Measuring Brake Wear Particles with a Real-Driving Emissions Sampling System on a Brake Dynamometer

Brake wear particles are recognized as one of the dominant sources of road transport particulate matter emissions and are linked to adverse health effects and environmental impact. The UNECE mandated the Particle Measurement Program to address this issue, by developing a harmonized sampling and measurement methodology for the investigation of brake wear particles on a brake dynamometer (dyno). However, although the brake dyno approach with tightly controlled test conditions offers good reproducibility, a multitude of changing vehicle and surrounding conditions make real-driving emissions measurement a highly relevant task. Here we show two different prototypes for on-road particle measurement with minimal impact of the measurement setup on the emission behavior, tested on a brake dyno. The prototypes cover only a part of the brake disc and allow for installation with minimal interventions on a commercial passenger car, while still closely following the harmonized methodology for brake dynos. Repeated WLTP Trip-10 cycles with different sampling flow rates were performed to investigate the thermal behavior and the particle aspiration efficiency of our setups. An additional self-defined cycle was used to compare the brake dyno emissions with prior on-road tests on a test track. We found that one prototype is more favorable in terms of the desired low thermal impact on the brakes. The other, which is intended to offer a better collection efficiency, leads to elevated brake temperatures with a positive correlation to measured PN and PM emissions. WLTP Trip-10 PN and PM10 emission factors we observed in the order of 3.44 to 5.5 × 109 #/km and 4.5 to 6 mg/km for prototypes one and two, respectively, while sampling exclusively from the outside of a single front brake disc of a medium class passenger vehicle. Following a similar driving cycle and system setup, PM10 and PM2.5 emissions were found to be 39% and 44% higher on-road compared to the dyno test.