Combustion Basics
What clean combustion requires, what the products of combustion tell you, and why analysis beats guessing.
Safety
What it is
Combustion is a rapid chemical reaction between fuel and oxygen that releases heat. Complete combustion of a hydrocarbon fuel with enough air produces mainly carbon dioxide and water vapour. Incomplete combustion produces carbon monoxide, soot and aldehydes.
Fuel + oxygen -> carbon dioxide + water vapour + heatThe ideal reaction. Real burners always use excess air to stay on the safe side of complete combustion.
Why it matters
Every combustion problem shows up in the flue gas before it shows up as a callback. A combustion analyser reads what is actually happening rather than what the flame looks like.
| Reading | What it indicates |
|---|---|
| Oxygen | How much excess air is present. Too little risks incomplete combustion, too much wastes heat up the flue |
| Carbon monoxide | Incompleteness. Rising carbon monoxide means something is wrong with air, fuel or the heat exchanger |
| Stack temperature | Heat leaving the appliance. Very high suggests poor heat transfer or overfiring |
| Draft | Whether the products of combustion are being removed as designed |
The three requirements
- Fuel at the correct pressure and rate, verified with a manometer against the data plate.
- Air in sufficient quantity, both for combustion and for dilution and ventilation as the appliance requires.
- A path for the products of combustion to leave, which means correct venting and adequate draft.
Flame appearance is not a measurement
Safety
Carbon monoxide
Local requirements
Combustion testing, acceptable carbon monoxide limits, response procedures and appliance shutdown criteria vary by jurisdiction, adopted code edition, the regulations in force and the manufacturer instructions.
Local Code Notice
Symptoms
Practice & Mastery
- Questions2
- Quiz1
- Combustion Basics Troubleshooting Scenarios2
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