Johnson, T., "Vehicular Emissions in Review," SAE Int. J. Engines 5(2):216-234, 2012, doi:10.4271/2012-01-0368.
This review paper summarizes major developments in vehicular emissions regulations and technologies (light-duty, heavy-duty, gasoline, diesel) in 2011. First, the paper covers the key regulatory developments in the field, including proposed criteria pollutant tightening in California; and in Europe, the newly proposed PN (particle number) regulation for direct injection gasoline engines, test cycle development, and in-use testing discussions. The proposed US LD (light-duty) greenhouse gas (GHG) regulation for 2017-25 is reviewed, as well as the finalized, first-ever, US HD (heavy-duty) GHG rule for 2014-17. The paper then gives a brief, high-level overview of key emissions developments in LD and HD engine technology, covering both gasoline and diesel. Emissions challenges include lean NOx remediation for diesel and lean-burn gasoline to meet both the emerging NOx and GHG regulations. NOx control technologies are then summarized, including SCR (selective catalytic reduction) with ammonia, and hydrocarbon-based approaches. Nitrous oxide (N₂O) emissions are also addressed. These technologies are achieving ≻95% deNOx efficiency averaged over the certification test cycles. PM (particulate matter) reduction technologies are evolving around new DPF (diesel particulate filter) materials for reduced back pressure and SCR integration. Next, DOC (diesel oxidation catalyst) developments are summarized. They mainly involve NO oxidation to NO₂ as a function of catalyst formulation and hydrocarbon oxidation parameters. Finally, the paper discusses some key developments gasoline emission controls. Advanced three-way catalysts improve with zone coating technology, and with precious metal thrifting. Sulfur impacts are significant on the new formulations. Finally, the emerging technology of GPFs (gasoline particulate filters) is summarized.