🔍 Key Concepts

• combustion air-to-fuel ratio and what happens when there is too much air • typical flame color for correct, rich, and lean combustion in oil-fired boilers • how excess air changes flame shape and brightness at the ends of the flame

💭 Think About

• Think about what a normal, properly adjusted boiler flame looks like. How does adding extra air affect the temperature and color at the outer edges of that flame? • Which choice best represents a cooler, more completely burned flame rather than an overly sooty or smoky one? • Eliminate any options that clearly indicate unburned fuel, soot, or very high local temperatures at the flame tips.

✅ Before You Answer

• Identify which flame descriptions suggest unburned fuel or soot (too little air, not too much). • Identify which descriptions suggest very high temperature and particle carryover rather than just excess air. • Focus on the option that indicates a lean, cooler, well‑mixed flame at the ends of the flame.