JP2006037899A - Exhaust gas treating device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve particle matter cohesion performance of an exhaust gas treating device using corona discharge. <P>SOLUTION: In this exhaust gas treating device, by arranging two types of electrodes, a discharge electrode 2 and a dust collecting electrode 4, inside an exhaust pipe of the internal combustion engine and applying high voltage to a space between the electrodes 2, 4 to generate corona discharge, exhaust particles in the exhaust gas are charged and collected. Negative charges carried by the collected exhaust particles are recovered via a coil 5. Since an electric current is suppressed by the action of the coil 5, the exhaust particles in the side opposite to the dust collecting electrode 4 are positively charged. Due to Coulomb force by such charges, cohesion of exhaust particles which have not reached the dust collecting electrode 4 and are negatively charged is promoted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust treatment device that collects exhaust particulates contained in exhaust gas of an internal combustion engine using corona discharge.

The treatment of fine particles contained in the exhaust of an internal combustion engine has become a major issue, and a method for electrostatically collecting fine particles using corona discharge in an exhaust pipe has been studied. Patent Document 2 below discloses an apparatus in which a plurality of linear discharge electrodes extending in the axial direction of a cylinder are arranged in a cylinder into which a gas containing smoke and exhaust particulates flows. A high voltage is applied between the discharge electrode and the cylindrical wall surrounding the discharge electrode as a dust collection electrode. Adsorb. In this device, the gas flowing in the cylinder can come into contact with the inner surface of the cylinder by further attaching the gas inlet to the cylinder in the circumferential direction of the cylinder so that a swirl flow is formed in the cylinder. In addition to substantially extending the length, centrifugal force is applied to the exhaust particles to improve the collection property.
JP 2003-144799 A

  However, in the technique of Patent Document 1, even if the adsorptivity to the inner surface of the cylinder is improved, the agglomeration property of the exhaust particulates is not necessarily improved.

  Therefore, an object of the present invention is to provide an exhaust treatment device for an internal combustion engine that can improve the cohesiveness of exhaust particulates.

According to the first aspect of the present invention, two kinds of electrodes, that is, a discharge electrode and a dust collection electrode are disposed in an exhaust pipe of an internal combustion engine, and a high voltage is applied between the electrodes to generate a corona discharge to generate an exhaust gas. In an exhaust treatment device for an internal combustion engine that charges and collects exhaust particulates in the interior,
In the middle of the current path for collecting the electric charges charged in the collected exhaust particulates, a current suppressing means for suppressing the current flowing in the current path is provided.

  When the charged exhaust particulates reach the dust collection electrode, the exhaust particulates release electric charges to the dust collection electrodes, and the emitted charges are collected from the current path. Since the current is suppressed by the action of the current suppressing means, the charged state of the exhaust particulates reaching the dust collecting electrode lasts for a certain time. Here, since the charged charge has moved to the dust collecting electrode side of the exhaust particulate, the exhaust particulate has a charge opposite in polarity to the charged charge on the side opposite to the dust collecting electrode. The coulomb force due to this charge promotes the aggregation of exhaust particulates that have not yet reached the dust collection electrode and are charged by corona discharge.

  According to a second aspect of the present invention, in the configuration of the first aspect of the present invention, the current suppressing means is constituted by an inductor.

  Current can be efficiently suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 show an exhaust treatment device for a diesel engine. The exhaust pipe 1 connected to the exhaust manifold of the engine has an exhaust gas passage having a circular cross section inside, and a corona discharge electrode 2 as a discharge electrode and a conductive net 4 as a dust collecting electrode are disposed therein. Thus, exhaust particulates (hereinafter referred to as PM as appropriate) in the exhaust gas are collected. The corona discharge electrode 2 has an elongated overall shape, and is attached to the holding plate 3 that closes the opening 101 of the tube wall of the exhaust pipe 1 through the corona discharge electrode 2. A portion 21 of the corona discharge electrode 2 projecting into the exhaust pipe 1 is bent in an L shape at the position of the axis C of the exhaust pipe 1 so that the tip side portion is directed in the downstream direction of the exhaust flow. The tip side portion of the corona discharge electrode 2 is a discharge portion 211 to which a negative high voltage from a direct current high voltage power source (not shown) is supplied. The discharge part 211 is, for example, a star-shaped flat plate member having a plurality of protrusions with the plate thickness direction taken as the axial direction. The corona discharge electrode 2 is electrically insulated from the exhaust pipe 1 and grounded.

  The conductive net 4 is arranged downstream of the exhaust flow from the discharge part 211 of the corona discharge electrode 2. The conductive mesh 4 is formed by circularly forming a conductive plate-like member having a mesh through which exhaust gas can flow, and the size is slightly smaller than the inner diameter of the exhaust pipe 1 at the mounting position. The conductive mesh 4 and the exhaust pipe 1 are connected by a coil 5 which is a plurality of inductors (4 in the illustrated example) arranged at equal intervals along the outer periphery of the conductive mesh 4 in the circumferential direction of the conductive mesh 4. Made. The coil 5 is composed of a conductive wire, one end of which is welded to the peripheral portion of the conductive net 4, and the other end is welded to the exhaust pipe 1 and its inner peripheral surface. Thereby, the conductive net 4 is mechanically and electrically connected via the exhaust pipe 1 and the coil 5.

  The operation of the exhaust treatment apparatus having the above configuration will be described. In FIG. 3, when a negative DC high voltage (for example, −20 KV) is applied to the discharge electrode 2 from a DC high voltage power supply, a corona discharge is generated in the vicinity of the discharge unit 211 and electrons are emitted ((1 in the figure)). )). As a result, oxygen with high electron affinity is negatively ionized ((2) in the figure), and adheres to nearby PM and is negatively charged ((3) in the figure). PM moves by the Coulomb force and the exhaust flow ((4) in the figure) and is electrostatically collected by the conductive net 4 ((5) in the figure). The electrons having negatively charged PM are emitted to the conductive net 4 ((6) in the figure).

The emitted electrons move from the conductive net 4 and are collected by the grounding part via the coil 5. At this time, due to the generation of the counter electromotive force in the coil 5, the amount of electrons moving, that is, the current shows a characteristic of gradually increasing as shown in FIG. 4, and the current value is suppressed. This characteristic is expressed by equation (1), where I is current, V is the voltage between the conductive net and ground, R is the resistance of the coil 5, L is the inductance of the coil 5, and t is the elapsed time.
I = (V / R) × [1-exp (−Rt / L)] (1)

  That is, the electrons charged with PM are not temporarily recovered to the grounding portion when PM reaches the conductive net 4, but stay temporarily for a time corresponding to the inductance of the coil 5.

  Now, as shown in FIG. 5, when the PM reaches the conductive net 4 and the electrons move to the conductive net 4 side of the PM (that is, the exhaust stream downstream side), the side of the PM opposite to the conductive net 4 is Electrons that are positively charged but have moved to the conductive net 4 side of the PM stay on the conductive net 4 side due to the current suppressing action of the coil 5, so that the side opposite to the conductive net 4 (that is, the upstream side of the exhaust flow) ) To maintain the positively charged state of PM. As a result, a Coulomb force acts between the negatively charged PM that has not reached the conductive net 4, and the aggregation of the PM is promoted.

  FIG. 6 shows the relationship between the rising speed of the current and the time for which the conductive net 4 holds the collected PM (conductive net holding time). For example, the rising speed of the current is represented by the changing speed of the current I at t = 0 in the equation (1). As known from the equation (1), the rising speed of the current increases as the inductance of the coil 5 is reduced. If the current rising speed is too high, when PM reaches the conductive net 4, electrons are instantaneously emitted to the conductive net 4 and collected to the ground via the coil 5, so that the PM is once collected. However, the tendency to be easily flown by the exhaust flow appears, and the conductive net holding time is shortened. On the other hand, if the current rising speed is slow and the ground resistance is substantially too large, the Coulomb force from the conductive net 4 cannot be sufficiently obtained. For this reason, PM tends to be easily flown in the exhaust flow without being collected, and the conductive net holding time is shortened. Therefore, it is desirable to set the inductance of the coil 5 that defines the current rising speed to a value that can obtain a sufficiently large conductive net retention time in consideration of such conflicting tendencies.

  Further, the coil 5 is disposed in the exhaust pipe 1 together with the conductive net 4, but is not necessarily limited to this configuration. The fixing member that fixes the exhaust treatment device to the vehicle and serves as a grounding portion, and the exhaust pipe It may be interposed between the two. In this case, the conductive net is connected to the pipe wall of the exhaust pipe by welding or the like, or the conductive net is wired from the fixing net and the coil is connected in the middle.

  Further, a current suppressing means such as a resistor may be used instead of the coil.

1 is a schematic configuration diagram of an exhaust treatment device for an internal combustion engine according to the present invention. It is sectional drawing which follows the II-II line in FIG. It is a schematic diagram for demonstrating the action | operation of this invention. It is a graph for demonstrating the action | operation of this invention. It is another schematic diagram for demonstrating the action | operation of this invention. It is another graph for demonstrating the action | operation of this invention.

Explanation of symbols

1 Exhaust pipe 2 Corona discharge electrode (discharge electrode)
4 Conductive mesh (dust collection electrode)
5 Coils (inductors, current suppression means)

Claims (2)

Two types of electrodes, a discharge electrode and a dust collection electrode, are arranged in the exhaust pipe of an internal combustion engine, and a high voltage is applied between the electrodes to generate a corona discharge to charge and trap exhaust particulates in the exhaust gas. In an exhaust gas processing device for an internal combustion engine,
An exhaust treatment apparatus for an internal combustion engine, characterized in that a current suppressing means for suppressing a current flowing in the current path is provided in the middle of a current path for collecting electric charges charged in the collected exhaust particulates.   2. The exhaust gas processing apparatus for an internal combustion engine according to claim 1, wherein the current suppressing means is an inductor.

Images