Selective Catalytic Reduction (SCR) of Nitrogen Oxide (NOx) emissions using ammonia or a 32.5%-urea solution has been used for many years in a variety of stationary applications. These applications include but are not limited to coal fired power plants, gas turbines, diesel locomotives, marine engines, as well as other stationary diesel and non-diesel engine applications.
Global emission limits for mobile heavy-duty diesel engines are becoming increasingly rigid. In response to this trend the diesel industry has begun testing and applying various emission control technologies to mobile applications. SCR is one such technology. Europe is the first major market to introduce SCR into the heavy-duty (class 8) as well as medium-duty (class 4-7) truck applications. The EURO4 standards (effective Oct. 2005/2006) and the EURO5 standard (effective 2008) favor SCR as the NOx reduction technology of choice in the European Union (EU).
The technology of choice in the United States (US) has yet to be decided. The 2004 model year marks the beginning of serious NOx reduction requirements with Exhaust Gas Recirculation (EGR) being the current primary choice throughout industry. The 2007 regulation raises the question of whether an after-treatment system is necessary to meet NOx and PM requirements. The 2010 regulation is clear. MicroProcessor controlled-catalytic systems will be necessary to meet the 0.2-g bhp/hr NOx regulation.
In the USA, heavy-duty engine and vehicle manufacturers have commenced development activities that are geared towards meeting US07 emission limits using SCR technology. SCR systems have been set-up for on-road testing and evaluation on heavy-duty trucks in the EU and USA [1, 2, 4].
The data presented in this paper demonstrates that SCR technology is capable of meeting the US 2007 emission ramp-in level by using a US engine without EGR. This engine has lower fuel consumption when compared with current engines meeting US 02 emission standards. Two system types are being presented. One type equipped with SCR only, and the second type with an SCR and Diesel Particulate Filter (DPF) combined. Ten of these low emission trucks have been on the road in the US since mid 2002 under customer operation conditions.