Abstract
Keywords:
Exhaust gas dispersion, cold start emissions, ambient air measurement, emission dilution
Abstract
Urban air quality is determined by exhaust gas dilution processes. Unfortunately this process is difficult to describe concerning particulate matter. As a consequence the aim of the following experiments was to clarify the dominating processes accompanying the dilution process of vehicle particle emissions. Ambient air measurements were performed under different size-scaled dilution conditions and under different cold start situations. Coagulation experiments were performed in a 9m long pipe also under cold and warm start conditions. Different nanoparticle quantities were measured among them, the PM10 mass with a TEOM (tapered element oscillating microbalance) and the number-size distribution with a SMPS (scanning mobility particle sizer). Additionally the extinction with a SICK extinction measurement device and the humidity was measured. The cold start emissions lead to particle emissions that consist of two types of particles, first mainly liquid particles and second soot particles. The liquid phase particle emissions disappear after a certain time and a pure soot emission remains. The experiments indicate that the previous state of the engine-tailpipe is of importance for liquid emissions but not for soot emissions, that means that a warmed up system produces less liquid phase emissions. Cold start particle emissions can be regarded as purely mixed with the ambient atmosphere and an immediate coagulation cannot be assumed. This can be inferred out of the decay from an unimodal into a bimodal number size distribution under dilution conditions, where accumulation of the aerosol occurs, and from coagulation experiments. A new method for determining a mass density function is derived. This allows for interpreting measurements according to a time dependent liquid uptake with respect to spherical particles.