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Revision Notes > Module 3 Characteristics of Combustion > Flashcards

Module 3 Characteristics of Combustion Flashcards

1
Q

Perfect Combustion

When you burn gas what products are produced in the perfect world

CH4 + 2O2 = ??? + ???

CH4 = Methane

O2 = Oxygen

A

CH4 + 2O2 = CO2 + 2H2O

CH4 = Methane

O2 = Oxygen

CO2 = Carbon Dioxide

H2O = Water

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2
Q

How to rectify:

Incomplete combustion caused by overgassing due to

1) excessive burner pressure
2) excessive gas rate

A

1) reset burner pressure (MI), check gas rate
2) If burner pressure is correct check injector size / condition

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3
Q

If you think the sensor on your combustion analyzer is not working properly how can you test it?

A

1) Cooker grill
2) Around cold saucepan on hob
3) MI calibration gas

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4
Q

What is an Open Flue Appliance and what type is it (A,B,C)?

A

1) Flue to exhaust combustion products outside, air drawn from room
2) Type B

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5
Q

Before starting a CPA what do you need to check re the appliance?

A

1) Appliance + flue installed as per MI
2) No obvious signs of damage etc which could cock up the results
3) Operating pressure and flame picture ok

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6
Q

What odour does natural gas have?

A

1) None it is odourless
2) Odour added

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7
Q

What is a flueless appliance and what type is it (A,B or C)?

A

1) Has no device to exhaust the combustion products outside
2) Type A

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8
Q

At CO level (ppm) should you turn everything off and ventilate the room?

A

30ppm

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9
Q

With a pre-mix burner if the air inlet becomes linted up (not blocked) do you get incomplete combustion?

A

1) No - less air passing through the venturi sucks (or ‘inspires’) less gas.
2) The ratio of air / gas stays the same
3) Less heat is generated

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10
Q

1) What sort of burner is this?

A

1) Pre-mix burner

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11
Q

What are the CO/CO2 ration action levels for central heating and combination boilers?

A

0.008

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12
Q

1) What sort of flame is this?
2) What % of air is ‘primary air’

A

1) Pre-aerated flame
2) 50%

Most common type of gas flame

Gas is aerated twice!

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13
Q

To ensure that appliaces work correctly gases with similar properties are grouped together in families.

What are the three families?

A

Family 1 - manufactured gases

Family 2 - Natural gases

Family 3 - LPG

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14
Q

Carbon Monoxide

Name three properties of the silent killer…

A

1) Colourless
2) Odourless
3) Tasteless

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15
Q

Name the 5 causes of incomplete combustion

A

1) Insufficient Air
2) Overgassing
3) Undergassing
4) Flame Impingement
5) Vitiation

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16
Q

What does Gas Safety Regulation no 33 state?

A

You are responsible to ensure that any appliance worked on does not pose a danger to people or property

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17
Q

Good or bad flame?

Why?

A

1) Bad flame

Why?

Floppy elongated flame

Luminosity evident

Unstable

Soot on burner bars, heat exchanger, chamber etc

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18
Q

Name the constituent that makes up 90% of natural gas

A

Methane CH4

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19
Q

How to rectify:

Incomplete combustion caused by flame impingement

A

1) Burner alignement
2) Burner pressure
3) If 1 & 2 ok check injectors

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20
Q

Flame Speed

You can measure how quickly a taper burns

Gas is the same - it will burn along the gas / air mixture

How many meters per second does natural gas burn at?

A

0.36m/s

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21
Q

Insufficient air for Combustion

1) Main causes
2) Ways to recity

A

Main issue found

1) Insufficient ventillation built in
1) Blocked ventilation / grilles / burner air ports
2) Bugger vents, a good clean!

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22
Q

Effects of Carbon Monoxide

What % volume of CO in air will kill you?

A

0.4%

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23
Q

How to rectify:

Incomplete combustion caused by blockage of inlet grill, primary air port or heat exchanger

A

Remove blockage and check appliance to see

1) If there are further blockages
2) It works

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24
Q

What type of flame is this?

Name some key characteristics

A

Post aerated flame

No primary air = floppy, unstable, uncontrolled and smokey flame

Luminos flame

=

incomplete combustion

=

carbon (soot)

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25
Q

What is the CPA testing procedure to measure CO on a type A appliance (space heater)?

A

1) Permanent ventilation clear
2) Windows / doors etc. shut
3) Run at max for 30 minutes, record results every minute

26
Q

Is natural gas lighter or heavier than air?

What is its specific gravity (SG)?

Specific gravity is the weight or mass of a substance

A

Lighter than air.

SG is 0.6

27
Q

What is the difference between Gross and Net Calorific Value (CV)

A

1) Gross CV - includes the heat trapped in the water vapour.

This trapped or latent heat, if usually lost via the flue unless you have a condensing boiler

2) Net CV - heat that can be transferred to the heat exchanger. Excludes the latent heat

28
Q

What is a Room Seal Appliance and what type is it (A,B,C)?

A

The combustion circuit (air supply, combustion chamber, heat exchanger, air in, exhaust out) is sealed to the room.
2) Type C

29
Q

With 5 volume of CO in the air will lead to severe headaches, nausea, weakness of knees, irritability, increased respiration and pulse rate and collapse in exertion within 4 to 5 hours of exposure?

a) 0.01%
b) 0.03%
c) 0.05%
d) 0.4%

A

c) 0.05%

30
Q

What % volume of CO in the air will lead to flushed skin, headaches, breathlessness and palpitations on exertion, within 4 to 5 hours of exposure?

a) 0.01%
b) 0.03%
c) 0.05%
d) 0.4%

A

b) 0.03%

31
Q

What % volume of CO in the air will cause tightness across the forehead with prolonged exposuare?

a) 0.01%
b) 0.03%
c) 0.05%
d) 0.4%

A

a) 0.01%

32
Q

Is Carbon monoxide lighter or heavier than air?

A

Is Carbon monoxide lighter or heavier than air?

SG of air is 1!

33
Q

Pre-aerated flames

Name 3 characterisitcs of pre-aerated flames

A

1) Well defined inner cone
2) Well defined outer blue flame
3) No signs of incomplete combustion

If there is incomplete combustion the flame goes yellow and floppy

34
Q

Name 3 signs of incomplete combustion

A

1) Staining around the appliance
2) Sooting in the appliance
3) Yellow, floppy flame

35
Q

If there are no MIs where should CO alarms be located:

A

1) Above door or windows
2) >300mm from wall
3) >150mm from ceiling
4) Between 1.8m and 3m from appliance

36
Q

For a boiler, if the CO/CO2 ratio is below xxx a full strip down and clean can be postponed for 12 months?

What is xxx

A

xxx = 0.004

37
Q

Is natural gas toxic?

A

No, however…

1) Too much in a confined space and you can suffocate
2) Incomplete combustion = carbon monoxide - very toxic

38
Q

What is the CPA testing procedure to measure CO on a type A appliance (cooker)?

A

1) Two biggest hobs – max with two saucepans + lids (1l water in each), grill highest position at max, oven GM5 or mid range
2) Measure CO every 1 min
3) Water boiling reduce to simmer

39
Q

Overgassing / Undergassing

Please name the:

1) Major Causes
2) Ways to Rectify

A

1) Wrong gas to air ratio
2) Adjust burner pressure (fixed air inlet port)

40
Q

Natures Balance

CH4 + 2O2 = CO2 + 2H2O

What do you notice about the above equation

A

1) There are equal numbers of atoms on each side fo the equation e.g. 1 x C on each side
2) There is enough oxygen (O) to convert all of the carbon

(C) to carbon dioxide (CO2)

41
Q

Incomplete Combustion

What happens if there is not enough oxygen available?

CH4 + 1.5O2 = ??? + ???

A

CH4 + 1.5O2 = CO + 2H2O

Lack of oxygen leads to the generation of carbon monoxide (CO) which is very toxic (0.4% in air can be fatal)

42
Q

If you suspect high levels of CO in a room where would you put CPA probe?

A

2m above the floor in the center of the room, at least 1m away from appliances

43
Q

What are the CO pass and fail rates on a type A appliance (cooker)?

A

1) Results each 1 min start to fall, total
2)
3) >90ppm at any time – fail

44
Q

If someone exhibits any signs of CO poisoning what are the 4 instructions you must give?

A

1) Vacate the property
2) Seek medical attention
3) Turn off all gas appliances

4) Get gas engineer to check it all out

45
Q

How much heat (energy) does 1m3 of gas provide

A

Roughly 39MJ/m3

That is 39 mega joules per meter cubed!

And is known as calorific value

46
Q

What are the four factors which affect the heat realeased from a burner?

A

1) The calorific value (CV)
2) The specific gravity (SG)
3) The injector size
4) The gas pressure

NB

47
Q

Post-Aerated Flames

Name 4 characteristics of this type of flame

A

1) Ragged
2) Luminous (yellow) colour
3) Tendenct to ‘lift off’
4) Typically burns with incomplete combustion

48
Q

What is the CPA testing procedure to measure CO on a type C appliance?

A

Run full until CO reading stabilizes or falls

49
Q

How much air does 1m3 of gas need to burn propoerly

A

1m3 of methane needs 2m3 of oxygen

Oxygen makes up ~20% of air hence 1m3 of gas requires 10m3 of air

50
Q

Flame Impingement and Chilling

Please describe:

1) Major causes
2) Ways to rectify

A

1) Impingement - flames disturbing each other. Cause - dirt or damage
1) Chilling - incorrect positioning of the burner. Gases chilled to below ignition point
3) Cleaning, repairs

51
Q

What steps would you take to measure CO in a room?

A

1) No smoking – before, during, after
2) Turn off all appliances
3) Open windows/doors until internal and external CO the same
4) Close all windows / doors
5) Measure for 15 minutes

52
Q

Flammability Limits

Gas needs some air to burn, too much gas or too much air and it won’t!

What percentage of gas in air will burn?

A

5% - 15%

53
Q

When servicing a boiler the CO/CO2 ratio is

A

Test the safety devices

54
Q

1) What sort of flame is this?
2) Where is it typically found?

A

1) Post-Aerated flame
2) Live Fuel Effect Fire (LFE)

55
Q

If you are called to a property because of a CO issue in which module of the BPEC can you find a decision tree outlining the steps that need to be taken to resolve the issue?

A

Module 3

56
Q

How does a pre-mix burner work?

A

1) Fan blows air in (under pressure)
2) The zero governor reduces the gas pressure to atmospheric
3) The air passes through a venturi creating a negtive pressure
4) This negative pressure sucks the gas in

57
Q

What is the CPA testing procedure to measure CO on a type A appliance (water heater)?

A

1) Permanent ventilation clear
2) Windows / doors etc. shut
3) Run at max for 5 minutes tops

58
Q

What is a Wobble number?

A

Is an indication of the heat output from a burner for a particular type of gas

59
Q

What is the CPA testing procedure to measure CO on a type B appliance?

A

Run full until CO reading stabilizes or falls

60
Q

Vitiation - incomplete combustion

Please describe:

1) Major causes
2) Ways to rectify

A

1) Blocked open flue
1) Leaking balanced flue
2) Clean and mend!

Combustion products get back into flame, lack of oxygen, flame lifts off, burns bad.

61
Q

In an appliance fails to achieve the right CO/CO2 ratio what GIUSP categories would a type A, B or C appliance get?

A

Type A – ID
Types B & C - AR

Revision Notes (26 decks)

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