Determining factors and parameterization of brake wear particle emission

Brake wear emission contributes to an increasingly significant proportion of vehicle-related particulate matter, but knowledge of its emission features and determining factors is still highly insufficient. Here, brake dynamometer experiments were conducted under controlled variables tests and real-world driving conditions to systematically investigate brake wear particle (BWP) emission. Compared to the decelerating process, the separating of pads and disc releases more BWPs, accounting for 47-76% of the total PM2.5 mass. Particle number and mass distributions exhibit bimodal (< 0.01 mu m and 0.8-1.2 mu m) and unimodal (2-5 mu m) patterns, respectively. Larger speed reduction exponentially amplifies BWP emission, and the significant enhancement of nanoparticles is proved to be related to the evaporation of organic constituents in the pads with threshold ranging from 170 ?C to 270 ?C. Emissions from front and rear brake assemblies don't agree with braking torque distribution, mainly attributive to the different braking pressures. A parameterization scheme for BWP emission based on kinetic energy loss is further established and proved to sufficiently predict the variation of BWP under real-world driving conditions. Being corrected by 1.8th power of the initial speed, the scheme improves the prediction.

Automated summary

Brake wear emission is becoming a significant contributor to vehicle-related particulate matter, but there is still limited knowledge about its emission features and determining factors. Experimental results show that separating brake pads and discs releases more particles, larger speed reduction exponentially increases emissions, and the enhancement of nanoparticles is related to the evaporation of organic constituents in the pads. The emissions from front and rear brake assemblies are not consistent with braking torque distribution due to different braking pressures. A parameterization scheme based on kinetic energy loss is developed to predict the variation of brake wear particle (BWP) emissions under real-world driving conditions.