DE102010005797A1 - Method for cleaning exhaust gas flow of burner points of internal combustion engine of motor vehicle by selective catalytic reduction, involves producing required ammonium hydroxide flow by ammonium hydroxide composition catalyzer - Google Patents

Abstract

The method involves producing a required ammonium hydroxide flow by an ammonium hydroxide composition catalyzer for the selective catalytic reduction. The ammonium hydroxide composition catalyzer transfers a nitric oxide flow and hydrogen flow. The nitric oxide flow is produced completely or partially by a burner point (1). A target intermediate pressure (15) is allowed, where the burner point is controlled according to the target intermediate pressure. An independent claim is also included for a motor vehicle with an exhaust gas cleaning unit for executing an exhaust gas flow cleaning method.

Description

The invention relates to a method for purifying an exhaust gas stream of a first combustion site and at least one further combustion point of an internal combustion engine by means of a selective catalytic reduction, with generating an exhaust gas stream necessary for the selective catalytic reduction by means of an ammonia synthesis catalyst reacting a nitrogen oxide stream and a hydrogen stream and generating the nitrogen oxide stream completely or at least partially by means of the first combustion station and a motor vehicle with a process according exhaust gas purification.

Methods for purifying an exhaust stream of combustors are known. In addition to carbon monoxide (CO) and hydrocarbons (HC), nitrogen oxides (NO _x ) in particular are among the environmentally hazardous, directly emitted primary pollutants which are produced during the operation of combustion engines of internal combustion engines, in particular diesel engines. It is known to use for the reduction of nitrogen oxide emissions, especially in diesel engines and / or lean-running gasoline engines, a selectively operating SCR catalyst which reduces with a reductant nitrogen oxides (NO _x ) to N ₂ and H ₂ O supplied. It is also known that the reductant fed to the SCR catalyst can be prepared by means of an on-board ammonia synthesis catalyst, for example by the Haber-Bosch process or by reaction of NO with H ₂ . The NO necessary for the reaction can be externally, z. B. by auxiliary burner, plasma reactor, etc. produced or provided internally by using a nitrogen oxide emitted by the internal combustion engine. The DE 101 64 833 A1 discloses a lean and fat operable internal combustion engine with an exhaust aftertreatment device comprising a nitrogen oxide storage catalyst and a particulate filter, wherein when flowing through lean exhaust gas of the nitrogen oxide storage catalyst removes the nitrogen oxides by storage and generated when flowing with rich exhaust ammonia by reducing stored and / or supplied nitrogen oxides and to the exhaust gas and a method for operating such an internal combustion engine. The exhaust gas aftertreatment device has, downstream of the nitrogen oxide storage catalytic converter, an SCR catalytic converter which reduces nitrogen oxides contained in the exhaust gas using the ammonia (NH ₃ ) generated by the nitrogen oxide storage catalytic converter. Continuous ammonia production is not possible.

The DE 199 09 933 A1 refers to an exhaust gas purifying plant having an ammonia generating catalyst for generating ammonia from nitrogen oxides contained in the exhaust gas to be purified and a nitrogen oxide reduction catalyst downstream thereof for reducing nitrogen oxides contained in the exhaust gas to be purified using the generated ammonia as a reducing agent and an operating method therefor. A nitrogen oxide adsorption catalyst arranged upstream of the ammonia generation catalyst is provided, and / or the ammonia generation catalyst is arranged in an exhaust pipe branch, through which only a part of the exhaust gas flows through a plurality of separately controllable combustion sources, while the remaining combustion sources bypass one or more others Ammonia generation catalyst are assigned to the nitrogen oxide reduction catalyst leading exhaust pipe branches. The portion of the combustion sources associated with the exhaust conduit branch of the ammonia generating catalyst is continuously or temporarily operated rich, and / or the one or more sources of combustion feeding the exhaust oxide absorption catalyst thereto are alternately operated lean and rich. At least half of the exhaust gas flow must be greased.

From the DE 10 2004 029 521 A1 It is known that in an internal combustion engine during operation at least temporarily in a first portion of the internal combustion engine, a richer fuel-air mixture is present than in a second portion. From the exhaust gas of the first portion of ammonia is generated. By means of the ammonia contained in the exhaust gas of the second portion of nitrogen oxide is reduced. Furthermore, it is known that at least temporarily less air is supplied to the first partial area than the second partial area, in which at least one inlet valve arrangement assigned to the first partial area is opened shorter and / or less than an inlet valve arrangement assigned to the second partial area.

The DE 10 2004 024 544 A1 discloses that during operation of an internal combustion engine at least temporarily ammonia is generated in an ammonia generating catalyst. This is used for selective catalytic reduction in a nitrogen oxide reduction catalyst. It is also disclosed that produced ammonia is at least temporarily converted into a solid substance, this solid substance temporarily stored and, if necessary, at least a portion of the solid material and / or ammonia recovered from this is supplied to the exhaust gas.

In the DE 103 57 402 A1 discloses a method of operating an internal combustion engine having a plurality of combustion chambers and an exhaust gas purification system, the exhaust gas purification system comprising an ammonia generation catalyst that only receives exhaust gas from at least a first combustion chamber, comprising the steps of: operating at least a second combustion chamber with a lean air-fuel mixture; Operating the at least one first combustion chamber with a less lean combustion air-fuel mixture; and generating an ammonia-producing low-oxygen atmosphere in the exhaust gas of the at least one first combustion chamber. The method comprises throttling an air supply to the at least one first combustion chamber and generating the oxygen deficiency in the exhaust gas of the at least one combustion chamber by supplying reductant to the exhaust gas of the at least one first combustion chamber after combustion.

From the DE 10 2004 027 823 A1 an internal combustion engine is known, the plurality of subregions and a device by which in at least a first portion of a different composition of the fuel-air mixture can be set as known in a second sub-range. Furthermore, an ammonia generating device is disclosed in which ammonia is produced and a nitrogen oxide reduction device in which nitrogen oxides can be reduced by means of the ammonia. It is also disclosed that it comprises a first device, with which only the air flowing in the first subarea can be throttled, and that it has at least one second device with which the oxygen concentration of the air flowing in the first subarea can be increased. A pressure in an intake passage is detected between an oxygen separator and an intake air throttle by means of a pressure sensor.

The object of the invention is to enable improved production of ammonia in a motor vehicle, the motor vehicle preferably storing and / or carrying no ammonia-containing and / or releasing operating adjuvants, in particular ensuring the highest possible refinement and / or smoothness of an internal combustion engine driving the motor vehicle is.

The object is achieved in a method for purifying an exhaust gas flow of a first combustion point and at least one further combustion point by predetermining a desired medium pressure and controlling the first combustion point as a function of the desired medium pressure. By means of the mean pressure of the medium, a mean pressure or working pressure occurring during combustion by means of the combustion chamber can be understood, the mean pressure or desired medium pressure being a measure of the mechanical energy which can be removed during combustion. Furthermore, the setpoint mean pressure can be understood as a default value for an actually occurring mean pressure of the first combustion point. Advantageously, the setpoint medium pressure can be selected such that it is the same or at least approximately the same for the first combustion point as a further medium pressure of the further combustion point. Advantageously, it can be ensured that at the first focal point and the at least one further focal point identical medium pressures occur, which allows a particularly high smoothness and smoothness of the engine. Advantageously, the first combustion point can be controlled as a function of the setpoint medium pressure so that an actual average pressure which corresponds to the setpoint medium pressure is set to this and / or is tracked.

In one embodiment of the method, determining an actual mean pressure of the first combustion point and controlling the first focal point in dependence on the desired mean pressure and the Istmitteldrucks are provided. Advantageously, a comparison between the setpoint medium pressure and the Istmitteldruck done so that controlled in the sense of a closed loop of the Istmitteldruck on the value of the Sollmitteldrucks and / or this can be tracked regulated.

In a further embodiment of the method, determining the Istmitteldrucks is provided by means of one of the first focal point associated glow plug with an integrated cylinder pressure sensor. Advantageously, the Istmitteldruck can be determined by measurement. Advantageously, it is possible to integrate the corresponding cylinder pressure sensor in an already necessary glow plug of the burner, wherein advantageously a particularly accurate measurement is possible, which also advantageously a particularly small space is claimed.

In a further embodiment of the method, determining the setpoint mean pressure is provided as a further actual mean pressure of the at least one further burning point. Advantageously, the desired medium pressure can be set to the mean pressure of the at least one further combustion point, so that advantageously the Istmitteldruck the first focal point is tracked to the further Istmitteldruck the at least one further focal point, it can be advantageously ensured that the first focal point and the at least one further focal point have same Istmitteldrücke or at least quasi same Istmitteldrücke. Alternatively and / or additionally, it is conceivable not to measure the mean pressure of the at least one further combustion point and / or the first combustion point, but alternatively to determine it by means of a model and / or a characteristic diagram.

In a further embodiment of the method, a control of the first combustion point is provided as a function of the desired mean pressure and one or more characteristic maps which have at least one of the following variables: a NO _x emission, a combustion air ratio, an internal efficiency and / or an exhaust gas recirculation rate.

Advantageously, these variables can be used as pilot control variables for pilot control of the medium pressure of the first combustion station. Under a NO _x emission, a raw emission of the internal combustion engine and / or at least one of the combustion stations of the internal combustion engine can be understood. A combustion air ratio can be understood as meaning a ratio expressible in the size λ between a combustion air supplied to the internal combustion engine and this supplied fuel. An internal efficiency may be understood as a measure of the conversion of chemical energy supplied in the form of the fuel into mechanical energy. An exhaust gas recirculation rate may be understood to mean a rate or a ratio of exhaust gas that has already taken part in a combustion as an addition to the fresh air.

In a further embodiment of the method, a control of a sucked air mass of the first combustion point and / or a control of the sucked air mass by means of a fully variable valve train are provided. Advantageously, by means of the fully variable valve train, an opening angle and / or an opening time of valves associated with the first combustion location can take place. This can advantageously be done independently of a valve control of the at least one further combustion point.

In a further exemplary embodiment of the device, a pilot control of the first combustion point is provided by means of a feedforward control processing the setpoint pressure for setting the Istmitteldrucks and / or controlling the first focal point by means of a difference of the Sollmitteldrucks minus the Istemitteldrucks processing controller. Advantageously, a pilot control, a regulation and / or a combination of the two can take place.

In a further embodiment of the method, a generation of the hydrogen stream is provided by means of a separate hydrogen generator. A hydrogen generator may be any generating unit for producing hydrogen, for example a separate burner, a plasma reactor and / or a storage unit for storing and releasing hydrogen.

In a further embodiment of the method, an adjustment of the nitrogen oxide stream and / or the hydrogen stream is provided as a function of an ammonia requirement of an ammonia synthesis catalyst downstream of the NO _x reduction catalyst. Advantageously, the NO _x reduction catalyst can be supplied as needed with the ammonia of the ammonia synthesis catalyst.

In a further embodiment of the method, a branching off of a partial nitrogen oxide stream of the nitrogen oxide stream and a conversion of the partial nitrogen oxide stream by means of the ammonia synthesis catalyst are provided. Advantageously, the nitrogen oxide stream can be divided so that the ammonia synthesis catalyst can be supplied exactly with the right amount of nitrogen oxide. A possibly existing excess amount of nitrogen oxide can be admixed with a remaining exhaust gas flow, which is at least one further combustion point.

In a further embodiment of the method, an increase of a nitrogen oxide oxide emission of the first combustion point in relation to the at least one further combustion point is provided by a factor f _NOX of at least 3. It has been recognized that advantageously, with a factor f _NOX of at least 3 in a four-cylinder engine, only one of the four combustion points of the four-cylinder engine suffices for generating the nitrogen oxide flow.

In a further embodiment of the method, an operation of the first combustion point is provided on a nitrogen oxide maximum. Advantageously, a comparatively high efficiency of the first combustion point can be realized during operation in the nitrogen oxide maximum. Furthermore, at maximum nitrogen oxide, a maximum amount of nitrogen oxide can be generated.

In a further embodiment of the method, a characterization of the nitrogen oxide stream by means of the factor f _NOX and / or by means of a NO substance flow is provided. Advantageously, the scheme and / or. Control by means of the factor f _NOX and / or carried out by means of the NO substance flow.

The object is also achieved in a motor vehicle having an exhaust gas purification for purifying an exhaust gas flow of a first combustion point and at least one further combustion point of an internal combustion engine by means of a selective catalytic reduction, designed, set up and / or designed to carry out a previously described method. This results in the advantages described above.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, various embodiments are described in detail. The same, functionally identical and / or similar parts are provided with the same reference numerals.

Show it:

1 a control and / or control scheme of a pressure control of a first combustion chamber of an internal combustion engine;

2 a schematic view of the engine and a downstream this exhaust purification; and

über einem Verhältnis f_NOX. 3 a diagram of a relationship

over a ratio f _NOX .

1 shows a control and / or control scheme for controlling a first burner 1 a partially illustrated internal combustion engine 3 , The internal combustion engine 3 For example, a total of four burners, so next to the first focal point 1 have three more burners. The internal combustion engine 3 or the first burner 1 of the internal combustion engine 3 is a regulator 5 upstream of the control. Optional is the first burner 1 a feedforward control 7 upstream, with corresponding signals of the controller 5 and the pilot control 7 superimposed the first focal point 1 Taxes.

The first burner 1 is a glow plug 9 with an integrated cylinder pressure sensor 11 assigned. The glow plug 9 is used to heat a combustible air-fuel mixture of the first focal point 1 , The glow plug 9 advantageously has the integrated cylinder pressure sensor 11 on, by means of an Istmitteldruck 13 the first burner 1 can be determined metrologically. The average pressure 13 is with a setpoint pressure 15 calculated or subtracted and as a controller input 17 the controller 5 fed. In addition, the setpoint pressure 15 the pilot control 7 fed for processing. The nominal medium pressure 15 corresponds to a Istmitteldruck further burners 19 of the internal combustion engine 3 , The average pressure 13 For example, it can also be measured by means of further cylinder pressure sensors 21 further the other burners 19 associated glow plugs are determined. For this purpose, these other cylinder pressure sensors 21 exhibit. Alternatively and / or additionally, it is possible to use the desired mean pressure 15 by means of a model and / or a map 23 to investigate.

The feedforward control 7 processes next to the setpoint pressure other input variables 25 , For example, a NO _x emission, a combustion air ratio, an internal efficiency, an exhaust gas recirculation rate and / or further operation and / or the mean pressure of the burners 1 . 19 of the internal combustion engine 3 distinctive sizes.

2 shows a schematic view of the internal combustion engine 3 as well as a downstream exhaust gas purification 27 , The in 2 schematically illustrated internal combustion engine 3 is part of a motor vehicle only partially shown 43 , by means of the internal combustion engine 3 is drivable.

The exhaust gas purification 27 has one of the other burners 29 downstream oxidation catalyst 29 on. The first burner 1 is an ammonia generation catalyst 31 downstream. The oxidation catalyst 29 and the ammonia generation catalyst 31 are connected in parallel and equally a NO _x reduction catalyst 33 upstream. The NO _x reduction catalyst 33 works on the principle of selective catalytic reduction and is designed as an SCR catalyst. By means of a control organ 35 can the exhaust gas of the first burner 1 in a variable ratio x the ammonia generation catalyst 31 and the oxidation catalyst 29 upstream.

Further, in a parallel branch between the first focal point 1 and the ammonia generation catalyst 31 a hydrogen generator 35 incorporated branches. By means of the hydrogen generator 36 may be the ammonia generation catalyst 31 for the production of ammonia necessary hydrogen are supplied.

The one from the first burner 1 produced nitrogen oxide stream and the hydrogen stream of the hydrogen generator 35 can the ammonia generation catalyst 31 for the synthesis of ammonia according to the following empirical formula: 2NO + 5H ₂ <-> 2NH ₃ + 2H ₂ O, for λ <1

For a simplified balance applies XNO _x, z (4) >> XNO _x z (1) = XNO _x z (2) = XNO _x z (3) and n. _Off , z (4) ≈ n. _Off , z (3) = n. _Exhaust , z (2) = n - _exhaust , z (1) and be _{z (4)} ≤ be _{z (1)} = be _{z (2)} = be _{z (3)} , where the ordinal numbers 1-3 for the other burners 9 and the ordinal number 4 for the first burner 1 , xNO _x for the NO _x concentration and be for a specific fuel consumption of the respective focal point 1 . 19 stand.

und der Wasserstoffstrom n ._H₂ zugeführt. Dem Oxidationskatalysator 29 wird der Stickoxidstrom

zugeführt, wobei y = 1 – x ist. Da bei dem Betrieb des Verfahrens in der Regel zwischen Mager- und Fettphasen differenziert wird, sind für die Bilanzierung über den Ammoniakerzeugungskatalysator die integralen Stoffmengen relevant.The ammonia generation catalyst 31 becomes the nitrogen oxide stream

and the hydrogen stream n. _{Supplied H₂} . The oxidation catalyst 29 becomes the nitrogen oxide stream

fed, where y = 1 - x. Since the operation of the process usually differentiates between lean and rich phases, the integral quantities are relevant for balancing via the ammonia generation catalyst.

In the case of the amount of nitrogen oxide, a distinction can be made between the fraction stored during the lean phases and the fraction supplied during the regeneration phases. As starting material leaves the ammonia generation catalyst 31 ideally (efficiency 100%) the amount of substance

A corresponding balance can also be made for the substance quantity balance of the exhaust gas flow of the internal combustion engine 3 be set up.

3 zeigt ein Schaubild eines Verhältnisses

über dem Verhältnis f_NOX für einen ersten Graph 37 für U_NOX = 25%, einen zweiten Graph 39 für U_NOX = 50% und einen dritten Graph 41 U_NOX = 100%. Es ist zu erkennen, dass vorteilhaft für f_NOX > 3 bei einem Betrieb in einem NO_x-Maximum für U_NOX = 100% eine Gemischanfettung der ersten Brennstelle 1 alleine genügt.A substance flow x · n to be added. _{Offsets, Z (4)} can be calculated as follows:

3 shows a diagram of a relationship

over the ratio f _NOX for a first graph 37 for U _NOX = 25%, a second graph 39 for U _NOX = 50% and a third graph 41 U _NOX = 100%. It can be seen that, advantageously, for f _NOX > 3, when operating in a NO _x maximum for U _NOX = 100%, a first-range mixture enrichment is provided 1 alone is enough.

LIST OF REFERENCE NUMBERS

1

focal point

3

internal combustion engine

5

regulator

7

feedforward

9

glow plug

11

Cylinder pressure sensor

13

Istmitteldruck

15

Target medium pressure

17

Controller input variable

19

further firing point

21

Cylinder pressure sensor

23

map

25

input

27

emission control

29

oxidation catalyst

31

Ammonia generating catalyst

33

NO _x reduction catalyst

35

control element

36

Hydrogen generator

37

graph

39

graph

41

graph

43

motor vehicle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10164833 A1 [0002]
• DE 19909933 A1 [0003]
• DE 102004029521 A1 [0004]
• DE 102004024544 A1 [0005]
• DE 10357402 A1 [0006]
• DE 102004027823 A1 [0007]

Claims (14)

Method for purifying an exhaust gas stream of a first combustion site ( 1 ) and at least one further burner ( 19 ) of an internal combustion engine ( 3 by means of a selective catalytic reduction, comprising: producing an ammonia stream necessary for the selective catalytic reduction by means of an ammonia synthesis catalyst which converts a nitrogen oxide stream and a hydrogen stream (US Pat. 31 ), - Generating the nitrogen oxide stream wholly or at least partially by means of the first burner ( 1 ), characterized by - predetermining a desired mean pressure ( 15 ), - controlling the first burner ( 1 ) as a function of the desired mean pressure ( 15 ). Method according to the preceding claim, comprising: - determining an average pressure ( 13 ) of the first burner ( 1 ), - controlling the first burner ( 1 ) as a function of the desired mean pressure ( 15 ) and the Istmitteldrucks ( 13 ). Method according to the preceding claim, comprising: - determining the average pressure ( 13 ) by means of one of the first focal point ( 1 ) associated glow plug ( 9 ) with an integrated cylinder pressure sensor ( 11 ). Method according to one of the preceding claims, comprising: determining the setpoint pressure ( 15 ) as a further Istmitteldruck the at least one further burner ( 19 ). Method according to one of the preceding claims, comprising: - controlling the first burner ( 1 ) as a function of the desired mean pressure ( 15 ) and one or more maps that have at least one of the following parameters ( 25 ): NO _x emission, combustion air ratio, internal efficiency, exhaust gas recirculation rate. Method according to one of the preceding claims, comprising at least one of the following: - Controlling a sucked air mass of the first combustion station ( 1 ), - Controlling the intake air mass by means of a fully variable valve train. Method according to one of the preceding claims, comprising at least one of the following: - pre-controlling the first burner ( 1 ) by means of a desired medium pressure ( 15 ) processing precontrol ( 7 ) for setting the average pressure ( 13 ), - rules of the first burner ( 1 ) by means of a difference of the desired mean pressure ( 15 ) minus the average pressure ( 13 ) processing controller ( 5 ). Method according to one of the preceding claims, comprising: - generating the hydrogen stream by means of a separate hydrogen generator ( 36 ). Method according to one of the preceding claims, comprising: adjusting the nitrogen oxide flow and / or the hydrogen flow in dependence on an ammonia requirement of the ammonia synthesis catalyst ( 31 ) downstream NO _x reduction catalyst ( 33 ). Method according to one of the preceding claims, comprising: - branching off a partial nitrogen oxide stream of the nitrogen oxide stream, - reacting the partial nitrogen oxide stream by means of the ammonia synthesis catalyst ( 31 ). Method according to one of the preceding claims, comprising: - increasing a nitrous oxide emission of the first burner ( 1 ) in relation to the at least one further combustion station ( 19 ) by a factor f _NOX of at least 3. Method according to one of the preceding claims, comprising: - operating the first burner ( 1 ) on a nitrogen oxide maximum. Method according to one of the preceding two claims, comprising: - Characterizing the nitrogen oxide stream by means of the factor f _NOX and / or by means of a NO substance flow. Motor vehicle ( 43 ) with an exhaust gas purification ( 27 ) for purifying an exhaust gas stream of a first combustion site ( 1 ) and at least one further burner ( 19 ) of an internal combustion engine ( 3 ) by means of a selective catalytic reduction, designed, furnished and / or constructed for carrying out a method according to one of the preceding claims.

Images