A number of surveys of emissions from cars in service have been carried out and an analysis has been made of the emissions from vehicles built to the various amendments to ECE regulation 15 in order to discover whether the downward trend in type approval limits has produced lower emissions in practice. The range of emissions measured in the surveys was wide, but the mean values for the 'tuned' vehicles complied in most cases with the type approval limits appropriate to the vehicle. The type approval limits were most easily met for the emissions of the oxides of nitrogen; more difficulty was found with the other pollutants. Statistical analysis of the data, comparing emissions from 03-amendment vehicles with others showed that only about one-third of the comparisons had a high probability of being significantly different. But the variability of the data and small sample sizes obscure the downward trend in the mean emissions of carbon monoxide and hydrocarbons from 'tuned' vehicles, which were comparable to the reductions in the type approval limits. More detailed study of emissions at different road speeds has shown that the ECE regulation 15 test cycle represents the higher concentrations of carbon monoxide and hyrocarbons, with concentrations falling rapidly at higher average speeds, and a reasonable estimate of oxides of nitrogen levels except for high-speed motoring. Modes of operating, other than a steady speed, are likely to produce higher emissions with high rates of acceleration giving very high emissions. The more detailed study of a vehicle between service intervals shows considerable increase in carbon monoxide and hydrocarbon concentrations, with servicing reducing emissions to meet the approved level again. (Author/publisher)
Abstract