Characterizing a Real-Driving Brake Emissions Sampling System on a Laboratory Test Bed 2023-01-1875

Brake wear emissions gained significant relevance with the upcoming Euro7 type approval within the European Union for brake emission measurement on the test bed. While the controlled brake test bed approach provides consistent results, real-driving emission (RDE) measurements are needed to better understand actual emission behavior due to varying vehicle and environmental conditions. The EU has already announced its interest in RDE testing. Here we present the results of an RDE brake wear sampling system with minimal thermal impact, where particles are only sampled from one side of the brake disc, characterized on a laboratory sampling system. The investigations aim to validate symmetric particle release and to confirm that doubling the measured RDE results effectively represents the reference emissions on the test bed. The discovered positive correlation between brake temperature and PN, PM_2.5, and PM₁₀ emissions under different cooling settings emphasizes the importance of our system with minimal interference with the vehicle's cooling behavior to maintain accurate emission results. Following the Trip-10 test cycle, we found deviations between the test bed and RDE sampling system ranged from -18% to +9% for PM_2.5, -12% to +24% for PM₁₀, and -23% to +0% for PN. Reasons could be potential particle losses, unequal wear of the inner and outer brake side, or particle crosstalk between both sides of the brake. Finding the optimum sampling flow within the tested range will lead to the desired agreement of results. Evaluating this brake’s emissions with both sampling systems following the WLTP-Brake cycle (used for the upcoming Euro7 legislation) resulted in 1.4-1.8 mg/km and 5.2-5.5 mg/km per front brake for PM_2.5 and PM₁₀, respectively. This would exceed the upcoming Euro7 limit more than twice on a vehicle basis.