A Comprehensive Evaluation of a Gaseous Portable Emissions Measurement System with a Mobile Reference Laboratory

Abstract

In-lab and on-road emission comparisons are made between AVL’s M.O.V.E GAS PEMS 493 system and the UCR mobile emissions laboratory (MEL), which served as a Federal Reference Method (FRM) for comparison and validation. These comparisons are made for three different heavy-duty engines with NO x emission certification levels ranging from 0.27 g/kWh (0.2 g/hph) to 5.4 g/kWh (4.0 g/hph). The brake-specific emissions during the Not-To-Exceed (NTE) engine operating zone are compared between the FRM and portable emission measurement systems (PEMS) to quantify the measurement uncertainty of the new commercial PEMS. Overall, the PEMS shows good correlation to the FRM and demonstrate its ability to measure a wide variety range of emission levels. The PEMS brake-specific NO x (bsNO x ) measurement is well-behaved with +5 to −10 % relative error over the 1.0 to 7.0-g/kWh range. Further, the relative NO x error ranged from a +15 to −15 % over the 0.1 to 1-g/kWh range. The relative NO x error increases sharply below 0.1 g/kWh from 15 % to more than 50 % at 0.02 g/kWh. The relative error below 0.10 g/kWh is high due to the very low NO x emission rates that approach the detection limit of both the raw PEMS and dilute FRM measurement methods. The PEMS bsCO2 average bias is observed to be slightly higher than the MEL reference laboratory at 2 % overall. The PEMS NMHC and CO emissions were on average −11.8 and −3.6 % compared to the MEL for the 2006 engine, respectively. The main purpose of this study was to determine the measurement uncertainty of recently released PEMS in comparison with legacy and ultra-low emission modern heavy-duty vehicles.