DE102009014361A1 - Exhaust gas treatment device and method for operating an exhaust gas treatment device - Google Patents

Abstract

The invention relates to an exhaust gas treatment device (10) for a vehicle, having an SCR catalytic converter (24) for reducing nitrogen oxides in the exhaust gas of an internal combustion engine (12). The SCR catalytic converter (24) is preceded by at least one turbocharger (16, 18). By means of a metering device (26), a reducing agent can be introduced into the exhaust gas at a point of introduction, which is preferably arranged upstream of a turbine (28) of the at least one turbocharger (18). Upstream of the point of introduction, an oxidation catalytic converter (22) is arranged. Furthermore, the invention relates to a method for operating such an exhaust gas treatment device (10).

Description

The The invention relates to an exhaust gas treatment device for a vehicle with a catalyst for reducing nitrogen oxides in an exhaust gas of an internal combustion engine, wherein the catalyst at least one turbocharger is connected upstream. The exhaust treatment device further comprises a metering device, by means of which a reducing agent is introduced into the exhaust gas at a point of introduction, wherein the discharge point arranged in the region of a turbine of at least one turbocharger is. Furthermore, the invention relates to a method for operating an exhaust treatment device.

The JP 2005061362 A describes an exhaust gas treatment device in which a SCR catalyst (SCR = selective catalytic reduction, selective catalytic reduction) is preceded by a turbocharger. An injector for introducing an aqueous urea solution into the exhaust gas is arranged upstream of a turbine of the turbocharger. The passage of the present in the form of the aqueous urea solution reducing agent through the turbine of the turbocharger here ensures a processing of the urea and providing ammonia upstream of the SCR catalyst. Selective catalytic reduction then converts nitrogen oxide contained in the exhaust gas of the internal combustion engine into nitrogen in the SCR catalytic converter with ammonia liberated from the aqueous urea solution.

The US Pat. No. 6,883,308 B2 describes an exhaust gas treatment device for a vehicle, in which by means of an injector, an aqueous urea solution in a receiving space for a turbine of a turbocharger can be introduced. The introduction point, which is arranged in the region of the turbine and at which the introduction of the aqueous urea solution into the receiving space for the turbine, is formed as an opening in the turbine housing. The treated urea solution is then reacted in an SCR catalyst.

When disadvantageous in such known from the prior art exhaust treatment devices is the circumstance that in some operating conditions the internal combustion engine undesirably lower Sales of nitrogen oxides in the catalyst for reducing nitrogen oxides present can.

task It is therefore an exhaust gas treatment device of the present invention or to provide a method of the type mentioned, which or which an improved nitrogen oxide conversion allows.

These The object is achieved by an exhaust gas treatment device having the features of claim 1, and by a method having the features of claim 11 solved. Advantageous embodiments with expedient developments of the invention are given in the dependent claims.

at the exhaust gas treatment device according to the invention for a vehicle, with a catalyst for reducing of nitrogen oxides in the exhaust gas of an internal combustion engine, wherein the catalyst is preceded by at least one turbocharger, and with a metering device, by means of which a reducing agent at a point of introduction into the exhaust gas can be introduced, which in the area a turbine of the at least one turbocharger is upstream arranged the Einleitstelle an oxidation catalyst.

Of the Oxidation catalyst ensures efficient conversion of unburned hydrocarbons and carbon monoxide already immediately or at least shortly after a cold start of the internal combustion engine. This prevents the catalyst from reducing Nitrogen oxides occupied by unburned hydrocarbons and thus is limited in its effectiveness. Even with longer Thrust and / or idle phases of the internal combustion engine is such poisoning or deactivation of the catalyst Occupancy with unburned hydrocarbons by means of the oxidation catalyst effectively prevented. By arranging the oxidation catalyst close to the engine in particular directly after cylinder outlet of the internal combustion engine the oxidation catalyst reaches its efficiency very quickly Oxidizing unburned hydrocarbons and carbon monoxide required operating temperature.

The Introducer for introducing the reducing agent in the exhaust gas is in the range of the turbine and thus also close to the internal combustion engine arranged. This ensures that in case of a Introducing an aqueous urea solution as Reducing agent, the necessary to treat the urea minimum temperature also already reached very quickly after starting the internal combustion engine is. The arranged in the turbine area discharge point can be arranged in a turbine housing, wherein in a receiving space of the turbine housing, a turbine wheel is received. The Reducing agent is then introduced via the discharge point in the Recording room introduced.

The urea processing and the ammonia uniform distribution is assisted by the fact that the turbine of at least one turbocharger for efficient mixing of the reducing agent with provides the exhaust. The introduction of the reducing agent can take place both upstream and downstream of the turbine. In the former case, the urea treatment and the Geichverteilung of ammonia released from urea is supported by the passage through the turbine. In the second case, the exhaust gas swirl generated by the turbine is advantageously used for mixing the reducing agent with the exhaust gas. This eliminates the need for a mixing element and a comparatively long and thus much space consuming processing line between the point of introduction and the catalyst. The catalyst for reducing nitrogen oxides is, even if downstream from the at least one turbocharger, still advantageously arranged comparatively close to the internal combustion engine and thus also reaches the required minimum temperature for a high conversion of nitrogen oxides very early after the start of the internal combustion engine.

By This overall very compact and close to the engine arrangement of oxidation catalyst and Catalyst for reducing nitrogen oxides can be a particularly low Packing volume and weight of the exhaust treatment device can be achieved. This is achieved with reduced costs and reduced fuel consumption of the vehicle.

In An advantageous embodiment of the invention is the discharge point upstream of the turbine of at least one turbocharger arranged. Compared to arranging the discharge point the turbine housing is thus a more efficient mixing reach of reducing agent and exhaust gas by means of the turbine.

In a further advantageous embodiment of the invention the exhaust treatment device a first turbocharger and a downstream of the first turbocharger arranged second turbocharger, the injection point downstream of the turbine of the first Turbocharger is arranged. As opposed to an alternative as well conceivable embodiment of the exhaust gas treatment device with two-stage turbocharging, in which the discharge point upstream the turbine of the first turbocharger is arranged here is a reduced temperature load of the discharge point given. About that In addition, the exhaust gas is already through the first turbine passage in a flow state which involves mixing exhaust gas and reducing agent favors.

When Furthermore, it has been found to be advantageous if the point of introduction has a in particular against a flow direction of the exhaust gas oriented, nozzle device and / or a baffle element and / or has a mixing device different from the turbine. A such (pre-) mixing device does not increase this the back pressure of the exhaust treatment device at. Through the nozzle device and / or at least one baffle element, for example a baffle plate, and / or the mixing device is an aqueous reducing agent as particularly fine spray can be generated at the discharge point in the exhaust gas.

These Means for providing the spray, ie nozzle device and / or impact element and / or mixing device are preferred designed so that droplet sizes with a Sauter diameter Smd of less than 100 .mu.m, in particular of less than 50 microns, are achievable. By the mentioned Measures, in particular by aligning the nozzle device contrary to the flow direction of the exhaust gas is the danger Damage to turbine blades of an optionally downstream the discharge point arranged turbocharger as a result of larger Droplets caused so-called water hammer diminished.

To the Protection of the blades of the turbine from water hammer can complement it or alternatively be provided to design the metering device so that they introduce the reducing agent into the exhaust gas in gaseous form allows. Also when introducing the reducing agent in gaseous form, such as gaseous ammonia, is mixed of the reducing agent with the exhaust gas through at least one turbine passage supported.

In a further advantageous embodiment of the invention the exhaust gas treatment device one, in particular coated, Particulate filter. This achieves further exhaust gas purification.

has the particulate filter on a noble metal-containing coating, so serves this particular facilitated regeneration of the particulate filter. The Regenerating can be done both actively, with a required increased temperature for a thermal burnup of particulate matter retained by the particulate filter with oxygen contained in the exhaust gas by introducing and oxidizing achieved by fuel into the exhaust upstream or in the particulate filter becomes. Additionally or alternatively, a passive regeneration be used, in which the soot particles by means of Nitrogen dioxide are oxidized. This passive regeneration will also referred to as the CRT effect of the particulate filter (CRT = continuous regenerating trap, continuously regenerating particle trap).

The particle filter can also form a unit together with the catalyst for reducing nitrogen oxides, wherein the particulate filter is then preferably at least partially with a kata lysatormaterial coated, which has the function of an SCR catalyst. As a result, a particularly compact design of the exhaust gas treatment device can be achieved. Alternatively, the particulate filter may be disposed downstream of the SCR catalyst for reducing nitrogen oxides. An optionally present oxidation catalytic coating of the particulate filter functions in this case in an advantageous manner as a so-called barrier catalyst for the oxidation of slipping through the SCR catalyst ammonia. Furthermore, a further oxidation catalytic converter can be arranged between the SCR catalytic converter and the particle filter. Such a further oxidation catalyst then also fulfills the function of a blocking catalyst.

In a further advantageous embodiment of the invention is a Bypass line provided for bypassing the turbine of at least one turbocharger. Such a bypass line is particularly suitable for two-stage Turbocharging to bypass the turbine of the second turbocharger. By Bypassing the turbine of the second turbocharger is even faster in particular after a cold start of the internal combustion engine, at the SCR catalyst the required minimum temperature for reach a high conversion of nitrogen oxides. The first turbocharger can then continue to provide charged charge air serve. However, even with a one-stage charge can bypass the turbocharger turbine for rapid heating of the SCR catalyst be used and then the Dosierfreigabe for the metering device take place for dosing of the reducing agent.

In Advantageously, the bypass line has a shut-off device on, by means of which the bypass line at least partially lockable is. This allows a desired exhaust flow through the Bypass line and / or adjusted by the turbine as needed become. Heating the SCR catalyst by bypassing the turbine at least one turbocharger stands out against alternatives, in which the internal combustion engine with an attached or late post-injection, through improved efficiency. Furthermore This is with an accumulated or late post-injection accompanying risk of oil thinning so not given.

In a further advantageous embodiment of the invention the exhaust gas treatment device at least one, in particular upstream of a Compressor of at least one turbocharger in an air supply tract opening, exhaust gas recirculation line. Especially such a low-pressure exhaust gas recirculation line can additionally or alternatively provided to a high-pressure exhaust gas recirculation line be in which the recirculated exhaust gas in the compressed charge air is introduced. Used as a reducing agent the aqueous urea solution used, so can the water from the aqueous urea solution over the low-pressure exhaust gas recirculation line into the combustion chamber enter the internal combustion engine and by reducing the Final combustion temperature to reduced raw emissions of nitrogen oxides to lead.

By the high specific heat capacity of the water can be so beneficial the consumption and power density the combustion can be improved. This contributes at reduced Reducing agent requirement for improved conversion efficiency in Reacting the nitrogen oxides, both during combustion as well as in the exhaust aftertreatment. In addition, it is so the thermodynamic efficiency of combustion can be improved.

After all it has proved to be advantageous if the metering device depending on a temperature of the turbine of the at least one turbocharger acting on exhaust gas controlled is. Thus, the introduction of the aqueous reducing agent specifically used for component protection, such as when the turbine particularly high exhaust gas temperatures, for example, temperatures of more as 850 ° C, is exposed.

According to one Another aspect of the invention enables a method for operating an exhaust gas treatment device for a Vehicle an improved nitrogen oxide conversion, in which a turbine at least one turbocharger from the exhaust gas of an internal combustion engine is flowed through, in which by means of a metering device a reducing agent introduced at a point of introduction into the exhaust gas which is arranged on the turbine of the at least one turbocharger is, and in which a downstream of the turbine arranged Catalyst for reducing nitrogen oxides flows through the exhaust gas becomes. This is an upstream of the discharge point arranged oxidation catalyst flows through the exhaust gas.

The for the exhaust gas treatment device according to the invention described preferred embodiments and advantages also apply to the invention Method for operating an exhaust gas treatment device.

The features and feature combinations mentioned above in the description as well as the below mentioned in the figure description and / or in the figure alone shown features and feature combinations are not only in the specified combination, but also usable in other combinations or in isolation, without to leave the scope of the invention.

Further Advantages, features and details of the invention will become apparent the claims, the following description of a preferred embodiment as well as the drawing.

These shows a schematic exhaust gas treatment device of a vehicle with two-stage turbocharging.

The figure shows an exhaust gas treatment device 10 for treating exhaust gas of a diesel engine 12 of a vehicle. An exhaust system of the exhaust gas treatment device 10 includes an exhaust manifold 14 , which with the cylinder outlets of the diesel engine 12 communicates. In the exhaust system is a high-pressure turbocharger 16 which is a low-pressure turbocharger 18 is downstream. Upstream of a turbine 20 of the high pressure turbocharger 16 is an oxidation catalyst 22 arranged.

The very close to the engine arranged oxidation catalyst 22 ensures that immediately after a cold start of the diesel engine 12 unburned hydrocarbons and carbon monoxide are very widely implemented. This prevents one downstream of the low pressure turbocharger 18 arranged SCR catalyst 24 exposed to unburned hydrocarbons and is poisoned. However, it may also be an arrangement of the oxidation catalyst 22 in the area between the turbine 20 of the high pressure turbocharger 16 and a turbine 28 of the low-pressure turbocharger 18 be provided. This allows the space between the exhaust manifold 14 and turbine 20 of the high pressure turbocharger 16 be optimized and a larger volume for the oxidation catalyst 22 will be realized.

For introducing an aqueous urea solution into the exhaust line, a metering valve is present 26 intended. Here is a discharge point, at which by means of the metering valve 26 the urea water solution can be introduced into the exhaust gas, downstream of the turbine 20 of the high pressure turbocharger 16 and upstream of the turbine 28 of the low-pressure turbocharger 18 arranged.

That's how the turbine works 28 of the low-pressure turbocharger 18 for an intensive mixing of exhaust gas with the finest droplets of the aqueous urea solution, for the treatment of the urea with release of ammonia and for an equal distribution of ammonia in the exhaust gas. As a result, it is possible to dispense with the provision of a processing line requiring a great deal of installation space and an additional mixing device which increases the exhaust gas counterpressure of the exhaust gas line. The oxidation catalyst 22 and the SCR catalyst 24 are arranged very close to the engine and reach so quickly their minimum required for treating the exhaust gas temperature even after the cold start of the diesel engine 12 ,

The metering valve 26 is controllable by means of a control device not shown herein, wherein an introduction of the aqueous urea solution in the exhaust line can also be provided when particularly high exhaust gas temperatures, such as temperatures of more than 850 ° C, otherwise to a very high thermal load on the turbine 28 would lead. In this case, the introduction of the aqueous urea solution can be provided as a pure temperature protection measure, regardless of a Stickstoffoxidverminderungsbedarf, in which to cool exhaust gases by applying heat of vaporization.

In a first bypass line to bypass the turbine 20 of the high pressure turbocharger 16 is a first control flap 30 arranged. Is this flap 30 opened, the exhaust gas preferably flows through the bypass line without the turbine 20 drive.

In an analogous way, the turbine 28 of the low-pressure turbocharger 18 also a bypass line, which by means of a second control valve 32 is releasable. If the exhaust bypassing the first turbine 20 and / or second turbine 28 the SCR catalyst 24 is supplied, this SCR catalyst achieved 24 its operating temperature is particularly fast.

With the achievement of the operating temperature of the SCR catalyst 24 the metering release can be done and it can through the metering valve 26 the aqueous urea solution are introduced into the exhaust gas. In this case, then blocking the bypass line leads to bypassing the turbine 28 by means of the control flap 32 for the rapid and efficient processing of the urea and the supply of ammonia. The ammonia liberated from the aqueous urea solution provides for the turbine 28 downstream SCR catalyst 24 for converting nitrogen oxides into nitrogen by Selective Catalytic Reduction (SCR).

Downstream of the SCR catalyst 24 is a particle filter 34 arranged. The particle filter 34 In this case, it has a noble metal coating which supports an active and passive regeneration. During active regeneration of the particle filter 34 by introducing fuel for burning off through the particulate filter 34 Particles removed from the exhaust stream is the metering valve 26 exposed to comparatively low thermal loads, since it is comparatively far away from the particle filter 34 and in addition the SCR catalyst 24 serves as a heat sink. The one with an oxidation-catalytically active coating provided particulate filter 34 at the same time serves as a barrier catalyst to prevent ammonia from leaking into the environment via the exhaust gas. Alternatively or additionally, the particulate filter 34 also have a catalytic coating with an SCR function. This will increase the total available active volume for nitrogen oxide reduction and the particulate filter 34 can additionally store ammonia. In addition to increasing nitrogen oxide reduction performance, it also prevents the escape of ammonia into the environment. If both a catalytic coating with oxidation function and with SCR function are provided, an oxidation catalytic effective coating section of the particle filter is preferred 34 arranged downstream with respect to SCR catalytic coating section.

Downstream of the particulate filter 34 the exhaust line has a branch 36 on, at which a low-pressure exhaust gas recirculation line 38 branches. The low-pressure exhaust gas recirculation line 38 opens after flowing through an exhaust gas recirculation cooler 40 upstream of a compressor 42 of the low-pressure turbocharger 18 in an air supply tract 44 of the diesel engine 12 , Upstream of the junction of the low pressure exhaust gas recirculation line 38 indicates the air supply tract 44 an air filter 46 on.

By means of a bypass line 48 is the compressor of the high pressure turbocharger 16 passable if no two-stage charging is to take place. Likewise, in the air supply tract 44 a charge air cooler 50 bypassed by a bypass line.

About the low-pressure exhaust gas recirculation line 38 is water from the urea-water solution in the air supply tract 44 and so into the combustion chamber of the diesel engine 12 recoverable. This can be used to produce a raw emission of nitrogen oxides from the diesel engine 12 while at the same time improving fuel consumption and power density.

In the present case, a multi-way exhaust gas recirculation system is provided which has a second exhaust gas recirculation line 52 includes. This also an exhaust gas recirculation cooler 54 having exhaust gas recirculation line 52 opens upstream of a charge air manifold in the air supply tract 44 in the figure is further a high-pressure pump 56 represented by means of which diesel at high pressure in the combustion chamber of the diesel engine 12 can be introduced.

In an alternative embodiment of the exhaust gas treatment device, not shown here, the metering valve 26 downstream of the oxidation catalyst 22 and upstream of the turbine 20 of the high pressure turbocharger 16 be arranged. Here then can the turbine 20 of the high pressure turbocharger 16 alone, or depending on the position of the control valves 30 . 32 only the turbine 28 of the low-pressure turbocharger 18 or both turbines 20 . 28 contribute to the mixing of exhaust gas and reducing agent.

In this embodiment, the metered addition of the aqueous urea solution upstream of the turbine 20 of the high pressure turbocharger 16 specifically for cooling the exhaust gas and thus reducing thermal stress on the turbine 20 be used.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - JP 2005061362 A [0002]
• US 6883308 B2 [0003]

Claims (12)

Exhaust treatment device for a vehicle, with a catalytic converter ( 24 ) for reducing nitrogen oxides in an exhaust gas of an internal combustion engine ( 12 ), wherein the catalyst ( 24 ) at least one turbocharger ( 16 . 18 ) is connected upstream, and with a metering device ( 26 ), by means of which a reducing agent at an inlet point into the exhaust gas can be introduced, which in the region of a turbine ( 28 ) of the at least one turbocharger ( 18 ), characterized in that an oxidation catalyst is arranged upstream of the point of introduction. Exhaust treatment device according to claim 1, characterized in that the inlet point upstream of the turbine ( 28 ) at least one turbocharger ( 18 ) is arranged. Exhaust treatment device according to claim 1 or 2, characterized in that the exhaust gas treatment device ( 10 ) a first turbocharger ( 16 ) and a downstream of the first turbocharger ( 16 ) arranged second turbocharger ( 18 ), wherein the injection point downstream of the turbine ( 20 ) of the first turbocharger ( 16 ) is arranged. Exhaust treatment device according to one of claims 1 to 3, characterized in that the inlet point a, in particular against a flow direction of the exhaust gas aligned, nozzle means and / or a baffle element and / or one of the turbine ( 28 ) has different mixing device. Exhaust treatment device according to one of claims 1 to 4, characterized in that the metering device ( 26 ) is designed for introducing the reducing agent into the exhaust gas in gaseous form. Exhaust treatment device according to one of claims 1 to 5, characterized in that the exhaust gas treatment device ( 10 ) a, in particular coated, particulate filter ( 34 ). Exhaust treatment device according to claim 6, characterized in that the particulate filter ( 34 ) downstream of the catalyst ( 24 ) is arranged for reducing nitrogen oxides, in particular with the interposition of a further oxidation catalyst. Exhaust treatment device according to one of claims 1 to 7, characterized in that a, in particular by means of a shut-off device ( 30 . 32 ) at least partially lockable, bypass line for bypassing the turbine ( 20 . 28 ) of the at least one turbocharger ( 16 . 28 ) is provided. Exhaust treatment device according to one of claims 1 to 8, characterized in that the exhaust gas treatment device ( 10 ) at least one, in particular upstream of a compressor ( 42 ) of the at least one turbocharger ( 18 ) into an air supply tract ( 44 ), exhaust gas recirculation line ( 38 . 52 ). Exhaust treatment device according to one of claims 1 to 9, characterized in that the metering device ( 26 ) depending on a temperature of the turbine ( 20 . 28 ) of the at least one turbocharger ( 16 . 18 ) acting on exhaust gas is controllable. Method for operating an exhaust gas treatment device ( 10 ) for a vehicle in which a turbine ( 20 . 28 ) at least one turbocharger ( 16 . 18 ) of exhaust gas of an internal combustion engine ( 12 ) is flowed through, wherein by means of a metering device ( 26 ) a reducing agent is introduced at a point of introduction into the exhaust gas, which in the region of the turbine ( 28 ) of the at least one turbocharger ( 18 ), and in which a downstream of the turbine ( 28 ) arranged catalyst ( 24 ) is passed through for the reduction of nitrogen oxides of the exhaust gas, characterized in that an upstream of the discharge point arranged oxidation catalyst ( 22 ) is flowed through by the exhaust gas. A method according to claim 11, characterized in that it by means of an exhaust gas treatment device ( 10 ) is carried out according to one of claims 1 to 10.