🔍 Key Concepts

• combustion air supply and how it affects flame appearance and sound • differences between smoke color (white vs black) and what each usually indicates in boilers • what happens to the flame and burner noise when there is insufficient oxygen for complete combustion

💭 Think About

• Think about what a burner flame looks and sounds like when it is starved of air but still getting fuel – does it usually become smoother and hotter, or unstable and noisy? • Consider which choice best matches the typical signs of incomplete combustion rather than problems like water carryover or over-firing. • Ask yourself: which option describes a condition commonly used by engineers as a clue that the fuel/air ratio is too rich (too much fuel, not enough air)?

✅ Before You Answer

• Verify which smoke color is normally associated with incomplete combustion and unburned fuel from oil-fired boilers. • Check which description (panting/rumbling, hissing/sputtering, white smoke, very hot fires) you’ve seen specifically linked to insufficient air in engineering texts. • Confirm that the symptom you pick would logically improve if you increased the air supply while keeping fuel rate the same.