Research Questions / Objective Non-exhaust particle emissions related to road-traffic pose a significant health threat for human beings. Due to their small size, inhalation of such particles can bring them not only into the blood circulation, but even inside the brain, where they favour serious diseases such as dementia. With the proposal for EURO 7, the European Commission therefore limits emissions by the brakes. Tyre abrasion is planned to be limited in a future tightening step. Therefore, a deepened knowledge about the generation and measurement of non-exhaust particle emissions is urgently necessary. The present work treats questions about testing for non-exhaust emissions. Methodology High-load driving cycles were performed on a drum-driven half-axle test bench. 1100 test cycles were performed. Brake disks, pads and tires were changed and weighed after every 100 test cycles (i.e. after one test day). The test bench chamber ventilation system was used for particle measurements in supply air, unfiltered exhaust air and filtered exhaust air ducts. Several measurement systems were used, such as DMPS (differential mobility particle sizer), APS (aerodynamic particle sizer) or OPS (optical particle sizer). In addition, flow velocity measurements were carried out with a hot film anemometer, which enabled isokinetic sampling. A HEPA H13 filter, used to filter the exhaust air, was analyzed after the measurements by REM/EDX (energy dispersive x-ray spectroscopy) to detect the elements trapped in the filter. Results After 11 test days / 1100 test cycles, 2.3 % of the total mass loss of tested components (brake disks, brake pads and tires) was found to be trapped in the HEPA filter. Therefore, large parts of the abrasion material were either too heavy to become airborne or were deposited within the test bench chamber itself and therefore not measured. Most particles were found in the range from 10 nm to 30 nm; a second peak within the particle size distribution occurred from 380 nm to 450 nm. Also, after each second run with new brake components and tires, measurements showed a solid repeatability. The elements C, S and O were found dominantly for the particles trapped in the filter. The content of different metals was significant as well, with highest proportions of Fe, Si, Ba and Na. Limitations of this study Due to the measurement setup, absolute numbers of particle number and size distribution can only be taken with caution: It is not known, how many of the brake and tire particles did not find their way to the exhaust duct and were therefore not measured. Also, measured particles could not be assigned to their origin (brake vs. tire). The analyzed high load driving cycles are certainly different to the average real driving behavior. However, this can be seen as an upper load limit on both brake and tires. Measurement systems did not correspond to the according UN GTR. What is new in this paper? Highly relevant non-exhaust emissions, which are about to be limited by the upcoming EURO 7 regulation, were measured in a half-axle test bench environment for the first time. In contrast to the regulations, the behavior under high load cycles was studied here: brake disk surface temperatures were constantly >350°C. Although limited by the measurement setup, this study gives a first impression of non-exhaust emission particle sizes, masses and element composition. Conclusions The performed high load driving cycle measurements led to significant emissions of brake and tire particles. 2.3% of the total mass loss of these components landed in a HEPA filter installed in the exhaust duct, mainly in the form of harmful, ultra-fine particles from 10 nm to 30 nm. While measured particles were dominated by elements such as carbon, sulfur and oxygen, various metals were found as well. Despite certain limits of the measurement setup, these results encourage further research on non-exhaust emissions, especially under high load conditions.
Dipl.-Ing. Ludwig Schubert, Junior Researcher, Institute of Automotive Engineering, Graz University of Technology; Dipl.-Ing. Michael Peter Huber, University Project Assistant, Institute of Automotive Engineering, Graz University of Technology; Dipl.-Ing. Severin Huemer-Kals, University Assistant, Institute of Automotive Engineering, Graz University of Technology; Prof. Dr. Peter Fischer, Head of Institute, Institute of Automotive Engineering, Graz University of Technology