JP2004316441A - Method for raising temperature of particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize fuel addition by post injection while surely avoiding a problem of clogging caused by unprocessed fuel addition. <P>SOLUTION: In a method for raising temperature of a catalyst bed of a particulate filter 12 by reaction heat generated when fuel which is added under unburned condition into exhaust gas 9 by executing post injection at an incombustible timing later than a compression top dead center with following main injection in a diesel engine 1 side is oxidized on oxidization catalyst of the catalyst regeneration type particulate filter 12 installed in a middle of an exhaust pipe 11, after injection is executed at a combustible timing right after main injection and pre post injection for keeping ember to extent to suppress temperature drop in a expansion stroke is added in a period between the after injection and the post injection under an operation condition that temperature of exhaust gas 9 is a predetermined temperature or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for raising the temperature of a particulate filter.
[0002]
[Prior art]
Particulate matter (particulate matter) discharged from the diesel engine is mainly composed of soot composed of carbonaceous material and SOF component (Soluble Organic Fraction: soluble organic component) composed of a high-boiling hydrocarbon component. Although it has a composition containing a small amount of sulfate (mist-like sulfuric acid component), as a measure to reduce this kind of particulates, it is necessary to equip a particulate filter in the middle of the exhaust pipe through which exhaust gas flows. This has been done conventionally.
[0003]
This kind of particulate filter has a porous honeycomb structure made of ceramic such as cordierite, and the inlets of the respective flow paths partitioned in a lattice are alternately plugged, and the inlets are not plugged. The outlets of the flow passages are sealed so that only the exhaust gas that has passed through the thin porous wall that defines each flow passage is discharged to the downstream side.
[0004]
Since the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging, and the particulate filter is removed. It is necessary to regenerate, but in the normal diesel engine operating state, there is little chance of obtaining a high exhaust temperature enough for the particulates to self-burn, so for example, an appropriate amount of platinum supported on alumina Commercialization of a catalyst regeneration type particulate filter integrally supporting an oxidation catalyst to which a rare earth element such as cerium is added has been promoted.
[0005]
That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted, the ignition temperature is lowered, and the particulates can be burned and removed even at a lower exhaust temperature than before. Further, by performing post-injection at a non-ignition timing later than the compression top dead center on the diesel engine side following the main injection on the diesel engine side, fuel is added to the exhaust gas unburned, and the added fuel is added. The reaction heat when (hydrocarbon) is oxidized on the oxidation catalyst of the particulate filter raises the catalyst bed temperature of the particulate filter to actively combust and remove trapped particulates and desorb retained sulfate. It is possible to do.
[0006]
Incidentally, this type of fuel addition by post-injection on the diesel engine side is also described in the following prior application 1 and prior application 2.
[0007]
[Prior application 1]
Japanese Patent Application No. 2001-355061 [Prior application 2]
Japanese Patent Application No. 2002-20374 [0008]
[Problems to be solved by the invention]
However, when the fuel added to the exhaust gas by the post-injection undergoes an oxidation reaction on the oxidation catalyst of the particulate filter, the chance of contact with the oxidation catalyst increases toward the rear part of the particulate filter, and the oxidation reaction of the added fuel increases. Is activated, so that the temperature of the front part of the particulate filter is harder to rise than that of the rear part, and the amount of catalyst necessary for simply raising the catalyst bed temperature at the rear part of the particulate filter to about 600 ° C. or more is obtained. In the operation state where the temperature of the exhaust gas is low, the addition fuel that cannot be completely processed is accumulated in the front part of the particulate filter that is not so high in temperature (low in catalytic activity). The front part of the filter becomes sticky and wet and particulates Attached easily, here particulates particulate filter continues reservoir without being oxidized is a problem of causing clogging in the early stage.
[0009]
The present invention has been made in view of the above circumstances, and has as its object to realize post-injection fuel addition while reliably avoiding the problem of clogging caused by untreated added fuel.
[0010]
[Means for Solving the Problems]
According to the present invention, a catalyst regeneration type particulate filter is provided in the middle of an exhaust pipe, and post injection is performed at a timing of non-ignition later than a compression top dead center on the engine side following main injection on an engine side to thereby supply fuel to exhaust gas. An operation in which the exhaust gas falls below a predetermined temperature in a heating method in which unburned fuel is added and the added fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter to raise the catalyst bed temperature of the particulate filter. In this state, after-injection is performed at a combustible timing immediately after the main injection, and a pre-post injection for continuing the embers to the extent that the temperature drop in the expansion stroke can be suppressed between the after-injection and the post-injection is added. It is a feature.
[0011]
Thus, in this case, the fuel added by the after-injection is burned at a timing that is difficult to be converted to an output, so that the thermal efficiency of the engine is reduced, and the calorific value of the calorific value of the fuel that is not used for power increases, thereby increasing the cylinder. The pre-post injection is added between the after injection and the post injection, so that the embers continue without igniting in the cylinder and the exhaust temperature drops during the expansion stroke. Since the exhaust gas temperature is suppressed, the temperature of the exhaust gas discharged from the engine can be significantly increased even in an operation state in which the exhaust gas temperature should be low.
[0012]
Then, the added fuel in the post-injection performed at the non-ignition timing at the time of opening the exhaust valve is accompanied by the high-temperature exhaust gas, and the catalyst bed temperature in the front part of the particulate filter rises and the added fuel is added. As a result of good gasification of the fuel in the exhaust gas, the risk that the added fuel is efficiently oxidized in the front part of the particulate filter and continues to remain untreated is avoided. The problem of clogging due to adhesion does not occur.
[0013]
Also, the present invention provides a catalyst regeneration type particulate filter provided with a flow-through type oxidation catalyst at the front stage in the middle of the exhaust pipe, and the timing of non-ignition timing later than the compression top dead center following the main injection on the engine side. The fuel is added to the exhaust gas in an unburned state by post-injection, and the heat of reaction when the added fuel oxidizes on the oxidation catalyst of the preceding stage raises the catalyst bed temperature of the subsequent particulate filter. In the temperature method, in an operating state where the exhaust gas temperature is equal to or lower than a predetermined temperature, after-injection is performed at a combustible timing immediately after the main injection, and a decrease in temperature during the expansion stroke between the after-injection and the post-injection can be suppressed. It is also characterized by adding a pre-post injection for maintaining the embers to a certain extent.
[0014]
Thus, also in this case, the added fuel by the after-injection is burned at a timing that is difficult to be converted into an output, so that the thermal efficiency of the engine is reduced, and the calorific value of the calorific value of the fuel that is not used for power increases. The exhaust temperature in the cylinder rises, and pre-post injection is added between this after injection and post-injection, so that the residual fire continues without misfiring in the cylinder and the exhaust temperature drops during the expansion stroke. Is suppressed, so that the temperature of the exhaust gas discharged from the engine can be significantly increased even in the operating state where the exhaust temperature should be low.
[0015]
Then, the added fuel in the post-injection performed at the non-ignition timing in accordance with the opening of the exhaust valve is accompanied by the high-temperature exhaust gas, and the catalyst bed temperature in the front part of the preceding oxidation catalyst rises and As a result of good gasification of the added fuel in the exhaust gas, the risk that the added fuel is efficiently oxidized in the front part of the preceding oxidation catalyst and continues to remain unprocessed is avoided. The problem of clogging due to adhesion of curate does not occur.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
1 to 3 show an example of an embodiment of 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 used as an intake pipe 5. To the compressor 2a of the turbocharger 2, the intake air 4 pressurized by the compressor 2a is sent to the intercooler 6 where it is 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 (FIG. 1 illustrates the case of in-line six cylinders).
[0018]
Further, exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to a turbine 2b of the turbocharger 2 via an exhaust manifold 10, and the exhaust gas 9 driving the turbine 2b is passed through an exhaust pipe 11. It is designed to be discharged outside the vehicle.
[0019]
In the middle of the exhaust pipe 11, a catalyst regeneration type particulate filter 12 integrally supporting an oxidation catalyst is mounted and held in a filter case 13, and is shown in an enlarged scale in FIG. As described above, the particulate filter 12 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths 12a partitioned in a lattice are alternately plugged, and the inlets are not plugged. As for 12a, the outlet thereof is plugged, and only the exhaust gas 9 that has passed through the porous thin wall 12b that defines each flow path 12a is discharged to the downstream side.
[0020]
A temperature sensor 14 for measuring the temperature of the exhaust gas 9 is provided at the inlet of the filter case 13, and a temperature signal 14 a of the temperature sensor 14 is controlled by an engine control computer (ECU: Electronic Control Unit). The information is input to the device 15.
[0021]
Since the control device 15 also serves as an engine control computer, it also controls fuel injection, and more specifically, an accelerator sensor 16 (which detects an accelerator opening as a load on the diesel engine 1). A fuel injection device for injecting fuel into each cylinder 8 of the diesel engine 1 based on an accelerator opening signal 16a from a load sensor) and a rotation speed signal 17a from a rotation sensor 17 for detecting the engine rotation speed of the diesel engine 1. A fuel injection signal 18 a is output to the fuel injection valve 18.
[0022]
Here, the fuel injection device 18 is constituted by a plurality of injectors 19 provided for each cylinder 8, and the solenoid valves of each of the injectors 19 are appropriately opened by the fuel injection signal 18a to control the fuel injection. The injection timing (valve opening timing) and the injection amount (valve opening time) of the fuel cell are appropriately controlled.
[0023]
On the other hand, the control device 15 determines the fuel injection signal 18a in the normal mode based on the accelerator opening signal 16a and the rotation speed signal 17a. In addition, the fuel injection is switched from the normal mode to the regeneration mode, and the post-injection is performed at a non-ignition timing later than the compression top dead center following the main injection of the fuel performed near the compression top dead center (crank angle 0 °). The signal 18a is determined.
[0024]
That is, when the post injection is performed at the non-ignition timing later than the compression top dead center following the main injection, unburned fuel (mainly hydrocarbons) is added to the exhaust gas 9 by the post injection. This means that the unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 12, and the heat of the reaction raises the catalyst bed temperature to burn and remove the particulates in the particulate filter 12. Become.
[0025]
However, in the control device 15, the temperature of the exhaust gas 9 from the diesel engine 1 is changed based on the accelerator opening signal 16a, the rotation speed signal 17a, and the temperature signal 14a from the temperature sensor 14. It is determined whether or not the operating state is low enough not to reach the target temperature (about 300 ° C.) necessary for obtaining the activity of the oxidation catalyst supported on the fuel cell 12, and the operating state is such that the exhaust gas temperature is low. In performing post-injection under the conditions determined as above, as shown in the control image in FIG. 3, after-injection B is performed at a combustible timing immediately after main injection A, and between post-injection B and post-injection D. The pre-post injection C for continuing the embers to such an extent that the temperature drop during the expansion stroke can be suppressed is added.
[0026]
Thus, when the exhaust purification device is operated by the control device 15, the added fuel by the after-injection B is burned at a timing that is difficult to be converted into an output, so that the thermal efficiency of the diesel engine 1 is reduced. The amount of heat not used for the power of the engine increases, the exhaust temperature in the cylinder rises, and the pre-post injection C is added between the after-injection B and the post-injection D to prevent misfiring in the cylinder. And the temperature of the exhaust gas 9 discharged from the diesel engine 1 is significantly increased even in the operating region where the exhaust temperature should be low, because the embers are continued and the decrease in the exhaust temperature during the expansion stroke is suppressed. Will be achieved.
[0027]
Here, the total amount of the main injection A and the after injection B is determined by the control device 15 based on the accelerator opening signal 16a from the accelerator sensor 16 so that a necessary output is obtained. If only the main injection A is executed, as shown by a two-dot chain line in FIG. 3, the peak temperature increases but the temperature immediately decreases, and if the pre-post injection C is not added after this, Since the temperature continues to decrease as it is, when the post-injection D is performed at the non-ignition timing in accordance with the opening of the exhaust valve, the temperature in the cylinder becomes significantly lower than that of the present embodiment, and the temperature difference T (see FIG. 3) occurs.
[0028]
On the other hand, in the present embodiment, the added fuel in the post-injection D, which is performed at the non-ignition timing at the time of opening the exhaust valve, accompanies the high-temperature exhaust gas 9, and the particulate filter 12 As a result, the temperature of the catalyst bed in the front portion rises and the added fuel gasifies well in the exhaust gas 9, so that the added fuel is efficiently oxidized in the front portion of the particulate filter 12 and continues to remain untreated. This avoids the risk of clogging due to particulates adhering thereto.
[0029]
Therefore, according to the above embodiment, when raising the catalyst bed temperature of the particulate filter 12 by adding fuel by the post-injection D, even if the exhaust gas temperature is low, the calorie amount not used for power by the after-injection B even in the operating state where the exhaust temperature is low. As a result, the temperature of the exhaust gas 9 discharged from the diesel engine 1 can be significantly increased by suppressing the decrease in the exhaust gas temperature during the expansion stroke by increasing the exhaust gas temperature and continuing the embers due to the pre-post injection C. The possibility that the added fuel continues to remain untreated in the front portion of the curated filter 12 can be eliminated, and the problem of clogging caused by the untreated added fuel can be reliably avoided.
[0030]
In the above, the case where the particulate filter 12 integrally supporting the oxidation catalyst is used alone is illustrated. However, in order to support the oxidation reaction of the collected particulates, the former stage of the particulate filter 12 is used. Needless to say, the present invention is also effective in a configuration provided with a flow-through type oxidation catalyst 20.
[0031]
That is, as shown in FIG. 4, in the case where the oxidation catalyst 20 is provided in front of the particulate filter 12 in the upper stage, and in the case where the particulate filter 12 in the lower stage is used alone, first, The rationale is that the oxidation reaction of the added fuel is activated and the internal temperature rises from the end on the most upstream side where the exhaust gas 9 flows into the rear part, and the oxidation catalyst 20 is located upstream of the particulate filter 12. In the configuration provided with, the additional fuel that cannot be processed is accumulated in the front part of the oxidation catalyst 20 of the former stage, and the front part of the oxidation catalyst 20 of the former stage becomes sticky and wet, so that the particulates easily adhere. However, there is a concern that the accumulation of particulates may cause clogging at an early stage.
[0032]
Therefore, with respect to such an embodiment in which the oxidation catalyst 20 is provided in front of the particulate filter 12, in performing the post-injection D under the conditions determined to be in the low exhaust temperature operating state, the combustion immediately after the main injection A is possible. By performing after-injection B at an appropriate timing and adding a pre-post injection C for continuing the embers to such an extent that the temperature drop during the expansion stroke can be suppressed between the after-injection B and the post-injection D, Similarly, since the temperature of the exhaust gas 9 discharged from the diesel engine 1 can be significantly increased, it is possible to eliminate the possibility that the added fuel may remain untreated in the front part of the oxidation catalyst 20 in the preceding stage. Thus, the problem of clogging caused by the untreated added fuel can be reliably avoided.
[0033]
The method for raising the temperature of the particulate filter of the present invention is not limited to the above-described embodiment, and the after-injection and the pre- and post-injection are continued for a predetermined time even after the fuel is added by the post-injection. May be kept high so that the wet state of the front part of the particulate filter or the oxidation catalyst at the preceding stage may be eliminated at an early stage, and various other changes may be made without departing from the gist of the present invention. Of course, it can be added.
[0034]
【The invention's effect】
According to the method for raising the temperature of the particulate filter of the present invention described above, when raising the catalyst bed temperature of the particulate filter by adding fuel by post-injection, even in an operation state where the exhaust gas temperature is low, the power by the after-injection is reduced. Since the exhaust gas temperature is increased by the amount of heat not used and the embers due to the pre-post injection continue to suppress the exhaust gas temperature decrease during the expansion stroke, the exhaust gas discharged from the diesel engine can be significantly heated. It is possible to eliminate the possibility that the added fuel remains untreated in the front part of the particulate filter or the preceding oxidation catalyst, and to reliably avoid the problem of clogging caused by the untreated added fuel. It is possible to achieve an excellent effect of being able to perform.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a sectional view showing details of the particulate filter of FIG. 1;
FIG. 3 is a graph showing a control image of fuel injection by the control device of FIG. 1;
FIG. 4 is an explanatory diagram relating to another embodiment of the present invention.
[Explanation of symbols]
1 diesel engine (engine)
8 Cylinder 9 Exhaust gas 11 Exhaust pipe 12 Particulate filter 15 Control device 18 Fuel injection device 20 Oxidation catalyst

Claims (2)

Equipped with a catalyst regeneration type particulate filter in the middle of the exhaust pipe, the fuel is left unburned in the exhaust gas by performing post-injection at the engine side at a non-ignition timing later than the compression top dead center following the main injection. In the temperature increasing method in which the added fuel is oxidized on the oxidation catalyst of the particulate filter by the reaction heat when raising the catalyst bed temperature of the particulate filter, in the operating state where the exhaust gas becomes a predetermined temperature or less, A post-injection for performing after-injection at a combustible timing immediately after the injection, and adding a pre-post injection for continuing the embers to such an extent that a temperature drop in an expansion stroke can be suppressed between the after-injection and the post-injection. How to raise the temperature of the curated filter. A catalyst regeneration particulate filter with a flow-through oxidation catalyst attached to the front stage is installed in the middle of the exhaust pipe, and the engine performs post-injection at the non-ignition timing later than the compression top dead center following the main injection following the main injection. In a heating method in which fuel is added to the exhaust gas in an unburned state by the unburned fuel, and the added fuel undergoes an oxidation reaction on the oxidation catalyst of the preceding stage, the reaction bed heats up the catalyst bed temperature of the subsequent particulate filter. In the operating state where the temperature becomes equal to or lower than the predetermined temperature, after-injection is performed at a combustible timing immediately after the main injection, and the embers are continued to such an extent that the temperature drop in the expansion stroke can be suppressed between the after-injection and the post-injection. A method for raising the temperature of a particulate filter, characterized by adding pre-post injection.

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