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∼10μm (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. • Brake particle characteristics within one brake and their evolutions were studied. • Underlying reasons for various emission characteristics were analyzed. • Potential pathway for PL1 control is to establish and stabilize the friction layer.