On-Road Evaluation of a PEMS for Measuring Gaseous In-Use Emissions from a Heavy-Duty Diesel Vehicle

On-road comparisons were made between a federal reference method mobile emissions laboratory (MEL) and a portable emissions measurement system (PEMS) to support validation of the engine “Not To Exceed” (NTE) emissions design and to evaluate the accuracy of PEMS. Three different brake specific emissions calculation equations (methods) were used as part of this research, with method one directly using engine speed and torque, and methods two and three including ECM fuel consumption and carbon balance fuel consumption. The brake specific NO_x emissions for the particular PEMS unit utilized in this program were consistently higher than those for the MEL. The brake specific (bs) NO_x NTE deltas were +0.63±0.31 g/kW-h (0.47±0.23 g/hp-h), +0.55±0.17 g/kW-h (0.41±0.13 g/hp-h), and +0.54±0.17g/kW-h (0.40±0.13g/hp-h) for methods one, two, and three respectively. The method one MEL bsNO_x average value was 3.17 g/kW-h (2.36 g/hp-h) relative to the applicable in-use NTE standard of 4.20 g/kW-h (3.13 g/hp-h). The percent difference relative to the NO_x NTE in-use standard ranged from 6% to 25% higher for method one, from 7 to 19% higher for method two, and from 7% to 19% for method three. The brake specific CO₂ emissions for the PEMS were consistently biased high relative to the MEL, with an average bias of 4.5% ±4%. Consistent differences between the PEMS were also measured for NMHC and CO emissions. These absolute differences were relatively small compared to the in-use NTE standards due to the low NMHC and CO emission levels.