Exhaust aftertreatment device

Abstract

An exhaust aftertreatment device for an internal combustion engine is disclosed which contains multiple, parallel channels of a porous material, such as cordierite or silicon carbide, in which about some of the channels are plugged at an upstream end and other channels remain unplugged. In one embodiment, the substrate has an SCR coating and the engine has a urea supply system. Other embodiments include using TWC and LNT formulations. Several washcoat configurations and other specific geometries and dimensions to encourage crossflow, diffusion, and adsorption are disclosed herein.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a device for treating exhaust gases from an internal combustion engine. In particular, the exhaust aftertreatment device contains parallel channels of a porous material with about half of the channels being plugged on the upstream end. The device is coated with a SCR (selective catalytic reduction) washcoat. BACKGROUND OF THE INVENTION [0002] Achieving low NOx (NO, nitric oxide, plus NO2, nitrogen dioxide) emissions from lean-burning engines, such as diesels is a challenge. To treat NOx emitted from diesel engines, SCRs and LNTs (lean NOx traps) have been developed. LNTs operate in a lean / rich cycle in which NOx is purged during lean operation and NOx is released and reacted in a shorter period of rich operation. A disadvantage of LNTs is that they significantly degrade diesel fuel economy. Although SCRs do not consume a large amount of extra fuel to react NOx, urea is supplied to the SCR to cause the NOx reaction. For v...

AI Technical Summary

Benefits of technology

[0006] In one embodiment, flow restrictors are placed in the open channels at the downstream end, i.e., the opposite end in which the plugs are placed. Preferably, the flow restrictors are placed in channels without plugs and not in channels with plugs, but flow restrictions could be placed in both the open or primary flow channels as well as the plugged or secondary flow channels to facilitate fabrication and avoid high cost.

[0008] A SCR according to the present invention provides superior control of NOx during transient operating conditions compared to prior art SCRs when equipped on a diesel vehicle (FIGS. 7 and 8). The NOx breakthrough during transients is reduced one-third to over three-fourths depending on the nature of the tip-in. By controlling transient emissions, overall diesel cycle NOx emissions are halved with the SCR of the present invention compared to the prior art.

[0009] Additionally, this concept improves steady state NOx efficiency by providing improved diffusion and subsequent kinetics by the effective storage mechanisms having a deeper penetration into and through the washcoat material applied to either or both sides of the porous substrate material. Washcoats and their placement in the channels can be varied to facilitate cross flow from the primary to the secondary channels. Traditional channel flow diffusion and kinetics with a shared packed bed or wall flow diffusion and kinetics are coupled in the present invention allowing more efficient systems at converting NOx.

Problems solved by technology

Achieving low NOx (NO, nitric oxide, plus NO2, nitrogen dioxide) emissions from lean-burning engines, such as diesels is a challenge.

A disadvantage of LNTs is that they significantly degrade diesel fuel economy.

However, during transient conditions, such as tip-ins (driver demand for a rapid increase in torque), a high concentration of NOx passes through the SCR unreacted.

SCRs have not achieved the extremely low NOx emission levels of gasoline engines with three-way catalysts, largely due to the large NOx breakthrough during transients.

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