Effects of Changing Ambient Humidity and Temperature on the Emissions of Carbureted Two- and Four-Stroke Hand-Held Engines

Effects of changing ambient humidity and temperature have been studied on the performance and emissions of a hand-held two-stroke and a hand-held four-stroke engine. The main effect of changes in ambient conditions is to change the intake air density and therefore the air-fuel ratio metered by the carburetor. Trends in the effects of humidity and temperature on emissions are predicted reasonably well by theoretical thermodynamic models. They suggest an improved correction for the dependence of NO_x on ambient conditions, as a function of both humidity and operational air-fuel ratio, which appears to collapse NO_x production data better than the existing K_H correction factor. They also suggest a simple procedure for tuning engines to design air-fuel ratios using the measured exhaust-gas %CO, which takes into account the prevailing ambient conditions.