Research and/or Engineering Question/Objective:
The measurement of non-exhaust particle emissions is a complex challenge due to the open system configuration of the vehicle brakes as well as tires. Consequently, particles are diluted immediately by the ambient air, which makes reproducible measurement a complex task. Furthermore, measurement conditions on the road are strongly influenced by continuously changing parameters (e.g., flow conditions, changing traffic conditions, particulate matter from other sources). The motivation of the present paper is to describe a methodology for the measurement of all vehicle related non-exhaust particle sources based on a mobile measurement vehicle. The objective is to compare different sources of particle emissions (brake, tire and road wear) under real driving conditions in real time.
A mobile measurement vehicle, which includes sampling systems for all relevant particle sources, is presented. A computational fluid dynamics model (CFD) is applied to enhance the layout of sampling systems for brake as well as for tire and road wear emissions (TRW). Based on a real drive emissions compliant (RDE) Ilmenau cycle, emission factors of brake dust emission are determined. Additionally emissions caused by the tire-road interface are investigated. Furthermore, the influence of the driving behavior is characterized.
An existing CFD simulation methodology was adjusted in order to account for tire and road wear specific effects of disperse phase flows. In addition to an existing sampling system for brake dust particles, a sampling device for TRW particles was developed. The CFD simulation was applied to increase the sampling and transport efficiency of the system as well as to reduce the influence of other particle sources. The sampling devices were adapted to a mobile measurement vehicle in order to measure particle emissions in dependency of the driving behavior of various test drivers. Based on this study a clear correlation between friction power and increased emissions was determined.
Limitations of this study:
Reproducibility of measurement results is significantly influenced by various factors such as driving behavior and ambient conditions. Numerical simulation in general can only provide an insight into the particle-flow interaction. Extensive experiments are necessary to validate the CFD model in terms of particle resuspension and dispersion caused by the vehicle tire. The influence of ambient particle sources (such as older diesel cars) on the measurement of TRW particles cannot be accurately estimated up to this point.
What does the paper offer that is new in the field in comparison to other works of the author:
The paper introduces a sampling setup suitable for the measurement of all non-exhaust particle sources emitted by passenger cars. A novel CFD-model was introduced accounting for the flow conditions around the vehicle wheelhouse and its effects on particle dilution. For test drives under RDE-conditions the influence of vehicle dynamic properties on different particle sources was analyzed.
Within this paper, a methodology was described including the development of suitable sampling devices for brake and TRW emissions using CFD simulation software. Applied to a mobile measurement vehicle, emission factors for brake dust emissions were determined. For TRW particles correlations between vehicle dynamic parameters and particle formation were shown.