Particulate emissions from ‘in-use’ motor vehicles—II. Diesel vehicles

Abstract

A detailed study has been undertaken of the exhaust particulate matter (EPM) emitted by 19 light-duty and 13 heavy-duty diesel vehicles. Eighteen of the light-duty vehicles were of the indirect injection types, whereas the heavy-duty ones were all four stroke. The light-duty vehicles were tested under a standard city drive cycle, the heavy-duty vehicles being subjected to a multi-mode test cycle. Although considerable variability was found in emission rates between individual vehicles of the same make and model, light-duty diesel vehicles emitted 3–6 g EPM kg⁻¹ of fuel consumed, which was six times as much as spark ignition (S.I.) vehicles. The heavy-duty diesel vehicles emitted most EPM, giving rise to >6.6g EPM kg⁻¹ on average. For both classes of diesel vehicles, higher EPM rates were generally associated with higher CO emission rates. Light-duty diesel EPM was found to consist mostly of C, two-thirds of which was in the ‘sooty’ or elemental (EC) form with the remainder organic (OC). The heavy-duty diesel EPM contained a higher proportion of OC than that from the light-duty diesels. Tests carried out with ¹³C-labelled lubricating oil indicated a significant oil contribution to EPM from diesel vehicles. In addition to measuring variations in EPM emission rates between different diesel vehicles, the influences of fuel supply, injection timing and fuel quality were also studied, using a light-duty indirect injection engine. Injection timing was found to have the greatest influence, with EPM emissions decreasing on retardation. The influence of injection timing was also assessed using a direct injection vehicle.