A numerical–experimental approach to assess emission performance of new generation engines during the cold transient

Abstract

Modern vehicles equipped with a spark ignition engine come with fuel injection and electronic mixture control, in combination with a three-way catalyst: as a result, carbon monoxide and unburned hydrocarbon cold emissions represent a significant share of total emissions if compared with those given off in hot conditions, so implying direct consequences on the air quality of metropolitan areas. The purpose of this research is to investigate the engine efficiency and emissive performance of last generation engines during the cold-start phase. For this aim, an experimental–analytical procedure was optimised and applied to study the cold emission behaviour of two motorcycles, characterised by similar technical specifications; the exhaust emissions of these motorcycles were measured on a chassis dynamometer in the laboratories of the National Research Council (CNR-Italy). By using this calculation procedure and the emission results measured during the experimental tests, the duration of the cold phase and the total emissions released during the cold-start transient were evaluated for carbon monoxide and unburned hydrocarbons. The average values of cold emission factors and warm-up transient durations obtained for unburned hydrocarbons were 1.05 g/km and 162 s, respectively. Regarding carbon monoxide, the average values of cold emission factors and warm-up transient durations were 14.9 g/km and 152 s, respectively. The results of this study are very useful for better characterising the emission levels of the last generation motorcycles under real urban conditions.