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Visual features of a pre-aerated flame
Sharp, stable, well defined, blue cone shape.
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Visual features of a post-aerated flame
Floppy, unstable, elongated, luminous yellow.
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zones of a flame (pre-aerated)
A-B burner head/port
B-C unburnt gas
C - flame front, this is where the combustion process begins.
C-D the reaction zone. This is where the chemical reaction takes place.
D - outer mantle. Is the hottest part of the flame.
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what are the 4 intermediary products that are formed during combustion but are not present in the POC when complete combustion occurs.
- Alcohol,
- Aldehydes,
- Carbon,
- Carbon Monoxide.
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Flame speed of a ng pre-aerated flame
Typically 0.36m/s
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Flame speed of a propane pre-aerated flame
0.46m/s
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what is light back and when does it occur
- Gas/air speed too slow,
- Flame front moves downwards into the mixing tube.
- Reaches injector.
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What is lift off and when does it occur
- Over-gassing,
- gas/air speed greater than flame speed,
- flame lifts from burner,
- flame may extinguish if mix is outside flammability limits.
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What are the properties of a flame
- Conducts a current:
- - ionisation
- - rectification.
- Emits light energy:
- - infra red (IR)
- - ultra violet (UV)
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Causes of incomplete combustion:
- Main cause is lack of oxygen to the burner.
- - reduced primary and/or secondary air.
- - inadequate ventilation
- - enlarged injectors/excessive burner pressure
- - vitiated air contaminated with other gases. Oxygen level below 18% accelerates CO production.
- Flame Chilling
- Flame Impingement
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