Search Results

The US EPA emission standards for 2010 on-highway and 2014 non-road diesel engines are extremely stringent, both in terms of oxides of nitrogen (NOX) and particulate matter (PM). Diesel engines typically operate lean and use at least 40-50 percent more air than what is needed for stoichiometric combustion of the fuel. As a result, significant excess oxygen (O₂) is present in diesel exhaust gas which prevents the application of the mature three-way catalyst (TWC) technology for NOX control used in gasoline engines. The objective of this work was to investigate whether or not the catalyzed DPF had a TWC-type of effect on NOX emissions and if so, why and to what extent when used on a diesel engine operating at reduced A/F ratio conditions.

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).

To evaluate the performance of a variety of commercially available exhaust emission control technologies, the Manufacturers of Emission Controls Association (MECA) sponsored a test program at Southwest Research Institute (SwRI). The test engine was a current design heavy-duty diesel engine operated on standard No. 2 diesel (368 ppm) and lower sulfur (54 ppm) diesel fuel. Technologies evaluated included: diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs), selective catalytic reduction (SCR), fuel-borne catalysts (FBCs) in combination with filters and oxidation catalysts, and combinations of the above technologies. The program was structured to demonstrate that a variety of exhaust emission control technologies, including exhaust gas recirculation, could be used to substantially reduce emissions from a modern MY 1998 heavy-duty diesel engine.