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Marine Engineering > Chapter 2 Fuels > Flashcards

Chapter 2 Fuels Flashcards

1
Q

The iso number for marine fuels is?

A

ISO 8217

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2
Q

Crude Petroleum classified into three types?

A
  1. Paraffin base residue after distillation contains more than 5% paraffin wax
  2. Asphalt base residue after distillation contains less than 2% paraffin wax and is mainly composed of asphalt(bitumen)
  3. Mixed base in which the residue after distillation contains between 2% and 5% paraffin wax mixed intimately with asphalt
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3
Q

Where is asphalt mainly found?

A

In residual oils and is an indefinite substance both hard and soft, being mainly combustible although hard asphalt can cause considerable gum deposits in IC engines

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4
Q

Give two examples of saturated hydrocarbons?

A

Paraffin and Napthenes

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5
Q

Give two examples of unsaturated hydrocarbons and where they might be found?

A

Aromatics and Olefines.

Usually found by molecular bonding alteration during later processing.

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6
Q

What are the two basic parts of the modern refinery process?

A

Atmospheric and vacuum distillation followed by catalytic and thermal cracking process.

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7
Q

What is specific volume?

A

m3/kg

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8
Q

With regards to fuel oil, what is density proportional to?

A

The energy that is extracted.

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9
Q

How do you define viscosity?

A

Resistance of fluids to change shape due to internal molecular friction of molecule with molecule of the fluid producing frictional drag

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10
Q

What are the two types of viscosity?

A

Absolute (dynamic) and Kinematic

Dynamic is difficult to determine

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11
Q

How is kinematic viscosity measured?

A

It is measured by capillary flow of a set volume of liquid from a fixed head (Poiseuille)

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12
Q

What is the SI method of measuring viscosity?

A

Kinematic measurement.

ISO 8217 uses the standard of mm2/s at 40°C

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13
Q

What is the viscosity of diesel oil at roughly 40°C?

A

Around 7 cSt

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14
Q

What are the factors influenced by viscosity?

A
  • Frictional drag effects
  • pipe flow losses
  • flow through orifices (atomisation)
  • load capacity between surfaces
  • fouling factor
  • spread factor
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15
Q

What is viscosity index?

A

A numerical value which measures the ability of an oil to resist viscosity change when the temperature changes

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16
Q

What trait would an oil with a high viscosity index posses?

A

An oil would be able to maintain a fairly constant viscosity despite a wide variation of temperatures.

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17
Q

Where would a high viscosity index be important onboard a ship?

A

Important for deck equipment, emergency generators and lifeboats due to large temperature ranges found in the winter months

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18
Q

Define flash point?

A

The minimum temperature that oil gives off a flammable vapour, which on the application of flame in a specified apparatus would cause a momentary ignition

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19
Q

What are the two types of tests for flash point and which one is lower?

A

Open and Closed tests

Closed tests give a lower value

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20
Q

What temperature flash point is regarded as dangerous?

A

Oil with a flash point below 22°C such as gasoline’s/benzenes

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21
Q

At what value of flash point are oils classed as safe?

A

Above 66°C

Oils such as gas diesel and fuel oils

22
Q

What is the minimum flash point for oils as described by SOLAS?

A

60°C

SOLAS II- 2 regulation 4 sets out the basic requirements for main engine and aux engine fuels

23
Q

Where does SOLAS say it is permissible to use fuel with a minimum flash point of 43°C?

A

Emergency generator so long as the fuel is not stored in a machinery space

24
Q

What is the temperature range that promote bacterial growth in fuel?

A

Between 15°C and 40°C

It is prudent best practice to avoid heating fuel in storage above 52°C

25
Q

When using oil with a high viscosity, requiring high degrees of heating for atomisation, how far from the flash point can the oil be heated to?

A

Within 20°C of the closed flash point

26
Q

What is the pour point?

A

The lowest temperature value at which an oil will flow under prescribed test conditions.

27
Q

What can happen if fuel is stored below is pour point?

A

Wax can build up on heating coils and at the bottom of tanks

28
Q

What is the Conradson method?

A

This test indicates the relative carbon-forming propensity of an oil.
This test is a method of determining the residual carbon.

29
Q

What is the maximum water content in fuel for residual fuel and diesel oil according to ISO 8217:2010?

A
  1. 5% by volume for residual fuel

0. 3% by volume for diesel fuel

30
Q

What is CCAI?

A

Calculated carbon aromaticity index

31
Q

What is the problem with aromatic compounds?

A

These compounds have a high resistance to auto ignition.

During 1990’s some ships had problems as bunkers had high levels of aromatic compounds

32
Q

What is the CCAI for residual fuel as set by ISO 8217?

A

870

33
Q

What is the problem with combustion caused by a high CCAI?

A

There is a direct correlation between CCAI and ignition delay.
With a longer ignition delay there is a larger build up of unburnt air/fuel mixture before the initial combustion takes place.
The combustion process moves on, the next stage is determined by how rapidly the remain vaporised fuel and oxygen can be mixed as the initial supply of oxygen close to the fuels boundary has been used in the first stage.
However if this happens to fast then very rapid rates of pressure rise in the cylinder can result in shock waves being transmitted, causing broken piston rings and overheating of metal surfaces.

34
Q

What is CCAI?

A

Calculated carbon aromaticity index

35
Q

What is the problem with aromatic compounds?

A

These compounds have a high resistance to auto ignition.

During 1990’s some ships had problems as bunkers had high levels of aromatic compounds

36
Q

What is the CCAI for residual fuel as set by ISO 8217?

A

870

37
Q

What is the problem with combustion caused by a high CCAI?

A

There is a direct correlation between CCAI and ignition delay.
With a longer ignition delay there is a larger build up of unburnt air/fuel mixture before the initial combustion takes place.
The combustion process moves on, the next stage is determined by how rapidly the remain vaporised fuel and oxygen can be mixed as the initial supply of oxygen close to the fuels boundary has been used in the first stage.
However if this happens to fast then very rapid rates of pressure rise in the cylinder can result in shock waves being transmitted, causing broken piston rings and overheating of metal surfaces.

38
Q

What does the Octane number represent?

A

This is indicative of the knock rating. Knocking or pinking are characteristics of some IC engine fuels, particularly in spark ignition engines. It can cause pre-ignition, overheat and damage.

39
Q

What is the normal speed of flame fronts from spark ignition?

A

18m/s

40
Q

What can happen if engine conditions/type of fuel used raises the temperature and pressure raised above the spontaneous ignition point?

A

Auto-ignition occurs.
This means by the time the last gas charge is reached the flame front speeds can reach 2.2km/s and detonation, temp rise and heavy shock waves occur.

41
Q

What is the test for the octane number?

A

ISO-octane (C8H16) with very good anti-knock properties and taken as upper limit 100.
Normal heptane (C7H16) with very poor anti-knock properties and is taken as lower limit 0.
The octane number is the percentage by volume of iso-octane in a mixture of iso-octane and normal heptane which has the same knock characteristics has the chosen fuel.
The test is conducted under fixed conditions on a standard engine which usually has electronic detonation detection.

42
Q

What is the Cetane number?

A

Is the indication of the ignition quality of Diesel fuel with the CCAI being the measure applied to residual fuels.
In a compression ignition engine, cold starting is often required; here the ignition delay (the time delay between injection and firing) can not be too long otherwise collected fuel will generate high pressures when it does ignite and diesel knock results.

43
Q

Speed and cetane number can be correlated.

What Cetane number is the minimum a high speed engine will find acceptable (above 13.3 rev/s)?

A

A Cetane number above 48 may be regarded as minimum

44
Q

What is the minimum Cetane number for diesel oil as set by ISO 8217:2010?

A

35 minimum.

45
Q

What is the test for determining the Cetane number?

A

Cetane is a paraffin hydrocarbon, hexadecane (C16H34) being its correct designation, of high ignition quality is taken as the upper limit of 100.
Alpha-methyl-naphthalene is of low ignition quality is taken as the lower limit of zero. Thus Cetane number is the percentage by volume of Cetane in a mixture of
Cetane and Alpha-methyl-naphthalene that matches the chosen fuel in ignition quality.

46
Q

What is crankcase oil dilution?

A

This is the percentage of fuel oil contamination of lubricating oil occurring in IC engines, which can seriously reduce the lubricity of the oil.

47
Q

What factors can cause severe corrosion of crankshafts?

A

The sulphur products produced from fuel oil mixing with any water in the lubricating system to form sulphuric acids.

48
Q

Why is it not possible to use automotive diesel onboard seagoing vessels?

A

The flash point of marine diesel is 60°C where as automotive is 55°C.
Thus it would require a change to the legislation of SOLAS.

49
Q

Why are there limits on the Sulphur content of marine fuels?

A

To reduce the SOx and particulate matter from the emissions of power plants on ships.

Annex VI. of MARPOL regulation 4 allows flag administrations to approve alternative means of compliance wug the exhaust emission limits that are at least compatible with the limits of engines using the low-sulphur fuel.

50
Q

If the FO is classed as heavier, what can be said about the viscosity, flash point and calorific value?

A

Viscosity and flash point increase, calorific value decreases

Marine Engineering (6 decks)

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