Framework for the assessment of PEMS (Portable Emissions Measurement Systems) uncertainty

Abstract

European regulation 2016/427 (the first package of the so-called Real-Driving Emissions (RDE) regulation) introduced on-road testing with Portable Emissions Measurement Systems (PEMS) to complement the chassis dynamometer laboratory (Type I) test for the type approval of light-duty vehicles in the European Union since September 2017. The Not-To-Exceed (NTE) limit for a pollutant is the Type I test limit multiplied by a conformity factor that includes a margin for the additional measurement uncertainty of PEMS relative to standard laboratory equipment. The variability of measured results related to RDE trip design, vehicle operating conditions, and data evaluation remain outside of the uncertainty margin. The margins have to be reviewed annually (recital 10 of regulation 2016/646). This paper lays out the framework used for the first review of the NOx margin, which is also applicable to future margin reviews. Based on experimental data received from the stakeholders of the RDE technical working group in 2017, two NOx margin scenarios of 0.24–0.43 were calculated, accounting for different assumptions of possible zero drift behaviour of the PEMS during the tests. The reduced uncertainty margin compared to the one foreseen for 2020 (0.5) reflects the technical improvement of PEMS over the past few years.

Emission Factors of a Euro VI Heavy-duty Diesel Refuse Collection Vehicle

“…A recent study at 20 mg/kWh levels found 10 mg/kWh measurement error (50%) [18]. In the EU, an uncertainty of approximately 45% at 80 mg/km levels was found (33 mg/km) assuming a drift of 5 ppm [16]. Thus, our older generation PEMS is between older PEMS assessments and the newer generation PEMS results (more details in Appendix B).…”

“…This Appendix gives the PEMS uncertainty of heavy-duty vehicles based on the analysis that was conducted for light-duty vehicles [16]. The uncertainty values were taken from the regulation requirements regarding accuracy, linearity etc.…”

“…At the moment, during PEMS on-road testing for type-approval and ISC testing, only NO x , CO, and total hydrocarbons (HC) are measured. Particle number (PN) will be introduced with step E. The measurement uncertainty of PEMS has been assessed in the United States of America (USA) [15] and recently in Europe for light duty vehicles [16]. Uncertainty estimations that range from 10 mg/kWh up to 600 mg/kWh were reported (approximately 20-60% of the emission levels) [15][16][17][18].…”

Evaluation of a 10 nm Particle Number Portable Emissions Measurement System (PEMS)

“…Due to their simplified design and the additional uncertainties of tailpipe sampling, studies showed that they have differences of up to 50%-60% from the regulatory laboratory systems. This was based on testing campaigns with many systems and vehicles and inter-laboratory correlation exercises (e.g., [8][9][10]).…”

Comparison of Portable Emissions Measurement Systems (PEMS) with Laboratory Grade Equipment

“…Thus, uncertainty associated to the measurements can be propagated through the data used for emissions calculations. According to a study by the Joint Research Centre (JRC) of the EU [9] the main sources of uncertainty are the exhaust flow meter (EFM), the gas analyzers, and their drift. The extra PEMS measurement uncertainty compared to the well-established and more accurate legislated method (measurement of bags from a full dilution tunnel) is covered by a margin that determines the conformity factor.…”