Influence of Collection System on the Tire Wear Emission Measurements

Abstract

Characterization of tire road wear particles (TRWP) is highly complex due to its open system and a multitude of influencing parameters that affect wear mechanisms and which are challenging to control. This study employs a three-step approach at a roller test bench—generation, collection, and analysis—to comprehensively understand and evaluate TRWP. The generation step encompasses various factors, such as tire and surface properties, as well as ambient and driving conditions. The collection step, positioned directly downstream of generation, is notably critical, as it directly affects the quantity and the characteristics of particles that proceed to final step. The analysis step includes the influence by the characteristics and limitations of the instruments used for particle characterization (online and offline methods). The design and efficiency of the collection system is therefore essential for ensuring that the collected particles are representative in quantity and quality of the actual emissions. This study evaluates the influence of different TRWP collection systems on physical characterization results, focusing on particulate matter (PM) emissions that impacting air quality and health. A pilot experiment was conducted under controlled conditions, maintaining identical parameters for TRWP generation and analysis. Two distinct collection systems were compared: a housing collection system, where the tire is encapsulated and separated from the brake and environment as much as possible, and a nozzle collection system, where the tire remains exposed. Systems were mounted on the same vehicle, with influencing parameters (e.g., air flow, instrumentation, positioning and materials) held constant. The experiment was performed on a dynamometer bench under fixed ambient conditions (temperature, humidity and air ventilation), with continuous monitoring of tire surface temperature. Simultaneous measurements of PM10 and PM2.5 mass concentrations, total particle number concentrations, and particle number size distributions were conducted. First results revealed significant differences in the physical characterization of TRWP between the two collection systems. The nozzle collection system consistently had a low yield, slightly above the background for both mass and number concentrations, whereas the housing system showed 3-10 times higher values. Moreover, flow rate and airspeed validation tests inside the collection systems during driving revealed a 15% variation in the nozzle system compared to only 4% in the housing. Although both systems have identical setup parameters, the open structure of the nozzle system led to greater instability with isokinetic conditions, thereby causing significant discrepancies in analysis step. This study underlines the critical impact of collection system design on the characterization of TRWP and the need for standardized methodologies in TRWP research. The results demonstrate that variations in boundary conditions and system limitations can significantly alter the outcomes, potentially leading to inaccurate interpretations of the data. By establishing a baseline for the methodological approach to TRWP collection and analysis, this work lays the foundation for developing robust, repeatable, and representative measurement for TRWP emissions. Such standardized methods are essential for accurate interpretation and comparison of results across studies, thereby advancing our understanding the impacts of TRWP.