The Repeatability and Reproducibility of Particle Number Measurements from a Heavy Duty Diesel Engine

Abstract

The Euro VI heavy duty on-highway engine emissions standards were recently implemented in the European Union (EU) countries requires the type approval of new engines to not only comply with lower NOx and PM emissions limits but also comply with the newly introduced limit on particle number. This study quantifies repeatability and reproducibility (R&R) of brake-specific particle number (BSPN) measurements by using three AVL particle counters (APC) under actual testing conditions. The study was conducted on a single, heavy duty diesel engine (2007 Cummins ISX 14.8 L 425 HP) equipped with a diesel oxidation catalyst and a diesel particulate filter (DPF). The conditioning of the DPF played a significant role in characterizing variation in particle number measurements. The R&R values were quantified based on 53 US on-highway transient Federal Test Procedure (FTP) test cycles with the total of 149 BSPN observations collected over the period of 68 days in five Constant Volume Sampler (CVS) test cells. The global average of the 149 BSPN observations (1.3918E + 11 #/kW-h) was used to calculate relative variation in BSPN for both the entire test process and for the APC units only. The BSPN measurement repeatability and reproducibility were 2.5 and 31.7 % of the global average, respectively. The variation due to measurement systems (APC) were 0.69 % (repeatability) and 6.2 % (reproducibility) of the global average. Most of the variation was due to reproducibility which comprised of 99.4 % of the total variation. The coefficient of variation (COV) of BSPN among three APC units varied between −19.1 and 17.9 % on 49 FTP test cycles. Overall, the very high reproducibility and COV between units suggest that the instrument should be checked for drift periodically. The frequent in-use calibration checks are required for various components of the particle number measurement system to ensure quality data required for engine certification.