NOx adsorber aftertreatment system for internal combustion engines

Abstract

The present invention provides for an NOx adsorber aftertreatment system for internal combustion engines which utilizes a parallel arrangement of an adsorber catalyst and a bypass. The exhaust flow from the engine is routed through the adsorber during lean operation. At a predetermined regeneration time (for example, when the adsorber catalyst is 20% full), the exhaust gas flow is reduced through the parallel leg that contains the adsorber catalyst to be regenerated (e.g., 20% through the catalyst leg, 80% of the flow to the bypass leg). A quantity of hydrocarbon is injected into the reduced-flow catalyst leg in order to make the mixture rich. Since the flow has been reduced in this leg, only a small fraction of the amount of hydrocarbon that would have been required to make the mixture rich during full flow is required. This will result in a substantial reduction in the fuel penalty incurred for regeneration of the adsorber catalyst. Once the leg has been regenerated, the exhaust flow is switched to flow 100% through the adsorber leg.

Description

TECHNICAL FIELD OF THE INVENTION [0001] The present invention generally relates to internal combustion engines and, more particularly, to an NOx adsorber aftertreatment system for internal combustion engines. BACKGROUND OF THE INVENTION [0002] As environmental concerns have led to increasingly strict regulation of engine emissions by governmental agencies, reduction of nitrogen-oxygen compounds (NOx) in exhaust emissions from internal combustion engines has become increasingly important. Current indications are that this trend will continue. [0003] Future emission levels of diesel engines will have to be reduced in order to meet Environmental Protection Agency (EPA) regulated levels. In the past, the emission levels of U.S. diesel engines have been regulated according to the EPA using the Federal Test Procedure (FTP) cycle, with a subset of more restrictive emission standards for California via the California Air Resources Board (CARB). For example, the Tier II emission standards, w...

AI Technical Summary

Benefits of technology

[0011] In one embodiment, a catalytic soot filter is positioned upstream from the adsorber. The additional hydrocarbon used to promote regeneration is injected into the catalytic soot filter. The catalytic soot filter, when used in combination with the adsorber, provides more time and surface area for the hydrocarbon to react with the oxygen. The catalytic soot filter will additionally reformulate some of the diesel fuel into hydrogen and carbon monoxide, which have been shown to be better reductants than diesel fuel.

[0012] In another embodiment, a catalytic soot filter is positioned downstream from the adsorber. The heat generated by the regenerating adsorber is transferred downstream to the soot filter, thereby heating the soot filter above the temperature required for regeneration. Additionally, any hydrocarbon that slips through the adsorber is burned in the catalytic soot filter, further raising the temperature. Such burning of the hydrocarbon slip in the catalytic soot filter obviates the need for a diesel oxidation catalyst, thereby reducing system cost and package size.

Problems solved by technology

Additionally, any hydrocarbon that slips through the adsorber is burned in the catalytic soot filter, further raising the temperature.

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