关键词：大气；废气排放；废气转化处理；大气污染
摘 要：The 2010 EPA emissions regulation for NOx is 0.2 g/bhr-hr, and the EPA has started to certify vehicles that can actually meet this regulation. Most manufacturers had initially opted instead to meet a Family Emission Limit (FEL) around 1.2-1.5 g/bhp-hr NOx with most of their vehicle emissions lying between the two standards. Currently the EPA has certified engines with both the Exhaust Gas Recirculation (EGR) and Selective Catalytic Reduction (SCR) technologies to meet the strict 0.2 g/bhr-hr NOx standard. While there is only one EGR system that has been certified by the EPA as meeting 2010 emissions regulations (Navistar, Inc.), there are several SCR systems that can meet this requirement (Cummins, Detroit Diesel, Volvo etc.). Moreover the SCR system in addition to meeting emissions regulations can result in a 3 to 5.5% increase in fuel efficiency. The SCR system typically uses a zeolite NOx adsorption catalyst that can selectively adsorb NOx molecules during lean burn operation and convert it to N2 and H2O with the injection of an urea water solution called Diesel Exhaust Fluid (DEF). It is the technology of choice for emissions control in Europe and several manufacturers have adopted this for the United States. SCR systems require tuning to work properly and systems can be tuned with either preexisting engine performance curves or with NOx/NH3 sensors. The use of NOx/NH3 sensors can provide closed loop control of the SCR system that can optimize the system for improved NOx reduction efficiencies and low NH3 slip. According to a recent review Reliable and accurate NOx sensors will be the key to the management of adsorption catalysts. The optimized use of SCR systems can increase the value for the customer with fuel and DEF savings (including reduced frequency and costs of the dealer servicing of the emissions system consumables) over the life of the vehicle helping defray the added cost of the system.