🔍 Key Concepts

• Combustion process in a boiler – what happens when fuel and air do NOT burn perfectly together • Difference between complete combustion and incomplete combustion • What the presence of carbon monoxide (CO) in flue gas tells you about how well the fuel is burning

💭 Think About

• Think about what gas you mainly expect when fuel burns perfectly with enough oxygen – is it CO or CO₂? • If you see a lot of carbon monoxide, what does that tell you about the amount of oxygen available or how well the fuel is burning? • Which option directly describes a situation where the fuel’s carbon is not fully converted to its final oxidation state?

✅ Before You Answer

• Remember that complete combustion of carbon produces carbon dioxide (CO₂), not carbon monoxide (CO) • Ask yourself if too much excess air would usually increase or decrease CO in the flue gases • Check which choice directly refers to the quality or degree of combustion, rather than the fuel type or air quantity alone