Influence of System Dynamics on Vibration and Particle Emissions in a Reduced-Scale Dynamometer

Abstract

Nonexhaust brake emissions represent a significant source of airborne particulate matter in urban environments. Although the effects of friction materials and braking conditions on particle generation have been extensively investigated, the role of friction-induced vibrations remains poorly understood. Pin-on-disk studies report a strong relationship between vibration intensity and particle emissions; however, these simplified configurations do not reproduce the structural complexity of braking systems. Moreover, the influence of changes in pad–disk test-rig dynamics on particle emissions has not been systematically investigated. This study addresses this gap by examining the relationship between friction-induced vibrations and particle emissions under controlled braking conditions. A reduced-scale inertia dynamometer was instrumented with an optical particle sizer and accelerometers to simultaneously measure airborne particle concentrations and vibrations during an SAE J2521 procedure. Two disk boundary conditions were compared: a standard supported configuration and a modified spaced configuration with lower structural stiffness and damping. Despite comparable friction coefficients and similar secondary-plateau coverage, the spaced configuration produced approximately 10% higher total number concentration and exhibited higher vibration amplitudes within low-frequency bands. On a brake-by-brake basis, particle emissions showed a weak, inverse, and nonmonotonic relationship with vibration amplitude, with the highest concentrations occurring at relatively low vibration levels. This behavior may indicate two vibration regimes: Below a critical threshold, increasing vibration amplitude may promote friction-layer stabilization and reduce particle emissions, whereas higher amplitudes may promote particle release. However, the existence of such a threshold requires further experimental verification. These findings support future full-scale dynamometer investigations under more realistic braking conditions.