Particulate matter from standard heavy-duty vehicles mechanical brakes: a multi parameter ranking approach

The contribution of non-exhaust emissions has become comparable to exhaust emissions because of strengthened legislations on the engine. This shift prompted the European Commission to work on the Euro 7 legislation, introducing new requirements including particles from mechanical brakes abrasion. Specific studies on heavy-duty friction materials are not so well represented yet. This study has for objective to close the gap, using a pin-on-disc tribometer following the same method as used in light-duty work. Transition temperature and emission profiles were mapped for seven heavy-duty friction materials. The results demonstrate a higher proportion of ultrafine particles for all friction materials after reaching a transition temperature. The transition temperature ranges from 150 to 230 °C. A clear difference between particle size distribution before and after the transition temperature is shown, with some materials displaying a 99% proportion of ultrafine particles. To illustrate the complexity of understanding the emission profiles, one material displays the lowest particle mass while having one of the highest particle number, leading to a dilemma when it comes to choosing a safe solution. To tackle this complexity, a desirability index method is proposed to rank these materials based on six parameters relating to tribological performances, particulate emissions and potential health effects. The full-system index identified HDV1 as the best of the seven candidates with a score of 0.49, while HDV6 scored a mere 0 on multiple criteria. The study concludes with the potential for the desirability index method to rank materials, including the transition temperature as an emission profile parameter. • A transition temperature (Tt) up to 230 °C is shown for all tested materials. • The Tt is accompanied with a shift towards the emission of nanoparticles. • Emission profiles can be characterised by a desirability index. • The desirability index can be used to rank friction materials.