Comparison of Full Flow Dilution, Partial Flow Dilution, and Raw Exhaust Particle Number Measurements

Abstract

The European regulations for heavy-duty engines allow full flow and partial flow dilution particle number (PN) measurements. This study focuses on the comparison of PN measurements from full flow systems (CVS) and partial flow dilution systems (PFDS), as well as from undiluted (RAW) exhaust. The impact of measurement location on PN count was evaluated on four engines in different test cells with the use of advanced AVL particle counter (APC) 489 and a Horiba MEXA -2100 solid particle counting system (SPCS). The APCs were used to measure diluted exhaust either from the CVS tunnel or from the PFDS, whereas SPCS was used to measure from either RAW exhaust or CVS tunnel. The SPCS used an additional direct sampling unit (DSU) for RAW measurements. The particle concentration reduction factor (PCRF) of 1000 was selected for all APC units, whereas SPCS PCRF was changed depending upon measurement location to ensure condensation particle counter (CPC) concentration remains within 10,000 particles/cm3. The insignificant differences in RAW PN measurements were found when PCRF settings of 2180, 11883, and 23990 were selected. The repeatability of APC at PFDS, determined from the engine without DPF, was within 2%, as expected. Similarly, repeatability of SPCS varied between 0.4 and 3.2% when RAW measurements were taken at engine-out (EO) and system-out (SO) locations. At the brake-specific PN (BSPN) level of 1013, the CVS, PFDS, and RAW were within ~ 13%. At the BSPN level of 1011, the RAW measurements were 7.9 ± 13.7% higher than CVS. Overall, on an average, the RAW PN measurements were within ± 15% of the reference measurement locations.