Investigations of airborne tire and brake wear particles using a novel vehicle design

Abstract

Non-exhaust emissions have become an increasingly important issue as their levels continue to rise and the health effects of particulate matter (PM) are more widely discussed. To address this issue, a vehicle demonstrator with integrated emission reduction of tires and brakes was developed as part of the Zero Emission Drive Unit Generation-1 (ZEDU-1) project. This novel concept includes the removal of tire road wear particles (TRWP) with a strong ventilation/filtering system and an enclosed multi-disk brake, making it a suitable tool for the investigation of non-exhaust emissions. Particle number (PN) and particle size distribution (PSD) measurements down to 2.5 nm were performed on a chassis dynamometer and on a test track. Due to the low background concentrations on the chassis dynamometer, it is possible to distinguish between tire and brake wear and to characterize even a small number of particle emissions. It could be shown that about 30 % less particles are emitted by the vehicle, when using the novel multi-disk brake instead of the conventional brake. The highest TRWP emissions were collected during acceleration and harsh braking. Characterization of the collected particles using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed diverse particle shapes and differences between particles generated on the dynamometer and on a test track.

Keywords: Energy-dispersive X-ray spectroscopy; Microplastic; Non-exhaust emissions; Scanning electron microscopy; Tire road wear particles; Tire wear; Ultrafine particles; Urban air quality.

Fig. 1

a ZEDU-1 demonstrator on the test track in Boxberg. b Sampling position for emission measurements. The simulated airflow path is displayed with colored lines indicating different pressure zones. b Reprinted (adapted), with permission, from (Wieser et al. 2022) © [2023] IEEE

Fig. 2

Comparison of a cycle driven with disk brake and without on the chassis dynamometer. The green curve refers to the CPC data using the disk brake; the blue curve corresponds to the CPC data using the multi-disk brake, showing only the tire emissions. The upper EEPS contour plot corresponds to the green curve, the lower one to the blue curve. In addition to the driven velocity (black), the acceleration is displayed on the right y-axis (gray), to emphasize the increase in deceleration

Fig. 3

WLTC recorded on the chassis dynamometer and on the test track in Boxberg, Germany. The green curves refer to the data from the chassis dynamometer; the blue curves correspond to the data from the test track. The lower EEPS contour plot corresponds to the green curve, the upper to the blue curve

Fig. 4

Comparison of PNC and PSD recorded with an OPS on the test track and on the chassis dynamometer

Fig. 5

SEM micrograph with Inlense detector at an EHT of 5 kV of particles collected by the ELPI + on the chassis dynamometer

Fig. 6

SEM micrograph of particles collected on the chassis dynamometer (left) and on the road (right). The figures were taken at an EHT of 5 kV (left) and 3 kV (right) with the SE2 detector

Fig. 7

Higher magnification of a TRWP particle (left) and a road wear particle (right) both with their corresponding EDS spectra. The images were taken at an EHT of 10 kV (left) and 3 kV (right) with the SE2 detector. The EDS spectra were recorded at 10 kV respectively

Fig. 8

SEM micrograph of particles collected on the chassis dynamometer (left), taken at 5 kV with the SE2 detector, and EDS spectrum of the largest particle, visible in the center of the left image (right), recorded at an EHT of 7.5 kV