Module 3 Characteristics of Combustion Flashcards
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
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
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
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
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
What odour does natural gas have?
1) None it is odourless
2) Odour added
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
At CO level (ppm) should you turn everything off and ventilate the room?
30ppm
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
1) What sort of burner is this?
1) Pre-mix burner
What are the CO/CO2 ration action levels for central heating and combination boilers?
0.008
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!
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
Carbon Monoxide
Name three properties of the silent killer…
1) Colourless
2) Odourless
3) Tasteless
Name the 5 causes of incomplete combustion
1) Insufficient Air
2) Overgassing
3) Undergassing
4) Flame Impingement
5) Vitiation
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
Good or bad flame?
Why?
1) Bad flame
Why?
Floppy elongated flame
Luminosity evident
Unstable
Soot on burner bars, heat exchanger, chamber etc
Name the constituent that makes up 90% of natural gas
Methane CH4
How to rectify:
Incomplete combustion caused by flame impingement
1) Burner alignement
2) Burner pressure
3) If 1 & 2 ok check injectors
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
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!
Effects of Carbon Monoxide
What % volume of CO in air will kill you?
0.4%
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
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)
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?
What is xxx
xxx = 0.004
Is natural gas toxic?
No, however…
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 1m3 of 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
