Assessment of In-Use NOx Emissions from Heavy-Duty Diesel Vehicles Equipped with Selective Catalytic Reduction Systems

Abstract

This work evaluated the nitrogen oxide (NOx) emissions of 277 heavy-duty diesel vehicles (HDDVs) from three portable emission measurement system testing programs. HDDVs in these programs were properly maintained before emission testing, so the malfunction indicator lamp (MIL) was not illuminated. NOx emissions of some HDDVs were significantly higher than the certification standard even during hot operations where exhaust temperature was ideal for selective catalytic reduction to reduce NOx. For engines certified to the 0.20 g/bhp-hr NOx standard, hot operation NOx emissions increased with engine age at 0.081 ± 0.016 g/bhp-hr per year. The correlation between emissions and mileage was weak because six trucks showed extraordinarily high apparent emission increase rates reaching several multiples of the standard within the first 15,000 miles of operation. The overall annual increase in NOx emissions for the HDDVs in this study was two-thirds of what was observed in real-world emissions for HDDVs at the Caldecott Tunnel over the past decade. The vehicles at the Caldecott Tunnel would include those without proper maintenance, and the inclusion of these vehicles possibly explains the difference in the rate of emission increase. The results suggest that HDDVs need robust strategies to better control in-use NOx emissions.

Emission Measurements on a Large Sample of Heavy-Duty Diesel Trucks in China by Using Mobile Plume Chasing

“…In addition, we listed the measurement results of Europe and the United States in Table S2. The measured NO X EFs of in-use HDTs were much higher than their counterparts in Europe − and the United States. − It was found that the BC emission levels were merely comparable to those of the U.S. fleets tested in 2009–2011 − and considerably higher than those in the United States after 2013 . This is due to the high emitters contributing considerably to the total emissions.…”

Utah Wintertime Measurements of Heavy-Duty Vehicle Nitrogen Oxide Emission Factors

“…However, the fact that we observe high NO x emissions in the newest HDV at all of the sites, an observation also reported by other researchers, suggests an issue that involves more than temperature differences. 42 There are no significant differences between Utah (7.19 ± 0.97 gNO x /kg of fuel) and Cottonwood, CA (7.5 ± 4.5 gNO x / kg of fuel) means for the newest vehicles, though Cottonwood uncertainties are very large. The Cottonwood measurements are different in that the higher means are not the result of a larger number of high-emission outliers but an increase in emissions between the 25th and 85th percentiles (Figure S12).…”

“…This is consistent with the hypothesis that lower ambient temperatures have lowered the SCR conversion efficiency (Figure S1) rather than increased the number of catalysts that are inoperative. However, the fact that we observe high NO x emissions in the newest HDV at all of the sites, an observation also reported by other researchers, suggests an issue that involves more than temperature differences …”

Evaluation of different injectors-swirl configurations on combustion and emissions characteristics in a medium-duty compression ignition diesel engine

“…Regarding ISNOx emissions, the F NOx is 0.46 to equalize the median merit function values with the fuel consumption. This consideration is done because the intended vehicle for the current engine is required to have a selective catalytic reduction destined to reduce this pollutant (these aftertreatment devices can have relatively high efficiency if the exhaust temperatures surpass a minimum threshold 42–44 ), although due to the differences of NOx reduction capabilities between laboratory tests and real-world use 45 the lowest value for this emissions is preferable.…”