JP5738155B2 - Engine reducing agent injection nozzle - Google Patents

Description

  The present invention relates to a reducing agent injection nozzle that injects a liquid reducing agent or a precursor thereof for reducing nitrogen oxides in engine exhaust into the exhaust pipe of the engine together with air.

  Conventionally, as an exhaust purification device that reduces nitrogen oxides NOx in engine exhaust gas, a reduction catalyst is disposed in the exhaust pipe of the engine, and a liquid reducing agent or a precursor thereof is supplied to the exhaust pipe upstream of the reduction catalyst. An apparatus for reducing nitrogen oxide NOx with a reduction catalyst is known.

  In the above exhaust purification apparatus, the reducing agent injection nozzle for injecting the liquid reducing agent or its precursor into the exhaust pipe is attached to the peripheral wall of the exhaust pipe and extends from the peripheral wall toward the axial center of the exhaust pipe. A nozzle having a nozzle tip bent in the exhaust flow direction and having a plurality of injection holes formed in the circumferential direction of the nozzle tip is used (see, for example, Patent Document 1 and Patent Document 2). .

Japanese Patent No. 4090972 Japanese Patent No. 3715985

  By the way, when the reducing agent injection nozzle has a bent part in the middle and injects pressurized air together with the liquid reducing agent or its precursor, each injection is influenced by the boundary layer generated at the bent part. Variations may occur in the amount of liquid reducing agent or precursor thereof injected from the holes.

  When the amount of the liquid reducing agent or its precursor injected from each injection hole varies, uneven distribution of the liquid reducing agent or precursor added to the exhaust gas occurs, and the conversion rate of nitrogen oxides NOx decreases. The problem arises.

  In view of the above-described problems of the prior art, an object of the present invention is to provide an engine reducing agent injection nozzle capable of suppressing variation in the amount of liquid reducing agent or its precursor injected from each injection hole. .

  For this reason, in the reducing agent injection nozzle according to the present invention, the diameter of the injection hole near the outside of the bent portion in the circumferential direction of the nozzle tip is made smaller than the diameter of the injection hole near the inside of the bend.

  According to the present invention, in the reducing agent injection nozzle provided with the bent portion, it is possible to suppress variation in the injection amount of the liquid reducing agent or its precursor compared to the case where the diameter of the injection hole is made uniform.

Schematic which shows the diesel engine in embodiment of this invention. The figure which shows the reducing agent injection nozzle with which the diesel engine of FIG. 1 is equipped. The elements on larger scale which show the front-end | tip part of the reducing agent injection nozzle of FIG. The partial expanded sectional view which shows the injection hole of the reducing agent injection nozzle of FIG. The schematic diagram for demonstrating arrangement | positioning of the injection hole of the reducing agent injection nozzle of FIG. The figure which shows the injection hole formation range (injection range) of the reducing agent injection nozzle of FIG. The graph which shows the injection quantity in each injection hole when making the injection hole of a reducing agent injection nozzle into a uniform diameter The figure which shows the reducing agent injection nozzle in which a nozzle front-end | tip part is inclined with respect to the flow direction of exhaust_gas | exhaustion.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an exhaust emission control device for an engine including a reducing agent injection nozzle according to the present invention.
In FIG. 1, an intake pipe 14 connected to an intake manifold 12 of a diesel engine 10 is heated to a high temperature by an air cleaner 16 for removing dust in the air, a compressor 18A of a turbocharger 18 and a turbocharger 18 in order from the upstream side. An intercooler 20 that cools the intake air and an intake collector 22 that smoothes the intake pulsation are disposed.

  On the other hand, an exhaust pipe 26 connected to the exhaust manifold 24 of the diesel engine 10 includes, in order from the upstream side, a turbine 18B of a turbocharger 18, a continuously regenerating DFP (Diesel Particulate Filter) device 28, and urea as a reducing agent precursor. A reducing agent injection nozzle 30 for injecting the aqueous solution, an SCR catalyst (reducing catalyst) 32 for reducing NOx using ammonia (reducing agent) generated by the urea aqueous solution, and an oxidation catalyst 34 for oxidizing the ammonia that has passed through the SCR catalyst 32. Etc. are arranged.

The continuous regeneration type DPF device 28 collects DOC (Diesel Oxidation Catalyst) 28A which is an oxidation catalyst for oxidizing at least NO (nitrogen monoxide) into NO ₂ (nitrogen dioxide) and PM (Particulate Matter) in exhaust gas. And a DPF 28B that is a filter to be used.
Instead of the continuous regeneration type DPF device 28, a CSF (Catalyzed Soot Filter) having an oxidation catalyst component added to a diesel particulate filter (DPF) and having an oxidation function as well as a filter function may be used.

The reducing agent injection nozzle 30 is supplied with the aqueous urea solution (reducing agent precursor) stored in the reducing agent tank 36 and the pressurized air (compressed air) stored in the air tank 39 by the reducing agent supply device 38. Is done. The reducing agent injection nozzle 30 injects the urea aqueous solution together with the pressurized air into the exhaust pipe 26 upstream of the SCR catalyst 32.
Here, the reducing agent supply device 38 controls the flow rate of the urea aqueous solution supplied to the reducing agent injection nozzle 30, that is, the urea aqueous solution supplied from the reducing agent tank 36 to the SCR catalyst 32.

In the present embodiment, ammonia as a reducing agent is used to cause a reduction reaction in the SCR catalyst 32. A urea aqueous solution that easily generates ammonia by hydrolysis is used as a reducing agent (ammonia) precursor as a reducing agent. Spray from the spray nozzle 30.
Note that an aqueous ammonia solution (liquid reducing agent) can be injected from the reducing agent injection nozzle 30.

In addition, for example, the exhaust path passes between the DPF 28B and the SCR catalyst 32 so that the exhaust gas passing through the DPF 28B changes the traveling direction by 180 °, proceeds in the opposite direction, and flows into the SCR catalyst 32. It can be formed so as to be folded.
Further, at least the reducing agent injection nozzle 30 and the SCR catalyst (oxidation catalyst) 32 disposed downstream of the reducing agent injection nozzle 30 may be provided, and the DPF 28B is disposed between the SCR catalyst 32 and the oxidation catalyst 34. Or the DPF 28B can be arranged downstream of the oxidation catalyst 34.

  The aqueous urea solution stored in the reducing agent tank 36 is supplied to the injection nozzle 30 via a reducing agent supply device 38 having a built-in pump, flow rate control valve, and the like. Here, the reducing agent supply device 38 can be divided into a pump module incorporating a pump and a dosing module incorporating a flow control valve. Further, the injection nozzle 30 can be integrated with the reducing agent supply device 38.

An exhaust temperature sensor 40 that detects an exhaust temperature as an example of an engine operating state is attached to the exhaust pipe 26 between the continuous regeneration type DPF device 28 and the injection nozzle 30.
The output signal of the exhaust temperature sensor 40 is input to a reducing agent addition control unit (DCU) 44 incorporating a computer.

  The reducing agent addition control unit 44 is connected to an engine control unit (ECU) 46 that electronically controls the diesel engine 10 via an in-vehicle network such as a CAN (Controller Area Network). The reducing agent addition control unit 44 reads information such as an engine speed and an engine load as an example of an engine operating state from an engine control unit (ECU) 46.

  Then, the reducing agent addition control unit 44 executes a control program stored in advance in a built-in ROM (Read Only Memory) or the like, thereby reducing according to engine operating conditions such as exhaust temperature, engine speed, and engine load. The agent supply device 38 is controlled to control the injection of the urea aqueous solution from the injection nozzle 30.

2-4 is a figure which shows the injection nozzle 30 in detail.
FIG. 2 is a cross-sectional view of a portion of the exhaust pipe 26 to which the injection nozzle 30 is attached, including the axis of the exhaust pipe 26 and the attachment portion of the injection nozzle 30.

The injection nozzle 30 is formed of a hollow pipe whose tip is closed, and extends from a mounting portion 26 a provided on the peripheral wall of the exhaust pipe 26 toward the axial center 26 b of the exhaust pipe 26 along the radial direction of the exhaust pipe 26. It is provided and is bent substantially perpendicularly toward the exhaust flow direction (downstream side) before the shaft center 26b, and a plurality of injection holes 301 are formed in the circumferential direction in the peripheral wall portion near the closed tip 30a.
That is, the injection nozzle 30 includes a nozzle base end portion 302 that extends from the mounting portion 26 a along the radial direction of the exhaust pipe 26 toward the shaft center 26 b, a bent portion 303, and the shaft center 26 b of the exhaust pipe 26. And a nozzle tip portion 304 extending substantially parallel to the exhaust downstream side.

3A and 3B are enlarged views of the nozzle tip portion 304. FIG.
As shown in FIGS. 3A and 3B, the injection holes 301 are formed in a plurality of rows in the axial direction of the nozzle tip 304, for example, in two rows, and the injection holes 301 are mutually connected between the rows. Are shifted in the circumferential direction, and four injection holes 301 are provided in the downstream example, and four injection holes 301 are also provided in the upstream example, for a total of eight injection holes 301. Is provided.

Further, as shown in FIG. 3A, the axis of each injection hole 301 is inclined from the radial direction of the nozzle tip 304 toward the exhaust downstream side. However, the axis of each injection hole 301 can be set in the radial direction of the nozzle tip 304.
FIG. 4 is a cross-sectional view of a portion of the nozzle tip 304 where the injection hole 301 is provided, and more specifically, a cross-sectional view taken along the line IV-IV in FIG. In FIG. 4, the axial center of the injection hole 301 is shown to coincide with the radial direction of the nozzle tip portion 304.
FIG. 5 is a diagram schematically showing the arrangement of the injection holes 301.

  As shown in FIGS. 4 and 5, among the injection holes provided in two rows in the axial direction on the peripheral wall in the vicinity of the closing tip 30 a of the nozzle tip 304, the upstream row indicates the injection holes indicated by broken lines in FIG. 4. 301a, 301c, 301e, 301g consists of four injection holes, and the downstream row consists of four injection holes 301b, 301d, 301f, 301h indicated by solid lines in FIG.

  Here, on the peripheral wall of the nozzle tip 304, if the angular position farthest from the mounting portion 26a (the angular position outside the bending) is the reference angular position α, the injection hole 301d and the injection hole 301e are separated from the reference angular position α. The injection hole 301c and the injection hole 301f are provided at positions separated by the same angle 3β in the left-right direction from the reference angle position α, and the injection hole 301b and the injection hole 301g are provided at positions separated by the same angle β in the left-right direction. Is provided at a position away from the reference angle position α by the same angle 5β in the left-right direction, and the injection hole 301a and the injection hole 301h are provided at positions away from the reference angle position α by the same angle 7β in the left-right direction. .

Here, the angle β is set to, for example, about 15 ° to 17 °, for example, 16.75 °.
That is, the eight injection holes 301a to 301h are at angular positions that are symmetric with respect to a plane including the axis 302a of the nozzle base end 302 and the axis 304a of the nozzle tip 304 (the axis of the injection nozzle 30). It is formed and provided on the side far from the mounting portion 26 a, in other words, on the portion of the bent portion 303 that is outside the bend.

  Furthermore, the diameters (diameters) of the injection holes 301a to 301h are not the same. As shown in FIGS. 4 and 5, the injection holes 301c, 301d, and 301e are formed to have the same diameter D1, and the other injection holes 301a and 301b are formed. , 301f to 301h are formed to have the same diameter D2, and the diameter D1 <the diameter D2. Here, for example, the diameter D1 is about 0.45 mm, and the diameter D2 is about 0.55 mm.

  That is, of the eight injection holes 301a to 301h, the diameters of the two injection holes 301d and 301e closest to the outer side of the bend (reference angle position α) are both formed to a small diameter D1, and the outer side of the bend (reference angle position α) is formed. ) Of the two injection holes 301c and 301f that are closest to each other, the upstream injection hole 301c is formed with a small diameter D1, and the downstream injection hole 301f is formed with a large diameter D2. The injection holes 301a, 301b, 301g, and 301h that are closer to the inside of the bend than 301c and 301f are all formed to have a large diameter D2.

Since the nozzle tip 304 of the injection nozzle 30 is disposed at a position closer to the mounting portion 26a than the axis 26b of the exhaust pipe 26, the distance to the peripheral wall of the exhaust pipe 26 in the radial direction of the nozzle tip 304 is not uniform. Instead, it is closer to the side closer to the mounting portion 26a, in other words, the portion that is inside the bend of the bent portion 303.
For this reason, when the urea aqueous solution is injected together with the pressurized air from the injection hole provided on the side near the mounting portion 26a of the nozzle tip 304, the urea aqueous solution adheres to the inner peripheral wall of the exhaust pipe 26, and the inner peripheral wall of the exhaust pipe 26 There is a possibility that the water evaporates from the urea aqueous solution adhering to the water, the urea is deposited, and urea is deposited.

  Therefore, the injection hole 301 is not provided on the side near the mounting portion 26a of the nozzle tip 304, in other words, the side near the inner peripheral wall of the exhaust pipe 26, and the distance to the inner peripheral wall of the exhaust pipe 26 is constant. The injection holes 301 are provided at the angular positions as described above to inject the urea aqueous solution. In this way, as shown in FIG. 6, since the urea aqueous solution is not injected from the position near the inner peripheral wall of the exhaust pipe 26, the amount of urea aqueous solution attached to the inner peripheral wall of the exhaust pipe 26 is reduced, and urea deposition is reduced. Can be suppressed.

The angle range (angle β, the number of injection holes) in which the injection holes 301 are provided is set as appropriate so as to suppress the addition variation of the urea aqueous solution while reducing the amount of the urea aqueous solution attached to the inner peripheral wall of the exhaust pipe 26. .
In addition, as described above, the diameters of the injection holes 301a to 301h are not the same, and the small-diameter D1 injection hole and the large-diameter D2 injection hole are provided, whereby the injection holes 301a to 301h are injected. The dispersion of the urea aqueous solution is suppressed.

FIG. 7 is a diagram showing the injection amount (g / h) of the urea aqueous solution from each injection hole when the injection holes 301a to 301h are arranged in the same manner as described above and all have the same diameter.
As shown in FIG. 7, among the eight injection holes 301a to 301h, two injection holes 301d and 301e that are closest to the outside of the bend, and two injection holes 301c that are next closest to the outside of the bend, The injection amount from the injection hole 301c, which is the upstream side of 301f, is greatly reduced as compared with the injection amounts from the other injection holes 301a, 301b, 301f, 301g, and 301h.

This is because a boundary layer is generated in the flow in the nozzle by the bent portion 303 and a difference occurs in the internal pressure between the outside and the inside of the bend (the inside pressure at the outside of the bend is lower than the inside), and the internal pressure As a result of being affected by the variation, it is presumed that the injection amount from the injection hole arranged outside the bending is reduced as compared with the injection amount from the injection hole arranged inside the bending.
Further, the two injection holes 301c and 301f closer to the inside of the bending than the two injection holes 301d and 301e are arranged at equivalent positions (symmetrical positions) in the angle position in the inner and outer directions of the bending, but the injection holes 301c. Is opened at a position closer to the bent portion 303 on the upstream side and is more greatly affected by the boundary layer and the like (because the internal pressure is lower), the injection amount compared to the downstream injection hole 301f. Is estimated to have decreased.

That is, when the diameters of the respective injection holes 301a to 301h are uniform, the angle position closer to the outer side of the bend and the upstream side closer to the bent portion 303 are more greatly affected by the bending, and the injection amount is reduced. Show a tendency to
Therefore, in order to suppress such variation in the injection amount, the diameter of the three injection holes 301c, 301d, and 301e, in which the injection amount decreases when compared with the other when the same diameter is set, is made smaller than the other three. By increasing the flow rate at the injection holes 301c, 301d, and 301e and increasing the injection amount (g / h), variations in the injection amounts at the injection holes 301a to 301h are suppressed.

  In other words, if the diameter of the injection hole 301 closer to the outside of the bend and closer to the bent portion 303 is made smaller, the injection amount from the injection hole in which the injection amount decreases compared to the other when the diameter is the same. The amount is increased relatively with respect to the injection amount at the other injection holes, and thereby variation in the injection amount from each injection hole 301 can be suppressed.

When the injection holes 301 are provided in only one row in the axial direction of the nozzle tip 304, there is no displacement of the injection holes in the upstream and downstream directions (difference in distance from the bent portion 303). By making the diameter of the injection hole close to the outside of the nozzle smaller than the diameter of the injection hole closer to the inside of the bend, variation in the injection amount from each injection hole 301 can be suppressed.
If variation in the amount of urea aqueous solution injected from each injection hole 301 can be reduced, uneven distribution of the urea aqueous solution added to the exhaust gas can be reduced, and the purification performance of nitrogen oxides NOx can be improved.

The injection hole 301 has a straight shape in which the diameter of the hole opened on the hollow inner peripheral surface of the nozzle tip 304 and the diameter of the hole opened on the outer peripheral surface are the same, and the hollow inner circumference of the nozzle tip 304. The diameter of the hole opened in the outer peripheral surface is larger than the diameter of the hole opened in the surface, and a tapered shape that spreads outward can be formed.
If the injection hole 301 is tapered, the spray angle of the urea aqueous solution injected from each injection hole 301 is wider than that of the straight shape, and the urea aqueous solution can be mixed more uniformly with the exhaust gas. Become.

Further, as shown in FIG. 8, the nozzle tip 304 of the injection nozzle 30 is moved closer to the axial center 26 b of the exhaust pipe 26 so as to approach the axial center 26 b of the exhaust pipe 26 as it approaches the closed tip 30 a from the bent portion 303. It can extend along the direction which crosses.
In this case, the bending angle of the bent portion 303 is smaller than that in the case of FIG. 2, the flow disturbance due to bending of the boundary layer and the like is reduced, and the variation in internal pressure is not smaller. By making it, the dispersion | variation in injection quantity can be suppressed smaller.

In addition, the diameter of the injection hole 301 is set to two, large and small, and three or more different diameters of the injection hole 301 are used depending on the angular position of the nozzle tip 304 and the distance from the bent part 303. In this case as well, the injection hole 301 closer to the outside of the bend and closer to the bent portion 303 has a smaller diameter.
Furthermore, when the injection holes 301 are provided in a plurality of rows in the axial direction of the nozzle tip portion 304, the plurality of injection holes extend along the axial direction of the nozzle tip portion 304 without shifting the injection holes in the circumferential direction between the plurality of rows. It can be arranged in a straight line.

10 Diesel engine 30 Injection nozzle 32 SCR catalyst (reduction catalyst)
36 Reducing agent tank 38 Reducing agent supply device 39 Air tank 301 Injection hole 302 Nozzle base end portion 303 Bending portion 304 Nozzle tip portion

Claims (4)

A reducing agent injection nozzle that injects a liquid reducing agent or a precursor thereof for reducing nitrogen oxide in the exhaust of the engine together with air into the exhaust pipe of the engine,
The reducing agent injection nozzle has a bent portion in the middle, extends into the exhaust pipe, and has a plurality of injection holes formed in the circumferential direction of the closed end portion,
A reducing agent injection nozzle for an engine, wherein a diameter of the injection hole near the outside of the bent portion in the circumferential direction of the tip portion is smaller than a diameter of the injection hole near the inside of the bend.   The reducing agent injection nozzle for an engine according to claim 1, wherein the diameter of the injection hole is made smaller as it is closer to the outside of the bend and closer to the bent portion. The injection holes are formed in a plurality of rows in the axial direction of the tip, and the positions of the injection holes are shifted in the circumferential direction between the rows, and are symmetrical with respect to a plane including the axis of the reducing agent injection nozzle. The injection hole is arranged so as to be an angular position of
The injection hole closest to the outside of the bend is formed with a small diameter, and among the injection holes closest to the outside of the bend, the upstream injection hole is formed with the small diameter, and the other injection holes are formed with a large diameter. The reducing agent injection nozzle for an engine according to claim 2, which is formed as described above. The reducing agent injection nozzle is attached to the peripheral wall of the exhaust pipe, and extends from the peripheral wall toward the axial center of the exhaust pipe, and then the exhaust flow direction by the bent portion on the near side of the axial center Extended towards
The reducing agent injection nozzle for an engine according to any one of claims 1 to 3, wherein the injection hole is provided except for a predetermined angle range that is inside the bending of the bent portion in a circumferential direction of the tip portion. .