What information does a flue gas analysis provide, and how is it used to tune combustion?

• A. Pressure and temperature readings; used to predict boiler failure.
• B. Humidity and soot levels; used to adjust flame color.
• C. CO2, O2, CO, and sometimes NOx; used to adjust the air-fuel ratio for efficient combustion and acceptable emissions.
• D. Only CO2 is measured; used to estimate heat content.

Answer: (C)

Flue gas analysis tells you how cleanly and efficiently the fuel is burning by reading the gases in the exhaust. CO2 indicates how completely the fuel is oxidized—more CO2 generally means a more complete burn. O2 shows how much excess air is present; too much O2 means wasted energy from extra air, while too little can lead to incomplete combustion. CO is a direct sign of incomplete burning or fuel-rich conditions, so keeping CO low signals a healthier, more efficient flame. NOx readings (when measured) help you gauge combustion temperature and potential emissions, since higher flame temperatures tend to create more NOx. By looking at these components together, you adjust the air supply and fuel flow to reach a balanced air-fuel ratio that maximizes CO2 and minimizes CO and unnecessary O2, achieving efficient combustion with acceptable emissions. Humidity, soot, or measuring only CO2 don’t provide the full picture needed to tune the burner effectively.