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Environmental Measurements Methods
Study of Brake Wear Particle Emissions: Impact of Braking and Cruising Conditions Ferdinand Heinrich Farwick zum Hagen, Marcel Mathissen, Tomasz Grabiec, Tim Hennicke, Marc Rettig, Jaroslaw Grochowicz, Rainer Vogt, and Thorsten Benter Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b07142 • Publication Date (Web): 02 Apr 2019 Downloaded from http://pubs.acs.org on April 3, 2019
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Environmental Science & Technology
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Study of Brake Wear Particle Emissions:
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Impact of Braking and Cruising Conditions
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Ferdinand H. Farwick zum Hagen,a,b,* Marcel Mathissen,a,* Tomasz
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Grabiec,c Tim Hennicke,c Marc Rettig,c Jaroslaw Grochowicz,c
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Rainer Vogt,a Thorsten Benterb
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aFord
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Aachen, Germany
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bBergische
Werke GmbH, Research and Innovation Center, Süsterfeldstraße 200, 52072
Universität Wuppertal, Department of Physical and Theoretical Chemistry,
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Gaußstraße 20, 42097 Wuppertal, Germany
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cFord
Werke GmbH, Henry-Ford-Straße 1, 50735 Köln, Germany
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*Corresponding authors: Ferdinand H. Farwick zum Hagen, e-mail address:
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[email protected]; Marcel Mathissen, e-mail address:
[email protected] 15
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Abstract
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A novel measurement setup is designed, constructed, and validated by theoretical simulations and
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by experiments enabling sensitive and loss-free brake particle emission investigations. With the
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goal to simulate realistic driving, a three-hour subsection of the Los Angeles City Traffic (LACT)
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cycle is selected as test cycle. The tests are performed with the front brake of a mid-size passenger
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vehicle under both static laboratory and more dynamic realistic conditions that include parasitic drag
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and vehicle brake temperatures (advanced vehicle simulations). A PM10 emission factor of around
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4.6 mg km-1 brake-1 is determined. During five cycle runs the emission factor in terms of particle
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number decreases by one order of magnitude. This decrease is accompanied by a shift of the
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critical brake temperature Tcrit, at which ultrafine particle emissions occur, from 140°C to 170°C.
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Investigations with advanced vehicle simulations generate brake temperatures below Tcrit and
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consequently do not show ultrafine particle emissions above background level. A particle number
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emission factor of approximately 4.9E10 km-1 brake-1 is estimated for realistic vehicle brake
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temperatures. Particle formation during cruising is clearly identified. The brake drag is estimated to
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contribute about 34 % to the total airborne particle mass emission.
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TOC Art
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Introduction
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Brake wear particulate matter is identified as one of the contributors to non-exhaust particle
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emissions in the transportation sector1. Especially in urban street canyons brake wear related PM10
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contributes up to 21 % to the total traffic related PM10 emissions2. A fraction of about 35-55 % of
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brake wear becomes airborne3-5 while the remaining fraction deposits either on the vehicle or at
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road sites6. In the framework of UNECE-GRPE-PM program7, a measurement procedure for brake
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wear particle emission is under discussion. The present paper demonstrates a concept for setup
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design and test procedures.
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In recent years, there has been a lot of effort in understanding the contribution of brake wear
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particles to ambient particulate matter, for example by receptor modelling8. The occurrence of brake
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wear particles is investigated through on-road5, 9-11 and laboratory measurements, which are further
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divided into either pin-on-disc12, 13 or dynamometer4, 14-17 tests. The latter is having the advantage of
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conducting tests in a reproducible manner, while preserving the brake as a full system: Test
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procedures that include environmental conditions, drive cycles, and vehicle load (inertia), are easily
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constrained. Although dynamometers are the basis for robust measurements, the methods of
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sampling and measuring brake wear particles deviate widely. The fact that setups are either open14,
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drawing aerosol samples deviate as well. For instance, non-isokinetic sampling leads to under- or
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overestimation of particle concentrations18. Another crucial point is the drive cycle. Numerous
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studies make use of an artificial set of brake stops from a set of speeds under constant
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decelerations in order to investigate emissions at even more constrained conditions. However,
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these procedures are not representative for realistic driving simulations. As investigations on
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realistic driving and braking are rare19, they are subject of the present study.
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The present paper presents a novel measurement setup that has been designed for brake emission
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investigations, considering quantification of emissions, high reproducibility, and high signal
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sensitivity. Results from realistic test cycles are presented in terms of cumulative emission factors
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and particle number (PN) and particle mass (PM) for each brake stop. In parallel, a more realistic
or completely enhoused16 prevents emission quantifications. Furthermore, the techniques of
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approach is established by simulating parasitic drag and realistic brake temperatures (later:
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advanced vehicle simulations). In this context, the relevance of emissions during cruising caused by
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brake drag is investigated. Although the effect has been reported qualitatively19, 20, hitherto its origin
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and relevance remained unclear.
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Material and Methods
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Measurement setup
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A Link 3900 brake dynamometer has been used, where the brake is located inside a test room. The
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air conditioning of the test room provided constant environmental conditions (pre-filtered air, 50 %
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relative humidity, 30 °C temperature). Inside the test room the particle measurement setup was
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installed as shown in figure 1.
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Figure 1 – Measurement setup. (a) The chamber and tubing is colored in grey and the measurement devices and their tubing are sketched similarly to the experimental arrangement. The air flow direction is indicated by red arrows. (b) Virtual image viewing onto the brake (blue, caliper; silver, disc; the cover plates of the chamber and parts of the drive shaft (yellow) are not shown). The measurement devices are colored in light blue. At the sampling point the inner arrangement of probes and the experimentally determined air velocity profile is shown. Measurement devices are arranged as follows: APS (1), OPS (2), ELPI+ (3), DT (4), PM impactor (5).
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At the end of the transport line a blower created a stable air flow of Qsetup=250±10 m³/h at negative
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pressure, which was roughly equivalent to the air flow through the wheel rim (CFD: ~264 m³/h at 70
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km/h). Directly in front of the blower a continuous flow measurement was performed using a Vortex
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ultrasonic sensor (Höntzsch VA40) combined with a honeycomb flow straightener. For constant air
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flow, the actual flow signal was used for feedback control of the blower. At the entrance of the
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tubing (dtube=150 mm), an HEPA H13 filter was installed ensuring that only clean air was entering
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the system. A completely sealed chamber (volume
