JP2005207289A - System for fuel addition in exhaust pipe of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent injected fuel from adhering to the inside wall of an exhaust pipe, sufficiently perform reduction-regeneration of an exhaust-gas purification catalyst, and improve the fuel economy. <P>SOLUTION: In the system for fuel addition in the exhaust pipe of a diesel engine, a fuel injection nozzles (20) are installed in the exhaust pipe (10) of the diesel engine (1). Fuel is injected from the fuel-injection nozzles to conduct reduction-regeneration of the exhaust-gas purification catalyst (11) provided in the exhaust pipe. The plurality of fuel-injection nozzles are provided so that injection axes (20a) are crossed each other. The injection nozzles are installed at equal intervals in the peripheral direction of the exhaust pipe. It is preferable that the injection axes are crossed each other roughly at one point, and that the fuel injection nozzles are composed of hole-type or slit type fuel-injection nozzles respectively having one or two injection holes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention, as a post-processing apparatus of the exhaust gas, NO _X storage reduction catalyst, is used in a diesel engine equipped with a reduced reproduction catalyst such DPNR preferred, an exhaust pipe fuel addition method of a diesel engine.

Recently, particulate matter in the exhaust gas of a diesel engine (hereinafter, referred to as PM) as a method for reducing or NO _X, it has been developed a variety of things. PM consists of three components, SOF, black smoke, sulfate + combined water. SOF composed of unburned fuel and oil, HC and CO in exhaust gas are oxidized and purified on the oxidation catalyst. The diesel particulate filter (hereinafter referred to as DPF) enables a significant PM reduction as one measure for reducing the pollution of diesel engine vehicles. The DPF is composed of a heat-resistant filter capable of collecting PM with high efficiency and a filter regenerating device for removing the PM collected by the filter. The filter regenerating device, for example, uses the collected PM as a light oil burner. For example, the filter is regenerated by incineration and removal.

On the other hand, the exhaust gas composition of a diesel engine is always in an oxygen-excess region, and there are very few components serving as a reducing agent, and the temperature region is wide, so that it is a very difficult environment for the catalyst. One type of catalyst for purifying NO _x in this oxygen-excess environment is a NO _x storage reduction type catalyst. This NO _x storage reduction type catalyst has a very high NO _x reduction rate, and is one of the promising options when it is required to meet very strict standards for NO _x . There is also a diesel particulate-NO _X reduction system (hereinafter referred to as DPNR) in which this NO _X storage reduction catalyst and the above-mentioned DPF are integrated.

_The NO _X storage and reduction type catalyst or DPNR described above, again robbing oxygen from NO ₃ which is formed by adsorbing NO _X, thereby it is necessary to perform a reproduction process of the filter. As one method for this purpose, there is an exhaust pipe fuel addition system in which fuel is added into the exhaust pipe to increase HC, CO, CO _2, H ₂ or the like (see, for example, Patent Document 1). In this exhaust pipe fuel addition system, for example, a pressurized fuel is led from a feed pump of an engine, and one hole type fuel injection nozzle 50 as shown in FIGS. 8 and 9 is attached to the upstream side of the catalyst in the exhaust pipe. Alternatively, the fuel is injected from the slit type fuel injection nozzle 51 as shown in FIGS. The hole type fuel injection nozzle 50 is formed from, for example, eight circular injection holes 50a opened at the tip portion, and the slit type fuel injection nozzle 51 is formed of one or a plurality of slit-like shapes opened at the tip portion. Fuel is injected from each of the injection holes 51a. In addition, in order to sufficiently reduce and regenerate the catalyst, it is necessary to instantaneously increase the fuel vapor concentration in the exhaust pipe to obtain a rich air-fuel ratio.
JP 2000-356137 A (pages 8-11, FIG. 6)

  However, in the conventional diesel engine exhaust pipe fuel addition method described above, fuel is added into the exhaust pipe by one hall type fuel injection nozzle 50 or slit type fuel injection nozzle 51. The hole-type fuel injection nozzle 50 is formed, for example, from eight circular injection holes 50a opened at the tip, and the slit-type fuel injection nozzle 51 is formed of one or more slit-like holes opened at the tip. Fuel is injected from each of the injection holes 51a.

  For this reason, as shown in FIG. 12, the injected fuel becomes streaks in the exhaust pipe 52, and most of the fuel adheres to the inner wall 53 of the exhaust pipe 52. As a result, as shown in FIG. 13, the fuel vapor directly reaching the catalyst is reduced to about half, while the fuel vapor adhering to the inner wall of the exhaust pipe and evaporating there reaches the catalyst with a slight time difference. To do. For this reason, the conventional exhaust pipe fuel addition method of a diesel engine has a problem that the fuel vapor concentration in the exhaust pipe cannot be instantaneously increased, and the catalyst cannot be sufficiently reduced and regenerated. Correspondingly, in order to increase the fuel vapor concentration to the concentration necessary for the reduction and regeneration of the catalyst, a large amount of fuel must be injected, resulting in a problem of worsening fuel consumption.

  The present invention has been made to solve such a problem, and prevents the injection fuel from adhering to the inner wall of the exhaust pipe to instantaneously increase the fuel vapor concentration in the exhaust pipe to near the theoretical fuel vapor concentration. Therefore, it is an object of the present invention to provide an exhaust pipe fuel addition method for a diesel engine that can sufficiently reduce and regenerate an exhaust gas purification catalyst and can significantly improve fuel efficiency.

  In order to solve the above-mentioned problems, the means employed by the present invention is a fuel injection nozzle provided in the exhaust pipe of a diesel engine, injecting fuel from the fuel injection nozzle, and an exhaust gas purification catalyst disposed in the exhaust pipe. In an exhaust pipe fuel addition system for a diesel engine that performs reduction regeneration, the fuel injection nozzle is composed of a plurality of injection nozzles and is disposed so that the injection axes intersect each other. Here, the injection axis is a center line of injection indicating the injection direction of each nozzle.

  According to this means, since the fuel injection nozzle is composed of a plurality of fuel injection nozzles arranged so that the injection axes intersect each other, the fuel injected from each fuel injection nozzle collides and mixes with each other. Optimal atomization is thus achieved, and the injected fuel is prevented from adhering to the inner wall of the exhaust pipe.

  It is desirable that the plurality of fuel injection nozzles be disposed at substantially equal intervals in the circumferential direction of the exhaust pipe. By arranging a plurality of fuel injection nozzles at substantially equal intervals in the circumferential direction of the exhaust pipe, the fuel injected from these fuel injection nozzles is uniformly collided and mixed in the exhaust pipe, and the fuel vapor Is uniformly supplied to the catalyst.

  The plurality of fuel injection nozzles are preferably arranged so that the injection axes intersect at substantially one point. By arranging the plurality of fuel injection nozzles so that the injection axes intersect at substantially one point, the fuel injected from each nozzle can be more reliably collided and mixed, and the injected fuel is connected to the inner wall of the exhaust pipe. It is further prevented from adhering to.

  The fuel injection nozzle is preferably composed of a hole type fuel injection nozzle or a slit type fuel injection nozzle having one or two injection holes. In this means, the fuel injected from each fuel injection nozzle collides and mixes with each other to prevent the injected fuel from adhering to the inner wall of the exhaust pipe. It is a hole type fuel injection nozzle or a slit type fuel injection nozzle to be injected, and the number of injection holes is not a large number (8) as in the prior art, but a small number (1 or 2). This collision and mixing can be performed more effectively.

  The fuel injection nozzle is preferably formed such that the injection axis is inclined backward from the center line of the nozzle body. In the case of this means, it is assumed that each fuel injection nozzle is attached to the exhaust pipe so that its injection axis is inclined rearward in the exhaust gas flow direction. In this case, by inclining the injection axis backward from the center line of the nozzle body, the attachment angle of each injection nozzle with respect to the exhaust pipe can be increased, and the attachment thereof is structurally easy.

  For example, the fuel injection nozzle is supplied with fuel from a feed pump of a diesel engine. The exhaust pipe fuel addition method of the present diesel engine is particularly suitable when relatively low pressure fuel is injected from the feed pump.

  As described above in detail, the diesel engine exhaust pipe fuel addition system of the present invention includes a fuel injection nozzle in the exhaust pipe of the diesel engine, and fuel is injected from the fuel injection nozzle and disposed in the exhaust pipe. In an exhaust pipe fuel addition system for a diesel engine that performs reduction regeneration of an exhaust gas purifying catalyst, a plurality of fuel injection nozzles are arranged and their injection axes intersect each other. The fuel vapor concentration in the exhaust pipe is brought close to the theoretical fuel vapor concentration, and the exhaust gas purification catalyst can be sufficiently reduced and regenerated, and the fuel efficiency can be remarkably improved. Play.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out an exhaust pipe fuel addition system for a diesel engine according to the present invention will be described in detail with reference to FIGS.

  1 is a schematic diagram showing an exhaust pipe fuel addition method of a diesel engine according to the present invention, FIG. 2 is a side sectional view showing a fuel injection nozzle of FIG. 1, and FIG. 3 is a bottom view showing the fuel injection nozzle of FIG. 4 is a bottom view showing another fuel injection nozzle, FIG. 5 is a bottom view showing still another fuel injection nozzle, and FIG. 6 is a side sectional view showing a mounting state of the fuel injection nozzle of FIG. 7 is a graph showing the operation of the fuel injection nozzle of FIG.

  As shown in FIG. 1, a diesel engine 1 includes a common rail 2 that supplies fuel to a fuel injection nozzle in the engine 1, a supply pump 3 that supplies high-pressure fuel to the common rail 2, and a fuel tank 5 to the supply pump 3. A feed pump 4 that supplies fuel, a fuel filter 6 that is interposed between the supply pump 3 and the feed pump 4, an ECU 7 that performs fuel control of the diesel engine 1, and the like are disposed.

In the exhaust pipe 10, for example, two fuel injection nozzles 20, an NO _x storage reduction catalyst 11 that is an example of a reduction regeneration catalyst, a muffler 12, and the like are disposed. The ECU 7 is electrically connected to the fuel injection nozzle of the engine 1, the supply pump 3, the feed pump 4, the fuel injection nozzle 20 in the exhaust pipe 10, and the like.

_The NO _X storage reduction type catalyst 11, while absorbing the NO _X in the exhaust gas flowing through the exhaust pipe 10, by increasing HC in exhaust gas, CO, a CO ₂ or H _2, regeneration processes occluded NO _X This is a so-called NO _x storage reduction catalyst. The catalyst 11 has a monolith support having a grid-like passage formed in the flow direction of the exhaust gas, and a coat layer formed on the monolith support and supporting a noble metal and a NO _x storage agent. Examples of the noble metal include Pt, and examples of the NO _x storage agent include alkali metals such as Li, Na, K, and Cs, alkaline earth metals such as Mg, Ca, and Ba, Y, La, Ce, and the like. There are rare earth metals such as Pr, Nd, Eu, Gd, and Dy. As the coating layer, alumina or the like is used.

  As shown in FIG. 2, the fuel injection nozzle 20 is composed of, for example, a hole-type fuel injection nozzle. The fuel injection nozzle 20 includes a cylindrical nozzle body 21 and a columnar valve shaft 30 that is inserted into the nozzle body 21 so as to be movable in the axial direction. The nozzle body 21 includes a fuel supply hole 22, a valve seat 23 seated by a conical seat portion 31 at the tip of the valve shaft 30, a guide hole 24 extending from the valve seat 23, and an injection extending in the circumferential direction from the guide hole 24. Hole 25. As shown in FIG. 3, the fuel injection nozzle 20 is provided with only one injection hole 25 composed of a small circular hole. As shown in FIG. 2, the fuel injection nozzle 20 is formed such that its injection axis 20a is inclined backward from the nozzle body center line 21a. Here, the injection axis 20 a is a center line of injection indicating the injection direction of each nozzle 20.

  The valve shaft 30 is opened and closed by an electromagnetic solenoid (not shown) controlled by the ECU 7. Further, the fuel injection nozzle includes a hole type fuel injection nozzle 36 having two injection holes 37 as shown in FIG. 4, and a slit type having one slit-like injection hole 39 as shown in FIG. The fuel injection nozzle 38 may be used. In this case, both the injection hole 37 of the hole type fuel injection nozzle 36 and the injection hole 39 of the slit type fuel injection nozzle 38 have their injection axes rearward from the center line of the nozzle body in the same manner as the fuel injection nozzle 20 described above. It is formed so as to be inclined.

  The fuel injection nozzle described above is not necessarily limited to a hole type fuel injection nozzle or a slit type fuel injection nozzle, and the number of injection holes is not limited to one or two.

  As shown in FIG. 6, the two fuel injection nozzles 20 are arranged at equal intervals in the circumferential direction of the exhaust pipe 10, that is, at a diameter position of the exhaust pipe 10. Further, the two injection nozzles 20 are attached so that their injection axes 20a are inclined rearward in the exhaust gas flow direction and intersect at substantially one point. As described above, since the fuel injection nozzle 20 is formed so that the injection axis 20a is inclined rearward from the nozzle body center line 21a, a large attachment angle of each fuel injection nozzle 20 to the exhaust pipe 10 is taken. Can be installed structurally. However, the mounting conditions such as the angle formed by the two fuel injection nozzles 20 and the angle formed by the axis of the exhaust pipe 10 are appropriately determined depending on the diameter of the exhaust pipe 10, the exhaust gas flow velocity, the distance to the catalyst 11, and the like. Is set.

  Next, the operation of the exhaust pipe fuel addition method of the diesel engine will be described.

The NO _x emission amount from the engine 1 varies depending on the engine speed, the accelerator opening, and the like. The ECU7 shown in FIG. 1, NO _X emission map for NO _X emissions from the engine 1 to vary by such a driving state is stored. The ECU 7 calculates the NO _x emission amount of the engine 1 based on this NO _x emission amount map, and integrates the NO _x occlusion amount occluded in the catalyst 11.

As _the NO _X storage agent carried on the coat layer of the catalyst 11, for example in the case of using Ba, the NO _X discharged from the engine 1 is reacted with O ₂ in the exhaust gas in the catalyst 11, further catalyst 11 in Ba (NO ₃ ) ₂ is produced by reacting with BaO and BaCO _3, and is stored in the catalyst 11 in this state. Thus, the exhaust gas is discharged into the atmosphere through the muffler 12 and the like in a state where the NO _x concentration is extremely low.

When the ECU 7 determines that the NO _x storage amount by the catalyst 11 exceeds a predetermined amount and the catalyst temperature is equal to or higher than the catalyst reducible temperature (for example, 200 to 450 ° C.), the fuel injection in the exhaust pipe 10 is performed. The electromagnetic solenoid of the nozzle 20 is activated. When the electromagnetic solenoid is activated, the valve shaft 30 shown in FIG. 2 is pulled up in the fuel injection nozzle 20, and the seat portion 31 of the valve shaft 30 is separated from the valve seat 23 of the nozzle body 21. As a result, the pressurized fuel from the feed pump 4 is injected from the fuel supply hole 22 through the guide hole 24 into the exhaust pipe 10 through the ejection hole 25. Since the feed pump 4 is for supplying fuel from the fuel tank 5 to the supply pump 3, the fuel pressure is relatively low.

By adding fuel into the exhaust pipe 10, the oxygen concentration in the exhaust gas decreases, and HC, CO, CO ₂ or H _{2 in} the exhaust gas as a reducing agent increases. As a result, Ba (NO ₃ ) ₂ stored in the catalyst 11 reacts with the reducing agent and is reduced to N ₂ . Further, the catalyst 11 acts as a highly selective reduction catalyst, and the NO ₃ reacts with HC and CO in the exhaust gas to become harmless N ₂ , CO ₂ and H ₂ O, and is discharged into the atmosphere. In this way, the ECU 7 operates the electromagnetic solenoid of the fuel injection nozzle 20 to appropriately control the injection amount and injection timing of the fuel injection in the exhaust pipe 10. When it is estimated that the reduction regeneration of the catalyst 11 is almost completed, the fuel injection from the fuel injection nozzle 20 is stopped.

  As shown in FIG. 6, the exhaust pipe fuel addition method of the diesel engine is such that two fuel injection nozzles 20 are arranged so that their injection axes 20 a intersect each other, so that they are injected from each injection nozzle 20. The fuels collide and mix with each other to achieve optimal atomization, and the injected fuel is prevented from adhering to the inner wall of the exhaust pipe. Therefore, most of the fuel injected from the fuel injection nozzle 20 is instantly vaporized in the exhaust gas. For this reason, as shown in FIG. 7, even with a small amount of fuel, the fuel vapor concentration in the exhaust pipe 10 suddenly rises to near the theoretical fuel concentration, the air-fuel ratio of the exhaust gas instantaneously becomes rich, and the exhaust gas purification catalyst Can be sufficiently reduced and regenerated. As described above, since sufficient reduction regeneration can be performed with a small amount of fuel, the fuel consumption is remarkably improved.

  Further, since the two fuel injection nozzles 20 are arranged at equal intervals in the circumferential direction of the exhaust pipe 10, the collision and mixing of the injected fuel are performed uniformly, and the fuel vapor is uniformly supplied to the catalyst 11. The Note that the fuel injection nozzles 20 do not necessarily need to be disposed at substantially equal intervals in the circumferential direction. Further, since the injection axes 20a of the two fuel injection nozzles 20 are arranged so as to intersect at substantially one point, the injected fuel collides and mixes more reliably, and the injected fuel adheres to the inner wall of the exhaust pipe. This is further prevented. The injection axis 20a is not necessarily arranged so as to intersect at substantially one point.

  In the above-described diesel engine exhaust pipe fuel addition system, two fuel injection nozzles 20 are disposed in the exhaust pipe 10. These two fuel injection nozzles 20 also prevent the injected fuel from adhering to the inner wall of the exhaust pipe with a very high probability. However, the fuel injection nozzle 20 is not necessarily limited to two, and may be three or more.

  Further, fuel is supplied from the feed pump 4 of the diesel engine 1 to the fuel injection nozzle 20. However, the fuel supply source is not necessarily limited to the feed pump, and for example, high-pressure fuel supplied from the common rail 2 can be used by adding improvements for high-pressure injection to the hall type fuel injection nozzle.

Although the above-described diesel engine exhaust pipe fuel addition method is implemented for the NO _x storage reduction catalyst 11, it is not limited to this, but other reduction regeneration type such as DPNR. Of course, the same can be applied to the catalyst. Moreover, the above-described diesel engine exhaust pipe fuel addition system is merely an example, and various modifications are possible based on the spirit of the present invention, which are not excluded from the scope of the present invention.

It is a trial figure which shows the exhaust pipe fuel addition system of the diesel engine of this invention. It is side surface sectional drawing which shows the fuel-injection nozzle of FIG. It is a bottom view which shows the fuel-injection nozzle of FIG. It is a bottom view which shows another fuel injection nozzle. It is a bottom view which shows another fuel injection nozzle. It is side surface sectional drawing which shows the attachment state of the fuel-injection nozzle of FIG. It is a graph which shows the action | operation of the fuel-injection nozzle of FIG. It is side surface sectional drawing which shows the conventional hall | hole type fuel injection nozzle. It is a bottom view which shows the hall | hole type fuel injection nozzle of FIG. It is side surface sectional drawing which shows the conventional slit type fuel injection nozzle. It is a bottom view which shows the slit type fuel injection nozzle of FIG. It is a graph which shows the attachment state of the conventional fuel injection nozzle. It is a graph which shows the action | operation of the conventional fuel injection nozzle.

Explanation of symbols

1 Diesel engine 2 Common rail 3 Supply pump 4 Feed pump 5 Fuel tank 6 Fuel filter 7 ECU
DESCRIPTION OF SYMBOLS 10 Exhaust pipe 11 Catalyst 12 Muffler 20 Fuel injection nozzle 20a Injection axis 21 Nozzle body 21a Nozzle body center line 22 Fuel supply hole 23 Valve seat 24 Guide hole 25 Injection hole 30 Valve shaft 31 Seat part 36 Fuel injection nozzle 37 Injection hole 38 Fuel Injection nozzle 39 Injection hole 50 Hall type fuel injection nozzle 50a Injection hole 51 Slit type fuel injection nozzle 51a Injection hole 52 Exhaust pipe 53 Inner wall

Claims (6)

  An exhaust gas purification catalyst (11) provided with a fuel injection nozzle (20, 36, 38) in an exhaust pipe (10) of a diesel engine (1), and injecting fuel from the fuel injection nozzle and disposed in the exhaust pipe In the diesel engine exhaust pipe fuel addition system for performing regenerative regeneration of the diesel engine, the fuel injection nozzle comprises a plurality of fuel injection nozzles and the injection axes (20a) are arranged to cross each other. Exhaust pipe fuel addition method.   2. The exhaust pipe of a diesel engine according to claim 1, wherein the plurality of fuel injection nozzles (20, 36, 38) are arranged at substantially equal intervals in a circumferential direction of the exhaust pipe (10). Fuel addition method.   The diesel engine according to claim 1 or 2, wherein the plurality of fuel injection nozzles (20, 36, 38) are arranged so that the injection axis (20a) intersects at substantially one point. Exhaust pipe fuel addition method.   The fuel injection nozzle comprises a hole type fuel injection nozzle (20, 36) or a slit type fuel injection nozzle (38) having one or two injection holes (25, 37, 39). Item 4. An exhaust pipe fuel addition system for a diesel engine according to any one of Items 1 to 3.   The diesel fuel according to claim 4, wherein the fuel injection nozzle (20, 36, 38) is formed such that the injection axis (20a) is inclined rearward from the nozzle body center line (21a). Engine exhaust pipe fuel addition method. The diesel engine according to any one of claims 1 to 5, wherein the fuel injection nozzle (20, 36, 38) is supplied with fuel from a feed pump (4) of the diesel engine (1). Exhaust pipe fuel addition method.

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