Characteristics of brake wear particle (BWP) emissions under various test driving cycles

Abstract

The characteristics of brake wear particle (BWP) emissions were investigated under five driving cycles (WLTP, NEDC, FTP, 3h-LACT, and WLTP-Brake) with a brake dynamometer. The gravimetric method and real-time particle measurement instruments (APS, OPC, DustTrak, and QCM) were used to measure the BWPs. As a result, the mass concentrations of BWPs measured by APS were similar to the gravimetric method results. However, OPC and DustTrak underestimated the mass concentration of BWPs compared to the gravimetric method results. The QCM was unfavorable for measuring the BWPs because a significant number of particles abruptly inflowed into the QCM during a short moment of braking. The density of BWPs was observed to be larger than 1.0 g/cm3 because the optical mode diameter of the BWPs was smaller than the aerodynamic mode diameter. The BWP emissions were shown to be proportional to the brake dissipation energy and brake initial velocity of each driving cycle. Although the same dissipation energy was applied by braking, more BWPs were found to be emitted at high initial velocity condition. Because, BWPs already deposited on brake disc and pad was emitted as new generated BWPs at high initial velocity condition. When the value obtained by multiplying the dissipation energy by the 3.8th power of the initial velocity was compared to the PM emission of the BWPs, the correlation was more obvious than when only considering the dissipation energy.