Effects of Combustion-Chamber Surface Temperature on the Exhaust Emissions of a Single-Cylinder Spark-Ignition Engine

The effect of combustion-chamber surface temperature on exhaust emissions was investigated for wide ranges of air-fuel ratio, speed and volumetric efficiency. Oxides of nitrogen (NO_x) emissions significantly increase with increasing surface temperature. This effect is strongest at lean air-fuel ratios. In rich mixtures, the demonstrated weak influence of surface temperature on NO_x emissions is attributed to NO decomposition reactions occurring during the expansion stroke. With the exception of the extremely lean condition (22.5 air-fuel ratio) the sensitivity of hydrocarbon (HC) emissions to surface temperature was found to be essentially independent of air-fuel ratio. No significant effect of surface temperature on carbon monoxide (CO) emissions was found.