Module 3 Characteristics of Combustion Flashcards by Patrick Walshe

Perfect Combustion

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

CH₄ + 2O₂ = ??? + ???

CH₄ = Methane

O₂ = Oxygen

CH₄ + 2O₂ = CO₂ + 2H₂O

CH4 = Methane

O2 = Oxygen

CO₂ = Carbon Dioxide

H₂O = Water

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How to rectify:

Incomplete combustion caused by overgassing due to

1) excessive burner pressure
2) excessive gas rate

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

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

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

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

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

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

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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What odour does natural gas have?

1) None it is odourless
2) Odour added

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

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

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

30ppm

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

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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1) What sort of burner is this?

1) Pre-mix burner

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

0.008

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

1) Pre-aerated flame
2) 50%

Most common type of gas flame

Gas is aerated twice!

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

What are the three families?

Family 1 - manufactured gases

Family 2 - Natural gases

Family 3 - LPG

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Carbon Monoxide

Name three properties of the silent killer…

1) Colourless
2) Odourless
3) Tasteless

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Name the 5 causes of incomplete combustion

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

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What does Gas Safety Regulation no 33 state?

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

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Good or bad flame?

Why?

1) Bad flame

Why?

Floppy elongated flame

Luminosity evident

Unstable

Soot on burner bars, heat exchanger, chamber etc

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Name the constituent that makes up 90% of natural gas

Methane CH₄

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How to rectify:

Incomplete combustion caused by flame impingement

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

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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?

0.36m/s

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Insufficient air for Combustion

1) Main causes
2) Ways to recity

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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Effects of Carbon Monoxide

What % volume of CO in air will kill you?

0.4%

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How to rectify:

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

Remove blockage and check appliance to see

1) If there are further blockages
2) It works

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What type of flame is this?

Name some key characteristics

Post aerated flame

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

Luminos flame

incomplete combustion

carbon (soot)

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

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

Is natural gas lighter or heavier than air? What is its specific gravity (SG)? Specific gravity is the weight or mass of a substance

Lighter than air. SG is 0.6

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

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

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

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

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%

c) 0.05%

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%

b) 0.03%

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) 0.01%

Is Carbon monoxide lighter or heavier than air?

Is Carbon monoxide lighter or heavier than air? SG of air is 1!

Pre-aerated flames Name 3 characterisitcs of pre-aerated flames

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

Name 3 signs of incomplete combustion

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

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

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

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

xxx = 0.004

Is natural gas toxic?

No, however... ## Footnote 1) Too much in a confined space and you can suffocate 2) Incomplete combustion = carbon monoxide - very toxic

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

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

Overgassing / Undergassing Please name the: 1) Major Causes 2) Ways to Rectify

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

Natures Balance CH₄ + 2O₂ = CO₂ + 2H₂O What do you notice about the above equation

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)

Incomplete Combustion What happens if there is not enough oxygen available? CH₄ + 1.5O₂ = ??? + ???

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)

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

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

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

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

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

1) Vacate the property 2) Seek medical attention 3) Turn off all gas appliances  4) Get gas engineer to check it all out

How much heat (energy) does 1m³of gas provide

Roughly 39MJ/m³ That is 39 mega joules per meter cubed! And is known as calorific value

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

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

Post-Aerated Flames Name 4 characteristics of this type of flame

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

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

Run full until CO reading stabilizes or falls

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

1m³ of methane needs 2m³ of oxygen Oxygen makes up ~20% of air hence 1m³ of gas requires 10m³ of air

Flame Impingement and Chilling Please describe: 1) Major causes 2) Ways to rectify

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

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

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

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?

5% - 15%

When servicing a boiler the CO/CO2 ratio is

Test the safety devices

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

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

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?

Module 3

How does a pre-mix burner work?

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

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

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

What is a Wobble number?

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

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

Run full until CO reading stabilizes or falls

Vitiation - incomplete combustion Please describe: 1) Major causes 2) Ways to rectify

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.

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

Type A – ID Types B & C - AR