Assessing a Vehicle’s Real World Brake Wear Particle Emissions on Public Roads

With the upcoming Euro 7 type approval for brake emission measurement on the testbed, non-exhaust emissions, and especially brake emissions, gained significant relevance. Even though the laboratory approach with tightly controlled test conditions offers good reproducibility, changing vehicle and surrounding conditions make real-driving emission (RDE) measurements necessary to better understand the actual emission behavior. Here we show a solution for measuring real-world brake emissions of a standard passenger vehicle on public roads. The car is equipped with our minimal invasive brake wear sampling system, which does not affect the brake temperature, and particle instrumentation adapted for on-board measurement while closely following the harmonized methodology for laboratory measurement. We connect on-board vehicle data such as brake pressure and actuation, acceleration, and speed profile with our external sensors for braking temperature and ambient conditions (humidity, temperature, and pressure), with the measurement instrumentation data for particle number and mass. We can close the knowledge gaps in the correlation between brake dyno and on-road testing with the vehicle fully equipped for on-board brake emission measurement. In conjunction with the recorded GPS data, we can identify emission hotspots that vary depending on the geographic location. This allows us to create city emission maps, including random and worst-case scenarios. We found that PM2.5 and PM10 emissions measured on a test track were within 3.8% and +14.5%, respectively, compared with a previous campaign on a brake dyno with a similar driving cycle and system setup. We verified findings that the temperature of the brake under testing was within ± 2°C compared to the brake without particle sampling. PM10 vehicle brake emissions measured on-road following the existing RDE testing specifications for exhaust emissions exceeded the upcoming Euro 7 brake emission limit by a factor of three. However, RDE exhaust requirements are not entirely suitable for RDE brake emission testing since the requirements are based on acceleration instead of deceleration rates for braking. For future RDE brake emission tests, the exhaust standards should be adopted to the specifications of braking requirements.