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Marine Engineering Glossary > Glossary > Flashcards

Glossary Flashcards

1
Q

Thrust Bearing

A

Two rings fore and aft of the collar secured to the hull rather than the shaft. Act as stoppers and in doing so transfer the thrust from the shaft to the hull.

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2
Q

Thrust bearing Rings

A

Referred to as the housing they are lined with easily replaceable alloy pads which greatly reduce the coefficient of friction. These alloy pads contain grooves through which lubricating oil flows.

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3
Q

Lubrication

A

Reduces friction, removes heat. prevents corrosion and cleanses.

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4
Q

Internal combustion engines

A

Requires oxygen, a combustible and heat to start ignition in order to function.

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5
Q

Compression Ignition Engine

A

Air is compressed and the temperature increases to the point where the fuel combusts.

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6
Q

Flash Point

A

The temperature at which the rate of vapour creation would result in momentary ignition.

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7
Q

Fire Point

A

The temperature at which the rate of vapour would create a continuous fire upon ignition

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8
Q

Autoignition Temperature

A

The point at which a spark is no longer necessary for combustion to occur

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9
Q

Cycle (5 Processes Of)

A

1) Induction
2) Compression
3) Combustion
4) Expansion
5) Expulsion

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10
Q

Engine Stroke

A

The full distance through which the piston passes.

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11
Q

Two Stroke Engines

A

Take 2 strokes to complete a cycle

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12
Q

4 Stroke Engines

A

Require 4 strokes to complete a cycle

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13
Q

Top Dead Center

A

Highest position the piston reaches within the cylinder

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14
Q

Bottom Dead Center

A

The lowest position the piston the piston reaches within the cylinder

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15
Q

3 Forms of Scavenging

A

1) Loop
2) Cross
3) Uniflow

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16
Q

Crosshead Pistons

A

Collect soot, preventing it from entering the crankshaft system. Allows for the use of a different form of lubrication on the piston head.

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17
Q

Trunk Piston Engine

A

For Higher speed engines

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18
Q

Back Plate

A

Provides support and rigidity, carries the seating for the crankshaft and main bearing housing.

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19
Q

A-Frame

A

Fabricated strength members which straddle the bed plate, carry the guides for crosshead engines.

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20
Q

Cylinder Liner

A

Easily replaceable and made of materials with good cooling properties. For two stroke engines, ports are cut into the liner

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21
Q

Scavenge Diaphragm

A

Only possible in crosshead engines, seals off the piston from the crankcase.

22
Q

Cylinder Head

A

Houses:

1) The exhaust valve (4 stroke and uniflow)
2) The intake valve (4 stroke)
3) Fuel injector
4) Relief valve (removes excess pressure)
5) Air starting valve

23
Q

Tie Bolts

A

Long Bolts connecting the cylinder block to the engines A frame. Constantly under tension, they increase the strength of the material as their compression counteracts tensile strain produced by the engine.

24
Q

Bedplate

A

Only for large two stroke engines, a platform which supports structural components while withstanding heavy fluctuating stresses.

25
Q

Cylinder Liners

A

Must:

1) readily transfer heat
2) retain lubricating oil
3) have high mechanical strength

26
Q

Cylinder Liner Mantainence

A

Replaced after a wear-down of 2%
The internal diameter is measured fore/aft and port/starboard several times along the liner
The typical rate of weardown is 0.01mm per 1000 hours.

27
Q

Cylinder Liner Weardown

A

Caused by:

1) Frictional Wear
2) Corrosion: water and SO3 produced via combustion bond to form sulphuric acid which condenses on the liner.
3) Abrasion: hard particles from combustion or lubricating oil and become trapped between the liner and piston ring.
4) Adhesion/Scuffing: Excessive heat or gas pockets due to the lack of lubrication

28
Q

Piston Cooling

A

Limits thermal stressing and thermal expansion

29
Q

Oil cooled pistons

A

1) Lower thermal capacity than water
2) Lower maximum safe temperature than water (above 56 degrees oil carbonises)
3) Oil is supplied under pressure via telescopic pipers or swinging links

30
Q

Water Cooled Pistons

A

1) danger of water leaking into the combustion chamber and contaminating fuel
2) Inhibitors needed to prevent corrosion
3) separate cooling system is necessary
4) Temp of 70 degrees can be sustained

31
Q

Thermal Stressing

A

Reduced by lowering the temperature gradient between material and coolant

32
Q

Top Piston Ring

A

aka fire ring as it is exposed to combustion

33
Q

Pistons Rings

A

The only part of the piston in contact with the cylinder lining
More than one ring is necessary as each ring has a small gap left from when it was inserted onto the piston ring. Multiple rings also help to distribute oil more effectively and act as reserve compression rings

34
Q

Scraper rings

A

Downward wedge on lip means that on the downward stroke they scrape of oil from the cylinder liner, which they then distribute on the upward stroke

35
Q

Crosshead

A

Forged steel block secured to the foot of the piston rod. Transfers the transverse component of the pistons movement to its guides.

36
Q

Top end bearing

A

Transmits full gas load from the piston to the connecting rod and crosshead

37
Q

Bottom end bearing

A

Transmits similar loads to those in the crankshaft

38
Q

Crankshaft

A

Receives and transmits the full power of the engine. Subject to high torsion and bending stresses.Either semi-built or welded. Statically built and dynamically balanced

39
Q

Flywheel

A

Solid wheel shaped to have a high mass and high inertia to store energy while the engine is running. Absorbs the energy at peak torque and returns it during low torque and deceleration. Smooths out fluctuation in engine speed

40
Q

Main Bearings

A

Support the crankshaft at each journal, subjected to heavy loads fluctuating in magnitude and direction

41
Q

Fuel Injectors

A

Atomise the fuel by passing it through tiny orifices under high pressure. The usual pressure is 250 bar.

42
Q

Spring Loaded Fuel Injector

A

Pressure is set by adjusting the resistance of the spring

43
Q

Hydraulic Fuel Injector

A

Pressure is created by a fuel pump, the injector creates no pressure itself

44
Q

For Crisp Combustion

A

1) Viscosity (resistance to flow) : specific to the injector
2) Atomisation: Breaking fuel into fine particles (increases surface area allowing for more effective combustion)
3) Penetration: The distance that fuel droplets travel into the compressed air.
4) Turbulence: Provision of air among the particles

45
Q

Fuel Pumps

A

One fitted per cylinder. Driven by the engine. Delivers the correct amount of fuel to the engine at the correct pressure and time.

46
Q

Turbocharger

A

Increase the mass of air which enters the engine, as a greater volume of available air means complete combustion is more likely. Uses the energy wasted in the exhaust.

47
Q

Pulsed Turbochargers

A

1) More efficient at low load
2) Highly responsive to change in speed
3) utilises the the thermal energy of exhaust gas and kinetic energy during the blowdown period.
4) direct connection between each cylinder and the turbocharger system
5) Earlier opening of exhaust valve maximises the pulse.
6) Limited to three cylinder per exhaust branch to stop interference with scavenging.

48
Q

Constant Pressure Turbochargers

A

1) every cylinder exhausts into a large receiver
2) No need for earlier opening of exhaust
3) turbocharger nozzle can be calibrated
4) More efficient at a higher load

49
Q

Air Starting System

A

1) High pressure air stored in ‘bottles’
2) Master Valve leads to individual air starting valves
3) Air starting valves are in the cylinder head
4) Distributor opens the appropriate valve
5) Bottles should have enough air for 12 consecutive starts

50
Q

Lubricating Oil System

A

Operates 24/7 to oppose condensation.

Marine Engineering Glossary (1 decks)

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