🔍 Key Concepts

• combustion efficiency in marine boilers • relationship between excess air, CO₂, and O₂ in flue gas analysis • signs of incomplete vs. complete combustion

💭 Think About

• When combustion is very efficient, what happens to the percentages of CO₂, O₂, and unburned fuel in the flue gas? • If you introduce more and more excess air into the burner, does the CO₂ percentage in the flue gas go up or down? Why? • What kind of burner or fuel problems would you expect to see if combustion were poor or incomplete?

✅ Before You Answer

• Match each choice with either good/efficient or poor/inefficient combustion and see which lines up with high CO₂ in the flue gas. • Recall that excess air tends to show up as higher O₂ and lower CO₂ in the flue gas, not the other way around. • Eliminate any options that would more likely cause low CO₂ and higher CO or smoke/soot instead of high CO₂.