JP3914751B2 - Exhaust purification method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification method.
[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 employed, the oxidation catalyst carried by the particulate filter has an active temperature range, and the exhaust temperature is below the lower limit of activation temperature. If the operation state (generally, the region where the exhaust temperature is low spreads in the light load operation region) continues, the oxidation catalyst will not be activated, so the particulates may not be burned and removed well, It has been studied to perform forced heating by attaching an electric heater, a fuel addition device, or the like.
[0007]
[Problems to be solved by the invention]
However, when an electric heater, a fuel addition device, etc. are attached, an electric system for energizing the electric heater, a fuel system for supplying fuel to the fuel addition device, etc. must be newly laid. Therefore, there is a problem that the system related to the regeneration of the particulate filter becomes complicated and the cost is increased. On the other hand, when forced heating by an electric heater or a fuel addition device is not performed, the particulate filter There is a possibility that the filter will be over trapped in a short period of time and the engine performance will be adversely affected by an increase in exhaust pressure, or a large amount of accumulated particulate will burn rapidly and the particulate filter may be melted.
[0008]
The present invention has been made in view of the above circumstances, and it is possible to achieve good regeneration of the particulate filter even in an operation region where the exhaust temperature of the particulate filter is difficult to oxidize and the exhaust temperature is extremely low. In addition, a forced heating means such as an electric heater or a fuel addition device is not required, and costs can be reduced, and the particulate filter can be reliably prevented from falling into an over trapped state in a short period of time. The purpose is that.
[0009]
[Means for Solving the Problems]
The present invention performs after-injection at a combustible timing immediately after main injection in an operation region where the exhaust temperature of the exhaust gas in which the oxidation reaction of fuel on the oxidation catalyst of the particulate filter is difficult, and compression after the after-injection. Adopts an injection pattern that performs post-injection at a non-ignition timing that is later than the dead center, and burns fuel at a timing that is difficult to convert to output by after-injection to raise the exhaust temperature, while post-injection is unburned in the exhaust gas The fuel added as it is is subjected to an oxidation reaction on the oxidation catalyst of the particulate filter, and the trapped particulates are burned by raising the catalyst bed temperature by the reaction heat.
[0010]
Thus, in this way, even in an operation region where the exhaust temperature is extremely low where it is difficult to spontaneously burn particulates, the fuel is burned at a timing that is difficult to convert to output by after injection, and the exhaust temperature is raised. As a result of the oxidation reaction of the unburned fuel added to the exhaust gas by post-injection on the oxidation catalyst of the particulate filter and raising the catalyst bed temperature by the reaction heat, the collected particulates are burned. Particulates collected in the curate filter are slowly burned spontaneously in an oxygen-deficient atmosphere that consumes oxygen due to the oxidation reaction of the fuel, and the particulate filter dissolves due to sudden high-temperature combustion of the particulates. It is possible to achieve good regeneration of the particulate filter while avoiding loss.
[0011]
Furthermore, in the present invention, an injection pattern is employed in which after-injection is performed at a combustible timing immediately after main injection in an operating region where the exhaust temperature is extremely low, where the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter is difficult. Then, fuel is burned at a timing that is difficult to convert to output by the after injection, the exhaust temperature is raised, and after this exhaust temperature rises, the catalyst bed temperature reaches a temperature that enables the oxidation reaction of the fuel, and then compressed after the after injection Switch to an injection pattern in which post-injection is performed at a non-ignition timing that is later than the top dead center, and the fuel that has been added to the exhaust gas unburned by the post-injection is oxidized on the oxidation catalyst of the particulate filter, and the reaction It is also possible to raise the catalyst bed temperature by heat and burn the collected particulates.
[0012]
The start timing of the post injection is preferably set in the range of the crank angle of 70 to 150 °, and the start timing of the after injection is set in the range of the crank angle of 0 to 30 °. preferable.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
FIG. 1 and FIG. 2 show an example of an embodiment of the present invention. In the exhaust purification method of this embodiment, as shown in FIG. 1, an automobile diesel engine 1 (internal combustion engine) passes through an exhaust manifold 2. Exemplified is a case where a catalyst regeneration type particulate filter 6 integrally supporting an oxidation catalyst is accommodated in a muffler 5 of an exhaust pipe 4 through which exhaust gas 3 discharged in this way flows. A filter case 7 that holds the particulate filter 6 forms an outer cylinder of the muffler 5.
[0015]
That is, a particulate filter 6 as shown in an enlarged view in FIG. 2 is accommodated in a filter case 7 having front and rear inlet pipes 8 and outlet pipes 9. The particulate filter 6 is made of ceramic. It has a porous honeycomb structure, and the inlets of the flow paths 6a partitioned in a lattice pattern are alternately sealed, and the outlets of the flow paths 6a that are not sealed are sealed. Only the exhaust gas 3 that has permeated through the porous thin wall 6b that partitions each flow path 6a is discharged to the downstream side.
[0016]
The inlet pipe 8 of the filter case 7 is equipped with a pressure sensor 10 for measuring the inlet gas pressure as over-collection determining means, and a detection signal 10a of the pressure sensor 10 is an engine control computer (ECU: Electronic Control Unit). On the other hand, in this control device 11, the fuel injection timing and the injection amount are directed to the fuel injection device 12 that injects fuel into each cylinder of the diesel engine 1. A commanded fuel injection signal 12a is output.
[0017]
Here, the fuel injection device 12 is composed of a plurality of injectors (not shown) provided for each cylinder, and the electromagnetic valves of these injectors are appropriately controlled to open by the fuel injection signal 12a, and the fuel is supplied. The injection timing (injection start timing and injection end timing) and the injection amount (valve opening time) are appropriately controlled.
[0018]
Further, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 13 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and the rotational speed is set at an appropriate position of the diesel engine 1. A rotation sensor 14 for detection is provided, and an accelerator opening signal 13a and a rotation speed signal 14a from the accelerator sensor 13 and the rotation sensor 14 are also input to the control device 11.
[0019]
In the control device 11, the fuel injection signal 12 a in the normal mode is determined based on the accelerator opening signal 13 a and the rotation speed signal 14 a, while the inlet gas pressure is determined by the detection signal 10 a from the pressure sensor 10. When an abnormal rise of the engine is confirmed, the mode is switched from the normal mode to the forced regeneration mode. As shown in FIG. 3, the compression top dead center is followed by the main fuel injection performed near the compression top dead center (crank angle 0 °). A fuel injection signal 12a for performing post injection at a non-ignition timing later than the point is determined. It should be noted that the start timing of the post injection may be set in the range of the crank angle of 70 to 150 °.
[0020]
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 3 by this post-injection. As a result, 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 naturally combusted. It will be.
[0021]
Here, supplementary description will be given of the above-described switching of the control device 11 from the normal mode to the forced regeneration mode. In this embodiment, the actually measured pressure of the inlet gas pressure is detected by the detection signal 10a from the pressure sensor 10. While the value is monitored, the estimated value of the inlet gas pressure in the current operation state based on the accelerator opening signal 13a and the rotational speed signal 14a is estimated, and the deviation between the predicted value and the actually measured pressure value is within the normal range. In the control device 11, it is determined whether or not there is a particulate residual amount (burned residue) collected in the particulate filter 6, and the inlet gas pressure of the particulate filter 6 is large. Since it rises above the normal range, it is determined that the particulate filter 6 has fallen into the over-collection state, and the normal mode is switched to the forced regeneration mode. Instead, it is then to be performed.
[0022]
FIG. 4 shows an example of a post-injection control map in the forced regeneration mode, in which three stages of injection amounts are set in accordance with the magnitude of the load in a light load region of a predetermined rotation speed or higher. Note that the unit of the injection amount of the post-injection is indicated by the volume of the fuel that is input by one injection of the injector per cylinder.
[0023]
Thus, when the operation is performed in the operation region where the exhaust gas temperature is low and it is difficult to spontaneously burn the particulates, the control device 11 switches the combustion injection pattern from the normal mode to the forced regeneration mode, followed by the main injection. When an injection pattern in which post-injection is performed at a timing of non-ignition later than the compression top dead center is adopted, the fuel that has been added unburned into the exhaust gas 3 by the post-injection is oxidized on the oxidation catalyst of the particulate filter 6. As a result of the reaction heat being generated and the catalyst bed temperature being maintained above the lower limit temperature of the oxidation catalyst, the particulates collected in the particulate filter 6 consume oxygen due to the oxidation reaction of the fuel. Particulate fill due to sudden high-temperature combustion of particulates due to slow spontaneous combustion in a deficient oxygen atmosphere While avoiding 6 erosion of it is possible to achieve a good reproduction of the particulate filter 6.
[0024]
In particular, in the above description, the start timing of the post injection is set so that the crank angle is in the range of 70 to 150 °. Therefore, when the post injection is started at such timing, the particulate combustion is started during natural combustion. The atmosphere can be surely made into an oxygen-deficient atmosphere, and the rapid high-temperature combustion of the particulates can be suppressed, so that the melting loss of the particulate filter 6 can be avoided more reliably.
[0025]
On the other hand, as described above, the exhaust temperature is so low that the fuel added by post-injection cannot oxidize on the oxidation catalyst of the particulate filter 6 (for example, the exhaust temperature is about 200 ° C. or less). In some cases, driving is performed.
[0026]
Thus, in order to achieve good regeneration of the particulate filter even in an operation region where the exhaust temperature is extremely low, the following method is adopted in the present invention.
[0027]
That is, regarding the forced regeneration mode by the control device 11, as shown in FIG. 5, after injection is performed at a combustible timing immediately after the main injection of fuel performed near the compression top dead center (crank angle 0 °), and the after injection. Subsequently, the fuel injection signal 12a for performing the post injection at the timing of non-ignition later than the compression top dead center is determined. About the start timing of after injection, it is good to set in the range of 0-30 degrees of crank angles.
[0028]
As this type of after-injection control map, for example, a map as shown in FIG. 6 may be adopted. In the example shown here, the magnitude of the load in a light load region of a predetermined rotation speed or higher. A two-stage injection amount is set according to the above.
[0029]
In short, if after-injection is performed at a combustible timing immediately after the main injection in this way, the thermal efficiency of the diesel engine 1 is reduced by burning at a timing at which the fuel of this after-injection is difficult to be converted to output, and the heat generation amount of the fuel The amount of heat that is not used for motive power increases, and the exhaust gas temperature rises, so that the temperature required for the fuel added in the subsequent post-injection to undergo an oxidation reaction on the oxidation catalyst of the particulate filter 6 is secured. It will be.
[0030]
Thus, if after-injection and post-injection are used in combination, even in an operating region where the exhaust temperature of the exhaust gas, on which the oxidation reaction of fuel on the oxidation catalyst of the particulate filter 6 is difficult, is appropriately performed by after-injection. Since the particulate filter 6 can be regenerated by raising the exhaust gas temperature and causing the post-injected fuel to oxidize well on the oxidation catalyst of the particulate filter 6, it is possible to force the conventional electric heater, fuel addition device, etc. It is possible to reliably avoid the possibility that the particulate filter 6 will fall into an over-collected state in a short period of time while reducing the cost by eliminating the need for a heating means.
[0031]
In addition, in the operation region where the exhaust temperature is extremely low, where the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter 6 is difficult, the method shown in FIG. As shown in FIG. 7, an injection pattern in which post-injection is performed 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 (crank angle 0 °). Separately set up an exhaust temperature increase mode with an injection pattern that performs only after injection at the timing when combustion is possible, and raises the exhaust temperature in the exhaust temperature increase mode with the injection pattern of FIG. 7 so that the catalyst bed temperature can oxidize the fuel After reaching the normalizing temperature, switch to the injection pattern of FIG. 3 in which post-injection is performed at a non-ignition timing later than the compression top dead center following after injection. The fuel added unburned care gas by the oxidation reaction on the oxidation catalyst in the particulate filter 6, it is also possible to burn the collected spent particulates by raising the catalyst bed temperature due to the reaction heat.
[0032]
The exhaust purification method of the present invention is not limited only to the above-described embodiment, and is always forcedly regenerated in a light load operation region where the exhaust temperature is low, without providing an over-collection determining means such as a pressure sensor. A mode setting that switches to the mode may be adopted, and when an over-collection determination means is provided, the measured value of the inlet gas pressure by the pressure sensor as described above and the current operation state In addition to the means to compare and determine the predicted value, a pressure sensor is placed before and after the particulate filter and the differential pressure between the inlet side and the outlet side is determined to determine the overcollected state, It is possible to adopt means for estimating the excessive collection state of the particulate filter with reference to distance, operation time, etc., and other various changes can be made without departing from the scope of the present invention. It is.
[0033]
【The invention's effect】
According to the exhaust purification method of the present invention described above, the following various excellent effects can be obtained.
[0034]
(I) According to the first and second aspects of the present invention, after-injection is performed even in an operating region where the exhaust temperature of the particulate filter is difficult to oxidize and the exhaust temperature is extremely low. By appropriately raising the exhaust gas temperature, it is possible to regenerate the particulate filter by oxidizing the post-injected fuel satisfactorily on the oxidation catalyst of the particulate filter, so that the conventional electric heater, fuel addition device, etc. It is possible to reliably avoid the possibility that the particulate filter will fall into an over-collected state in a short period of time while reducing the cost by eliminating the need for a heating means. Furthermore, the particulates collected in the particulate filter are slowly burned spontaneously in an oxygen-deficient atmosphere where oxygen is consumed by the oxidation reaction of the fuel. Filter damage can be avoided.
[0035]
(II) According to the invention described in claim 3 of the present invention, the post-injection is started in the range of the crank angle of 70 to 150 °, so that the atmosphere during the spontaneous combustion of the particulates is surely made the oxygen-deficient atmosphere. In addition, it is possible to prevent the particulate filter from being damaged more reliably by suppressing the rapid high-temperature combustion of the particulates.
[0036]
(III) According to the invention described in claim 4 of the present invention, the exhaust temperature can be increased more effectively by starting the after-injection within a crank angle range of 0 to 30 °.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing details of the particulate filter of FIG.
FIG. 3 is a graph showing an example of an injection pattern for performing post injection following main injection.
FIG. 4 is a graph showing an example of a control map for post-injection.
FIG. 5 is a graph showing an example of an injection pattern of the present invention using both after injection and post injection.
FIG. 6 is a graph showing an example of a control map of after-injection.
FIG. 7 is a graph showing an example of an injection pattern in which only after injection is performed after main injection according to the present invention combined with post injection.
[Explanation of symbols]
3 exhaust gas 4 exhaust pipe 6 particulate filter 11 control device 12 fuel injection device 12a fuel injection signal

Claims (4)

  In the operating region where the exhaust temperature of the exhaust gas, where the oxidation reaction of the fuel on the oxidation catalyst of the particulate filter is difficult, the after-injection is performed at a combustible timing immediately after the main injection, and is later than the compression top dead center following the after-injection. Adopting an injection pattern in which post-injection is performed at the timing of non-ignition, fuel is burned at a timing that is difficult to convert to output by after-injection and the exhaust temperature is raised, while post-injection is added to the exhaust gas as unburned An exhaust purification method characterized in that fuel is oxidized on an oxidation catalyst of a particulate filter, and the trapped particulates are burned by raising the catalyst bed temperature by the reaction heat.   Adopting an injection pattern in which after-injection is performed at a combustible timing immediately after the main injection in an operating region where the exhaust temperature of the exhaust gas is difficult to oxidize the fuel on the oxidation catalyst of the particulate filter. Non-ignition slower than the compression top dead center following after injection after the temperature of the catalyst reaches the temperature that enables the oxidation reaction of the fuel by raising the exhaust temperature by burning the fuel at a timing that is difficult to convert Switch to the injection pattern that performs post injection at the timing of this, and the fuel added unburned in the exhaust gas by the post injection is oxidized on the oxidation catalyst of the particulate filter, and the catalyst bed temperature is raised by the reaction heat A method for purifying exhaust gas, wherein the collected particulates are burned.   The exhaust purification method according to claim 1 or 2, wherein the start timing of the post injection is set in a range of a crank angle of 70 to 150 °.   The exhaust purification method according to claim 1, 2 or 3, wherein the start timing of after injection is set in a range of a crank angle of 0 to 30 °.

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