Small Vessel Second Engineer 060-01 Exam: Marine Diesel Engineering
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Questions and Answers

Describe the working principle of the four stroke cycle.

The four-stroke cycle consists of intake, compression, power, and exhaust strokes. In the intake stroke, the fuel-air mixture is drawn into the cylinder; during compression, the mixture is compressed; power stroke involves ignition and combustion of the mixture to produce power; and finally, the exhaust stroke releases the exhaust gases.

Explain what is meant by the term pulse system in large medium speed diesel engine turbo chargers.

The pulse system in turbochargers refers to the use of pulse exhaust gases to drive the turbine. It utilizes the intermittent, pulsating flow of exhaust gases to spin the turbine wheel, providing efficient energy transfer.

Explain the advantage the pulse system has over the constant pressure system in large medium speed diesel engine turbo chargers.

The advantage of the pulse system over the constant pressure system lies in its ability to harness exhaust gas energy more effectively. The pulsating flow in the pulse system matches the engine's operation, improving overall efficiency.

Identify the component parts A-E in the section of timing chain shown in the figure below.

<p>A - Camshaft Sprocket, B - Crankshaft Sprocket, C - Tensioner, D - Guide Rail, E - Timing Chain</p> Signup and view all the answers

Explain the reasons why chains may elongate or slacken in service and the areas that may wear.

<p>Chains may elongate or slacken due to wear and stretching over time. The chain tensioner and guide rails are common areas that may wear, affecting chain alignment and tension.</p> Signup and view all the answers

Explain the purpose of relief valves fitted in diesel engine crankcases, and outline the circumstances that may cause them to operate.

<p>Relief valves are fitted in diesel engine crankcases to release excess pressure that may build up inside the crankcase. They operate when there is an abnormal increase in crankcase pressure, which can occur due to factors like worn piston rings, crankcase ventilation system malfunction, or blow-by from the combustion chambers.</p> Signup and view all the answers

Explain the purpose of the header tank in the main engine cooling water system, and why both heaters and coolers may be fitted in such systems.

<p>The header tank in the main engine cooling water system serves as an expansion tank, allowing for the expansion and contraction of the coolant as temperatures change, and also maintains a positive pressure in the system. Heaters and coolers are fitted to maintain the desired operating temperature range of the coolant, with heaters warming the coolant when necessary, and coolers removing excess heat.</p> Signup and view all the answers

With reference to tube type heat exchangers, explain the purpose of baffle plates, sliding tube plate, tell-tale ring, vent cock, and anodes.

<p>Baffle plates direct the flow of fluids through the heat exchanger for efficient heat transfer. The sliding tube plate allows for thermal expansion of the tubes. The tell-tale ring indicates any leakage between the two fluids. The vent cock is used to remove air from the system during commissioning. Anodes help prevent corrosion of the heat exchanger by sacrificial oxidation.</p> Signup and view all the answers

Explain, with the aid of a diagram, the operation of a solenoid operated, battery powered electric starting system for an internal combustion engine. Also, explain the term 'pre-engaged starter'.

<p>A solenoid operated, battery powered electric starting system uses a solenoid switch to engage the starter motor with the engine's flywheel ring gear when the ignition key is turned. The battery provides power to the starter motor, which then cranks the engine. A pre-engaged starter is one where the starter motor pinion gear is always engaged with the flywheel ring gear, eliminating the need for a solenoid switch.</p> Signup and view all the answers

With reference to abnormal turbocharger vibration, explain the possible causes while operating at a steady speed, and describe how these causes may be minimized.

<p>Abnormal turbocharger vibration at steady speeds can be caused by factors like unbalanced rotating components, worn bearings, or fouling of the turbine or compressor wheels. These causes can be minimized through proper maintenance, balancing of components, timely replacement of worn parts, and ensuring clean air and exhaust gas flow.</p> Signup and view all the answers

Sketch a hydraulically operated, multi-plate, friction clutch, labelling the main components.

<p>[A sketch of a hydraulically operated, multi-plate, friction clutch should be provided, with labels for the main components such as the pressure plate, clutch discs, clutch housing, hydraulic actuator, and release bearing.]</p> Signup and view all the answers

With reference to reduction gearing, explain the purpose of the magnetic filter in the lubricating oil system, why the surface finish of the gear teeth is important, and why EP lubricating oil is preferred.

<p>The magnetic filter in the lubricating oil system removes ferrous particles from the oil, preventing damage to the gears. The surface finish of the gear teeth is important for smooth meshing and reducing wear. EP (Extreme Pressure) lubricating oil is preferred because it contains additives that provide better protection against high loads and shock loading conditions experienced in reduction gearing.</p> Signup and view all the answers

Explain the term 'blow-by' in the context of diesel engine crankcases, and its potential impact on crankcase pressure.

<p>Blow-by refers to the leakage of combustion gases past the piston rings and into the crankcase during the combustion process. Excessive blow-by can lead to an abnormal increase in crankcase pressure, necessitating the operation of relief valves to prevent damage to the crankcase.</p> Signup and view all the answers

Study Notes

Four Stroke Cycle

  • The four-stroke cycle is a sequence of events that occur in an internal combustion engine to convert fuel into mechanical energy.
  • The four strokes are intake, compression, power, and exhaust.
  • During intake, the piston moves down, creating a vacuum that draws air into the cylinder.
  • During compression, the piston moves up, compressing the air.
  • During power, the compressed air is ignited by a spark plug or fuel injection, causing the air to expand and push the piston down, producing power.
  • During exhaust, the piston moves up, pushing the burnt gases out of the cylinder.

Pulse System

  • A 'pulse system' in turbochargers refers to the design where the exhaust gases enter the turbine directly.
  • The pulse system utilizes the pressure waves generated by the engine's exhaust pulses to drive the turbine.
  • The pressure waves reinforce each other, resulting in a more efficient energy transfer to the turbine.

Pulse System Advantages

  • The pulse system in turbochargers offers advantages in terms of improved turbocharger response and efficiency compared to constant pressure systems, particularly for large, medium-speed diesel engines.
  • The energy from exhaust pulses directly drives the turbine, reducing energy loss and increasing response.
  • The pulsed flow also promotes better scavenging of the exhaust gases, leading to improved engine performance.

Timing Chain Component Parts

  • A: Guide rail
  • B: Tensioner
  • C: Idler gear
  • D: Chain
  • E: Sprocket

Chain Elongation and Slackening

  • Chain elongation can be caused by wear on the pins and bushings, as well as stretching of the chain links, leading to increased slack.
  • Chain slackening can also be due to wear on the sprocket teeth.
  • The wear can occur due to factors like improper lubrication, excessive load, high temperature, contamination, or age.

Areas of Wear

  • The areas susceptible to wear in a chain drive include:
    • The pins and bushings of the chain links
    • The sprocket teeth
    • The guide rails and tensioner components

Relief Valves

  • Relief valves in diesel engine crankcases serve to relieve excess pressure buildup within the crankcase.
  • Excessive pressure can occur due to blow-by gases, which are combustion gases that leak past the piston rings.
  • When pressure exceeds a set limit, the relief valve opens, venting the excess pressure, typically into the atmosphere or an exhaust manifold.

Header Tank

  • Header tank in a diesel engine cooling water system acts as a reservoir for the coolant.
  • It provides a space for expansion of the coolant when heated, preventing pressure buildup in the system.
  • The tank also helps maintain a consistent coolant level and allows for easy filling or topping up.

Heaters and Coolers

  • Heaters in cooling water systems are used to pre-heat the coolant during cold starts, improving engine performance and reducing wear.
  • Coolers, often called heat exchangers, are utilized to cool the coolant after it passes through the engine, preventing overheating.

Tube Type Heat Exchanger Components

  • Baffle Plates: Reduce turbulence and help direct the flow of the fluids, enhancing heat transfer efficiency.
  • Sliding Tube Plate: Used for cleaning tubes and for maintenance.
  • Tell-Tale Ring: Indicates the condition of the heat exchanger, detecting leaks by showing the presence of coolant in the system.
  • Vent Cock: Allows for venting air trapped in the system, ensuring proper functioning.
  • Anodes: Provide sacrificial protection against corrosion, extending the lifespan of the heat exchanger.

Solenoid Operated Electric Starting System

  • A solenoid-operated, battery-powered starting system uses a solenoid to energize the starting motor.
  • When the ignition switch is turned to start, it sends a signal to the solenoid.
  • The solenoid activates the starting motor, engaging a gear that meshes with the engine crankshaft.
  • The starting motor rotates the engine crankshaft, initiating combustion and starting the engine.

Pre-engaged Starter

  • A pre-engaged starter remains engaged with the engine crankshaft even when not engaged in starting.
  • This allows for a quicker start, as there is no need to engage the starter gear.
  • The starter motor is generally designed to run at a lower speed for prolonged use.

Turbocharger Vibration: Possible Causes

  • Unbalanced impeller: An unbalanced impeller can cause vibration, particularly at steady speeds.
  • Worn bearings: Worn bearings can cause both vibration and noise.
  • Loose or worn mounting: Impeller vibration can be amplified due to loose or worn mounting bolts, creating additional noise.
  • Foreign objects in the system: Foreign objects lodged in the turbocharger components may cause vibrational problems.

Minimizing Vibration

  • Balancing the impeller
  • Replacing worn bearings
  • Tightening or replacing worn mounting bolts
  • Removing any foreign objects from the system
  • Using a low vibration turbocharger design

Hydraulically Operated Clutch

  • A: Clutch housing
  • B: Pressure plate
  • C: Friction discs
  • D: Hydraulic actuator
  • E: Release bearing
  • F: Clutch release lever

Reduction Gear Components and Function

  • Magnetic Filter: Removes metallic particles from the lubricating oil system.
  • Surface Finish: A smooth gear tooth surface finish reduces wear, promotes better lubrication, and minimizes noise.
  • EP Lubricating Oil: EP (Extreme Pressure) lubricating oil is preferred for reduction gears because it provides additional protection against high loads, wear, and extreme temperatures.

Blow-by

  • Blow-by in a diesel engine crankcase refers to the combustion gases that escape past the piston rings and enter the crankcase.
  • It leads to increased crankcase pressure and can contaminate the lubricating oil.
  • Excessive blow-by can indicate poor piston ring sealing or damage, potentially affecting engine performance.

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Description

Prepare for the Small Vessel Second Engineer 060-01 exam on Marine Diesel Engineering administered by the Scottish Qualifications Authority. The exam is scheduled for Friday, 14 May 2021 from 1400 to 1600 hrs. The paper includes 100 marks and candidates must achieve a minimum of 50 marks to pass.

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