Exhaust gas-purifying device

Abstract

Provided is a plasma assisted exhaust emission control device with less electric power consumption and with no harmful gas discharged into atmosphere. A filter body 7 is constituted by porous members through which exhaust gas 2 passes for capturing of particulates in the exhaust gas 2 and is provided with rod-like and cylindrical electrodes 9 and 10 so as to generate plasma in the filter body 7, thereby providing a plasma regenerative particulate filter 11. The particulate filter 11 is accommodated in a filter casing within an exhaust pipe 3. Oxidation catalysts 16 and are arranged respectively upstream and downstream of adjacent to the particular filter 11 in the filter casing 12 so as to obtain heat insulation effect to the particulate filter 11.

Description

TECHNICAL FIELD [0001] The present invention relates to an exhaust emission control device for removing particulates in exhaust gas from an internal combustion engine such as diesel engine. BACKGROUND ART [0002] Particulates or particulate matter discharged from a diesel engine is mainly constituted by carbonic soot and a soluble organic fraction (SOF) of high-boiling hydrocarbon and contains a trace of sulfate (misty sulfuric acid fraction). In order to suppress such kind of particulates from being discharged into atmosphere, it has been envisaged as shown in FIG. 1 that a particulate filter 4 is incorporated in an exhaust pipe 3 through which exhaust gas 2 from a diesel engine 1 flows. [0003] As detailedly shown in FIG. 2, the particulate filter 4 comprises a filter body 7 in the form of a porous honeycomb made of ceramics such as cordierite. The filter body 7 has passages 5 or grid-like compartments with inlets alternately plugged by plugs 8, the passages 5 with the unplugged inl...

AI Technical Summary

Benefits of technology

[0021] According to an exhaust emission control device of the invention, various meritorious effects can be obtained as follows.

[0022] (I) Even in a condition of operation with lower exhaust temperature such as light-load operation, the particulates captured by the filter body can be effectively burned off by the aid of plasma. Moreover, due to the heat insulation effect by the upstream and downstream oxidation catalysts, the filter body can be rapidly elevated in temperature into environment for ready burn-off of the particulates, so that the particulates can be burned off with a shorter electric discharge time than they could conventionally, whereby electric power consumption can be substantially reduced.

[0023] (II) The harmful gas such as highly concentrated CO or HC generated due to combustion of the particulate with relatively low temperature by the aid of plasma can be oxidized into harmless CO2 or H2O when it passes through the downstream oxidation catalyst and is discharged. Thus, the harmful gas is prevented from remaining in the exhaust gas finally discharged into the atmosphere.

[0024] (III) NO occupying majority of NOx in the exhaust gas can be converted into highly reactive NO2 when the exhaust gas passed through the upstream oxidation catalyst, which can substantially accelerate the oxidation reaction of the particulates under a condition of operation with relatively high exhaust temperature. This promotes spontaneous combustion of the particulates by no aid of plasma to obtain sufficient burn-off.

[0025] (IV) When the plasma regenerative particulate filter is divided into a plurality of smaller units which are arranged in parallel with each other in the filter casing, voltage for electric discharge being separately applied to the respective smaller units, even a power source with relatively small capacity will suffice. Regeneration of the filter through plasma can be also attained during stoppage of an engine for example in a vehicle with an idle stopper.

[0026] (V) When employed are porous members constituting the filter body and integrally carrying oxidation catalysts, the oxidation reaction of the particulates captured by the filter body can be accelerated by the oxidation catalysts,, so that the particulates can be further reliably burned off in a region of operation with lower exhaust temperature.

Problems solved by technology

However, when an operation or driving with temperature at or above a predetermined temperature requisite tends not to continue for a long time, for example, in a vehicle such as a shuttle-bus running mainly on congested city roads, there may be a fear that an accumulated particulate amount exceeds a treated amount, disadvantageously resulting in clogging of the particulate filter 4.

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