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Upcoming directives for emission limits on heavy-duty diesel vehicles (HDDV) in the USA, the EU, and in Japan will set high standards in performance of emission control systems to reduce pollutants, especially of NOx and PM. This is true for conversion performance as well as durability of these systems. Homogeneous SCR catalyst has been on the road in Europe and the US for many years by now with good performance in emission conversion as well as in on-road durability [5, 6, 7]. This paper reports the results of mechanical durability testing of homogeneous SCR catalyst. The work has been part of the qualification for the upcoming implementation for EURO4 as well as US07 into the production phase. Much of durability data that has been published by now, does address specifically passenger car and light duty applications. Requirements, as spelled out by OEMs of the heavy-duty industry have been derived of different boundary conditions.

SCR technology has proven its ability to significantly reduce NOx emissions. Hence it has become an outstanding solution to be used to meet future emission limits in Europe, Japan and North America. To add even more confidence towards the introduction of SCR technology, the implementation of NOx sensors will become mandatory for on-board emission control systems. To demonstrate the usefulness of NOx sensors, a typical North American On-Highway Truck was chosen as a demonstration vehicle. It was equipped with vertically mounted, extruded SCR catalysts, a urea dosing system, and NOx-sensors. In order to achieve EURO 5 or even lower emission limits in NOx and PM, attempts were made to equip the system with oxidation catalysts upstream of the SCR catalyst as well as upstream of the turbine. Some changes had to be made to the model year 2000 engine calibration to reduce PM emissions to EURO 4 and 5 levels.

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).

Exhaust gas recirculation (EGR) has long been used in gasoline and light-duty diesel engines as a NOx reduction tool. Recently imposed emission regulations led several heavy-duty diesel engine manufacturers to adopt EGR as part of their strategy to reduce NOx. The effectiveness of this technology has been widely documented, with NOx reduction in the range of 40 to 50 percent having been recorded. An inevitable consequence of this strategy is an increase in particulate emission, especially if EGR was used in high engine load modes. Selective catalytic reduction (SCR), a method for NOx reduction, is widely used in stationary applications. There is growing interest and activity to apply it to mobile fleets equipped with heavy-duty diesel engines. Results of this work indicate that SCR has the potential to dramatically reduce NOx in diesel exhaust. Reductions greater than 70 percent were reported by several including the Institute's previous work (SAE Paper No. 1999-01-3564).

The diesel engine has long been the most energy efficient powerplant for transportation. Moreover, diesels emit extremely low levels of hydrocarbon and carbon monoxide that do not require post-combustion treatment to comply with current and projected standards. It is admittedly, however, difficult for diesel engines to simultaneously meet projected nitrogen oxides and particulate matter standards. Traditionally, measures aimed at reducing one of these two exhaust species have led to increasing the other. This physical characteristic, which is known as NOx/PM tradeoff, remains the subject of an intense research effort. Despite this challenge, there is significant evidence that heavy-duty highway engine manufacturers can achieve substantial emission reductions. Many development programs carried out over the last five years have yielded remarkable results in laboratory demonstrations.