JP3686666B1 - Engine exhaust purification system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purification device for an engine for improving exhaust purification efficiency and reducing exhaust resistance.
SOLUTION: A reduction catalyst 4 disposed in an exhaust system of an engine 1 for reducing and purifying nitrogen oxide in exhaust gas with a reducing agent; and an exhaust upstream side of the reduction catalyst 4 in an exhaust pipe 2 of the exhaust system An exhaust purification device for an engine comprising an injection nozzle 12 for supplying the reducing agent to the exhaust pipe 2, which is disposed across the exhaust pipe 2 on the exhaust upstream side of the injection nozzle 12 and has an exhaust pipe at the center. A partition plate 6 having fins 8 for generating a swirling flow with respect to the exhaust gas passing through the exhaust gas 2, and having an exhaust hole formed in a dotted shape in the peripheral region of the fins 8 for exhausting the exhaust gas; A pipe that includes the fin 8 inside and is joined to the partition plate 6 and has an exhaust introduction hole that introduces the exhaust gas flowing out from the exhaust hole of the partition plate 6 on the side surface in the vicinity of the fin 8. 2a.
[Selection] Figure 1

Description

  The present invention relates to an engine exhaust purification device that uses a reducing agent to reduce and remove nitrogen oxides (NOx) in exhaust gas. More specifically, the present invention relates to an exhaust purification device that generates a swirl flow in an exhaust passage by providing swirl flow generating means. At the same time, the exhaust gas flowing out from the exhaust hole around the swirling flow generating means is introduced into the vicinity of the swirling flow generating means, thereby improving the exhaust purification efficiency and reducing the exhaust resistance. Is.

In a conventional exhaust purification device, a NOx reduction catalyst is disposed in an exhaust passage of an engine, and a reducing agent such as an aqueous urea solution is injected from an injection nozzle provided on the exhaust upstream side of the NOx reduction catalyst. And NOx in the exhaust gas and the reducing agent are subjected to a catalytic reduction reaction with a NOx reduction catalyst to purify NOx into a harmless component (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2001-20724

  However, in such a conventional exhaust purification device, when the reducing agent is injected to the exhaust upstream side of the NOx reduction catalyst, there is a possibility that the mixing of the reducing agent and the exhaust becomes insufficient. If the mixing of the reducing agent and the exhaust gas is insufficient, the reducing agent flows in a biased manner to the NOx reduction catalyst, which may reduce the exhaust purification efficiency.

  SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an engine exhaust purification device that addresses such problems and improves exhaust purification efficiency and reduces exhaust resistance.

  In order to achieve the above object, an exhaust emission control device for an engine according to the present invention is provided in an exhaust system of the engine and reduces and purifies nitrogen oxides in exhaust gas with a reducing agent, and an exhaust passage of the exhaust system. An exhaust purification device for an engine having an injection nozzle for supplying the reducing agent to the exhaust upstream side of the reduction catalyst, the exhaust purification device being disposed across the exhaust passage on the exhaust upstream side of the injection nozzle. The central portion is provided with a swirling flow generating means for generating a swirling flow with respect to the exhaust gas passing through the exhaust passage, and is provided with an exhaust hole formed in a dotted area in the peripheral area of the swirling flow generating means and through which the exhaust flows out. Exhaust gas that forms part of the plate and the exhaust passage, is joined to the partition plate including the swirl flow generating means, and flows out from the exhaust hole of the partition plate on the side surface in the vicinity of the swirl flow generation unit Arrangement with exhaust introduction holes to introduce It is those with a door.

  With such a configuration, a swirl flow generating means is provided in the central portion of the partition plate arranged across the exhaust passage on the exhaust upstream side of the injection nozzle to generate a swirl flow with respect to the exhaust so that the swirl of the partition plate can be generated. A part of the exhaust is caused to flow out from the exhaust holes formed in the form of dots in the peripheral region of the flow generating means, and the exhausted exhaust gas is swirled from the exhaust introduction holes formed on the side surfaces of the pipes constituting a part of the exhaust passage. Introduced in the vicinity of the generating means, a reducing agent is supplied from the injection nozzle to the exhaust passage, and nitrogen oxides in the exhaust gas are reduced and purified by the reducing agent. Thus, the mixing of the reducing agent and the exhaust is promoted by the swirling flow, the exhaust purification efficiency is improved, and the exhaust resistance is reduced while maintaining the swirling flow.

  Further, the swirl flow generating means forms a plurality of cuts with a side extending radially with respect to the central portion of the partition plate, and bends the outer end portion at a predetermined angle toward the exhaust downstream side, It consists of a plurality of fins formed so as to generate a swirling flow. As a result, a plurality of cuts are formed with the lines extending radially with respect to the central portion of the partition plate, and the outer ends thereof are bent at a predetermined angle toward the exhaust downstream to form a plurality of fins. The swirl flow is generated in the exhaust by the plurality of fins.

  The exhaust introduction hole is formed so that the exhaust upstream side edge portion is located on the exhaust upstream side of the tip of the fin of the swirl flow generating means. As a result, the exhaust gas is introduced into the exhaust gas upstream of the tip of the fin of the swirl flow generating means through the exhaust gas introduction hole.

  According to the first aspect of the present invention, the swirl flow generating means is formed in the central portion of the partition plate arranged across the exhaust passage on the upstream side of the exhaust of the injection nozzle to generate the swirl flow in the exhaust, Exhaust and exhaust holes are provided in the form of scattered spots in the peripheral area of the swirl flow generating means of the plate, and exhaust introduction holes are formed on the side surfaces of the pipes constituting a part of the exhaust passage, and part of the exhaust is introduced into the exhaust holes and By introducing into the vicinity of the swirling flow generating means through the hole, the exhaust gas swirling flow promotes the mixing of the reducing agent injected and supplied from the injection nozzle with the exhaust to improve the exhaust purification efficiency, Can be prevented from concentrating on the swirling flow generating means, and the exhaust resistance can be reduced.

  Moreover, according to the invention which concerns on Claim 2, the notch which makes the dividing plate into a broken line the side extended radially with respect to the center part is made in the partition plate, and the outer end part is made a predetermined angle toward exhaust downstream. Since the plurality of fins are formed by bending, a swirling flow can be generated in the exhaust gas with a simple configuration.

  According to the third aspect of the present invention, the exhaust introduction hole is formed so that the exhaust upstream side edge portion is located on the exhaust upstream side of the tip of the fin of the swirling flow generating means. A swirling flow can be maintained. Therefore, the mixture of the reducing agent and the exhaust can be further promoted, and the exhaust purification efficiency can be further improved.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an engine exhaust gas purification apparatus according to the present invention. This exhaust purification device uses a reducing agent to reduce and remove nitrogen oxides (NOx) in the exhaust. Exhaust gas from the engine 1 using gasoline or light oil as fuel is discharged into the atmosphere via an exhaust pipe 2 serving as an exhaust passage. Specifically, the exhaust pipe 2 is provided with an oxidation catalyst 3 of nitric oxide (NO) and a NOx reduction catalyst 4 as a reduction catalyst 4 in order from the exhaust upstream side.

The oxidation catalyst 3 generates NO ₂ by oxidizing NO in the exhaust gas passing through the exhaust pipe 2 by an oxidation reaction. For example, a material excellent in heat resistance and corrosion resistance such as ceramic cordierite or stainless steel. A honeycomb type catalyst supporting a noble metal such as platinum on the surface of a porous member such as alumina is attached to a monolith type catalyst carrier having a cross section having a honeycomb shape. The oxidation catalyst 3 is housed in a substantially cylindrical case 5 having a larger diameter than the exhaust pipe 2, and the exhaust gas passing through the exhaust pipe 2 flows in contact with the catalyst in the catalyst shell. As a result, NO in the exhaust gas is oxidized (combusted) and converted to NO ₂ to improve the NOx removal rate in the downstream NOx reduction catalyst 4. Simultaneously with the oxidation reaction of NO, hydrocarbons (HC), carbon monoxide (CO), etc. in the exhaust gas are reduced by the oxidation reaction.

  Further, in the case 5, a circular partition plate 6 having an outer shape substantially equal to the inner diameter of the case is mounted across the case 5 on the exhaust downstream side, and a NOx reduction catalyst 4 described later is accommodated. A pipe 2a constituting a part of the exhaust pipe 2 connected to the case 7 is connected to communicate the spaces 5a and 7a in both cases 5 and 7, thereby securing an exhaust passage. As shown in FIG. 2, the partition plate 6 has a plurality of fins 8 as swirl flow generating means for generating a spiral swirl flow with respect to the exhaust gas around the axis of the pipe 2a at the center (FIG. 2). In FIG. 4, the exhaust holes 9 are formed in the form of dots in the peripheral region of the fins 8. As shown in FIG. 2, the fin 8 is provided with a substantially bowl-shaped cut 8b having a side line 8a extending in a direction orthogonal to the central portion of the partition plate 6 as shown in FIG. The outer end portion 8c is bent at a predetermined angle toward the exhaust downstream (indicated by an arrow A in the figure) to form a substantially propeller type, and a swirling flow is generated in the exhaust. The number and angle of the fins 8 are appropriately determined based on the specifications of the engine 1, the inner diameter of the pipe 2a, the inner diameter of the case 5, and the like.

  Further, as shown in FIG. 3, an exhaust introduction hole 10 is formed in the vicinity of the tip 8 d of the fin 8 on the side surface of the pipe 2 a so that the exhaust gas flowing out from the exhaust hole 9 of the partition plate 6 is exhausted from the exhaust introduction hole 10. It can be introduced into the vicinity of the tip 8d of the fin 8 in the pipe 2a. As shown in FIG. 4A, the exhaust introduction hole 10 is preferably formed such that the exhaust upstream side edge portion 10 a is located on the exhaust upstream side with respect to the tip 8 d of the fin 8.

  A NOx reduction catalyst 4 is housed in a case 7 connected to the case 5 of the oxidation catalyst 3 by a pipe 2a. This NOx reduction catalyst 4 is for reducing and purifying NOx in the exhaust gas passing through the exhaust pipe 2 with a reducing agent. For example, a honeycomb-shaped cross section made of ceramic cordierite or Fe-Cr-Al heat-resistant steel is used. A zeolite-type active component is supported on the monolith type catalyst carrier. The NOx reduction catalyst 4 is activated when the active component supported on the catalyst carrier is supplied with a reducing agent, and effectively purifies NOx in the exhaust gas into a harmless substance. The case 7 has a substantially cylindrical shape having a larger diameter than the exhaust pipe 2.

  Further, in the case 7, a circular fixing plate 11 having an outer shape substantially equal to the inner diameter of the case 7 is provided across the case 7 on the upstream side of the exhaust gas of the NOx reduction catalyst 4. A pipe 2a communicating with the case 5 is fixed to the opening. The end 2b of the pipe 2a is expanded in a bell mouth shape toward the exhaust downstream side (arrow A direction).

  An ammonia slip oxidation catalyst (not shown) is disposed downstream of the NOx reduction catalyst 4, so that ammonia that could not be treated by the NOx reduction catalyst 4 is oxidized and brominated and discharged. ing.

  Further, an injection nozzle 12 is disposed in the pipe 2a on the upstream side of the NOx reduction catalyst 4, and the reducing agent and the pressure air are piped from the reducing agent supply device (not shown) through the injection nozzle 12. 2a is injected and supplied. Here, the injection nozzle 12 has its tip portion extending toward the downstream side substantially parallel to the exhaust flow direction (arrow A direction), but protrudes substantially perpendicular to the exhaust flow direction in the pipe 2a. It is good as it is.

  The reducing agent, for example, urea aqueous solution (urea water) injected and supplied from the injection nozzle 12, is hydrolyzed by the exhaust heat in the pipe 2a and the water vapor in the exhaust, and easily generates ammonia. The obtained ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 4 to be purified into water and harmless gas. Note that the reducing agent used is not limited to urea water, and may be, for example, an aqueous ammonia solution.

Next, the operation of the engine exhaust gas purification apparatus configured as described above will be described.
Exhaust gas discharged by starting the engine 1 flows into the oxidation catalyst 3 through the exhaust pipe 2, and the oxidation catalyst 3 oxidizes NO in the exhaust gas by an oxidation reaction to become NO ₂ . The exhaust gas containing NO ₂ is swirled by the fins 8 of the partition plate 6 disposed in the case 5 and flows as a swirling flow in the direction of arrow A in the pipe 2a.

  At the same time, urea water is injected from the injection nozzle 12 into the pipe 2a in the direction of arrow A. The urea water injected from the injection nozzle 12 is hydrolyzed by exhaust heat and water vapor in the exhaust to produce ammonia. The ammonia and the exhaust gas flow into the NOx reduction catalyst 4 while being mixed. Then, in the NOx reduction catalyst 4, ammonia and NOx in the exhaust gas react with each other, whereby the NOx in the exhaust gas is purified into water and harmless gas.

  In this case, since urea water is injected and supplied to the swirling flow of the exhaust, mixing of the urea water and the exhaust is promoted. Thereby, the hydrolysis of urea water is promoted, and the ammonia generated from the exhaust gas and the urea water is mixed substantially uniformly. Further, since the end 2b of the pipe 2a has a bell mouth-like diameter, the swirling exhaust gas diffuses along the inner wall of the end 2b of the pipe 2a having a bell-mouth-like diameter, and the end 2b. From the exhaust gas upstream space 7a of the NOx reduction catalyst 4 in the case 7. As a result, the exhaust gas in which ammonia is substantially uniformly mixed flows into the NOx reduction catalyst 4 substantially uniformly, and the exhaust gas purification action in the NOx reduction catalyst 4 is further promoted.

  A part of the exhaust gas flowing out of the oxidation catalyst 3 flows into the space 5c surrounded by the partition plate 6 and the side surface 5b of the case 5 from the exhaust hole 9 formed in the partition plate 6 shown in FIG. Further, the air is introduced into the pipe 2a near the tip 8d of the fin 8 from the exhaust introduction hole 10 formed on the side surface of the pipe 2a. As a result, the exhaust does not concentrate on the fin 8 portion, and a part thereof is dispersed and flows out from the exhaust hole 9 and flows into the pipe 2a from the exhaust introduction hole 10, so that the exhaust resistance is reduced.

  In this case, as shown in FIG. 4 (a), the exhaust upstream side edge 10 a of the exhaust introduction hole 10 is formed so as to be located on the exhaust upstream side of the tip 8 d of the fin 8. The swirling flow of the generated exhaust is hardly disturbed by the exhaust introduced from the exhaust introduction hole 10. FIG. 5 (a) is an embodiment of FIG. 4 (a), in which the distance Δa between the tip 8d of the fin 8 and the exhaust upstream side edge portion 10a of the exhaust introduction hole 10 is −2.5 mm. . According to this, the swirling flow of the exhaust gas is maintained, and the urea water injected from the injection nozzle 12 diffuses widely and flows into the NOx reduction catalyst 4 substantially uniformly. On the other hand, as shown in FIG. 4B, when the exhaust upstream side edge portion 10a of the exhaust introduction hole 10 is formed so as to be located on the exhaust downstream side by Δb from the tip 8d of the fin 8, FIG. As shown in (b), the swirling flow of the exhaust is suppressed by the exhaust introduced from the exhaust introduction hole 10, and the diffusion of the urea water injected from the injection nozzle 12 is suppressed. Note that FIG. 5B is a reference example, and is obtained when Δb is +13.2 mm. In this way, if the edge 10a on the exhaust upstream side of the exhaust introduction hole 10 is positioned on the exhaust upstream side of the tip 8d of the fin 8, the swirl flow of the exhaust is maintained.

  Thus, according to the exhaust emission control device for an engine of the present invention, the fin 8 is formed in the central portion of the partition plate 6 disposed across the case 5 of the oxidation catalyst 3 to generate a swirling flow in the exhaust, Exhaust holes 9 are provided in the form of dots in the peripheral region of the fins 8 of the partition plate 6 and the exhaust introduction holes 10 are formed on the side surfaces of the pipe 2a joined to the partition plate 6 including the fins 8 therein. By introducing a part into the vicinity of the tip 8d of the fin 8 through the exhaust hole 9 and the exhaust introduction hole 10, the exhaust resistance can be reduced while maintaining the swirling flow of the exhaust generated by the fin 8. it can. Therefore, the mixing of urea water injected from the injection nozzle 12 and the exhaust can be promoted and the diffusion of the urea water can be promoted to flow into the NOx reduction catalyst 4 substantially uniformly, thereby improving the exhaust purification efficiency. Can do.

1 is a schematic configuration diagram showing an embodiment of an exhaust emission control device for an engine according to the present invention. It is a top view which shows the structural example of the partition plate applied to the said embodiment. It is sectional drawing which expands and shows the case part which accommodates the oxidation catalyst of the said embodiment. It is explanatory drawing which shows the positional relationship of the fin front end of the said embodiment, and the exhaust upstream edge part of an exhaust introduction hole. FIG. 5 is an explanatory diagram showing the relationship between the positional relationship of FIG. 4 and the diffusion state of urea water injected from the injection nozzle, where (a) is an example and (b) is a reference example.

Explanation of symbols

1 ... Engine 2 ... Exhaust pipe (exhaust passage)
2a ... Piping 4 ... NOx reduction catalyst (reduction catalyst)
6 ... Separator plate 8 ... Fin (swirl flow generating means)
8d ... tip 9 ... exhaust hole 10 ... exhaust introduction hole 10a ... exhaust upstream edge 12 ... injection nozzle

Claims (3)

A reduction catalyst that is disposed in the exhaust system of the engine and that reduces and purifies nitrogen oxides in the exhaust with a reducing agent, and an injection that supplies the reducing agent to the exhaust upstream side of the reduction catalyst in the exhaust passage of the exhaust system An exhaust emission control device for an engine comprising a nozzle,
The swirl flow generating means is disposed on the exhaust upstream side of the injection nozzle so as to cross the exhaust passage, and a swirl flow generating means for generating a swirl flow with respect to the exhaust passing through the exhaust passage is provided at the center, and the periphery of the swirl flow generating means A partition plate that is formed in a dotted pattern in the region and has exhaust holes for exhausting the exhaust,
A part of the exhaust passage is formed, the swirl flow generating means is included inside and joined to the partition plate, and the exhaust gas flowing out from the exhaust hole of the partition plate is introduced into a side surface in the vicinity of the swirl flow generating means. Piping with exhaust introduction holes;
An exhaust purification device for an engine characterized by comprising:   The swirling flow generating means makes a plurality of cuts with a side extending radially with respect to the central portion of the partition plate as a broken line, and bends an outer end portion thereof at a predetermined angle toward the exhaust downstream to exhaust the exhaust. 2. The exhaust emission control device for an engine according to claim 1, comprising a plurality of fins formed so as to generate a swirling flow.   3. The exhaust purification of an engine according to claim 2, wherein the exhaust introduction hole is formed so that an exhaust upstream side edge portion thereof is located on an exhaust upstream side of a tip end portion of a fin of the swirl flow generating means. apparatus.

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