Four heavy-duty and medium-duty diesel vehicles were tested in six different aftertreament configurations using a chassis dynamometer to characterize the occurrence of nucleation (the conversion of exhaust gases to particles upon dilution). The aftertreatment included four different diesel particulate filters and two selective catalytic reduction (SCR) devices. All DPFs reduced the emissions of solid particles by several orders of magnitude, but in certain cases the occurrence of a volatile nucleation mode could increase total particle number emissions. The occurrence of a nucleation mode could be predicted based on the level of catalyst in the aftertreatment, the prevailing temperature in the aftertreatment, and the age of the aftertreatment. The particles measured during nucleation had a high fraction of sulfate, up to 62% of reconstructed mass. Additionally the catalyst reduced the toxicity measured in chemical and cellular assays suggesting a pathway for an inverse correlation between particle number and toxicity. The results have implications for exposure to and toxicity of diesel PM.

Emissions from four heavy-duty and medium-duty diesel vehicles were tested in six different aftertreatment configurations using a chassis dynamometer. The aftertreatment included four different diesel particle filters (DPF) and two prototype selective catalytic reduction (SCR) devices for NO(x) control. The goal of the project was to fully characterize emissions from various in-use vehicles meeting the 2007 particulate matter (PM) standard for the United States and California and to provide a snapshot of emissions from 2010 compliant vehicles. The aftertreatment devices all worked as designed, realizing significant reductions of PM and NO(x). The DPF realized > 95% PM reductions irrespective of cycle and the SCRs > 75% NO(x) reductions during cruise and transient modes, but no NO(x) reductions during idle. Because of the large test matrix of vehicles and aftertreatment devices, we were able to characterize effects on additional emission species (CO, organics, and nucleation mode particles) from these devices as a function of their individual characteristics. The two predicting parameters were found to be exhaust temperature and available catalytic surface in the aftertreatment, which combine to create varying degrees of oxidizing conditions. The aftertreatments were not found to incur a fuel penalty.

Emissions were measured from seven heavy-duty (HD) on-road vehicles that were operated along six common route types used for freight transport in California. All vehicles had engines that were certified to the 0.01 g/bhp-h particulate matter (PM) and either a 0.2, 0.3, or 2.3 g/bhp-h nitrogen oxide (NOx) standard. Diesel vehicles had low carbon monoxide (CO) and total hydrocarbon (THC) emissions below brake-specific standards, with route averages ranging from 0.24 to 3.35 g CO/ mi and from 0.02 to 0.45 g THC/mi. Diesel vehicles equipped with selective catalytic reduction (SCR) had route average NOx emissions ranging from 0.58 to 3.99 g/mi (0.16 to 0.96 g/bhp-h). NOx emissions were less route-dependent for the one vehicle with a 12-L compressed natural gas (CNG) engine and threeway catalyst (TWC), with route averages ranging from 0.16 to 0.46 g/mi (0.06 to 0.13 g/bhp-h). The ranking of certification NOx emissions for the seven engines reported during enginedynamometer-based certification was not maintained during real-world testing; for example, highway driving NOx emissions were lower than certification values for some engine families and higher than certification values for others. Route-average gravimetric particulate matter (PM) emissions ranged from 4 to 12 mg/ mi, which on a brake-specific basis were at least two times below the 0.01 g/bhp-h standard. Ion speciation of PM emissions indicated that the most prevalent species were sulfate (SO 4 2− ) for the model year (MY) 2007 diesel vehicle equipped with a diesel particulate filter (DPF) and no SCR, nitrate (NO 3 − ) for conventional diesel vehicles with a DPF and SCR, and sodium (Na + ) was the most abundant species for the CNG vehicle. NOx and PM emissions were compared to, and show generally good agreement with, the latest California mobile source model (EMFAC2014).

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