JP2005163699A - Particulate filter regeneration method - Google Patents

Abstract

The present invention provides a particulate filter regeneration method capable of reliably avoiding a situation in which added HC cannot be completely processed on an oxidation catalyst of a particulate filter.
SOLUTION: HC is added to exhaust gas 3 upstream of a catalyst regeneration type particulate filter 6 installed in the middle of an exhaust pipe 4 and collected by reaction heat when the added HC undergoes an oxidation reaction on the catalyst. With regard to a method for forcibly regenerating the particulate filter 6 by burning the spent particulates, the filter bed temperature is controlled over the required time under a temperature condition higher than the catalyst activation temperature lower than the self-combustion temperature of the particulates by controlling the addition of HC. By this, most of the particulates are slowly incinerated by spontaneous fire from self-ignition by catalysis, and after that, the filter bed temperature is raised above the self-combustion temperature of the particulates by further HC addition. Finish incineration.
[Selection] Figure 1

Description

  The present invention relates to a method for regenerating a particulate filter.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot composed of carbonaceous matter and SOF content (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this kind 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.

  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.

  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.

  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.

  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 to perform forced regeneration of the particulate filter by adding HC (hydrocarbon) to the exhaust gas further upstream.

  In other words, if HC is added upstream of the particulate filter, the added HC undergoes an oxidation reaction on the oxidation catalyst of the particulate filter, and the heat of reaction raises the filter bed temperature and burns out the particulate. Thus, regeneration of the particulate filter is achieved.

Incidentally, the method of actively forcibly regenerating this type of particulate filter is also taken up in the following Patent Document 1 and Patent Document 2, and in the description in these documents, the fuel injection device of the engine is described. On the other hand, HC addition is executed by performing post-injection at a non-ignition timing later than the compression top dead center following the main injection of fuel performed near the compression top dead center.
JP 2003-83139 A JP 2003-155913 A

  However, conventionally, the amount of HC required to raise the filter bed temperature to the self-combustion temperature of the collected particulates (about 600 ° C.) is executed from the beginning. Since the particulate filter was forcibly regenerated by continuing to add HC with an amount slightly reduced from the initial HC addition amount to maintain the combustion temperature, the contact portion of the particulate filter with the porous thin wall of the particulate filter In this case, it is burned in advance within a few minutes with the assistance of the oxidation catalyst at a high temperature of about 600 ° C., and a large gap is formed here, so that the particulate deposition layer is lifted and divided apart, It is peeled off from the porous thin wall by the flow of exhaust gas and blown up behind each flow path. Results causes abnormal combustion, there is a possibility of causing deterioration of the catalyst on the particulate filter by overheating due to the abnormal combustion.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to eliminate abnormal combustion of particulates and to eliminate the possibility of causing catalyst deterioration in the particulate filter.

  The present invention adds HC to the exhaust gas upstream of the catalyst regeneration type particulate filter equipped in the middle of the exhaust pipe, and the particulates collected by the reaction heat when the added HC undergoes an oxidation reaction on the catalyst. In the method for forcibly regenerating the particulate filter by burning the particulate filter, by controlling the addition of HC, the filter bed temperature is maintained for a required time at a temperature condition higher than the catalyst activation temperature lower than the particulate self-combustion temperature. The majority of the particulates are slowly incinerated by spontaneous fire from self-ignition by catalysis, and after that, the filter bed temperature is raised above the self-combustion temperature of the particulates by further HC addition and finish incineration It is characterized by.

  Thus, in this way, most of the particulates are slowly incinerated by natural fire spreading, and when they are reduced to the amount that can be burned out at once, they are finished incinerated at the self-combustion temperature. The phenomenon that the deposited layer of the curate is peeled off from the porous thin wall and accumulated behind each flow path does not occur, and abnormal combustion of the particulate is avoided beforehand.

  In other words, the spontaneous spread of particulates also proceeds along the catalyst surface of the porous thin wall with the aid of the oxidation catalyst, but a large gap as in the case where the temperature is increased from the beginning to the high self-combustion temperature is lost. The phenomenon of rapid formation with the wall does not occur, and the natural fire spreads slowly while staying at the deposition site while the portions are in contact with the porous thin wall.

  Particulates deposited on the porous thin wall of the particulate filter burn so that the layer thickness gradually decreases without raising or dividing from the porous thin wall, and most of the particulates. When it is incinerated by natural fire spreading, it is incinerated at the self-combustion temperature and burned out at once.

  Since most of the particulates are slowly incinerated by spontaneous fire from self-ignition by catalysis, it is only necessary to carry out limited addition of HC to promote self-ignition of particulates and finish incineration. Thus, the amount of HC added is suppressed to the necessary minimum, and deterioration of fuel consumption is avoided as much as possible.

  Further, in the present invention, when raising the temperature to a temperature condition for slowly incinerating most of the particulates by natural flame spread, the after-treatment at a combustible timing immediately after the main injection up to a predetermined temperature that does not satisfy the temperature condition. Increase the temperature by injection or by using the after injection and exhaust throttle together, and then add HC by post-injection around 90-120 ° after compression top dead center to impregnate the particulate filter with HC mist. After that, it is preferable to raise the temperature to the above temperature condition by performing post-injection around 50 to 70 ° after compression top dead center.

  Furthermore, when more specifically practicing the present invention, it is preferable that the temperature condition for slowly incinerating most of the particulates by natural fire is about 350 to 580 ° C., and the particulates are finish incinerated. Further HC addition for this purpose may be performed by post-injection around 50 to 120 ° after compression top dead center.

  According to the above-described method for regenerating a particulate filter of the present invention, a phenomenon in which a particulate deposition layer is peeled off from a porous thin wall and blown up behind each flow path does not occur. Since abnormal combustion can be avoided in advance, the possibility of catalyst deterioration in the particulate filter due to overheating due to this abnormal combustion can be eliminated, and HC that promotes self-ignition of particulates and finish incineration Since the addition only needs to be executed in a limited manner, various excellent effects can be obtained, such as the amount of HC added can be suppressed to the minimum necessary and deterioration of fuel consumption can be avoided as much as possible.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 3 show an example of an embodiment of the present invention. In the particulate filter regeneration method of the present embodiment, as shown in FIG. 1, an automobile diesel engine 1 is passed through an exhaust manifold 2 as shown in FIG. When a catalyst regeneration type particulate filter 6 integrally carrying an oxidation catalyst is accommodated in the muffler 5 of the exhaust pipe 4 through which the exhaust gas 3 is exhausted (front stage of the particulate filter 6) The filter case 7 that holds the particulate filter 6 forms an outer cylinder of the muffler 5.

  That is, a particulate filter 6 as shown in an enlarged view in FIG. 2 is accommodated inside the filter case 7, and this particulate filter 6 has a porous honeycomb structure made of ceramic, and has a lattice structure. The inlets of the respective flow paths 6a partitioned in a shape are alternately sealed, and the outlets of the flow paths 6a whose inlets are not sealed are sealed. Only the exhaust gas 3 that has permeated through the porous thin wall 6b is discharged to the downstream side.

  In the example shown here, a temperature sensor 8 is provided on the outlet side of the filter case 7, and a detection signal 8a of the temperature sensor 8 is supplied to a control device 9 constituting an engine control computer (ECU: Electronic Control Unit). In this control device 9, the detected value of the temperature sensor 8 is used as a substitute value for the filter bed temperature for the HC addition control in the forced regeneration of the particulate filter 6 as described in detail below. It is designed to be used.

  Further, since the control device 9 also serves as an engine control computer, it is also responsible for control relating to fuel injection. More specifically, the control device 9 detects an accelerator opening as a load of the diesel engine 1. Fuel injection for injecting fuel into each cylinder of the diesel engine 1 based on an accelerator opening signal 11a from the engine 11 (load sensor) and a rotation speed signal 12a from the rotation sensor 12 that detects the engine rotation speed of the diesel engine 1 A fuel injection signal 10 a is output to the device 10.

  Here, the fuel injection device 10 is composed of a plurality of injectors provided for each cylinder, and the solenoid valve of each injector is appropriately controlled to be opened by the fuel injection signal 10a, and the fuel injection timing. In addition, the injection amount is appropriately controlled.

  On the other hand, in the control device 9, the fuel injection signal 10a in the normal mode is determined based on the accelerator opening signal 11a and the rotation speed signal 12a. On the other hand, the particulate filter 6 needs to be forcibly regenerated. In this case, the normal mode is switched to the regeneration mode, and after the main injection of fuel performed near the compression top dead center (crank angle 0 °), the post injection is performed at an appropriate timing later than the compression top dead center. The fuel injection signal 10a of the pattern is determined.

  That is, when post injection is performed at a timing later than the compression top dead center following main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 3 by this post injection. Thus, the unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 6, and the catalyst bed temperature rises due to the reaction heat, and the particulates in the particulate filter 6 are burned and removed. .

  However, in this embodiment, the particulates spontaneously spread under a temperature condition (about 350 to 580 ° C.) where the particulates deposited on the particulate filter 6 are lower than the self-combustion temperature (about 600 ° C.) and higher than the catalyst activation temperature. Based on the knowledge that the control unit 9 controls the post-injection (HC addition), the filter bed temperature is maintained for the required time under the above temperature condition, and most of the particulates are self-catalyzed by the catalytic action. Slow incineration is performed by spontaneous fire from ignition, and then the filter bed temperature is raised to the self-combustion temperature of the particulates by further addition of HC, and finish incineration is performed.

  Further, when the temperature condition for spontaneously spreading the particulates is not satisfied when the regeneration mode is switched, the fuel injection device 10 can combust immediately after the main injection by the fuel injection signal 10a from the control device 9. After injection is performed at the timing, the exhaust brake 13 on the upstream side of the particulate filter 6 is throttled as exhaust throttling means by the opening command signal 13a from the control device 9.

  Thus, when forced regeneration of the particulate filter 6 is required, when the control device 9 switches from the normal mode to the regeneration mode, the temperature condition (about 350 to 580 ° C.) for spontaneously spreading the particulates is reached. Up to a predetermined temperature (about 240 ° C.) that is not satisfied, after-injection by the fuel injection device 10 is executed, and the fuel by the after-injection is burned at a timing that is difficult to be converted into output, thereby reducing the thermal efficiency of the diesel engine 1 and generating heat of the fuel The amount of heat not used for power in the amount increases, and the exhaust temperature rises.

  Further, it is better that the exhaust brake 13 is also throttled in response to the execution of the after injection, and the exhaust gas 3 is increased in pressure upstream from this, so that the exhaust temperature is raised, and the exhaust resistance is increased so that the cylinder is increased. It is difficult for the intake air having a relatively low temperature to flow into it, and the residual amount of the exhaust gas 3 having a relatively high temperature is increased, and the air in the cylinder containing a large amount of the exhaust gas 3 having a relatively high temperature becomes the next compression stroke. The exhaust gas temperature can be further increased by compressing at the end of the explosion stroke.

  When the exhaust gas 3 is heated to a predetermined temperature by these after-injection and exhaust throttling, post-injection is performed for about 5 to 10 seconds at a relatively late timing around 90 to 120 ° after compression top dead center. The particulate filter 6 is impregnated with the HC mist added to the exhaust gas 3, and then the post-injection is performed for about 5 seconds at a relatively early timing around 50 to 70 ° after the compression top dead center. The temperature of the gas 3 is raised to about 350 to 400 ° C.

  That is, when post injection is executed at a relatively early timing around 50 to 70 ° after compression top dead center, the fuel of the post injection is ignited in the cylinder and the temperature of the exhaust gas 3 is increased to about 350 to 400 ° C. It will be.

  As a result, the HC mist impregnated in the particulate filter 6 is oxidized by the heat of the exhaust gas 3 heated to about 350 to 400 ° C., and the filter bed temperature rises at once due to the reaction heat and collected. The spent particulates are self-ignited by the catalytic action, and then gradually burn and spread by natural fire spread.

  And until the natural flame spread of particulates becomes full-scale, the temperature conditions necessary for the natural flame spread are maintained for the required time while appropriately using the after-injection and the exhaust throttle, thereby slowing the majority of the particulates by the natural flame spread. Incinerate.

  Thereafter, the temperature at which the outlet temperature of the particulate filter 6 exceeds 350 ° C. and the HC purification rate of the oxidation catalyst of the particulate filter 6 exceeds 100% as shown in the graph of FIG. If it is confirmed based on the detection value of the sensor 8, further post-injection is performed at a timing around 50 to 120 ° after compression top dead center, so that the filter bed temperature reaches the self-combustion temperature of about 600 ° C. of the particulates. Raise the temperature and incinerate.

  If forced regeneration of the particulate filter 6 is performed in this way, most of the particulates are slowly incinerated by natural fire spreading, and when the amount is reduced to the amount that can be burned out at once, it is finished incinerated at the self-combustion temperature. As a result, a phenomenon in which the particulate deposit layer is peeled off from the porous thin wall 6b and sprayed to the rear of each flow path 6a does not occur, and abnormal combustion of the particulate is avoided in advance.

  That is, in the prior art, since the particulates were tried to be incinerated at once by raising the temperature to the high self-combustion temperature from the beginning, as shown schematically in FIG. 4, the porous thin wall of the collected particulates shown in black The contact portion with respect to 6b is pre-incinerated within a few minutes with the assistance of the oxidation catalyst at a high temperature of about 600 ° C., and a large gap is formed here, so that the particulate deposition layer rises and Next, as shown schematically in FIG. 5, the gas is separated from the porous thin wall 6b by the flow of the exhaust gas 3 and blown and accumulated behind each flow path 6a, and the accumulated particulates cause abnormal combustion. There was a fear.

  On the other hand, the spontaneous spreading of particulates also proceeds along the catalyst surface of the porous thin wall 6b with the aid of the oxidation catalyst, but there is a large gap as in the case where the temperature is raised from the beginning to the high self-combustion temperature. The phenomenon of rapid formation between the porous thin wall 6b does not occur, and natural fire spread proceeds slowly while the portions remain in contact with the porous thin wall 6b and remain at the deposition site.

  Then, the particulates deposited on the porous thin wall 6b of the particulate filter 6 have a layer thickness without causing lifting or division from the porous thin wall 6b, as schematically shown in FIGS. As the particles gradually burn out, most of the particulates shown in black in the figure are burned by natural fire, and then burned at the self-combustion temperature and burned all at once. Note that even if the phenomenon shown in FIGS. 4 and 5 occurs again in finish combustion, the amount of soot accumulated in the rear portion is small, so that the temperature is not high enough to cause the catalyst to be thermally deteriorated.

  Therefore, according to the above-described embodiment, a phenomenon in which the particulate deposition layer is peeled off from the porous thin wall 6b and sprayed to the rear of each flow path 6a does not occur, and abnormal combustion of the sprayed particulates is prevented. Therefore, the possibility of catalyst deterioration in the particulate filter 6 due to overheating due to the abnormal combustion can be eliminated.

  In addition, since most of the particulates are slowly incinerated by spontaneous fire from self-ignition due to the oxidative heat of HC by catalysis, HC addition that promotes self-ignition of particulates and finish incineration is limitedly performed. Thus, the amount of HC added can be suppressed to the minimum necessary, and the deterioration of fuel consumption can be avoided as much as possible.

  The method for regenerating a particulate filter according to the present invention is not limited to the above-described embodiment. As a means for adding HC to the exhaust gas upstream of the particulate filter, the injection pattern of the fuel injection device is used. As an example of this type of HC addition, for example, from the exhaust manifold to the exhaust pipe, the post injection is performed at a timing that does not ignite later than the compression top dead center following the main injection. It is possible to separately provide an injector for adding HC at any location in the exhaust flow path, and to add HC to the exhaust gas by this injector, and to reduce the exhaust flow rate appropriately It is not always necessary to use an exhaust brake, and an exhaust throttle valve may be separately provided in the middle of the exhaust pipe. It, other, can of course be modified in various ways without departing from the gist of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which shows the detail of the particulate filter of FIG. It is a graph which shows the relationship between the HC purification rate of an oxidation catalyst, and temperature. It is a schematic diagram which shows the state by which the deposit layer of the particulate floated and was divided | segmented apart. FIG. 5 is a schematic diagram showing a state where the particulate deposition layer of FIG. 4 is accumulated behind each flow path. It is a schematic diagram which shows a mode that most particulates are incinerated by natural fire spreading. It is a schematic diagram which shows the state which the natural fire spread further from FIG. It is a schematic diagram which shows the state which the natural fire spread further from FIG.

Explanation of symbols

3 exhaust gas 4 exhaust pipe 6 particulate filter 8 temperature sensor 8a detection signal 9 control device 10 fuel injection device 10a fuel injection signal 13 exhaust brake 13a opening command signal

Claims (4)

  HC is added to the exhaust gas upstream from the catalyst regeneration type particulate filter installed in the middle of the exhaust pipe, and the collected particulates are burned by reaction heat when the added HC undergoes an oxidation reaction on the catalyst. In the method for forcibly regenerating the particulate filter, by controlling the addition of HC, the filter bed temperature is maintained for a required time at a temperature condition higher than the catalyst activation temperature lower than the self-combustion temperature of the particulate, and thereby the particulate It is characterized by the fact that most of it is incinerated slowly by spontaneous fire from self-ignition by catalysis, and then the filter bed temperature is raised to the self-combustion temperature of the particulate by further addition of HC and finish incineration. How to regenerate the particulate filter.   When raising the temperature to a temperature condition for slowly incinerating most of the particulates by natural fire, after injection at a combustible timing immediately after main injection up to a predetermined temperature that does not satisfy the temperature condition, or the after injection The temperature is raised by using an exhaust throttle together, and then post-injection is performed around 90 to 120 ° after compression top dead center to add HC and impregnate the particulate filter with HC mist. 2. The method for regenerating a particulate filter according to claim 1, wherein the temperature is raised to the temperature condition by performing post-injection around 50 to 70 degrees after the dead point.   The method for regenerating a particulate filter according to claim 1 or 2, wherein a temperature condition for slowly incinerating most of the particulates by natural fire is about 350 to 580 ° C.   The regeneration of a particulate filter according to claim 1, 2 or 3, characterized in that further HC addition for finishing incineration of the particulate is performed by post-injection at around 50 to 120 ° after compression top dead center. Method.

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