Brake Wear Particle Emissions of a Passenger Car Measured on a Chassis Dynamometer

Abstract

Brake wear emissions with a special focus on particle number (PN) concentrations were investigated during a chassis dynamometer measurement campaign. A recently developed, well-characterized, measurement approach was applied to measure brake particles in a semi-closed vehicle setup. Implementation of multiple particle measurement devices allowed for simultaneous measurement of volatile and solid particles. Estimated PN emission factors for volatile and solid particles differed by up to three orders of magnitude with an estimated average solid particle emission factor of 3·10 9 # km −1 brake −1 over a representative on-road brake cycle. Unrealistic high brake temperatures may occur and need to be ruled out by comparison with on-road temperature measurements. PN emissions are strongly temperature dependent and this may lead to its overestimation. A high variability for PN emissions was found when volatile particles were not removed. Volatiles were observed under high temperature conditions only which are not representative of normal driving conditions. The coefficient of variation for PN emissions was 1.3 without catalytic stripper and 0.11 with catalytic stripper. Investigation of non-braking sections confirmed that particles may be generated at the brake even if no brakes are applied. These "off-brake-event" emissions contribute up to about 30% to the total brake PM 10 emission.EFs depend on parameters like the type of the friction material, the type of the brake assembly, and the applied driving conditions [11]. Following the development of a WLTP-based braking cycle in 2018 [7], most studies focused on the application of realistic braking patterns, but still the range of reported EFs remained relatively wide [12][13][14]. Similarly, experimentally measured brake wear PM 2.5 EFs vary from 0.1 mg·km −1 to 5 mg·km −1 per vehicle [8,11,13]. Finally, particle number (PN) EFs reported by various researchers also appear to be inconsistent [12,[14][15][16]. This is probably due to more variations on the setup and measurement protocols when PN related studies are examined. One has to keep in mind that traffic related PN emissions, particularly ultrafine particle emissions, are becoming more relevant due to demonstrated negative health effects [17,18].One important reason for the observed inconsistencies in the measurement of PM and PN EFs is the lack of a standardized methodology for sampling and measuring brake wear particle emissions [7]. Indeed, in most references provided previously, different sampling and measurement setups were employed. Brake wear particles can be studied in a relatively controlled environment in the laboratory or under uncontrolled real-world conditions on the road [19,20]. Laboratory studies can be carried out at full vehicle level on a roller chassis bench [21], at brake couple level on a brake dynamometer [11,[22][23][24][25][26][27], or at brake component level on a pin-on-disc configuration [28][29][30][31][32]. Table 1 gives an overview of different methods applied by different researchers...

Physical Characterization of Brake-Wear Particles in a PM10 Dilution Tunnel

“…To our knowledge there is no published data on the emissions over the novel WLTP cycle. Chassis dyno measurements of PN over the Los Angeles City Traffic (LACT) cycle were reported to systematically result in large number of volatile particles being released that were efficiently removed by a CS [14]. Non-volatile PN emissions (3 × 10 9 #/km/brake) were within the range of what we measured over the WLTP.…”

“…The peak disc temperature is commonly suggested as an indicator for the onset of thermal release of material from the brakes [14,16,24]. However, this lumped parameter does not properly represent the actual temperature on the contact area between pads and disc.…”

“…Different approaches have been employed for the characterization of brake-wear emissions, ranging from on-road measurements [13] to chassis dynamometer [14], brake dynamometer [13,15,16] and pin-on disc configurations [17]. One of the major challenges in any measurement configuration relates to the inherent difficulties in sampling and transporting super-micron particles [13].…”

Enhancing near-road exposure assessment

“…Because regulations have so far been targeted almost exclusively at tailpipe emissions and vehicle miles traveled continue to increase, it has been predicted that non-tailpipe PM emissions and their contribution to near-road PM concentrations may exceed tailpipe PM emissions at some point in the future (Grigoratos and Martini 2015;Rexeis and Hausberger 2009), and may have already done so in some locations (Southern Ontario Centre 2019). Though there is currently no non-exhaust emission standard, recent work by the UN Particle Measurement Programme (PMP) has sought to design a standard method for testing brake-wear particles; a novel particle measurement setup for on-road investigation of brake wear particles (Farwick Zum Hagen et al 2019) and a real-world braking cycle (Mathissen et al 2019) have been reported. Non-tailpipe PM emissions include transition metals, which are of toxicological interest because they may cause proinflammatory effects (Gerlofs-Nijland et al 2019).…”

The Development of Strategies to Reduce Exhaust Emissions from Passenger Cars in Rzeszow City—Poland. A Preliminary Assessment of the Results Produced by the Increase of E-Fleet

“…The main greenhouse gases emitted by human activities are carbon dioxide, methane, nitric oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride [17][18][19]. Apart from greenhouse gases, emissions of particulate matter, especially those with the dimensions PM2.5 and 10 [20][21][22], are extremely dangerous to health and the environment.…”