsional vibration; D. Describe how the natural vibration frequency of the system could be modified.

Q4. (a) Explain the factors you would consider in deciding whether to open up a cylinder unit for an overhaul? After opening the unit and preparing for assembly, how would you decide whether to renew or re-use piston rings? 

(b) List the causes of piston ring failure which may result in gas leakage or ring breakage.

Q5. Explain why the use of residual fuels for the operation of large slow speed or medium-speed engines, may be responsible for the following problems with turbocharger nozzles, shrouds and blades and how in each, the problem may be minimized:

A. Build-up of deposits; 

B. Hot corrosion; 

C. Erosion.

Q6. 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 trimming 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.

Q7. Fatigue is one of the main causes of crankshaft failure. A. Indicate on a Sketch the most likely location of a fatigue crack; B. How is a fatigue failure identified; C. Describe initiation of a fatigue crack; D. Sketch and Describe the methods used to inhibit fatigue cracks.

Q8. During the past 4 months since you have joined the ship as a second engineer, a number of main engine exhaust valves have suffered cracking and corrosion at the seating faces. Write a report to the superintendent covering the following points; A. An explanation detailing how the problem became evident. B. Your action upon recognising the extent and seriousness of the problem C. Your reasoned views regarding the positive causes of the problem D. Your recommendations to avoid future incidents.

Q9. Sketch and describe the arrangement of a main engine camshaft chain. Describe the repair procedure following fracture of one chain link during the operation of the engine. Give possible reasons for the failure and explain how the chain is set initially at the correct degree of tension.