A dilution tunnel was designed for the characterization of brake-wear particle emissions up to 10 µm on a brake dyno. The particulate matter emission levels from a single front brake were found to be 4.5 mg/km (1.5 mg/km being smaller than 2.5 µm) over a novel real-world brake cycle, for a commercial Economic Commission for Europe (ECE) pad. Particle Number (PN) emissions as defined in exhaust regulations were in the order of 1.5 to 6 × 10 9 particles per km per brake (#/km/brake). Concentration levels could exceed the linearity range of full-flow Condensation Particle Counters (CPCs) over specific braking events, but remained at background levels for 60% of the cycle. Similar concentrations measured with condensation and optical counters suggesting that the majority of emitted particles were larger the 300 nm. Application of higher braking pressures resulted in elevated PN emissions and the systematic formation of nano-sized particles that were thermally stable at 350 • C. Volatile particles were observed only during successive harsh braking events leading to elevated temperatures. The onset depended on the type of brakes and their prehistory, but always at relatively high disc temperatures (280 to 490 • C).
In this study, different disc brakes and friction materials are evaluated with respect to particle emission output and characteristic features are derived. The measurements take place on an inertia dynamometer using a constant volume sampling system. Brake wear particle emission factors of different disc concepts in different sizes are determined and compared, using a grey cast iron disc, a tungsten carbide-coated disc and a carbon ceramic disc. The brakes were tested over a section (trip #10) novel test cycle developed from the database of the worldwide harmonized Light-Duty vehicles Test Procedure (WLTP). First, brake emission factors were determined along the bedding process using a series of trip-10 tests. The tests were performed starting from unconditioned pads, to characterize the evolution of emissions until their stabilization. In addition to number- and mass-related emission factors (PM2.5–PM10), the particle size distribution was determined. Another focus was the evaluation of temperature ranges and the associated challenges in the use of temperature readings in a potential regulation of brake wear particle emissions. The results illustrate the challenges associated with establishing a universal bedding procedure and using disc temperature measurements for the control of a representative braking procedure. Using tungsten carbide coated discs and carbon ceramic discs, emission reduction potentials of up to 70% (PM10) could be demonstrated along the WLTP brake cycle. The reduction potential is primarily the result of the high wear resistance of the disc, but is additionally influenced by the pad composition and the temperature in the friction contact area.
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