JP3904768B2 - Diesel engine exhaust gas particulate filter cleaning and regeneration device - Google Patents

Diesel engine exhaust gas particulate filter cleaning and regeneration device Download PDF

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Publication number
JP3904768B2
JP3904768B2 JP25173399A JP25173399A JP3904768B2 JP 3904768 B2 JP3904768 B2 JP 3904768B2 JP 25173399 A JP25173399 A JP 25173399A JP 25173399 A JP25173399 A JP 25173399A JP 3904768 B2 JP3904768 B2 JP 3904768B2
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Prior art keywords
dpf
exhaust gas
catalyst
nox
particulates
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JP2001073748A (en
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正敏 下田
満 細谷
浩伸 茂木
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日野自動車株式会社
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/023Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
    • F01N3/0231Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using special exhaust apparatus upstream of the filter for producing nitrogen dioxide, e.g. for continuous filter regeneration systems [CRT]
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00Adding substances to exhaust gases
    • F01N2610/03Adding substances to exhaust gases the substance being hydrocarbons, e.g. engine fuel

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to processing of exhaust gas from a diesel engine, and more particularly, to a method for preventing clogging of a particulate filter for diesel engine exhaust gas or regeneration of the filter (including partial cleaning processing) and an apparatus therefor.
[0002]
[Prior art]
A filter (DPF: Diesel Particulate Filter) has been installed and used in an exhaust pipe system in order to filter out particulates in exhaust gas from a diesel engine. This particulate is mainly derived from fuel, and is a particulate carbonaceous material made of soot, organic solvent-soluble organic material (SOF), or the like. As a filter for capturing and removing such particulates from exhaust gas, a monolith multi-tube having a wire mesh packed layer of a heat-resistant or refractory material; a refractory material, for example, a breathable microporous partition wall made of cordierite Structure: Metal skeleton (skeleton) or foam structure (eg, open cell structure such as Raney nickel). In the monolith multi-tubular structure, the upstream end is closed and the downstream end is closed (A), and the upstream end is closed and the downstream end is opened (B). The partition wall between the tube portions (A) to (B) is, for example, about 1 mm in thickness and is microporous. The gas can pass through the partition wall. The exhaust gas enters from the upstream opening of the pipe (A), passes through the microporous partition wall, moves into the pipe (B), and flows out from the downstream opening end. At this time, the particulates are substantially captured by the microporous partition walls and removed from the exhaust gas. However, when such particulate trapping continues for a long period of time, there is a problem in that the accumulation of particulates causes clogging of the microporous partition wall (filter) and prevents normal exhaust gas discharge. . Such a clogging phenomenon occurs in the same way at the gap between meshes when a wire mesh packed layer filter is employed, and at the pores in the case of a skeleton structure filter. Therefore, preventing such clogging or clogging or clogging a filter that has been clogged or clogged in timely, quickly and efficiently, or at least partially cleaned, is always good and necessary. The filter filtration performance must be maintained to ensure the smooth passage and exhaust of exhaust gas.
As a means for cleaning the DPF, in the conventionally proposed one, an electric resistance heating wire is provided on the filter body, and the filter is energized to heat the filter when it is contaminated with the carbonaceous deposit. Or by removing the carbonaceous deposits by de-rinsing and cleaning the filter periodically or when necessary using a gas (eg air) flow, and the carbonaceous material particles removed at that time There is a method in which a gas flow containing gas is brought to combustion conditions in another place and the carbonaceous material is burned and removed. However, none of them is practical for use in a diesel engine.
U.S. Pat. No. 4,902,487 describes particulates trapped on a filter with NO as an oxidant. 2 A gas is brought into contact at a temperature of 400 ° C. or less to burn (oxidize) the trapped particulate, and carbon oxide (CO 2 , CO) is described as being removed, and NO acting as its oxidant 2 NO in the exhaust gas is reduced by the action of the platinum group metal catalyst arranged upstream of the filter. 2 It is also shown that it can be obtained by conversion to
Japanese Patent Application Laid-Open No. 63-51947 discloses a highly heat conductive metal plating (Cu or Ag) on a refractory three-dimensional structure or a filter made of a carrier having an inorganic oxide coating thereon. Further, a particulate combustion catalyst filter is disclosed, in which a catalyst plating layer of at least one kind of noble metal of Pt, Pd, and Rh is formed thereon.
Japanese Patent Application Laid-Open No. 3-213146 discloses a heat-resistant porous foam type exhaust gas purifying filter having a relatively low density on the inlet side and a part in which particulates easily enter and a high density thin layer on the outlet side. There is disclosed a filter comprising a trapping part, and carrying at least one catalyst component of Cs; Cu; or Ce / La; And the synergistic effect of coexisting transition metals and rare earth elements with particulates is emphasized.
[0003]
[Problems to be solved by the invention]
The inventors of the present invention have completed the present invention through intensive studies and studies on practical cleaning means of DPF. That is, the present invention can efficiently purify a filter used to filter out particulates contained in exhaust gas from a diesel engine over the entire operating condition range of the diesel engine. To provide a practical means and apparatus for easily preventing harmful clogging, ensuring effective removal of particulates and maintaining good filtration characteristics that do not hinder engine operation at all times. Its main purpose is.
[0004]
[Means for Solving the Problems]
According to the first aspect of the present invention, in an exhaust gas recirculation (EGR) type diesel engine that returns a part of exhaust gas to the intake pipe, the intake pipe system is provided with an intake control valve; One or more of a gas recirculation passage, an exhaust control valve, a reducing agent supply system, a NOx occlusion reduction catalyst, and a DPF (diesel particulate filter) for filtering out particulates in exhaust gas; (1) During the operation in the normal lean state, NO is mainly NO by the NOx storage reduction catalyst. 2 Oxidized into the form of the catalyst and occluded in the catalyst, and continued to operate in this lean state, the NOx occlusion reduction catalyst occluded and occluded. 2 The breakthrough NO is caused to occur. 2 , The particulate trapped on the downstream DPF is oxidized and removed, and when the desired DPF cleaning is achieved, the lean operation is terminated. (2) Next, the intake air Switching to rich operation by one or more of the control valve, EGR, exhaust control valve, or reducing agent introduction, so that NO already stored in the NOx storage catalyst 2 The NOx storage reduction catalyst is regenerated by reducing the catalyst, and when the regeneration is completed, the above (1) continuation of the operation under the lean condition and NO 2 There is provided a NOx occlusion reduction catalyst juxtaposition type DPF cleaning device which returns to DPF cleaning due to breakthrough and then repeats the cycle of (2) regeneration of NOx reduction occlusion catalyst under a rich state. NO in the above (1) 2 The time required for cleaning due to breakthrough is sufficient on the order of several tens of seconds, for example, about 30 to 60 seconds, and the time required for catalyst regeneration under the rich state (2) is as short as 5 seconds or less, for example. Is enough.
Conventionally, it is known to use a NOx storage reduction catalyst for purification of diesel engine exhaust gas. Such a catalyst is constituted, for example, by supporting platinum (oxidation catalyst component) and barium (occlusion agent component) on a support made of alumina. During operation in the lean state, if NOx in the exhaust gas contacts the catalyst, NO 2 It is oxidized into the form and occluded there. The chemical process that occurs here is typically NO + O. 2 ⇒NO 2 It is represented by Conventionally, when the limit of the storage capacity of the catalyst approaches (it can be detected by a NOx sensor), NO. 2 For the purpose of preventing breakthrough of the occlusion catalyst due to the above, switching from the lean state to the rich state has been performed. By this switching, reducing substances (for example, hydrocarbons, reducing agents, carbon monoxide, etc.) are present in the exhaust gas, and the stored NO. 2 Is N due to the action of reducing substances. 2 And is released from the storage catalyst, and thus the storage capacity of the storage catalyst is restored (that is, the storage catalyst is regenerated). As an example of the reaction in this case, for example, NO 2 + HC + CO⇒N 2 + CO 2 + H 2 O may be mentioned, where HC (hydrocarbon) and CO (carbon monoxide) are reducing substances.
In the present invention, NO 2 Unlike the above-described prior art, in which the storage catalyst is regenerated before the NOx storage catalyst breakthrough (or breakthrough) occurs due to NOx, the NOx storage catalyst is regenerated intentionally to delay NO. 2 Allows the storage catalyst to break through over time. NO that broke through the storage catalyst 2 Acts as an oxidizing agent for particulates (carbonaceous material; C) trapped in DPF, for example, NO 2 + C (Particulate) ⇒N 2 + CO 2 By this reaction, the deposited particulates are oxidized and removed, and thus such NO is removed. 2 If the breakthrough state is continued for a while, DPF cleaning is conveniently achieved. Once the desired degree of cleaning of the DPF is achieved, it is switched to normal lean operation. The degree of completion of DPF cleaning can be mainly detected by monitoring, for example, with a NOx sensor installed on the downstream side of the DPF. In this case, a NOx sensor for control can be added at an appropriate place to monitor the degree of completion of cleaning more accurately. The most important feature of the above aspect of the present invention is NO that has been conventionally avoided. 2 This is because the breakthrough of the occlusion catalyst is effectively utilized for cleaning regeneration of the subsequent contaminated DPF.
A specific example of the implementation apparatus of the first aspect of the present invention will be described with reference to FIG. In the apparatus shown in FIG. 1, the exhaust pipe 2 extends from the diesel engine 1 through the manifold, and the EGR pipe 3 branches from the middle thereof to return to the intake pipe 16 of the engine to form an EGR passage. The EGR pipe is provided with an EGR adjustment valve 4 on the way. The intake pipe 16 from the air cleaner 17 to the engine is provided with an intake control valve valve 5 on the upstream side of the EGR return position. After branching the EGR pipe, the exhaust pipe further extends, and the exhaust control valve 6 and the reducing agent supply pipe 13 are provided in the middle of the EGR pipe, and then the temperature sensor 10 is provided, and the NOx occlusion reduction catalyst 8 and the DPF 9 are provided downstream thereof. Built-in. A NOx sensor 11 is provided on the downstream side of the DPF. The exhaust pipe is finally provided with a muffler muffler. The reducing agent supply pipe 13 is supplied with a reducing agent (for example, light oil) from the reducing agent tank via the pump 7. A rotation sensor 14 and a load sensor 15 are installed in the engine and send detection data to the computer 12. The temperature sensor 10 and the NOx sensor 11 also send detection data to the computer 12. Based on these input data, the computer operates any one of the intake control valve 5, EGR control valve 4, exhaust control valve 6 and reducing agent supply pump 7 alone or in an appropriate combination to obtain a necessary lean state or rich state. And produce temperature conditions suitable for catalyst regeneration.
In the above apparatus, NOx and particulates discharged from the diesel engine 1 pass through the exhaust pipe 2, NOx is occluded in the NOx occlusion reduction catalyst 8, and particulates are captured by the DPF 9. In the NOx storage reduction catalyst 8, NOx, for example NO, is mainly NO. 2 Oxidized and occluded, but near or beyond its occlusion limit, NO 2 Is discharged at the catalyst outlet in the form of (NO 2 Breakthrough), oxidize and purify trapped particulates on the DPF. On the other hand, the existence of NOx occlusion on the NOx occlusion catalyst 8 is estimated by a NOx sensor, and after checking that the temperature of the catalyst inlet is appropriate, a rich state is formed and the NOx occlusion catalyst 8 is regenerated. At this time, smoke (particulate) is exhausted from the engine, but is captured by the DPF 9, which is oxidized and purified in a timely manner as described above.
[0005]
FIG. 2 shows the lean state, the air-fuel ratio (λ) in the rich state (upper stage) observed in the implementation of the apparatus according to the first aspect of the present invention, and the NOx (NO) on the outlet side of the NOx storage reduction catalyst. 2 ) Changes in concentration (lower part) versus time are shown in a pattern diagram. It is normally operated in a lean state with a λ value exceeding about 2, and NOx from the NOx storage reduction catalyst. 2 Due to the increased breakthrough, its action as an oxidant allows the DPF to be cleaned quickly and without the need for too high temperatures, then the air-fuel ratio value is switched to a rich state (λ <1), By reducing components such as HC added, NO 2 The NOx occlusion reduction catalyst in a saturated state is reduced and regenerated. As described above, the rich state can be continued in a short time on the order of several seconds.
[0006]
In the first mode shown in FIG. 1, the recirculation passage for recirculating a part of the exhaust gas has an exhaust gas inlet provided on the upstream side of the catalyst and the DPF. An exhaust gas inlet may be provided on the downstream side of the DPF, and a similar DPF cleaning effect can be achieved.
[0007]
According to the second aspect of the present invention, the filter (DPF) provided in the exhaust pipe system carries the catalyst for oxidizing and burning the trapped particulates in order to filter out the particulates in the exhaust gas from the diesel engine. In the DPF cleaning apparatus, the catalyst contains any one of silver; copper and its oxide; and a combination of silver, copper and its oxide and ceria. The catalyst may be composed of platinum, or may be composed of a combination of platinum, silver, copper and ceria.
[0008]
The cleaning device according to the second aspect of the present invention, for example, converts a DPF in the form of a monolith multi-tubular structure having a breathable microporous partition wall made of cordierite as described above into an aqueous slurry containing a catalytic metal compound and a binder. It can be prepared by a generally known dip coating method of dipping, pulling, drying and baking. The starting catalytic metal compound is preferably water-soluble. For example, silver nitrate (AgNO Three ), Copper nitrate [Cu (NO Three ) 2 ] And the like. Ceria (cerium oxide) is used in the form of a fine powder. The binder is preferably alumina sol, silica sol, etc., and those skilled in the art can easily select and employ it.
[0009]
In general, a temperature of about 600 ° C. or higher is required to oxidize and burn trapped particulates without supporting the catalyst on the DPF in this mode. It is not likely to occur under conditions, but only in the full load range. Therefore, the trapped particulates cannot be removed from the DPF, except in rare cases, such as when the DPF is heated to such a high temperature, for example by electrothermal means, or the temperature of the exhaust gas becomes such a high temperature. However, in the catalyst-supported DPF according to this aspect of the present invention, the combustion start temperature of the particulates is greatly reduced, and is approximately 400 to 450 ° C., which substantially matches the range often generated as the exhaust gas temperature in the normal operating conditions of the diesel engine. It was found to become. For example, in the experimental example, the particulate combustion start temperature is about 450 ° C. in the silver supported DPF, the combustion start temperature is about 430 ° C. in the copper supported DPF, and the combustion start temperature is about 400 ° C. in the silver / copper / ceria supported DPF. It was found that the DPF can be self-cleaned over a fairly wide temperature range from the middle load range to the full load range. This result is shown graphically in FIG. FIG. 8 also shows the results of using an unsupported DPF for comparison, and “baseline” in the figure means the combustion start temperature in the unsupported DPF, This value is generally in the range of approximately 550 ° C to 600 ° C.
[0010]
Thus, the DPF cleaning device supporting the special catalyst according to the second aspect of the present invention can cover a significant portion of the exhaust gas temperature range under normal diesel engine operating conditions with respect to DPF self-cleaning. However, the cleaning device according to this aspect expands the DPF cleaning temperature range (especially to the low temperature side) by using the above-mentioned known electric heating means and backwash cleaning by gas flow as an auxiliary, if necessary. , Its practicality can be enhanced. Even if a cleaning device using electric heating means is additionally provided, the opportunity and time for the electric heat cleaning operation can be reduced, and the power consumption for that is also low. Even when a DPF contaminated or clogged by particulate capture is backwashed with a gas flow, the frequency of backwashing operations can be significantly reduced.
[0011]
In the third aspect of the present invention, a noble metal-based oxidation catalyst is provided upstream of the DPF, and some components in the exhaust gas composition, for example, NOx, SOF (organic solvent-soluble organic substance) are modified in advance. This is a DPF cleaning device that allows exhaust gas to flow into the DPF. In the exhaust gas recirculation (EGR) type diesel engine that returns a part of the exhaust gas to the intake pipe, the apparatus of the third aspect includes an intake control valve in the intake pipe system; Equipped with a passage, exhaust control valve, noble metal oxidation catalyst, and DPF (diesel particulate filter) in series for filtering and removing particulates in exhaust gas; intake amount and exhaust control by intake control valve during engine operation By adjusting at least one of the exhaust gas amount by the valve and the recirculated exhaust gas amount by the EGR, the temperature of the exhaust gas flowing into the noble metal-based oxidation catalyst and the DPF is controlled to prevent particulate accumulation on the DPF, or A DPF cleaner characterized by forming conditions of an appropriate oxidizing atmosphere to prevent clogging of DPF clogging It is a packaging apparatus.
[0012]
Before describing the third aspect of the present invention, various ranges of exhaust gas temperatures under normal conditions of a diesel engine when the exhaust gas is treated in combination with an oxidation catalyst upstream of the DPF. The outline of the action of the oxidation catalyst on the particulates is described. (1) In the temperature range of about 100 to 250 ° C., the soot component in the particulate does not burn even when it comes into contact with the oxidation catalyst, and goes to the DPF where it is trapped. Further, the organic solvent soluble organic substance (SOF) in the particulate is partially burned and reduced by the oxidation catalyst. Therefore, in this temperature range, most of the particulates go to the downstream DPF and are captured there. (2) In a temperature range of about 250 to 450 ° C., NOx (for example, NO) in the exhaust gas is converted to NO by the oxidation catalyst. 2 (Eg, NO + O 2 ⇒NO 2 ). This NO 2 Acts as an oxidant and burns particulates (mainly soot components) deposited on the DPF, which cleans and regenerates the DPF (eg, NO 2 + C⇒N 2 + CO 2 ). In this temperature range, SOF is well oxidized and reduced. (3) In the temperature range of about 450 to 550 ° C., the above NOx oxidation reaction turns from equilibrium to the reverse direction, and NO useful as an oxidant for DPF cleaning. 2 Production is reduced or NO 2 Returns to NOx (eg, NO). Accordingly, in this way, under the reduction or absence of the oxidant, soot combustion gradually begins to decrease, and the particulates on the DPF cannot be removed. (4) In the temperature range exceeding about 550 ° C., the particulates self-combust, so that the DPF can self-regenerate. The inventors of the present invention have a stage in which particulate deposition occurs on the DPF, that is, the above temperature range of about 100 to 250 ° C. (1); and combustion removal of the particulate deposited on the DPF is stopped or reduced. In particular, pay attention to the existence of the temperature range (3) of about 450 to 550 ° C., and control the temperature of the exhaust gas so as not to cause the phenomenon appearing in these two temperature ranges. The idea was to shift to the temperature range of (2) in the case of the temperature range of 1) and to shift to the temperature range of (4) in the case of the temperature range of (3).
[0013]
Therefore, in the third aspect of the present invention, in both the temperature ranges of about 100 to 250 ° C. of (1) and about 450 to 550 ° C. of (3), particulates are deposited on the DPF, or on the DPF. In view of the fact that the accumulated particulates are not burned off, when the exhaust gas temperature is in both such ranges, at least one of the intake control valve, exhaust control valve and EGR is used to Up to the upper temperature range [Sanichi, (1) to (2) NO 2 From the (3) to the (4) self-combustion stage] By increasing the exhaust gas temperature, the particulates do not accumulate on the DPF, and the particulates deposited on the DPF burn It is intended to be removed. The individual actions of the exhaust gas temperature control means in this embodiment need not be described, but increase in the hydrocarbon (HC) concentration in the exhaust gas by EGR; intake control valve and / or exhaust control valve In the present invention, at least one of the reduction of the exhaust gas amount due to the catalyst; and the exothermic heat of the oxidation reaction by the catalyst is appropriately used in the present invention. The operation of these temperature control means can be performed by a computer. In this aspect, in some cases, even if the oxidation catalyst is omitted, it is possible to perform the necessary required temperature control by appropriate application of the EGR and the intake control valve / exhaust control valve. This is a modification of the third aspect of the present invention.
[0014]
FIG. 3 is a schematic diagram of an example of a specific apparatus according to the third aspect of the present invention. In the apparatus shown in FIG. 3, the exhaust pipe 2 extends from the diesel engine 1 through the manifold, and the EGR pipe 3 branches from the middle of the exhaust pipe 2 to return to the intake pipe 16 of the engine to form an EGR passage. The EGR pipe is provided with an EGR adjustment valve 4 on the way. The intake pipe 16 from the air cleaner 17 toward the engine is provided with the intake adjustment valve 5 on the upstream side of the EGR return position. After branching the EGR pipe, the exhaust pipe further extends, and is provided with an exhaust control valve 6 and a temperature sensor 10 in the middle of the EGR pipe. Built-in, and finally equipped with a muffler muffler (not shown). Detection data of the temperature sensor 10 that detects the temperature of the exhaust gas is sent to the computer 12. Depending on the temperature value, the computer sends out an output signal for operating at least one of the EGR control valve 4, the intake control valve 5, the exhaust control valve 6, or an appropriate combination, and the temperature as described above. Shift from range 1 (about 100-250 ° C.) to temperature range 2 (about 250-450 ° C .: DPF purification stage by oxidation), and temperature range 3 (about 450-550 ° C.) to temperature range 4 (self-combustion stage) Shift to. For reference, an example of a flowchart of computer control based on exhaust gas temperature data is illustrated in FIG. The temperature values in the figure are examples and are not limiting values.
[0015]
In another preferred embodiment of the third aspect, a pressure sensor is provided upstream of the oxidation catalyst and the DPF to detect the degree of clogging of the DPF or the degree of contamination thereof, and the detection data is obtained. When it is detected that the exhaust gas pressure in the exhaust pipe exceeds a predetermined value within a predetermined allowable range, for example, 200 mmHg, compared with the atmospheric pressure, the EGR control valve and the intake control valve are sent to the computer 12 The exhaust gas temperature shift may be performed by operating at least one of the exhaust control valves or an appropriate combination. For reference, an example of a flowchart in the case of computer control based on the pressure data is illustrated in FIG. The pressure values in the figure are illustrative and not limiting.
[0016]
In such a specific example, a pressure parameter can be adopted in addition to the exhaust gas temperature parameter as a criterion for performing the DPF cleaning operation, and the cleaning operation starts until a predetermined exhaust gas pressure is detected. If the postponed control is performed, there is a practical advantage that the frequency of DPF cleaning is generally reduced. In these cases, the completion point of the DPF cleaning operation is determined based on the pressure value data from the pressure sensor, and an operation stop signal is output from the computer.
[0017]
The oxidation catalyst used in the third embodiment of the present invention comprises a noble metal such as platinum (Pt) or palladium (Pd) supported on a carrier such as alumina. In practice, the water-soluble noble metal compound, alumina Z powder and binder ( For example, alumina sol, silica sol) is mixed with water to form an aqueous slurry, and a refractory ceramic (for example, cordierite) honeycomb carrier is dipped in this, and is then lifted, dried, and fired by a known dip coating method. Can be manufactured.
[0018]
The first to third aspects of the present invention have been described when a part of the exhaust gas is introduced from the upstream side of a catalyst (NOx storage catalyst or oxidation catalyst) or DPF in order to introduce a part of the exhaust gas to the recirculation passage. However, in any of these aspects, it has been confirmed that even if the exhaust gas recirculation inlet is provided on the downstream side of the DPF (see FIG. 4), the objects and effects of the present invention are equivalently achieved. Therefore, it is also within the scope of the present invention to provide an exhaust gas inlet of the exhaust gas recirculation passage on the downstream side of the DPF. FIG. 4 is an enlarged view of the DPF installation portion of the exhaust pipe system, and shows a case where an exhaust gas inlet to the EGR pipe 3 is provided on the downstream side of the DPF 9.
[0019]
In any of the above aspects of the present invention, it is possible to improve the accuracy of the control output for operating the DPF cleaning device by attaching a rotation sensor and a load sensor to the diesel engine and inputting information from them to the computer. Is possible.
[0020]
Furthermore, the present invention provides another NO. 2 A regenerative DPF cleaning device is also provided. That is, the NOx oxidation catalyst and NO in the exhaust pipe system from the diesel engine 2 A regenerative DPF (diesel particulate filter) is provided in series, and NO is usually generated from NOx by the action of a NOx oxidation catalyst. 2 A diesel engine DPF cleaning device that removes collected and accumulated particulates on a DPF by oxidative combustion using the oxidizing power of the DPF, and (a) an excessive amount of particulates in the DPF more than a predetermined amount is disposed before and after the DPF. (B) sensor means for detecting the state of exhaust gas temperature, NOx concentration, etc .; (c) detection signals of means (a) and (b) above. NO required to remove excessive deposition particulates on the DPF 2 The fuel injection timing for the diesel engine is advanced in order to temporarily increase the amount of NOx to be generated and to temporarily generate in the exhaust gas conditions such as a temperature suitable for oxidative combustion removal of the excessively accumulated particulates. A command signal for setting the displacement in the direction or the direction in which the timing is delayed is output to the fuel injection pump, and the pressure sensor detects when the removal of the excessive accumulation particulates is completed or finished to a desired level as a result of the timing displacement fuel injection. Said DPF cleaning device comprising: electronics processor means for outputting a command signal for returning the fuel injection timing to the original normal position as judged from the detection signal from the means (a), toward the fuel injection pump; It is. By including an oxidation catalyst in the DPF itself of this embodiment, it is possible to promote the oxidation combustion of the deposited particulates and improve the removal effect thereof.
[0021]
NO above 2 An example of a regenerative DPF cleaning device is shown schematically in FIG. The exhaust gas discharged from the diesel engine 51 passes through the exhaust manifold 52 and the exhaust pipe 53 and is introduced into the subsequent DPF cleaning device main body 54. The inside of the DPF cleaning device main body 54 has a structure in which a NOx oxidation catalyst 61 is disposed on the upstream side and a DPF 62 that is a particulate collection device is disposed on the downstream side. When the exhaust gas is introduced into the DPF cleaning device, it first passes through the NOx oxidation catalyst 61, the particulates are collected by the DPF 62, and other components are released to the outside through the exhaust pipe. At this time, in the region where the exhaust gas temperature is approximately 200 to 450 ° C., the NOx catalyst effectively acts to oxidize NOx (mainly NO) in the exhaust gas and has strong oxidizing power. 2 It becomes. The particulates collected and deposited in the DPF are NOs with this strong oxidizing power. 2 Can be removed by combustion.
[0022]
In the present invention, NO 2 In order to completely and stably remove particulates by oxidation and combustion, various sensors are used to detect the state of particulate collection and deposition in the DPF 62 and the regeneration of the DPF. When such particulates are accumulated or when such a state is occurring), the engine operating state (mainly fuel injection timing) is controlled to regenerate the DPF or to the DPF. In order to prevent further accumulation of the exhaust gas temperature range, NO 2 This is to optimize the generation promotion and the prevention of particulate generation. When the balance between the particulate collection amount and the particulate oxidative combustion removal amount in the DPF cleaning device main body 54 is lost and the accumulation of particulates on the DPF 62 starts to increase, the pressure sensors 59 disposed before and after the DPF An increase in the back pressure is detected, a back pressure (rise) value signal is sent to the ECU / EDU 55, and data signals for monitoring and monitoring other driving conditions are also provided, such as a rotation sensor 56, an accelerator (load) sensor 57, Input from the NOx sensor 58 and the temperature sensor 60 to the ECU / EDU 55 (see FIG. 5). Based on these data, the ECU / EDU 55 optimizes the exhaust gas temperature (preferably in the range of about 300 to 400 ° C.) and NO. 2 In order to promote the generation of this, a signal instructing the fuel injection pump 63 to change the injection timing (mainly the advance angle) is sent.
[0023]
When the particulates accumulated in the DPF start to be combusted by the above control, the pressure sensor 59 and the temperature sensor 60 detect the temperature increase and the back pressure decrease of the exhaust gas accompanying the particulate combustion, and the ECU / EDU 55 Judges the regeneration status of the DPF 62, controls the engine again if necessary, and repeats this cycle until it is judged that the particulate removal in the DPF has ended. FIG. 6 shows a block diagram of input / output of the ECU / EDU control. In this figure, detection data signal inputs from various sensors 6 to 9 and an instruction signal output to the fuel injection pump after analyzing the data are shown.
[0024]
Conventional NO 2 In the regenerative type DPF cleaning device, NOx in the exhaust gas is strongly oxidized using NOx in the exhaust gas in a temperature range as limited as described above. 2 NO generated by oxidation to 2 The soot (particulate) collected in the DPF is burned and removed to regenerate the DPF, which is also referred to as a continuous regeneration trap. 2 Generation depends on the exhaust gas temperature. For example, in the low temperature range up to about 200 ° C, NOx⇒NO 2 Conversion is suppressed, particulate removal is not performed, and particulate collection continues in the DPF, so that the amount of particulate accumulation on the DPF gradually increases and clogging of the DPF occurs over a period of time. Therefore, an excessive increase in the back pressure occurs, which may cause a decrease in engine operation performance.
[0025]
In contrast to the drawbacks of the prior art as described above, in the DPF cleaning device of the present invention shown in FIGS. 5 and 6, the exhaust gas temperature is in a low temperature range, and particulate deposition in the DPF is expected. Controls the operating state of the engine (mainly by shifting the fuel injection timing in the advance direction or the direction in which the timing is delayed) to generate exhaust gas conditions suitable for particulate removal. It is possible to effectively prevent an increase in the amount of particulates deposited over time, and thus maintain maintenance-free and stable DPF performance over a long period of time.
[0026]
The present invention also provides another embodiment of NO. 2 A regenerative DPF cleaning device is also provided. That is, means for supplying heating fuel into the exhaust pipe system from the diesel engine as needed; combustion of the supplied fuel to obtain a high temperature and NOx having high oxidizing power 2 An oxidation catalyst for conversion to NO; and NO for filtering off particulates 2 In a DPF cleaning device in which a regenerative DPF (diesel particulate filter) is arranged in series, the oxidation catalyst is provided with a heater heating means, and the temperature of the inflowing exhaust gas is NOx NO in the oxidation catalyst. 2 Amount of NO required for DPF cleaning too low for conversion to 2 If this does not occur, the heater heating means is actuated to raise the temperature of the oxidation catalyst and the required amount of NO. 2 The particulates accumulated on the DPF are removed to the required level, and in these operations, data signals provided from the engine speed sensor, load sensor and exhaust gas temperature sensor are input, The DPF cleaning device is provided with a computer that outputs control signals for ON / OFF of heating fuel supply and adjustment of the supply amount thereof, and ON / OFF of heater heating and adjustment of the heating intensity based on . In this apparatus, the heater heating can be controlled so that the particulates are burned and removed by the heater heating before reaching the DPF. An oxidation catalyst that promotes oxidative combustion of particulates may be included in the DPF itself, and the addition of such a catalyst can further improve the DPF cleaning effect.
[0027]
FIG. 7 shows an outline of an embodiment of the above-described heating fuel supply / heater heating type DPF cleaning apparatus. A fuel supply pump 105 and a fuel supply nozzle 113 are attached as means for supplying heating fuel (generally hydrocarbons such as light oil) to the exhaust pipe 102 from the diesel engine 101, and a heater heating means is provided downstream thereof. A catalyst 107 and a DPF 108 are attached, and a muffler 109 is further attached. The computer 111 receives data signals detected by a rotation sensor 103, a load sensor 104 attached to the engine, and a temperature sensor 114 attached to the exhaust pipe. On the basis of these input data, the computer 111 issues an operation instruction signal to the fuel supply pump 105 when it is determined that heating fuel supply is necessary, and also includes a catalyst 107 with a heater and a current supply power source (battery) for its operation. An instruction signal is also sent to the controller 112 connected to the. This control is performed with respect to ON / OFF of the fuel supply for heating and its supply amount, ON / OFF of heater heating, and heating intensity. The catalyst 107 with a heater is made of, for example, a main body in which a stainless sheet is wound in a coil, and the surface thereof is coated with an oxidation catalyst and has a heating wire. The DPF 108 is, for example, a cordierite or SiC filter, similar to the above. In the DPF cleaning device of this aspect of the present invention, the DPF collection particulates can be burned and removed even in a region where the temperature of the exhaust gas is low, and the clogging of the DPF can be effectively prevented. As a result, good performance of the DPF can be maintained over a long period of time.
[Brief description of the drawings]
FIG. 1 is a schematic view of a DPF cleaning device according to a first embodiment of the present invention.
2 is a time pattern diagram of the lean and rich states of the apparatus of FIG. 1 and the NOx concentration on the NOx storage reduction catalyst outlet side versus time. FIG.
FIG. 3 is a schematic view of a DPF cleaning device according to a third embodiment of the present invention.
FIG. 4 is a partially enlarged view showing an exhaust gas introduction port to an EGR pipe provided on the downstream side of the DPF.
FIG. 5: NO according to the present invention 2 Schematic of an example of an aspect of a regenerative type DPF cleaning device.
6 is an ECU / EDU input / output flowchart for device control in FIG. 5;
FIG. 7 shows NO according to the present invention. 2 Schematic of another example of a regenerative type DPF cleaning device.
FIG. 8 is a graph showing the particulate combustion start temperature of various catalyst-supported DPFs compared with the value of the unsupported DPF.
FIG. 9 is an example of a flowchart of computer control of DPF cleaning based on exhaust gas temperature data.
FIG. 10 is an example of a flowchart of computer control of DPF cleaning based on exhaust gas pressure data.
[Explanation of symbols]
1 Diesel engine
2 Exhaust pipe
3 EGR pipe
4 EGR control valve
5 Intake control valve
6 Exhaust control valve
7 Reducing agent supply pump
8 NOx storage reduction catalyst (or noble metal oxidation catalyst)
9 DPF
10 Temperature sensor
11 NOx sensor
12 computers
16 Intake pipe
17 Air cleaner
51 diesel engine
52 Exhaust manifold
53 Exhaust pipe
54 DPF cleaning device
55 ECU / EDU
56 Rotation sensor
57 Accelerator (load) sensor
58 NOx sensor
59 Pressure sensor
60 Temperature sensor
61 NOx oxidation catalyst
62 DPF
63 Fuel injection pump
101 diesel engine
102 Exhaust pipe
103 Rotation sensor
104 Load sensor
105 Fuel supply pump for heating
106 Fuel (light oil) tank
107 Heater (with catalyst if necessary)
108 DPF
109 Muffler
110 Heater power supply (battery)
111 computers
112 controller
113 Fuel supply nozzle for heating
114 Temperature sensor

Claims (1)

  1. In an exhaust gas recirculation (EGR) type diesel engine that returns a part of the exhaust gas to the intake pipe, the intake pipe system has an intake control valve; the exhaust pipe system has an exhaust gas circulation passage, an exhaust control valve, and a reducing agent supply One or more of the systems, NOx storage reduction catalyst, and DPF (diesel particulate filter) for filtering and removing particulates in exhaust gas are provided in series; (1) During operation in a normal lean state in the NO by the NOx storage reduction catalyst primarily oxidized in the form of NO 2 allowed storage on the catalyst, yet the operation at the lean state continues by storing beyond the storage capacity of the NOx storage reduction catalyst NO 2 so as to produce a breakthrough, the breakthrough NO 2 by the action particulates by oxidation removal that is captured on the DPF downstream as an oxidizing agent that, optionally When the DPF cleaning is achieved, the operation in the lean state is terminated. (2) Next, the rich operation state is achieved by one or more of the intake control valve, EGR, exhaust control valve, and reducing agent introduction. In this way, NO 2 already stored in the NOx storage catalyst is reduced and removed to regenerate the NOx storage catalyst. When the regeneration is completed, the above operation (1) under the lean condition is performed again. A NOx occlusion reduction catalyst juxtaposition type DPF cleaning device characterized by repeating the cycle of resuming NOx occlusion reduction catalyst in the rich state of (2) after returning to DPF cleaning due to continuation and NO 2 breakthrough.
JP25173399A 1999-09-06 1999-09-06 Diesel engine exhaust gas particulate filter cleaning and regeneration device Expired - Fee Related JP3904768B2 (en)

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