| Popis: |
One of the major issues in road transport today is poor air quality and the associated negative health impacts. In particular, diesel vehicles are found to contribute substantially to atmospheric levels of particulate matter (PM) and ozone (O3). Pollutant mass emission rates from motor vehicles vary greatly according to their operating mode. Consequently, changes in road layout or traffic behaviour may have a significant impact on local air quality. Improved understanding of the underlying emission mechanisms can help at the traffic planning stage in order to assess environmental impacts and aid in the design of more efficient air quality management methods. However, existing planning tools do not adequately represent the variable and transient nature of pollutant emission rates from vehicles, especially with regard to emissions of PM. This thesis addresses the issue of how motor vehicles, and in particular, light-duty diesel vehicles contribute to local air pollution. It does so with reference to a series of experiments conducted with a 1999 model-year Ford Focus turbo-diesel test vehicle. The vehicle was equipped with an on-board monitoring system developed and validated for this research to address the shortcomings of existing devices. The resultant data are used to examine the second-by-second mass emission rates of pollutant species, including PM. The extension of an existing instantaneous model for gaseous pollutants to represent PM emissions is then examined, with an adjustment to the model structure found to improve emission estimates. The experimental techniques developed in this thesis are compared to reference data obtained using a chassis dynamometer emissions test facility. The models are compared to the on-board measurements for both laboratory and on-road tests. These comparisons show that on-board monitoring offers a more precise representation of the pollutant mass emission rates than the modelling techniques considered. Nevertheless, the model performance is sufficiently good to suggest that realistic estimates may be obtained through the simulation of vehicle trajectories and the associated pollutant emission rates. Importantly, the techniques developed in this research are able to replicate the high-emission episodes associated with transient vehicle operation. This offers the possibility to assess the impact of traffic management schemes on PM emission levels more accurately than has previously been possible. |
