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∙109 # 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 PM10 emission.
Highlights
Brake wear emissions is a topic which has received increased attention over recent years
The aim of the current paper is to present a measurement approach for sampling and measuring brake wear particles at a chassis dynamometer level
The maximum brake disc temperatures at the enclosed measurement wheel are approximately 110 ◦ C higher than observed at an unmodified wheel in the field. This can be seen as a limitation of the measurement method adopted in the present study as the estimated particle number (PN) emission factors are expected to be higher on the dynamometer than these expected from the same vehicle in the field
Summary
Brake wear emissions is a topic which has received increased attention over recent years. This is reflected by the continuously increasing number of non-exhaust related studies published over the last 25 years worldwide [1], with most of them addressing brake wear PM emissions. One of the main reasons why non-exhaust emissions were overlooked in the past was due to their relative relevance to air quality. Road transport emissions were dominated to almost 90% by exhaust emissions [2,3]. Non-exhaust emissions have become an important topic– scientifically–and at a political level [5]
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