🔍 Key Concepts

• Boiler combustion efficiency and what complete vs. incomplete combustion looks like • Typical stack (exhaust) colors and what they indicate (soot, unburned fuel, water vapor, or overheating) • Relationship between excess fuel/air and visible smoke color

💭 Think About

• Think about which color suggests that fuel is being burned cleanly with minimal soot or unburned particles leaving the stack • Consider which colors are associated with unburned carbon or oil carryover, and which are associated with water or improper atomization • Eliminate any colors that clearly suggest contamination, soot, or burning of impurities in the fuel

✅ Before You Answer

• Recall which stack color is associated with soot and unburned carbon (incomplete combustion) • Recall which stack color can indicate water vapor or poor atomization, not necessarily efficient burning • Make sure the option you choose represents clean, nearly invisible exhaust that suggests complete combustion