JP3831677B2 - Preventing sulfate poisoning of particulate filters - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing sulfate poisoning of a particulate filter.
[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 alumina loaded with platinum 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, since SO ₂ derived from sulfur in the fuel exists in the exhaust gas of the diesel engine, this SO ₂ is oxidized by air on the oxidation catalyst of the particulate filter and sulfate is generated. If the stagnation of the sulfate in the particulate filter is left for a long period of time, the oxidation catalyst of the particulate filter is poisoned and deteriorates, whereby the particulates are burned and removed to achieve self-regeneration. There is a possibility that the performance may be deteriorated, or the filter case holding the particulate filter may be corroded.
[0007]
However, according to the knowledge obtained by the present inventors, the liquid-state sulfate produced on the oxidation catalyst of the particulate filter is stagnant in the rear part of the particulate filter due to the flow of exhaust gas. It is known that the sulfate can be removed if the catalyst bed temperature at the rear part of the particulate filter can be raised above a predetermined temperature, and HC (hydrocarbon) is added to the exhaust gas upstream from the particulate filter. The HC is oxidized on the oxidation catalyst of the particulate filter, and the heat of reaction raises the catalyst bed temperature of at least the rear part of the particulate filter to a predetermined temperature or higher, and the sulfate retained in the rear part of the particulate filter is removed. Japanese Patent Application No. 2002-3781 discloses a specific method of gasification and desorption To have already filed.
[0008]
[Problems to be solved by the invention]
However, when the fuel added to the exhaust gas 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 HC is activated. Therefore, the temperature of the front part of the particulate filter is less likely to rise than that of the rear part. Just the amount of HC necessary to raise the catalyst bed temperature of the rear part of the particulate filter to about 550 ° C is added. If the operating condition changes drastically immediately after the addition is completed and the temperature of the particulate filter suddenly drops, the front of the particulate filter that is not too hot (low catalytic activity) HC that could not be processed by the part collected, and this caused the front part of the particulate filter Liable to adhere particulates become sticky wet state, the particulate filter was a possibility of causing clogging in the early continues reservoir without here that particulates are oxidized.
[0009]
The present invention has been made in view of the above-described circumstances, and it is possible to remove sulfate retained in the particulate filter by adding HC without causing clogging of the particulate filter at an early stage. The purpose is to be.
[0010]
[Means for Solving the Problems]
The present invention relates to a method for preventing sulfate poisoning of a particulate filter that is provided in the middle of an exhaust pipe through which exhaust gas from an internal combustion engine flows and that integrally supports an oxidation catalyst, and is provided in the exhaust gas upstream of the particulate filter. HC is added to the catalyst, and the HC is oxidized on the oxidation catalyst of the particulate filter. The heat of reaction raises the catalyst bed temperature of at least the rear part of the particulate filter to a predetermined temperature or more, and While the remaining sulfate is gasified and desorbed, immediately after the addition of HC, the exhaust temperature is increased on the upstream side of the particulate filter, so that the catalyst bed temperature in the front part of the particulate filter is received from the exhaust gas. The heat and the reaction heat transmitted from the rear part raise it synergistically, By oxidizing the untreated HC in the front part of the particulate filter, the particulate adhering to the front part is caused to flow backward in a dry state, and the particulate is oxidized in the rear part of the particulate filter. It is a feature.
[0011]
Thus, in this way, when it is determined that the sulfate in the particulate filter needs to be removed based on the operating time, the integrated value of the combustion injection amount, etc., the exhaust gas is introduced into the exhaust gas upstream from the particulate filter. When HC is added, the HC oxidizes on the oxidation catalyst of the particulate filter to generate reaction heat, and this reaction heat raises the catalyst bed temperature in the rear part of the particulate filter to a predetermined temperature or higher. Since the retained sulfate is gasified and desorbed, the deterioration of the oxidation catalyst and corrosion of the filter case and the like are prevented in advance.
[0012]
That is, when the fuel added to the exhaust gas 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 HC is activated. As a result, the temperature of the rear part of the particulate filter rises ahead of the front part.
[0013]
Then, immediately after the addition of HC, the exhaust temperature rises on the upstream side of the particulate filter, so that the exhaust gas whose temperature has increased gives heat to the front part of the particulate filter and is active in the rear part of the particulate filter. As a result of heat transferred to the front part of the particulate filter, the heat generated by the oxidized HC oxidation reaction increases the catalyst bed temperature in the front part of the particulate filter synergistically, increasing the catalytic activity of the front part, The untreated HC accumulated together with the particulates is oxidized, so that the particulates adhering to the front part of the particulate filter are dried to flow backward, and the particulates have already increased in activity. It will be oxidized in the rear part of the particulate filter
[0014]
Note that raising the exhaust temperature upstream of the particulate filter is effective at raising the catalyst bed temperature in the front part of the particulate filter because it is performed at the timing immediately after the end of the addition of HC. Even if the exhaust temperature is raised at the timing of removal, it is difficult to raise the catalyst bed temperature in the front part of the particulate filter to the required temperature only by the heat given from the exhaust gas, and it is supported by the reaction heat of the added HC Because the catalyst bed temperature can be received simultaneously from the rear part of the particulate filter, the catalyst bed temperature in the front part of the particulate filter can be increased efficiently.
[0015]
Further, in the present invention, when adding fuel into the exhaust gas upstream from the particulate filter, HC is added by controlling the fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas. Alternatively, it is possible to add HC by directly injecting at least one of fuel and oil into the exhaust gas in the exhaust passage upstream of the particulate filter.
[0016]
Furthermore, in the present invention, when the exhaust temperature is increased on the upstream side of the particulate filter immediately after the end of the addition of HC, the exhaust temperature may be increased by narrowing down an appropriate portion of the exhaust passage.
[0017]
That is, if the exhaust passage is narrowed down as appropriate, the exhaust gas temperature is increased by increasing the exhaust gas upstream, and the intake air having a relatively low temperature is less likely to flow into the cylinder due to the increased exhaust resistance. As a result, the residual amount of exhaust gas having a relatively high temperature increases, and even if the air in the cylinder containing a large amount of the exhaust gas having a relatively high temperature is further compressed in the compression stroke and reaches the explosion stroke, the exhaust gas temperature can be further increased. A rise will be planned.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0019]
1 to 3 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine (internal combustion engine) equipped with a turbocharger 2, and intake air introduced from an air cleaner 3. 4 is introduced into the compressor 2a of the turbocharger 2 through the intake pipe 5 and pressurized, and the pressurized intake air 4 is distributed and introduced to each cylinder of the diesel engine 1 via the intercooler 6.
[0020]
Further, exhaust gas 8 discharged from each cylinder of the diesel engine 1 through the exhaust manifold 7 is sent to the turbine 2b of the turbocharger 2 through the exhaust pipe 9, and the exhaust gas 8 driving the turbine 2b is of a catalyst regeneration type. The particulates are collected through the particulate filter 10 and then discharged outside the vehicle.
[0021]
Here, the specific structure of the particulate filter 10 is as shown in FIG. 2, and this particulate filter 10 has a porous honeycomb structure made of ceramic, and each flow path partitioned in a lattice shape. 11 are alternately sealed, and the outlets of the flow paths 11 that are not sealed are sealed at the outlets, and pass through the porous thin walls 12 that define the flow paths 11. Only the exhaust gas 8 is discharged downstream.
[0022]
In this embodiment, a temperature sensor 13 for measuring the temperature of the exhaust gas 8 is provided on the outlet side of the particulate filter 10, and a detection signal 13a of the temperature sensor 13 is an engine control computer (ECU: Electronic). On the other hand, in this control device 14, the fuel injection timing to the fuel injection device 15 for injecting fuel into each cylinder of the diesel engine 1 and A fuel injection signal 15a for commanding the injection amount is output.
[0023]
Here, the fuel injection device 15 is constituted by a plurality of injectors (not shown) provided for each cylinder, and the solenoid valve of each injector is controlled to open by the fuel injection signal 15a, and the fuel injection timing. In addition, the injection amount (valve opening time) is appropriately controlled.
[0024]
Further, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 16 (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 17 for detection is provided, and an accelerator opening signal 16a and a rotation speed signal 17a from the accelerator sensor 16 and the rotation sensor 17 are also input to the control device 14.
[0025]
In the control device 14, the fuel injection signal 15a in the normal mode is determined based on the accelerator opening signal 16a and the rotation speed signal 17a, while the sulfate in the particulate filter 10 needs to be removed. When this occurs, the normal mode is switched to the desulfurization mode based on the detection signal 13a of the temperature sensor 13, and when the desulfurization mode is switched, the operation is performed near the compression top dead center (crank angle 0 °) in the normal mode. A fuel injection signal 15a having an injection pattern that delays the fuel injection timing that has been determined is determined.
[0026]
That is, when the fuel injection timing is delayed in this manner, the exhaust gas 8 in the middle of combustion is exhausted from the cylinder, resulting in the generation of exhaust gas 8 in which a large amount of unburned fuel (HC: hydrocarbon) remains. As a result, HC is substantially added to the exhaust gas 8.
[0027]
Further, an exhaust brake 18 capable of adjusting the opening degree for narrowing the flow path of the exhaust pipe 9 to an appropriate opening degree is provided at an appropriate position upstream of the particulate filter 10, and the exhaust brake 18 is provided with a control device. In this embodiment, the desulfurization mode is selected by the control device 14 and the fuel injection timing is delayed, so that the exhaust gas is exhausted. Immediately after the completion of the addition of HC to the gas 8, the exhaust brake 18 is instructed to perform another operation independent of the original operation to the exhaust brake 18, and the exhaust brake 18 is used as an exhaust throttle means for raising the exhaust temperature as will be described later. It can be used.
[0028]
Here, when a specific control procedure in the control device 14 is shown in a flowchart in FIG. 3, a value obtained by multiplying the fuel injection amount q and the operation time t in step S1 is used as a guideline for the amount of accumulated sulfate, and this value is a predetermined value. It is determined whether or not the set value A has been exceeded. If “YES” is determined in step S1, it is determined that the sulfate in the particulate filter 10 needs to be removed, and the process proceeds to step S2. The same determination is repeated until the determination of “YES” is not made.
[0029]
Next, in step S2, the exhaust temperature T _O on the outlet side of the particulate filter 10 detected by the temperature sensor 13 exceeds the set temperature T _A at which an oxidation reaction can be performed on the oxidation catalyst of the particulate filter 10. If “YES” is determined in step S2, it is determined that the sulfate in the particulate filter 10 needs to be removed, and the process proceeds to step S3. "" Is not repeated, the same determination from step S1 is repeated.
[0030]
In step S3, HC addition control for executing HC addition to the exhaust gas 8 is started by delaying the fuel injection timing as described above. This HC addition control is performed in the next step. S4 exhaust temperature T _O of the discharge side of the particulate filter 10 detected by the temperature sensor 13 is continued until it enters a temperature range such that less and T _C with a predetermined set temperature T _B and above at ( "NO Is repeated).
[0031]
Further, the exhaust gas temperature T _O of the discharge side of the particulate filter 10 is determined to have entered a temperature zone of about 550 around ℃ such that less and T _C above a predetermined set temperature T _B at step S4 In such a case, it is determined that at least the catalyst bed temperature in the rear part of the particulate filter 10 has reached the temperature range around 550 ° C. necessary for gasifying and removing the sulfate, and more HC is added. The process proceeds to step S5 so as not to continue.
[0032]
In step S5, exhaust temperature increase control for narrowing the exhaust flow rate is started by the exhaust brake 18, and this exhaust temperature increase control is performed in the following step S6 where the control duration t _O exceeds a predetermined set time t _A. ("NO" determination is repeated) until "YES" is selected when the control continuation time t _O exceeds a predetermined set time t _A and the process ends. Yes.
[0033]
In this exhaust gas temperature increase control, the exhaust gas flow rate is narrowed down by the exhaust brake 18 that has received a closing operation command from the control device 14 as the opening command signal 18a, and the exhaust gas 8 upstream is boosted to increase the exhaust gas temperature. Rise.
[0034]
That is, the following relational expression P · V / T = constant is determined for the temperature T, the exhaust pressure P, and the flow rate V of the exhaust gas 8, and the exhaust pressure P is increased by narrowing the exhaust passage. If the flow rate V is kept constant, the temperature T of the exhaust gas 8 greatly increases with respect to a predetermined operation state.
[0035]
In addition, since the exhaust resistance of the diesel engine 1 is increased, it is difficult for intake air having a relatively low temperature to flow into the cylinder, and the residual amount of the exhaust gas 8 having a relatively high temperature is increased. The exhaust temperature is further increased by the air in the cylinder containing a large amount of 8 being compressed in the next compression stroke and reaching the explosion stroke.
[0036]
At the time of such exhaust temperature increase control, the fuel injection signal 15a (fuel injection command) of an injection pattern in which after injection is added from the control device 14 to the fuel injection device 15 at a combustible timing immediately after the main injection. In this way, after-injection fuel burns at a timing when it is difficult to convert it to output, the thermal efficiency of the diesel engine 1 is lowered, and it is not used for power in the amount of heat generated by the fuel. The amount of heat increases, and the exhaust temperature is further increased.
[0037]
Thus, if the operation control of the present embodiment is performed by such a control device 14, when it is determined by the control device 14 that the sulfate in the particulate filter 10 needs to be removed, the fuel injection by the control device 14 is performed. The control is switched from the normal mode to the desulfurization mode, the timing of fuel injection is delayed from the normal time, and high-temperature exhaust gas 8 with a large amount of unburned fuel (HC) is generated, which is contained in the exhaust gas 8 in a large amount. The HC component oxidizes on the oxidation catalyst of the particulate filter 10 to generate reaction heat.
[0038]
Here, when the HC component in the exhaust gas 8 undergoes an oxidation reaction on the oxidation catalyst of the particulate filter 10, the chance of contact with the oxidation catalyst increases toward the rear portion of the particulate filter 10, and the oxidation reaction of the HC component. Therefore, the temperature of the rear part of the particulate filter 10 is increased in advance of the front part.
[0039]
Then, if the catalyst bed temperature in the rear part of the particulate filter 10 rises to about 550 ° C. due to the reaction heat caused by the oxidation reaction of the HC component in the exhaust gas 8 on the oxidation catalyst, the sulfate retained here Is gasified and desorbed as SO ₂ gas, and the sulfate is removed from the particulate filter 10.
[0040]
Further, immediately after the end of the addition of HC, the exhaust flow rate is narrowed down by the exhaust brake 18 that has received the closing operation command as the opening command signal 18a from the control device 14, and the exhaust gas 8 upstream of this is boosted. Since the exhaust gas temperature is increased, the exhaust gas 8 whose temperature has increased gives heat to the front part of the particulate filter 10 and the heat generated by the oxidation reaction of HC activated in the rear part of the particulate filter 10 is particulate. As a result of being transmitted to the front part of the filter 10, the catalyst bed temperature of the front part of the particulate filter 10 increases synergistically to increase the catalytic activity of the front part, and is not accumulated in the wet state with the particulates. The treated HC is oxidized and adhered to the front portion of the particulate filter 10. Particulates there are flowed backward becomes dry state, so that the particulates are already oxidized in the rear portion of the particulate filter 10 has increased the activity.
[0041]
Note that raising the exhaust temperature upstream of the particulate filter 10 is effective in raising the catalyst bed temperature in the front portion of the particulate filter 10 because it is performed at the timing immediately after the end of the addition of HC. Even if the exhaust temperature is raised at the timing when this is removed, it is difficult to raise the catalyst bed temperature in the front part of the particulate filter 10 to the required temperature only by the heat given from the exhaust gas 8, and the added HC The catalyst bed temperature in the front part of the particulate filter 10 can be increased efficiently because the support by the reaction heat can be simultaneously received from the rear part of the particulate filter 10.
[0042]
Therefore, according to the above embodiment, the exhaust gas temperature is raised immediately after the end of the addition of HC and the catalyst bed temperature at the front portion of the particulate filter 10 is synergistically generated by the heat received from the exhaust gas 8 and the reaction heat transmitted from the rear portion. Therefore, the untreated HC in the front portion of the particulate filter 10 can be oxidized, and the particulate adhering to the front portion can be oxidized in a dry state and flowed backward without any trouble. Since it can be processed, HC can be added without causing the particulate filter 10 to be clogged at an early stage, and the sulfate staying in the particulate filter 10 can be removed.
[0043]
In this embodiment, the timing of fuel injection into the cylinder is delayed more than usual to generate the high-temperature exhaust gas 8 with a large amount of unburned fuel (HC), and thereby the HC in the exhaust gas 8 is generated. Although the fuel is added, the fuel is injected before and after (at least one of) the main injection of the fuel, and this fuel is attached to the wall surface in the cylinder, so that it is difficult to gasify and unburned in the exhaust gas 8 Not only the method of adding fuel by leaving a lot of unburned fuel in the exhaust gas 8 by controlling the fuel injection into the cylinder in this manner, As shown by a two-dot chain line in FIG. 1, an injector 19 is inserted through an appropriate position of the exhaust pipe 9 (or the exhaust manifold 7 is acceptable), and at least one of fuel and oil is directly injected into the exhaust gas 8 by the injector 19. Then add HC It may be so.
[0044]
In addition, the method for preventing sulfate poisoning of the particulate filter of the present invention is not limited to the above-described embodiment, and it is not always necessary to use an exhaust brake to narrow down an appropriate portion of the exhaust passage. Of course, an exhaust throttle valve may be separately provided in the middle of the pipe, and various modifications can be made without departing from the scope of the present invention.
[0045]
【The invention's effect】
According to the above-described method for preventing sulfate poisoning of the particulate filter of the present invention, the exhaust temperature is raised immediately after the end of the addition of HC, and the catalyst bed temperature at the front portion of the particulate filter is received from the exhaust gas and the heat received from the exhaust gas. Since the reaction heat is transmitted to increase synergistically, the untreated HC in the front part of the particulate filter can be oxidized, and the particulate adhering to the front part is dried to the rear. Since it can be oxidized without trouble by flowing, HC can be added without causing clogging of the particulate filter at an early stage, and the sulfate staying in the particulate filter can be removed. An excellent effect can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a cross-sectional view showing details of the particulate filter of FIG.
FIG. 3 is a flowchart showing a specific control procedure in the control device of FIG. 1;
[Explanation of symbols]
1 Diesel engine (internal combustion engine)
8 Exhaust gas 9 Exhaust pipe (exhaust flow path)
10 Particulate Filter 14 Control Device 15 Fuel Injection Device 15a Fuel Injection Signal 18 Exhaust Brake 18a Opening Command Signal 19 Injector

Claims (4)

A method for preventing sulfate poisoning of a particulate filter that is installed in the middle of an exhaust pipe through which exhaust gas from an internal combustion engine circulates and that integrally supports an oxidation catalyst, where HC is added to the exhaust gas upstream from the particulate filter Then, the HC is oxidized on the oxidation catalyst of the particulate filter, and the heat of the reaction raises the catalyst bed temperature of at least the rear part of the particulate filter to a predetermined temperature or more and stays in the rear part of the particulate filter. While the sulfate is gasified and desorbed, immediately after the addition of HC, the exhaust temperature is increased on the upstream side of the particulate filter, so that the catalyst bed temperature in the front part of the particulate filter receives the heat from the exhaust gas and the rear part. Increased synergistically with the heat of reaction transmitted from It is characterized in that the untreated HC in the front part of the filter is oxidized to flow the particulates adhering to the front part in a dry state, and the particulates are oxidized in the rear part of the particulate filter. To prevent sulfate poisoning of particulate filters. 2. The method for preventing sulfate poisoning of a particulate filter according to claim 1, wherein HC is added by controlling fuel injection into the cylinder to leave a large amount of unburned fuel in the exhaust gas. 2. The method according to claim 1, wherein HC is added by directly injecting at least one of fuel and oil into the exhaust gas in an exhaust passage upstream of the particulate filter. . 4. The method of preventing particulate poisoning of a particulate filter according to claim 1, wherein the exhaust temperature is raised by narrowing down an appropriate portion of the exhaust passage.

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