Design of a Laboratory Sampling System for Brake Wear Particle Measurements

Brake wear is one of the dominant sources of traffic-related particulate matter emissions and is associated with various adverse environmental and health hazards. To address this issue, the UNECE mandated the Particle Measurement Program to develop a harmonized methodology for sampling and measuring brake wear particles with a full-flow sampling tunnel on a brake dynamometer. Here we present the design of a novel, fully PMP compliant sampling tunnel. The dimensions and general layout of the tunnel are based on minimization of super-micron particle losses and consideration of space limitations in brake-dynamometer setups as well as the need for efficient utilization of the test facilities (reduced testing times). Numerical calculations suggested that the critical section of the system is the sampling train from the sample probes to the instrumentation inlet/filter holder. An optimal sampling train flow of ~10 l/min was identified and formed the basis for the design of a dedicated PM sampler. The developed sampling tunnel was subsequently used to test a reference brake system on a fully electric brake dynamometer. Dedicated tests verified that the produced brake-wear particles are properly mixed and the flow profile stabilized at the sampling plane. Measured PM and PN emissions were found to agree within ±20 % to levels determined in two previous campaigns where the same brake system was tested with the same instrumentation. Considering the vastly different enclosure and sampling tunnel designs employed at these test facilities, the good agreement observed further verifies the findings of the numerical analysis indicating the sampling train as the most critical section in brake-wear particle measurements.