Method and Device for Purifying an Exhaust Gas Flow of a Lean-Burning Internal Combustion Engine

Abstract

A method and device for purifying an exhaust gas flow of a lean-burning internal combustion engine, with a particle filter which stores particles both in rich and lean operation of the internal combustion engine and which has at least one catalytically active component on which in lean operation of the internal combustion engine defined exhaust gas components, in particular carbon monoxides and/or hydrocarbons are oxidized, the particle filter furthermore having at least one catalytically active component on which in rich operation of the internal combustion engine defined nitrogen oxides are converted into ammonia using hydrogen present in the exhaust gas flow, the ammonia being temporarily stored in at least one SCR catalytic converter which is connected downstream to the particle filter in the exhaust gas flow direction, and the SCR catalytic converter having at least one catalytically active component on which in lean operation of the internal combustion engine defined nitrogen oxides are reduced using the ammonia which has been temporarily stored in the SCR catalytic converter by selective catalytic reduction (SCR).

1 . A method for purifying an exhaust gas flow of a lean-burning internal combustion engine, with a particle filter which stores particles both in rich and lean operation of the internal combustion engine and which has at least one catalytically active component on which in lean operation of the internal combustion engine defined exhaust gas components, in particular carbon monoxides and/or hydrocarbons are oxidized, the particle filter furthermore having at least one catalytically active component on which in rich operation of the internal combustion engine defined nitrogen oxides are converted into ammonia using hydrogen present in the exhaust gas flow, the ammonia being temporarily stored in at least one SCR catalytic converter which is connected downstream to the particle filter in the exhaust gas flow direction, and the SCR catalytic converter having at least one catalytically active component on which in lean operation of the internal combustion engine defined nitrogen oxides are reduced using the ammonia which has been temporarily stored in the SCR catalytic converter ( 4 ) by selective catalytic reduction (SCR). 
   
   
       2 . The method according to  claim 1  wherein the particle filter has at least one catalytically active component on which the carbon-containing particles which have been stored or attached in the particle filter ( 3 ) are continuously or permanently oxidized. 
   
   
       3 . The method according to  claim 1  wherein an oxidation catalytic converter is connected upstream from the particle filter and in it defined exhaust gas components are at least partially oxidized, in particular nitrogen monoxide (NO) is oxidized to nitrogen dioxide (NO 2 ) by means of oxygen (O 2 ). 
   
   
       4 . The method according to  claim 2  wherein the carbon-containing particles are continuously oxidized according to the following equation:
   C+2 NO 2 →2 NO+CO 2      with C=carbon, NO 2 =nitrogen dioxide, NO=nitrogen oxide, CO 2 =carbon dioxide.   
   
   
       5 . The method according  claim 1  wherein in the exhaust gas flow direction upstream from the particle filter a given amount of fuel is metered into the exhaust gas flow at given times for oxidation, in particular for rapid oxidation of the carbon-containing particles. 
   
   
       6 . The method according to of  claim 3  to in the exhaust gas flow direction upstream from the oxidation catalytic converter fuel is metered into the exhaust gas flow in a defined manner. 
   
   
       7 . The method according to  claim 1  wherein the exhaust gas flow supplied to the particle filter is heated up to a given temperature by means of heat supply at given times, in particular by exothermal reaction of metered fuel on the oxidation catalytic converter. 
   
   
       8 . The method according to  claim 4  wherein the controlled raising of the exhaust gas temperature oxidation of the carbon-containing particles takes place according to the following equation:
   C+O 2 →CO 2      with C=carbon, O 2 =oxygen, CO 2 =carbon dioxide.   
   
   
       9 . The method according to  claim 1  wherein lean operation of the internal combustion engine in an oxidation catalytic converter and/or in a particle filter carbon monoxides (CO) and hydrocarbons (C x H y ) are oxidized according to the following equations:
   2 CO+O 2 →C 2    (1)     4 C x H y +4 x+y O 2 →2 y H 2 O+4 x CO 2    (2)   with O 2 =oxygen, CO 2 =carbon dioxide, H 2 O=water.   
   
   
       10 . The method according to  claim 1  wherein rich operation of the internal combustion engine in the particle filter nitrogen oxides, in particular nitrogen monoxide (NO), are converted according to the following equation into ammonia (NH 3 ):
   NO+NO 2 +2 CO 4 H 2 →2 NH 3 +H 2 O+2 CO 2      with NO 2 =nitrogen dioxide, H 2 =hydrogen, CO=carbon monoxide, H 2 O=water, CO 2 =carbon dioxide.   
   
   
       11 . The method according to  claim 1  wherein selective catalytic reduction on the SCR catalytic converter takes place according to the following equation:
   2 NM 3 +NO+NO 2 →4 N 2 +3 H 2 O   
   
   
       12 . A device for purification of an exhaust gas flow of an internal combustion engine, in particular for executing the method according to  claim 1 ,
 with at least one particle filter which is located in the exhaust gas line of the internal combustion engine and which has at least one catalytically active component on which in lean operation of the internal combustion engine defined exhaust gas components, in particular carbon monoxides and/or hydrocarbons, can be oxidized,   the particle filter furthermore having at least one catalytically active component on which in rich operation of the internal combustion engine defined nitrogen oxides can be converted into ammonia using the hydrogen present in the exhaust gas flow,   at least one SCR catalytic converter in which ammonia can be temporarily stored is connected downstream to at least one particle filter and   the SCR catalytic converter having at least one catalytically active component on which in lean operation of the internal combustion engine defined nitrogen oxides can be reduced by selective catalytic reduction (SCR) using the ammonia which has been temporarily stored in the SCR catalytic converter.   
   
   
       13 . The device according to  claim 12  wherein the particle filter has at least one catalytically active component on which the carbon-containing particles attached or stored in the particle filter can be continuously or permanently oxidized. 
   
   
       14 . The device according to  claim 12  wherein an oxidation catalytic converter in which defined exhaust gas components can be at least partially oxidized is connected upstream from the particle filter. 
   
   
       15 . The device according to  claim 12  wherein there is a fuel metering device by means of which fuel can be metered into the exhaust gas flow upstream from at least one particle filter. 
   
   
       16 . The device according to  claim 12  wherein a controlled temperature rise can be set by means of the metered fuel. 
   
   
       17 . A method of treating an exhaust gas of an internal combustion engine, comprising:
 routing said gas through a particle filter provided with a first catalytically active component functional under lean operating conditions of said engine to oxidize carbon monoxides and hydrocarbons, and a second catalytically active component functional under rich operating conditions of said engine to produce ammonia;   routing said gas through a downstream convertor provided with a third catalytically active component functional under lean operating conditions of said engine to reduce nitrogen oxides using ammonia; and   routing said ammonia produced in said particle filter to said downstream converter, and temporarily storing it therein for reaction with said nitrogen oxides.   
   
   
       18 . The method of  claim 17  including oxidizing carbon containing particles in said particle filter by means of a fourth catalytically active component. 
   
   
       19 . An assembly for treating the exhaust gas of an internal combustion engine comprising:
 means for routing a flow of such gas from said engine;   a particulate filter disposed in said routing means, provided with a first catalytically active component functional under lean operating conditions of said engine to oxidize carbon monoxide and hydrocarbons, and a second catalytically active component functional under rich operating conditions of said engine to produce ammonia;   a converter disposed in said routing means downstream of said particle filter, provided with a third catalytically active component functional under lean operating conditions of said engine to reduce nitrogen oxides using ammonia; and   means for routing ammonia produced in0 said particle filter to said converter, and temporarily storing and ammonia therein for reaction with said nitrogen oxides.   
   
   
       20 . An assembly according to  claim 19  wherein said particle filter includes a fourth catalytically active compound functional to oxidize carbon containing particles.