Patent Application
20060248881
The present invention relates to a system for injecting fuel into a diesel engine exhaust pipe, suitable for use in a diesel engine that includes a NOx occlusion reduction type catalyst or DPNR or other reduction regeneration type catalyst as an exhaust gas posttreatment device.
In recent years, various systems have been developed for reducing particulate matter (hereinafter referred to as the PM) and NOx in an exhaust gas. The PM is composed of an SOF, soot, and sulphate+absorbed water. The SOF, which is composed of unburned fuel and oil, and HC and CO in the exhaust gas are oxidized and purified by an oxidation catalyst. A diesel particulate filter (hereinafter referred to as the DPF) is capable of considerably reducing the PM and used to make diesel engine automobiles environmentally friendly. The DPF comprises a heat-resistant filter, which is capable of capturing the PM with high efficiency, and a filter regeneration device, which is used to remove the PM captured by the filter. Some filter regeneration devices regenerate the filter by burning the captured PM away with a light oil burner or the like.
Meanwhile, the exhaust gas composition for use in a diesel engine is in an extremely unfavorable environment for catalysts because it is always in an oxygen excess region, scarce of an element that serves as a reducer, and distributed over a wide temperature range. In this oxygen excess environment, a NOx occlusion reduction type catalyst is available as a catalyst for NOx purification. The NOx occlusion reduction type catalyst exhibits an extremely high NOx reduction rate. Therefore, when very stringent NOx control requirements are to be complied with, the use of a NOx occlusion reduction type catalyst is a workable choice. A diesel particulate-NOx reduction system (hereinafter referred to as the DPNR), which is a combination of the NOx occlusion reduction type catalyst and the aforementioned DPF, is also available.
When the aforementioned NOx occlusion reduction type catalyst or DPNR is employed, it is necessary to remove oxygen from NO3, which is formed upon NOx occlusion, and use the removed oxygen to perform a filter regeneration process. A system for injecting fuel into an exhaust pipe (disclosed, for instance, by Patent Document 1), which injects fuel into an exhaust pipe for the purpose of increasing the amount of HC, CO, CO2, or H2, is used as a system for oxygen removal and filter regeneration. For example, this system introduces pressurized fuel from an engine feed pump, and injects the fuel from a holed fuel injection nozzle 50 (see
The holed fuel injection nozzle 50 injects fuel, for instance, from eight circular injection openings 50a in the leading end. The slit fuel injection nozzle 51 injects fuel from one or a plurality of injection slits 51a in the leading end. To provide adequate catalyst reduction and regeneration, it is necessary to provide a rich air-fuel ratio by quickly raising the fuel vapor concentration in the exhaust pipe.
Patent Document 1: Japanese Patent Laid-open No.2000-356137
As described above, the conventional system for injecting fuel into a diesel engine exhaust pipe injects fuel into the exhaust pipe via a holed fuel injection nozzle 50 or a slit fuel injection nozzle 51. The holed fuel injection nozzle 50 injects the fuel, for instance, from eight circular injection openings 50a in the leading end. The slit fuel injection nozzle 51 injects the fuel from one or a plurality of injection slits 51a in the leading end.
Therefore, the injected fuel streaks in the exhaust pipe 52 as shown in
As such being the case, the conventional system for injecting fuel into a diesel engine exhaust pipe cannot provide adequate catalyst reduction and regeneration because it cannot quickly raise the fuel vapor concentration in the exhaust pipe. To raise the fuel vapor concentration as needed for catalyst reduction and regeneration, it is necessary to inject a large amount of fuel. However, injecting a large amount of fuel decreases fuel efficiency.
The present invention has been made to solve the above problem. It is an object of the present invention to provide a system for injecting fuel into diesel engine exhaust pipe for adequately reducing and regenerating an exhaust gas purification catalyst and remarkably increasing fuel efficiency by preventing injected fuel from adhering to the inner wall of the exhaust pipe and quickly raising the fuel vapor concentration in the exhaust pipe to a level close to a theoretical fuel vapor concentration.
To solve the above problem, the present invention provides a system for injecting fuel into a diesel engine exhaust pipe for use in a diesel engine that includes a fuel injection nozzle in its exhaust pipe. This system injects fuel from the fuel injection nozzle and reduces and regenerates an exhaust gas purification catalyst that is installed in the exhaust pipe. The fuel injection nozzle comprises a plurality of injection nozzles whose injection axis lines intersect with each other. The injection axis line means an injection center line that indicates the injection direction of each nozzle.
The employed fuel injection nozzle comprises the plurality of fuel injection nozzles, which are installed so that their injection axis lines intersect with each other. Therefore, the fuels injected from the fuel injection nozzles collide with each other and mix to provide optimum atomization, thereby preventing the injected fuels from adhering to the inner wall of the exhaust pipe.
It is preferred that the plurality of fuel injection nozzles be arranged in the circumferential direction of the exhaust pipe and positioned at substantially equal spacing intervals. When the plurality of fuel injection nozzles are arranged in the circumferential direction of the exhaust pipe and positioned at substantially equal spacing intervals, the fuels injected from the fuel injection nozzles uniformly collide with each other and mix within the exhaust pipe. As a result, the fuel vapor is evenly supplied to the catalyst.
It is preferred that the plurality of fuel injection nozzles be positioned so as to intersect their injection axis lines at substantially one point. When the plurality of fuel injection nozzles are positioned so as to intersect their injection axis lines at substantially one point, the fuels injected from the nozzles collide with each other and mix with increased certainty, thereby further preventing the injected fuels from adhering to the inner wall of the exhaust pipe.
It is preferred that the fuel injection nozzles be holed or slit fuel injection nozzles having one or two injection openings. The system according to the present invention causes the fuels injected from the fuel injection nozzles to collide with each other and mix, thereby preventing the injected fuels from adhering to the inner wall of the exhaust pipe. Therefore, the optimum nozzles are holed or slit fuel injection nozzles that inject fuel linearly. Further, the use of one or two injection openings is more appropriate than the conventional use of eight or more injection openings because the use of one or two injection openings provides more effective fuel collision and mixture.
It is preferred that the injection axis lines of the fuel injection nozzles be inclined rearward from the nozzle main body center lines. The system according to the present invention assumes that the injection axis lines of the fuel injection nozzles are inclined rearward, that is, in an exhaust gas flow direction. When the injection axis lines are inclined rearward from the nozzle main body center line, the injection nozzle mounting angle relative to the exhaust pipe is allowed to be great. Consequently, the injection nozzle structure is such that the injection nozzles can be installed with ease.
For example, a diesel engine feed pump supplies fuel to the fuel injection nozzles. The system for injecting fuel into diesel engine exhaust pipe fuel according to the present invention is particularly suitable for a situation where relatively low pressure fuel supplied from the feed pump is to be injected.
As described in detail above, the present invention provides a system for injecting fuel into a diesel engine exhaust pipe for use in a diesel engine that includes a fuel injection nozzle in its exhaust pipe. This system injects fuel from the fuel injection nozzle and reduces and regenerates an exhaust gas purification catalyst that is installed in the exhaust pipe. The fuel injection nozzle comprises a plurality of injection nozzles whose injection axis lines intersect with each other. Therefore, the present invention prevents injected fuel from adhering to the inner wall of the exhaust pipe, and ensures that the fuel vapor concentration in the exhaust pipe is close to a theoretical fuel vapor concentration. This makes it possible to adequately reduce and regenerate the exhaust gas purification catalyst and remarkably increase fuel efficiency.
A system for injecting fuel into a diesel engine exhaust pipe according to an embodiment of the present invention will now be described in detail with reference to FIGS. 1 to 7.
As shown in
An exhaust pipe 10 contains, for instance, two fuel injection nozzles 20, a NOx occlusion reduction type catalyst 11, which is an example of a reduction regeneration type catalyst, and a muffler 12. The ECU 7 is electrically connected to the fuel injection nozzle in the engine 1, the supply pump 3, the feed pump 4, the fuel injection nozzles 20 in the exhaust pipe 10, and the like.
The NOx occlusion reduction type catalyst 11 is a so-called NOx occlusion reduction type catalyst that occludes NOx in an exhaust gas flow in the exhaust pipe 10, and performs a regeneration process on the occluded NOx by increasing the amount of HC, CO, CO2, or H2 in the exhaust gas. The catalyst 11 includes a monolith carrier for which a lattice-shaped path is formed in the direction of an exhaust gas flow, and a coat layer that is formed on the monolith carrier and used to support a precious metal and a NOx occlusion agent. Pt is used, for instance, as the precious metal. Li, Na, K, Cs, or other alkaline metal, Mg, Ca, Ba, or other alkaline earth metal, or Y, La, Ce, Pr, Nd, Eu, Gd, Dy, or other rare earth metal is used, for instance, as the NOx occlusion agent. Alumina or the like is used as the coat layer.
As shown in
The valve stem 30 is opened/closed by a solenoid, not shown, that is controlled by the ECU 7. The fuel injection nozzle may be a holed fuel injection nozzle 36 having two injection holes 37 as shown in
The fuel injection nozzle described above is not limited to a holed fuel injection nozzle or slit fuel injection nozzle. Further, the number of injection holes is not limited to one or two.
As shown in
The operation performed by the system for injecting fuel into a diesel engine exhaust pipe will now be described.
The amount of NOx that is discharged from the engine 1 varies, for instance, with the engine speed and accelerator opening. The ECU 7, which is shown in
When, for instance, Ba is used as the NOx occlusion agent, which is supported by the coat layer of the catalyst 11, the NOx discharged from the engine 1 reacts with O2 in the exhaust gas within the catalyst 11. The NOx further reacts with BaO and BaCO3 in the catalyst 11 to generate Ba(NO3)2. In the resulting state, the NOx is occluded by the catalyst 11. With the NOx concentration extremely lowered, the exhaust gas is then discharged into the atmosphere via the muffler 12 and the like.
The ECU 7 activates the solenoid for the fuel injection nozzle 20 in the exhaust pipe 10 when it judges that a predetermined amount is exceeded by the amount of NOx occluded by the catalyst 11 and that the catalyst temperature is not lower than a catalyst reduction temperature (e.g., 200 to 450° C.). When the solenoid is activated, the valve stem 30 shown in
When the fuel is injected into the exhaust pipe 10 as described above, the oxygen concentration in the exhaust gas decreases and HC, CO, CO2, or H2 in the exhaust gas, which serves as a reducer, increases in amount. As a result, Ba(NO3)2, which is occluded by the catalyst 11, reacts with the above reducer and reduces to N2. Further, the catalyst 11 acts as a highly selective reduction catalyst so that the above NO3 reacts with HC and CO in the exhaust gas to generate harmless N2, CO2, and H2O, which are eventually discharged into the atmosphere. As described above, the ECU 7 activates the solenoid for the fuel injection nozzle 20 to properly control the amount of fuel injection in the exhaust pipe 10 and the fuel injection timing. When it is estimated that the reduction and regeneration of the catalyst 11 are virtually completed, the ECU 7 stops the fuel injection from the fuel injection nozzle 20.
In the system for injecting fuel into a diesel engine exhaust pipe, the two fuel injection nozzles 20 are installed so that their injection axis lines 20a intersect with each other as shown in
Therefore, even when the amount of fuel is small, the fuel vapor concentration in the exhaust pipe 10 suddenly increases to a theoretical fuel vapor concentration as indicated in
Further, since the two fuel injection nozzles 20 are arranged in a circumferential direction of the exhaust pipe 10 and positioned at equal spacing intervals, the injected fuels uniformly collide with each other and mix. As a result, the fuel vapor is evenly supplied to the catalyst 11. The fuel injection nozzles 20 need not always be arranged in a circumferential direction and positioned substantially at equal spacing intervals. Furthermore, the two fuel injection nozzles 20 are positioned so that their injection axis lines 20a intersect at substantially one point. Therefore, the injected fuels collide with each other and mix with increased certainty, thereby further preventing the injected fuels from adhering to the inner wall of the exhaust pipe. The fuel injection nozzles 20 need not always be positioned so as to intersect their injection axis lines 20a at substantially one point.
In the system for injecting fuel into a diesel engine exhaust pipe described above, the exhaust pipe 10 is provided with two fuel injection nozzles 20. These two fuel injection nozzles 20 also prevent the injected fuels from adhering to the inner wall of the exhaust pipe with an extremely high probability. However, the number of fuel injection nozzles 20 is not always limited to two. Alternatively, three or more fuel injection nozzles may be used.
The feed pump 4 of the diesel engine 1 supplies fuel to the fuel injection nozzles 20. However, the source of fuel supply is not always limited to the feed pump. For example, the holed fuel injection nozzles may be modified to provide high-pressure injection and permit the use of high-pressure fuel supplied from the common rail 2.
The system for injecting fuel into a diesel engine exhaust pipe described above is applied to the NOx occlusion reduction type catalyst 11. However, the present invention is not limited to the use of the NOx occlusion reduction type catalyst 11. The present invention can also be applied to a DPNR or other reduction regeneration type catalyst. The foregoing description of the system for injecting fuel into a diesel engine exhaust pipe is to be considered in all respects only as illustrative and not restrictive. It should be understood by those skilled in the art that various modifications may be made without departing from the spirit and scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-013747 | Jan 2004 | JP | national |
