Brake Emission Testing Process – Assuring Repeatability and Reproducibility of Emission Measurement Results

Non-exhaust emissions are clearly one of the focal points for the upcoming Euro 7 legislation. The new United Nations Global Technical Regulation (UN GTR) defining the framework for brake emission measurements is about to be officially published. The first amendment to this text is already on the way through the United Nations Economic Commission for Europe (UNECE) hierarchy for decision making. In real life, the final emission factor as the ultimate result of a test is influenced by inaccuracies of numerous parts of the measurement system as well as additional contributing factors like the performance of the particulate filter handling process, which might not be primarily related to equipment specifications. The regulation’s definitions set the basic requirements for testing, whilst establishing a robust and efficient testing process requires a thorough assessment of the influencing factors on the measurement quality, which in turn can be described using e.g., repeatability and reproducibility. This study shows these influences of the system’s inherent sources of imperfection on result quality, based on theoretical relations, simulations, measurement results and experience gathered during productive brake emission testing. Essential process performance indicators are derived to allow suitably low uncertainty of results for homologation and development purposes. Based on this, it might make sense for testing organizations to tighten their internal technical specifications for specific topics beyond current regulation’s requirements to allow efficient testbed operation and deliver superior data quality. Considering lower absolute emission levels in the future, understanding these influencing factors will get even more important.