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 NO
x 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 NO
x in diesel exhaust. Reductions greater than 70 percent were reported by several including the Institute's previous work (SAE Paper No.
1999-01-3564). Some limitations of this NO
x reduction method may include low exhaust temperatures into the catalyst such as those experienced in low engine load conditions, and potential ammonia slip resulting from high urea rates required for good NO
x conversion.
Diesel particulate filters (DPF), known for their ability in reducing PM, have previously suffered from regeneration, reliability, and durability problems. Now they are being included in plans for serial production. In their advanced development and planned production configurations, DPFs may use fuel-borne catalysts (FBC) to improve their overall performance.
Development and evaluation of these technologies performed at SwRI indicated that EGR was best suited for part load conditions, while SCR was better for high load conditions. This paper describes the application of EGR, SCR and DPF technology to a heavy-duty on-highway diesel engine. Regeneration as well as the overall performance of the DPF was further enhanced with a cerium-based fuel-borne catalyst.