Humidity Effects on Engine Nitric Oxide Emissions at Steady-State Conditions

The effect of humidity change on engine nitric oxide emission during operation on the engine dynamometer was found to be a function of air-fuel ratio, observed nitric oxide concentration level, and observed humidity level. Equations and graphs to adjust nitric oxide concentrations for humidity change were derived. Adjustments in NO concentration varied from 2-9 ppm per grain moisture change in absolute humidity.