EP2568137A1 - Heated injection system for exhaust gas systems of Diesel engines - Google Patents

Heated injection system for exhaust gas systems of Diesel engines Download PDF

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Publication number
EP2568137A1
EP2568137A1 EP11180569A EP11180569A EP2568137A1 EP 2568137 A1 EP2568137 A1 EP 2568137A1 EP 11180569 A EP11180569 A EP 11180569A EP 11180569 A EP11180569 A EP 11180569A EP 2568137 A1 EP2568137 A1 EP 2568137A1
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EP
European Patent Office
Prior art keywords
reducing agent
injection device
reducing
exhaust gas
ammonia
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP11180569A
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German (de)
French (fr)
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EP2568137B1 (en
Inventor
Yasser Mohammed Sayed Yacoub
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Ford Global Technologies LLC
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Ford Global Technologies LLC
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Publication date
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Priority to EP11180569.3A priority Critical patent/EP2568137B1/en
Priority to US13/592,231 priority patent/US20130064744A1/en
Priority to CN2012103325472A priority patent/CN102989316A/en
Publication of EP2568137A1 publication Critical patent/EP2568137A1/en
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Publication of EP2568137B1 publication Critical patent/EP2568137B1/en
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/36—Arrangements for supply of additional fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/16—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an electric heater, i.e. a resistance heater
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/01—Adding substances to exhaust gases the substance being catalytic material in liquid form
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/03—Adding substances to exhaust gases the substance being hydrocarbons, e.g. engine fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/10—Adding substances to exhaust gases the substance being heated, e.g. by heating tank or supply line of the added substance
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/14—Arrangements for the supply of substances, e.g. conduits
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/6416—With heating or cooling of the system
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/8593—Systems
    • Y10T137/87571—Multiple inlet with single outlet
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/8593—Systems
    • Y10T137/87571—Multiple inlet with single outlet
    • Y10T137/87652—With means to promote mixing or combining of plural fluids

Definitions

  • the present invention relates to an injection device for feeding reducing agents into an exhaust system of an internal combustion engine for reducing nitrogen oxide emissions, in particular a diesel engine. Further objects of the present invention relate to a method for reducing nitrogen oxides in exhaust gases of internal combustion engines and to the use of a reducing agent mixture for reducing nitrogen oxides in exhaust gases.
  • the LNT catalyst has a coating with platinum group metals. These catalyze various redox reactions between the stored NOx and the CO or HC acting as reducing agents, with NOx being converted into nitrogen and water. After the stored NOx is converted, the engine is returned to lean operation and the storage cycle begins again.
  • An LNT catalyst of the aforementioned type is for example from the EP 1 004 347 B1 known.
  • the catalyst disclosed herein is bi-layered with a first layer being responsible for NOx storage and a second layer containing noble metal components for NOx removal. This catalyst is maintained continuously, ie not in alternating operation lean / rich and in this case reaches a conversational rate of about 20 to 30% of the nitrogen oxides flowing through.
  • SCR Selective Catalytic Reduction
  • the chemical reaction on the SCR catalyst is selective, ie it is preferred to reduce the nitrogen oxides (NO, NO 2) while suppressing undesirable side reactions (such as the oxidation of sulfur dioxide to sulfur trioxide) .
  • the SCR catalysts are often used in Used in combination with soot particle filters and oxidation catalysts.
  • a reducing agent for which ammonia (NH 3 ) is typically used.
  • the required ammonia is usually not used directly, ie in pure form, but used in the form of a 32.5% aqueous urea solution, which is uniform in the industry is called AdBlue®.
  • AdBlue® a 32.5% aqueous urea solution
  • the composition is regulated in DIN 70070. The reason that the required ammonia is not carried in pure form is the danger of this substance.
  • Ammonia has a corrosive effect on the skin and mucous membranes (especially on the eyes) and also forms an explosive mixture in the air.
  • urea solution is formed during injection into the hot exhaust gas stream by a decomposition reaction ammonia and carbon dioxide.
  • the ammonia thus produced is then available in the downstream SCR catalyst.
  • a Komproportionierungsrepress takes place, with water (H 2 O) and nitrogen (N 2 ) are formed.
  • the SCR catalysts typically distinguish between two different types of catalysts. One type consists essentially of titanium dioxide, vanadium pentoxide and tungsten oxide. The other type uses zeolites.
  • the amount of injected urea depends on the engine's nitrogen oxide emissions and thus on the current speed and torque of the engine.
  • the consumption of urea-water solution is - depending on the raw emission of the engine - about 2 to 8% of the diesel fuel used. It must therefore be carried along a corresponding tank volume, which is perceived in part as disadvantageous. In particular, this complicates the use in diesel-powered passenger cars, since an additional tank must be provided.
  • AdBlue ® must be variably injected. So far, it must be adapted to the NOx in the exhaust gas mass flow via a so-called feed ratio. If too much urea is metered in, the ammonia formed from it can no longer react with NOx. With this incorrect dosage, ammonia can enter the environment. Since ammonia can already be detected in very small concentrations, this leads to an odor nuisance.
  • SCR catalysts are usually able to store nitrogen oxides over a period of time, for example, until the exhaust pipe, the engine to operating temperature and the exhaust gas stream has the required temperature.
  • the required minimum exhaust gas temperature for optimal operation is often not achieved, for example in city traffic, so that after a certain period of operation, the maximum storage capacity of the SCR catalyst is exceeded and nitrogen oxides enter the environment.
  • the exhaust gas temperature for quantitative decomposition of the urea into ammonia and carbon dioxide may not be sufficient, so that insufficient amounts of ammonia can be formed.
  • the latter problem can be at least partially compensated by an increase in the injected amount of urea, but the actual amount of formed catalytically active ammonia is then difficult to predict. That's the way it works As the amount of urea injected increases, more ammonia is also formed than is consumed in the SCR catalyst, causing ammonia to enter the environment. This is undesirable for reasons of odor nuisance and also from a toxicological point of view.
  • DE 103 48 800 A1 proposed a diesel exhaust aftertreatment system comprising a reducing agent supply system in which the reducing agent is brought to the required temperature by means of a heating element.
  • the supplied reducing agent is evaporated in the form of an aqueous urea solution when injected into the exhaust stream largely independent of the exhaust gas temperature or decomposed to release ammonia.
  • the amount of reducing agent actually present in the exhaust gas flow is independent of the exhaust gas temperature.
  • a comparable system is from the DE 10 2006 049 591 A1 or the off DE 10 2007 029 674 A1 in which also a reducing agent is preheated in the form of a urea solution via an electrically described heat exchanger and sprayed in the gaseous state in the exhaust gas stream.
  • a device for post-treatment of exhaust gases of a self-igniting internal combustion engine in which via the fuel pump of the diesel engine diesel fuel is introduced into the exhaust gas stream by means of an upstream of an SCR catalyst arranged injection nozzle. That is, in this described arrangement, instead of using an ammonia-releasing system, diesel fuel is used as the reducing agent.
  • diesel fuel is used as the reducing agent.
  • a glow plug is located in the vicinity of the injection device with which the diesel fuel is heated above its vaporization point.
  • the object of the present invention was to provide an improved injection device of the aforementioned type which, with as small amounts of reducing agent as possible, allows a complete removal of the nitrogen oxides in the exhaust gas stream independently of its temperature. In addition, a further pollution and pollution of the exhaust system should be largely avoided.
  • an injection device for feeding reducing agents into an exhaust system of an internal combustion engine for reducing the nitrogen oxide output, wherein the injection device is connected to a respective reservoir for a first and a second, liquid at room temperature reducing agent and an injector and an evaporation device for the first and second reducing agents.
  • the solution according to the invention provides for the use of two liquid reducing agents which are converted into the gaseous state before being injected into the exhaust gas flow.
  • the evaporation device can have, for example, an electrically operated heating device, in particular a glow plug.
  • the injection device according to the invention can be used in principle in any type of exhaust gas treatment systems with an SCR catalyst.
  • further catalysts such as an LNT or a soot particle filter can be used.
  • a further subject of the present invention is therefore an exhaust gas purification system for an internal combustion engine for reducing nitrogen oxide emissions comprising an SCR catalyst and an injection device according to the invention arranged upstream thereof, as well as optional further purification elements such as an LNT and / or a soot particle filter optionally upstream of the injection device or downstream of the SCR catalyst are arranged.
  • any known SCR catalyst can be used as the SCR catalyst.
  • the optional additional cleaning elements such as an LNT and / or a soot particle filter.
  • the first reducing agent is an ammonia-releasing liquid, in particular an aqueous urea solution such as AdBlue®, and the further reducing agent is a hydrocarbon compound, in particular a fuel such as diesel fuel.
  • AdBlue® aqueous urea solution
  • the further reducing agent is a hydrocarbon compound, in particular a fuel such as diesel fuel.
  • the ratio of diesel fuel to 32.5% urea solution can be varied over wide ranges and also be adjusted individually depending on the operating parameters of the vehicle.
  • the ratio between aqueous urea solution of the aforementioned concentration, ie AdBlue®, to diesel fuel may range from 1:10 to 10: 1, preferably from 1: 8 to 8: 1.
  • the injection device according to the invention can also be designed such that depart from the reservoir for the ammonia-releasing liquid an ammonia line and from the fuel tank a fuel line, which open into a 3-way valve, which is connected via a reducing agent line to the injector.
  • a 3-way valve By means of the 3-way valve can be variably adjusted, for example, depending on the operating parameters of the engine via an example electronically controlled adjusting the aforementioned volume ratios between the two reducing agents.
  • a mixing device may be provided, which is preferably arranged in the reducing agent line. With this, an emulsion can be produced from the aforementioned liquid reducing agents.
  • the reducing agent line in the conveying direction of the reducing agent is directed to the heating device in an advantageous manner.
  • this is assigned at least one conveying device for the first and second reducing agent, which is provided in particular on the reducing agent line.
  • a conveying device for the first and second reducing agent, which is provided in particular on the reducing agent line.
  • a continuous reducing agent flow can be ensured.
  • a conveyor for example, a pump is considered.
  • This can also build a delivery pressure, so that the reducing agent are pressed with positive pressure against the heater and then into the exhaust stream.
  • the reducing agents can be finely distributed before evaporation, for example via a spray nozzle, which further accelerates the evaporation process.
  • the mixing device is integrated in the conveyor.
  • Another object of the present invention relates to a method for reducing nitrogen oxides in exhaust gases, in particular in exhaust gases of diesel-powered internal combustion engines, comprising the exhaust gas treatment by means of an SCR catalyst, wherein by means of an upstream of the SCR catalyst arranged injection device, a first and a second at room temperature liquid reducing agent are at least partially vaporized by means of a heater and admixed to the exhaust stream via an injector.
  • the present invention further relates to the use of a mixture of a hydrocarbon compound, in particular diesel fuel, and an ammonia-releasing reducing agent, in particular an aqueous urea solution such as AdBlue®, for reducing nitrogen oxides in exhaust gases, in particular in exhaust gases of diesel-powered internal combustion engines.
  • a hydrocarbon compound in particular diesel fuel
  • an ammonia-releasing reducing agent in particular an aqueous urea solution such as AdBlue®
  • Fig. 1 is a schematic structure of a diesel engine with connected emission control system 1 analogous to DE 103 48 800 A1 shown.
  • the system comprises a reciprocating engine 2 in the form of a turbocharged diesel engine, which receives fresh air via an air filter 3 on its intake side, which is precompressed by a compressor 4a of a turbocharger 4.
  • the compressor 4a of the turbocharger 4 is driven by its exhaust gas turbine 4b via a common shaft.
  • the combustion gases of the reciprocating engine 2 are discharged through an exhaust pipe 5 consisting of several pipe segments.
  • an oxidation catalyst 6 is arranged, at the outlet side in the downstream direction of the exhaust pipe 5, an SCR catalyst 7 is connected, at its output, in turn, a rear muffler 8 connects.
  • an injection device 9 for an aqueous urea solution (AdBlue®) is attached. About this is fed by means of a reducing agent supply line 10 supplied aqueous urea solution to an electrically operated heating element and thus introduced in gaseous form into the exhaust pipe 5.
  • the nitrogen oxides formed during operation of the turbo diesel engine 2 are first stored in the SCR catalyst and converted into water vapor and nitrogen in a comproportionation reaction by ammonia gas produced during the decomposition reaction of the urea upon contact with the heating element 11 or the hot exhaust gases.
  • FIG. 2 an exhaust gas cleaning system 20 is shown with an injection device 21 according to the invention for the supply of reducing agents in the exhaust system of the turbo diesel engine 2.
  • injection device 21 for the supply of reducing agents in the exhaust system of the turbo diesel engine 2.
  • the same reference numerals describe identical components in the off FIG. 1 known device. In the following, therefore, only the essential differences of the two systems will be discussed.
  • the injection device 21 is connected to a respective reservoir 22, 23 for a first and second reducing agent, ie 32.5% aqueous urea solution on the one hand and diesel fuel on the other hand.
  • the connection takes place starting from the reservoir 22 of the aqueous urea solution via an ammonia line 24 and from the reservoir 23 for diesel fuel via a fuel line 25.
  • the ammonia line 24 and the fuel line 25 open into an electronically controllable 3-way valve 26, of which a reducing agent line 28th goes off, which opens into an injector. This consists of an atomizer nozzle, not shown here.
  • a conveyor 28 is provided with integrated mixing unit, with which the two reducing agents promoted, mixed and pressurized into the injector to be pressed.
  • the reducing agent stream is directed to a heater 29.
  • the heating device 29 consists of an electrically heated glow plug, with the aid of which the mixture of aqueous urea solution and diesel fuel and the urea is thereby at least partially decomposed to ammonia and carbon dioxide, before this gaseous mixture in the portion of the exhaust pipe 5 upstream of the SCR catalyst. 7 is fed.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust Gas After Treatment (AREA)

Abstract

The device (21) has two reservoirs (22, 23) for storing two reducing agents, respectively at room temperature. A heating device (29) heats the two reducing agents and is designed as an electrically operated heating device i.e. glow plug. The two reducing agents are formed as a Adblue(RTM: aqueous urea solution) and hydrocarbon compound i.e. diesel fuel, respectively. An ammonia line (24) and a fuel line (25) extend from the two storage vessels, respectively and open out in a 3-way valve (26) that is connected to an injector via a reducing agent line (27). Independent claims are also included for the following: (1) an emission control system for a combustion engine for reducing nitrogen oxide emissions (2) a method for reducing nitrogen oxides in exhaust gases.

Description

Die vorliegende Erfindung betrifft eine Injektionseinrichtung zur Einspeisung von Reduktionsmitteln in ein Abgassystem einer Brennkraftmaschine zur Verringerung des Stickoxidausstoßes, insbesondere eines Dieselmotors. Weitere Gegenstände der vorliegenden Erfindung betreffen ein Verfahren zur Reduzierung von Stickoxiden in Abgasen von Brennkraftmaschinen sowie die Verwendung einer Reduktionsmittelmischung zur Reduzierung von Stickoxiden in Abgasen.The present invention relates to an injection device for feeding reducing agents into an exhaust system of an internal combustion engine for reducing nitrogen oxide emissions, in particular a diesel engine. Further objects of the present invention relate to a method for reducing nitrogen oxides in exhaust gases of internal combustion engines and to the use of a reducing agent mixture for reducing nitrogen oxides in exhaust gases.

Aus dem Stand der Technik sind unterschiedliche Abgasreinigungssysteme bekannt. Nach einer ersten Möglichkeit wird in einem LNT (lean NOx trap) NOx aus dem hindurch geführten Abgasstrom absorbiert und temporär gespeichert. Da die Speicherkapazität eines LNT naturgemäß begrenzt ist, müssen das gespeicherte NOx von Zeit zu Zeit entfernt werden. Hierzu werden die Betriebsparameter des Motors vom Magerbetrieb während des Speicherungsvorgangs in einen Fettbetrieb geändert. Im Fettbetrieb wird der Motor mit in Bezug auf die Verbrennungsluft überstöchiometrischen Mengen an Kraftstoff betrieben. Dies führt zu einer Anreicherung der Verbrennungsabgase an Kohlenmonoxid (CO) und Kohlenwasserstoffen (kurz: HC). Gleichzeitig erhöht sich durch den Fettbetrieb die Abgastemperatur. In der Folge erhöht sich die Temperatur im LNT-Katalysator, wobei jetzt zusätzlich CO und HC aus den Abgasen während des Fettimpulsbetriebs in den LNT gelangen.Different emission control systems are known from the prior art. After a first possibility, NOx is absorbed from the exhaust gas flow passed through and temporarily stored in an LNT (lean NOx trap). Since the storage capacity of an LNT is naturally limited, the stored NOx must be removed from time to time. For this purpose, the operating parameters of the engine are changed from lean operation during the storage operation in a rich operation. In rich operation, the engine is operated with more than stoichiometric amounts of fuel relative to the combustion air. This leads to an enrichment of the combustion exhaust gases to carbon monoxide (CO) and hydrocarbons (short: HC). At the same time, the exhaust gas temperature increases due to the rich operation. As a result, the temperature in the LNT catalyst increases, with additional CO and HC from the exhaust gases now entering the LNT during rich-pulse operation.

Der LNT-Katalysator weist eine Beschichtung mit Metallen der Platingruppe auf. Diese katalysieren verschiedene Redoxreaktionen zwischen dem gespeicherten NOx und dem als Reduktionsmitteln fungierenden CO beziehungsweise HC, wobei NOx zu Stickstoff und Wasser umgesetzt wird. Nach Umsetzung des gespeicherten NOx wird der Motor wieder in den Magerbetrieb überführt und der Speicherkreislauf beginnt von Neuem.The LNT catalyst has a coating with platinum group metals. These catalyze various redox reactions between the stored NOx and the CO or HC acting as reducing agents, with NOx being converted into nitrogen and water. After the stored NOx is converted, the engine is returned to lean operation and the storage cycle begins again.

Die zur Reduktion des gespeicherten NOx in herkömmlichen LNT-Katalysatoren eingesetzten Edelmetalle erhöhen die Kosten dieses Katalysators signifikant. Zudem ist die Herstellung derartiger Systeme kostspielig. Weiterhin sind manche Katalysatorsysteme empfindlich gegenüber Katalysatorgiften wie Schwefelwasserstoff und anderen Schwefelverbindungen, die bei der Verbrennung von schwefelhaltigem Kraftstoff entstehen können und die katalytische Aktivität beeinflussen. Zwar können auch diese Verbindungen von der Edelmetallbeschichtung in aller Regel zersetzt werden, jedoch reduzieren die hierfür erforderlichen hohen Katalysatortemperaturen die Lebensdauer des Katalysators deutlich.The precious metals used to reduce the stored NOx in conventional LNT catalysts significantly increase the cost of this catalyst. In addition, the production of such systems is expensive. Furthermore, some are catalyst systems sensitive to catalyst poisons such as hydrogen sulfide and other sulfur compounds that may be produced by combustion of sulfur-containing fuel and affect catalytic activity. Although these compounds can usually be decomposed by the noble metal coating, but the high catalyst temperatures required for this purpose significantly reduce the life of the catalyst.

Ein LNT-Katalysator der vorgenannten Art ist beispielsweise aus der EP 1 004 347 B1 bekannt. Der hierin offenbarte Katalysator ist zweischichtig aufgebaut, wobei eine erste Schicht für die NOx Speicherung zuständig ist und eine zwe i-te Schicht Edelmetallkomponenten enthält, mit deren Hilfe NOx abgebaut werden soll. Dieser Katalysator wird kontinuierlich, also nicht im Wechselbetrieb mager/fett unterhalten und erreicht hierbei eine Konversationsrate von etwa 20 bis 30% der durchströmenden Stickoxide.An LNT catalyst of the aforementioned type is for example from the EP 1 004 347 B1 known. The catalyst disclosed herein is bi-layered with a first layer being responsible for NOx storage and a second layer containing noble metal components for NOx removal. This catalyst is maintained continuously, ie not in alternating operation lean / rich and in this case reaches a conversational rate of about 20 to 30% of the nitrogen oxides flowing through.

Neben den vorgenannten LNT-Katalysatoren sind weitere Katalysatorsysteme bekannt, die unter Verwendung von extern eingespeisten Reduktionsmitteln den Stickoxidgehalt in Abgasen verringern. Das Reduktionsmittel wird in der Regel mittels einer Injektionseinrichtung in den Abgasstrom eingespritzt. Für die eigentliche Umsetzung sorgt dann ein stromabwärts der Injektionseinrichtung angeordneter sogenannter SCR-Katalysator. Mit SCR (Selective Catalytic Reduktion) bezeichnet man die Technik der selektiven katalytischen Reduktion von Stickoxiden in Abgasen von Feuerungsanlagen, Müllverbrennungsanlagen, Gasturbinen, Industrieanlagen und Motoren. Die chemische Reaktion am SCR-Katalysator ist selektiv, d.h. es werden bevorzugt die Stickoxide (NO, NO2 reduziert, während unerwünschte Nebenreaktionen (wie z. B. die Oxidation von Schwefeldioxid zu Schwefeltrioxid) weitestgehend unterdrückt werden. Die SCR-Katalysatoren werden oft in Kombination mit Rußpartikelfiltern und Oxidationskatalysatoren eingesetzt.In addition to the aforementioned LNT catalysts, further catalyst systems are known which reduce the nitrogen oxide content in exhaust gases using externally fed reducing agents. The reducing agent is usually injected by means of an injection device into the exhaust gas stream. For the actual implementation then provides a downstream of the injection device arranged so-called SCR catalyst. SCR (Selective Catalytic Reduction) refers to the technology of selective catalytic reduction of nitrogen oxides in exhaust gases from combustion plants, waste incineration plants, gas turbines, industrial plants and engines. The chemical reaction on the SCR catalyst is selective, ie it is preferred to reduce the nitrogen oxides (NO, NO 2) while suppressing undesirable side reactions (such as the oxidation of sulfur dioxide to sulfur trioxide) .The SCR catalysts are often used in Used in combination with soot particle filters and oxidation catalysts.

Für die vorgenannte Reduktionsreaktion wird ein Reduktionsmittel benötigt, wozu typischerweise Ammoniak (NH3) verwendet wird. Der benötigte Ammoniak wird hierbei in der Regel nicht direkt, d. h. in reiner Form, verwendet, sondern in Form einer 32,5%igen wäßrigen Harnstofflösung eingesetzt, welche in der Industrie einheitlich mit AdBlue® bezeichnet wird. Die Zusammensetzung ist in der DIN 70070 geregelt. Der Grund dafür, dass der benötigte Ammoniak nicht in reiner Form mitgeführt wird, ist die Gefährlichkeit dieses Stoffes. Ammoniak wirkt auf Haut und Schleimhäute (insbesondere auch auf die Augen) ätzend, zudem bildet es an der Luft ein explosionsfähiges Gemisch.For the aforementioned reduction reaction, a reducing agent is needed, for which ammonia (NH 3 ) is typically used. The required ammonia is usually not used directly, ie in pure form, but used in the form of a 32.5% aqueous urea solution, which is uniform in the industry is called AdBlue®. The composition is regulated in DIN 70070. The reason that the required ammonia is not carried in pure form is the danger of this substance. Ammonia has a corrosive effect on the skin and mucous membranes (especially on the eyes) and also forms an explosive mixture in the air.

Aus der vorgenannten Harnstoff-Lösung entsteht beim Einsprühen in den heißen Abgasstrom durch eine Zersetzungsreaktion Ammoniak und Kohlendioxid. Der auf diese Weise erzeugte Ammoniak steht dann in dem stromabwärts angeordneten SCR-Katalysator zur Verfügung. Bei der Umsetzung von Ammoniak mit den Stickoxiden im Abgas findet eine Komproportionierungsreaktion statt, wobei Wasser (H2O) und Stickstoff (N2) entstehen. Bei den SCR-Katalysatoren wird typischerweise zwischen zwei verschiedenen Arten von Katalysatoren unterschieden. Die eine Art besteht im Wesentlichen aus Titandioxid, Vanadiumpentoxid und Wolframoxid. Die andere Art verwendet Zeolithe.From the above-mentioned urea solution is formed during injection into the hot exhaust gas stream by a decomposition reaction ammonia and carbon dioxide. The ammonia thus produced is then available in the downstream SCR catalyst. In the reaction of ammonia with the nitrogen oxides in the exhaust, a Komproportionierungsreaktion takes place, with water (H 2 O) and nitrogen (N 2 ) are formed. The SCR catalysts typically distinguish between two different types of catalysts. One type consists essentially of titanium dioxide, vanadium pentoxide and tungsten oxide. The other type uses zeolites.

Die Menge des eingespritzten Harnstoffs ist von der motorischen Stickoxidemission und damit von der momentanen Drehzahl und dem Drehmoment des Motors abhängig. Der Verbrauch an Harnstoff-Wasser-Lösung beträgt - abhängig von der Rohemission des Motors - etwa 2 bis 8% des eingesetzten Dieselkraftstoffs. Es muß deshalb ein entsprechendes Tankvolumen mitgeführt werden, was zum Teil als nachteilig empfunden wird. Insbesondere erschwert dies den Einsatz in Dieselbetriebenen Personenkraftwagen, da ein zusätzlicher Tank vorgesehen werden muß.The amount of injected urea depends on the engine's nitrogen oxide emissions and thus on the current speed and torque of the engine. The consumption of urea-water solution is - depending on the raw emission of the engine - about 2 to 8% of the diesel fuel used. It must therefore be carried along a corresponding tank volume, which is perceived in part as disadvantageous. In particular, this complicates the use in diesel-powered passenger cars, since an additional tank must be provided.

Durch eine selektive katalytische Reduktion werden Stickoxide aus dem Abgas zu großen Teilen entfernt. Im Gegensatz zum Dieselpartikelfilter (DPF) oder den oben beschriebenen LNTs stellt sich für die Schadstoffreduktion kein Kraftstoffmehrverbrauch ein, da ein SCR-Katalysator im Gegensatz zu den vorgenannten Katalysatoren im Betrieb keine zeitweise Abwendung von optimalen Verbrennungsverhältnissen erfordert.By a selective catalytic reduction nitrogen oxides are removed from the exhaust gas to a large extent. In contrast to the diesel particulate filter (DPF) or the LNTs described above, no additional fuel consumption is created for the pollutant reduction, since an SCR catalyst, in contrast to the aforementioned catalysts during operation does not require temporary avoidance of optimal combustion conditions.

Bei der Verwendung der SCR-Technologie in z. B. Lastfahrzeugen ergeben sich aufgrund des für den Betrieb benötigten Ammoniaks in Form von AdBlue® weitere Notwendigkeiten. So muß dieser als weiterer Betriebsstoff wegen seiner besonderen Eigenschaften in einem Edelstahl- oder Kunststofftank mitgeführt und kontinuierlich in den Abgasstrom eingesprüht werden. Dadurch ergibt sich neben dem SCR-Katalysator und der Einsprühanlage die Notwendigkeit eines zweiten, meist kleineren Tanks neben dem Dieseltank.When using the SCR technology in z. As trucks arise due to the ammonia required for the operation in the form of AdBlue ® more needs. So this must be carried as another fuel because of its special properties in a stainless steel or plastic tank and sprayed continuously into the exhaust stream. This results in addition to the SCR catalyst and the injection system, the need for a second, usually smaller tank next to the diesel tank.

Zudem ist beim Betrieb zu beachten, dass AdBlue® variabel eingespritzt werden muß. Er muß bisher über ein so genanntes Feed-Verhältnis dem NOx im Abgasmassenstrom angepaßt werden. Wird dabei zuviel Harnstoff zudosiert, so kann das daraus gebildete Ammoniak nicht mehr mit NOx reagieren. Bei dieser Fehldosierung kann Ammoniak in die Umgebung gelangen. Da Ammoniak bereits in sehr kleinen Konzentrationen wahrgenommen werden kann, führt dies zu einer Geruchsbelästigung.In addition, it should be noted during operation that AdBlue ® must be variably injected. So far, it must be adapted to the NOx in the exhaust gas mass flow via a so-called feed ratio. If too much urea is metered in, the ammonia formed from it can no longer react with NOx. With this incorrect dosage, ammonia can enter the environment. Since ammonia can already be detected in very small concentrations, this leads to an odor nuisance.

Während die vorgenannten katalytischen Reaktionen bei hohen Abgastemperaturen mit ausreichender Geschwindigkeit ablaufen, sind die Umsetzungsgrade bei geringen Abgastemperaturen in der Regel nicht befriedigend. Zwar sind SCR-Katalysatoren in der Regel imstande, Stickoxide über einen gewissen Zeitraum zu speichern, beispielsweise bis die Abgasleitung der Motor auf Betriebstemperatur sind und der Abgasstrom die benötigte Temperatur aufweist. Allerdings wird die erforderliche Mindestabgastemperatur für den optimalen Betrieb beispielsweise im Stadtverkehr häufig nicht erreicht, so dass nach einer bestimmten Betriebszeit die maximale Speicherkapazität des SCR-Katalysators überschritten wird und Stickoxide in die Umwelt gelangen.While the aforementioned catalytic reactions occur at high exhaust gas temperatures with sufficient speed, the degrees of conversion at low exhaust gas temperatures are generally not satisfactory. Although SCR catalysts are usually able to store nitrogen oxides over a period of time, for example, until the exhaust pipe, the engine to operating temperature and the exhaust gas stream has the required temperature. However, the required minimum exhaust gas temperature for optimal operation is often not achieved, for example in city traffic, so that after a certain period of operation, the maximum storage capacity of the SCR catalyst is exceeded and nitrogen oxides enter the environment.

Gleichzeitig ist die Abgastemperatur für eine quantitative Zersetzung des Harnstoffs in Ammoniak und Kohlendioxid möglicherweise nicht ausreichend, so dass nicht ausreichende Mengen an Ammoniak gebildet werden können. Zwar kann das letztgenannte Problem zumindest teilweise durch eine Erhöhung der eingespritzten Harnstoffmenge kompensiert werden, jedoch ist die tatsächliche Menge an gebildetem katalytisch aktivem Ammoniak dann nur noch schwer vorhersagbar. So kann es bei Erhöhung der eingespritzten Harnstoffmenge auch dazu kommen, dass mehr Ammoniak gebildet wird als im SCR-Katalysator verbraucht wird, wodurch Ammoniak in die Umwelt gelangt. Dies ist aus Gründen der Geruchsbelästigung und auch aus toxikologischer Sicht unerwünscht.At the same time, the exhaust gas temperature for quantitative decomposition of the urea into ammonia and carbon dioxide may not be sufficient, so that insufficient amounts of ammonia can be formed. Although the latter problem can be at least partially compensated by an increase in the injected amount of urea, but the actual amount of formed catalytically active ammonia is then difficult to predict. That's the way it works As the amount of urea injected increases, more ammonia is also formed than is consumed in the SCR catalyst, causing ammonia to enter the environment. This is undesirable for reasons of odor nuisance and also from a toxicological point of view.

Um diesem Problem zu begegnen wird in DE 103 48 800 A1 ein Diesel-Abgasnachbehandlungssystem vorgeschlagen, welches ein Reduktionsmittelzuführsystem umfasst, bei dem das Reduktionsmittel mittels eines Heizelements auf die erforderliche Temperatur gebracht wird. Durch die Heizeinrichtung wird das zugeführte Reduktionsmittel in Form einer wäßrigen Harnstofflösung beim Einsprühen in den Abgasstrom weitestgehend unabhängig von der Abgastemperatur verdampft bzw. unter Freisetzung von Ammoniak zersetzt. Dadurch ist die im Abgasstrom tatsächlich vorhandene Reduktionsmittelmenge unabhängig von der Abgastemperatur.To counter this problem is in DE 103 48 800 A1 proposed a diesel exhaust aftertreatment system comprising a reducing agent supply system in which the reducing agent is brought to the required temperature by means of a heating element. By the heater, the supplied reducing agent is evaporated in the form of an aqueous urea solution when injected into the exhaust stream largely independent of the exhaust gas temperature or decomposed to release ammonia. As a result, the amount of reducing agent actually present in the exhaust gas flow is independent of the exhaust gas temperature.

Ein hierzu vergleichbares System ist aus der DE 10 2006 049 591 A1 oder der aus DE 10 2007 029 674 A1 bekannt, bei denen ebenfalls ein Reduktionsmittel in Form einer Harnstofflösung über einen elektrisch beschriebenen Wärmetauscher vorgeheizt und im gasförmigen Zustand in den Abgasstrom eingesprüht wird.A comparable system is from the DE 10 2006 049 591 A1 or the off DE 10 2007 029 674 A1 in which also a reducing agent is preheated in the form of a urea solution via an electrically described heat exchanger and sprayed in the gaseous state in the exhaust gas stream.

Wie bereits eingangs dargelegt, ist der Einsatz einer Harnstofflösung mit gewissen Problemen verbunden, insbesondere das Erfordernis des Mitführens einer weiteren nachzufüllenden Flüssigkeit neben dem eigentlichen Kraftstoff.As already stated at the outset, the use of a urea solution is associated with certain problems, in particular the requirement of carrying a further liquid to be replenished in addition to the actual fuel.

Aus der EP 0 708 230 B1 ist deshalb eine Einrichtung zum Nachbehandeln von Abgasen einer selbstzündenden Brennkraftmaschine bekannt, bei der über die Kraftstoffpumpe des Dieselmotors Dieselkraftstoff in den Abgasstrom mittels einer stromaufwärts eines SCR-Katalysators angeordneten Einspritzdüse eingebracht wird. D. h., bei dieser beschriebenen Anordnung wird anstellte eines ammoniakfreisetzenden Systems Dieselkraftstoff als Reduktionsmittel verwendet. Damit bei der vorbeschriebenen Anordnung der Dieselkraftstoff unabhängig von der Abgastemperatur gasförmig in den Abgastrakt eingespritzt wird, befindet sich in der Nähe der Injektionseinrichtung eine Glühkerze, mit welcher der Dieselkraftstoff über seinen Verdampfungspunkt hinaus erwärmt wird. Diese Lösung hat zwar den Vorteil, dass im Gegensatz zu den vorbeschriebenen Systemen kein zusätzlicher Vorratstank für die wäßrige Harnstofflösung vorgehalten werden muß, was insbesondere bei Personenkraftwagen häufig zu Platzproblemen führt.From the EP 0 708 230 B1 Therefore, a device for post-treatment of exhaust gases of a self-igniting internal combustion engine is known in which via the fuel pump of the diesel engine diesel fuel is introduced into the exhaust gas stream by means of an upstream of an SCR catalyst arranged injection nozzle. That is, in this described arrangement, instead of using an ammonia-releasing system, diesel fuel is used as the reducing agent. In order for the diesel fuel to be gaseously injected into the exhaust gas tract in the above-described arrangement, regardless of the exhaust gas temperature, a glow plug is located in the vicinity of the injection device with which the diesel fuel is heated above its vaporization point. Although this solution has the advantage that in contrast to the systems described above, no additional storage tank for the aqueous urea solution must be held, which often leads to space problems, especially in passenger cars.

Bei diesem System wird es jedoch zum Teil als nachteilig empfunden, dass größere Mengen an Dieselkraftstoff zur Stickoxidbeseitigung erforderlich sind, was letztlich den Kraftstoffverbrauch erhöht. Zudem entstehen hierbei wiederum Reaktionsprodukte, die sich negativ auf die Abgaswerte auswirken können oder durch entsprechende Vorrichtungen, d.h. in der Regel Katalysatoren, wieder entfernt werden müssen. Rückstände des eingespritzten Dieselkraftstoffs können überdies zu unerwünschten Ablagerungen im Abgassystem führen.In this system, however, it is sometimes felt to be disadvantageous that larger amounts of diesel fuel for nitrogen oxide removal are required, which ultimately increases fuel consumption. In addition, reaction products which can have a negative effect on the exhaust gas values or which are produced by corresponding devices, i. usually catalysts, must be removed again. Residues of the injected diesel fuel can also lead to undesirable deposits in the exhaust system.

Die Aufgabe der vorliegenden Erfindung bestand nun darin, eine verbesserte Injektionseinrichtung der vorgenannten Art zur Verfügung zu stellen, welche mit möglichst geringen Mengen an Reduktionsmittel eine weitestgehend vollständige Beseitigung der Stickoxide im Abgasstrom unabhängig von dessen Temperatur ermöglicht. Zusätzlich soll eine weitere Schadstoffbelastung und eine Verschmutzung des Abgassystems weitestgehend vermieden werden.The object of the present invention was to provide an improved injection device of the aforementioned type which, with as small amounts of reducing agent as possible, allows a complete removal of the nitrogen oxides in the exhaust gas stream independently of its temperature. In addition, a further pollution and pollution of the exhaust system should be largely avoided.

Diese Aufgabe wird gelöst durch eine Injektionseinrichtung zur Einspeisung von Reduktionsmitteln in ein Abgassystem einer Brennkraftmaschine zur Verringerung des Stickoxidausstoßes, wobei die Injektionseinrichtung mit jeweils einem Vorratsbehälter für ein erstes sowie ein zweites, bei Raumtemperatur flüssiges Reduktionsmittel verbunden ist und einen Injektor sowie eine Verdampfungseinrichtung für das erste und zweite Reduktionsmittel umfaßt.This object is achieved by an injection device for feeding reducing agents into an exhaust system of an internal combustion engine for reducing the nitrogen oxide output, wherein the injection device is connected to a respective reservoir for a first and a second, liquid at room temperature reducing agent and an injector and an evaporation device for the first and second reducing agents.

Mit anderen Worten sieht die erfindungsgemäße Lösung die Verwendung von zwei flüssigen Reduktionsmitteln vor, welche vor dem Einspritzen in den Abgasstrom in den gasförmigen Zustand überführt werden. Hierfür kann die Verdampfungseinrichtung beispielsweise eine elektrisch betriebene Heizeinrichtung aufweisen, insbesondere eine Glühkerze.In other words, the solution according to the invention provides for the use of two liquid reducing agents which are converted into the gaseous state before being injected into the exhaust gas flow. For this purpose, the evaporation device can have, for example, an electrically operated heating device, in particular a glow plug.

Die erfindungsgemäße Injektionseinrichtung kann im Prinzip in jeder Art von Abgasaufbereitungssystemen mit einem SCR-Katalysator eingesetzt werden. So können in an sich bekannter Weise zusätzlich zum SCR-Katalysator weitere Katalysatoren wie ein LNT oder ein Rußpartikelfilter eingesetzt werden. Ein weiterer Gegenstand der vorliegenden Erfindung ist folglich ein Abgasreinigungssystem für eine Brennkraftmaschine zur Verringerung des Stickoxidausstoßes umfassend einen SCR-Katalysator und eine stromaufwärts hiervon angeordnete erfindungsgemäße Injektionseinrichtung, sowie optionaler weiterer Reinigungselemente wie ein LNT und/ oder ein Rußpartikelfilter, die wahlweise stromaufwärts der Injektionseinrichtung oder stromabwärts des SCR-Katalysators angeordnet sind. Als SCR-Katalysator kann im Prinzip jeder an sich bekannte SCR-Katalysator verwendet werden. Gleiches gilt für die optional vorhandenen weiteren Reinigungselemente wie ein LNT und/ oder ein Rußpartikelfilter.The injection device according to the invention can be used in principle in any type of exhaust gas treatment systems with an SCR catalyst. Thus, in a manner known per se, in addition to the SCR catalyst, further catalysts such as an LNT or a soot particle filter can be used. A further subject of the present invention is therefore an exhaust gas purification system for an internal combustion engine for reducing nitrogen oxide emissions comprising an SCR catalyst and an injection device according to the invention arranged upstream thereof, as well as optional further purification elements such as an LNT and / or a soot particle filter optionally upstream of the injection device or downstream of the SCR catalyst are arranged. In principle, any known SCR catalyst can be used as the SCR catalyst. The same applies to the optional additional cleaning elements such as an LNT and / or a soot particle filter.

In vorteilhafter Ausgestaltung der erfindungsgemäßen Injektionseinrichtung ist das erste Reduktionsmittel eine Ammoniak freisetzende Flüssigkeit, insbesondere eine wäßrige Harnstofflösung wie AdBlue®, und das weitere Reduktionsmittel eine Kohlenwasserstoffverbindung, insbesondere ein Kraftstoff wie beispielsweise Dieselkraftstoff. Die Verwendung dieser zwei unterschiedlichen Reduktionsmittel ist von Vorteil, da durch den teilweisen Ersatz der wäßrigen Harnstofflösung bei gleichbleibender Stickoxideliminierungsrate der Verbrauch an zusätzlich mitzuführender Harnstofflösung erheblich reduziert werden kann. Gleichzeitig ist durch die Kombination von Harnstofflösung und Dieselkraftstoff der Anteil der durch die Dieselkraftstoffeinspritzung entstehenden zusätzlichen Schadstoffe deutlich verringert. Außerdem wird der Kraftstoffmehrverbrauch durch den Einsatz der Ammoniak freisetzenden Flüssigkeit gemindert.In an advantageous embodiment of the injection device according to the invention, the first reducing agent is an ammonia-releasing liquid, in particular an aqueous urea solution such as AdBlue®, and the further reducing agent is a hydrocarbon compound, in particular a fuel such as diesel fuel. The use of these two different reducing agents is advantageous since the partial replacement of the aqueous urea solution at a constant nitrogen oxide removal rate can considerably reduce the consumption of additional urea solution to be entrained. At the same time, the proportion of additional pollutants resulting from diesel fuel injection is significantly reduced by the combination of urea solution and diesel fuel. In addition, the fuel consumption is reduced by the use of the ammonia-releasing liquid.

Das Verhältnis von Dieselkraftstoff zu 32,5%iger Harnstofflösung kann über weite Bereiche variiert werden und auch in Abhängigkeit der Betriebsparameter des Fahrzeugs individuell angepaßt werden. So kann das Verhältnis zwischen wäßriger Harnstofflösung der vorgenannten Konzentration, also AdBlue®, zu Dieselkraftstoff im Bereich von 1:10 bis 10:1 liegen, vorzugsweise 1:8 bis 8:1.The ratio of diesel fuel to 32.5% urea solution can be varied over wide ranges and also be adjusted individually depending on the operating parameters of the vehicle. Thus, the ratio between aqueous urea solution of the aforementioned concentration, ie AdBlue®, to diesel fuel may range from 1:10 to 10: 1, preferably from 1: 8 to 8: 1.

Die erfindungsgemäße Injektionseinrichtung kann weiterhin derart ausgestaltet sein, dass von dem Vorratsbehälter für die Ammoniak freisetzende Flüssigkeit eine Ammoniakleitung und von dem Kraftstoffbehälter eine Kraftstoffleitung abgehen, die in einem 3-Wege-Ventil münden, welches über eine Reduktionsmittelleitung mit dem Injektor verbunden ist. Mittels des 3-Wege-Ventils können über eine beispielsweise elektronisch angesteuerte Verstelleinheit die vorgenannten Volumenverhältnisse zwischen den beiden Reduktionsmitteln variabel eingestellt werden, insbesondere in Abhängigkeit der Betriebsparameter des Motors.The injection device according to the invention can also be designed such that depart from the reservoir for the ammonia-releasing liquid an ammonia line and from the fuel tank a fuel line, which open into a 3-way valve, which is connected via a reducing agent line to the injector. By means of the 3-way valve can be variably adjusted, for example, depending on the operating parameters of the engine via an example electronically controlled adjusting the aforementioned volume ratios between the two reducing agents.

Auch wenn sich eine wäßrige Harnstofflösung und Dieselkraftstoff nicht homogen miteinander vermischen lassen, ist es von Vorteil, wenn die beiden Reduktionsmittel möglichst gleichmäßig verteilt in den Abgasstrom eingebracht werden. Hierzu kann eine Mischeinrichtung vorgesehen sein, die vorzugsweise in der Reduktionsmittelleitung angeordnet ist. Mit dieser kann aus den vorgenannten flüssigen Reduktionsmitteln eine Emulsion erzeugt werden.Even if an aqueous urea solution and diesel fuel can not be mixed homogeneously with one another, it is advantageous if the two reducing agents are distributed as evenly as possible into the exhaust gas flow. For this purpose, a mixing device may be provided, which is preferably arranged in the reducing agent line. With this, an emulsion can be produced from the aforementioned liquid reducing agents.

Um eine möglichst quantitative Verdampfung der Reduktionsmittel vor dem Einbringen in den Abgasstrom zu ermöglichen ist in vorteilhafter Weise die Reduktionsmittelleitung in Förderrichtung der Reduktionsmittel auf die Heizeinrichtung gerichtet.In order to allow the most quantitative possible evaporation of the reducing agent prior to introduction into the exhaust gas flow, the reducing agent line in the conveying direction of the reducing agent is directed to the heating device in an advantageous manner.

Nach einer weiteren Ausgestaltung der erfindungsgemäßen Injektionseinrichtung ist diese wenigstens eine Fördereinrichtung für das erste und zweite Reduktionsmittel zugeordnet, welche insbesondere an der Reduktionsmittelleitung vorgesehen ist. Auf diese Weise kann ein kontinuierlicher Reduktionsmittelstrom sichergestellt werden. Als Fördereinrichtung kommt beispielsweise eine Pumpe in Betracht. Diese kann zudem einen Förderdruck aufbauen, so dass die Reduktionsmittel mit Überdruck gegen die Heizeinrichtung und dann in den Abgasstrom eingepreßt werden. Auf diese Weise können die Reduktionsmittel vor dem Verdampfen beispielsweise über eine Zerstäuberdüse fein verteilt werden, was den Verdampfungsvorgang weiter beschleunigt.According to a further embodiment of the injection device according to the invention, this is assigned at least one conveying device for the first and second reducing agent, which is provided in particular on the reducing agent line. In this way, a continuous reducing agent flow can be ensured. As a conveyor, for example, a pump is considered. This can also build a delivery pressure, so that the reducing agent are pressed with positive pressure against the heater and then into the exhaust stream. In this way, the reducing agents can be finely distributed before evaporation, for example via a spray nozzle, which further accelerates the evaporation process.

Nach einer bevorzugten Ausführungsform der erfindungsgemäßen Injektionseinrichtung ist die Mischeinrichtung in die Fördereinrichtung integriert.According to a preferred embodiment of the injection device according to the invention, the mixing device is integrated in the conveyor.

Ein weiterer Gegenstand der vorliegenden Erfindung betrifft ein Verfahren zur Reduzierung von Stickoxiden in Abgasen, insbesondere in Abgasen von dieselbetriebenen Brennkraftmaschinen, das die Abgasaufbereitung mittels eines SCR-Katalysators umfaßt, wobei mittels einer stromaufwärts vom SCR-Katalysator angeordneten Injektionseinrichtung ein erstes und ein zweites bei Raumtemperatur flüssiges Reduktionsmittel mittels einer Heizeinrichtung wenigstens teilweise verdampft und dem Abgasstrom über einen Injektor beigemischt werden.Another object of the present invention relates to a method for reducing nitrogen oxides in exhaust gases, in particular in exhaust gases of diesel-powered internal combustion engines, comprising the exhaust gas treatment by means of an SCR catalyst, wherein by means of an upstream of the SCR catalyst arranged injection device, a first and a second at room temperature liquid reducing agent are at least partially vaporized by means of a heater and admixed to the exhaust stream via an injector.

Die vorliegende Erfindung betrifft weiterhin die Verwendung einer Mischung einer Kohlenwasserstoffverbindung, insbesondere Dieselkraftstoff, und eines Ammoniak freisetzenden Reduktionsmittels, insbesondere einer wäßrigen Harnstofflösung wie AdBlue®, zur Reduzierung von Stickoxiden in Abgasen, insbesondere in Abgasen von Dieselbetriebenen Brennkraftmaschinen.The present invention further relates to the use of a mixture of a hydrocarbon compound, in particular diesel fuel, and an ammonia-releasing reducing agent, in particular an aqueous urea solution such as AdBlue®, for reducing nitrogen oxides in exhaust gases, in particular in exhaust gases of diesel-powered internal combustion engines.

Die vorliegende Erfindung wird anhand des folgenden Ausführungsbeispiels und zweier Figuren genauer erläutert. Darin zeigt die

Fig. 1:
eine bekannte Injektionseinrichtung für eine wäßrige Harnstofflösung gemäß dem Stand der Technik, sowie
Fig. 2:
eine erfindungsgemäße Injektionseinrichtung für eine wäßrige Harnstofflösung und Dieselkraftstoff.
The present invention will be explained in more detail with reference to the following embodiment and two figures. In it shows the
Fig. 1:
a known injection device for an aqueous urea solution according to the prior art, as well as
Fig. 2:
an injection device according to the invention for an aqueous urea solution and diesel fuel.

In Fig. 1 ist ein schematischer Aufbau eines Dieselmotors mit angeschlossenem Abgasreinigungssystem 1 analog der DE 103 48 800 A1 dargestellt. Das System umfaßt einen Hubkolbenmotor 2 in Form eines Dieselmotors mit Turboaufladung, der auf seiner Ansaugseite über einen Luftfilter 3 Frischluft bezieht, die von einem Verdichter 4a eines Turboladers 4 vorverdichtet wird. In an sich bekannter Weise wird der Verdichter 4a des Turboladers 4 durch dessen abgasseitige Turbine 4b über eine gemeinsame Welle angetrieben.In Fig. 1 is a schematic structure of a diesel engine with connected emission control system 1 analogous to DE 103 48 800 A1 shown. The system comprises a reciprocating engine 2 in the form of a turbocharged diesel engine, which receives fresh air via an air filter 3 on its intake side, which is precompressed by a compressor 4a of a turbocharger 4. In a manner known per se, the compressor 4a of the turbocharger 4 is driven by its exhaust gas turbine 4b via a common shaft.

Die Verbrennungsgase des Hubkolbenmotors 2 werden durch ein aus mehreren Rohrsegmenten bestehendes Abgasrohr 5 abgeleitet. In dem Abgasrohr 5 ist stromabwärts vom Turbolader 4 ein Oxidationskatalysator 6 angeordnet, an dessen Auslaßseite in stromabwärtiger Richtung des Abgasrohres 5 ein SCR-Katalysator 7 angeschlossen ist, an dessen Ausgang sich wiederum ein Endschalldämpfer 8 anschließt. Zwischen dem Oxidationskatalysator 6 und dem SCR-Katalysator 7 ist eine Injektionseinrichtung 9 für eine wäßrige Harnstofflösung (AdBlue®) angebracht. Über diese wird mittels einer Reduktionsmittelversorgungsleitung 10 zugeführte wäßrige Harnstofflösung an einem elektrisch betriebenen Heizelement verdampft und damit gasförmig in das Abgasrohr 5 eingebracht.The combustion gases of the reciprocating engine 2 are discharged through an exhaust pipe 5 consisting of several pipe segments. In the exhaust pipe 5 downstream of the turbocharger 4, an oxidation catalyst 6 is arranged, at the outlet side in the downstream direction of the exhaust pipe 5, an SCR catalyst 7 is connected, at its output, in turn, a rear muffler 8 connects. Between the oxidation catalyst 6 and the SCR catalyst 7, an injection device 9 for an aqueous urea solution (AdBlue®) is attached. About this is fed by means of a reducing agent supply line 10 supplied aqueous urea solution to an electrically operated heating element and thus introduced in gaseous form into the exhaust pipe 5.

Die im Betrieb des Turbodieselmotors 2 entstehenden Stickoxide werden zunächst im SCR-Katalysator gespeichert und durch bei der Zersetzungsreaktion des Harnstoffs bei Kontakt mit dem Heizelement 11 bzw. den heißen Abgasen entstehenden Ammoniakgas in einer Komproportionierungsreaktion zu Wasserdampf und Stickstoff umgesetzt.The nitrogen oxides formed during operation of the turbo diesel engine 2 are first stored in the SCR catalyst and converted into water vapor and nitrogen in a comproportionation reaction by ammonia gas produced during the decomposition reaction of the urea upon contact with the heating element 11 or the hot exhaust gases.

In Fig. 2 ist ein Abgasreinigungssystem 20 mit einer erfindungsgemäßen Injektionseinrichtung 21 zur Einspeisung von Reduktionsmitteln in das Abgassystem des Turbodieselmotors 2 dargestellt. Hierbei beschreiben gleiche Bezugsziffern identische Bauteile die bei der aus Figur 1 bekannten Vorrichtung. Im Folgenden wird somit nur auf die wesentlichen Unterschiede der beiden Systeme eingegangen.In Fig. 2 an exhaust gas cleaning system 20 is shown with an injection device 21 according to the invention for the supply of reducing agents in the exhaust system of the turbo diesel engine 2. Here, the same reference numerals describe identical components in the off FIG. 1 known device. In the following, therefore, only the essential differences of the two systems will be discussed.

Die Injektionseinrichtung 21 ist an jeweils einen Vorratsbehälter 22, 23 für ein erstes bzw. zweites Reduktionsmittel angeschlossen, d. h. 32,5%ige wäßrige Harnstofflösung einerseits und Dieselkraftstoff andererseits. Die Verbindung erfolgt ausgehend von dem Vorratsbehälter 22 der wäßrigen Harnstofflösung über eine Ammoniakleitung 24 und vom Vorratsbehälter 23 für Dieselkraftstoff über eine Kraftstoffleitung 25. Die Ammoniakleitung 24 und die Kraftstoffleitung 25 münden in einem elektronisch steuerbaren 3-Wege-Ventil 26, von dem eine Reduktionsmittelleitung 28 abgeht, die in einen Injektor mündet. Dieser besteht aus einer vorliegend nicht dargestellten Zerstäuberdüse. In der Reduktionsmittelleitung 27 ist eine Fördereinrichtung 28 mit integrierter Mischeinheit vorgesehen, mit der die beiden Reduktionsmittel gefördert, vermischt und mit Druck beaufschlagt in den Injektor gepreßt werden. Innerhalb des Injektors ist der Reduktionsmittelstrom auf eine Heizeinrichtung 29 gerichtet. Die Heizeinrichtung 29 besteht aus einer elektrisch beheizten Glühkerze, mit deren Hilfe das Gemisch aus wäßriger Harnstofflösung und Dieselkraftstoff verdampft und der Harnstoff dabei zumindest teilweise zu Ammoniak und Kohlendioxid zersetzt wird, bevor diese gasförmige Mischung in das Teilstück des Abgasrohres 5 stromaufwärts vom SCR-Katalysator 7 eingespeist wird.The injection device 21 is connected to a respective reservoir 22, 23 for a first and second reducing agent, ie 32.5% aqueous urea solution on the one hand and diesel fuel on the other hand. The connection takes place starting from the reservoir 22 of the aqueous urea solution via an ammonia line 24 and from the reservoir 23 for diesel fuel via a fuel line 25. The ammonia line 24 and the fuel line 25 open into an electronically controllable 3-way valve 26, of which a reducing agent line 28th goes off, which opens into an injector. This consists of an atomizer nozzle, not shown here. In the reducing agent line 27, a conveyor 28 is provided with integrated mixing unit, with which the two reducing agents promoted, mixed and pressurized into the injector to be pressed. Within the injector, the reducing agent stream is directed to a heater 29. The heating device 29 consists of an electrically heated glow plug, with the aid of which the mixture of aqueous urea solution and diesel fuel and the urea is thereby at least partially decomposed to ammonia and carbon dioxide, before this gaseous mixture in the portion of the exhaust pipe 5 upstream of the SCR catalyst. 7 is fed.

Claims (12)

Injektionseinrichtung (21) zur Einspeisung von Reduktionsmitteln in ein Abgasreinigungssystem (20) einer Brennkraftmaschine (2) zur Verringerung des Stickoxidausstoßes, wobei die Injektionseinrichtung (21) mit jeweils einem Vorratsbehälter (22, 23) für ein erstes sowie ein zweites bei Raumtemperatur flüssiges Reduktionsmittel verbunden ist und einen Injektor sowie eine Verdampfungseinrichtung (29) für das erste und zweite Reduktionsmittel umfaßt.Injection device (21) for feeding reducing agents into an exhaust gas purification system (20) of an internal combustion engine (2) for reducing nitrogen oxide output, wherein the injection device (21) is connected to a respective reservoir (22, 23) for a first and a second liquid reducing agent at room temperature and comprising an injector and an evaporation means (29) for the first and second reducing agents. Injektionseinrichtung nach Anspruch 1,
dadurch gekennzeichnet, dass
die Verdampfungseinrichtung (29) eine elektrisch betriebene Heizeinrichtung aufweist, insbesondere eine Glühkerze.Injection device according to claim 1,
characterized in that
the evaporation device (29) has an electrically operated heating device, in particular a glow plug. Injektionseinrichtung nach Anspruch 1 oder 2,
dadurch gekennzeichnet, dass
das erste Reduktionsmittel eine Ammoniak freisetzende Flüssigkeit, insbesondere eine wäßrige Harnstofflösung, und das zweite Reduktionsmittel eine Kohlenwasserstoffverbindung ist, insbesondere ein Kraftstoff wie Dieselkraftstoff.Injection device according to claim 1 or 2,
characterized in that
the first reducing agent is an ammonia-releasing liquid, in particular an aqueous urea solution, and the second reducing agent is a hydrocarbon compound, in particular a fuel such as diesel fuel. Injektionseinrichtung nach Anspruch 3,
dadurch gekennzeichnet, dass
von dem Vorratsbehälter (22) für die Ammoniak freisetzende Flüssigkeit eine Ammoniakleitung (24) und von dem Kraftstoffvorratsbehälter (23) eine Kraftstoffleitung (25) abgehen, die in einem 3-Wege-Ventil (26) münden, welches über eine Reduktionsmittelleitung (27) mit dem Injektor verbunden ist.Injection device according to claim 3,
characterized in that
from the reservoir (22) for the ammonia-releasing liquid an ammonia line (24) and from the fuel reservoir (23) a fuel line (25) depart, which open in a 3-way valve (26) which via a reducing agent line (27) connected to the injector. Injektionseinrichtung nach Anspruch 4,
dadurch gekennzeichnet, dass
in der Reduktionsmittelleitung (27) eine Mischeinrichtung vorgesehen ist.Injection device according to claim 4,
characterized in that
in the reducing agent line (27) is provided a mixing device. Injektionseinrichtung nach Anspruch 4 oder 5,
dadurch gekennzeichnet, dass
die Reduktionsmittelleitung (27) in Förderrichtung auf die Heizeinrichtung (29) gerichtet ist.Injection device according to claim 4 or 5,
characterized in that
the reducing agent line (27) is directed in the conveying direction to the heating device (29). Injektionseinrichtung nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass
der Injektionseinrichtung (21) wenigstens eine Fördereinrichtung (28) für das erste und zweite Reduktionsmittel zugeordnet ist, welche insbesondere an der Reduktionsmittelleitung (27) vorgesehen ist.Injection device according to one of the preceding claims, characterized in that
the injection device (21) is associated with at least one conveying device (28) for the first and second reducing agent, which is provided in particular on the reducing agent line (27). Injektionseinrichtung nach Anspruch 7,
dadurch gekennzeichnet, dass
die Mischeinrichtung in die Fördereinrichtung (28) integriert ist.Injection device according to claim 7,
characterized in that
the mixing device is integrated in the conveying device (28). Abgasreinigungssystem (20) für eine Brennkraftmaschine (2) zur Verringerung des Stickoxidausstoßes umfassend einen SCR-Katalysator (7) und eine stromaufwärts hiervon angeordnete Injektionseinrichtung (21) nach einem der Ansprüche 1 bis 8, sowie optionaler weiterer Reinigungselemente wie ein LNT (6) und/oder ein Rußpartikelfilter, die wahlweise stromaufwärts der Injektionseinrichtung oder stromabwärts des SCR-Katalysators (7) angeordnet sind.An exhaust gas purification system (20) for an internal combustion engine (2) for reducing nitrogen oxide output comprising an SCR catalytic converter (7) and an injection device (21) arranged upstream thereof according to one of claims 1 to 8, and optional further purification elements such as an LNT (6) and or a soot particle filter, which are optionally arranged upstream of the injection device or downstream of the SCR catalyst (7). Verfahren zur Reduzierung von Stickoxiden in Abgasen, insbesondere in Abgasen von dieselbetriebenen Brennkraftmaschinen (2), das die Abgasaufbereitung mittels eines SCR-Katalysators (7) umfaßt, wobei mittels einer stromaufwärts vom SCR-Katalysator (7) angeordneten Injektionseinrichtung (21) ein erstes und ein zweites bei Raumtemperatur flüssiges Reduktionsmittel mittels einer Heizeinrichtung (29) wenigstens teilweise verdampft und dem Abgasstrom über einen Injektor beigemischt werden.A method for reducing nitrogen oxides in exhaust gases, in particular in exhaust gases of diesel-powered internal combustion engines (2) comprising the exhaust gas treatment by means of an SCR catalyst (7), wherein by means of an upstream of the SCR catalyst (7) arranged injection means (21) a first and a second liquid reducing agent at room temperature is at least partially vaporized by means of a heating device (29) and admixed to the exhaust gas stream via an injector. Verfahren nach Anspruch 10,
dadurch gekennzeichnet, dass
das Volumenverhältnis von erstem zu zweitem Reduktionsmittel 10 : 1 bis 1 : 10 beträgt, insbesondere 8 : 1 bis 1 : 8.Method according to claim 10,
characterized in that
the volume ratio of first to second reducing agent is 10: 1 to 1:10, in particular 8: 1 to 1: 8. Verwendung einer Mischung einer Kohlenwasserstoffverbindung, insbesondere Dieselkraftstoff, und eines Ammoniak freisetzenden Reduktionsmittels, insbesondere einer wäßrigen Harnstofflösung, zur Reduzierung von Stickoxiden in Abgasen, insbesondere in Abgasen von dieselbetriebenen Brennkraftmaschinen (2).Use of a mixture of a hydrocarbon compound, in particular diesel fuel, and an ammonia-releasing reducing agent, in particular an aqueous urea solution, for the reduction of nitrogen oxides in exhaust gases, in particular in exhaust gases of diesel-powered internal combustion engines (2).
EP11180569.3A 2011-09-08 2011-09-08 Heated injection system for exhaust gas systems of Diesel engines Active EP2568137B1 (en)

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US13/592,231 US20130064744A1 (en) 2011-09-08 2012-08-22 Heated injection system for diesel engine exhaust systems
CN2012103325472A CN102989316A (en) 2011-09-08 2012-09-10 Heated injection system for diesel engine exhaust systems

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