US20110030350A1 - Exhaust gas purifying apparatus - Google Patents
Exhaust gas purifying apparatus Download PDFInfo
- Publication number
- US20110030350A1 US20110030350A1 US12/850,080 US85008010A US2011030350A1 US 20110030350 A1 US20110030350 A1 US 20110030350A1 US 85008010 A US85008010 A US 85008010A US 2011030350 A1 US2011030350 A1 US 2011030350A1
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- US
- United States
- Prior art keywords
- exhaust gas
- purification apparatus
- urea water
- gas purification
- urea
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000003054 catalyst Substances 0.000 claims abstract description 132
- 230000003647 oxidation Effects 0.000 claims abstract description 77
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 77
- 238000000746 purification Methods 0.000 claims abstract description 75
- WTHDKMILWLGDKL-UHFFFAOYSA-N urea;hydrate Chemical compound O.NC(N)=O WTHDKMILWLGDKL-UHFFFAOYSA-N 0.000 claims abstract description 73
- 230000003197 catalytic effect Effects 0.000 claims abstract description 40
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims abstract description 28
- 239000004202 carbamide Substances 0.000 claims abstract description 28
- 230000003301 hydrolyzing effect Effects 0.000 claims abstract description 23
- 238000000354 decomposition reaction Methods 0.000 claims abstract description 22
- 238000010531 catalytic reduction reaction Methods 0.000 claims abstract description 16
- 238000002347 injection Methods 0.000 claims description 29
- 239000007924 injection Substances 0.000 claims description 29
- 239000013618 particulate matter Substances 0.000 claims description 17
- 238000011144 upstream manufacturing Methods 0.000 claims description 15
- 239000000463 material Substances 0.000 claims description 14
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 5
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 claims description 4
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 claims description 4
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 2
- ZNOKGRXACCSDPY-UHFFFAOYSA-N tungsten trioxide Chemical compound O=[W](=O)=O ZNOKGRXACCSDPY-UHFFFAOYSA-N 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 117
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 92
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 62
- 229910021529 ammonia Inorganic materials 0.000 description 29
- 238000006460 hydrolysis reaction Methods 0.000 description 20
- 230000007062 hydrolysis Effects 0.000 description 19
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 14
- 238000006722 reduction reaction Methods 0.000 description 10
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 9
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 7
- 229910002092 carbon dioxide Inorganic materials 0.000 description 7
- 239000001569 carbon dioxide Substances 0.000 description 7
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 7
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 6
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 6
- 239000010949 copper Substances 0.000 description 6
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 5
- 229910002091 carbon monoxide Inorganic materials 0.000 description 5
- 229930195733 hydrocarbon Natural products 0.000 description 5
- 150000002430 hydrocarbons Chemical class 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 239000010931 gold Substances 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 4
- 150000004706 metal oxides Chemical class 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 3
- 239000003638 chemical reducing agent Substances 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 229910052709 silver Inorganic materials 0.000 description 3
- 239000004332 silver Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000003213 activating effect Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 230000035484 reaction time Effects 0.000 description 2
- 239000010948 rhodium Substances 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- ODUCDPQEXGNKDN-UHFFFAOYSA-N Nitrogen oxide(NO) Natural products O=N ODUCDPQEXGNKDN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- WYTGDNHDOZPMIW-RCBQFDQVSA-N alstonine Natural products C1=CC2=C3C=CC=CC3=NC2=C2N1C[C@H]1[C@H](C)OC=C(C(=O)OC)[C@H]1C2 WYTGDNHDOZPMIW-RCBQFDQVSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- VSZWPYCFIRKVQL-UHFFFAOYSA-N selanylidenegallium;selenium Chemical compound [Se].[Se]=[Ga].[Se]=[Ga] VSZWPYCFIRKVQL-UHFFFAOYSA-N 0.000 description 1
- -1 silica (SiO2) Chemical class 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
Images
Classifications
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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
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
- F01N3/2073—Selective catalytic reduction [SCR] with means for generating a reducing substance from the exhaust gases
-
- 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
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
-
- 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
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
- F01N13/0097—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are arranged in a single housing
-
- 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
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/103—Oxidation catalysts for HC and CO only
-
- 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
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main 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
- F01N2240/40—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 a hydrolysis 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
- F01N2510/00—Surface coverings
Definitions
- the present invention relates to an exhaust gas purification apparatus and, more specifically, to an exhaust gas purification apparatus having a urea selective catalytic reduction (hereinafter referred to merely as SCR) system for reducing nitrogen oxides (NOx) in exhaust gas emitted from a diesel engine.
- SCR selective catalytic reduction
- the urea SCR system has been developed for reducing NOx in exhaust gas emitted from a diesel engine.
- the urea SCR system employs an SCR catalyst for converting NOx into nitrogen (N2) and water (H2O) by chemical reaction between NOx and ammonia (NH3) generated by hydrolysis of urea water.
- the SCR catalyst is provided in the exhaust passage between the engine and the muffler. Furthermore, an oxidation catalyst and an injection valve for injecting urea water into the exhaust gas are provided upstream of the SCR catalyst.
- the oxidation catalyst oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas into water (H2O) and carbon dioxide (CO2) and also promotes the oxidation of nitrogen oxide (NO) into nitrogen dioxide (NO2).
- Another oxidation catalyst is provided downstream of the SCR catalyst for promoting the oxidation of ammonia unreacted with NOx so as to prevent emission of the unreacted ammonia into the atmosphere.
- a diesel particulate filter (hereinafter referred to merely as DPF) is also provided in the exhaust passage between the engine and the muffler for reducing particulate matter (PM) such as carbon in the exhaust gas.
- the exhaust gas purification apparatus including the urea SCR system and the DPF has many components provided between the engine and the muffler and requires a large space for mounting of such components to a vehicle. Therefore, a downsized urea SCR system has been proposed for facilitating the installation of the system in the vehicle.
- the exhaust gas purification apparatus of the above Published Japanese Translation has accomplished the improvement of the efficiency of chemical reaction by the catalytic module in the catalytic device by ensuring uniform distribution of the reducing agent in the exhaust gas with the aid of the exhaust gas flow caused by the mixing device for reducing NOx in the exhaust gas effectively.
- the exhaust gas purification apparatus achieves reduction of the distance between the injection device and the catalytic device and of the structural space of the apparatus.
- the distance that the injected urea water moves before reaching catalytic device should be long so that the time for urea water or the reducing agent to stay upstream of the catalytic device is long enough for the hydrolysis of urea water.
- the exhaust gas purification apparatus improves the efficiency of hydrolysis by providing the hydrolytic catalytic module in the catalytic device.
- the present invention is directed to providing an exhaust gas purification apparatus for improving the efficiency of the reduction of NOx in comparison to urea water usage.
- An exhaust gas purification apparatus includes an oxidation catalyst provided in a passage through which exhaust gas flows, a urea decomposition accelerator, a selective catalytic reduction catalyst provided downstream of the urea decomposition accelerator and a urea water supplying device for supplying urea water to the urea decomposition accelerator.
- the urea decomposition accelerator is provided downstream end surface of the oxidation catalyst and has at least one of hydrophilic function and hydrolytic catalytic function.
- FIG. 1 is a schematic view showing an exhaust gas purification apparatus according to a first embodiment of the present invention and its associated components;
- FIG. 2 is a schematic cross sectional view of the exhaust gas purification apparatus of FIG. 1 ;
- FIG. 3 is a schematic cross sectional view of an exhaust gas purification apparatus according to a second embodiment of the present invention.
- the exhaust gas purification apparatus 101 is employed in a vehicle equipped with a diesel engine.
- an engine assembly including an engine 1 and the exhaust gas purification apparatus 101 is designated generally by reference numeral 10 .
- the engine 1 has a plurality of cylinders 1 A each having an intake port 1 B to which an intake manifold 4 is connected for distributing intake air to the respective cylinders 1 A.
- the intake manifold 4 has an inlet 4 A to which an engine intake pipe 3 is connected and the engine intake pipe 3 is further connected to a compressor housing 8 A of a turbocharger 8 .
- the compressor housing 8 A is connected to an intake pipe 2 through which outside air is introduced.
- an exhaust manifold 5 is connected to a plurality of exhaust ports 1 C of the engine 1 for collecting exhaust gas emitted from the respective exhaust ports 1 C.
- An outlet 5 A of the exhaust manifold 5 is connected to a turbine housing 8 B of the turbocharger 8 , to which the exhaust gas purification apparatus 101 having a substantially cylindrical shape is connected and disposed adjacent to a lateral side of the engine 1 .
- the exhaust gas purification apparatus 101 is connected to an exhaust pipe 6 , the downstream end of which is further connected to a muffler 7 .
- the intake pipe 2 , the turbocharger 8 , the engine intake pipe 3 and the intake manifold 4 cooperate to form an intake system of the vehicle, while the exhaust manifold 5 , the turbocharger 8 , the exhaust gas purification apparatus 101 , the exhaust pipe 6 and the muffler 7 cooperates to form an exhaust system of the vehicle.
- the engine 1 , the engine intake pipe 3 , the intake manifold 4 , the exhaust manifold 5 and the turbocharger 8 cooperate to form the aforementioned engine assembly 10 .
- the exhaust gas purification apparatus 101 includes a casing 11 having a substantially cylindrical shape.
- the casing 11 has an upstream end face 11 A to which the outlet 8 B 2 of the turbine housing 8 B of the turbocharger 8 is connected and a downstream end face 11 B to which the upstream end 6 A of the exhaust pipe 6 is connected.
- the casing 11 communicates internally with the turbine housing 8 B and the exhaust pipe 6 .
- the cylindrical casing 11 houses therein an oxidation catalyst layer 12 supporting an oxidation catalyst and a diesel particulate filter (DPF) 14 as a particulate matter collecting device disposed downstream of the oxidation catalyst layer 12 with respect to the flow of exhaust gas in the casing 11 .
- the oxidation catalyst layer 12 and the DPF 14 are made in the form of a layer extending perpendicular to the axis of a cylindrical portion 11 C of the casing 11 over the entire radial dimension of the interior of the cylindrical portion 11 C.
- the oxidation catalyst layer 12 and the DPF 14 are disposed spaced apart each other thereby to form therebetween a space 16 .
- the oxidation catalyst layer 12 supports thereon the oxidation catalyst for oxidizing hydrocarbons (HC) and carbon monoxide (CO) into water (H2O) and carbon dioxide (CO2) and also promoting the oxidation of nitrogen monoxide (NO) into nitrogen dioxide (NO2).
- the oxidation catalyst of the oxidation catalyst layer 12 uses material such as platinum (Pt), palladium (Pd), rhodium (Rh), silver (Ag), iron (Fe), copper (Cu), nickel (Ni), gold (Au) or a mixture of two or more of these materials.
- the DPF 14 is made of a porous material such as ceramic for capturing particulate matter (PM) contained in the exhaust gas.
- the DPF 14 has an (urea) SCR catalyst 15 as a selective catalytic reduction catalyst supported thereon, e.g., by coating.
- the selective catalytic reduction catalyst serves to promote the chemical reaction selectively among specific chemical substances.
- the SCR catalyst 15 catalyzes the reaction between nitrogen oxide (NOx) and ammonia (NH3) thereby to reduce NOx into nitrogen (N2) and water (H2O).
- Material of the SCR catalyst 15 includes an oxide of zirconium (Zr), titanium (Ti), silicon (Si), cerium (Ce), or tungsten (W), a complex of these oxides and a ZSM-5 type zeolite partially replaced by a metal such as iron (Fe) and copper (Cu).
- the oxidation catalyst layer 12 supports on at least a part of the downstream end surface 12 B thereof with regard to the flow of exhaust gas, i.e., on the surface thereof facing the DPF 14 , a hydrophilic layer 13 having a hydrophilic function and forming the urea decomposition accelerator of the invention.
- the hydrophilic layer 13 is formed by coating the end surface 12 B of the oxidation catalyst layer 12 with a catalytic material that has a hydrolytic catalytic function for accelerating the hydrolysis and a hydrophilic function.
- This catalytic material having the hydrolytic catalytic function and the hydrophilic function includes a metal oxide such as silica (SiO2), alumina (Al2O3), ceria (CeO2), titania (TiO2), tungsten oxide (WO3) and the like.
- Material forming the hydrophilic layer 13 is made of a single metal oxide or a combination of the above metal oxides.
- the performance for hydrolysis of the hydrophilic layer 13 can be improved by adding silver (Ag) or platinum (Pt) other than the above metal oxides to the material forming the hydrophilic layer 13 .
- An injection valve 18 that is an electromagnetic valve is provided in the cylindrical portion 11 C of the casing 11 at a position between the oxidation catalyst layer 12 (or the hydrophilic layer 13 ) and the DPF 14 (or the SCR catalyst 15 ). Specifically, the position is closer to the oxidation catalyst layer 12 (or the hydrophilic layer 13 ) than the DPF 14 (or the SCR catalyst 15 ).
- the injection valve 18 forms a urea water supplying device of the invention.
- the injection valve 18 is connected to a urea water tank 19 provided in a vehicle (not shown) and operable to inject urea water into the space 16 of the casing 11 .
- the injection valve 18 is provided at a position that is adjacent to and immediately downstream of the hydrophilic layer 13 so that urea water is injected by the injection valve 18 toward the downstream end surface 12 B of the oxidation catalyst layer 12 , i.e., the downstream surface 13 B of the hydrophilic layer 13 .
- the injection valve 18 is electrically connected to a dosing control unit (DCU) 30 that controls the opening and closing operation of the injection valve 18 .
- the urea water tank 19 has an electric pump for supplying urea water to the injection valve 18 .
- the electric pump is electrically connected to the DCU 30 and the pump operation is controlled by the DCU 30 .
- a cylindrically-shaped mixer 17 is provided on the upstream end surface 14 A of the DPF 14 for distributing substances in the exhaust gas uniformly over the end surface 14 A.
- the mixer 17 has a structure that is similar to that disclosed in Published Japanese Translation H06-509020 of PCT international publication or Japanese Patent Application Publication 2006-9608.
- the mixer disclosed in Published Japanese Translation H06-509020 is made in the form of a lattice that divides the gas passage into plural cells so as to cause the gas flowing through each cell to flow spirally and also to flow toward the adjacent cell. This helps the substances in the exhaust gas to spread uniformly in the whole passage.
- the mixer disclosed in Japanese Patent Application Publication 2006-9608 has plural plates each extending perpendicularly to the direction of gas flow, which provides serpentine gas passage serving to distribute the substances in the gas uniformly.
- Another oxidation catalyst layer 20 that supports oxidation catalyst for oxidizing ammonia is provided in the exhaust pipe 6 downstream of the exhaust gas purification apparatus 101 .
- Platinum (Pt), palladium (Pd), silver (Ag), iron (Fe), copper (Cu), nickel (Ni), gold (Au) or the like may be employed as the material of the oxidation catalyst of the oxidation catalyst layer 20 .
- An exhaust gas temperature sensor 52 is provided upstream of the oxidation catalyst layer 12 and also downstream of the upstream end face 11 A of the casing 11 for detecting the temperature of exhaust gas.
- the exhaust gas temperature sensor 52 is electrically connected to the DCU 30 and sends detected temperature information to the DCU 30 .
- a first NOx sensor 51 is provided in the casing 11 at a position upstream of the exhaust gas temperature sensor 52 for detecting the NOx concentration and a second NOx sensor 53 is provided downstream of the downstream end face 11 B of the casing 11 , more specifically, at a position downstream of the oxidation catalyst layer 20 in the exhaust pipe 6 , for detecting the NOx concentration.
- the first and the second NOx sensors 51 , 53 are electrically connected to the DCU 30 and send information about the NOx concentration to the DCU 30 .
- the exhaust gas purification apparatus 101 having the SCR catalyst 15 and the DPF 14 integrated together is mounted to the engine assembly 10 at a position adjacent to the engine 1 (refer to FIG. 1 ).
- FIG. 1 while the engine 1 is running, outside air is flowed into the compressor housing 8 A of the turbocharger 8 through the intake pipe 2 .
- the air is pumped by a compressor wheel (not shown) in the compressor housing 8 A and flowed to the engine intake pipe 3 under an increased pressure.
- the air is flowed into a cylinder 1 A in the engine 1 through the engine intake pipe 3 and the intake manifold 4 .
- the air in the cylinder 1 A is mixed with fuel (light oil) supplied into the cylinder 1 A and the fuel is ignited spontaneously for combustion.
- Exhaust gas produced by the combustion is discharged into the exhaust manifold 5 through a plurality of exhaust ports 1 C to be collected by the exhaust manifold 5 and then flows into the turbine housing 8 B of the turbocharger 8 .
- the exhaust gas flowing through the turbine housing 8 B increases rotation speed of the turbine wheel (not shown) in the turbine housing 8 B and the compressor wheel connected to the turbine wheel and then is discharged into the exhaust gas purification apparatus 101 .
- the exhaust gas flows through the oxidation catalyst layer 20 , the exhaust pipe 6 and the muffler 7 and then is discharged outside the vehicle (not shown).
- all the exhaust gas flowed into the exhaust gas purification apparatus 101 flows firstly through the oxidation catalyst layer 12 . While the exhaust gas flows through the oxidation catalyst layer 12 , hydrocarbons and carbon monoxide in the exhaust gas are oxidized into carbon dioxide and water, and part of NO is oxidized into NO2 that can be reduced easily. After flowing through the oxidation catalyst layer 12 , the exhaust gas flows through the hydrophilic layer 13 and the mixer 17 and then into the DPF 14 supporting the SCR catalyst 15 . PM in the exhaust gas is captured by the DPF 14 .
- the DCU 30 activates the electric pump in the urea water tank 19 and also opens the injection valve 18 for injection of urea water from the injection valve 18 toward the hydrophilic layer 13 located upstream of the space 16 .
- the injected urea water is adsorbed on the surface 13 B of the hydrophilic layer 13 .
- the urea water injected onto the surface 13 B of the hydrophilic layer 13 is dispersed in radial directions of the cylindrical portion 11 C of the casing 11 due to the hydrophilic property of the hydrophilic layer 13 and is adsorbed uniformly on the surface 13 B.
- the oxidation catalyst layer 12 has therein the heat due to the exhaust gas flowing therethrough and also the reaction heat due to the oxidation of NO and the like in the exhaust gas.
- the urea water adsorbed on the surface 13 B of the hydrophilic layer 13 is hydrolyzed into ammonia and carbon dioxide (CO2) by the heat that the oxidation catalyst layer 12 has, the heat of the exhaust gas flowing through the hydrophilic layer 13 and also the hydrolytic catalytic function of the hydrophilic layer 13 .
- the urea water is then adsorbed uniformly on the surface 13 B of the hydrophilic layer 13 and, therefore, the reaction time required for the hydrolysis can be ensured, with the result that the urea water is hydrolyzed into ammonia effectively.
- ammonia is generated uniformly on the surface 13 B of the hydrophilic layer 13 .
- the hydrolysis takes place with a high efficiency. Furthermore, the urea water can make use of the heat of hot exhaust gas immediately after being emitted from the turbocharger 8 of the engine 1 . Therefore, the urea water can easily ensure the heat and the temperature required for the hydrolysis. Moreover, urea water is injected and hydrolyzed into ammonia in the region that is downstream of the oxidation catalyst layer 12 and, therefore, no ammonia flows into the oxidation catalyst layer 12 and is oxidized by the oxidation catalyst of the oxidation catalyst layer 12 .
- Ammonia generated on the hydrolysis is dispersed uniformly in radial directions of the cylindrical portion 11 C of the casing 11 and flows to the mixer 17 together with the exhaust gas. Ammonia is further dispersed while flowing through the mixer 17 and then flows into the DPF 14 . Ammonia that is flowed into the DPF 14 together with the exhaust gas reduces NOx contained in exhaust gas including NO and NO2 into N2 by the catalytic reaction of the SCR catalyst 15 . After being dispersed uniformly on the hydrophilic layer 13 , ammonia is dispersed again at the mixer 17 and then supplied uniformly to the entire DPF 14 and the SCR catalyst 15 , thereby reducing NOx effectively at the SCR catalyst 15 .
- Unreacted ammonia which has not been used in the reduction of NOx is discharged outside the exhaust gas purification apparatus 101 together with exhaust gas.
- the exhaust gas containing residual unreacted ammonia and N2 after flowing through the DPF 14 where PM is removed is discharged from the exhaust gas purification apparatus 101 into the exhaust pipe 6 .
- the exhaust gas thus discharged into the exhaust pipe 6 flows through the oxidation catalyst layer 20 provided in the exhaust pipe 6 and then is discharged through the muffler 7 outside the vehicle (not shown). Since the residual ammonia in the exhaust gas is oxidized and decomposed while flowing through the oxidation catalyst layer 20 , no harmful ammonia is discharged outside.
- the catalyst has a characteristic that it activates the catalytic action at a temperature more than a predetermined temperature.
- the DCU 30 is operated to open the injection valve 18 when the temperature detected by the exhaust gas temperature sensor 52 is the predetermined temperature at which the SCR catalyst 15 is activated or higher, and to close the injection valve 18 when the detected temperature is under the predetermined temperature.
- the DCU 30 determines whether or not NOx reduction should be performed depending on the temperature detected by the exhaust gas temperature sensor 52 .
- the DCU 30 controls the injection quantity of urea water by adjusting the opening of the injection valve 18 based on the NOx concentration detected by the first NOx sensor 51 .
- the DCU 30 controls the injection quantity of urea water by adjusting the opening of the injection valve 18 based on the NOx concentration detected by the second NOx sensor 53 , that is the NOx concentration of exhaust gas after flowing through the SCR catalyst 15 and the oxidation catalyst layer 20 .
- the DCU 30 increases the injection quantity of urea water by opening the injection valve 18 further.
- the DCU 30 adjusts the supply quantity of urea water to the SCR catalyst 15 , i.e., the supply quantity of ammonia, thereby controlling the NOx reduction performance of the exhaust gas purification apparatus 101 .
- the exhaust gas purification apparatus 101 is disposed adjacent to the engine 1 and, therefore, hot exhaust gas immediately after being emitted from the engine 1 flows into the exhaust gas purification apparatus 101 through the turbocharger 8 . Furthermore, the heat generated by the engine 1 is imparted to the exhaust gas purification apparatus 101 located adjacent to the engine 1 and transmitted inward through outer wall of the casing 11 .
- the oxidative catalyst layer 12 , the hydrophilic layer 13 and the DPF 14 supporting the SCR catalyst 15 all disposed inside the casing 11 are subject to the heat of the hot exhaust gas and the heat imparted from the engine 1 and, therefore, the temperature of the respective components tends to increase.
- the temperature increasing rate of the respective components, i.e., the oxidation catalyst of the oxidation catalyst layer 12 , the hydrophilic catalyst of the hydrophilic layer 13 and the SCR catalyst 15 in the exhaust gas purification apparatus 101 during a cold start of the engine 1 is improved and the time required for activating each catalyst is shortened. Eventually, the performance of NOx reduction is improved.
- the exhaust gas purification apparatus 101 of the present invention includes the oxidation catalyst layer 12 provided in exhaust gas passage, the hydrophilic layer 13 that is provided at least on the downstream end surface 12 B of the oxidation catalyst layer 12 and having at least one of the hydrophilic function and the hydrolytic catalytic function, the SCR catalyst 15 provided downstream of the hydrophilic layer 13 and the injection valve 18 for supplying urea water to the hydrophilic layer 13 .
- the urea water supplied to the hydrophilic layer 13 is dispersed and adsorbed on the hydrophilic layer 13 by the hydrophilic function and can make use of the heat generated by the oxidation of NO to NO2 and the heat of the exhaust gas flowing through the oxidation catalyst layer 12 . Therefore, urea water is hydrolyzed very efficiently and ammonia resulting from the hydrolysis of the urea water is dispersed uniformly over the hydrophilic layer 13 . Thus, the hydrolysis of urea water into ammonia is accomplished with high efficiency, which helps to improve the reaction of the ammonia in the SCR catalyst 15 .
- the hydrolysis reaction of urea water supplied to the hydrophilic layer 13 is accelerated by the heat of the oxidation catalyst layer 12 and the heat due to the hydrolytic catalytic function of the hydrophilic layer 13 , thereby improving the efficiency of the hydrolysis.
- the reduction of NOx in the exhaust gas purification apparatus 101 using the urea water can be improved by the hydrophilic function and the hydrolytic catalytic function of the hydrophilic layer 13 . Since the efficiency of hydrolysis of urea water is improved by providing the hydrophilic layer 13 , the distance between the hydrophilic layer 13 and the SCR catalyst 15 can be shortened, thereby making it possible for the exhaust gas purification apparatus 101 to be made small.
- the injection valve 18 supplies urea water at a position downstream of the hydrophilic layer 13 , neither urea water is supplied to the oxidation catalyst layer 12 nor ammonia produced by the hydrolysis of urea water flows through the oxidation catalyst layer 12 . Therefore, the oxidation of ammonia into NOx by the oxidation catalyst of the oxidation catalyst layer 12 can be prevented. Due to the structure where the DPF 14 supports the SCR catalyst 15 , the SCR catalyst 15 and the DPF 14 are formed integrally, thereby making it possible for the entire apparatus to be formed small. Furthermore, since the oxidation catalyst layer 12 , the hydrophilic layer 13 , the SCR catalyst 15 formed integrally with the DPF 14 and the injection valve 18 are all housed in the single casing 11 , the entire apparatus can be made still smaller.
- the exhaust gas purification apparatus 101 is mounted to the engine assembly 10 and the hot exhaust gas emitted from the engine assembly 10 is introduced into the exhaust gas purification apparatus 101 .
- the heat that the engine assembly 10 generates in operation is transmitted inside the casing 11 of the exhaust gas purification apparatus 101 . Therefore, the time for the temperature of the hydrophilic layer 13 to be increased to the level required for the hydrolysis of urea water and also for the temperature of the SCR catalyst 15 to the level required for activating the SCR catalyst 15 during a cold start of the engine can be shortened, with the result that the NOx reduction performance can be improved.
- the exhaust gas purification apparatus 102 according to a second embodiment of FIG. 3 is made by modifying the DPF 14 supporting the SCR catalyst 15 of the exhaust gas purification apparatus 101 according to the first embodiment.
- the following description will use the same reference numerals for the common elements or components in the first and the second embodiments, and the description of such elements or components will be omitted.
- the oxidation catalyst layer 12 having on the downstream side thereof the hydrophilic layer 13 , an SCR catalyst layer 25 supporting the SCR catalyst and the DPF 24 are provided in this order in the downstream direction in the casing 11 of the exhaust gas purification apparatus 102 .
- the oxidation catalyst layer 12 and the SCR catalyst layer 25 are disposed across the space 16 and the SCR catalyst layer 25 and the DPF 24 are disposed adjacent to each other.
- the mixer 17 is provided on the upstream end surface 25 A of the SCR catalyst layer 25 .
- the exhaust gas introduced into the casing 11 flows through the mixer 17 after flowing through the oxidation catalyst layer 12 and the hydrophilic layer 13 .
- NOx contained exhaust gas is reduced into N2 in the SCR catalyst layer 25
- PM contained in exhaust gas is captured in the DPF 24 and the resulting exhaust gas is discharged outside the exhaust gas purification apparatus 102 .
- the rest of the structure and the operation of the exhaust gas purification apparatus 102 according to the second embodiment is the same as those of the exhaust gas purification apparatus 101 according to the first embodiment. The description of such structure or operation will be omitted.
- the exhaust gas purification apparatus 102 according to the second embodiment offers the same advantageous effects as the exhaust gas purification apparatus 101 according to the first embodiment.
- the exhaust gas purification apparatus 102 reduces the deterioration of the catalytic function of the SCR catalyst layer 25 due to the heat caused by burning PM and improves the durability of the SCR catalyst layer 25 .
- the exhaust gas purification apparatuses 101 and 102 according to the first and the second embodiments are provided in the engine assembly 10 having the turbocharger 8 , respectively, but the present invention is not limited to this structure.
- the exhaust gas purification apparatuses 101 and 102 may be directly connected to the outlet 5 A of the exhaust manifold 5 , respectively.
- the exhaust gas purification apparatuses 101 and 102 may be provided spaced apart from the engine assembly 10 , respectively.
- the oxidation catalyst layer 12 , the SCR catalyst layer 25 , the DPF 24 and the injection valve 18 are all provided in the casing 11 of the exhaust gas purification apparatus 102 , but the present invention is not limited to this structure.
- the DPF 24 may be provided outside the casing 11 separately from the other components.
- the oxidation catalyst layer 20 is provided separately from the exhaust gas purification apparatuses 101 , 102 , but the present invention is not limited to this structure.
- the oxidation catalyst layer 20 may be provided inside the casing 11 downstream of the DPF 14 , 24 of the exhaust gas purification apparatuses 101 , 102 , respectively.
- the injection valve 18 is provided downstream of the oxidation catalyst layer 12 so as to supply urea water to the hydrophilic layer 13 in the exhaust gas purification apparatuses 101 , 102 according to the first and the second embodiments, respectively, but the present invention is not limited to this structure.
- the injection valve may be so arranged that urea water is supplied toward the upstream side of the oxidation catalyst layer 12 .
- the supplied urea water can be hydrolyzed while flowing through the oxidation catalyst layer 12 and, therefore, the efficiency of the hydrolysis of urea water can be improved.
- urea water is dispersed while flowing through the oxidation catalyst layer 12 , urea water can be dispersed and adsorbed more uniformly on the hydrophilic layer 13 . Accordingly, ammonia produced by the hydrolysis of urea water can be dispersed and be supplied to the SCR catalyst more uniformly.
- the efficiency of the reduction of NOx by ammonia in the SCR catalyst is improved.
- the hydrophilic layer 13 is supported on part of the downstream end surface 12 B of the oxidation catalyst layer 12 in the first and the second embodiments, the hydrophilic layer 13 may be supported on the entire end surface 12 B of the oxidation catalyst layer 12 .
- the single hydrophilic layer 13 having the hydrolytic catalytic function and the hydrophilic function is used as the urea decomposition accelerator in the first and the second embodiments, but the present invention is not limited to this structure.
- the single hydrophilic layer serving as the urea decomposition accelerator may be formed of two different layers, one layer of which is a hydrophilic layer made of a material having only the hydrophilic function and the other layer of which is a hydrolytic catalytic layer made of a material having only the hydrolytic catalytic function for accelerating the hydrolysis of urea water.
- the hydrophilic layer should preferably be provided downstream of the hydrolytic catalytic layer, that is on the side facing the DPF 14 and 24 of the first and the second embodiments, respectively.
- the urea decomposition accelerator may be formed of only the hydrophilic layer made of the material having the hydrophilic function. Since urea water dispersed and adsorbed on the hydrophilic layer can make use of the heat of the oxidation catalyst layer 12 , urea water is hydrolyzed efficiently and the resulting ammonia is dispersed uniformly over the entire hydrophilic layer.
- the urea decomposition accelerator may be formed of only the hydrolytic catalytic layer made of the material having the hydrolytic catalytic function. In this case, urea water making use of the heat of the oxidation catalyst layer 12 is subject to the hydrolytic catalytic function by the hydrolytic catalytic layer and, therefore, the efficiency of the hydrolysis can be improved.
- the casing 11 of the exhaust gas purification apparatuses 101 , 102 according to the first and the second embodiments, respectively is cylindrically-shaped, but the casing 11 according to the present invention is not limited to this shape.
- the casing 11 may be formed with a cross-section including a prism such as quadratic prism, a sphere or an ellipsoid.
- the mixer 17 may be dispensed with in the first and the second embodiments.
Abstract
An exhaust gas purification apparatus includes an oxidation catalyst provided in a passage through which exhaust gas flows, a urea decomposition accelerator, a selective catalytic reduction catalyst provided downstream of the urea decomposition accelerator and a urea water supplying device for supplying urea water to the urea decomposition accelerator. The urea decomposition accelerator is provided downstream end surface of the oxidation catalyst and has at least one of hydrophilic function and hydrolytic catalytic function.
Description
- The present invention relates to an exhaust gas purification apparatus and, more specifically, to an exhaust gas purification apparatus having a urea selective catalytic reduction (hereinafter referred to merely as SCR) system for reducing nitrogen oxides (NOx) in exhaust gas emitted from a diesel engine.
- The urea SCR system has been developed for reducing NOx in exhaust gas emitted from a diesel engine. The urea SCR system employs an SCR catalyst for converting NOx into nitrogen (N2) and water (H2O) by chemical reaction between NOx and ammonia (NH3) generated by hydrolysis of urea water.
- The SCR catalyst is provided in the exhaust passage between the engine and the muffler. Furthermore, an oxidation catalyst and an injection valve for injecting urea water into the exhaust gas are provided upstream of the SCR catalyst. The oxidation catalyst oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas into water (H2O) and carbon dioxide (CO2) and also promotes the oxidation of nitrogen oxide (NO) into nitrogen dioxide (NO2). Another oxidation catalyst is provided downstream of the SCR catalyst for promoting the oxidation of ammonia unreacted with NOx so as to prevent emission of the unreacted ammonia into the atmosphere.
- A diesel particulate filter (hereinafter referred to merely as DPF) is also provided in the exhaust passage between the engine and the muffler for reducing particulate matter (PM) such as carbon in the exhaust gas. The exhaust gas purification apparatus including the urea SCR system and the DPF has many components provided between the engine and the muffler and requires a large space for mounting of such components to a vehicle. Therefore, a downsized urea SCR system has been proposed for facilitating the installation of the system in the vehicle.
- Published Japanese Translation 2001-511494 of PCT International Publication discloses an exhaust gas purification apparatus that includes a mixing device functioning as a gas-guiding device, an injection device for injecting urea water as a reducing agent and a catalytic device provided downstream of the injecting device and including a hydrolytic catalytic module and an SCR catalytic module. The hydrolytic catalytic module is provided upstream of the SCR catalytic module in the catalytic device. The same Published Japanese Translation discloses another exhaust gas purification device in which a second mixing device is provided between the injecting device and the catalytic device.
- The exhaust gas purification apparatus of the above Published Japanese Translation has accomplished the improvement of the efficiency of chemical reaction by the catalytic module in the catalytic device by ensuring uniform distribution of the reducing agent in the exhaust gas with the aid of the exhaust gas flow caused by the mixing device for reducing NOx in the exhaust gas effectively. In addition, the exhaust gas purification apparatus achieves reduction of the distance between the injection device and the catalytic device and of the structural space of the apparatus. However, for ensuring the time that is long enough for urea water to be hydrolyzed, the distance that the injected urea water moves before reaching catalytic device should be long so that the time for urea water or the reducing agent to stay upstream of the catalytic device is long enough for the hydrolysis of urea water. When the structural space of the exhaust gas purification apparatus is reduced, urea water is supplied to the SCR catalytic module without being hydrolyzed sufficiently into ammonia. The exhaust gas purification apparatus improves the efficiency of hydrolysis by providing the hydrolytic catalytic module in the catalytic device.
- However, when the structural space of the exhaust gas purification apparatus is reduced, it is difficult for the apparatus to provide a distance between the hydrolytic catalytic module and the SCR catalytic module that is long enough to ensure the reaction time for urea water to be hydrolyzed. Therefore, if the structural space of the exhaust gas purification apparatus attempted to be reduced, the quantity of unreacted urea water supplied to the SCR catalytic module without being hydrolyzed into ammonia increases, with the result that the efficiency of the reduction of NOx in comparison to urea water usage deteriorates.
- The present invention is directed to providing an exhaust gas purification apparatus for improving the efficiency of the reduction of NOx in comparison to urea water usage.
- An exhaust gas purification apparatus includes an oxidation catalyst provided in a passage through which exhaust gas flows, a urea decomposition accelerator, a selective catalytic reduction catalyst provided downstream of the urea decomposition accelerator and a urea water supplying device for supplying urea water to the urea decomposition accelerator. The urea decomposition accelerator is provided downstream end surface of the oxidation catalyst and has at least one of hydrophilic function and hydrolytic catalytic function.
- Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
- The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:
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FIG. 1 is a schematic view showing an exhaust gas purification apparatus according to a first embodiment of the present invention and its associated components; -
FIG. 2 is a schematic cross sectional view of the exhaust gas purification apparatus ofFIG. 1 ; and -
FIG. 3 is a schematic cross sectional view of an exhaust gas purification apparatus according to a second embodiment of the present invention. - The following will describe the embodiments of the exhaust gas purification apparatus according to the present invention with reference to
FIGS. 1 through 3 . Referring toFIGS. 1 and 2 showing the first embodiment, the exhaust gas purification apparatus which is designated generally by 101 and its associated components will be described. The exhaustgas purification apparatus 101 is employed in a vehicle equipped with a diesel engine. - Referring to
FIG. 1 , an engine assembly including anengine 1 and the exhaustgas purification apparatus 101 is designated generally byreference numeral 10. Theengine 1 has a plurality ofcylinders 1A each having anintake port 1B to which anintake manifold 4 is connected for distributing intake air to therespective cylinders 1A. Theintake manifold 4 has aninlet 4A to which anengine intake pipe 3 is connected and theengine intake pipe 3 is further connected to acompressor housing 8A of aturbocharger 8. Thecompressor housing 8A is connected to anintake pipe 2 through which outside air is introduced. - On the other hand, an
exhaust manifold 5 is connected to a plurality ofexhaust ports 1C of theengine 1 for collecting exhaust gas emitted from therespective exhaust ports 1C. Anoutlet 5A of theexhaust manifold 5 is connected to aturbine housing 8B of theturbocharger 8, to which the exhaustgas purification apparatus 101 having a substantially cylindrical shape is connected and disposed adjacent to a lateral side of theengine 1. The exhaustgas purification apparatus 101 is connected to anexhaust pipe 6, the downstream end of which is further connected to amuffler 7. Theintake pipe 2, theturbocharger 8, theengine intake pipe 3 and theintake manifold 4 cooperate to form an intake system of the vehicle, while theexhaust manifold 5, theturbocharger 8, the exhaustgas purification apparatus 101, theexhaust pipe 6 and themuffler 7 cooperates to form an exhaust system of the vehicle. Theengine 1, theengine intake pipe 3, theintake manifold 4, theexhaust manifold 5 and theturbocharger 8 cooperate to form theaforementioned engine assembly 10. - Referring to
FIG. 2 , the exhaustgas purification apparatus 101 includes acasing 11 having a substantially cylindrical shape. Thecasing 11 has anupstream end face 11A to which the outlet 8B2 of theturbine housing 8B of theturbocharger 8 is connected and adownstream end face 11B to which theupstream end 6A of theexhaust pipe 6 is connected. Thecasing 11 communicates internally with theturbine housing 8B and theexhaust pipe 6. - The
cylindrical casing 11 houses therein anoxidation catalyst layer 12 supporting an oxidation catalyst and a diesel particulate filter (DPF) 14 as a particulate matter collecting device disposed downstream of theoxidation catalyst layer 12 with respect to the flow of exhaust gas in thecasing 11. Theoxidation catalyst layer 12 and theDPF 14 are made in the form of a layer extending perpendicular to the axis of acylindrical portion 11C of thecasing 11 over the entire radial dimension of the interior of thecylindrical portion 11C. Theoxidation catalyst layer 12 and theDPF 14 are disposed spaced apart each other thereby to form therebetween aspace 16. - The
oxidation catalyst layer 12 supports thereon the oxidation catalyst for oxidizing hydrocarbons (HC) and carbon monoxide (CO) into water (H2O) and carbon dioxide (CO2) and also promoting the oxidation of nitrogen monoxide (NO) into nitrogen dioxide (NO2). The oxidation catalyst of theoxidation catalyst layer 12 uses material such as platinum (Pt), palladium (Pd), rhodium (Rh), silver (Ag), iron (Fe), copper (Cu), nickel (Ni), gold (Au) or a mixture of two or more of these materials. - The
DPF 14 is made of a porous material such as ceramic for capturing particulate matter (PM) contained in the exhaust gas. TheDPF 14 has an (urea)SCR catalyst 15 as a selective catalytic reduction catalyst supported thereon, e.g., by coating. The selective catalytic reduction catalyst serves to promote the chemical reaction selectively among specific chemical substances. TheSCR catalyst 15 catalyzes the reaction between nitrogen oxide (NOx) and ammonia (NH3) thereby to reduce NOx into nitrogen (N2) and water (H2O). Material of theSCR catalyst 15 includes an oxide of zirconium (Zr), titanium (Ti), silicon (Si), cerium (Ce), or tungsten (W), a complex of these oxides and a ZSM-5 type zeolite partially replaced by a metal such as iron (Fe) and copper (Cu). - The
oxidation catalyst layer 12 supports on at least a part of thedownstream end surface 12B thereof with regard to the flow of exhaust gas, i.e., on the surface thereof facing theDPF 14, ahydrophilic layer 13 having a hydrophilic function and forming the urea decomposition accelerator of the invention. Thehydrophilic layer 13 is formed by coating theend surface 12B of theoxidation catalyst layer 12 with a catalytic material that has a hydrolytic catalytic function for accelerating the hydrolysis and a hydrophilic function. This catalytic material having the hydrolytic catalytic function and the hydrophilic function includes a metal oxide such as silica (SiO2), alumina (Al2O3), ceria (CeO2), titania (TiO2), tungsten oxide (WO3) and the like. Material forming thehydrophilic layer 13 is made of a single metal oxide or a combination of the above metal oxides. The performance for hydrolysis of thehydrophilic layer 13 can be improved by adding silver (Ag) or platinum (Pt) other than the above metal oxides to the material forming thehydrophilic layer 13. - An
injection valve 18 that is an electromagnetic valve is provided in thecylindrical portion 11C of thecasing 11 at a position between the oxidation catalyst layer 12 (or the hydrophilic layer 13) and the DPF 14 (or the SCR catalyst 15). Specifically, the position is closer to the oxidation catalyst layer 12 (or the hydrophilic layer 13) than the DPF 14 (or the SCR catalyst 15). Theinjection valve 18 forms a urea water supplying device of the invention. Theinjection valve 18 is connected to aurea water tank 19 provided in a vehicle (not shown) and operable to inject urea water into thespace 16 of thecasing 11. Theinjection valve 18 is provided at a position that is adjacent to and immediately downstream of thehydrophilic layer 13 so that urea water is injected by theinjection valve 18 toward thedownstream end surface 12B of theoxidation catalyst layer 12, i.e., thedownstream surface 13B of thehydrophilic layer 13. Theinjection valve 18 is electrically connected to a dosing control unit (DCU) 30 that controls the opening and closing operation of theinjection valve 18. Theurea water tank 19 has an electric pump for supplying urea water to theinjection valve 18. The electric pump is electrically connected to theDCU 30 and the pump operation is controlled by theDCU 30. - A cylindrically-shaped
mixer 17 is provided on theupstream end surface 14A of theDPF 14 for distributing substances in the exhaust gas uniformly over theend surface 14A. Themixer 17 has a structure that is similar to that disclosed in Published Japanese Translation H06-509020 of PCT international publication or Japanese Patent Application Publication 2006-9608. The mixer disclosed in Published Japanese Translation H06-509020 is made in the form of a lattice that divides the gas passage into plural cells so as to cause the gas flowing through each cell to flow spirally and also to flow toward the adjacent cell. This helps the substances in the exhaust gas to spread uniformly in the whole passage. On the other hand, the mixer disclosed in Japanese Patent Application Publication 2006-9608 has plural plates each extending perpendicularly to the direction of gas flow, which provides serpentine gas passage serving to distribute the substances in the gas uniformly. - Another
oxidation catalyst layer 20 that supports oxidation catalyst for oxidizing ammonia is provided in theexhaust pipe 6 downstream of the exhaustgas purification apparatus 101. Platinum (Pt), palladium (Pd), silver (Ag), iron (Fe), copper (Cu), nickel (Ni), gold (Au) or the like may be employed as the material of the oxidation catalyst of theoxidation catalyst layer 20. - An exhaust
gas temperature sensor 52 is provided upstream of theoxidation catalyst layer 12 and also downstream of theupstream end face 11A of thecasing 11 for detecting the temperature of exhaust gas. The exhaustgas temperature sensor 52 is electrically connected to theDCU 30 and sends detected temperature information to theDCU 30. Afirst NOx sensor 51 is provided in thecasing 11 at a position upstream of the exhaustgas temperature sensor 52 for detecting the NOx concentration and asecond NOx sensor 53 is provided downstream of thedownstream end face 11B of thecasing 11, more specifically, at a position downstream of theoxidation catalyst layer 20 in theexhaust pipe 6, for detecting the NOx concentration. The first and thesecond NOx sensors DCU 30 and send information about the NOx concentration to theDCU 30. As described above, the exhaustgas purification apparatus 101 having theSCR catalyst 15 and theDPF 14 integrated together is mounted to theengine assembly 10 at a position adjacent to the engine 1 (refer toFIG. 1 ). - The following will describe the operation of the exhaust
gas purification apparatus 101 according to the first embodiment and its associated components with reference toFIGS. 1 and 2 . Referring toFIG. 1 , while theengine 1 is running, outside air is flowed into thecompressor housing 8A of theturbocharger 8 through theintake pipe 2. The air is pumped by a compressor wheel (not shown) in thecompressor housing 8A and flowed to theengine intake pipe 3 under an increased pressure. The air is flowed into acylinder 1A in theengine 1 through theengine intake pipe 3 and theintake manifold 4. Then, the air in thecylinder 1A is mixed with fuel (light oil) supplied into thecylinder 1A and the fuel is ignited spontaneously for combustion. - Exhaust gas produced by the combustion is discharged into the
exhaust manifold 5 through a plurality ofexhaust ports 1C to be collected by theexhaust manifold 5 and then flows into theturbine housing 8B of theturbocharger 8. The exhaust gas flowing through theturbine housing 8B increases rotation speed of the turbine wheel (not shown) in theturbine housing 8B and the compressor wheel connected to the turbine wheel and then is discharged into the exhaustgas purification apparatus 101. After flowing through the exhaustgas purification apparatus 101, the exhaust gas flows through theoxidation catalyst layer 20, theexhaust pipe 6 and themuffler 7 and then is discharged outside the vehicle (not shown). - Referring to
FIG. 2 , all the exhaust gas flowed into the exhaustgas purification apparatus 101 flows firstly through theoxidation catalyst layer 12. While the exhaust gas flows through theoxidation catalyst layer 12, hydrocarbons and carbon monoxide in the exhaust gas are oxidized into carbon dioxide and water, and part of NO is oxidized into NO2 that can be reduced easily. After flowing through theoxidation catalyst layer 12, the exhaust gas flows through thehydrophilic layer 13 and themixer 17 and then into theDPF 14 supporting theSCR catalyst 15. PM in the exhaust gas is captured by theDPF 14. - Meanwhile, the
DCU 30 activates the electric pump in theurea water tank 19 and also opens theinjection valve 18 for injection of urea water from theinjection valve 18 toward thehydrophilic layer 13 located upstream of thespace 16. - The injected urea water is adsorbed on the
surface 13B of thehydrophilic layer 13. Specifically, the urea water injected onto thesurface 13B of thehydrophilic layer 13 is dispersed in radial directions of thecylindrical portion 11C of thecasing 11 due to the hydrophilic property of thehydrophilic layer 13 and is adsorbed uniformly on thesurface 13B. - The
oxidation catalyst layer 12 has therein the heat due to the exhaust gas flowing therethrough and also the reaction heat due to the oxidation of NO and the like in the exhaust gas. The urea water adsorbed on thesurface 13B of thehydrophilic layer 13 is hydrolyzed into ammonia and carbon dioxide (CO2) by the heat that theoxidation catalyst layer 12 has, the heat of the exhaust gas flowing through thehydrophilic layer 13 and also the hydrolytic catalytic function of thehydrophilic layer 13. The urea water is then adsorbed uniformly on thesurface 13B of thehydrophilic layer 13 and, therefore, the reaction time required for the hydrolysis can be ensured, with the result that the urea water is hydrolyzed into ammonia effectively. Furthermore, since the urea water is dispersed and adsorbed uniformly on thesurface 13B of thehydrophilic layer 13, ammonia is generated uniformly on thesurface 13B of thehydrophilic layer 13. - Since the urea water dispersed and adsorbed on the hydrolytic catalyst as described above is hydrolyzed, the hydrolysis takes place with a high efficiency. Furthermore, the urea water can make use of the heat of hot exhaust gas immediately after being emitted from the
turbocharger 8 of theengine 1. Therefore, the urea water can easily ensure the heat and the temperature required for the hydrolysis. Moreover, urea water is injected and hydrolyzed into ammonia in the region that is downstream of theoxidation catalyst layer 12 and, therefore, no ammonia flows into theoxidation catalyst layer 12 and is oxidized by the oxidation catalyst of theoxidation catalyst layer 12. - Ammonia generated on the hydrolysis is dispersed uniformly in radial directions of the
cylindrical portion 11C of thecasing 11 and flows to themixer 17 together with the exhaust gas. Ammonia is further dispersed while flowing through themixer 17 and then flows into theDPF 14. Ammonia that is flowed into theDPF 14 together with the exhaust gas reduces NOx contained in exhaust gas including NO and NO2 into N2 by the catalytic reaction of theSCR catalyst 15. After being dispersed uniformly on thehydrophilic layer 13, ammonia is dispersed again at themixer 17 and then supplied uniformly to theentire DPF 14 and theSCR catalyst 15, thereby reducing NOx effectively at theSCR catalyst 15. - Unreacted ammonia which has not been used in the reduction of NOx is discharged outside the exhaust
gas purification apparatus 101 together with exhaust gas. - Therefore, the exhaust gas containing residual unreacted ammonia and N2 after flowing through the
DPF 14 where PM is removed is discharged from the exhaustgas purification apparatus 101 into theexhaust pipe 6. The exhaust gas thus discharged into theexhaust pipe 6 flows through theoxidation catalyst layer 20 provided in theexhaust pipe 6 and then is discharged through themuffler 7 outside the vehicle (not shown). Since the residual ammonia in the exhaust gas is oxidized and decomposed while flowing through theoxidation catalyst layer 20, no harmful ammonia is discharged outside. - The catalyst has a characteristic that it activates the catalytic action at a temperature more than a predetermined temperature. The
DCU 30 is operated to open theinjection valve 18 when the temperature detected by the exhaustgas temperature sensor 52 is the predetermined temperature at which theSCR catalyst 15 is activated or higher, and to close theinjection valve 18 when the detected temperature is under the predetermined temperature. Thus, theDCU 30 determines whether or not NOx reduction should be performed depending on the temperature detected by the exhaustgas temperature sensor 52. - Furthermore, the
DCU 30 controls the injection quantity of urea water by adjusting the opening of theinjection valve 18 based on the NOx concentration detected by thefirst NOx sensor 51. Similarly, theDCU 30 controls the injection quantity of urea water by adjusting the opening of theinjection valve 18 based on the NOx concentration detected by thesecond NOx sensor 53, that is the NOx concentration of exhaust gas after flowing through theSCR catalyst 15 and theoxidation catalyst layer 20. For example, when the NOx concentration detected by thesecond NOx sensor 53 exceeds a predetermined level, theDCU 30 increases the injection quantity of urea water by opening theinjection valve 18 further. Thus, theDCU 30 adjusts the supply quantity of urea water to theSCR catalyst 15, i.e., the supply quantity of ammonia, thereby controlling the NOx reduction performance of the exhaustgas purification apparatus 101. - Referring to
FIG. 1 , the exhaustgas purification apparatus 101 is disposed adjacent to theengine 1 and, therefore, hot exhaust gas immediately after being emitted from theengine 1 flows into the exhaustgas purification apparatus 101 through theturbocharger 8. Furthermore, the heat generated by theengine 1 is imparted to the exhaustgas purification apparatus 101 located adjacent to theengine 1 and transmitted inward through outer wall of thecasing 11. - Referring to
FIG. 2 , theoxidative catalyst layer 12, thehydrophilic layer 13 and theDPF 14 supporting theSCR catalyst 15 all disposed inside thecasing 11 are subject to the heat of the hot exhaust gas and the heat imparted from theengine 1 and, therefore, the temperature of the respective components tends to increase. The temperature increasing rate of the respective components, i.e., the oxidation catalyst of theoxidation catalyst layer 12, the hydrophilic catalyst of thehydrophilic layer 13 and theSCR catalyst 15 in the exhaustgas purification apparatus 101 during a cold start of theengine 1 is improved and the time required for activating each catalyst is shortened. Eventually, the performance of NOx reduction is improved. - Thus, the exhaust
gas purification apparatus 101 of the present invention includes theoxidation catalyst layer 12 provided in exhaust gas passage, thehydrophilic layer 13 that is provided at least on thedownstream end surface 12B of theoxidation catalyst layer 12 and having at least one of the hydrophilic function and the hydrolytic catalytic function, theSCR catalyst 15 provided downstream of thehydrophilic layer 13 and theinjection valve 18 for supplying urea water to thehydrophilic layer 13. - The urea water supplied to the
hydrophilic layer 13 is dispersed and adsorbed on thehydrophilic layer 13 by the hydrophilic function and can make use of the heat generated by the oxidation of NO to NO2 and the heat of the exhaust gas flowing through theoxidation catalyst layer 12. Therefore, urea water is hydrolyzed very efficiently and ammonia resulting from the hydrolysis of the urea water is dispersed uniformly over thehydrophilic layer 13. Thus, the hydrolysis of urea water into ammonia is accomplished with high efficiency, which helps to improve the reaction of the ammonia in theSCR catalyst 15. The hydrolysis reaction of urea water supplied to thehydrophilic layer 13 is accelerated by the heat of theoxidation catalyst layer 12 and the heat due to the hydrolytic catalytic function of thehydrophilic layer 13, thereby improving the efficiency of the hydrolysis. Thus, the reduction of NOx in the exhaustgas purification apparatus 101 using the urea water can be improved by the hydrophilic function and the hydrolytic catalytic function of thehydrophilic layer 13. Since the efficiency of hydrolysis of urea water is improved by providing thehydrophilic layer 13, the distance between thehydrophilic layer 13 and theSCR catalyst 15 can be shortened, thereby making it possible for the exhaustgas purification apparatus 101 to be made small. - Since the
injection valve 18 supplies urea water at a position downstream of thehydrophilic layer 13, neither urea water is supplied to theoxidation catalyst layer 12 nor ammonia produced by the hydrolysis of urea water flows through theoxidation catalyst layer 12. Therefore, the oxidation of ammonia into NOx by the oxidation catalyst of theoxidation catalyst layer 12 can be prevented. Due to the structure where theDPF 14 supports theSCR catalyst 15, theSCR catalyst 15 and theDPF 14 are formed integrally, thereby making it possible for the entire apparatus to be formed small. Furthermore, since theoxidation catalyst layer 12, thehydrophilic layer 13, theSCR catalyst 15 formed integrally with theDPF 14 and theinjection valve 18 are all housed in thesingle casing 11, the entire apparatus can be made still smaller. - The exhaust
gas purification apparatus 101 is mounted to theengine assembly 10 and the hot exhaust gas emitted from theengine assembly 10 is introduced into the exhaustgas purification apparatus 101. The heat that theengine assembly 10 generates in operation is transmitted inside thecasing 11 of the exhaustgas purification apparatus 101. Therefore, the time for the temperature of thehydrophilic layer 13 to be increased to the level required for the hydrolysis of urea water and also for the temperature of theSCR catalyst 15 to the level required for activating theSCR catalyst 15 during a cold start of the engine can be shortened, with the result that the NOx reduction performance can be improved. - The exhaust
gas purification apparatus 102 according to a second embodiment ofFIG. 3 is made by modifying theDPF 14 supporting theSCR catalyst 15 of the exhaustgas purification apparatus 101 according to the first embodiment. The following description will use the same reference numerals for the common elements or components in the first and the second embodiments, and the description of such elements or components will be omitted. - Referring to
FIG. 3 , theoxidation catalyst layer 12 having on the downstream side thereof thehydrophilic layer 13, anSCR catalyst layer 25 supporting the SCR catalyst and theDPF 24 are provided in this order in the downstream direction in thecasing 11 of the exhaustgas purification apparatus 102. Theoxidation catalyst layer 12 and theSCR catalyst layer 25 are disposed across thespace 16 and theSCR catalyst layer 25 and theDPF 24 are disposed adjacent to each other. Themixer 17 is provided on theupstream end surface 25A of theSCR catalyst layer 25. - The exhaust gas introduced into the
casing 11 flows through themixer 17 after flowing through theoxidation catalyst layer 12 and thehydrophilic layer 13. NOx contained exhaust gas is reduced into N2 in theSCR catalyst layer 25, PM contained in exhaust gas is captured in theDPF 24 and the resulting exhaust gas is discharged outside the exhaustgas purification apparatus 102. - The rest of the structure and the operation of the exhaust
gas purification apparatus 102 according to the second embodiment is the same as those of the exhaustgas purification apparatus 101 according to the first embodiment. The description of such structure or operation will be omitted. - The exhaust
gas purification apparatus 102 according to the second embodiment offers the same advantageous effects as the exhaustgas purification apparatus 101 according to the first embodiment. - When PM is burned in the
DPF 24 in the exhaustgas purification apparatus 102 for preventing the accumulation of PM, the influence of the combustion heat on the SCR catalyst of theSCR catalyst layer 25 is reduced as compared with the exhaustgas purification apparatus 101 according to the first embodiment. The exhaustgas purification apparatus 102 reduces the deterioration of the catalytic function of theSCR catalyst layer 25 due to the heat caused by burning PM and improves the durability of theSCR catalyst layer 25. - The exhaust
gas purification apparatuses engine assembly 10 having theturbocharger 8, respectively, but the present invention is not limited to this structure. When theengine assembly 10 dispenses with theturbocharger 8, the exhaustgas purification apparatuses outlet 5A of theexhaust manifold 5, respectively. The exhaustgas purification apparatuses engine assembly 10, respectively. - In the second embodiment, the
oxidation catalyst layer 12, theSCR catalyst layer 25, theDPF 24 and theinjection valve 18 are all provided in thecasing 11 of the exhaustgas purification apparatus 102, but the present invention is not limited to this structure. For example, only theDPF 24 may be provided outside thecasing 11 separately from the other components. - In the first and second embodiments, the
oxidation catalyst layer 20 is provided separately from the exhaustgas purification apparatuses oxidation catalyst layer 20 may be provided inside thecasing 11 downstream of theDPF gas purification apparatuses - The
injection valve 18 is provided downstream of theoxidation catalyst layer 12 so as to supply urea water to thehydrophilic layer 13 in the exhaustgas purification apparatuses oxidation catalyst layer 12. The supplied urea water can be hydrolyzed while flowing through theoxidation catalyst layer 12 and, therefore, the efficiency of the hydrolysis of urea water can be improved. Since urea water is dispersed while flowing through theoxidation catalyst layer 12, urea water can be dispersed and adsorbed more uniformly on thehydrophilic layer 13. Accordingly, ammonia produced by the hydrolysis of urea water can be dispersed and be supplied to the SCR catalyst more uniformly. Thus, the efficiency of the reduction of NOx by ammonia in the SCR catalyst is improved. - Although the
hydrophilic layer 13 is supported on part of thedownstream end surface 12B of theoxidation catalyst layer 12 in the first and the second embodiments, thehydrophilic layer 13 may be supported on theentire end surface 12B of theoxidation catalyst layer 12. - The single
hydrophilic layer 13 having the hydrolytic catalytic function and the hydrophilic function is used as the urea decomposition accelerator in the first and the second embodiments, but the present invention is not limited to this structure. The single hydrophilic layer serving as the urea decomposition accelerator may be formed of two different layers, one layer of which is a hydrophilic layer made of a material having only the hydrophilic function and the other layer of which is a hydrolytic catalytic layer made of a material having only the hydrolytic catalytic function for accelerating the hydrolysis of urea water. In this case, the hydrophilic layer should preferably be provided downstream of the hydrolytic catalytic layer, that is on the side facing theDPF - The urea decomposition accelerator may be formed of only the hydrophilic layer made of the material having the hydrophilic function. Since urea water dispersed and adsorbed on the hydrophilic layer can make use of the heat of the
oxidation catalyst layer 12, urea water is hydrolyzed efficiently and the resulting ammonia is dispersed uniformly over the entire hydrophilic layer. On the other hand, the urea decomposition accelerator may be formed of only the hydrolytic catalytic layer made of the material having the hydrolytic catalytic function. In this case, urea water making use of the heat of theoxidation catalyst layer 12 is subject to the hydrolytic catalytic function by the hydrolytic catalytic layer and, therefore, the efficiency of the hydrolysis can be improved. - The
casing 11 of the exhaustgas purification apparatuses casing 11 according to the present invention is not limited to this shape. Thecasing 11 may be formed with a cross-section including a prism such as quadratic prism, a sphere or an ellipsoid. - Furthermore, the
mixer 17 may be dispensed with in the first and the second embodiments.
Claims (11)
1. An exhaust gas purification apparatus comprising:
an oxidation catalyst provided in a passage through which exhaust gas flows;
a urea decomposition accelerator, wherein the urea decomposition accelerator is provided downstream end surface of the oxidation catalyst and has at least one of a hydrophilic function and a hydrolytic catalytic function;
a selective catalytic reduction catalyst provided downstream of the urea decomposition accelerator; and
a urea water supplying device for supplying urea water to the urea decomposition accelerator.
2. The exhaust gas purification apparatus according to claim 1 , wherein the urea water supplying device supplies urea water toward downstream surface of the urea decomposition accelerator.
3. The exhaust gas purification apparatus according to claim 1 , wherein the urea water supplying device is an injection valve provided at a position that is between the urea decomposition accelerator and the selective catalytic reduction catalyst and closer to the urea decomposition accelerator than the selective catalytic reduction catalyst.
4. The exhaust gas purification apparatus according to claim 1 , further comprising:
a particulate matter collecting device for capturing particulate matter contained in the exhaust gas, wherein the particulate matter collecting device is formed integrally with the selective catalytic reduction catalyst.
5. The exhaust gas purification apparatus according to claim 4 , wherein the particulate matter collecting device is provided downstream of the selective catalytic reduction catalyst.
6. The exhaust gas purification apparatus according to claim 4 , further comprising:
a mixer provided on upstream end surface of the particulate matter collecting device or the selective catalytic reduction catalyst for distributing substances in the exhaust gas over the end surface of the particulate matter collecting device or the selective catalytic reduction catalyst.
7. The exhaust gas purification apparatus according to claim 1 , further comprising:
a casing housing the oxidation catalyst, the urea decomposition accelerator, the selective catalytic reduction catalyst and the urea water supplying device.
8. The exhaust emission purification apparatus according to claim 1 , further comprising:
an exhaust gas temperature sensor provided upstream of the oxidation catalyst for detecting a temperature of the exhaust gas;
a first NOx sensor provided upstream of the oxidation catalyst for detecting NOx concentration;
a second NOx sensor provided downstream of the selective catalytic reduction catalyst for detecting NOx concentration; and
a dosing control unit electrically connected to the first and the second NOx sensors, the exhaust gas temperature sensor and the urea water supplying device, wherein, when the temperature detected by the exhaust gas temperature sensor is as high as a temperature at which the selective catalytic reduction catalyst is activated, the dosing control unit activates the urea water supplying device to supply urea water, and when the temperature detected by the exhaust gas temperature sensor is under the temperature at which the selective catalytic reduction catalyst is activated, the dosing control unit activates the urea water supplying device to stop supplying urea water, wherein the dosing control unit controls supply quantity of urea water based on NOx concentrations detected by the first and the second NOx sensors.
9. The exhaust gas purification apparatus according to claim 1 , wherein the exhaust gas purification apparatus is fixed to an engine assembly.
10. The exhaust gas purification apparatus according to claim 1 , wherein the urea decomposition accelerator is formed by coating the downstream end surface of the oxidation catalyst with a material that has a hydrolytic catalytic function and a hydrophilic function.
11. The exhaust gas purification apparatus according to claim 10 , wherein the material includes at least one of silica (SiO2), alumina (Al2O3), ceria (CeO2), titania (TiO2) and tungsten oxide (WO3).
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2009182741A JP2011033000A (en) | 2009-08-05 | 2009-08-05 | Exhaust emission control device |
JPP2009-182741 | 2009-08-05 |
Publications (1)
Publication Number | Publication Date |
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US20110030350A1 true US20110030350A1 (en) | 2011-02-10 |
Family
ID=42985543
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US12/850,080 Abandoned US20110030350A1 (en) | 2009-08-05 | 2010-08-04 | Exhaust gas purifying apparatus |
Country Status (4)
Country | Link |
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US (1) | US20110030350A1 (en) |
EP (1) | EP2295754B1 (en) |
JP (1) | JP2011033000A (en) |
KR (1) | KR20110014524A (en) |
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CN102852602A (en) * | 2011-06-27 | 2013-01-02 | 北汽福田汽车股份有限公司 | SCR (selective catalytic reduction) system for vehicles |
US20140161679A1 (en) * | 2012-11-07 | 2014-06-12 | Johnson Matthey Public Limited Company | Exhaust system |
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KR102072063B1 (en) * | 2012-03-29 | 2020-01-31 | 바스프 코포레이션 | Multi-component filters for emissions control |
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Also Published As
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JP2011033000A (en) | 2011-02-17 |
KR20110014524A (en) | 2011-02-11 |
EP2295754B1 (en) | 2012-12-19 |
EP2295754A1 (en) | 2011-03-16 |
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