NOx is primarily formed under what condition?

• A. Low temperature during combustion
• B. High temperatures during combustion
• C. Cold ambient conditions
• D. High air velocity

Answer: (B)

NOx formation is driven by flame temperature. When the combustion temperature gets very high, nitrogen and oxygen in the air begin reacting to form nitrogen oxides. This thermal NOx mechanism becomes significant as the peak temperature rises, so higher flame temperatures lead to much more NOx. If the temperature stays lower, the reactions happen much more slowly and NOx production stays small. Cold ambient conditions don’t raise the flame temperature, and while how quickly the mixture burns or how long it remains in the flame can influence NOx somewhat, they don’t determine NOx levels as strongly as the actual peak temperature does.