DE10349899B4 - Process for the regeneration of a particulate filter - Google Patents

Abstract

A process for the regeneration of a particulate filter (28) of a motor vehicle through which an exhaust gas is fed, wherein an oxidizable reformate gas (40; 44; 56) from a hydrocarbon reformer (30) is fed into the exhaust gas before or in the particulate filter (28) and the exhaust gas is fed by catalytic oxidation The hydrocarbon reformer (30) generates reformate gas (40, 44, 56) for a fuel cell system (6) and regenerates the particulate filter (28) Part of the reformed gas (40; 44; 56) is branched off from the fuel cell system (6), characterized in that depleted reformate gas (56) is branched off from a fuel cell stack (34) of the fuel cell system (6) and the amount of the reformate gas ( 56) is changed controlled.

Description

The invention relates to a method for regenerating a particle filter of a motor vehicle through which an exhaust gas flows and to a motor vehicle having an internal combustion engine, a particle filter arranged in an exhaust line of the internal combustion engine, and a hydrocarbon reformer.

It is expected that the future emissions legislation for motor vehicles, at least in the European Community, the USA and Japan, will be increasingly tightened in terms of particulate emissions. To meet further reduced emission limits for particles, it will therefore be necessary to subject the exhaust gas to an additional aftertreatment.

To reduce the emission of diesel soot and other in the combustion of a fuel in the internal combustion engine of a motor vehicle resulting particulate exhaust gas components, it has long been known to pass the exhaust gas through a arranged in the exhaust pipe particulate filter. In particular, when the vehicle is operated for a long time in the low load range, this particulate filter must be regenerated from time to time, the particles retained by the filter are removed from the filter surfaces to ensure proper functioning of the particulate filter over its remaining term. To regenerate the particulate filter, it is necessary to heat the filter itself and / or the exhaust gas stream passing through the filter in order to burn the particles retained by the filter and thereby to convert them into gaseous reaction products.

Previously known methods provide either a slow passive regeneration of the particulate filter with NO ₂ by the CRT effect at temperatures above 250 ° C or a rapid active thermal regeneration by reaction of carbon soot with oxygen from a temperature of 550 ° C, wherein the the latter method is also suitable for emergency regeneration of the filter.

However, since the minimum temperatures required for these methods in the exhaust pipe of an internal combustion engine, especially in city traffic rarely or never be achieved, an additional heating of the filter or the exhaust gas must take place. This additional heating is usually brought about by an intervention in the engine management. A distinction is made on the one hand between purely motor-side heating measures in the form of an intervention in the combustion process and on the other hand catalytic heating measures, for example in the form of a late post-injection, in which the heat generated at the surface of an oxidation catalyst for heating the exhaust stream and for the regeneration of the downstream particulate filter is utilized ,

However, both methods have the disadvantage that they result in increased fuel consumption due to less favorable engine operation and possible oil dilution due to fuel input.

Basically, from the prior art US 2003/0143442 A1 , the DE 199 13 794 A1 as well as the US 5,409,784 known.

Proceeding from this, the present invention seeks to improve a method and a motor vehicle of the type mentioned in that regeneration of the particulate filter without intervention in the engine management and without the associated unfavorable operating conditions of the engine is made possible.

This object is achieved in that the exhaust gas before its entry into the particulate filter from a hydrocarbon reformer oxidative reformat gas is supplied to the regenerated by a catalytic oxidation of the reformate soot layer on the surface of the particulate filter directly or indirectly by heating the exhaust gas on the to heat for an active thermal regeneration required temperatures.

The relatively high calorific value of the reformate gas and the low ignition temperatures of the hydrogen contained in the reformate H ₂ and carbon monoxide CO already at low temperatures to a very rapid onset of catalytic oxidative conversion of the reformate gas and thus to rapid heating of the particulate filter or the exhaust gas flowing through it and thus to a rapid initiation of the regeneration, in which the particles deposited in the particle filter are oxidized and converted into gaseous reaction products.

In addition, since the supply of reformate gas is independent of the particular mode of operation of the internal combustion engine, the regeneration of the particulate filter can be completely decoupled from engine operation, thereby avoiding intervention in the engine management for filter regeneration, thereby simplifying it. In addition, the overall fuel consumption can be reduced.

The catalytic oxidation of the reformate gas can be arranged in a front of the particulate filter in the exhaust pipe of the internal combustion engine Oxidation catalyst or preferably within the catalytically coated particulate filter itself to avoid high thermal stress of the oxidation catalyst. In the former case, the reformate gas is expediently supplied to the exhaust gas prior to its entry into the oxidation catalyst disposed in the exhaust conduit to oxidize it within the oxidation catalyst to heat the exhaust stream to the temperatures of more than 550 ° C required for active thermal regeneration in which the soot particles deposited in the particle filter react with the residual oxygen in the heated exhaust gas to form gaseous reaction products.

In the last-mentioned case, the reformate gas is expediently fed to the exhaust gas after it leaves the oxidation catalytic converter and is preferably fed into the exhaust gas line shortly before the particle filter in order to minimize heat losses.

If, as in some motor vehicles, in the exhaust pipe two oxidation catalysts are present, one of which is located in the vicinity of the internal combustion engine to ensure a high exhaust gas inlet temperature, the reformate gas is the exhaust gas after its exit from the first and before entering the supplied to the second oxidation catalyst.

The hydrocarbon reformer, from which the reformate gas used for the regeneration of the particulate filter originates, may be an independent component which generates only the reformate gas required for regeneration of the particulate filter and possibly the reforming gas required to heat the oxidation catalyst and therefore does not require a downstream gas purification unit. Preferably, however, it is part of a fuel cell system of the motor vehicle, which generates the electrical energy required to operate various consumers of the vehicle.

In both cases, the fuel used to operate the internal combustion engine is preferably converted in the reformer. While the reformate gas thus generated from an independent component is fed directly into the exhaust pipe, it is preferably branched off from a fuel cell system between the reformer and a fuel cell stack, the removal can be done in front of or behind a gas cleaning unit, if the fuel cell system is equipped with such a unit , Alternatively, it is also possible to divert depleted reformate gas in the form of anode residual gas behind the fuel cell stack and feed it into the exhaust pipe.

Further advantageous embodiments will become apparent from the combination of the features mentioned in the dependent claims.

The invention will be explained in more detail with reference to the accompanying drawings in several embodiments. Show it:

1 : a schematic representation of a non-inventive motor vehicle with internal combustion engine, catalyst and particulate filter, which can be acted upon for regeneration with reformate gas from a reformer serving for a power supply fuel cell system;

2 : A schematic representation of a non-inventive modification of the motor vehicle 1 ;

3 : A schematic representation of a further, non-inventive modification of the motor vehicle from 1 ;

4 : A schematic representation of yet another modification of the invention of the motor vehicle 1 ,

1 shows a schematic representation of a part of a non-inventive motor vehicle with an internal combustion engine 2 , one of the internal combustion engine 2 Downstream exhaust treatment device 4 and a fuel cell system 6 , The internal combustion engine 2 has an air intake device 8th on, comprising an air supply line 10 with a throttle 12 , by the ambient air 38 in combustion chambers of the cylinders 16 of the internal combustion engine 2 is sucked. The internal combustion engine 2 also has an exhaust manifold 18 on that in an exhaust pipe 20 opens, through which the combustion of the fuel in the combustion chambers of the cylinder 16 produced exhaust gases to the exhaust treatment device 4 passed and after their treatment in the exhaust treatment device 4 through an exhaust 22 be delivered to the environment.

The exhaust treatment device 4 consists essentially of an oxidation catalyst 24 , one of the oxidation catalyst 24 upstream lambda probe 26 , as well as the catalyst 24 downstream particle filter 28 , which filters the particulate matter contained in the exhaust gas, in particular soot particles from incompletely combusted fuel, from the exhaust gas flow and their exit through the exhaust 22 prevented in the environment.

The fuel cell system 6 consists essentially of a hydrocarbon reformer 30 , a gas purification unit 32 and a fuel cell stack 34 , In the reformer 30 become Hydrocarbons, preferably for the operation of the internal combustion engine 2 used fuel 36 , such as gasoline or diesel fuel, with supply of compressed ambient air 38 or exhaust gas of the internal combustion engine via a partial oxidation or autothermal reforming in an oxidizable reformate gas 40 which contains significant amounts of hydrogen H ₂ (up to 45% by volume) and carbon monoxide CO (up to 20% by volume). As further ingredients, the reformate gas 40 Carbon dioxide CO ₂ , water vapor H ₂ O, nitrogen N ₂ , methane CH ₄ and small amounts of residual hydrocarbons containing about two to five carbon atoms. Advantageously, in the reformer 30 carried out a reforming process for which little or no water is needed, so that the eventual need for water by recycling water from the fuel cell stack 34 can be covered and a refueling of water is unnecessary. These requirements are met, for example, if in the reformer 30 catalytic partial hydrocarbon oxidation (CPO) or autothermal reforming (ATR) of the fuel occurs as known in the art.

The reformate gas 40 from the reformer 30 is through a line 42 in the gas cleaning unit 32 supplied, which may for example consist of a shift stage and / or a selective oxidation reactor and serves to the proportion of carbon monoxide or other undesirable constituents in the reformate gas 40 on one for use in the fuel cell stack 34 reduce the appropriate value. From the gas cleaning unit 32 the purified reformate gas flows 44 through a pipe 46 in the fuel cell stack 34 , In the fuel cell stack 34 From this, electrical energy is generated via connections 48 can be delivered to consumers of the motor vehicle. Next arises in the fuel cell stack 34 Cathode residual gas and anode residual gas, both containing water vapor that may be condensed for use in reforming and stored in a tank (not shown). The in 1 illustrated fuel cell stack 34 contains PEM fuel cells, which are the upstream of the gas purification unit 32 make necessary.

From the line 42 or from the line 46 one branches with a metering valve 50 provided connection line 52 through which a part of the pressurized reformate gas 40 respectively. 44 for regeneration of the particulate filter 28 in the exhaust treatment unit 4 in the exhaust pipe 20 can be supplied, in which the connecting line 52 before the oxidation catalyst 24 empties.

For regeneration of the particle filter 28 If necessary, the metering valve 50 opened and reformat gas 40 respectively. 44 in the exhaust pipe 20 fed from where it enters the catalyst 24 flows. Inside the catalyst 24 becomes the reformate gas 40 respectively. 44 completely catalytically oxidized by means of the oxygen contained in the exhaust gas O ₂ . The amount of reformate gas supplied 40 respectively. 44 is so small that the oxygen O _{2 is} not completely consumed, so that the exhaust still sufficient residual oxygen O ₂ for the combustion of the particulate filter 28 contains deposited particles. In the catalytic oxidation of the reformate gas 40 respectively. 44 in the oxidation catalyst 24 The following reactions take place by way of example: CO + 1 / 2O ₂ → CO ₂ + Δ (1) H ₂ + 1 / 2O ₂ → H _{2 O} + Δ (2) C _m H _n + (m + n) / 4) O ₂ → n / 2H ₂ O + m CO ₂ + Δ (3)

By in these exothermic reactions on the surface of the oxidation catalyst 24 amount of heat released Δ is the through the exhaust pipe 20 in the particle filter 28 flowing exhaust gas strongly heated, so it enters the particle filter 28 has a temperature of about 550 ° C.

The residual oxygen O ₂ contained in the exhaust gas then effects in the particle filter 28 a combustion of the deposited there, consisting predominantly of carbon black particles according to the reaction: C + O ₂ + Δ → CO ₂ (4) the resulting gaseous reaction products, mostly CO ₂ , through the exhaust 22 be discharged into the environment.

In contrast to the embodiment of 1 opens the connection line 52 in the likewise not inventive embodiment of 2 behind the oxidation catalyst 24 and immediately before the particle filter 28 in the exhaust pipe 20 , causing excessive thermal load of the oxidation catalyst 24 can be avoided. In this case, that will be in the line 20 added reformate gas 40 respectively. 44 inside the catalytically coated with a noble metal particulate filter 28 itself catalytically oxidized. Due to the targeted oxidation of the reformate gas 40 respectively. 44 inside the particulate filter 28 can be achieved there a maximum temperature increase. Furthermore, heat losses can be minimized and the limited amounts of oxidizable material present in the reformate gas or available reformate gas 40 respectively. 44 be used optimally.

In the non-inventive embodiment in 3 contains the exhaust pipe 20 in front of the particle filter 28 two spaced apart oxidation catalysts 24a and 24b between which the connecting line 52 in the exhaust pipe 20 empties.

At the in 4 illustrated embodiment of the invention is made in place of the reformer 30 or the gas cleaning unit 32 exiting reformate gas 40 respectively. 44 Hydrogen-containing anode residual gas 56 , that is depleted reformate gas, from the fuel cell stack 34 for regeneration of the particulate filter 28 used. The anode residual gas, after its exit from the fuel cell stack 34 through a pipe 58 either before or after the oxidation catalyst 24 in the exhaust pipe 20 fed. In the line 58 is a metering valve 50 arranged, with which the quantity of into the exhaust pipe 20 supplied anode residual gas 56 can be changed controlled.

Of course, the supply of the reformate gas 40 . 44 respectively. 56 also directly into the oxidation catalyst (s) 24 or 24b or directly into the particle filter 28 take place, especially if a distributed metered addition of the reformate gas is intended to the reaction zones in the filter 28 spread over a larger area.

Next, the fuel cell stack 34 In place of the PEM fuel cells also contain high-temperature fuel cells (SOFC), not the reformer 30 downstream gas cleaning unit 32 require, so in this case the reformate gas for the regeneration of the particulate filter 28 either between the reformer 30 and the fuel cell stack 34 or can be branched off behind the latter.

Claims (13)

Process for the regeneration of a particle filter through which an exhaust gas flows ( 28 ) of a motor vehicle, wherein an oxidation-capable reformate gas ( 40 ; 44 ; 56 ) from a hydrocarbon reformer ( 30 ) in front of or in the particle filter ( 28 ) is supplied into the exhaust gas and the exhaust gas by catalytic oxidation of the supplied reformate gas ( 40 ; 44 ; 56 ) is heated to temperatures above 550 ° C, and wherein the hydrocarbon reformer ( 30 ) Reformate gas ( 40 ; 44 ; 56 ) for a fuel cell system ( 6 ) and for the regeneration of the particulate filter ( 28 ) a part of the reformate gas ( 40 ; 44 ; 56 ) from the fuel cell system ( 6 ), characterized in that depleted reformate gas ( 56 ) from a fuel cell stack ( 34 ) of the fuel cell system ( 6 ) is branched off and the amount of the reformate gas supplied to the exhaust gas ( 56 ) is changed controlled. Process according to claim 1, characterized in that the reformate gas ( 40 ; 44 ; 56 ) contains as oxidizable constituents at least hydrogen (H2) and carbon monoxide (CO). Process according to claim 1 or 2, characterized in that the reformate gas ( 40 ; 44 ; 56 ) the exhaust gas after its exit from a front of the particulate filter ( 28 ) arranged oxidation catalyst ( 24 ) is supplied. Process according to claim 1 or 2, characterized in that the reformate gas ( 40 ; 44 ; 56 ) the exhaust gas before entering one of the particulate filters ( 28 ) arranged oxidation catalyst ( 24 ) is supplied. Process according to claim 1 or 2, characterized in that the reformate gas ( 40 ; 44 ; 56 ) the exhaust after leaving a first and before entering a second before the particulate filter ( 28 ) arranged oxidation catalyst ( 24a . 24b ) is supplied. Process according to claim 1 or 2, characterized in that the reformate gas ( 40 ; 44 ; 56 ) directly into the particle filter ( 28 ) is supplied. Motor vehicle with an internal combustion engine ( 2 ) and one in an exhaust pipe ( 20 ) of the internal combustion engine ( 2 ) arranged particulate filter ( 28 ), as well as with a hydrocarbon reformer ( 30 ), with feeders ( 50 . 52 ) for supplying reformate gas ( 40 ; 44 ; 56 ) from the hydrocarbon reformer ( 30 ) in the exhaust pipe ( 20 ) in front of the particle filter ( 28 ) or in the particle filter ( 28 ) and the hydrocarbon reformer ( 30 ) Part of a fuel cell system ( 6 ), which one with the reformate gas ( 40 ; 44 ) from the reformer ( 30 ) fuel cell stack ( 34 ), and wherein the supply means ( 50 . 52 ) a connection line ( 52 ) and through the exhaust pipe ( 20 ) flowing exhaust gas by catalytic oxidation of the supplied reformate gas ( 40 ; 44 ; 56 ) is heated to temperatures above 550 ° C, characterized in that the connecting line ( 52 ) behind the fuel cell stack ( 34 ) from a line with depleted reformate gas ( 56 ), wherein in the line a metering valve ( 50 ) is arranged, with which the amount of in the exhaust pipe ( 20 ) supplied reformate gas ( 56 ) is controlled controlled. Motor vehicle according to claim 7, characterized in that the supply means ( 50 . 58 ) a connection line ( 58 ) comprising the hydrocarbon reformer ( 30 ) with the exhaust pipe ( 20 ) or the particle filter ( 28 ) connects. Motor vehicle according to claim 8, characterized in that the connecting line ( 58 ) a metering valve ( 50 ). Motor vehicle according to claim 8 or 9, characterized in that the connecting line ( 58 ) behind an oxidation catalyst ( 24 ) in the exhaust pipe ( 20 ) opens. Motor vehicle according to claim 7 or 8, characterized in that the connecting line ( 52 ) in front of an oxidation catalyst ( 24 ) in the exhaust pipe ( 20 ) opens. Motor vehicle according to claim 7 or 8, characterized in that the connecting line ( 58 ) between two oxidation catalysts ( 24a . 24b ) in the exhaust pipe ( 20 ) opens. Motor vehicle according to one of claims 7 to 12, characterized in that the particle filter is coated catalytically.

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