The Fundamental properties & influencing factors of brake particulate emissions session will take place on Thursday May 19th and will be chaired by Marcel Mathissen of Ford Werke GmbH and co-chaired by Athanasios Mamakos of AVL.
Topics and speakers for the session include:
Investigation of the influence of roughness on the wear and emission behaviour of brake pads
Malte Sandgaard, TU Braunschweig
The reduction of exhaust emissions resulted in other emission sources becoming the focus of public interest. Brakes and tyres were identified as the main emitters in vehicles with new exhaust standards. Compared to tyres, brakes have a higher hazard potential due to the chemical compositions and the high-temperature processes combined with the emissions of ultra-fine particles in the boundary layer. The investigation of brake emissions is mostly carried out in enclosed and controlled test environments, where both the concentration and the size spectrum of individual applications are analysed. For the most part, dynamometer is used, where only a limited amount of information can be obtained on the correlation between wear, emissions, surface signatures and friction parameters during brake applications. For the basic investigations of the characteristics of the contact between brake disc and brake pad, mainly pin-on-disc test benches, are used. For this purpose, the Automated Universal Tribotester (AUT) is used at the Institute for Dynamics and Vibration (IDS), which, in addition to recording the friction parameters such as the coefficient of friction, has quasi in-situ measurement options for the surfaces. In addition to determining the wear behaviour, surface properties such as roughness parameters can also be determined.
The aim of this work is to investigate the influence of surface properties, in particular of various roughness parameters, on the emission behaviour of individual brake pairings. The basis for this is the interaction between the occurrence of holes (reservoirs) and patches, the so-called Surface Reservoir Dynamic. It was observed that the emission characteristics change significantly with the number of reservoirs and the degree of filling of the reservoirs associated with low roughness.
Comparative study of size distribution and chemical composition of emissions from low steel and NAO friction materials
Alessandro Mancini, Brembo S.p.A
Significant efforts are currently on going to decrease the non-exhaust emissions from transport sector.
As far as the brake system is concerned, these efforts are mostly associated with the research of new friction couples and technological solutions capable to reduce the generation of fine particulate at the brake pad – disc interface. An additional strategy to reduce the environmental impact of brake emissions can arise from: a) increasing the emission particle dimensions; and b) tailoring their chemical composition. Consequently, prior to perform any environmental and toxicological assessment, it is fundamental to characterize the emissions in terms of composition, dimensions, and morphology.
At this regard, the work proposes an effective analytical method for the ex-situ characterization of fine particulates (PM10) emitted in air and coarser emissions falling directly to the ground, as obtained by the coupling of Low Steel and NAO friction materials and a reference grey cast iron disc. The Particle Size Distribution (PSD) and chemical composition of the emissions are investigated by the means of a multi-technique protocol based on Scanning Electron Microscopy (SEM), Laser Diffraction (LD), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD).
Results unveil the complex interplay existing between each typology of investigated friction material and the morphology/chemical composition of the corresponding emitted particulates.
Evaluation of different influencing parameters on the result of brake particle emission measurements
Katharina Kolbeck, BMW Group
Since fine dust particles in the ambient air emitted by cars, trucks and busses are identified as a health risk, emissions from combustion engines are limited by law. The increasing change from combustion to electric power train as well as the use of gasoline and diesel particulate filters lead to a focus shift to other fine dust sources like tire or brake wear. To further reduce the fine dust pollution caused by road transportation, it is planned to limit particle emissions of brake systems of passenger vehicles by law. The PMP informal working group of the UNECE is already working on a measuring cycle and a suitable test method for this purpose for several years. Hence, a draft of a test protocol was published in June 2021 and is validated in a inter-laboratory study (ILS) at different labs The proposal describes a method to test a single brake-vehicle-combination.
The analysis of the market in this regard reveals an extremely large number of possible pairings. Combined with the proposed duration of a complete test-run, this leads to a very high demand of testing to determine the variety of brake emissions of existing vehicle fleets in different markets. Hence, it is crucial to understand whether there are physical correlations between different test combinations to estimate the emission levels of brake-vehicle-pairings. The aim of this study is to investigate the influence of different vehicle and brake parameters in regard of the measured particle number and mass emission. In addition, the results are analysed for physically relevant correlations. This is done using various test series in which only individual test parameters, such as the size of the brake disc or the vehicle weight, are varied.
The study also tries to address the effect of different measures for noise, vibration and harshness (NVH) of the brake system on the particle number and mass emission results. The results show that plausible predictions of the emission are possible for the variation of specific test parameters. On the other hand, there are test parameters that require additional information or even a separate emission test when they are changed.
Reproducibility of brake emissions chemical composition: a first inter-laboratory assessment
Alessandro Mancini, Brembo S.p.A
Moving towards more environmental-friendly brake systems requires the mass and number reduction of their emissions. Moreover, limiting the emissions eco-toxicological behaviour is an additional strategy to reduce their environmental impact. This can be reached by increasing the overall dimensions of the emitted particulates as well as by suitably tailoring their chemical composition. As far as the latter point is concerned, sound understanding of both the chemical modifications occurring at the tribological interface and the emissions chemical composition is needed. Furthermore, to achieve reliable eco-toxicological assessments of specific braking pairs, the reproducibility of the chemical composition of their emissions has to be verified as stable and constant at least over the time and the testing sites.
Therefore, this work proposes a first example of inter-laboratory assessment of the chemical composition of emissions generated by brakes. More in detail, the same friction couple composed by a standard grey cast-iron braking disc and a standard copper-free ECE R90 friction material is tested at the dynamometric bench in two different testing laboratories over the same braking cycle (WLTP). The generated PM10 emissions are then collected by the mean of suitable sampling lines and analysed for both their elemental and phase composition, respectively by the mean of Energy Dispersive Spectroscopy (SEM-EDS) and X-Ray Diffraction (XRD). Finally, the emissions compositional results are compared to evaluate their variability level. Notably, the results shown in the contribution represent a first example of inter-laboratory assessment of the chemical composition of the emissions generated by brakes, thus widening the field of standardization also to the chemistry of such emissions.
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