Exhaust emission control device

Abstract

An exhaust emission control device includes a reducing agent adding valve for injecting a reducing agent into an exhaust pipe. The adding valve has a tip end portion having a nozzle and facing an internal space of the exhaust pipe. The tip end portion is disposed outwardly of an inner circumferential surface of the exhaust pipe. The adding valve is kept out of direct striking contact with the exhaust gas and hence is substantially free from thermal degradation and adhesion of deposits.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]The present application is based on and claims priority from Japanese Patent Application No. 2007-112153, filed Apr. 20, 2007, the content of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to an exhaust emission control device for purifying engine exhaust gas by reduction with a reducing agent.[0004]2. Description of the Related Art[0005]Exhaust emission control devices for purifying engine exhaust gas by way of reduction of nitrogen oxides (NOx) with a reducing agent are known heretofore. The reducing agent is urea water, for example, in which instance ammonia (NH3) generated from urea by decomposition reacts with NOx in the presence of a catalyst to produce harmless nitrogen (N2) and water (H2O), thereby purifying the NOx.[0006]One example of such known exhaust emission control devices is disclosed in Japanese Patent Laid-open Publication (JP-A) No. ...

AI Technical Summary

Benefits of technology

[0012]The collision scattering mechanism promotes atomization of the injected reducing agent, ensuring uniform and efficient scattering or dispersal of the reducing agent into the exhaust gas.

[0014]With this arrangement, the reducing agent adding valve, the collision scattering mechanism and a part of the entire exhaust pipe can be assembled into a single module. This will provide an increased degree of freedom in arranging the reducing agent adding valve and the collision scattering mechanism.

[0016]This arrangement ensures reliable collision of the injected reducing agent with the collision scattering mechanism and the resulting high scattering efficiency of the reducing agent.

[0018]With this conversion into the swirling flow, dispersion or scattering of the reducing agent into the exhaust gas can be achieved with improved efficiency.

Problems solved by technology

With this arrangement, however, since the tip end portion of the adding valve is subjected to high temperatures due to direct striking contact with the exhaust gas, there is a risk of the adding valve being thermal degraded or deposits adhering to the body of the adding valve.

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