Brake wear particles from various temperatures: emission characteristics, generation processes and evolutions

Brake particle emissions are receiving global attention and are a major focus in the Euro 7 and China 7 regulations. Based on a 1/5 scale brake dynamometer, this study investigated the brake particle emissions from NAO-cast iron brake assemblies under various temperatures (350 °C, 450 °C, and 550 °C). Particles with the size of 1∼10 μm (PL1) were analyzed. In low temperature single brakes, PL1 emissions exhibited a sharp initial increase followed by a gradual decline due to the absence and subsequent formation of secondary plateaus, where the contribution of particles at 8–10 μm decreased as braking progressed. Under high IBT (initial brake temperature) conditions, multiple PL1 spikes occurred within a single brake, driven by the dynamic formation and rupture of secondary plateaus. The rupture was influenced by reduced adhesive strength and thermal degradation-induced gases. The relative standard deviation of average PL1 concentrations stabilized at 7.90 %–16.38 % under thermally stable conditions, yet the average PL1 concentrations varied with thermally stable temperatures, leading to different emissions even under identical braking conditions. Increasing IBT from 25 °C to 100 °C amplified PL1 spikes by 2–10 times due to weakened mechanical strength and reduced actual contact area. Additionally, high-temperature pretreatment further elevated PL1 emissions by 2–5 times, promoting abrasive wear and increasing the contribution of particles at 5–10 μm. These findings provided new insight into the brake particle emission characteristics under continuous high-temperature brakes and the underlying reasons.