US20100043406A1 - Exhaust emission control apparatus for internal combustion engine - Google Patents

Exhaust emission control apparatus for internal combustion engine Download PDF

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Publication number
US20100043406A1
US20100043406A1 US12/520,555 US52055507A US2010043406A1 US 20100043406 A1 US20100043406 A1 US 20100043406A1 US 52055507 A US52055507 A US 52055507A US 2010043406 A1 US2010043406 A1 US 2010043406A1
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Prior art keywords
nox
layer
ozone
catalyst
exhaust gas
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US12/520,555
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English (en)
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Hirohito Hirata
Masaya Ibe
Mayuko Osaki
Masaya Kamada
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Toyota Motor Corp
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Toyota Motor Corp
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Assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA reassignment TOYOTA JIDOSHA KABUSHIKI KAISHA ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KAMADA, MASAYA, IBE, MASAYA, HIRATA, HIROHITO, OSAKI, MAYUKO
Publication of US20100043406A1 publication Critical patent/US20100043406A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/10—Preparation of ozone
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/10—Oxidants
    • B01D2251/104—Ozone
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B01D2255/1021—Platinum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/204—Alkaline earth metals
    • B01D2255/2042—Barium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/902—Multilayered catalyst
    • B01D2255/9022—Two layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/91—NOx-storage component incorporated in the catalyst
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/38—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an ozone (O3) generator, e.g. for adding ozone after generation of ozone from air
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

  • the present invention relates to an exhaust emission control apparatus for an internal combustion engine.
  • a conventional exhaust emission control apparatus includes an NOx occlusion reduction type catalyst.
  • an exhaust path of an internal combustion engine is provided with a catalyst and with a substance capable of occluding NOx (hereinafter also referred to as the “NOx retention substance”).
  • NOx retention substance a substance capable of occluding NOx
  • the catalyst reach its activation temperature and fully exercise its activation function.
  • the catalyst temperature is low.
  • the conventional exhaust emission control apparatus addresses the above problem by adding ozone (O 3 ) to the exhaust gas at internal combustion engine startup. Adding ozone to the exhaust gas oxidizes NOx in the exhaust gas to accelerate an NOx occlusion reaction. Consequently, even when the catalyst is not fully active at the time, for instance, of internal combustion engine startup, the use of the above-described conventional technology makes it possible to accelerate NOx occlusion and purify the exhaust gas.
  • the above-described NOx occlusion reduction type catalyst is formed so that a layer containing a catalyst and an NOx retention substance is coated onto a base material (which may also be referred to as a support).
  • This type of NOx occlusion reduction type catalyst tends to have a smaller exhaust gas purification capacity (a smaller capacity of purifying NOx, HC, and CO) than a conventional three-way catalyst without an NOx retention substance. It means that the exhaust gas purification function of the above-described NOx occlusion reduction type catalyst is blocked.
  • An object of the present invention is to provide an exhaust emission control apparatus that is used with an internal combustion engine to occlude and reduce NOx without blocking the exhaust gas purification function of a catalyst.
  • the first aspect of the present invention is an exhaust emission control apparatus for an internal combustion engine, comprising:
  • an NOx occlusion reduction type catalyst which is positioned in an exhaust path of the internal combustion engine
  • ozone supply means which supplies ozone so that the ozone mixes with an exhaust gas flowing into the NOx occlusion reduction type catalyst
  • the NOx occlusion reduction type catalyst includes a cell in which the exhaust gas flows, an inner surface of the cell being coated with a first layer and a second layer, the first layer and the second layer being provided in the order named from the inner surface of the cell, the first layer containing an NOx retention substance, the second layer including a noble metal and permitting the passage of NOx, the amount of the NOx retention substance in the second layer is smaller than that in the first layer.
  • the second aspect of the present invention is the exhaust emission control apparatus according to the first aspect, wherein the amount of the NOx retention substance contained in the second layer is substantially zero.
  • the third aspect of the present invention is the exhaust emission control apparatus according to the first or the second aspect, further comprising:
  • ozone supply amount adjustment means for adjusting an ozone supply amount so that the mole ratio of ozone to nitrogen monoxide (NO) in a gas mixture flowing into the NOx occlusion reduction type catalyst is greater than 1.
  • the fourth aspect of the present invention is the exhaust emission control apparatus according to the third aspect, wherein the ozone supply amount adjustment means adjusts the ozone supply amount so that the mole ratio of ozone (O 3 ) to nitrogen monoxide (NO) in the gas mixture flowing into the NOx occlusion reduction type catalyst is not smaller than 2.
  • an NOx retention layer and a catalyst layer are independently formed. Therefore, the catalyst can properly exercise its exhaust gas purification function. It is thought that the NOx retention substance is a catalyst poison for a noble metal element and is a factor of decreasing the exhaust gas purification capacity of the catalyst.
  • the first aspect of the present invention forms the NOx retention layer and catalyst layer independently in a layer form and accelerates an NOx occlusion reaction by ozone supply means without resort to the catalyst layer. This makes it possible to occlude and reduce NOx while inhibiting the NOx retention substance from acting as a catalyst poison to keep the catalyst's exhaust gas purification function intact.
  • the second aspect of the present invention makes it possible to suppress the influence of the catalyst poison with higher effectiveness than in the first aspect.
  • NO in the exhaust gas can be oxidized to generate NO 3 , N 2 O 5 , and other nitrogen oxides of higher order than NO 2 (generate HNO 3 as well if water exists).
  • This makes it possible to increase the amounts of NO 3 , N 2 O 5 , and other nitrogen oxides of higher order than NO 2 , which are contained in the exhaust gas that flows into an NOx retention member.
  • an NOx occlusion reaction can be accelerated to increase the exhaust gas purification capacity.
  • a sufficient amount of ozone can be supplied as needed to generate NO 3 , N 2 O 5 , and other nitrogen oxides of higher order than NO 2 (generate HNO 3 as well if water exists) by oxidizing NO.
  • the NOx occlusion reaction can be effectively accelerated to increase the exhaust gas purification capacity.
  • FIG. 1 is a diagram illustrating configuration of an exhaust emission control apparatus according to a first embodiment of the present invention.
  • FIGS. 2A and 2B are diagrams illustrating configuration of the apparatus according to the first embodiment.
  • FIG. 3 is a flowchart illustrating a routine that the ECU executes in the first embodiment.
  • FIG. 4 is a diagram to describe result of experiment for the first embodiment.
  • FIG. 5 is a diagram to describe result of experiment for the first embodiment.
  • FIGS. 6A and 6B are diagrams to describe result of experiment for the first embodiment.
  • FIGS. 7A to 7C are diagrams to describe result of experiment for the first embodiment.
  • FIG. 8 is a diagram to describe result of experiment for the first embodiment.
  • FIG. 1 is a diagram illustrating an exhaust emission control apparatus according to a first embodiment of the present invention.
  • the exhaust emission control apparatus according to the first embodiment includes a catalytic device 20 , which is placed in an exhaust path 12 of an internal combustion engine 10 .
  • An NOx occlusion reduction type catalyst 22 is placed in the catalytic device 20 .
  • an exhaust gas passing through the exhaust path 12 flows into the catalytic device 20 and then into the NOx occlusion reduction type catalyst 22 .
  • the NOx occlusion reduction type catalyst 22 is formed when a base material (hereinafter also referred to as a support) is coated with a layer containing an NOx retention substance (hereinafter also referred to as the “NOx retention layer”) and a layer containing a noble metal (hereinafter also referred to as the “catalyst layer”).
  • the NOx retention layer is capable of occluding NOx in the exhaust gas and releasing the occluded NOx in a high-temperature or rich atmosphere.
  • the catalyst layer is capable of inducing a reaction between NOx and HC or CO and decomposing the NOx into N 2 , H 2 O, CO 2 , etc. Employing the configuration described above makes it possible to effectively purify NOx contained in the exhaust gas.
  • FIG. 2(A) is a cross-sectional left side view that is taken along line A-A in FIG. 1 to illustrate the NOx occlusion reduction type catalyst 22 .
  • the NOx occlusion reduction type catalyst 22 includes a ceramic base material 25 having a circular outline.
  • the base material 25 is honeycombed to include a plurality of rectangular cells 24 . The cells 24 run through the base material 25 in the direction of the depth of FIG. 2(A) so that the exhaust gas can be distributed in that direction.
  • FIG. 2(B) is an enlarged view of one cell 24 .
  • Each cell 24 is one of a plurality of partitions provided by the base material 25 .
  • Each cell 24 includes an NOx retention layer 26 and a catalyst layer 27 . These layers are provided on the surface of the base material 25 individually and sequentially from the side of the base material 25 .
  • a flow path 28 is formed in each cell 24 and positioned inside the catalyst layer 27 . The flow path 28 is extended in the direction of the depth of FIG. 2(B) so that the exhaust gas is distributed through the flow path 28 .
  • the NOx retention layer 26 is formed by coating the base material 25 with an NOx retention material containing BaCO 3 .
  • BaCO 3 functions as an NOx retention substance (also referred to as an NOx occlusion agent) that occludes NOx in the exhaust gas as nitrate (or more specifically, Ba(NO 3 ) 2 ).
  • the occluded Ba(NO 3 ) 2 is actively released when mainly the exhaust gas is rich or when the NOx retention substance temperature is high.
  • the catalyst layer 27 is formed by coating the NOx retention layer 26 with a catalytic material containing Pt or other noble metal. Pt or other noble metal functions as an active site that simultaneously activates the oxidation reaction of CO and HC and the reduction reaction of NOx. Thus, the catalyst layer 27 functions as a three-way catalyst that simultaneously purifies NOx, CO, and HC. The catalyst layer 27 is gas permeable to let NOx move between the flow path 28 and NOx retention layer 26 .
  • the apparatus according to the first embodiment also includes an ozone supply device 30 as shown in FIG. 1 .
  • the ozone supply device 30 is in communication with an air inlet 34 .
  • the ozone supply device 30 can acquire air from the air inlet 34 , generate ozone (O 3 ), and supply the generated ozone downstream.
  • O 3 ozone
  • the configuration, function, and other characteristics of an ozone generator which generates ozone from air will not be described in detail because a variety of related technologies are publicly known.
  • the ozone supply device 30 has an ozone injection orifice 32 which injects a gas within the catalytic device 20 .
  • the ozone injection orifice 32 is positioned upstream of the NOx occlusion reduction type catalyst 22 in the catalytic device 20 .
  • the ozone or air can be added to the exhaust gas passing through the exhaust path 12 .
  • the added ozone or air then mixes with the exhaust gas so that the resulting gas mixture flows into the NOx occlusion reduction type catalyst 22 .
  • the exhaust emission control apparatus includes an ECU (Electronic Control Unit) 50 .
  • the ECU 50 is connected to the ozone supply device 30 .
  • the ECU 50 transmits a control signal to the ozone supply device 30 for the purpose of controlling the timing and amount of ozone injection.
  • the use of the above-described configuration makes it possible to supply ozone at desired timing.
  • the ozone supply device 30 can add ozone to the exhaust gas as needed. This makes it possible to effectively purify the exhaust gas by oxidizing NOx in the exhaust gas during a gas phase reaction.
  • the ECU 50 is also connected, for instance, to various sensors which are provided for the internal combustion engine 10 . Therefore, the ECU 50 can acquire information, for instance, about the temperature, engine speed Ne, air-fuel ratio A/F, load, and intake air amount of the internal combustion engine 10 .
  • the NOx retention substance (BaCO 3 in the first embodiment) contained in the NOx retention member is capable of occluding NOx in the exhaust gas.
  • the noble metal contained in the catalyst (Pt, Rh, Pd, etc. in the first embodiment) functions as an active site during exhaust gas purification. To achieve NOx occlusion and reduction and exhaust gas purification with high efficiency, it is important that the above functions be exercised effectively in a coordinated manner.
  • NOx occlusion reduction type catalyst can accelerate the NOx occlusion reaction by promoting the oxidation of NOx by using the catalyst. Further, when NOx is to be released, the catalyst can purify the exhaust gas.
  • the exhaust gas purification capacity of the catalyst (the capacity for purifying NOx, HC, and CO) becomes smaller than that of a conventional three-way catalyst that does not contain an NOx retention substance.
  • the NOx retention substance acts as a catalyst poison for the catalyst (noble metal element) and impairs the catalyst's activation function.
  • the exhaust emission control apparatus configures the NOx occlusion reduction type catalyst 22 by providing the base material 25 with the NOx retention layer 26 and catalyst layer 27 separately so as to provide these two layers as independent layers.
  • the catalyst's exhaust gas purification capacity decreases when the NOx retention substance acts as a catalyst poison.
  • the first embodiment prevents the NOx retention substance from acting as a catalyst poison for the catalyst layer 27 because the NOx retention layer 26 and catalyst layer 27 are formed independently of each other.
  • the following describes operations that are performed for NOx occlusion and NOx release when the configuration according to the first embodiment is employed.
  • the NOx occlusion reduction type catalyst 22 has the catalyst layer 27 .
  • the catalyst layer 27 includes Pt or other noble metal and can simultaneously purify NOx, CO, and HC (this function may be hereinafter referred to as the “exhaust gas purification function”).
  • exhaust gas purification function this function may be hereinafter referred to as the “exhaust gas purification function”.
  • the catalyst it is necessary that the catalyst be heated to an adequate activation temperature. Therefore, when the internal combustion engine 12 starts up, particularly at a cold temperature, it is difficult to purify NOx contained in the exhaust gas because the temperature of the NOx occlusion reduction type catalyst 22 is low.
  • the present embodiment causes the NOx retention layer 26 to occlude NOx. Further, to accelerate such an NOx occlusion, the present embodiment uses the ozone supply device 30 to supply ozone in such a manner that ozone mixes with the exhaust gas flowing into the NOx occlusion reduction type catalyst 22 .
  • NOx in the exhaust gas is oxidized to facilitate NOx occlusion.
  • the NOx oxidized by ozone reaches the NOx occlusion reduction type catalyst 22 and flows into the flow path 28 within each cell 24 .
  • the NOx flows in the flow path 28 , it passes through the catalyst layer 27 , which is not yet heated to its activation temperature, and then reaches the NOx retention layer 26 . Subsequently, an occlusion reaction occurs in the NOx retention layer 26 so that NOx is occluded as nitrate.
  • the above-described operation it is possible to occlude NOx in the exhaust gas even in a situation where the catalyst layer 27 of the NOx occlusion reduction type catalyst 22 has not reached its activation temperature at startup of the internal combustion engine 12 .
  • the temperature of the NOx occlusion reduction type catalyst 22 rises. Therefore, when an adequate period of time elapses after startup of the internal combustion engine 12 , the temperature of the catalyst layer 27 in the NOx occlusion reduction type catalyst 22 reaches an activation temperature. Consequently, when the catalyst layer 27 reaches its activation temperature and is ready to fully exercise its exhaust gas purification function, the first embodiment shuts off the supply of ozone and exercises control to slightly enrich the fuel injection amount of the internal combustion engine 12 .
  • the present embodiment is configured so that the NOx retention layer 26 and catalyst layer 27 are formed independently of each other. This configuration prevents the NOx retention substance from acting as a catalyst poison for the catalyst layer 27 . Consequently, the present embodiment makes it possible to purify the exhaust gas effectively without blocking the exhaust gas purification function of the catalyst layer 27 .
  • the present embodiment prevents the NOx retention substance from acting as a catalyst poison because the NOx retention layer 26 and catalyst layer 27 are formed independently of each other. This makes it possible to prevent the exhaust gas purification capability of the catalyst layer 27 from being hindered. Further, the present embodiment causes the ozone supply device 30 to supply ozone and accelerates the NOx occlusion reaction without resort to the catalyst. Therefore, NOx can be occluded and reduced while fully exercising the exhaust gas purification function of the catalyst.
  • NOx when an NOx oxidation method based on ozone is used, NOx can be oxidized with increased certainty during a gas phase reaction without resort to the catalyst even when the temperature is low at the time, for instance, of internal combustion engine startup.
  • water vapor exists nitric acid arises and easily reacts with the NOx retention substance. This makes it possible to occlude NOx with high efficiency.
  • the NOx occlusion reduction type catalyst 22 corresponds to the “NOx occlusion reduction type catalyst” according to the first aspect of the present invention
  • the ozone supply device 30 corresponds to the “ozone supply means” according to the first aspect.
  • the cell 24 corresponds to the “cell” according to the first aspect of the present invention
  • the NOx retention layer 26 corresponds to the “first layer” according to the first aspect
  • the catalyst layer 27 corresponds to the “second layer” according to the first aspect.
  • FIG. 3 is a flowchart illustrating a routine that the ECU 50 executes in the first embodiment.
  • the routine is executed when the internal combustion engine 10 starts at a low temperature (e.g., at a cold start).
  • step S 100 performs step S 100 to supply ozone. More specifically, the ECU 50 transmits a control signal to the ozone supply device 30 so that ozone is supplied at a predetermined flow rate. Ozone injection then occurs in accordance with the control signal. As a result, NO in the exhaust gas is oxidized to NO 3 so that an occlusion reaction occurs efficiently within the NOx retention layer 26 .
  • step S 110 the routine performs step S 110 to judge whether an O 3 supply shutoff condition is established. More specifically, step S 110 is performed to judge whether a certain period of time, which is required for the catalyst layer 27 to reach its activation temperature and is predetermined, for instance, during an experiment, has elapsed. When the obtained judgment result does not indicate that the O 3 supply shutoff condition is established, the routine concludes that the catalyst layer 27 has not reached its activation temperature, and repeats steps S 100 and beyond.
  • step S 130 shuts off the supply of O 3 , and controls the operating status of the internal combustion engine 10 so that the air-fuel ratio changes from stoichiometric to slightly rich.
  • the NOx occluded in the NOx retention layer 26 is released.
  • the released NOx then reaches the catalyst layer 27 , and becomes reduced and purified. Subsequently, the routine comes to an end.
  • FIG. 4 shows a measurement system that was used for the experiment.
  • the measurement system includes a model gas generator 230 and a plurality of gas cylinders 232 in order to generate a model gas which represents the exhaust gas of an internal combustion engine.
  • the model gas generator 230 can mix the gases in the gas cylinders 232 to create the following simulant gas:
  • the model gas generator 230 is in communication with an electric furnace in which a test piece 222 is placed.
  • FIG. 5 is an enlarged view of the test piece 222 and its vicinity.
  • the test piece 222 is configured so that an embodiment sample 224 is housed in a quartz tube.
  • the experiment involves the use of a comparative example for which the same experiment is to be conducted as with the embodiment sample 224 with a later-described comparative sample substituted for the embodiment sample 224 .
  • the measurement system shown in FIG. 4 includes an oxygen cylinder 240 .
  • the downstream end of the oxygen cylinder 240 is in communication with flow rate control units 242 , 244 .
  • the flow rate control unit 242 is in communication with the ozone generator 246 .
  • the ozone generator 246 receives oxygen which is supplied from the oxygen cylinder 240 , and generates ozone.
  • the ozone generator 246 communicates with the downstream end of the model gas generator 230 and the upstream end of the test piece 222 through an ozone analyzer 248 and a flow rate control unit 250 .
  • the downstream end of the flow rate control unit 244 directly communicates with the ozone analyzer.
  • turning ON the ozone generator 246 supplies a gas mixture of O 3 and O 2 to the upstream end of the test piece 222 whereas turning OFF the ozone generator 246 supplies only O 2 to the upstream end of the test piece 222 .
  • the measurement system shown in FIG. 4 makes it possible to create the following two types of gases, which differ in composition. Each of these gases is to be injected into the test piece 222 and will be hereinafter simply referred to as an “injection gas.”
  • the flow rate control unit 250 can supply the injection gas at a desired flow rate.
  • FIGS. 6(A) and 6(B) illustrate an embodiment sample and a comparative sample that were used during the experiment.
  • FIG. 6(A) shows a cell of the embodiment sample 224 which is also shown in FIG. 5 .
  • FIG. 6(B) shows a cell of the comparative sample 324 .
  • the comparative sample 324 uses the same honeycombed base material as the embodiment sample 224 , but is coated in a manner different from that for the embodiment sample 224 .
  • the embodiment sample 224 shown in FIG. 6(A) was prepared by performing the procedure described below. First of all, ⁇ -Al 2 O 3 was dispersed in ion exchange water. An aqueous solution of barium acetate was then added. The resulting mixture was heated to remove water from it, dried at 120° C., and pulverized to powder. The powder was then burned for two hours at 500° C. The burnt powder was immersed in a solution containing ammonium hydrogen carbonate, and then dried at 250° C. to obtain barium that was supported on Al 2 O 3 (hereinafter also referred to as the “barium-supported catalyst”). The support quantity of barium was 0.2 mole per 120 g of ⁇ -Al 2 O 3 .
  • platinum-supported catalyst platinum that was supported on Al 2 O 3 (hereinafter also referred to as the “platinum-supported catalyst”).
  • the support quantity of platinum was 4 g per 120 g of ⁇ -Al 2 O 3 .
  • a 30 mm diameter, 50 mm long, and 4 mil/400 cpsi cordierite honeycomb 125 was coated with the barium-supported catalyst and burned for one hour at 450° C. to obtain a Ba-supported catalyst layer 126 .
  • the coating amount was such that Al 2 O 3 was coated at a rate of 60 g/L.
  • the honeycomb 125 which was coated as described above, was further coated with the platinum-supported catalyst and burned for one hour at 450° C. to obtain a Pt-supported catalyst layer 127 .
  • the coating amount was such that Al 2 O 3 was coated at a rate of 60 g/L.
  • the embodiment sample 224 having two layers of catalyst coating was obtained by performing the above process.
  • the obtained embodiment sample 224 was such that the overall Pt support quantity was 2 g, and that the Ba support quantity was 0.1 mole/Al 2 O 3 120 g, and further that the coating amount was 120 g/L (Al 2 O 3 ).
  • the comparative sample 324 which is shown in FIG. 6(B) , was prepared by performing the procedure described below. First of all, ⁇ -Al 2 O 3 was dispersed in ion exchange water. An aqueous solution of barium acetate was then added. The resulting mixture was heated to remove water from it, dried at 120° C., and pulverized to powder. The powder was then burned for two hours at 500° C. The burnt powder was immersed in a solution containing ammonium hydrogen carbonate, and then dried at 250° C. to obtain the barium-supported catalyst.
  • the obtained barium-supported catalyst was dispersed in ion exchange water. An aqueous solution containing dinitro-diammine platinum was then added to support Pt. The resulting mixture was dried, pulverized, and burned for one hour at 450° C. In this manner, a comparative coating catalyst was obtained.
  • the obtained catalyst was such that the barium support quantity was 0.1 mole per 120 g of ⁇ -Al 2 O 3 , and that the platinum support quantity was 2 g per 120 g of ⁇ -Al 2 O 3 .
  • a 30 mm diameter, 50 mm long, 4 mil/400 cpsi cordierite honeycomb 325 was coated with the comparative coating catalyst, which was prepared as described above, and burned for one hour a 450° C. to obtain a PtBa catalyst layer 326 .
  • the coating amount was such that Al 2 O 3 was coated at a rate of 120 g/L.
  • the prepared comparative sample 324 was similar to the embodiment sample 224 in that the overall Pt support quantity was 2 g, and that the Ba support quantity was 0.1 mole/Al 2 O 3 120 g, and further that the coating amount was 120 g/L (Al 2 O 3 ).
  • the embodiment sample 224 and comparative sample 324 were configured so that they contained the same amounts of Pt and Ba.
  • the injection gas was supplied when the temperature was between 30° C. and 300° C. When the temperature was between 300° C. and 500° C., only the simulant gas was distributed without supplying the injection gas.
  • FIG. 7(B) is an image illustrating the amount of a component of the exhaust gas flowing downstream, which was determined by multiplying the concentration of the gas flowing downstream of the test piece 222 by the test time.
  • the amount of the component flowing downstream was calculated by multiplying the product of a component concentration, which was detected by an exhaust gas analyzer, and a gas flow rate by the test time.
  • the above calculated values were then used to determine the exhaust gas purification efficiency as shown in FIG. 7(C) . More specifically, the amount of a component flowing downstream ( FIG. 7(B) ) was subtracted from the amount of gas supplied within the measurement time ( FIG. 7(A) ). The obtained value was then divided by the amount of gas supplied within the measurement time ( FIG. 7(A) ) to calculate the exhaust gas purification efficiency as a percentage.
  • FIG. 8 is a graph illustrating a first portion of the results of the experiment.
  • the graph in FIG. 8 indicates that the use of the embodiment sample 224 exhibited higher purification efficiencies for NOx, HC, and CO than the use of the comparative sample 324 .
  • the first embodiment coats the base material 25 with the NOx retention layer 26 that contains BaCO 3 .
  • the material for the NOx retention layer is not limited to the one described above.
  • an alkali metal such as Na, K, Cs, or Rb
  • an alkali earth metal such as Ba, Ca, or Sr
  • a rare earth element such as Y, Ce, La, or Pr
  • Y, Ce, La, or Pr can be used as needed, as described in Japanese Patent No. 3551346.
  • the composition of the nitrate is not limited to Ba(NO 3 ) 2 , which is mentioned in connection with the first embodiment. It should be noted that Ba has a large occlusion capacity (1 mole of Ba can occlude 3 moles of NO 3 ), exhibits higher thermal stability than the other materials, and is suitable as an NOx retention substance for use with an exhaust emission control apparatus.
  • the base material may also be made of various publicly known substances such as a ceramic or metal.
  • the base material 25 having cells 24 partitioned in a reticular pattern is coated with the NOx retention layer 26 and catalyst layer 27 .
  • the present invention is not limited to the use of such a base material.
  • Variously shaped, publicly known base materials may also be used with the present invention.
  • reaction formula [1] may be referred to as the “first formula;” reaction formula [2], the “second formula;” and reaction formula [3], the “third formula.”
  • reaction formula [3] the “third formula.”
  • the third formula only the arrow indicating a rightward reaction is included; however, a leftward reaction may also occur.
  • the second modification induces the reaction indicated by the second formula by adding ozone in such a manner that the mole ratio of ozone to NO in the gas mixture is greater than 1. More specifically, ozone addition is made so that the following relational expression is met by the ratio between mol(O 3 ), which is a mole equivalent of the amount of ozone in the gas mixture, and mol(NO), which is a mole equivalent of the amount of nitrogen monoxide in the gas mixture:
  • the second modification is configured so that the substance quantity of ozone to be added is greater than the substance quantity of NO in the exhaust gas. Therefore, an adequate amount of ozone can be supplied to generate NO 3 and N 2 O by oxidizing NO (to induce the reactions indicated in the second and third formulae). As a result, the amounts of high-order nitrogen oxides in the exhaust gas can be certainly increased to achieve NOx occlusion effectively.
  • the process described above is implemented when the ECU 50 performs a “process for adjusting an ozone supply amount so that the mole ratio of ozone to nitrogen monoxide (NO) in a gas mixture flowing into the NOx occlusion reduction type catalyst is greater than 1” (ozone supply amount adjustment process).
  • This process can be performed, for instance, before step S 100 of the routine shown in FIG. 3 .
  • the ozone supply amount for providing the above mole ratio can be defined, for instance, by allowing the ECU 50 to estimate the molar quantity of NOx contained in the exhaust gas in accordance with the operating status (engine speed Ne, air-fuel ratio A/F, load, intake air amount, etc.) of the internal combustion engine 10 and calculate the flow rate of ozone to be supplied in accordance with the estimated molar quantity of NOx.
  • the third modification adjusts the ozone supply amount so that the mole ratio between ozone and NO in the gas mixture is not smaller than 2 (Mol(O 3 )/Mol(NO) ⁇ 2). This ensures that an adequate amount of ozone remains after the reaction indicated in the first formula and contributes to the reactions indicated in the second and third formulae, thereby certainly increasing the amounts of high-order nitrogen oxides.
  • the third modification makes it possible to supply an adequate amount of ozone for generating NO 3 and N 2 O 5 by oxidizing NO and effectively accelerate the NOx occlusion reaction.
  • the process described above is implemented when the ECU 50 performs a “process for adjusting an ozone supply amount so that the mole ratio of ozone (O 3 ) to nitrogen monoxide (NO) in the gas mixture flowing into the NOx occlusion reduction type catalyst is not smaller than 2.” This process can be performed, for instance, before step S 100 of the routine shown in FIG. 3 .
  • the first embodiment is configured so as to supply ozone with the ozone supply device 30 installed outside the catalytic device 20 and the ozone injection orifice 32 positioned inside the catalytic device 20 .
  • Ozone may be added to the exhaust gas by using various publicly known ozone generation devices methods.
  • a configuration for generating ozone directly by plasma discharge may be formed within the exhaust path 12 or catalytic device 20 .
  • the NOx retention member may not only occlude NOx but also adsorb NOx. More specifically, the NOx occlusion reduction type catalyst 22 may not only occlude NOx but also adsorb NOx. Therefore, the “retention” operation performed by the NOx retention member means not only the “occlusion” of NOx but also the “adsorption” of NOx.
  • the amount of NOx retention substance contained in the catalyst layer 27 be substantially zero.
  • the present invention is not limited to the use of such a catalyst layer.
  • the present invention may alternatively be configured so that the catalyst layer 27 contains a smaller amount of NOx retention substance than the NOx retention layer 26 .

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Biomedical Technology (AREA)
  • Environmental & Geological Engineering (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
US12/520,555 2006-12-28 2007-12-20 Exhaust emission control apparatus for internal combustion engine Abandoned US20100043406A1 (en)

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JP2006355587A JP2008163871A (ja) 2006-12-28 2006-12-28 内燃機関の排気ガス浄化装置
PCT/JP2007/074533 WO2008081735A1 (ja) 2006-12-28 2007-12-20 内燃機関の排気ガス浄化装置

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Cited By (4)

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US20100239480A1 (en) * 2009-03-17 2010-09-23 Korea Institute Of Science And Technology Method And Apparatus For The Treatment Of Nitrogen Oxides Using An Ozone And Catalyst Hybrid System
US20100307133A1 (en) * 2009-06-05 2010-12-09 Toyota Jidosha Kabushiki Kaisha Exhaust gas control apparatus for internal combustion engine, and method of controlling the same
US20110120105A1 (en) * 2009-11-24 2011-05-26 Wen-Lo Chen Engine waste gas treatment method and apparatus
US20210172835A1 (en) * 2019-12-05 2021-06-10 Southwest Research Institute Generation of Nitrogen Dioxide for Use with Burner-Based Exhaust Replication System

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CN105927343B (zh) * 2016-06-07 2018-12-21 灵武市伟畅机械科技有限公司 一种内燃机排气装置
WO2020083171A1 (zh) * 2018-10-22 2020-04-30 上海必修福企业管理有限公司 一种发动机尾气臭氧净化系统和方法

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US6162409A (en) * 1999-03-15 2000-12-19 Arthur P. Skelley Process for removing Nox and Sox from exhaust gas
US20030143140A1 (en) * 2002-01-29 2003-07-31 Shuen-Cheng Hwang Process for the removal of impurities from gas streams

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Publication number Priority date Publication date Assignee Title
US20100239480A1 (en) * 2009-03-17 2010-09-23 Korea Institute Of Science And Technology Method And Apparatus For The Treatment Of Nitrogen Oxides Using An Ozone And Catalyst Hybrid System
US20100307133A1 (en) * 2009-06-05 2010-12-09 Toyota Jidosha Kabushiki Kaisha Exhaust gas control apparatus for internal combustion engine, and method of controlling the same
EP2273081A1 (de) * 2009-06-05 2011-01-12 Toyota Jidosha Kabushiki Kaisha Abgassteuerungsvorrichtung für einen Verbrennungsmotor und Verfahren zu ihrer Steuerung
US20110120105A1 (en) * 2009-11-24 2011-05-26 Wen-Lo Chen Engine waste gas treatment method and apparatus
US20210172835A1 (en) * 2019-12-05 2021-06-10 Southwest Research Institute Generation of Nitrogen Dioxide for Use with Burner-Based Exhaust Replication System
US11573155B2 (en) * 2019-12-05 2023-02-07 Southwest Research Institute Generation of nitrogen dioxide for use with burner-based exhaust replication system

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