Reproducibility of Physico-Chemical Properties in Brakes Emissions Generated at Different Dynamometric Benches 2023-01-1877

In recent years, brakes emission tests have become increasingly standardized to meet progressively stricter intra and inter laboratory reproducibility requirements. In particular, following the recent EURO 7 regulation proposal, WLTP-Brake cycle has surged as EU standard braking sequence to determine emission factors of investigated brake systems. Furthermore, the UN GTR (United Nations Global Technical Regulation) on Laboratory Measurement of Brake Emissions for Light-Duty Vehicles collects all the information needed to perform emission tests in laboratory. This includes design specifications for the testing platforms as well as the typology and configuration of measuring instruments. Notably, laboratory emission tests are also increasingly used to collect particulates for chemical characterization, since the compositional information is crucial to: i) provide correct assessment of their toxicological and environmental behavior; and ii) better understand tribological and emission mechanisms. Therefore, this work specifically aims at investigating the topic of the inter laboratory reproducibility of physico-chemical properties in particulates generated by the same friction couple when collected during emission tests carried out on different testing platforms. In particular, the contribution focuses on the comparison of PM₁₀ emissions generated by three different friction couples (i.e., ECE R90 Low Steel, NAO and Inorganic-bound friction materials coupled against grey cast iron brake discs) during sets of WLTP tests performed at two different facilities. More in detail, a wide physico-chemical characterization performed by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDXS) and X-Ray Diffraction (XRD) analysis is used to unveil the inter laboratory reproducibility of both the particle size distribution and the chemical composition of corresponding twin particulates collected at the two testing laboratories. The reported results will provide useful insights regarding the variability level to be currently expected in selected physico-chemical properties of non-exhaust emissions from brakes when collected in different testing facilities.