What is the typical target range for excess oxygen in combustion?

• A. 2 to 5 percent
• B. 0 to 1 percent
• C. 8 to 12 percent
• D. 15 to 20 percent

Answer: (A)

In combustion, you want a small cushion of extra oxygen beyond what’s strictly needed to burn the fuel. This slight excess ensures complete oxidation even if there are momentary changes in fuel or air flow. The typical target range for that excess oxygen is about 2 to 5 percent. Keeping it in this range helps avoid incomplete combustion, which would produce CO or unburned hydrocarbons, while not wasting energy by pulling in a lot of extra air that cools the flame and lowers efficiency. Values much higher, like 8–12% or 15–20%, show up when there’s far more air than needed and lead to heat losses and reduced fuel efficiency. Values near 0–1% leave little margin for variations and can risk incomplete combustion. The 2–5% range is the balanced, commonly taught target.