WO2007136148A1

WO2007136148A1 - Exhaust gas purifying device for diesel engine with exhaust gas recirculation line

Info

Publication number: WO2007136148A1
Application number: PCT/KR2006/003030
Authority: WO
Inventors: Hong-Seok Jung; Yun-Guen Cho; Woo-Jin Lee; Yong-Woo Kim; Joon-Seok Min; Do-Woan Kim
Original assignee: SK Corp; SK Energy Co Ltd
Current assignee: SK Corp; SK Energy Co Ltd
Priority date: 2006-05-24
Filing date: 2006-08-01
Publication date: 2007-11-29
Anticipated expiration: 2008-11-24
Also published as: JP2007315372A; JP4398963B2

Abstract

The present invention relates to an exhaust gas purifying device for a diesel engine, more particularly, the present invention provides an exhaust gas purifying device for a diesel engine, in which a nitrogen oxides reducing (DeNOx) catalyst unit and a diesel particulate filter (DPF) unit are provided successively from an upstream of exhaust gas flow, a diesel fuel injector is provided at a front end portion of the nitrogen oxides reducing catalyst unit, and an exhaust gas recirculation (EGR) line is provided for entering a portion of exhaust gas from a rear end of the diesel particulate filter unit to an intake manifold of an engine. The exhaust gas purifying device of the present invention has an excellent nitrogen oxides reduction performance and a superior efficiency of removing particulate matter, carbon monoxide and hydrocarbon.

Description

EXHAUST GAS PURIFYING DEVICE FOR DIESEL ENGINE WITH EXHAUST

GAS RECIRCULATION LINE

[Technical Field] The present invention relates to an exhaust gas purifying device for a diesel engine which can reduce or remove effectively nitrogen oxides (NO_x) and particulate matter contained in exhaust gas of a diesel engine.

[Background Art]

Based on a fuel-efficiency and an excellent reliability, the diesel engine has been used widely for the vehicle, the vessel and the ordinary industrial purposes, the diesel engine can be operated with a large output and load so that a demand for the diesel engine is continuously increased. Also, in the 3L car program or the Super Car Project which has been promoted to develop a fuel-efficient vehicle, an adoption of the diesel engine is nearly established so that an increased demand for the vehicle in which the diesel engine is mounted is anticipated. However, since exhaust gases discharged from such diesel vehicles hold approximately 40 percent of total atmospheric contamination, the developed countries recognize that the diesel vehicles are mainly responsible for air pollution. In order to cope with the above situation, every country- reinforces a regulation for exhaust gas from the diesel vehicles .

Air pollution discharged from the diesel vehicles is mainly caused by nitrogen oxides (NO_x) and particulate matter

(PM) . Accordingly, a target substance of an exhaust gas regulation for the diesel vehicles is nitrogen oxides and particulate matter. In order to cope with the above regulations, the related technologies which emphasize on a delay of the time at which diesel fuel is injected, a reduction of concentration of nitrogen oxides achieved by an exhaust gas recirculation and an improvement of combustion performance of the engine for reducing particulate matter have been developed. As the method for reducing nitrogen oxides, the selective catalytic reduction method is used. In the above method, nitrogen oxides is reduced to nitrogen and oxygen on a catalyst through a reducing agent.

At this time, ammonia, urea or hydrocarbon can be used as the reducing agent used in the selective catalytic reduction reaction. However, there is a drawback in that a separate infrastructure is required for supplying ammonia or urea, and so hydrocarbon is preferred as the reducing agent. Light oil, paraffin oil, propylene, propane, ethylene and butylenes are instanced as hydrocarbon.

On the other hand, as the method for reducing particulate matter, a diesel particulate filter (DPF) method has been used widely, this method can be classified into a continuous recycling type and a forced recycling type according to a manner of recycling particulate matter captured on a filter. In the continuous recycling method, nitrogen oxide (NO) is converted into nitrogen dioxide (NO₂) by an oxidation catalyst provided at a front end of the diesel particulate filter to recycle particulate matter. In order to recycle actively particulate matter, the subsidiary equipment is used in the forced recycling method for increasing compulsorily a temperature of the filter. In the forced recycling method, there are manners in which an electricity is discharged through an electrode formed on the diesel particulate filter, a temperature of the filter is increased by using an electrical heater, particulate matter is recycled by installing a plasma reactor at a front end portion of the diesel particulate filter or particulate matter is burned by injecting diesel fuel.

As the conventional exhaust gas purifying device of the diesel engine, the exhaust gas purifying device, in which the diesel particulate filter (DPF) on which the oxidation catalyst is supported is disposed at an upstream side of an exhaust gas passage, a hydrocarbon selective reduction type nitrogen oxides reducing (DeNO_x) catalyst is arranged at a downstream side and a diesel fuel injector is provided between the diesel particulate filter and the nitrogen oxides reducing catalyst, has been known.

However, the conventional exhaust gas purifying device is not competent enough for removing effectively and simultaneously not only nitrogen oxides, particulate matter, but also carbon monoxide (CO) and total hydrocarbon (THC) at a mid temperature range.

On the other hand, the exhaust gas recirculation (EGR) system has been used for reducing nitrogen oxides. In general, the exhaust gas recirculation system has been used as the method in which exhaust gas is flowed from a rear end of a turbine of the turbo charger to a front side of a compressor of the turbo charger to lower a combustion temperature of the engine and reduce nitrogen oxides. However, the above method has drawbacks in that since a great quantity of particulate matter is contained in exhaust gas discharged from the turbine of the turbo charger, of particulate matter applies a load to the engine and lowers a fuel- efficient of the engine. Also, in the above method, since nitrogen oxides is reduced and particulate matter is increased according to an increase of an exhaust gas recirculation rate, there is a limitation of reduction nitrogen oxides by applying the exhaust gas recirculation. In addition, since the exhaust gas recirculation (EGR) system is provided with a valve controlled by an engine controller and an exhaust gas recirculation cooler for lowering a temperature of exhaust gas to be circulated, a lay-out of the engine is poor caused by a complicated and an efficiency is not so high, whereby there is a disadvantage when the above system is applied.

As the technology for improving the problem of the conventional exhaust gas recirculation system, an exhaust gas recirculation line connecting a side of the diesel particulate filter and a front end of blower of the turbo charger is disclosed in Koran Patent Publication No. 367666. In the above patent, the exhaust gas recirculation line is not provided with an engine controller and an exhaust gas recirculation cooler and the like and circulates a portion of exhaust gas to improve an easiness of a configuration of device. However, the above patent has a disadvantage in that since a reduction of nitrogen oxides is performed by only the exhaust gas recirculation line, the reduction efficiency for nitrogen oxides contained in exhaust gas is substantially low.

Also, the exhaust gas purifying device in which the exhaust gas recirculation system is used together with the nitrogen oxides reducing (DeNO_x) catalyst is disclosed in U. S. Patent No. 5,924,280, the above patent discloses the exhaust gas recirculation system for re-circulating exhaust gas from an upper end of the nitrogen oxides reducing (DeNO_x) catalyst to an intake manifold. As described above, however, the above patent has drawbacks in that since exhaust gas containing a great quantity of particulate matter is re-circulated, particulate matter applies a load to the engine and lowers a fuel- efficiency of the engine. Also, the exhaust gas recirculation system of the above patent comprises an exhaust gas recirculation valve and a controller for controlling the valve so that the configuration of device is complicated.

[Disclosure] [Technical Problem] The inventors of the present invention have invented the exhaust gas purifying device provided with a nitrogen oxides reducing catalyst and a diesel particulate filter installed sequentially from an upstream of flow of exhaust gas and a diesel fuel injector installed at an upper end of the nitrogen oxides reducing catalyst, and filed as Korean Patent Application No. 10-2005-0102494. As compared with the conventional exhaust gas purifying system, a nitrogen oxides reduction efficiency of the device disclosed the above patent application is superior. In order to meet the requirement for nitrogen oxides reduction efficiency which is more tightened recently, however, the present inventor have studied the exhaust gas purifying device and finally developed the exhaust gas purifying device further comprising the exhaust gas recirculation line.

Accordingly, an object of the present invention is to provide an exhaust gas purifying device for a diesel engine comprising a nitrogen oxides reducing catalyst and a diesel particulate filter and having a remarkable enhanced nitrogen oxides reduction performance.

Also, another object of the present invention is to provide an exhaust gas purifying device for a diesel engine having an excellent nitrogen oxides reduction performance at a temperature of 250 ~ 600 °C which is an actual temperature of exhaust gas, a high particulate matter removal efficiency and being capable of removing carbon monoxide (CO) and total hydrocarbon (THC) .

In order to achieve the above objects, the present inventors have made an effort and invented the exhaust gas purifying device for a diesel engine, comprising a nitrogen oxides reducing catalyst unit and a diesel particulate filter unit provided successively from an upstream of flow of exhaust gas,- a diesel fuel injector provided at a front end portion of the nitrogen oxides reducing catalyst unit; and an exhaust gas recirculation line for entering a portion of exhaust gas from a rear end of the diesel particulate filter unit to an intake manifold of an engine.

[Technical Solution]

The present invention relates to an exhaust gas purifying device for a diesel engine which can reduce or remove effectively nitrogen oxides (NO_x) and particulate matter contained in exhaust gas of an diesel engine, more particularly, the present invention provides an exhaust gas purifying device for a diesel engine, in which a nitrogen oxides reducing (DeNO_x) catalyst unit and a diesel particulate filter (DPF) unit are provided successively from an upstream of flow of exhaust gas, a diesel fuel injector is provided at a front end portion of the nitrogen oxides reducing catalyst unit, and an exhaust gas recirculation (EGR) line is provided for entering a portion of exhaust gas from a rear end of the diesel particulate filter unit to an intake manifold of an engine. Here, the exhaust gas recirculation (EGR) line does not comprise a separate additional adjusting valve or a controller.

Also, the exhaust gas purifying device according to the present invention can further comprise a diesel oxidation catalyst (DOC) , a diesel oxidation catalyst can be placed at a front end portion of a diesel fuel injector, between the diesel fuel injector and a nitrogen oxides reducing catalyst, between the nitrogen oxides reducing catalyst and a diesel particulate matter removing filter or between the diesel particulate matter removing filter and an inlet section of exhaust gas recirculation line, and at least one diesel oxidation catalyst can be provided at the above mentioned locations .

Below, the present invention will be described in more detail.

The exhaust gas purifying device for the diesel engine according to the present invention injects diesel fuel to reduce nitrogen oxides (hereinafter, referred to as "NO_x") at a nitrogen oxides reducing catalyst unit (hereinafter, referred to as "DeNO_x catalyst unit"), reduces particulate matter (PM) accumulated on a diesel particular filter (hereinafter, referred to as "DPF" ) unit through a combustion of diesel fuel and simultaneously removes carbon monoxide (CO) and total hydrocarbon. Also, the present invention discloses the exhaust gas purifying device provided with an exhaust gas recirculation (hereinafter, referred to as "EGR") line for guiding a portion of exhaust gas from a rear end of the DPF to an intake manifold to reduce NO_x.

In the exhaust gas purifying device according to the present invention, a portion of NO_x is reduced by providing the EGR line and NO_x is removed in the DeNO_x catalyst provided in an exhaust gas passage, and so the exhaust gas purifying device of the present invention can removed nitrogen oxides more effectively than the convention exhaust gas purifying device. Also, nitrogen oxides is additionally removed by the catalyst applied on the DPF provided at a rear end of the DeNO_x catalyst unit so that there is an advantage in that a nitrogen oxides reduction efficiency of the exhaust gas purifying device according to the present invention is definitely superior to that of the conventional exhaust gas purifying device and the reduction of NOx becomes high in a mid- temperature range of 250 ~ 350 "C

In the present invention, most of • particulate matter is removed on the DPF unit. In a case that diesel fuel is injected at a front end of the DeNO_x catalyst unit, diesel fuel is uniformly distributed while diesel fuel is passed through the DeNO_x catalyst, and so a temperature at which the DPF is regenerated can be lowered. Furthermore, the present invention can remove more effectively carbon monoxide (CO) and total hydrocarbon (THC) removed in the conventional exhaust gas purifying device.

Since carbon monoxide can not be removed in the DeNO_x catalyst unit, amount of carbon monoxide is increased if only the DeNO_x catalyst is existed. In the present invention, however, carbon monoxide can be removed effectively at a temperature of 200^°C or more due to platinum-group component of the DPF unit. Also, total hydrocarbon is not removed in the DeNO_x catalyst unit. In particular, if diesel fuel as reducing agent is injected for removing nitrogen oxides, a greater quantity of hydrocarbon is contained in exhaust gas as compared with the case that diesel fuel is not injected. In order to solve the above problem, in the present invention, exhaust gas is passed through the DeNO_x catalyst so that increased hydrocarbon which is not reacted can be removed effectively on the DPF unit .

Further, if at least one diesel oxidation catalyst (DOC) is provided at a front end portion of the diesel fuel injector, between the diesel fuel injector and a nitrogen oxides reducing catalyst, between the nitrogen oxides reducing catalyst and a diesel particulate filter or between the diesel particulate filter and an inlet section of the exhaust gas recirculation line, the diesel oxidation catalyst converts nitrogen oxide (NO) in exhaust gas into nitrogen dioxide (NO₂) to enable a recycling in the diesel particulate filter to be carried smoothly, and it is possible to increase a reducing efficiency of total hydrocarbon (THC) including soluble organic fraction.

[Advantageous Effects]

The exhaust gas purifying device for a diesel engine according to the present invention is the exhaust gas purifying device having an excellent nitrogen oxides reduction performance at a temperature of 250 ~ 600 "C which is an actual temperature of exhaust gas and a superior particulate matter removal efficiency, the present invention has the advantages in that a selective reduction of nitrogen oxides is carried out by injecting diesel fuel and a reduction of nitrogen oxides is carried out simultaneously by the exhaust gas recirculation so that a nitrogen oxides reduction efficiency is significantly enhance and particulate matter can be removed effectively by the particulate filter provided at a rear end of the nitrogen oxides reducing catalyst.

Also, regardless of an operation state of the engine which causes a difference in the nitrogen oxides reduction performance according to a temperature of exhaust gas, the exhaust gas purifying device of the present invention has an excellent nitrogen oxides reduction performance and a superior efficiency of removing particulate matter, carbon monoxide and hydrocarbon . [Description of Drawings]

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

Fig. 1 is a view illustrating an exhaust gas purifying device according to the present invention;

Fig. 2 is a graph showing changes of nitrogen oxides and particulate matter according to an exhaust gas recirculation (EGR) rate;

Fig. 3 is a view of a nitrogen oxides reducing catalyst unit consisting of one nitrogen oxides reducing catalyst layer; and

Fig. 4 is a view of a nitrogen oxides reducing catalyst unit consisting of three (3) nitrogen oxides reducing catalyst layers .

<Explanation of reference numerals for designating main components in the drawings> 1 : Nitrogen oxides reducing (DeNO_x) catalyst unit

2 : Diesel particulate filter (DPF) unit

3 : Diesel fuel injector 4 : Exhaust gas recirculation (EGR) line

5 : Intake manifold 6 : Turbo charger 6a : Compressor 6b : Turbine 7 : Diesel engine 8 : Air filter 9 : Intercooler 10 Diesel fuel injection controlling unit 11 : Fuel tank.

[Best Mode]

Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings .

An exhaust gas purifying device placed in an exhaust passage of a diesel engine as one embodiment of the present invention is illustrated in Fig. 1. According to Fig. 1, a DeNO_x catalyst unit 1 is provided at an upstream side of flow of exhaust gas, and a DPF unit 2 is provided in series with the DeNO_x catalyst unit, and a diesel fuel injector 3 is installed at a front end portion of the DeNO_x catalyst unit. A EGR line 4 connecting a rear end of the DPF unit and an intake manifold 5 placed at an upper end of a compressor of turbo charger of an engine. The EGR system according to the present invention has an advantage in that the system is not provided with an additional EGR cooler, an EGR valve and an EGR controller so that the device can be configured easily. A portion of exhaust gas is automatically flowed into the EGR system according to an air flow in the intake manifold 5 and this exhaust gas is mixed with the intaken air and then entered in the engine 7 through the compressor 6a of the turbocharger 6. Exhaust gas of the diesel engine 7 is exhausted through a turbine 6b of the turbocharger. The DeNO_x catalyst unit 1 and the diesel particulate filter (DPF) 2 are provided sequentially in the exhaust passage and the diesel fuel injector 3 is provided at a front end portion of the DeNO_x catalyst unit. It is preferred that an exhaust gas recirculation (EGR) rate of the exhaust gas purifying device according to the present invention is in the range of 0.1 to 15%, this EGR rate is adjusted according to the diameter of the exhaust gas recirculation line. If the exhaust gas recirculation rate is 0.1% or less, the NO_x reducing effect is scarcely obtained, and if the exhaust gas recirculation rate exceeds 15%, particulate matter exhausted from the engine is significantly increased so that a load is applied to the DPF filter and a function of the DPF filter can not be obtained effectively. If the exhaust gas recirculation rate is adjusted to be in the above range, the NO_x reduction efficiency can be increased while particulate matter is scarcely increased, and in addition to the NO_x reduction efficiency obtained by the DeNO_x catalyst unit 1, the NO_x reduction efficiency which is remarkably increased can be achieved. Also, all particulate matter contained in exhaust gas is removed in the DPF unit 2, while diesel fuel injected from the diesel fuel injector 3 provided at a front end of the DeNO_x catalyst unit 1 is passed through the DeNO_x catalyst, diesel fuel is uniformly distributed so that a temperature at which the DPF is recycled can be lowered. Diesel fuel is flowed from a fuel tank 11 into the diesel fuel injector by an inflowing pump (not shown) and then injected from the diesel fuel injector, amount of the diesel to be injected and a time at which diesel fuel is injected is controlled by a diesel fuel injection controlling unit 10.

The DeNO_x catalyst unit 1, the DPF unit 2 and the diesel fuel injector 3 in the exhaust gas purifying device according to the present invention are illustrated in Fig. 3 and Fig. 4. Fig. 3 shows the DeNO_x catalyst unit consisting of one nitrogen oxides reducing catalyst layer and Fig. 4 shows the DeNO_x catalyst unit consisting of a plurality of nitrogen oxides reducing catalyst layers. Referring to Fig. 4, in the DeNO_x catalyst unit, a plurality of DeNO_x catalyst layers are adjacent in stack and disposed successively. If a plurality of DeNO_x catalyst layers are disposed in stack and disposed successively to form the DeNO_x catalyst unit, a surface area through which exhaust gas is passed is increased, and so the NO_x reduction efficiency can be enhanced. Also, the NO_x reduction efficiency can be increased by forming the DeNO_x catalyst layers made of the catalysts which differ from each other or varying the catalyst content so that there are advantages in that the DeNO_x catalyst unit has the excellent NO_x reduction efficiency in the various temperature ranges and has excellent NO_x reduction performance regardless of an operation state of the engine which causes a difference in the NO_x reduction performance according to a temperature of exhaust gas . The catalyst on which silver component, copper component or mixture thereof is supported is employed as the DeNO_x catalyst unit according to the present invention, material which can be used for supporting silver component is selected from silver (Ag) which is in a resolved state, silver oxide (Ag₂O) , silver chloride (AgCl) , silver nitrate (AgNO₃) , silver sulfate (Ag₂SO₄) or mixture thereof, and material which can be used for supporting copper component is selected from copper (Cu) which is in a reduced state, copper oxide, copper acetate, copper nitride, copper sulfate or mixture thereof. Alumina (Al₂O₃) , silica (SiO₂) , titania (TiO₂) , ceria (CeO₂) , zirconia

(ZrO₂) or zeolite can be used as washcoat supporting the catalyst, and it doesn't matter that mixture of two or more selected from the above materials can be used. Among the materials as mentioned above, the most excellent performance of reducing nitrogen oxides is obtained by using alumina as the washcoat .

The washcoat is used in a state coated on a supporter, it is preferred that the usage of washcoat is 0.5 to 4g/in³ based on the entire catalyst content. At this time, if the washcoat content is less than 0.5 g/in³, an absolute quantity of the supported catalyst is insufficient so that a performance of the catalyst is significantly lowered and if the washcoat content exceeds 4 g/in³, a performance of the catalyst is not increased any more and it is not easy to manufacture the catalyst.

The support of the nitrogen oxides reducing catalyst is a flow-through type made of thermostable ceramic or metal, and in more detail can be exemplified by cordierite honeycomb structural body.

It is preferred that silver component, copper component or mixture thereof in the catalyst is used such that the above component content is 0.1 to 10 wt% based on a weight of the washcoat. If the above component content is less than 0.1 wt%, an absolute quantity of component performing a catalytic function is insufficient so that a performance of the catalyst is significantly lowered, and if the above component content exceeds 10 wt%, component is existed in a state of the metallic element which is unfavorable to a reaction so that a performance of the catalyst is significantly lowered.

Also, platinum-group component is additionally supported on the DeNO_x catalyst according to the present invention to obtain more excellent nitrogen oxides reduction performance at

a temperature in the range of 250 ~ 600°C which is an actual temperature of exhaust gas. The nitrogen oxides reduction performance of the nitrogen oxides reducing catalyst according to the present invention is excellent at a temperature in the

range of 250 ~ 600°C which is an actual temperature of exhaust gas, and the DeNO_x catalyst has the characteristic in that, in the case that the platinum-group catalyst is additionally supported, the nitrogen oxides reduction performance is more excellent at a temperature in the range of 350 ~ 450 °C.

Metal which can be used as platinum-group noble metal supported In the DeNO_x catalyst unit can be composed with one component or mixture of two or more components selected from platinum, palladium, ruthenium, iridium and rhodium. Palladium nitrate, palladium chloride, tetramine palladium dichloride and the like can be used as the starting material for palladium. Also, chloroplatinic acid, diamine nitritoplatinum, diamine tetrachroloplatinum and the like can be used as the starting material for platinum, and rhodium chloride, rhodium nitrate, triamine rhodium hexachloride and the like can be used as the starting material for rhodium. Also, it is preferred that the platinum-group metal content is in the range of 0.0001 to 0.5 wt%, more preferably, 0.0005 to 0.2 wt%, further more preferably, 0.001 to 0.1 wt%. If the platinum- group metal content is less than 0.0001 wt%, platinum-group metal won't help to improve the DeNO_x catalyst unit, and if the platinum-group metal content exceeds 0.5 wt%, a performance of the DeNO_x catalyst unit is rapidly lowered. The DPF is a filter in which a platinum-group catalyst is supported, the element supported as the platinum-group catalyst is one or more selected from a group consisting of platinum, palladium, iridium and rhodium. Platinum or palladium is more preferable element supported as the platinum-group catalyst. A content of platinum-group catalyst supported in the DPF is in the range of 0.01 wt% to 5wt% in the washcoated support. If the platinum-group catalyst content is less than 0.01 wt%, particulate matter removing effect is not produced, and if the platinum-group catalyst content exceeds 5 wt%, a performance of the DPF is not improved any more so that this condition can be disadvantageous economically.

In addition to the platinum-group filter, oxidation co- catalyst component can be supported additionally in the DPF. Oxidation co-catalyst component can function as a role by which an oxidation of sulfur dioxide is restrained or a surface activity of the platinum-group catalyst is increased. In general, the platinum-group catalyst has a high activity in an oxidation reaction of soluble organic fraction. However, sulfur dioxide (SO₂) which is burning product of sulfur contained in light-oil is oxidized and converted into sulfate. Consequently, an undesirable result that particulate matter is inversely increased is generated. In order to improve the above problems, one catalyst component or more selected from vanadium, tungsten or molybdenum can be used additionally in the platinum-group catalyst. Preferably, the content of one catalyst component or more selected from vanadium, tungsten or molybdenum is in the range of 0.01 wt% to 2wt% in the washcoated support. If the above catalyst component content is less than 0.01 wt%, the effect of restraining an oxidation of sulfurous acid gas is not produced, and if the above catalyst component content exceeds 2 wt%, an addition of the above catalyst component is meaningless so that it is not economical to add the catalyst component. Also, since alkali metal such as potassium (K) , magnesium (Mg) and the like has the flow- ability at a low temperature, alkali metal increases a surface activity of the platinum-group catalyst to facilitate a contact between the catalyst and particulate matter, thereby increasing the reaction ratio. Preferably, the alkali metal content is in the range of 0.01 wt% to lwt% in the washcoated support. If the alkali metal content is less than 0.01 wt%, the effect of increasing the reaction rate of the platinum- group catalyst is not produced, and if the alkali metal content exceeds 1 wt%, an addition of the above alkali metal is meaningless so that it is not economical to add the alkali metal. Also, alumina (Al₂O₃), silica (SiO₂), titania (TiO₂), ceria (CeO₂) , zirconia (ZrO₂) or zeolite can be used as a carrier supporting the above catalyst component, and it doesn' t matter that mixture of two or more selected from the above materials can be used

The DPF according to the present invention removes accumulated particulate matter using exhaust gas heated by oxidizing the injected diesel fuel at a front end portion of the nitrogen oxides reducing catalyst. In order to employ safely the filter although a temperature of the DPF is excessively increased, at this time, it is preferred that the support is made of cordierite having an excellent heat- resisting property, ceramic containing silicon carbide (SiC) or alloy material comprising nickel alloy or FeCr alloy. In the case that the supporter is made of material having an excellent heat-resisting property, there are advantages in that the device can be operated safely although high temperature heat is generated when recycling the DPF and it is possible to save diesel fuel to be injected by utilizing heat generated when excessive particulate matter is oxidized.

Below, the present invention will be described in more detail in connection with the preferred embodiments. However, it should be understood that the embodiments of the present invention can be modified into various aspects and the scope of the present invention is not limited by the specific embodiment described below.

[Experimental example 1]

The nitrogen oxides reducing (DeNO_x) catalyst was manufactured as follows. Gamma alumina powder (surface area: 210m²/gr, volume of porous: 0.5cc/gr, specific gravity: 0.8g/cc), acetic acid and secondary distilled water were mixed, the mixture was then pulverized through a wet type ball mill for 24 hours to manufacture uniform alumina slurry. The above mixture was pulverized through the wet type ball mill such that an average particle size of alumina was 2 to 8 micrometers .

The manufactured alumina slurry was wash-coated with cordierite honeycombs with a diameter of 11.25 inches, a length of 3 inches and a cell density of 400 cpsi (cells per square inch) such that the supporting amount of alumina become 3 g/in³. A temperature in the calcination furnace was increased from a normal temperature to 120 ^°C at the rate of 3°C/min., the alumina slurry was then dried at a temperature of 120 °C for 3 hours. Next, a temperature in the calcination furnace was increased from 120 ^°C to 550 ^°C at the rate of 3^°C/min., the alumina slurry was then calcined at a temperature of 550 °C for 3 hours.

Next, the dried cordierite in which alumina was supported was impregnated with a solution manufactured by dissolving silver nitrate and chloroplatinic acid as a platinum precursor, such that silver content was 2.0 wt% and platinum catalyst component content was 0.001 wt% in the alumina, the dried cordierite was then calcined at a temperature of 120 ⁰C for 3 hours and a temperature of 550 "C for 3 hours like the condition for wash-coating the alumina.

[Experimental example 2]

The diesel particulate filter (DPF) was manufactured as follows. In a flask with an inner volume of 2 liters, polyvinylpyrrolidone (available from Aldrich Chemical Corp., average molecular weight of 10,000) of 252 grams was dissolved in the diluted water of 1 liter to make uniform solution. Chloroplatinic acid of 30.4 grams and methanol of 1 liter were added to the uniform solution and the solution was then stirred. This solution was refluxed at a temperature of 80^°C for 6 hours and filtrated to obtain dark-brown colored platinum colloid solution of 2,070 grams in which platinum content is 0.62 wt%. Ammonium molybdate of 15.4 grams and potassium hydroxide of 10 grams were putted in diluted water of 250 milliliter, respectively, and diluted water is then stirred to manufacture aqueous solution of molybdenum and aqueous solution of potassium.

Platinum colloid solution, aqueous solution of molybdenum and aqueous solution of potassium produced as the above were mixed at the same weight ratio to obtain metallic salt colloid solution for the catalyzed filter. The wall- flow shaped ceramic filter (available from the Corning Corp) with a diameter of 11.25 inches, a length of 14 inches and a cell density of 200 cpsi. was used as a supporter for the catalyzed filter. Wash coat solution of 7 wt% made by mixing titania and silica was deposited on the honeycomb monolith and the honeycomb monolith was then dried and calcined. Mixed colloid solution for the catalyzed filter was supported on the washcoated support such that platinum content becomes 0.27 wt%, molybdenum content become 0.16 wt% and potassium content become 0.077 wt% in the washcoated support. Colloid solution was dried at a temperature of 120^°C for 3 hours and calcined at a temperature of 550 ^°C for 4 to 6 hours to produce the diesel particulate filter.

[Example 1] Performance estimation of the exhaust gas purifying device -1 The nitrogen oxides reducing catalyst manufactured according to the experimental example 1 and the diesel particulate filter manufactured according to the experimental example 2- were connected continuously to each other and then placed the canning made of stainless steel. As illustrated in Fig. 1, a pipe having a diameter of 1/2 inch and made of stainless steel was connected to a side surface of an exhaust pipe at a rear end of the DPF and connected to a side of a front end of the turbo charger. At this time, the obtained exhaust gas recirculation (EGR) ratio was 5%. The tests for estimating an exhaust gas reduction and a particulate matter reduction were carried out in Japan 13 Mode for a large-sized diesel vehicle. The engine having a piston displacement of 11 liters and manufactured by the Daewoo Motor Co. Ltd in Korea was used for the above estimation test. A turbocharger and a intercooler are applied to the used engine. The tests were carried out under the conditions of a specific RPM and torque prescribed in the test mode of the engine dynamometer. At this time, diesel fuel used for carrying out the tests was extremely low sulfur diesel fuel with sulfur content of 50 ppm. The test results shows that carbon monoxide was reduced by 93%, hydrocarbon was reduced by 32%, nitrogen oxides was reduced 55% and particulate matter was reduced by 93% or more.

Table 1. Results of test for estimating an exhaust gas reduction and a particulate matter reduction for the engine manufactured Daewoo Motors .

[Comparative example 1] Performance estimation of the exhaust gas purifying device -2

Only except for the exhaust gas circulation pipe used in example 1, the nitrogen oxides reducing catalyst manufactured according to the experimental example 1 and the diesel particulate filter manufactured according to the experimental example 2 were connected continuously to each other and then placed the canning made of stainless steel. The tests for estimating an exhaust gas reduction and a particulate matter reduction were carried out in Japan 13 Mode for a large-sized diesel vehicle. The tests were carried out under the conditions of a specific RPM and torque prescribed in the test mode of the engine dynamometer. At this time, diesel fuel used for carrying out the tests was extremely low sulfur diesel fuel with sulfur content of 50 ppm. The test results shows that carbon monoxide was reduced by 92%, hydrocarbon was reduced by 34%, nitrogen oxides was reduced 38% and particulate matter was reduced by 93% or more.

Table 2. Results of test for estimating an exhaust gas reduction and a particulate matter reduction for the engine manufactured Daewoo Motors.

[industrial Applicability]

The exhaust gas purifying device for a diesel engine according to the present invention is the exhaust gas purifying device having an excellent nitrogen oxides reduction performance at a

temperature of 250 ~ 600°C which is an actual temperature of exhaust gas and a superior particulate matter removal efficiency, the present invention has the advantages in that a selective reduction of nitrogen oxides is carried out by injecting diesel fuel and a reduction of nitrogen oxides is carried out simultaneously by the exhaust gas recirculation so that a nitrogen oxides reduction efficiency is significantly enhance and particulate matter can be removed effectively by the particulate filter provided at a rear end of the nitrogen oxides reducing catalyst.

Also, regardless of an operation state of the engine which causes a difference in the nitrogen oxides reduction performance according to a temperature of exhaust gas, the exhaust gas purifying device of the present invention has an excellent nitrogen oxides reduction performance and a superior efficiency of removing particulate matter, carbon monoxide and hydrocarbon .

Claims

[CLAIMS]

[Claim l]

An exhaust gas purifying device for a diesel engine, comprising a nitrogen oxides reducing (DeNO_x) catalyst unit and a diesel particulate filter (DPF) unit provided successively from an upstream of exhaust gas flow; a diesel fuel injector provided at a front end portion of the nitrogen oxides reducing catalyst unit; and an exhaust gas recirculation (EGR) line for entering a portion of exhaust gas from a rear end of the diesel particulate filter unit to an intake manifold of an engine; wherein the exhaust gas recirculation (EGR) line does not comprise a separate additional adjusting valve or a controller.

[Claim 2]

The exhaust gas purifying device for the diesel engine as set forth in claim 1, wherein the exhaust gas recirculation (EGR) rate is in the range 0.1 to 15%.

[Claim 3]

The exhaust gas purifying device for the diesel engine as set forth in claim 1, wherein the nitrogen oxides reducing catalyst unit consists of a plurality of DeNO_x catalyst layers disposed adjacently in a stack.

[Claim 4]

The exhaust gas purifying device for the diesel engine as set forth in claim 3, wherein the adjacent nitrogen oxides reducing catalyst layers contains catalyst compositions or composition contents which differ from one another.

[Claim 5] The exhaust gas purifying device for the diesel engine as set forth in claim 1, wherein the exhaust gas purifying device further comprises at least one diesel oxidation catalyst placed at a front end portion of a diesel fuel injector, between the diesel fuel injector and a nitrogen oxides reducing catalyst, between the nitrogen oxides reducing catalyst and a diesel particulate filter or between the diesel particulate filter and an inlet section of an exhaust gas recirculation line.

[Claim 6]

The exhaust gas purifying device for the diesel engine as set forth in any one selected from claim 1 to claim 5, wherein the diesel particulate filter comprises a platinum-group catalyst supported thereon. [Claim 7]

The exhaust gas purifying device for the diesel engine as set forth in claim 6, wherein platinum-group component is one or more selected from the group consisting of platinum, palladium, iridium and rhodium.

[Claim 8]

The exhaust gas purifying device for the diesel engine as set forth in claim 7, wherein the diesel particulate filter comprises a platinum component supported thereon.

[Claim 9]

The exhaust gas purifying device for the diesel engine as set forth in claim 6, wherein the diesel particulate filter is the supporter made of thermal stable ceramic or metal and washcoated with one or more selected from alumina, silica, titania, ceria, zirconia or zeolite.

[Claim lθ]

The exhaust gas purifying device for the diesel engine as set forth in claim 9, wherein the diesel particulate filter contains platinum component supported therein and the platinum component content is 0.01 to 5 wt% in the washcoated support. [Claim 11]

The exhaust gas purifying device for the diesel engine as set forth in claim 10, wherein the diesel particulate filter contains one or more oxidation co-catalyst components selected from vanadium, tungsten, molybdenum, magnesium or potassium supported additionally therein.

[Claim 12] The exhaust gas purifying device for the diesel engine as set forth in claim 11, wherein a content of the oxidation co- catalyst component is 0.01 to 2 wt% in the washcoated support if the oxidation co-catalyst component is one or more selected from vanadium, tungsten or molybdenum and a content of the oxidation co-catalyst component is 0.01 to 1 wt% in the washcoated support if the oxidation co-catalyst component is one or more selected from magnesium or potassium.

[Claim 13] The exhaust gas purifying device for the diesel engine as set forth in claim 6, wherein the nitrogen oxides reducing catalyst unit contains silver component, copper component or mixture thereof supported therein.

[Claim 14] The exhaust gas purifying device for the diesel engine as set forth in claim 13, wherein the nitrogen oxides reducing catalyst unit the support made of thermostable ceramic or metal and washcoated with one or more selected from alumina, silica, titania, ceria, zirconia or zeolite

[Claim 15]

The exhaust gas purifying device for the diesel engine as set forth in claim 14, wherein the nitrogen oxides reducing catalyst unit contains silver component supported therein and silver component content is 0.1 to 10 wt% in the washcoat.

[Claim 16]

The exhaust gas purifying device for the diesel engine as set forth in claim 15, wherein the nitrogen oxides reducing catalyst unit contains platinum-group catalyst component supported additionally therein and platinum-group catalyst component content is 0.0001 to 0.5 wt% in the washcoat.

[Claim 17]

The exhaust gas purifying device for the diesel engine as set forth in claim 16, wherein the nitrogen oxides reducing catalyst unit contains platinum-group catalyst component supported additionally therein and platinum-group catalyst component content is 0.001 to 0.1 wt% in the washcoat .

[Claim 18]

The exhaust gas purifying device for the diesel engine as set forth in claim 17, wherein platinum-group component is one or more selected from the group consisting of platinum, palladium, iridium and rhodium.

[Claim 19] The exhaust gas purifying device for the diesel engine as set forth in claim 18, wherein platinum-group catalyst component is platinum.