DE102005038187A1 - Exhaust gas cleaning device for lean-burn engines comprises a catalyst for removing nitrogen oxides from an internal combustion engine exhaust gas stream which is guided in a first partial system and in a second connected partial system - Google Patents

Abstract

Exhaust gas cleaning device comprises a catalyst (15) for removing nitrogen oxides from an internal combustion engine exhaust gas stream (12) which is guided in a first partial system (20) and in a second connected partial system (30). Each partial system contains a heating unit (22, 32) for adjusting the exhaust gas temperature. An independent claim is also included for a method for operating an exhaust gas cleaning device. Preferred Features: The exhaust gas is from both partial systems is fed in an exhaust gas mixing site (14) in the exhaust gas flow direction (19) upstream of the catalyst. A particle filter (23, 33) is arranged in each partial system.

Description

The The invention relates to an exhaust gas purification device and a method for operating the same according to the preambles of the independent claims.

It is known in diesel vehicles to use particulate filters, and to reduce ammonia-containing additives to reduce nitrogen oxide emissions. From the published patent WO 99/39809 A1 is an SCR catalyst (SCR = selective catalytic reduction) known, in which by adding be reduced by ammonia nitrogen oxides.

As is known, soot particle filters must be regenerated at regular intervals, whereby stored soot particles are burned in certain operating phases of the internal combustion engine. The exothermic combustion leads to increased exhaust gas temperatures, which can endanger both the particulate filter and downstream catalysts, such as Denox catalysts or SCR catalysts to remove nitrogen oxides. The publication DE 196 18 397 A1 discloses a method for regenerating a soot particulate filter in which additional fuel is added to a predetermined catalyst temperature above its light-off temperature to achieve soot humidification to reduce ignition temperature in the particulate filter.

Of the Invention is based on the object, an exhaust gas purification device and to provide a method of operating the same, thus providing reliable removal from soot and Nitrogen oxides in the exhaust gas of an internal combustion engine achieved as possible component gentle becomes.

The The object is achieved by the Characteristics of the independent claims solved. Favorable price and further developments of the invention are the further claims remove.

at an exhaust gas purification device according to the invention, especially for Lean-burn engines, with a catalyst for the removal of nitrogen oxides from the exhaust stream of an internal combustion engine, is the exhaust stream in some cases in two parts in a first subsystem and one in addition parallel in terms of flow second subsystem feasible. In each subsystem is in each case a heating unit for targeted adjustment an exhaust gas temperature provided. In the heating unit can in Exhaust gas containing hydrocarbons and carbon monoxide are oxidized. pollutants can reliable converted and / or withheld become. A regeneration of one preferably in each of the subsystems Particulate filter can be made while the other particulate filter works normally and soot particles Retains in the exhaust stream. Thereby, that the exhaust gas can be supplied in duplicate is, can Exhaust gas mass flows with different temperature levels are mixed to a favorable mixing temperature in front of a catalyst for removing nitrogen oxides from the exhaust gas to reach. Due to the twin-flow design, exhaust gas mass flows and exhaust gas temperatures be coordinated with each other to an operation of the optimize downstream catalytic converter. In addition, the possibility given, the exhaust gas mass flows dependent on the subsystems from a regeneration state of the particulate filter and to avoid temperature peaks in the particle filter. An invasive Incorporation of hydrocarbons can be avoided by the heating unit become.

Prefers is exhaust from both subsystems in an exhaust gas mixing point in the exhaust gas flow direction upstream of a catalyst for the removal of nitrogen oxides merge. Thereby the resulting exhaust gas temperature can be adjusted so that the operation of the catalyst in a favorable range for the conversion of pollutants, in particular nitrogen oxides, can take place. The catalyst is preferably an SCR catalyst. Furthermore, it is expediently the catalyst a unit for the introduction and treatment of HWL (Urea-water solution) assigned.

Conveniently, the distribution of the exhaust gas flow takes place on the subsystems with a separate partial flow damper in each subsystem.

In a regeneration phase of the particulate filter may be for removal In particular of stored soot particles additionally hydrocarbon, in particular Fuel, fed be to a suitable heat of the Achieve exhaust gas. The additional supplied The amount of fuel expediently depends on the desired temperature the exhaust gas leaving the heating unit and is at the exhaust gas mass flow adapted in the subsystem. This is expediently in the exhaust gas flow direction upstream of the heating unit, a supply of fuel, in particular an injector, provided.

By the heating unit, it is advantageously possible to provide a heat of reaction of exhaust gas of the heating unit for the regeneration of a particulate filter. By the amount of the heating unit in the regeneration phase supplied fuel and / or exhaust gas mass flow can be set actively and selectively a desired temperature of the exhaust gas in a suitable temperature range for Regulated regeneration of the subsequent particulate filter can be used. This is preferably carried out in each case depending on the soot loading of the particulate filter.

Conveniently, is consecutive in each subsystem in exhaust flow direction switched the heating unit, the particle filter and a unit to Removal of hydrocarbons and carbon monoxide arranged. The latter unit advantageously serves to protect the following Catalyst for the removal of nitrogen oxides. The unit is preferably an oxidation catalyst, in particular any by an active Regeneration of the particulate filter resulting hydrocarbons and carbon monoxide removed.

The inventive method for operating an exhaust gas purification device provides that the Exhaust gas stream is distributed in at least two subsystems, wherein a Temperature of an exhaust gas mass flow in at least one subsystem is targeted.

Prefers the respective exhaust gas mass flow in the two subsystems depends on an exhaust gas temperature at the entrance of a catalyst for removal adjusted by nitrogen oxides. This allows targeted temperature of the catalyst are limited and a damage of the same by a unwanted overheating be avoided.

Prefers the exhaust gas mass flow in each of the two subsystems through passed a particle filter.

A Exhaust gas temperature in the exhaust gas mass flow of the respective subsystem can be adjusted specifically, in particular, increased to a regeneration to effect a downstream particulate filter. As a result of that a heat of the exhaust gas is used for regeneration, the particulate filter can be active and be regenerated regulated. Advantageously, in the other subsystem the particle filter continue to operate normally and soot particles out retain the exhaust stream.

Preferably can while a regeneration of the particulate filter in one of the subsystems be reduced in the relevant subsystem of the exhaust gas mass flow. This is already a correspondingly small amount of hydrocarbon sufficient, by oxidation in a heating unit, the temperature increase of the Exhaust mass flow causes. This leads to a consumption saving during operation in the whole system of the exhaust gas purification device. By regulation of the Exhaust gas mass flow through partial flow flaps in each subsystem can the burnup process of soot in Particulate filter especially in transient operation of the internal combustion engine be controlled much better, which advantageous temperature peaks can be avoided in the particle filter.

Becomes heated exhaust gas from the subsystem in which the regeneration of the Particulate filter, before being fed to a catalyst to remove nitrogen oxides by adding exhaust gas from the other Subsystem cooled, can the optimal operation of the catalyst by limiting the temperature can be reached. This is preferably done in one Abgasmischstelle, where the exhaust gas mass flows of the subsystems merged and be mixed to a mixing temperature. In the catalyst is preferably Nitric oxide to nitrogen and water by previously in one unit for the introduction and preparation of a urea-water solution produced Ammonia reduced.

The Invention is especially for so-called lean-burn engines suitable.

Further Advantages and details of the invention are described below a preferred embodiment described in the drawing explained in more detail, without to this embodiment limited to be.

there the single figure shows a schematic representation of a preferred Embodiment of an emission control device according to the invention.

The figure is a preferred exhaust gas purification device 10 to be taken, which is particularly suitable for lean-burn engines. The exhaust gas purification device 10 an internal combustion engine, not shown, comprises a first subsystem 20 to which a second subsystem 30 runs parallel. The subsystems 20 . 30 branch at a branching point 13 in the exhaust tract 11 , The in both subsystems 20 . 30 guided exhaust gas mass flows unite again in an exhaust gas mixing point 14 and become a catalyst designed as an SCR catalyst 15 supplied for the removal of nitrogen oxides. At the entrance 16 is a HWL unit 18 for the introduction and treatment of a urea-water solution (HWL), which provides ammonia, which in the SCR catalyst 15 to reduce the nitrogen oxides (NOx) in the exhaust gas in nitrogen and water is needed. The purified exhaust gas leaves the catalyst 15 at its exit 16 ,

At the branching point 13 is at the beginning in every subsystem 20 . 30 a partial flow flap 21 respectively. 31 arranged, with each separately the exhaust gas mass flow in each subsystem 20 . 30 sett bar is. Instead of two separate flaps may be in the branching point 13 However, a single flap or another actuator may be provided to adjust the exhaust gas streams in the respective subsystems.

In the first subsystem 20 follows in exhaust gas flow direction 19 the partial flow flap 21 a heating unit 22 , via a feeder designed as an injector 25 Hydrocarbon is fed. On the preferably designed as an oxidation catalyst heating unit 22 follows as a particulate filter designed particulate filter 23 to which there is a unity 24 for removal of hydrocarbons and carbon monoxide follows (HC and CO slip), resulting in a regeneration of the particulate filter 23 can form. The unit 24 is preferably also formed as an oxidation catalyst. The two subsystems 20 . 30 are identically constructed, with a corresponding partial flow flap 32 , a heating unit 32 with a hydrocarbon feed 35 , a particle filter 33 and one unit 34 for removal of hydrocarbons and carbon monoxide in the subsystem 30 ,

Due to the partial double-flow guidance of the exhaust gas in the first subsystem 20 and to the flow parallel arranged second subsystem 30 can at the exhaust mixing point 14 one for the operation of the SCR catalyst 15 favorable mixing temperature of the exhaust gas mass flows of the subsystem 20 . 30 can be set, in particular, in the regeneration mode of the particulate filter 23 or 33 the exhaust gas temperature to be limited.

For example, in subsystem 20 the particle filter 23 regenerated and in the particle filter 23 Incinerated soot burned, the second subsystem 30 continue to operate normally. Will be in a subsystem 20 or 30 the particle filter ter 23 or 33 regenerated, takes place in the other subsystem 30 or 20 no regeneration of the particulate filter 33 or 23 instead of and vice versa. By a suitable adjustment of the two partial flow flaps 21 and 31 the exhaust gas mass flow in the first subsystem 20 during the regeneration phase of the local particle filter 23 reduced.

The exhaust gas mass flow in the first subsystem 20 In this phase, only a small proportion of the total exhaust gas flow exiting the internal combustion engine into the exhaust gas tract is preferred 12 , This requires only a small amount of hydrocarbon at the feed 25 in the heating unit 22 be added to the soot in the particulate filter 23 burn. Due to the reduced amount of exhaust gas in the particle filter 23 may be a local overheating of the particulate filter 23 be prevented. The high exhaust gas temperatures resulting from the soot combustion can be achieved by mixing the exhaust gas mass flow into the subsystem 20 with the exhaust gas mass flow in the subsystem 30 in the exhaust mixing point 14 again on one for the reaction of the selective catalytic reduction of the catalyst 15 suitable lower level, which reduces the risk of destruction of the catalyst 15 counteracts and also an improved function of the selective catalytic reduction of the catalyst 15 at Rußabbrand in each particle filter 23 or 33 allows.

A regulation of Rußabbrands in each particle filter 23 or 33 of the first subsystem 20 or in the second subsystem 30 can by regulating the respective exhaust gas mass flow through the partial flow valves 25 . 35 respectively. The combustion process can be controlled much better, especially in transient operation of the internal combustion engine, and temperature peaks in the respective particle filter to be regenerated 23 . 33 can be avoided.

Claims (13)

Exhaust gas purification device, in particular for lean-burn engines, with a catalyst ( 15 ) for the removal of nitrogen oxide from the exhaust gas stream ( 12 ) of an internal combustion engine, wherein the exhaust gas flow ( 12 ) partially in duplicate in a first subsystem ( 20 ) and a second subsystem ( 30 ), whereby in each subsystem ( 20 . 30 ) each have a heating unit ( 22 . 32 ) is provided for the targeted adjustment of an exhaust gas temperature. Exhaust gas purification device according to claim 1, characterized in that exhaust gas from both subsystems ( 20 . 30 ) in an exhaust gas mixing point ( 14 ) in the exhaust gas flow direction ( 19 ) upstream of a catalyst ( 15 ) is merge to remove nitrogen oxides. Exhaust gas purification device according to claim 1 or 2, characterized in that in each subsystem ( 20 . 30 ) a particle filter ( 23 . 33 ) is arranged. Exhaust gas purification device according to one of the preceding claims, characterized in that each subsystem ( 20 . 30 ) a partial flow flap ( 21 . 31 ) for the division of the exhaust gas flow ( 12 ) having. Exhaust gas purification device according to one of the preceding claims, characterized in that in each subsystem ( 20 . 30 ) in the exhaust gas flow direction ( 19 ) upstream of the heating unit ( 22 . 32 ) a feeder ( 25 . 35 ) of fuel is provided. Emission control device according to one of preceding claims, characterized in that a heat tone of exhaust gas of the heating unit ( 22 . 32 ) for the regeneration of the particulate filter ( 23 . 33 ) is provided. Exhaust gas purification device according to one of the preceding claims, characterized in that in each subsystem ( 20 . 30 ) in the exhaust gas flow direction ( 19 ) connected in series the heating unit ( 22 . 32 ), the particle filter ( 23 . 33 ) and a unit ( 24 . 34 ) for the removal of hydrocarbons and carbon monoxide from the exhaust gas mass flow in the subsystem ( 20 . 30 ) are arranged. Method for operating an exhaust gas purification device according to one of the preceding claims, wherein an exhaust gas stream of an internal combustion engine is conducted into the exhaust gas purification device, characterized in that the exhaust gas flow ( 12 ) into at least two subsystems ( 20 . 30 ), wherein a temperature of an exhaust gas mass flow in at least one subsystem ( 20 . 30 ) is targeted. A method according to claim 8, characterized in that the exhaust gas mass flow in the two subsystems ( 20 . 30 ) depending on an exhaust gas temperature at the entrance ( 13 ) of a catalyst ( 15 ) is adjusted to remove nitrogen oxides. A method according to claim 8 or 9, characterized in that the exhaust gas mass flow in each of the two subsystems ( 20 . 30 ) through a particle filter ( 23 . 33 ). Method according to one of claims 8 to 10, characterized in that an exhaust gas temperature in the exhaust gas mass flow of one of the subsystems ( 20 . 30 ) is specifically increased to a regeneration of a particulate filter ( 23 . 33 ) to effect. A method according to claim 11, characterized in that during a regeneration of the particulate filter ( 23 . 33 ) in one of the subsystems ( 20 . 30 ) in the subsystem concerned ( 20 . 30 ) the exhaust gas mass flow is reduced. Method according to one of claims 11 or 12, characterized in that heated exhaust gas from the subsystem ( 20 . 30 ), in which the regeneration of the particulate filter ( 23 . 33 ), before being fed to a catalyst ( 15 ) for removing nitrogen oxides by adding exhaust gas from the other subsystem ( 20 . 30 ) is cooled.