Comprehensive Analysis of Current Primary Measures to Mitigate Brake Wear Particle Emissions from Light-Duty Vehicles

Abstract

Exhaust regulations and improved exhaust gas treatment systems have already initiated the trend that brings emissions from brakes and tires to the forefront of traffic-induced particulate matter. The health and environmental relevance of particulate matter has resulted in regulators, industry, and research institutions prioritising the mitigation of non-exhaust particle emissions. To this end, under the umbrella of the United Nations Economic Commission for Europe World Forum for Harmonisation of Vehicle Regulations (UNECE WP.29), the Working Party on Pollution and Energy (GRPE) mandated the Particle Measurement Programme Informal Working Group (PMP-IWG) to develop a Global Technical Regulation (GTR) for measuring brake dust. The standards and procedures defined within the GTR should eventually form the basis for the introduction of a Euro 7 limit value for brake emissions. The purpose of this measurement campaign is to provide an exemplary overview of the emission behaviour of wheel brakes and friction pairings currently available on the market and to identify possible reduction potential with regard to particulate emissions. All measurements were carried out taking into account the draft GTR valid at the time of execution. For the investigations, brakes were selected using the example of different vehicle classes, brake concepts (disc and drum brake), vehicle axles (front and rear axle), and alternative friction materials (brake disc and pads/shoes). Thus, the use of wear-resistant discs and improved brake pad compositions are able to achieve significantly lower emissions. In addition, the measurement of brake dust emissions from vehicles with different levels of electrification was considered. Electrical braking was modelled and applied to the Worldwide Harmonised Light-Duty Vehicles Test Procedure (WLTP) Brake Cycle, which has demonstrated high emission reduction potentials depending on the electrification level.

Investigation of Brake-Wear Particle Emissions from Regenerative-Friction Brake Coordination Systems via Dynamometer Testing

“…0.107) based on actual vehicles. These results indicate the need for vehicle-specific friction brake share coefficients, a conclusion consistent with a previous study [17]. Using electrified vehicle brakes as FFBs and a single coefficient for each group does not allow for fair brake-wear particle measurements, especially fair PN measurements.…”

“…Friction brakes that share coefficients that depend on the electric vehicle type have been implemented in this method to allow third-party laboratories to perform tests based on the GTR24 procedure. Although this friction brake share coefficient was the first step of the study of brake wear particle emissions for vehicle with regenerative brake systems, the method does not represent actual regenerative braking characteristics and needs to be improved [17]. Based on environmental policy making processes in Japan [18], the Automotive Emissions Expert Committee of Japan has been discussing this issue and is in the process of developing the Future Measures to Reduce Automobile Emissions (Fifteenth Report).…”

Iron Oxide and Hydroxide Speciation in Emissions of Brake Wear Particles from Different Friction Materials Using an X-ray Absorption Fine Structure

“…Mass loss as a wear factor was 9.31 mg/km per brake with ECE pads (Figure 1). A comparison of these results to the benchmarks of a previous interlaboratory study (ILS) [8] revealed that higher emissions were observed in that study than in this study (6.5 mg/km per brake with NAO pads and 21 mg/km per brake with ECE pads) [26,27]. NAO was developed to optimize comfort (reduction of noise and rim contamination), and this study (Figure 1) as well as previous studies have shown higher emissions with ECE than with NAO [26].…”

Ultrafine particle emissions from dry clutches: number concentration, size distribution and chemical composition

“…Similarly, Storch et al 21 reported that wear particles from drum brakes initially accumulated in the drum but began escaping from the drum once saturation of the accumulation was reached. This resulted in a steady state level of emissions after an initial phase.…”