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The PN counter as a “black box” – a novel approach to a universal PN calibration standard for automotive exhaust
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
Air pollution from particulates is an ongoing challenge for public health in the European Union. High standards for ambient air quality are complemented by emission limits, e.g. for road vehicles that pose a major source of air-borne particulates in urban areas. Therefore the EU has triggerd the development of a multitude of PN measurement instruments as legislative tools to enforce automotive PN emission standards. These tools are: stationary particle counters used on the chassis dynamometer (since Euro 5b, 2011), portable PN-PEMS for RDE on-road measurements (Euro-6d TEMP, 2017), and low-cost instruments for the periodical technical inspection at the tailpipe (PTI)(national standards in CH, BE, NL, DE, 2020-21). While they are meant to measure the same PN in automotive exhaust, they are defined and calibrated differently and independently. The legal description of stationary PN counters and PN-PEMS leads to systematic differences between these instruments, both in technical implementation and PN counting behavior. This is even truer for the new, simplified PTI instruments. Today, there is no means of directly comparing PN measurements from different instruments. This is aggravated by a dominance of manufacturer calibrations with not necessarily disclosed procedures. This presentation proposes a novel calibration approach. It regards the PN counter as a “black box” and describes its performance independent of the instrument design and of the underlying legislation. The calibration yields an “absolute” PN value that can be directly compared among instruments. It allows easy accreditation and full metrological traceability to international standards. It is designed to improve the correlation of PN measurements EU-wide. This brings the measurement quality of PN closer to that of gaseous pollutants. As a matter of fact, accurate measurements are a major means to encourage OEMs to compete for the cleanest vehicle technology and also hold them accountable in case of exceedance.