JPH10266830A - Reducing agent feeder for exhaust emission purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reducing agent feeder which can vaporize the reducing agent well with low electric power by preventing scattering of the reducing agent and improving the heat transfer efficiently. SOLUTION: The reducing agent feeder has a heating chamber A for accommodating a heating element 2 which heats and vaporizes a liquid reducing agent, and is provided with a leading-in pipe 11 to lead the reducing agent into the heating chamber A and a supply-pipe 12 to supply the vaporized reducing agent into an exhaust pipe. A heating surface 21 of the heating element 2 is covered with a porous protecting member 4 which consists of a metallic net, so that the liquid reducing agent gets into the inside to be vaporized, thereby scattering can be prevented. Moreover, the heating element 2 with the porous protecting member 4 are maintained in a heat insulating case 3, and the heat from the heating element 2 can be effectively transfered to the reducing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for supplying a reducing agent to a catalyst for purifying nitrogen oxides (NOx) contained in exhaust gas from an internal combustion engine.

[0002]

2. Description of the Related Art In a diesel engine or a lean burn gasoline engine, it has become a major problem to reduce NOx contained in exhaust gas. For this reason, a NOx catalyst is installed in the exhaust pipe, and N
Reduction and purification of Ox is performed. NOx
It is known that the NOx purification rate can be improved by supplying a hydrocarbon as a reducing agent upstream of the catalyst, inside the NOx catalyst, or both (see JP-A-7-208150).
No.).

As an example of the supply form of the reducing agent, a supply device having a built-in heating element is installed outside or inside the exhaust pipe, and the liquid reducing agent is heated and vaporized and supplied into the exhaust pipe. There is something. FIG. 4 shows an example of such a configuration. The reducing agent supply device has a case 1 provided in the vicinity of an exhaust pipe P, and the inside of the case 1 is a heating room A for the reducing agent. In the heating chamber A, a heating element 2 is laid on the entire bottom surface, and heats and vaporizes a liquid reducing agent introduced from an introduction pipe 11 connected to a left side wall in the drawing. The gaseous reducing agent is supplied into the exhaust pipe P from the supply pipe 12 connected to the right side wall, and is introduced into the NOx catalyst while being mixed with the exhaust gas flowing through the exhaust pipe P.

[0004]

However, in the reducing agent supply device having the above structure, the heating and vaporization of the reducing agent
There were the following problems. That is, when the liquid reducing agent (indicated by L in the figure) introduced into the heating chamber A comes into contact with the heating surface (upper surface) 21 of the heating element 2 heated to the boiling point or higher, the reducing agent is heated. The substance evaporates as soon as it comes in contact with.
However, at this time, only the reducing agent in the vicinity of the contact surface 21 is vaporized, that is, so-called film boiling occurs, and the vaporized reducing agent expands in volume, so that much of the reducing agent which is still liquid is scattered. If the scattered reducing agent (indicated by L1 in the drawing) adheres to the upper wall surface of the heating chamber A or the wall of the supply pipe 12, it is not vaporized because it is away from the heating surface 21 and is not supplied to the NOx catalyst. was there.

On the other hand, the apparatus described in Japanese Patent Application Laid-Open No. 7-208150 has a structure in which a particulate catalyst is disposed around a glow plug as a heating element, and the above-described reduction is performed by a catalyst surrounding the heating element. It has a structure that can reduce scattering of the agent. However, this structure has a low heat transfer coefficient because the contact between the heating element and the particulate catalyst is point contact, and also uses alumina having a low thermal conductivity as a catalyst, so that the heat of the heating element is low. Not easily transmitted to reducing agents.
For this reason, there is a problem that a large amount of electric power is required to vaporize the reducing agent, and a device that can efficiently vaporize the reducing agent at a lower cost is desired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reducing agent supply device capable of preventing scattering of a reducing agent, improving heat transfer efficiency, and satisfactorily vaporizing the reducing agent with low power. I do.

[0007]

According to a first aspect of the present invention, there is provided an exhaust gas purifying catalyst having a reducing agent supply device provided in an exhaust gas flow passage for reducing and purifying nitrogen oxides in the exhaust gas. A device for supplying a gaseous reducing agent, which heats the liquid reducing agent, a heating chamber in which a heating element that vaporizes is accommodated, and an introduction path for introducing the liquid reducing agent into the heating chamber, A supply path for supplying the vaporized reducing agent to the exhaust gas flow path. Then, at least the surface of the heating element that becomes a heating surface for heating and vaporizing the reducing agent is covered with a porous protective member made of metal, and the heat generating element is heat-insulated with a material having low thermal conductivity together with the porous protective member. It is characterized in that it is held in a member.

The problem with the conventional reducing agent supply apparatus shown in FIG. 4 is that the liquid reducing agent comes into contact with a smooth heating surface having a temperature higher than its boiling point to cause film boiling, and that the heating surface has a problem. This is due to the low thermal conductivity from the to the reducing agent. In the present invention,
Since the surface serving as the heat generating surface of the heating element is covered with the porous protective member, the reducing agent is heated and vaporized in the porous protective member, and can be prevented from scattering to the outside. In addition, since the porous protective member is made of a metal material having good thermal conductivity, and furthermore, these heating elements and the porous protective members are held in a heat insulating member, heat from the heating elements can be efficiently reduced. Can be transmitted. Therefore, the reducing agent introduced into the heating chamber is
Without being scattered, it can be effectively vaporized with low power and supplied to the exhaust purification catalyst.

Specifically, the heating element has a rectangular cross section, and its upper surface and side surfaces are covered with the porous protection member. The heating element and the porous protection member are provided in a rectangular groove provided on the upper surface of the heat insulating member. It can be configured to be fitted and fixed inside (claim 2).

In the above configuration, the reducing agent enters the inside of the porous protective member exposed from the heating chamber through the upper surface, and is heated and vaporized. Since the surface of the porous protective member except the upper surface is covered with the heat insulating member, the heat of the heating element can be efficiently transmitted to the reducing agent.

Alternatively, the heating element is formed in a circular cross section and its peripheral surface is covered with the porous protection member, and the heating element and the porous protection member are provided on the upper surface of the heat insulating member.
It may be configured to be fitted and fixed in a U-shaped groove (claim 3).

Preferably, the introduction path is opened into the heating chamber above the heating element. Thus, the liquid reducing agent introduced into the heating chamber can be promptly guided to the upper portion of the heating element.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1A shows the overall configuration of the reducing agent supply device. The reducing agent supply device has a sealed case 1 made of a material having high heat resistance such as stainless steel, and has a heating chamber A formed therein. In the heating chamber A, a case 1
An introduction pipe 11 serving as an introduction path for the reducing agent extends through the left side wall of the case 1 and opens near the center of the case 1. On the other hand, a supply pipe 12 serving as a supply path for a reducing agent, which communicates with an exhaust pipe (not shown), which is a flow path for exhaust gas, is provided on the upper right side wall of the case 1.
Is connected. These introduction pipe 11 and supply pipe 12
Is fixed to the case 1 by means such as welding or press fitting.

A heat-insulating case 3 as a heat-insulating member for accommodating a heating element is provided below the introduction pipe 11 so as to bridge between left and right side walls of the case 1. One end of the introduction pipe 11 is connected to a storage section of a reducing agent (not shown) so as to introduce a liquid reducing agent such as light oil onto a heating element held in a heat insulating case 3 as a heat insulating member. .

FIG. 1B shows the details of the heat insulating case 3.
It is shown in (c). As shown in the figure, the heat insulating case 3 is a rectangular parallelepiped,
The upper surface has a groove 31 extending at a constant depth. In the groove 31, a flat heating element 2 is disposed with the porous protective member 4 covering the top and side surfaces. The heating element 2 is formed, for example, by printing a thin film of platinum on an alumina substrate to form a resistor. The heating element 2 generates heat by connecting a lead wire 22 to the thin film and applying a voltage.

The porous protection member 4 is made of a metal net made of a highly heat-resistant metal material such as stainless steel and having a mesh of 10 or more in a U-shaped cross section.
The upper surface and the side surface of the heating element 2, that is, the surface serving as the heating surface 21 for heating and vaporizing the reducing agent are covered. The heat insulating case 3 is made of a material having high heat resistance and low thermal conductivity, such as alumina, to prevent the heat of the heating element 2 from dissipating to the surroundings, and to efficiently heat the reducing agent.

The effect of the above configuration will be described with reference to the schematic diagram of FIG. When the liquid reducing agent L is introduced into the heating chamber A from the introduction path 11, the liquid reducing agent L comes into contact with the porous protection member 4 that covers the heating surface 21 of the heating element 2 and enters the inside. At this time, the metal net constituting the porous protection member 4 is heated by the heating element 2 to a temperature higher than the boiling point of the reducing agent. However, the reducing agent enters the space inside the metal net and is heated therein. ,
The conventional film boiling does not occur. That is, also in the above configuration, film boiling occurs microscopically on the contact surface between the fine wire surface of the metal constituting the metal net and the entered reducing agent, but the reducing agent remains inside the porous protective member 4. Since the liquid is trapped in the space, the amount of the liquid scattered to the outside is extremely small.

Accordingly, macroscopically, the gaseous reducing agent G vaporized inside the porous protective member 4 sequentially moves upward and passes through the reducing agent supply passage 12 to the NOx catalyst in the exhaust pipe P. Will be supplied. At this time, since the porous protection member 4 is made of a metal material having high thermal conductivity, the heat of the heating element 4 can be efficiently transmitted to the reducing agent. In addition, since the heating element 2 and the porous protective member 4 are held in the heat insulating case 3, it is possible to prevent the heat not involved in the heating and vaporization of the reducing agent from escaping to the outside, and to efficiently vaporize the reducing agent with lower power. can do.

FIGS. 3 (a) and 3 (b) show another embodiment of the present invention. In this embodiment, the case 1 has a cylindrical shape, and a liquid reducing agent is introduced into an upper portion thereof. Tube 11,
The supply pipe 12 for the vaporized reducing agent is connected. Case 1
The inside is a heating chamber A, and a heat insulating case 3 as a heat insulating member formed in a substantially U shape is disposed along the inner peripheral surface of the lower half portion. In the U-shaped groove 31 of the heat-insulating case 3, there is provided a columnar heating element 2 whose entire outer peripheral surface is covered with a porous protective member 4 made of a metal net. Uses a glow plug. Other configurations are the same as those of the embodiment shown in FIG.

According to the above configuration, the same effect of effectively heating and evaporating the reducing agent with low power can be obtained by preventing the liquid reducing agent from scattering and using the heat of the heating element efficiently. Can be

[Brief description of the drawings]

FIG. 1A is an overall sectional view of a reducing agent supply device according to an embodiment of the present invention, FIG. 1B is a perspective view of a heat insulating case,
(C) is a sectional view of the heat insulating case.

FIG. 2 is a diagram for explaining the operation and effect of the device of the present invention;
FIG. 3 is an overall schematic enlarged sectional view of a reducing agent supply device.

FIG. 3A is an overall sectional view of a reducing agent supply device according to another embodiment of the present invention, and FIG. 3B is a sectional view of a heat insulating case.

FIG. 4 is an overall schematic sectional view of a conventional reducing agent supply device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sealed case 11 introduction pipe (introduction path) 12 supply pipe (supply path) 2 heating element 21 heating surface 3 heat insulation case (heat insulation member) 4 porous protection member P exhaust pipe (flow path of exhaust gas)

Continued on the front page (72) Inventor Naohisa Oyama 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Prefecture Inside the Japan Auto Parts Research Institute, Inc. (72) Inventor Kazuya Kibe 1-Toyota-cho, Toyota-shi, Aichi Prefecture (72) Inventor Shinya Hirota 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (4)

[Claims] 1. A reducing agent supply device for supplying a gaseous reducing agent to an exhaust gas purification catalyst provided in an exhaust gas flow passage for reducing and purifying nitrogen oxides in the exhaust gas, the device comprising a liquid reducing agent. A heating chamber for accommodating a heating element that heats and vaporizes the gas; an introduction path for introducing a liquid reducing agent into the heating chamber; and a supply path for supplying the vaporized reducing agent to the exhaust gas passage. And heating the heating element, at least heating the reducing agent, covering the surface serving as a heat generating surface for vaporization with a porous protective member made of metal, and the heat generating element is made of a material having low thermal conductivity together with the porous protective member. A reducing agent supply device for an exhaust purification catalyst, wherein the reducing agent supply device is held in a heat insulating member. 2. The heating element has a rectangular cross section, and its upper surface and side surfaces are covered with the porous protection member. The heating element and the porous protection member are fitted into a rectangular groove provided on the upper surface of the heat insulating member. 2. The reducing agent supply device for an exhaust purification catalyst according to claim 1, which is fixedly attached. 3. The heating element has a circular cross section and its peripheral surface is covered with the porous protection member. The heating element and the porous protection member are formed in a U-shaped groove provided on the upper surface of the heat insulating member. 2. The reducing agent supply device for an exhaust purification catalyst according to claim 1, wherein the reducing agent supply device is fitted and fixed to the exhaust gas purifying catalyst. 4. The reducing agent supply device for an exhaust purification catalyst according to claim 1, wherein the introduction path is opened in the heating chamber above the heating element.