Abstract
Reduction of non-exhaust airborne particulate matter (PM), leading to adverse effects in respiratory system, is an urgent task. In this work, we evaluated the impact of raw materials in friction materials on PM emission due to brake wear for passenger vehicle. Time- and temperature-dependent measurements using dynamometer were made for low-steel friction materials with varied abrasives and lubricant(graphite). The brake emission factor (BEF) for graphite of varied sizes ranged from 6.48 to 7.23 mg/km/vehicle. The number concentration indicates that smaller graphite (10 μm) produces more nano-sized particles than larger size (700 μm) by >50%. Depending on abrasives, BEF was found to be varied as large as by three-times, ranging from 4.37 to 14.41 mg/km/vehicle. As hardness of abrasive increases (SiC > Al2O3 > ZrSiO4), higher BEF was obtained, suggesting that abrasive wear directly contributes to emissions, evidenced by surface topology. Temperature-dependent data imply that particle emission for SiC abrasive is initiated at lower speed in WLTC cycle, where disc temperature (Tdisc) is ~100 °C, than that for ZrSiO4 (Tdisc >120 °C). Analysis of wear debris suggests that larger micron-sized particles include fragmented Fe lumps from disc, whereas smaller particles are, in part, formed by combination of oxidation and aggregation of nano-sized particles into small lumps.
Highlights
Particulate matter (PM) denotes solid particles and liquid droplets in the atmosphere, which is a cause of air pollution
We have shown that abrasive wear mechanism is more dominant in low-steel pads than nonsteel, and solid lubricating behavior of low-temperature-melting Cu and Sn is critical for reduction of PM emission [24,25]
The PM10 emission factors, expressed as the amount of airborne particulate matter emitted per distance per vehicle, was reported
Summary
Particulate matter (PM) denotes solid particles and liquid droplets in the atmosphere, which is a cause of air pollution. The airborne particle from vehicles is partly originated from exhaust emission from incomplete combustion and volatilization of organic substances, and non-exhaust emission is created as a wear product of brake, tire, and road together with their resuspension [1,2]. The aerodynamic radii of particulate matter ranges from nanometer- to micrometer-scale according to braking condition. The brake wear emission has been reported to be increased by more than 20% per year in Toronto during 2011–2016 [4]. Brake wear emission factors for light-duty vehicles (LDVs) in on-road tests in driving environments yielded quite a range of values, from 1.0–11.9 mg/km/vehicle (PM10), depending on the site and conditions [1,2]. Direct dynamometric measurements estimated PM emission factors; PM10 ranging of 3.0–8.0 mg/km/vehicle and PM2.5 ranging 2.1–5.5 mg/km/vehicle [1,8,9,10,11,12]
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