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EuroBrake 2022: Standardisation & future outlook on brake particulate emission testing

The Standardisation & future outlook on brake particulate emission testing session will take place on Thursday May 19th and will be chaired by Carlos Aguledo of Link Engineering Co. and co-chaired by David Hesse of TU Ilmenau.

Topics and speakers for the session include:

Brake-wear PM and PN instrumentation round robin

Katharina Kolbeck, BMW Group

In the context of the PMP Inter-Laboratory Study (ILS), several brake systems were circulated at different laboratories to characterize their brake-wear particulate emissions following the recently developed PMP measurement methodology. Each laboratory is required to employ its own dynamometer, sampling system and measurement instrumentation, including PM2.5, PM10, 10 nm total particle number (PN) and optionally 10 nm solid particle number. The absence of reference measurement instrumentation circulated to the participating laboratories was mainly due to time constraints.

Given the challenges associated with the characterization of brake-wear particles and the limited experience with the application of the new methodology, it is important to also assess the contribution of the measurement instrumentation on the repeatability and reproducibility of the novel methodology. To this end, a set of measurement instrumentation was circulated in three laboratories participating in the ILS. The instrumentation included two AVL PM samplers and the associated cyclones for PM2.5 and PM10 quantification, as well as two AVL Particle Counters (APCs). One APC was unmodified and fully compliant with the Global Technical Regulation (GTR) 15 as recently updated for 10 nm measurements. This includes the use of a full-flow CPC with a cut-off size at 10 nm, and a catalytic stripper at 350ºC. The second APC was a modified 10 nm version operating with its heaters deactivated, and the catalytic stripper removed. Both the APCs and the internal CPCs were calibrated in an iso-certified calibration line before the start of the campaign. Their calibration was also validated at the end of the measurement campaign. All three laboratories performed measurements with the two reference brake systems, one of which was tested with two different types of brake-pads. Some additional investigations were performed at each lab. These included testing of two different brake systems, one of which used drum-brakes, as well as investigations of an alternative bedding-in procedure.

In this talk an overview of the measured particulate emissions including both mass and number, is presented. The reference brake systems allowed for the assessment of the repeatability and the reproducibility of the measurement results for each metric. These figures when compared to the official statistics of the entire ILS will help assess the contribution of measurement instrumentation on the overall accuracy or the measurement methodology. The talk will also address the robustness as well as improvement potential in the methodology, based on the results with the additional brake systems and the alternative bedding-in procedure.

Real-driving emissions sampling system for brake wear particle measurement

Michael Peter Huber, TU Graz

Brake wear is well recognized as one of the dominant sources of traffic-induced particulate matter emissions. A first standardized measurement methodology is currently being developed by UNECE's Particle Measurement Program.

The approach is based on isolated single brakes on dedicated brake test beds, where the test conditions can be tightly controlled. However, the actual real-world emission behaviour of a brake system is influenced by many changing factors depending on the vehicle and a multitude of surrounding conditions. This makes real driving emissions measurement of brake dust a highly relevant but also very challenging task, considering minimal impact of the measurement setup on the emission behaviour.

In this paper, we show the design of a novel brake particle sampling system with minimal influence on the thermal behaviour of the brake, supported by numerical simulation studies. The proposed setup covers only part of the brake disc on one side and allows for installation with minimal interventions at the brake mount and rim. The particle-collecting grommet and the sampling line were carefully designed to minimize larger particle losses. The sampling system was implemented in a commercial passenger car and equipped with particulate matter measurement instruments, closely following the ongoing standardization for brake dyno emission testing. Repeated real driving tests on a test track were successfully performed with different sampling flow rates. The results demonstrate the validity of the proposed approach, indicating promising particulate matter collection efficiency with sufficiently high sampling flow.

Intelaboratory accuracy study (ILS) for variability and effects of the braking systems during brake emission testing

Theodoros Grigoratos, European Commission JRC

The quantification of variability and effects from testing different brakes at different facilities is a critical input to the rollout of a protocol from the World Forum for Harmonization of Vehicle Regulations to characterize brake emissions using inertia dynamometers. Having 17 laboratories from around the world testing five different brake corners is a reliable manner to quantify the sensitivity and ruggedness of the PMP protocol.

The first part of the paper presents an overview of the structure of the ILS and the different brake corners under testing. The second part presents a taxonomy and high-level description of the dynamometer facilities related to enclosure style, constant volume sampling system, and instrumentation for measuring particulate mass (PM) and particle number (PN).

The high-level results combined with the lessons learned (from the perspective of actual results, project execution, and project integration) will conform a basis for enhancing and detailing as needed the upcoming protocol from the PMP for vehicles categories M1 and N1. All combined will enable results to repeat and compare across different brakes, friction materials, and testing facilities.

Establishment of brake wear emission analysis techniques

Tetsuro Kimura, Akebono Brake Industry

We reported the measurement method of brake wear emission to know the material balance / particle size distribution and the technology to observe / analyse (element level) nano-sized particles at 2017 (EB2018-VDT-004) and 2018 (EB2019-EBS-011). From these studies, we were able to estimate that the brake wear emission was divided into four categories and found that most of the wear powders are agglomerated, and the particle diameter grows by repeated agglomeration.

In this study, to make clear the generation mechanism of brake wear emission, we report a technique of deagglomerating agglomerated particles and analysing them with FE-SEM.

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