Teruo Nakada

Emission reduction study for meeting new requirements with advanced diesel engine technology

Tier 2 Emission standards enacted by the U.S. Environmental Protection Agency (EPA) require substantial emission reductions for new vehicles, including those with diesel engines. The standards are fuel neutral, and all light duty vehicles must eventually meet a fleet averaged emission level of Bin 5. To improve the emission capability for diesel engines, several advanced technologies have been investigated. These technologies include: common rail FIE with multi-injection capability, enhanced cooled EGR system with increased flow capability, variable geometry turbo charger, and a lower compression ratio piston. A new combustion approach using premixed diesel combustion was applied in the low load area for improving NO x and soot emissions significantly in the FTP-75 test cycle. Applying these technologies, engine out NO x was substantially reduced while maintaining similar soot levels . An aftertreatment system with lean NO x trap (LNT) catalysts and a catalyzed soot filter was studied on a demonstration vehicle. The aftertreatment system was prepared for evaluation by thermal aging to useful vehicle life. A regeneration strategy for the LNT has been developed which provides NO x reduction efficiency, while minimizing the fuel penalty and HC slip to the tail pipe. A new combustion approach using premixed diesel combustion was also applied to the rich composition in order to reduce HC slip and soot emission. After aging with a simulated 120kmile aging cycle, this system showed greater than 90% reduction for PM and 60% reduction for NO x emission in the FTP-75 test cycle.

A New NOx Reduction Catalyst System for Diesel Engine with High Sulfur Tolerance

A new concept of highly efficient and sulfur tolerant NOx reduction catalyst for diesel engines has been demonstrated. This catalyst has a double-layer construction and is composed of Pt and Rh as the precious metals, oxygen storage materials and some other catalytic components. Periodic lean/rich operation similar to the Lean NOx Trap catalyst was found to improve the highly efficient NOx reduction activity in a laboratory reactor test. As a result, this catalyst has the feature of high NOx reduction in a temperature window from 150°C to 350°C, and of high oxidation activity even in a lower temperature condition for HC and CO. Sulfur poisoning characteristics were also evaluated in a laboratory reactor test. The results showed that the proper desulfation procedure with a relatively low temperature environment enabled the stored sulfur to be reomved, and to maintain the NOx reduction efficiency for asignificantly long time period. In an application of this catalyst to HSDI diesel engines for passenger vehicle, the results of NOx reduction efficiency were demonstrated to be over 80% in steady state conditions under the periodic rich combustion operation. The sulfur tolerance in an actual diesel engine exhaust gas was also evaluated under the condition of using 50ppm and 350ppm sulfur diesel fuel. When applying a suitable rich combustion of the diesel engine, even after poisoning with 350ppm sulfur fuel for a good while, it was possible to remove the stored sulfur and have no deterioration of NOx conversion efficiency.