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This paper presents a new substrate for Lean NOx Traps (LNT) which enables high NOx conversion efficiency, even after long-term aging, when using alkali metals as the NOx adsorber. When a conventional metal honeycomb is used as the LNT substrate, the chromium in the metal substrate migrates into the washcoat and reacts with the alkali metals after thermal aging. In order to help prevent this migration, we have developed a new substrate where a fine -alumina barrier is precipitated to the surface of the metal substrate. The new substrate is highly capable of preventing migration of chromium into the washcoat and greatly enhances the NOx conversion. The durability of the new substrate and emission test using a test vehicle are also examined.

Recently, Spark-Assisted HCCI has been developed to improve combustion robustness. On the other hand, there needs to be an aftertreatment system which can purify both stoichiometric and lean exhaust gas to meet stringent emission regulations. The difficulty of exhaust aftertreatment under lean conditions is not only NOx conversion but also HC conversion. This is because in addition to the lower exhaust gas temperature there is more paraffin in the HCCI gas. A new catalyst system which includes TWC at the close-coupled position and a lean catalyst at the underfloor position was developed. The underfloor lean catalyst has the ability of HC conversion (especially paraffin) and of NOx conversion. This concept for lean exhaust from Spark-Assisted HCCI can achieve high NOx and HC conversion efficiencies.