Plain definitions of the combustion and carbon-monoxide terms that come up across the gas modules.
Combustion has its own vocabulary, and the terms turn up across CCN1, CPA1, CKR1 and HTR1. These plain definitions are for revision; act on a calibrated analyser and the full procedure, not on definitions alone.
- Combustion: the chemical reaction of burning, where fuel gas combines with oxygen from the air and releases heat.
- Complete combustion: burning with enough air so the fuel is fully reacted, giving mainly carbon dioxide and water vapour and a clean, stable, mainly blue flame.
- Incomplete combustion: burning with too little air or poor mixing, which leaves unburnt products and can release carbon monoxide.
- Carbon monoxide (CO): a toxic gas produced by incomplete combustion that has no colour, taste or smell, which is why it is so dangerous.
- Carbon dioxide (CO2): a normal product of complete combustion, measured by the analyser and used alongside CO to judge combustion quality.
- Stoichiometric (ideal) ratio: the exact air-to-gas proportion that would, in theory, burn the fuel completely with no air left over.
- Excess air: the extra air supplied above the ideal amount to make sure combustion is complete in practice.
- Aeration: the air mixed with the gas at the burner before it burns; too little aeration tends towards yellow, sooty flames.
- Flame lift and light-back: faults where the flame lifts off the burner or burns back towards the injector, both signs the burner is not running as designed.
- Vitiation: the using-up of oxygen in the room air, which worsens combustion if fresh air is not supplied.
Keep these definitions handy when reading a flame or an analyser, and confirm any technical detail against the current combustion and carbon-monoxide guidance.