State of art : Characterization of braking particles from car emissions
Résumé
The problem of particles emitted by car brakes is a new challenge. However, estimations show that emissions of car brakes account for 10% to 30% of the traffic-related pollution. Recent developments of particle filters on engines significantly reduced exhaust pollution; consequently, the proportionate contribution to pollution from brake wear particles is destined to increase, and this source of pollution will probably be blamed as engine emissions are today. Thus, the potential health risk associated with braking particles could lead to a specific regulation. Braking converts a vehicle’s kinetic energy into thermal energy as a result of the friction between disc and pads. The friction between a composite pad made of a polymer matrix loaded with abrasive and lubricant compounds and a metallic disc causes wear on both parts. This wear, or matter loss, occurs via a complex tribological process, often with the creation of a transformed layer on the surface, before being released by the pad and disc. The nature and the number of fine particles emitted from the contact, potentially airborne, not only depend on the pad and disc composition, but also on conditions of tribological solicitations. In order to reduce aerosol particles emission, a better understanding of particle generation mechanisms is essential. This will enable the optimization of the sampling process, the material choice, and the braking protocol. To anticipate any future regulation requirements, automobile field needs a world methodological consensus on the topic. This communication aims to specify the reliable approach to characterize emitted particles during a dynamometric test. Several stakeholders have already developed measurement equipment adapted to braking emissions. However, the current poor consensus on the required testing protocol raises questions. Olofsson et al. focus on understanding emission mechanisms while presenting an interest on on-road tests. Other authors approach the challenge with a more applicative research of dynamometer and their instrumentations. Previous investigations enable identifying bottlenecks and their solution. The first approach to these questions consists of improving knowledge of particles emitted by braking. By precisely characterizing those particles, authors study their behavior towards their environment and during sampling. Thus, authors attempt to adapt specific metrology according to size and compositions of detected particles.