DE102007006625A1 - Nitrogen oxide part reducing method for internal combustion engine, involves converting reducing agent precursor at hydrolysis catalyst to reducing agent, and partially heating exhaust gas in electrically heatable catalyzer-carrier body - Google Patents

Abstract

The method involves partially converting a reducing agent precursor at a hydrolysis catalyst to a reducing agent, which is collectively conveyed with exhaust gas to a reduction catalyzer for selective catalystic reduction. The exhaust gas is partially heated in an electrically heatable catalyzer-carrier body operated with a heating power of 0.5 to 3 kilowatts. The exhaust gas is flown through the catalyzer-carrier body, and complete exhaust gas flow is electrically heated. An independent claim is also included for a device for reducing part of nitrogen oxide in exhaust gas of an internal combustion engine.

Description

object The present invention is a method and an apparatus for reducing the proportion of nitrogen oxides in the exhaust gas of an internal combustion engine. In particular, the method according to the invention is based and the device according to the invention on the method the selective catalytic reduction of nitrogen oxides (SCR, selective Catalytic reduction) and can be particularly mobile in the exhaust system Internal combustion engines, for example in automobiles for use come.

by virtue of steadily increasing legal limits that the exhaust gases from internal combustion engine are more mobile in exhaust systems Consumers often different exhaust aftertreatment steps necessary, the more exhaust aftertreatment components necessary do. For example, to fulfill of exhaust gas regulations for diesel engines Particulate filters, oxidation catalysts and measures to reduce the level of nitrogen oxides be formed in the exhaust. Especially with diesel engines whose exhaust usually has lower temperatures than other types of engines this means that, depending on the operating condition, nothing more any component of exhaust gas of sufficiently high temperature is reached. This can lead to dependence from the operating condition, the temperature of at least one component of Exhaust system under the for an implementation of an exhaust gas component necessary minimum temperature falls.

Of these, The invention is based on the object, a method and a device for reducing the proportion of nitrogen oxides in To provide exhaust gas of an internal combustion engine, with which the Disadvantages of the prior art are at least reduced and In particular, an exhaust treatment largely independent from the temperature of the exhaust gas is possible.

The The object is achieved by a method and a device with the features of the independent claims. The respective dependent claims are advantageous Training courses addressed.

The inventive method for reducing the Proportion of nitrogen oxides (NOx) in the exhaust gas of an internal combustion engine, wherein the at least one reducing agent precursor is on a Hydrolysis catalyst at least partially to a reducing agent is reacted, which together with the exhaust a reduction catalyst for selective catalytic reduction, is characterized in that the exhaust gas at least temporarily in at least one electrically heatable catalyst carrier body is heated.

By reducing agent precursor is meant a substance which can chemically react to or release a reducing agent for the selective catalytic reduction of nitrogen oxides. Preferred as the reducing agent precursor is urea which serves as a precursor of the reducing agent ammonia. A hydrolysis catalyst is understood here to mean a component which catalyzes a hydrolysis reaction, in particular a hydrolysis of at least one reducing agent precursor, to at least one reducing agent. The hydrolysis catalyst may comprise a catalyst carrier body which is equipped with at least one hydrolysis-catalyzing substance; in particular, the hydrolysis catalyst may comprise a honeycomb body with channels through which a fluid can pass, which has a corresponding catalytically active coating, for example based on a ceramic washcoat. Accordingly, the reduction catalyst designates a component which catalyzes a selective catalytic reduction of nitrogen oxides. The Reduktionskataly capacitor can be a catalyst carrier body which is equipped with at least one substance catalyzing the reduction reaction. In particular, the reduction catalytic converter can comprise a honeycomb body with channels through which a fluid can pass, which has a corresponding catalytically active coating, for example based on a ceramic washcoat. The electrically heatable catalyst carrier body can in particular as in the WO-A-92/13636 be formed configured, the contents of which in relation to the training and control of the electrically heatable catalyst carrier body is made in full content. The content of this document is insofar included in the disclosure of this document.

The at least temporary heating of the exhaust gas with an electrically heatable catalyst carrier body allows an early onset of the selective catalytic reduction of the nitrogen oxides after a cold start of the internal combustion engine. In particular, in the treatment of the exhaust gas of diesel engines can be guaranteed at temperature fluctuations, the exhaust gas at temperatures below the minimum temperature for hydrolysis of the reducing agent precursor, in particular urea, to a reducing agent, especially ammonia, a hydrolysis of the reducing agent precursor. When sinking below the minimum temperature of the selective catalytic reduction, a decrease in the temperature of the exhaust gas and / or the reduction catalyst below this minimum temperature can be prevented in a particularly advantageous manner, so that a continuous reaction of the nitrogen oxides and a breakthrough of nitrogen oxides and / or the reducing agent by the Reduction catalyst can be prevented. Particularly advantageous is the storage and addition of the Reducing agent precursor in the form of an aqueous solution, for example in the form of a urea-water solution. Such is available on the market under the brand names AdBlue, Denoxium and DenoxiumPlus.

Farther can so even with sudden load changes, for example from full load to overrun in an automobile, an implementation allow the nitrogen oxides, in which the exhaust gas electrically is heated.

When It has proven advantageous, as part of the hydrolysis an exhaust-outside reducing agent production unit, in an exhaust-external evaporation device for evaporation the urea-water solution in the flow direction is formed before the hydrolysis catalyst. In an advantageous way here can be a hydrolysis of the reducing agent precursor with the water included in the aqueous solution respectively.

alternative At least temporarily, the entire exhaust gas stream is electrically heated.

in this connection takes place in an advantageous manner, a common and simple Addition of the reducing agent in liquid form, solid Shape and / or vapor to the entire exhaust stream. This has the particular advantage that the hydrolysis catalyst as electrically heatable catalyst carrier body can be formed, in a particularly advantageous manner as used a kind of control element of the thermal processes in the exhaust system can be. The heating of the entire exhaust stream here has the Advantage on that a quick regulation of the temperatures at least a component in the exhaust system, such as the hydrolysis catalyst and / or the reduction catalyst but also, for example, a particulate filter can be done.

According to one advantageous embodiment of the invention Process catalyzes the electrically heatable catalyst carrier body an oxidation reaction, in particular the oxidation of nitric oxide to nitrogen dioxide. Preference is given to a procedure, in which the exhaust gas after flowing through the electrically heated Catalyst carrier body, so the oxidation catalyst, flows through a particulate filter and / or the reduction catalyst. The heated exhaust gas can in this case also for the regeneration of the particulate filter be used while the nitrogen dioxide in particular as part of a CRT operation (CRT, continuous regenerating trap, continuously regenerating particle trap) of the particulate filter used for the regeneration of carbon.

Prefers Here is a procedure in which the exhaust after Flow through the electrically heatable catalyst carrier body a Device for reducing the number of particles flows through the exhaust gas. This device may in particular be a particle filter, in particular act an open particulate filter, in particular no alternately closed channels with intervening having porous wall.

According to one further advantageous embodiment of the invention Process catalyzes the electrically heatable catalyst carrier body at least in some areas a hydrolysis reaction, in particular from urea to ammonia. Thus, in particular, electrically heatable catalyst carrier body and hydrolysis catalyst be designed to save space in the form of a component.

According to one further advantageous embodiment of the invention Process catalyzes the electrically heatable catalyst carrier body at least in some areas the selective catalytic reduction of nitrogen oxides.

Prefers is an embodiment in which the electrically heatable catalyst carrier body in the exhaust system downstream of a reductant precursor feed is formed and a hydrolysis of the reducing agent precursor and / or catalyzing the selective catalytic reduction of nitrogen oxides Coating has.

Farther advantageous is an embodiment in which by means of the electric heatable catalyst carrier body an aggregate state change of Reducing agent precursor takes place.

Especially advantageous here is the at least partial evaporation of a liquid Reducing agent precursor, in particular an aqueous reducing agent precursor solution. Alternatively or additionally, the electrically heatable Catalyst carrier body have a mixing function, which is achieved, for example, that a cross flow in the catalyst carrier body permitting design, for example, with openings in the walls adjacent Channels, is selected.

• a) dem Hydrolysekatalysator und
• b) dem Reduktionskatalysator.

According to a further advantageous embodiment of the method according to the invention, an electrically current can flow through the electrically heatable catalyst carrier body, wherein the current is supplied when the temperature of the exhaust gas before or the temperature in at least one of the following catalysts is less than 200 ° C:

• a) the hydrolysis catalyst and
• b) the reduction catalyst.

This advantageously allows one thermal control, which prevents a drop in the temperature of the exhaust gas in the hydrolysis, the hydrolysis, the exhaust gas in the reduction catalyst and / or the reduction catalyst below the respective required for the execution of the respective reaction minimum temperature.

• a) dem Hydrolysekatalysator und
• b) dem Reduktionskatalysator.

According to a further advantageous embodiment of the method according to the invention, the electrically heatable catalyst carrier body. can be traversed by an electric current, wherein the power supply is interrupted when the temperature of the exhaust gas before or the temperature in at least one of the following catalyst at 300 ° C or more:

• a) the hydrolysis catalyst and
• b) the reduction catalyst.

This advantageously allows a thermal control, which overheating the components of the exhaust system like the hydrolysis catalyst, the reduction catalyst, the particulate filter and / or the oxidation catalyst effectively prevented. moreover can be saved in this way power. Preferably takes place an interruption of the power supply at temperatures of 250 ° C and fewer.

According to one further advantageous embodiment of the invention Method is the electrically heatable catalyst carrier body at least temporarily with a heating power of 0.5 kW (kilowatts) operated up to 3 kW.

These Heat outputs allow advantageously a rapid heating the exhaust gas even at high mass flows. Prefers the heating power is in the range of 1 to 1.5 kW.

• i) die Temperatur des Abgases vor dem Hydrolysekatalysator;
• ii) die Temperatur des Hydrolysekatalysators;
• iii) die Temperatur des Abgases vor dem Reduktionskatalysator;
• iv) die Temperatur des Reduktionskatalysators; und
• v) die Temperatur einer Reduktionsmittelverdampfereinheit.

According to a further advantageous embodiment of the method according to the invention, at least one of the following temperatures is determined:

• i) the temperature of the exhaust gas before the hydrolysis catalyst;
• ii) the temperature of the hydrolysis catalyst;
• iii) the temperature of the exhaust gas before the reduction catalyst;
• iv) the temperature of the reduction catalyst; and
• v) the temperature of a reducing agent evaporator unit.

• a) Messen und
• b) Berechnen.

In this context, the determination of the at least one temperature is understood to mean at least one of the following methods:

• a) Measuring and
• b) Calculate.

in this connection For example, temperature models of, for example, the Reduction catalyst taking into account the reaction conditions for Use come. Also preferred are methods in which measured Temperatures, in particular a first component, as support points for models for calculating the temperature, in particular a second component, are used. For example, the Temperature of the hydrolysis catalyst as a support point the calculation of the temperature used in the reduction catalyst become. Preference may also be in the past measured Temperatures as support points in the calculation of temperatures be used.

According to one further advantageous embodiment of the invention The method is a heating of the electrically heatable catalyst carrier body prevented if no reducing agent precursor supplied can be.

This is particularly the case when due to too low Temperature no reducing agent precursor supplied can be, for example, because no implementation of the reducing agent precursor to reducing agent due to too low evaporator temperature an external evaporator can be done.

According to one further advantageous embodiment of the invention Method is the electrically heatable catalyst carrier body flows through the exhaust gas before the exhaust reducing agent precursor is supplied, wherein the electrically heatable catalyst carrier body catalyzes an oxidation reaction.

In such a trained process management located upstream of the reducing agent precursor supply oxidation catalyst can be used as a thermal actuator under a thermal control in a particularly advantageous manner. The oxidation catalyst in this case preferably has a volume which corresponds to 0.2 to 1.5 times the displacement of the internal combustion engine, preferably 0.5 to 0.8 times the displacement. Should a construction be appropriate WO-A-92/13636 are selected for the oxidation catalyst, the volume given for the volume including the supporting catalyst applies.

• a) eine Hydrolysereaktion und
• b) eine Reduktionsreaktion.

According to a further advantageous embodiment of the method according to the invention, the exhaust gas flows through the electrically heatable catalyst carrier body after reducing agent precursor is fed, wherein the electrically heatable catalyst carrier body catalyzes at least one of the following reactions:

• a) a hydrolysis reaction and
• b) a reduction reaction.

This allows advantageously the formation of a combined Hydrolysis and reduction catalyst acting as a thermal actuator can be used in the thermal control of the exhaust system.

According to one further advantageous embodiment of the invention Method, further heating measures are carried out, if a sufficiently high heat output is not due to the electric heated honeycomb body is achievable.

This may in particular be the case when the battery of the motor vehicle not enough power for electric heating Can provide. Further heating measures include in particular a post-injection in at least one Cylinder, throttling the machine, etc. Additionally and alternatively, a recovery of kinetic energy, For example, used during a braking or deceleration process become.

Farther preferred is a process control in which the heating power to the amount of reducing agent precursor to be incorporated and / or reducing agent is adjusted by taking into account, for example how strong the exhaust gas is by the addition of the reducing agent precursor and / or reducing agent, by hydrolysis, thermolysis and the like cools.

The disclosed for the inventive method Details and advantages are in the same way to the invention Device transferable and vice versa.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 92/13636 A [0006, 0031]

Claims (21)

A method for reducing the proportion of nitrogen oxides (NOx) in the exhaust gas of an internal combustion engine, wherein at least one reducing agent precursor is reacted on a hydrolysis catalyst at least partially to a reducing agent, which is fed together with the exhaust gas to a reduction catalyst for selective catalytic reduction, characterized in that the Exhaust gas is at least temporarily heated in at least one electrically heatable catalyst carrier body. The method of claim 1, wherein at least temporarily the entire exhaust gas stream is electrically heated. Method according to one of the preceding claims, in which the electrically heatable catalyst carrier body can be traversed by an electric current, wherein the Power is supplied when the temperature of the exhaust gas before or the temperature in at least one of the following catalysts lower than 200 ° C is: a) the hydrolysis catalyst and b) the reduction catalyst. Method according to one of the preceding claims, in which the electrically heatable catalyst carrier body can be traversed by an electric current, wherein the Power supply is interrupted when the temperature of the exhaust gas before or the temperature in at least one of the following catalysts at 300 ° C or more: a) the hydrolysis catalyst and b) the reduction catalyst. Method according to one of the preceding claims, in which the electrically heatable catalyst carrier body at least temporarily with a heating power of 0.5 kW (kilowatts) up to 3 kW is operated. Method according to one of the preceding claims, where at least one of the following temperatures is determined: i) the temperature of the exhaust gas before the hydrolysis catalyst; ii) the temperature of the hydrolysis catalyst; iii) the temperature the exhaust gas before the reduction catalyst; iv) the temperature the reduction catalyst; and v) the temperature of a reducing agent evaporator unit. The method of claim 6, wherein the at least a temperature determined by at least one of the following methods becomes: a) Measuring and b) Calculate. Method according to one of the preceding claims, in which a heating of the electrically heatable catalyst carrier body is inhibited if no reducing agent precursor are supplied can. Method according to one of the preceding claims, in which the exhaust gas is the electrically heatable catalyst carrier body flows through before reducing agent precursor supplied is, wherein the electrically heatable catalyst carrier body a Oxidation reaction catalysed. Method according to one of the preceding claims, in which the exhaust gas is the electrically heatable catalyst carrier body flows through after reducing agent precursor is supplied, wherein the electrically heatable catalyst carrier body catalyses at least one of the following reactions: a) one Hydrolysis reaction and b) a reduction reaction. Method according to one of the preceding claims, in which further heating measures are carried out, if a sufficiently high heat output is not due to the electric heated honeycomb body is achievable. Device for reducing the proportion of nitrogen oxides (NOx) in the exhaust gas of an internal combustion engine, comprising at least a reductant precursor addition to add a reductant precursor, a hydrolysis catalyst for the at least partial reaction of a Reducing agent precursor to a reducing agent and a reduction catalyst for selective catalytic reduction of nitrogen oxides, characterized in that the device at least an electrically heatable catalyst carrier body includes. Apparatus according to claim 12, wherein at least one of the following catalysts as an electrically heatable catalyst carrier body is executed: a) the hydrolysis catalyst; b) the reduction catalyst; c) an oxidation catalyst; and d) a particle filter. Device according to one of claims 12 or 13, in which the electrically heatable catalyst carrier body is formed as an oxidation catalyst, the upstream the reducing agent precursor addition is formed. The apparatus of claim 14, wherein the oxidation catalyst has a volume which the 0.2 to 1.5 times the displacement of the internal combustion engine, preferably 0.5 to 0.8 times the capacity corresponds. Device according to one of claims 12 to 15, in which the electrically heatable catalyst carrier body downstream of the reductant precursor addition is formed and catalyzes at least one of the following reactions: a) the at least partial hydrolysis of the reducing agent precursor to reducing agents and b) the at least partially selective catalytic reduction of nitrogen oxides. Apparatus according to claim 16, wherein the electric heatable catalyst carrier body a volume which is 0.1 to 1 times the displacement of the internal combustion engine, preferably corresponds to 0.2 to 0.4 times the displacement. Device according to one of claims 12 to 17, in which the electrically heatable catalyst carrier body a cell density of 200 to 400 cpsi (cells per square inch, cells per square inch). Device according to one of claims 12 to 18, in which the electrically heatable catalyst carrier body has for a fluid flow channels on and is constructed so that a mixing of the flow adjacent channels can take place. Device according to one of claims 12 to 19, in which the electrically heatable catalyst carrier body is formed of metallic layers, at least partially have macroscopic structures that are responsible for a fluid form flowable channels. Apparatus according to claim 20, wherein the metallic Layers at least partially have microscopic structures whose Amplitude less than 30% of the amplitude of the macroscopic structures, preferably less than 20%, more preferably less than 10%.