Controlling brake particle emissions: New brake disc needs more attention

Existing studies on how brake discs influence particle emissions have mainly focused on surface treatments, materials, and coatings. However, the impact of brake disc usage mileage on particle emissions remains unclear. Given this, experiments were conducted using a running-loss method with ELPI+ to measure particle number concentrations and size distributions, and the results were further validated on a 1/5 scale brake dynamometer under controlled braking cycles. The results from running-loss method show that new brake discs increase the brake PN by 2 orders of magnitude, with dominant particles below 100 nm. This increase is attributed to hard asperities on the disc surface, which promote both mechanical wear (furrow effect) and localized thermal processes (load concentration), enhancing debris release and ultrafine particle formation. In contrast, disc surface hardness and thermal conductivity were not primary influencing factors. Dynamometer results confirmed substantially higher emissions from new discs compared with used ones, with PM1 emissions increasing by up to two orders of magnitude. These results highlight that brake discs, particularly in their initial usage phase, play a critical role in brake particle emissions.