🔍 Key Concepts

• relationship between CO2 percentage and excess air in stack gases • how fuel-to-air ratio affects combustion efficiency and flue gas composition • difference between complete combustion, excess air, and secondary combustion

💭 Think About

• If more excess air is supplied to the burner, what happens to the fraction of CO2 in the total stack gas volume? • How does increasing the fuel-to-air ratio change the products in the stack gas (CO, CO2, O2)? • Does a lower CO2 percentage in the flue gas always mean higher fuel economy, or can it indicate something else in the combustion process?

✅ Before You Answer

• Compare high CO2, low O2 situation versus low CO2, high O2 situation in stack gas • Think about what approaching secondary combustion really means in practical boiler/burner operation • Ask: does increasing fuel economy necessarily reduce the measured CO2 percentage, or is it more closely tied to minimizing excess air?