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Review of Diesel Emissions and Control
ISSN: 1946-3952, e-ISSN: 1946-3960
Published April 12, 2010 by SAE International in United States
Citation: Johnson, T., "Review of Diesel Emissions and Control," SAE Int. J. Fuels Lubr. 3(1):16-29, 2010, https://doi.org/10.4271/2010-01-0301.
This review summarizes the latest developments in diesel emissions regarding regulations, engines, NOx (nitrogen oxides) control, particulate matter (PM) reductions, and hydrocarbon (HC) and CO oxidation.
Regulations are advancing with proposals for PN (particle number) regulations that require diesel particulate filters (DPFs) for Euro VI in 2013-14, and SULEV (super ultra low emission vehicle) fleet average light-duty (LD) emissions likely to be proposed in California for ~2017. CO₂ regulations will also impact diesel engines and emissions, probably long into the future.
Engine technology is addressing these needs. Heavy-duty (HD) research engines show 90% lower NOx at the same PM or fuel consumption levels as a reference 2007 production engine. Work is starting on HD gasoline engines with promising results. In light duty (LD), engine downsizing is progressing and deNOx is emerging as a fuel savings strategy.
Much has recently been reported on optimized selective catalytic reduction (SCR) systems. The SCR catalyst can be placed before, after, or on the DPF. Work is progressing on non-urea ammonia systems, mixed zeolite catalysts, and on fundamental understanding on issues like ammonia storage, sulfur impacts, and reaction mechanisms. Developments on HC-based deNOx, like lean NOx traps (LNTs), result in a better understanding of durability, reduction in desulfation temperatures, and the use of LNT+SCR systems, wherein the LNT is calibrated to generate ammonia for use in a downstream SCR.
PM control is very effective. US2007 HD engines are very clean, with the DPF systems delivering PM, HC, and CO emissions at levels lower than 10% of the regulation. DPF regeneration advances are reported in strategy, modeling PM loading, and catalyst utilization. The effect of catalyst coatings on PN emissions, and behavior of captured ash is becoming better understood. NO₂-based regeneration of soot is very critical for proper functioning of partial filters. Biodiesel effects on DPF functions are becoming clearer.
Finally, diesel oxidation catalysts (DOCs) are being developed for use with premixed combustion engine strategies that function better at low temperatures, low oxygen levels, and at high HC+CO levels. The problem of platinum (Pt) migration to SCR catalysts from DOCs exposed to high temperatures for long times (850°C, 16 hours) is alleviated somewhat by using palladium (Pd) to replace some of the platinum.