This review covers recent developments in regulations to limit diesel emissions, engine technology, and remediation of nitrogen oxides (NOx) and particulate matter (PM). The geographical focus of regulatory development is now the European Union (EU), where Euro V and Euro VI regulations
for light-duty engines have been finalised for implementation in 2009 and 2014, respectively. The regulations are much more loosely drawn than those for the U.S., but options exist for adapting European vehicles to the U.S. market. Europe is just beginning to address heavy-duty regulations
for 2013 and beyond. Engine technology is making very impressive progress, with clean combustion strategies in active development, mainly for U.S. light-duty application. Work with heavy-duty research engines is more focused on traditional approaches, and will provide numerous engine/aftertreatment
options for complying with the stringent U.S. 2010 regulations. NOx control is focusing on selective catalytic reduction (SCR) for diverse applications. Zeolite catalysts will be the mainstay of this technology for Japan and the U.S., and perhaps even for some Euro V-compliant applications.
The emphases are on low-temperature operation, secondary emissions and system optimisation. Lean NOx traps (LNTs) are effective up to about 60 to 70% deNOx efficiency, and are being considered for light-duty applications. There is growing interest in supplementing LNT performance with integrated
SCR, which utilises ammonia generated in the LNT during rich regenerations. Diesel particulate filter (DPF) technology is at a stage of optimisation and cost reduction. Very sophisticated management strategies are being utilised, which open up options for the use of new filter materials and
alternative system architectures. Issues with secondary emissions are emerging and are being addressed.
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