Polystyrene (PS) that has been exposed to ultraviolet
light (UV)
undergoes partial dehydrogenation of the alkane polymer backbone which
increases its surface energy. Exploiting this photochemistry, we exposed
polystyrene films to UV light using a photomask to induce a patterned
photochemical reaction producing regions in the film with differing
surface energy. Upon heating the solid polymer film with the preprogrammed
surface energy pattern to a liquid state, the polymer flows from the
low surface energy unexposed regions to high surface energy exposed
regions. This flow creates three-dimensional topography by the Marangoni
Effect, which describes convective mass transfer due to surface energy
gradients. The topographical features can be permanently preserved
by quenching the film below its glass to liquid transition temperature.
Their shape and organization are only limited by the pattern on the
photomask.
More stringent emission requirements for nonroad diesel engines introduced with U.S. Tier 4 Final and Euro Stage IV and V regulations have spurred the development of exhaust aftertreatment technologies. In this study, several aftertreatment configurations consisting of diesel oxidation catalysts (DOC), diesel particulate filters (DPF), Cu zeolite-, and vanadium-based selective catalytic reduction (SCR) catalysts, and ammonia oxidation (AMOX) catalysts are evaluated using both Nonroad Transient (NRTC) and Steady (8-mode NRSC) Cycles in order to understand both component and system-level effects of diesel aftertreatment on emissions of polycyclic aromatic hydrocarbons (PAH) and their nitrated derivatives (nitro-PAH). Emissions are reported for four configurations including engine-out, DOC+CuZ-SCR+AMOX, V-SCR+AMOX, and DOC+DPF+CuZ-SCR+AMOX. Mechanisms responsible for the reduction, and, in some cases, the formation of PAH and nitro-PAH compounds are discussed in detail, and suggestions are provided to minimize the formation of nitro-PAH compounds through aftertreatment design optimizations. Potency equivalency factors (PEFs) developed by the California Environmental Protection Agency are then applied to determine the impact of aftertreatment on PAH-derived exhaust toxicity. Finally, a comprehensive set of exhaust emissions including criteria pollutants, NO2, total hydrocarbons (THC), n-alkanes, branched alkanes, saturated cycloalkanes, aromatics, aldehydes, hopanes and steranes, and metals is provided, and the overall efficacy of the aftertreatment configurations is described. This detailed summary of emissions from a current nonroad diesel engine equipped with advanced aftertreatment can be used to more accurately model the impact of anthropogenic emissions on the atmosphere.
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