JP3892452B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an engine exhaust purification device (hereinafter referred to as “exhaust purification device”) that uses a reducing agent to reduce and remove nitrogen oxides (NOx) in exhaust gas, and more particularly to a technique for improving exhaust purification efficiency. .

As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device disclosed in Japanese Patent Laid-Open No. 2001-20724 (Patent Document 1) has been proposed.
Such an exhaust purification device mixes exhaust gas and a reducing agent by disposing a NOx reduction catalyst in the exhaust passage of the engine and injecting a reducing agent such as an aqueous urea solution from an injection nozzle provided upstream of the exhaust of the NOx reduction catalyst. Let Then, NOx in the exhaust gas and a reducing agent are subjected to a catalytic reduction reaction by a NOx reduction catalyst to purify NOx into a harmless component.
Japanese Patent Laid-Open No. 2001-20724

However, in such an exhaust purification device, when the reducing agent is injected upstream of the NOx reduction catalyst, the mixing of the reducing agent and the exhaust may be insufficient. If the mixing of the reducing agent and the exhaust gas is insufficient as described above, the reducing agent is biased to flow into the NOx reduction catalyst, which may reduce the exhaust purification efficiency.
Accordingly, in view of the above-described conventional problems, the present invention provides a fin that generates a swirl flow that spirally swirls around the axis of the exhaust passage in the exhaust upstream of the injection position of the reducing agent in the injection nozzle. It is an object to improve the exhaust gas purification efficiency in the NOx reduction catalyst by mixing the reducing agent injected from the injection nozzle and the exhaust gas substantially uniformly.

For this reason, the invention according to claim 1 is arranged in a case formed in a diameter larger than the exhaust passage of the engine, with a predetermined interval from the exhaust upstream side end portion , and by the reducing agent, nitrogen oxidation in the exhaust is performed. A reduction catalyst for reducing and purifying substances, an injection nozzle for injecting and supplying a reducing agent into an exhaust passage located upstream of the exhaust of the case, and an exhaust upstream of the injection position of the reducing agent in the injection nozzle. And a swirl flow generating means for generating a swirl flow that spirally swirls around the axis of the exhaust passage, wherein the injection nozzle generates the swirl flow The reducing agent is injected and supplied to the exhaust in which the swirling flow is generated by the means, and the exhaust passage located upstream of the exhaust of the case is expanding in a bell mouth shape toward the exhaust downstream. K And wherein the projecting within.

According to a second aspect of the present invention, the swirling flow generating means extends at a predetermined angle with respect to a flow direction of the exhaust gas on an outer peripheral surface of the injection nozzle extending substantially on the axial center of the exhaust passage toward the exhaust downstream side. A plurality of thin plate-like fins.
The invention according to claim 3 is characterized in that the swirling flow generating means is further provided on an inner peripheral surface of the exhaust passage.

According to a fourth aspect of the present invention, the exhaust passage can be divided upstream of the injection nozzle, and the swirl flow generating means is a gasket interposed between flanges that connect the divided portions of the exhaust passage. A thin plate-like fin is formed by causing a slit to be formed and extending at a predetermined angle with respect to the flow direction of the exhaust gas.

  According to the first aspect of the present invention, the swirl flow that spirally swirls around the axial center of the exhaust passage is generated in the engine exhaust by the swirl flow generating means. And since the reducing agent is injected and supplied from the injection nozzle to the exhaust gas in which the swirling flow is generated, mixing of the reducing agent and the exhaust gas is promoted. Thereby, since the exhaust gas in which the reducing agent is mixed substantially uniformly flows into the reduction catalyst, the purification efficiency of the exhaust gas in the reduction catalyst can be improved.

Further, since the swirl flow generating means is provided upstream of the exhaust position of the reducing agent in the injection nozzle, the reducing agent injected and supplied from the injection nozzle does not adhere to the swirl flow generating means. Thereby, the component of the reducing agent does not deposit on the swirling flow generating means .

At this time, the exhaust in which the swirling flow is generated flows into the case having a diameter larger than that of the exhaust passage while diffusing along the inner peripheral surface of the exhaust passage whose diameter is expanded in a bell mouth shape. As a result, the exhaust gas diffuses rapidly and flows into the reduction catalyst substantially uniformly, so that the exhaust gas purification efficiency in the reduction catalyst can be improved.

According to the invention described in any one of claims 2 to 4 , the swirling flow generating means can be easily formed. In particular, according to the fourth aspect of the present invention, it is possible to easily generate a swirling flow in the exhaust gas simply by changing the gasket.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a configuration diagram of an exhaust emission control device according to the present invention.
An exhaust pipe 2 that is an exhaust passage of the engine 1 is provided with an oxidation catalyst 3 that oxidizes nitrogen monoxide in the exhaust to nitrogen dioxide and a NOx reduction catalyst 4 that reduces and purifies NOx in order from the exhaust upstream. It is installed. An injection nozzle 5 is provided in the exhaust pipe 2a between the oxidation catalyst 3 and the NOx reduction catalyst 4 to inject and supply an aqueous urea solution as a reducing agent into the exhaust pipe 2a. A urea aqueous solution is supplied to the injection nozzle 5 according to the engine operating state. In this embodiment, an aqueous urea solution is used as the reducing agent, but an aqueous ammonia solution, light oil mainly containing hydrocarbons, or the like may be used.

  The NOx reduction catalyst 4 includes a catalyst carrier 7 carrying, for example, a zeolite-based active component in a substantially cylindrical case 6 formed larger in diameter than the exhaust pipe 2a. The catalyst carrier 7 is disposed with a first predetermined distance L1 from the exhaust upstream end 6a of the case 6. Accordingly, a space 8 is formed inside the case 6 on the exhaust upstream side of the catalyst carrier 7. An exhaust pipe 2a having an open end 2b serving as an exhaust inflow portion is inserted into the approximate center of the exhaust upstream end 6a of the case 6. The exhaust pipe 2 a is disposed so that the end 2 b is separated from the catalyst carrier 7 by the second predetermined distance L 2, and the vicinity of the end 2 b is fixed to the case 6 by the fixing plate 9. Further, the inner peripheral surface of the end portion 2b expands in a bell mouth shape toward the exhaust downstream side in the space 8. The second predetermined interval L2 is appropriately determined based on the specifications of the engine 1, the inner diameter of the exhaust pipe 2a, the inner diameter of the case 6, and the like. The first predetermined interval L1 may be slightly wider than the second predetermined interval L2 so that the end 2b formed in a bell mouth shape is disposed in the case 6.

  The exhaust pipe 2a is provided with a plate 10 on the exhaust upstream side of the injection nozzle 5 for generating a swirl flow spirally swirling around the axis of the exhaust pipe 2a. As shown in FIG. 2, the plate 10 has fins as swirl flow generating means extending at a predetermined angle with respect to the flow direction of the exhaust gas by causing a cut in a thin plate having substantially the same shape as the cross section of the exhaust pipe 2a. A plurality of 11 are formed. The number and angle of the fins 11 are appropriately determined based on the specifications of the engine 1, the inner diameter of the exhaust pipe 2a, the inner diameter of the case 6, and the like.

  According to the above configuration, the exhaust of the engine 1 passes through the fins 11 and generates a swirl flow that spirally swirls around the axis of the exhaust pipe 2a. Then, a urea aqueous solution in an amount corresponding to the operating state of the engine 1 is injected and supplied from the injection nozzle 5 to the exhaust gas in which the swirl flow is generated. The urea aqueous solution injected from the injection nozzle 5 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.

At this time, the exhaust gas of the engine 1 passes through the oxidation catalyst 3, so that nitrogen monoxide in the exhaust gas is oxidized into nitrogen dioxide. As a result, the ratio of nitrogen monoxide in the exhaust gas decreases, and the ratio of nitrogen monoxide and nitrogen dioxide in the exhaust gas approaches the optimum ratio for purification in the NOx reduction catalyst 4, so that the NOx reduction catalyst 4 The exhaust gas purification efficiency is improved.
Further, since the swirl flow is generated in the exhaust gas by the plate 10 and the urea aqueous solution is injected and supplied to the exhaust gas in which the swirl flow is generated, mixing of the urea aqueous solution and the exhaust gas is promoted. As a result, hydrolysis of the urea aqueous solution is promoted, and the exhaust gas and ammonia generated from the urea aqueous solution are mixed substantially uniformly. Further, since the end portion 2b of the exhaust pipe 2a expands in a bell mouth shape, the exhaust in which the swirling flow is generated diffuses along the inner peripheral surface of the bell mouth-shaped exhaust pipe 2a from the end portion 2b. It flows into the space 8 and diffuses rapidly in the space 8. As a result, the exhaust gas in which ammonia is substantially uniformly mixed flows into the catalyst carrier 7 of the NOx reduction catalyst 4 substantially uniformly, so that the exhaust gas purification efficiency in the NOx reduction catalyst 4 can be improved.

Further, since the plate 10 is provided upstream of the exhaust of the injection nozzle 5, the urea aqueous solution supplied by injection from the injection nozzle 5 does not adhere to the plate 10. Thereby, urea which is a component of the urea aqueous solution does not deposit on the plate 10.
FIG. 3 is a diagram simulating the exhaust flow in the exhaust pipe 2a and the space 8 on the premise that the end 2b is formed in a bell mouth shape. FIG. 5A shows the flow of exhaust when the plate 10 is not provided upstream of the exhaust nozzle 5, and FIG. 5B shows the case where the plate 10 is provided upstream of the exhaust nozzle 5. Shows the flow of exhaust. As a result, on the premise that the end 2b is formed in a bell mouth shape, when the plate 10 is provided, it can be found that the exhaust gas diffuses more in the space 8 and flows into the catalyst carrier 7 substantially uniformly. .

  Instead of providing the plate 10, as shown in FIG. 4, the outer peripheral surface of the injection nozzle 5 that extends the substantially axial center of the exhaust pipe 2 a toward the exhaust downstream side, and the injection hole 5 a that injects the urea aqueous solution. A plurality of fins 12 extending at a predetermined angle with respect to the flow direction of the exhaust may be provided upstream of the exhaust as a swirl flow generating means. Further, as shown in FIG. 5, a plurality of fins 13 extending upstream from the nozzle hole 5a and extending at a predetermined angle with respect to the flow direction of the exhaust are provided as swirl flow generating means on the inner peripheral surface of the exhaust pipe 2a. May be. Thereby, like the plate 10, since the swirl flow is generated in the exhaust gas before the urea aqueous solution is injected and supplied, the same effect can be exhibited. Further, by providing the fin 12 on the outer peripheral surface of the injection nozzle 5 extending substantially axially of the exhaust pipe 2a toward the exhaust downstream side, and providing the fin 13 on the inner peripheral surface of the exhaust pipe 2a, a stronger swirling flow can be achieved. It is possible to further promote the mixing of the urea aqueous solution and the exhaust gas.

  As shown in FIG. 6, the exhaust pipe 2 a is expanded in a substantially tapered shape between the plate 10 and the NOx reduction catalyst 4 toward the exhaust downstream side until it has substantially the same diameter as the NOx reduction catalyst 4. May be. When the exhaust gas generating the swirling flow passes through the exhaust pipe 2a having a tapered diameter, the exhaust gas turns along the inner peripheral surface of the exhaust pipe 2a and goes outward in the radius of the exhaust pipe 2a. Spread. Thus, the exhaust gas is sufficiently diffused in the exhaust pipe 2a and flows into the catalyst carrier 7 substantially uniformly, so that the exhaust gas purification efficiency in the NOx reduction catalyst 4 can be improved. At this time, if the diameter of the exhaust pipe 2a is increased at least at a part between the injection nozzle 5 and the NOx reduction catalyst 4 in a substantially tapered shape toward the exhaust downstream side, the same effect can be exhibited. Further, in this way, the exhaust pipe 2a is enlarged in a substantially tapered shape at least at a part between the injection nozzle 5 and the NOx reduction catalyst 4, and at least one of the fins 12 and the fins 13 is used instead of the plate 10. Even if it provides, the same effect can be exhibited.

  In addition, as shown in FIG. 7, when the exhaust pipe 2a between the oxidation catalyst 3 and the injection nozzle 5 can be divided and the divided exhaust pipe 2a is connected to each other by the flange 20, The fins 11 may be formed on the gasket 21 interposed in the flange 20. At this time, for example, as shown in FIG. 8, a central disc portion punched as an exhaust passage when the gasket 21 is molded is used to cause a cut in the gasket 21 and cause a predetermined flow direction of the exhaust. A plurality of fins 11 extending at an angle are formed. As a result, like the plate 10, a swirling flow is generated in the exhaust gas before the urea aqueous solution is injected and supplied. Therefore, when the exhaust pipe 2a divided between the oxidation catalyst 3 and the injection nozzle 5 is connected to each other by the flange 20, only the gasket 21 is changed and other parts are changed. The effect similar to that of the plate 10 can be easily achieved.

Configuration diagram of an embodiment of an exhaust emission control device of the present invention The perspective view which shows the structure of a plate same as the above The flow of exhaust in the exhaust pipe and space in the same as above is shown, (a) is a reference diagram when a plate is not provided, (b) is a reference diagram when a plate is provided. FIG. 3 is a structural diagram showing the shape of fins in another embodiment of the exhaust emission control device of the present invention The shape of the fin in other embodiment same as the above is shown, (a) is a front view, (b) is a side view. Structural diagram showing the shape of the exhaust pipe in another embodiment Configuration diagram of another embodiment of the exhaust emission control device of the present invention The perspective view which shows the shape of the gasket in the same as the above

Explanation of symbols

1 Engine 2, 2a Exhaust pipe 2b End 4 NOx reduction catalyst 5 Injection nozzle 5a Injection hole 10 Plate 11, 12, 13 Fin 20 Flange 21 Gasket

Claims (4)

A reduction catalyst that is disposed in a case having a larger diameter than the exhaust passage of the engine at a predetermined interval from the exhaust upstream end , and that reduces and purifies nitrogen oxides in the exhaust with a reducing agent;
An injection nozzle that injects a reducing agent into an exhaust passage located upstream of the exhaust of the case ;
A swirl flow generating means that is disposed upstream of the exhaust position of the reducing agent in the injection nozzle and generates a swirl flow that spirally swirls around the axis of the exhaust passage in the exhaust;
An exhaust emission control device for an engine comprising:
The injection nozzle injects and supplies the reducing agent to the exhaust gas in which the swirl flow is generated by the swirl flow generation means ,
An exhaust purification device for an engine, wherein the exhaust passage located upstream of the exhaust of the case projects into the case with its tip portion expanding in a bell mouth shape toward the exhaust downstream side . A plurality of the swirl flow generating means are provided in a thin plate shape on the outer peripheral surface of the injection nozzle extending toward the exhaust downstream side with the substantially axial center of the exhaust passage extending at a predetermined angle with respect to the exhaust flow direction. The engine exhaust gas purification apparatus according to claim 1, wherein the engine exhaust gas purification apparatus is a fin . The engine exhaust gas purification apparatus according to claim 2 , wherein the swirl flow generating means is further provided on an inner peripheral surface of the exhaust passage . The exhaust passage can be divided upstream of the exhaust of the injection nozzle, and
The swirling flow generating means is formed by making a cut in a gasket interposed between flanges connecting the divided portions of the exhaust passage, and a plurality of the swirling flow generating means are provided to extend at a predetermined angle with respect to the flow direction of the exhaust. 2. The engine exhaust gas purification device according to claim 1 , wherein the fin is a thin plate-like fin.

Images