Study of Brake Wear Particle Emissions: Impact of Braking and Cruising Conditions

Abstract

A novel measurement setup is designed, constructed, and validated by theoretical simulations and by experiments enabling sensitive and loss-free brake particle emission investigations. With the goal to simulate realistic driving, a 3 h subsection of the Los Angeles City Traffic (LACT) cycle is selected as test cycle. The tests are performed with the front brake of a midsize passenger vehicle under both static laboratory and more dynamic realistic conditions that include parasitic drag and vehicle brake temperatures (advanced vehicle simulations). A PM₁₀ emission factor of around 4.6 mg km^-1 brake^-1 is determined. During five cycle runs the emission factor in terms of particle number decreases by 1 order of magnitude. This decrease is accompanied by a shift of the critical brake temperature T_crit, at which ultrafine particle emissions occur, from 140 to 170 °C. Investigations with advanced vehicle simulations generate brake temperatures below T_crit and consequently do not show ultrafine particle emissions above background level. A particle number emission factor of approximately 4.9 × 10¹⁰ km^-1 brake^-1 is estimated for realistic vehicle brake temperatures. Particle formation during cruising is clearly identified. The brake drag is estimated to contribute about 34% to the total airborne particle mass emission.