JP4094966B2 - Exhaust purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device.
[0002]
[Prior art]
Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.
[0003]
This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.
[0004]
Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust. For example, an appropriate amount for platinum-supported alumina A catalyst regeneration type particulate filter in which an oxidation catalyst formed by adding a rare earth element such as cerium is integrally supported is being put to practical use.
[0005]
That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.
[0006]
However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. If the operation state at the temperature continues, the particulate filter may not be regenerated well, and the particulate filter may fall into an excessive collection state, and the particulate filter is in a stage where the amount of accumulated particulates has increased. It has been considered that the particulate filter is forcibly regenerated by adding fuel to the exhaust gas further upstream.
[0007]
That is, if fuel is added by post-injection or the like upstream of the particulate filter, the HC gas generated by the added fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter, and the heat of reaction causes the catalyst bed temperature to increase. The particulates are burned out and the particulate filter is regenerated.
[0008]
A method for forcibly regenerating this type of particulate filter is also described in the following Patent Document 1 and Patent Document 2, which are unpublished prior applications.
[0009]
[Patent Document 1]
Japanese Patent Application No. 2001-355061 [Patent Document 2]
Japanese Patent Application No. 2002-20374
In addition, in an exhaust purification system equipped with a flow-through type oxidation catalyst in front of the particulate filter, particularly for the purpose of supporting the oxidation reaction of collected particulates, the HC gas is oxidized by the oxidation catalyst in the previous stage of the particulate filter. The reaction generates heat of reaction, and the exhaust gas heated by the reaction heat is introduced into the particulate filter, so that it is possible to achieve forced regeneration of the particulate filter from a lower exhaust temperature. .
[0011]
[Problems to be solved by the invention]
However, in the past, it was usual to produce the oxidation catalyst supported on the particulate filter in the subsequent stage and the flow-through type oxidation catalyst in the previous stage with the same catalyst raw material, so platinum catalyst was to be supported on both. A large amount of precious metals such as these are required, and there is a problem that the implementation cost increases.
[0012]
The present invention has been made in view of the above-described circumstances, and an object thereof is to reduce the implementation cost in an exhaust purification apparatus equipped with an oxidation catalyst in the previous stage of a catalyst regeneration type particulate filter.
[0013]
[Means for Solving the Problems]
The present invention provides a filter case in the middle of an exhaust pipe through which exhaust gas from an internal combustion engine circulates. A flow-through type oxidation catalyst is accommodated in the front stage of the filter case, and a catalyst regeneration type partition is provided in the subsequent stage. In the exhaust gas purification apparatus containing the curate filter, the amount of noble metal per unit volume of the catalyst raw material supported on the downstream particulate filter is less than the amount of noble metal per unit volume of the catalyst raw material supported on the preceding oxidation catalyst , Fuel addition means for adding fuel to the exhaust gas upstream of the oxidation catalyst is provided .
[0014]
Thus, in this way, compared with the conventional method in which the same catalyst raw material as the catalyst raw material supported on the preceding stage oxidation catalyst is supported on the subsequent particulate filter, the catalyst supported on the subsequent particulate filter. The cost required for the raw material becomes low, and the implementation cost in the exhaust gas purification apparatus in which the oxidation catalyst is provided in the front stage of the catalyst regeneration type particulate filter is significantly reduced as compared with the prior art.
[0015]
On the other hand, with regard to the fact that the particulate filter can be regenerated without hindrance even if the same catalyst raw material as the catalyst raw material supported on the preceding oxidation catalyst is not supported on the subsequent particulate filter, the inventors have conducted intensive research. It has been confirmed through the process.
[0016]
That is, when the catalyst regeneration type particulate filter is equipped with an oxidation catalyst in the previous stage, the exhaust gas heated by the reaction heat generated by the oxidation reaction in the previous stage oxidation catalyst is introduced into the particulate filter, By introducing the exhaust gas whose temperature has been increased, the catalyst bed temperature of the particulate filter is increased from the front part to the rear part, and the oxidation treatment of the particulates is favorably promoted in the entire region.
[0017]
For this reason, in the latter-stage particulate filter, its own catalyst bed temperature is stably maintained at a high temperature by the reaction heat accompanying the particulate oxidation treatment performed in the entire region, and is supported on the latter-stage particulate filter. Even if the amount of the precious metal per unit volume is smaller than that of the preceding oxidation catalyst side, the collected particulates can be burned out without any trouble, and the particulate filter can be regenerated well.
[0018]
In the present invention, employing a fuel injector for injecting fuel into each cylinder of the internal combustion engine as fuel addition means, leaving a lot of unburned fuel by controlling the fuel injection into the cylinder in the exhaust gas Thus, the fuel may be added.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
1 to 3 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 is an intake pipe 5. And the intake air 4 pressurized by the compressor 2a is sent to the intercooler 6 to be cooled, and the intake air 4 further flows from the intercooler 6 to the intake manifold 7. It is guided and distributed to each cylinder 8 of the diesel engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 1).
[0021]
Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.
[0022]
A filter case 12 is interposed in the middle of the exhaust pipe 11, and a catalyst regeneration type particulate filter 13 that integrally carries an oxidation catalyst is provided in the rear stage in the filter case 12. As shown schematically in FIG. 2, the particulate filter 13 has a porous honeycomb structure made of ceramic, and each flow path 13 a (cell) partitioned in a lattice shape. The flow passages 13a in which the inlets are alternately sealed and the entrances are not sealed are sealed in the outlets, and permeate through the porous thin walls 13b partitioning the flow passages 13a. Only the exhaust gas 9 is discharged downstream.
[0023]
A flow-through type oxidation catalyst 14 having a honeycomb structure as shown in an enlarged view in FIG. 3 is accommodated in the filter case 12 immediately before the particulate filter 13. A large number of flow paths 14a (cells) opened in the direction are defined by the cell walls 14b.
[0024]
Then, the amount X [g / L] of noble metal per unit volume of the catalyst raw material supported on the particulate filter 13 at the subsequent stage is the amount Y [g / L of noble metal per unit volume of the catalyst raw material supported on the preceding oxidation catalyst 14. ].
[0025]
Here, the amount of noble metal Y [g / L] per unit volume of the catalyst raw material supported on the preceding oxidation catalyst 14 is appropriately set so that the HC gas generated by the added fuel can be oxidized at the target temperature without any trouble. On the other hand, the amount X [g / L] of the noble metal per unit volume of the catalyst raw material supported on the particulate filter 13 in the latter stage is within the range in which the regeneration without any trouble described later can be secured. ] Is set to be less as much as possible.
[0026]
In the example shown here, a control device 15 constituting an engine control computer (ECU: Electronic Control Unit) is connected to an accelerator sensor 16 (load sensor) that detects the accelerator opening as a load of the diesel engine 1. An accelerator opening signal 16a and a rotation speed signal 17a from a rotation sensor 17 that detects the engine rotation speed of the diesel engine 1 are input. The accelerator opening signal 16a and the rotation speed signal 17a are input to the accelerator opening signal 16a. Based on this, a fuel injection signal 18 a is output to a fuel injection device 18 that injects fuel into each cylinder 8 of the diesel engine 1.
[0027]
Here, the fuel injection device 18 is composed of a plurality of injectors 19 provided for each cylinder 8, and the electromagnetic valves of these injectors 19 are appropriately controlled to open by the fuel injection signal 18a. The injection timing (valve opening timing) and the injection amount (valve opening time) are appropriately controlled.
[0028]
On the other hand, in the control device 15, the fuel injection signal 18a in the normal mode is determined based on the accelerator opening signal 16a and the rotation speed signal 17a. On the other hand, it is necessary to perform regeneration control of the particulate filter 13. In this case, the mode is switched from the normal mode to the regeneration mode, and the non-ignition timing (start timing is 90 ° crank angle) after the main injection of fuel performed near the compression top dead center (crank angle 0 °). The fuel injection signal 18a is determined so as to perform the post-injection in the range of .degree.
[0029]
That is, when post-injection is performed at a non-ignition timing later than the compression top dead center following main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 9 by this post-injection. As a result, the HC gas generated by the unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 13, and the catalyst bed temperature rises due to the reaction heat, thereby causing the particulate matter in the particulate filter 13. Will be burned off.
[0030]
Thus, when it becomes necessary to perform regeneration control of the particulate filter 13, the regeneration mode is selected by the control device 15, and the fuel injection pattern is switched from the normal mode to the regeneration mode by the control device 15. As a result of adopting an injection pattern in which post-injection is performed at the timing of non-ignition later than the compression top dead center following main injection, fuel added unburned into exhaust gas 9 by the post-injection is highly concentrated by thermal decomposition As a result, the exhaust gas 9 passing through the oxidation catalyst 14 is significantly heated by the oxidation reaction by the oxidation catalyst 14 and is heated by the oxidation catalyst 14. When the gas 9 is introduced into the particulate filter 13, the entire area of the particulate filter 13 is heated to a high temperature. It is satisfactorily burned off so that the regeneration of the particulate filter 13 is achieved.
[0031]
Here, if it supplementarily demonstrates, if the oxidation catalyst 14 is not arrange | positioned in the front | former stage of the particulate filter 13, the high concentration HC gas produced | generated by fuel addition will be the particulate filter 13. However, the substantial oxidation reaction in this type tends to be biased toward the rear part of the particulate filter 13, and only the rear part of the particulate filter 13 is heated to the front. Particulate burnout is likely to occur in the part.
[0032]
On the other hand, if the oxidation catalyst 14 is arranged in front of the particulate filter 13, even if the oxidation reaction in the oxidation catalyst 14 is biased toward the rear part, the temperature of the exhaust gas 9 passing therethrough is high. If possible, the introduction of the exhaust gas 9 makes it possible to increase the temperature of the particulate filter 13 over the entire region from the front portion to the rear portion.
[0033]
Then, when the temperature of the entire area of the particulate filter 13 is increased and the oxidation process of the particulates is favorably promoted throughout the entire area, the catalyst bed temperature of the particulate filter 13 itself is stabilized by the reaction heat accompanying the oxidation process. As a result, the noble metal amount X [g / L] per unit volume supported on the subsequent particulate filter 13 is changed to the noble metal amount Y per unit volume supported on the preceding oxidation catalyst 14. Even if the amount is less than [g / L], the collected particulates can be burned out without any hindrance, and the particulate filter 13 can be favorably regenerated.
[0034]
Therefore, according to the above-described embodiment, the same catalyst raw material as the catalyst raw material supported on the preceding oxidation catalyst 14 is supported on the subsequent particulate filter 13 as compared with the conventional method in which the latter particulate filter 13 supports the same catalyst raw material. The cost required for the catalyst raw material to be squeezed becomes low, and the implementation cost in the exhaust gas purification apparatus in which the oxidation catalyst 14 is provided in the preceding stage of the catalyst regeneration type particulate filter 13 can be significantly reduced.
[0035]
The exhaust emission control device of the present invention is not limited to the above-described embodiment. In the above embodiment, the fuel injection device is used as the fuel addition means, and the fuel is performed near the compression top dead center. Fuel is added to the exhaust gas by performing post-injection at a timing of non-ignition later than the compression top dead center following the main injection of the engine, but the timing of main injection into the cylinder is delayed from normal The fuel may be added to the exhaust gas, and only the means for adding fuel by controlling the fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas. In addition, an injector may be provided as a fuel addition means at an appropriate position of the exhaust pipe (or an exhaust manifold is acceptable), and fuel may be directly injected into the exhaust gas by this injector, It is of course that various changes and modifications may be made without departing from the scope and spirit of the present invention.
[0036]
【The invention's effect】
According to the above-described exhaust purification apparatus of the present invention, the same catalyst raw material as the catalyst raw material to be carried on the preceding oxidation catalyst is carried on the subsequent particulate filter as compared with the conventional method in which the latter particulate filter is carried. The cost required for the catalyst raw material to be reduced is low, and it is possible to achieve an excellent effect that the implementation cost in the exhaust purification apparatus equipped with an oxidation catalyst in the previous stage of the catalyst regeneration type particulate filter can be remarkably reduced as compared with the prior art.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment for carrying out the present invention.
2 is a cross-sectional view schematically showing the structure of the particulate filter shown in FIG. 1. FIG.
FIG. 3 is a perspective view showing the structure of the oxidation catalyst of FIG. 1 with a part cut away.
[Explanation of symbols]
1 Diesel engine (internal combustion engine)
8 cylinder 9 exhaust gas 12 filter case 13 particulate filter 14 oxidation catalyst 18 fuel injection device (fuel addition means)

Claims (2)

A filter case is placed in the middle of an exhaust pipe through which exhaust gas from the internal combustion engine flows, and a flow-through type oxidation catalyst is accommodated in the front stage of the filter case, and a catalyst regeneration type particulate filter is accommodated in the subsequent stage. In the exhaust gas purification apparatus, the amount of the noble metal per unit volume of the catalyst raw material supported on the particulate filter in the subsequent stage is less than the amount of the noble metal per unit volume of the catalyst raw material supported on the preceding oxidation catalyst. An exhaust emission control device comprising fuel addition means for adding fuel to exhaust gas upstream . A fuel injection device that injects fuel into each cylinder of the internal combustion engine is adopted as a fuel addition means, and fuel addition is performed by controlling fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas. The exhaust emission control device according to claim 1 , wherein the exhaust purification device is configured as described above.

Images