Laboratory measurements of airborne emissions from car brakes for clean air

Abstract: Brake systems are used to safely stop vehicles. The brake pads are pressed against the brake disc, transforming the kinetic energy of the vehicle into heat to be dissipated. In this process a tribological contact causing wear takes place at the interface of the pads and disc: particles are generated, a fraction of which is airborne and therefore creates an aerosol. To meet demands on air quality and sustainable transport, significant challenges are to find means to measure particles, and provide solutions able to decrease such source of emissions.Paper A proposes a test cycle executed in an inertia brake dynamometer during which a measurement of the airborne particles is carried out: the sampling point is close to the source of emissions. The experimental results are then analysed to determine how many particles are generated per test section.Paper B presents a redesign of an inertial disc brake dynamometer with the aim to have clean air while measuring particles, and isokinetic sampling. A comparison in terms of number and size distributions of the brake emissions with and without control of the cleanness of the intake air is studied.Paper C is the ranking, from the non-exhaust brake emissions point of view, of five different current brake pair materials using the novel redesigned inertia disc brake dynamometer. Particles are both counted, collect on filters and weighed.Paper D investigates the evolution of the friction performance in terms of friction coefficient and emissions, over five repetitions of the same test procedure – so considering the running-in effect. The friction performance is discussed as a consequence of the dominating wear mechanisms.Paper E conducts a study on real driving data that are transformed into a brake dynamometer testing procedure by an energy–temperature approach. The consequent emissions study allows the calculation of brake emission factors.Paper F presents a comparison of the brake particle emissions measurement when volatile and semi-volatile organic compounds (if any), as for exhaust emissions, are thermal treated before being measured.Paper G illustrates a holistic approach, developed within the REBRAKE EU-financed project, for reducing airborne emissions for car brakes by 50% integrating different perspectives: the tribological testing of the friction pair at different scale levels, the analysis of the relevant wear products and correlated wear mechanisms, the development of specific contact mechanics simulation approaches, and the optimisation of the friction pair materials.

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