Influence of Caliper Position on Particle Emission Test Results in Heavy-Duty Brake Emission Test Systems

Brake wear is a major contributor to non-exhaust particulate emissions, and standardized measurement methods are currently being extended from light-duty (LD) to heavy-duty (HD) vehicles. However, differences in brake geometry and operating conditions may influence particle transport and sampling representativeness in HD brake emission test systems. This study investigates the influence of brake caliper position on particle emissions and mixing uniformity in an HD brake emission test setup. Experiments were conducted using a dynamometer-based system with four sampling probes distributed across the sampling plane. Emissions of particulate mass (PM10, PM2.5) and particle number (solid and total particle number emissions for particles >10 nm) were measured for two caliper orientations (horizontal and vertical). Mixing quality was assessed by comparing probe-specific emission results to the plane-averaged value. The results show that the vertical orientation was associated with 34% higher PM10 and 40% higher PM2.5 emissions on average, a significant increase. Particle number emissions also increased on average, but the differences were small relative to test repeatability. The more pronounced effect on PM suggests that the caliper position mainly influences the transport and losses of larger particles, which contribute more to PM. In contrast, the uniformity of particle concentration across the sampling plane was similar for both configurations, with deviations comparable to those reported for LD systems. These findings should be considered in the interpretation of results obtained with any similar test systems, comparisons between such systems, and literary reviews.