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In recent years, catalyst systems such as a lean NOx trap (LNT) catalyst system and a urea selective catalytic reduction (SCR) system have been developed to obtain cleaner diesel emissions. At Nissan, we developed an emission control system for meeting Tier 2 Bin 5 requirements in 2003. On the basis of that technology, a new HC-NOx trap catalyst system has now been developed that complies with the SULEV standards without increasing the catalyst volume and precious metal loading. Compliance with the SULEV standards requires a further reduction of HC (NMHC) emissions by 84% and NOx by 60% compared with the emission performance Tier 2 Bin 5 compliant catalyst system. Consequently high conversion performance for both HCs and NOx is needed. An investigation of HC emission behavior under the FTP75 mode showed that a reduction of cold-phase HCs was critical for meeting the standard. Large quantities of HCs above C4 are emitted in the cold state.

To improve the fuel economy via high EGR, combustion stability is enhanced through the addition of hydrogen, with its high flame-speed in air-fuel mixture. So, in order to realize on-board hydrogen production we developed a fuel reformer which produces hydrogen rich gas. One of the main issues of the reformer engine is the effects of reformate gas components on combustion performance. To clarify the effect of reformate gas contents on combustion stability, chemical kinetic simulations and single-cylinder engine test, in which hydrogen, CO, methane and simulated gas were added to intake air, were executed. And it is confirmed that hydrogen additive rate is dominant on high EGR combustion. The other issue to realize the fuel reformer was the catalyst deterioration. Catalyst reforming and exposure test were carried out to understand the influence of actual exhaust gas on the catalyst performance.

Diesel exhaust contains a lower level of hydrocarbons, which serve as the reductant for the NOx catalyst, than gasoline engine exhaust. An investigation was made of several methods for maximizing the performance of NOx catalysts for direct-injection diesel engines. First, the catalysts were given an HC adsorption capability and then their characteristics were tailored to the HC species contained in diesel exhaust. This HC adsorption capability is designed to achieve better utilization of the HC species in diesel exhaust as a reductant. Second, catalyst performance was examined under passive and active conditions. Excellent catalyst performance was obtained under a passive condition, because at high engine loads, NOx catalysts with an HC adsorption capability can utilize HCs adsorbed under low engine load conditions to reduce NOx.

A fuel reformer system that uses a steam reforming reaction in the exhaust gas recirculation (EGR) line with a catalyst was earlier proposed.(1) An analysis of engine test results revealed that not only hydrogen (H2) but also a H2 rich reformate additive in the air-fuel mixture was effective in suppressing knocking. To improve fuel economy via a high compression ratio, the knock limit is extended through the addition of H2 with its high octane number. In order to produce H2 on-board, we have proposed a fuel reformer for which the additions to the engine are an injector and a catalyst in the existing cooled EGR system. This method produces thicker H2 gas from gasoline by using heat and water vapor in the exhaust gas. The reformate mainly consists of H2, CO and CH4.

On-board hydrogen generation technology using a fuel reforming catalyst is an effective way to improve the fuel efficiency of automotive internal combustion engines. The main issue to be addressed in developing such a catalyst is to suppress catalyst deterioration caused by carbon deposition on the catalyst surface due to sulfur adsorption. Enhancing the hydrocarbon and water activation capabilities of the catalyst is important in improving catalyst durability. It was found that the use of a rare earth element is effective in improving the water activation capability of the catalyst. Controlling the hydrocarbon activation capability of the catalyst for a good balance with water activation was also found to be effective in improving catalyst durability.