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The in-line hydrocarbon (HC) adsorber is a passive after-treatment technology to address cold-start hydrocarbons in automotive engine exhaust gas. A major technical challenge of the in-line HC adsorber is the difference between the HC release temperature of the adsorber and the light-off temperature of the burn-off (BO) Catalyst. We call this phenomenon the “reversed-temperature difference”. To reduce the reversed temperature difference, NGK has proposed a new “In-line HC Adsorber System” which consists of light-off (LO) Catalyst + Barrel Zeolite Adsorber (BZA), with a hole through the center, BO Catalyst and secondary air injection management (SAE 970266). This, our latest paper, describes the evaluation of various adsorbents and the effect of the center hole on the Adsorber BZA. The adsorber system, which had the Adsorber BZA with a 25mm ϕ center hole and adsorbent coated, confirmed 30% lower FTP NMHC emission versus a system with no center hole or adsorbent coating.

In order to meet the strict automobile emission regulations in the U.S.A. and Europe, new aftertreatment technologies such as the EHC and HC Adsorber have been developed to reduce the cold start emissions. The EHC is obviously effective in reducing emissions, but has the demerits of a large electric power demand and a complicated power control system to support it (13). A by-pass type HC adsorber system has the concerns of unreliable by-pass valves and complicated plumbing (10). A major technical challenge of the in-line type HC adsorber was the difference between the HC desorption temperature and the light-off temperature of the burn-off catalyst. This paper describes the evaluation results of a completely passive “In-line HC Adsorber System” which can reduce the cold start emissions without the application of any type of mechanical or pneumatic control valve in the exhaust system.

Thermal shock failures have been considered as one of the most significant issues for wall flow type ceramic diesel particulate filters during their regeneration. This paper describes the experiments which were conducted in order to study effects of heating rates of the accumulated diesel particulate on the thermal shock failure of the filters using an NGK soot generator. The results showed favorable heating rates of the particulate in terms of the amounts of the accumulated particulate up to which the filters are safely regenerated.

In applying ceramic honeycomb wall flow type filters to the after-treatment systems of diesel particulate from engines, the melting and thermal shock failures of ceramic diesel particulate filters (DPF) have been considered as one of the most significant issues during regeneration. This paper gives the results of experiments on the effects of cell structure i.e., wall thickness and cell density, on the melting and thermal shock regeneration failure of DPF and proposes an optimized cell structure for DPF in terms of the regeneration failure and the pressure drop which is also considered to be one of the especially important issues in fuel economy for heavy duty vehicle application.

The in-line hydrocarbon(HC) adsorber is one type of passive after-treatment technology which can reduce the cold start hydrocarbon from automobile engine exhaust gas. However, major technical issues to be resolved for practical use of this system are 1)the temperature difference between HC desorption from the adsorbent and activation of the catalyst to burn-off the desorbed HCs and 2)the ability to adsorb a wide range of HC molecule sizes in the cold exhaust gas. Recent zeolite development has resulted in an unique adsorbent capable of adsorbing small HC molecules as well as large to some degree, even under aqueous conditions. This adsorbent also features a relatively high HC desorption temperature. As a result, an In-line HC adsorber system has been developed, which can trap more unburned HCs during the engine cold start phase and burn-off the desorbed HCs more efficiently in the desorption phase by using this unique adsorbent.