JP4799340B2 - Structure of liquid reducing agent injection nozzle - Google Patents

Description

  The present invention relates to a structure of a liquid reducing agent injection nozzle used in an exhaust purification system that reduces NOx in exhaust using a liquid reducing agent, and in particular, liquid reduction that enhances the utilization efficiency of the liquid reducing agent injected into an exhaust passage. The present invention relates to the structure of the agent injection nozzle.

  As an exhaust purification system for removing NOx contained in engine exhaust, a liquid reducing agent is injected and supplied to an upstream exhaust passage of a reduction catalyst disposed in an engine exhaust system, whereby NOx in the exhaust, liquid reducing agent, and Exhaust gas purification devices have been proposed that purify NOx into harmless components through a catalytic reaction. The liquid reducing agent is stored in a storage tank in a liquid state at room temperature, and a required amount is injected and supplied from an injection nozzle (see, for example, Patent Document 1 and Patent Document 2).

In such an exhaust purification system, the injection nozzle 1 is protruded from the wall surface of the exhaust pipe 3 as an exhaust passage as shown in FIG. 6 toward the center of the pipe, and the bent nozzle tip 1A is in the exhaust flow direction (see FIG. It is fixed to the exhaust pipe 3 via the boss portion 4 so as to face the downstream side substantially in parallel with the arrow A in FIG. A broken line arrow in the figure shows, for example, an aqueous urea solution as a liquid reducing agent with respect to the flow direction A of exhaust gas from a large number of nozzle holes 2 formed in the vicinity of the tip of the nozzle tip 1A in the radial direction from the nozzle axis. As shown in FIG. 2, the injection is supplied in a substantially right angle direction, and the injected liquid reducing agent is diffused and mixed into the exhaust gas by the flow of the exhaust gas to improve the NOx purification rate by the reduction catalyst.

  By the way, this type of injection nozzle 1 is usually one in which eight nozzle holes (indicated by the spraying directions 2a to 2h) are formed at substantially equal intervals in the circumferential direction as shown in FIG. Although used, the conventional arrangement of the eight injection holes is a nozzle in which the injection direction 2a of one of the eight injection holes protrudes from the wall surface of the exhaust pipe 3 toward the pipe center as shown in FIG. The arrangement is such that it overlaps the intermediate portion 1B when viewed from the flow direction of the exhaust gas. For this reason, the spray overlapping the nozzle intermediate portion 1B is not easily diffused and mixed by the exhaust flow, and the amount of the liquid reducing agent contributing to the reduction reaction is reduced.

  In addition, as shown in the figure, the conventional structure for mounting the injection nozzle 1 is such that a part of the nozzle base end portion 1C is fitted into the boss portion 4 attached to the exhaust pipe 3 and fixed by, for example, a bolt 6 or the like. The tip of the portion 4 protrudes from the inner wall surface of the exhaust pipe 3 into the exhaust pipe 3, and the useless space portion 5 is generated in the fitting portion where the nozzle base end portion 1 </ b> C of the boss portion 4 is fitted. ing. For this reason, a turbulent flow is generated in the exhaust flow at the mounting portion of the boss 4 to affect the diffusion and mixing of a part of the spray, and the amount contributing to the reduction reaction of the sprayed liquid reducing agent is reduced. Yes.

  The present invention has been made paying attention to the above problems, and eliminates the injection direction that overlaps the nozzle portion when viewed from the flow direction of the exhaust gas, prevents the turbulent flow of the exhaust gas at the mounting portion of the boss portion, An object of the present invention is to provide a structure of a liquid reducing agent injection nozzle capable of increasing the utilization efficiency.

Therefore, the invention of claim 1, the nitrogen oxides in the exhaust passage wall surface upstream of said reduction catalytic converter in the exhaust passage is interposed a reduction catalyst for purifying a liquid reducing agent, larger than the nozzle intermediate portion and the nozzle tip nozzle base end portion formed in the diameter is attached through a boss portion, said nozzle intermediate portion protruding towards the center from the wall surface of the exhaust passage, toward the nozzle tip on the downstream side of the exhaust gas flow direction In a liquid reducing agent injection nozzle that is bent and supplies the liquid reducing agent from a large number of injection holes formed around the nozzle tip, the injection direction of each nozzle hole around the nozzle tip is the exhaust gas with arranging formed so as not to overlap with the nozzle intermediate portion as viewed from the flow direction, the nozzle base end portion attached to the boss portion, is formed in substantially the same shape as the nozzle base end engaging portion of the boss portion The exhaust The fitting portion facing the road and the front end surface of the nozzle base end part, has a structure of the liquid reducing agent injection nozzle, characterized in that formed such that the exhaust passage wall substantially flush.

  As in the second aspect, eight nozzle holes may be provided at substantially equal intervals around the nozzle tip.

According to the present invention, the nozzle intermediate portion protruding toward the center from the wall surface side of the exhaust passage does not get in the way, and the flow of exhaust hits all the sprays injected from the nozzle holes, Dispersion of the liquid reducing agent is excellent because it is possible to prevent the occurrence of turbulent flow due to the boss when a nozzle with a nozzle base end larger than the nozzle middle and nozzle tip is attached via the boss. The liquid reducing agent that can be mixed and supplied by injection can be used for the reduction reaction without waste. Therefore, the utilization efficiency of the liquid reducing agent can be improved, and the fuel consumption can be improved as the consumption amount of the liquid reducing agent is reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram showing an embodiment of an exhaust purification system to which a liquid reducing agent injection nozzle structure according to the present invention is applied.
In FIG. 1, this exhaust purification system reduces and removes NOx discharged from a diesel engine, gasoline engine or the like mounted on a vehicle using a liquid reducing agent. In an exhaust pipe 12 as an exhaust passage connected to an exhaust manifold 11 of an engine 10 that uses gasoline or light oil as fuel, nitrogen monoxide (NO) is converted into nitrogen dioxide (NO ₂ ) from the upstream side in the exhaust flow direction. An oxidation catalyst 13 that oxidizes, a NOx reduction catalyst 14 that reduces and purifies NOx with ammonia obtained by hydrolyzing a urea aqueous solution, and an ammonia oxidation catalyst 15 that oxidizes the ammonia that has passed through the NOx reduction catalyst 14 are sequentially disposed. Is done.

  An upstream side of the NOx reduction catalyst 14 is provided with a liquid reducing agent injection nozzle 20 for supplying and supplying a urea aqueous solution as a liquid reducing agent, and the urea aqueous solution stored in the storage tank 16 passes through the supply pipe 17. To the reducing agent supply device 18, and is supplied to the exhaust pipe 12 by the reducing agent supply device 18 through the injection nozzle 20 together with the pressure air. The reducing agent supply device 18 is controlled by a control unit (not shown) having a built-in computer, and supplies a necessary amount of urea aqueous solution corresponding to the engine operating state to the injection nozzle 20 while mixing with pressure air.

In such an exhaust purification system, the urea aqueous solution injected and supplied from the injection nozzle 20 is hydrolyzed by exhaust heat and water vapor in the exhaust to generate ammonia. The generated ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 14 to be purified into water and harmless gas. At this time, in order to improve the NOx purification rate by the NOx reduction catalyst 14, the NO by the oxidation catalyst 13 is oxidized to NO _2, to improve the ratio between NO and NO ₂ in the exhaust gas suitable for catalytic reduction reaction . Further, since the ammonia that has passed through the NOx reduction catalyst 14 is oxidized by the ammonia oxidation catalyst 15 disposed downstream of the exhaust gas, it is possible to prevent ammonia that emits a strange odor from being released into the atmosphere as it is.

Here, the structure of the liquid reducing agent injection nozzle 20 of the present embodiment will be described in detail with reference to FIGS.
2 to 4, in the injection nozzle 20 of the present embodiment, the nozzle base end portion 20 </ b> C is formed to have a larger diameter than the nozzle front end portion 20 </ b> A and the nozzle intermediate portion 20 </ b> B, and the nozzle base end portion 20 </ b> C is fixed to the exhaust pipe 12. The boss portion 22 is fixed by, for example, a bolt 23 or the like. A part of the nozzle base end portion 20C is fitted into the nozzle base end fitting portion 22A of the boss portion 22 fixed to the exhaust pipe 12, and the nozzle intermediate portion 20B following the nozzle base end portion 20C is the wall surface side of the exhaust pipe 12 The nozzle tip portion 20A that protrudes from the tube center direction and continues to the intermediate portion 20B is bent toward the downstream side in the exhaust gas flow direction A. An injection hole 21 is formed around the nozzle tip 20A as shown in FIG. As shown in FIG. 4, eight nozzle holes 21 are provided around the nozzle tip portion 20A at substantially equal intervals, and an aqueous urea solution is jetted and supplied as a liquid reducing agent outward from the axial center of the nozzle tip portion 20A. The nozzles 21 are arranged around the nozzle tip portion 20A so that the injection directions 21a to 21h of the nozzle holes 21 do not overlap the nozzle intermediate portion 20B when viewed from the exhaust flow direction A.

Further, a nozzle base end portion 20C to be fitted to the nozzle base end portion fitting portion 22A of the boss portion 22 is formed in substantially the same shape as the nozzle base end portion fitting portion 22A and faces the exhaust pipe 12. The front end surfaces 22a and 20a of the fitting portion 22A and the nozzle base end portion 20C are formed in a curved shape so as to be substantially the same as the inner wall surface of the exhaust pipe 12 as shown in FIGS.
According to the liquid reducing agent injection nozzle structure of the present embodiment, there is no injection direction that overlaps the intermediate portion 20B of the injection nozzle 20 when viewed from the exhaust flow direction A in all the injection directions 21a to 21h. The flow of exhaust directly hits all the sprays of ˜21 h, and the reducing agent spray can be diffused and mixed into the exhaust without waste. Further, the base end portion 20C of the injection nozzle 20 is formed in accordance with the shape of the fitting portion 22A of the boss portion 22 so that the conventional space portion 5 shown in FIGS. The front end surface 22a of the fitting portion 22A of the boss portion 22 facing the inside of the pipe 12 and the front end surface 20a of the injection nozzle base end portion 20C are substantially flush with the inner wall surface of the exhaust pipe 12 and the inner wall surface of the exhaust pipe 12 Since the step is eliminated, the generation of turbulent flow can be prevented and the flow of exhaust gas becomes smooth. As a result, the amount of liquid reducing agent remaining on the wall surface of the exhaust pipe 12 can be reduced, the use efficiency of the liquid reducing agent can be improved, and the fuel consumption can be improved by reducing the consumption of the liquid reducing agent.

  In the above embodiment, the number of nozzle holes of the injection nozzle is eight, which is the same as the conventional number, and the overlapping of the injection direction and the nozzle middle part is eliminated by shifting the formation position of the nozzle holes in the circumferential direction. The number of holes is not limited to eight. As shown in FIG. 5, the number of injection holes whose injection direction overlaps the nozzle middle part is abolished to seven, and the seven injection holes are the same as the conventional one. It is good also as a structure formed in a position.

The conceptual diagram which shows embodiment of the exhaust gas purification system which applies the liquid reducing agent injection nozzle of this invention The figure which shows the attachment state which shows embodiment of the liquid reducing agent injection nozzle of this invention Enlarged view of the nozzle tip of the injection nozzle of the same embodiment. Explanatory drawing of positional relationship between nozzle hole arrangement around nozzle tip and nozzle middle part The figure which shows another arrangement form of a nozzle hole The figure which shows the attachment state of the conventional liquid reducing agent injection nozzle Explanatory drawing of the positional relationship between the nozzle hole arrangement around the conventional nozzle tip and the nozzle middle part

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 12 Exhaust pipe 14 NOx reduction catalyst 16 Storage tank 18 Reducing agent supply apparatus 20 Liquid reducing agent injection nozzle 20A Nozzle tip part 20B Nozzle intermediate part 20C Nozzle base end part 21 Injection hole 22 Boss part 22A Nozzle base end part fitting part

Claims (2)

A nozzle base end portion formed larger in diameter than the nozzle intermediate portion and the nozzle tip portion on the exhaust passage wall surface upstream of the reduction catalyst of the exhaust passage provided with a reduction catalyst for reducing and purifying nitrogen oxide with a liquid reducing agent is a boss. attached via the part, said nozzle intermediate portion protruding towards the center from the wall surface of the exhaust passage, said nozzle tip and bent toward the downstream side of the exhaust gas flow direction, around the nozzle tip In a liquid reducing agent injection nozzle for supplying the liquid reducing agent from a plurality of formed nozzle holes,
Each of said injection holes around the nozzle tip, with its injection direction is disposed and formed so as not to overlap with the nozzle intermediate portion as viewed from the flow direction of the exhaust, the nozzle base end portion attached to said boss portion, The boss portion is formed in substantially the same shape as the nozzle base end fitting portion, and the front end surfaces of the fitting portion and the nozzle base end facing the exhaust passage are substantially flush with the exhaust passage inner wall surface. A structure of a liquid reducing agent injection nozzle, which is formed as described above.   The structure of the liquid reducing agent jet nozzle according to claim 1, wherein eight nozzle holes are provided at substantially equal intervals around the nozzle tip.

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