🔍 Key Concepts

• complete vs. incomplete combustion in a boiler furnace • relationship between air supply, fuel burning, and visible smoke • what stack appearance tells you about excess air or insufficient air

💭 Think About

• Think about what happens to fuel if there is not enough oxygen to burn it completely. How would that show up in the exhaust? • Which option would you expect if the fuel is burning very cleanly with plenty of air, and which would you expect if combustion is dirty or incomplete? • Consider which answer choices indicate more complete combustion and which indicate less complete combustion.

✅ Before You Answer

• Identify which choices suggest incomplete combustion products or visible signs (color of flame, color of smoke). • Ask yourself: with insufficient air, do you expect unburned fuel or perfectly burned fuel in the gases? • Verify which stack condition is typically associated with soot or unburned carbon when air is low.