DE102006014073A1 - Exhaust gas after-treatment device for internal-combustion engine, has selective catalytic reduction catalytic converter unit for selective catalytic reduction of nitrogen oxides with exhaust gas inlet and exhaust gas outlet - Google Patents

Abstract

The device has a selective catalytic reduction (SCR) catalytic converter unit (10) for selective catalytic reduction of nitrogen oxides with an exhaust gas inlet (12) and an exhaust gas outlet (14). The unit is provided with a parallel connection of a SCR main catalytic converter (18) and a SCR auxiliary catalytic converter (20). The main converter is designed for complete exhaust gas mass flow through the unit, and the auxiliary converter is designed for a smaller exhaust gas flow than the main converter. A blocking device of the unit blocks the exhaust gas flow through the main converter.

Description

The The present invention relates to an exhaust aftertreatment device and an exhaust aftertreatment method for an internal combustion engine with an SCR catalyst unit for selective catalytic reduction of nitrogen oxides.

In Automotive technology are particularly in diesel internal combustion engines To reduce the nitrogen oxides in the exhaust gas mass flows so-called SCR catalysts known. For selective catalytic reduction of nitrogen oxides is in the exhaust gas mass flow usually an aqueous urea solution (HWL) injected, from which ammonia is formed, which at appropriate Temperature in the SCR catalyst with the nitrogen oxides as reducing agent responding. SCR catalysts are commonly used in vehicles used with other types of catalysts and particulate filters.

to effective reduction of nitrogen oxides require the SCR catalysts a Catalyst temperature which is above a light-off temperature of about 170 ° C to 200 ° C is. In city operation, the exhaust gas temperature is at low load phases often below this light-off temperature. This leads to a warm catalyst, for example during long idle periods cools and then at subsequent High load phases are not immediately ready for use.

The The present invention has been made in view of this problem. It is therefore an object of the invention to provide an exhaust aftertreatment device and an exhaust aftertreatment method for an internal combustion engine with an SCR catalyst unit, where the efficiency the entire system is improved in dynamic driving.

In this context is from the DE 197 40 702 C1 an exhaust aftertreatment device with an SCR catalyst is known, with which the nitrogen oxide emission is to be reduced in particular at load increases and warming up of the internal combustion engine. For this purpose, a bypass to the exhaust gas passage is provided upstream of the SCR catalyst, through which the exhaust gas mass flow can be passed through an adsorption catalyst in certain operating conditions (rapid load increase, warm-up) in which the nitrogen oxides contained in the exhaust gas are adsorbed.

According to the present The invention achieves the above object by an exhaust aftertreatment device with the features of claim 1 and an exhaust aftertreatment process with the features of claim 15 solved. Advantageous embodiments and further developments of the invention are the subject of the respective Dependent claims.

The Exhaust after-treatment device for an internal combustion engine has an SCR catalyst unit for selective catalytic reduction of nitrogen oxides with an exhaust gas inlet and an exhaust gas outlet on. According to the invention this SCR catalyst unit on: a parallel connection of a SCR main catalyst and an SCR minor catalyst, the SCR main catalyst for the complete Exhaust gas mass flow through the SCR catalyst unit is designed and the SCR by-pass catalyst for designed a lower exhaust gas mass flow than the SCR main catalyst is; a locking device for blocking the exhaust gas mass flow through the SCR main catalyst; and a control device for controlling the operation of the locking device such that the exhaust gas mass flow is locked by the SCR main catalyst when the exhaust gas temperature falls below a predetermined temperature, with a light-off temperature of the main SCR catalyst.

Of the SCR main catalyst has a specific light-off temperature, Above the reduced nitrogen oxides in the flowing exhaust gas mass flow become. If the light-off temperature occurs during a dynamic engine operation falls below the exhaust gas temperature, the engine is usually operated at very low load and the exhaust gas mass flows also low. In the map areas with very low exhaust gas mass flow and low exhaust gas temperature can therefore be the SCR main catalyst be locked by the locking device. The whole, in this Case lower exhaust mass flow then flows through the SCR by-pass catalyst, which is dimensioned so that it contains the nitrogen oxides in these lower Exhaust gas mass flow can reduce.

By the shutdown or locking of the SCR main catalyst at low Exhaust gas temperatures will cool of the SCR main catalyst through flowing through Exhaust gases avoided. If the internal combustion engine then again at higher Load operated so that the exhaust gas temperature again over the Light-off temperature of the SCR main catalyst increases, the Locking device reopened. The SCR main catalytic converter is immediately ready for use as it through the cooler Exhaust gas mass flow not cooled has, and can reduce the nitrogen oxides. In addition, preferably also continues the SCR by-pass catalyst is switched into the exhaust stream and can also flows through exhaust gas become.

Locking of the SCR main catalyst by the low-exhaust lock-up device Thus, in dynamic operation, for example in the inner city area, the SCR main catalytic converter is heated outside low-load phases and does not cool sufficiently within the low-load phases of the internal combustion engine that are connected to very low exhaust gas temperatures Higher exhaust gas temperature must first be heated up again until it reaches its effectiveness. Thus, the efficiency of the entire system is significantly increased in the dynamic operation of the internal combustion engine.

The Locking device is preferably at the outlet of the SCR main catalyst provided, but may also be attached to his entrance.

When Measure of the exhaust gas temperature For example, one may be detected by a temperature sensing device detected temperature of the exhaust gas mass flow through the SCR catalyst unit, a volume of the volume detected by a volume detecting device Exhaust gas mass flow through the SCR catalyst unit, a through a Load detection device detected load state of the internal combustion engine or are used, which sizes in certain reciprocal Relate to each other.

In An embodiment of the invention has the SCR side catalyst a lower light-off temperature than the SCR main catalyst and is for exhaust gas temperatures below about 250 ° C, preferably below about 200 ° C designed. In addition, the SCR Nebenkatalysator for example for exhaust gas mass flows of about 10-20% of those of the SCR main catalyst designed. Accordingly the SCR side catalyst has a volume which is preferably only about 10-20% of the SCR main catalyst volume is.

In Another aspect of the invention is the SCR minor catalyst Furthermore provided with a nitric oxide storage coating.

In A still further embodiment of the invention, the SCR catalyst unit further a flow guide for conducting essentially the entire exhaust gas mass flow through the SCR main catalyst open Locking device on. If the SCR side catalyst with the nitrogen oxide storage coating is provided by the flow guide prevents the exhaust gas mass flows with very high temperatures through the SCR by-pass catalyst and the heated coating then oxidizing the reducing agent. For the SCR by-pass catalyst can therefore advantageously a coating with oxidation catalytic Effect chosen become. The flow guide For example, as a fixed guide or an adjustable Flap element be formed.

In an embodiment of the invention, the locking device is through the control device by compressed air (in particular in the case of Commercial vehicles), by electric actuators or by the exhaust back pressure self-actuated.

The Temperature sensing device for the exhaust gas temperature can upstream, downstream and / or within the SCR catalyst unit be arranged.

In Another embodiment of the invention is in the usual way upstream of SCR catalyst unit comprises a reducing agent adding device for Injecting a reducing agent provided in the exhaust gas mass flow. This is preferably an adding device for aqueous urea solution or another, with regard to nitrogen oxide reduction in oxidizing Conditions selective reducing agent.

The Exhaust gas aftertreatment process for a Internal combustion engine with an SCR catalyst unit for selective catalytic reduction of nitrogen oxides is characterized according to the invention characterized the SCR catalytic converter unit is a parallel circuit of an SCR main catalytic converter and an SCR minor catalyst wherein the SCR main catalyst for the entire exhaust gas mass flow is designed by the SCR catalyst unit and the SCR side catalyst for a lesser Exhaust gas mass flow is designed as the SCR main catalyst; and that the exhaust gas mass flow is blocked by the SCR main catalyst, if the exhaust gas temperature falls below a predetermined temperature, which is related to a light-off temperature of the SCR main catalyst.

When Measure of the exhaust gas temperature is a temperature of the exhaust gas mass flow through the SCR catalyst unit, a volume of the exhaust gas mass flow through the SCR catalyst unit, detected a load state of the internal combustion engine or the like.

Of the Exhaust gas mass flow through the SCR main catalyst is in particular blocked if the exhaust gas temperature is the light-off temperature of the SCR main catalytic converter below. And preferably will be above the given Temperature substantially the entire exhaust gas mass flow through the SCR main catalyst directed.

With This method also has the effects described above and benefits.

Above and other features and advantages of the invention will become apparent from the following description of a preferred, non-limiting embodiment of the invention with reference to the accompanying drawings better understandable. Show:

1 a schematic representation of the structure of an SCR catalyst unit according to a preferred embodiment of the present invention; and

2 a schematic timing diagram for explaining the operation of the SCR catalyst unit of 1 ,

In 1 schematically is the structure of an SCR catalyst unit 10 an exhaust aftertreatment device of an internal combustion engine, in particular a diesel engine of a commercial vehicle. The SCR catalyst unit 10 consists in particular of a common housing 11 with an upstream exhaust inlet 12 and a downstream exhaust outlet 14 , in which an SCR main catalyst 18 and an SCR minor catalyst 20 are arranged in parallel. Upstream of the SCR catalyst unit 10 is a reducing agent adding device in the usual way ( 16 ), for example, for injecting an aqueous urea solution (HWL) into the exhaust gas mass flow to provide ammonia as a reducing agent for the nitrogen oxides. Alternatively, gaseous ammonia or ammonia can also be injected directly in aqueous solution. Accordingly, the main SCR catalyst 18 and the SCR minor catalyst 20 for the selective reduction of nitrogen oxides under oxidizing conditions using the preferably selectively acting reducing agent. The catalysts 18 . 20 are preferably designed as so-called full catalysts or as coated catalysts in honeycomb construction.

For detecting the exhaust gas temperature are one or more temperature sensing devices 22 - 25 upstream, downstream and / or within the SCR catalyst unit 10 arranged.

Instead of a direct measurement of the exhaust gas temperature by the temperature sensing device (s) 22 - 25 In principle it is also possible, as a measure of this exhaust gas temperature, to determine a volume of the exhaust gas mass flow through the SCR catalyst unit detected by a volume detection device 10 to use a load state of the internal combustion engine or the like detected by a load detecting device, since these quantities are in certain mutual relationship to each other.

The SCR main catalyst 18 is for the entire exhaust gas mass flow through the SCR catalyst unit 10 designed and has a usual light-off temperature of about 170-200 ° C. The SCR by-pass catalyst 20 on the other hand is for significantly lower exhaust gas mass flows, for example of about 10-20% of that of the main SCR catalytic converter 20 designed. In addition, the SCR by-pass catalyst has 20 a lower light-off temperature than the SCR main catalyst 18 , For example, it is designed for operation in an exhaust gas temperature range below about 200-250 ° C.

The SCR by-pass catalyst 20 is also preferably provided with a coating that can store nitrogen oxides. The coating is preferably designed so that nitrogen oxides, in particular at low temperatures of, for example, less than 200 ° C can be stored. In the case of a temperature-induced low catalytic nitrogen oxide conversion thus nitrogen oxides can be removed by storage at least partially from the exhaust stream.

Preferably at the outlet of the SCR main catalyst 20 , but optionally also at the entrance, is still a blocking device 26 for blocking the exhaust mass flow through the SCR main catalyst 18 or switching off the SCR main catalytic converter 18 arranged. This locking device 26 is by an electronic control device 28 depending on the temperature sensing device (s) 22 - 25 measured exhaust gas temperature. The operation of the locking device 26 itself is preferably carried out in commercial vehicles with compressed air (as in the illustration of 1 indicated), but can also be done by electric actuators or independently by the exhaust back pressure.

In contrast, the SCR minor catalyst 20 not switched or always open and therefore can always be traversed by the exhaust gases of the internal combustion engine.

Upstream of the main SCR catalytic converter 18 and the SCR minor catalyst 20 is in the case 11 the SCR catalyst unit 10 further a flow guide 30 in the form of a solid guide (as in 1 shown) or an adjustable flap element arranged.

For large exhaust gas mass flows and open locking device 26 is through this flow guide 30 essentially the entire exhaust gas mass flow through the SCR main catalytic converter 18 passed, which is dimensioned for these large exhaust gas mass flows. This avoids the nitrogen oxide storage coating of the SCR by-pass catalyst 20 through the exhaust gas masses Higher temperature streams is heated and then oxidized the reducing agent. At low exhaust gas temperature, ie with the locking device closed 26 , And small exhaust gas mass flows reach this despite the Strömungsleiteinrichtung 30 through the SCR by-pass catalyst 20 ,

As with conventional exhaust aftertreatment device, the SCR catalyst unit 10 be combined with other catalysts and / or particulate filters for the aftertreatment of the exhaust gases of the internal combustion engine.

It will now be the operation of the SCR catalyst unit 10 explained in more detail.

The SCR main catalyst 18 has a light-off temperature below which it can reduce only a few or no nitrogen oxides. The exhaust gas temperature in the system is detected by the temperature sensing device (s) 22 - 25 determined.

If an exhaust gas temperature is reached in a dynamic operation of the internal combustion engine (eg when driving the motor vehicle in the inner city area), which is the light-off temperature of the SCR main catalyst 18 or falls below a predetermined level higher predetermined temperature, the internal combustion engine is usually operated at very low load, so that the exhaust gas mass flows are low. Typically, these are operating points with an engine load or engine speed that are less than about 20% of their respective nominal values. In these Kennfeldberei surfaces with low exhaust gas temperature and low exhaust gas mass flows, the locking device 26 through the control device 28 operated, ie closed. The entire exhaust gas mass flow then flows through the SCR by-pass catalyst 20 , which is sufficiently dimensioned for these lower exhaust gas mass flows.

By disabling or disabling the SCR main catalyst 18 At low exhaust gas temperatures, the SCR main catalyst will cool down 18 avoided by the flowing exhaust gases. If the internal combustion engine is later operated again at higher load in dynamic operation, so that the exhaust gas temperature in the SCR catalyst unit 10 above the light-off temperature of the main SCR catalytic converter 18 lies or at least above a possibly also computational ascertained SCR main catalyst temperature, then the blocking device 28 through the control device 28 opened again. The SCR main catalyst 18 is, since he has not cooled down or only insignificantly in the meantime, immediately ready for use to reduce the nitrogen oxides in the exhaust gas mass flow.

The blocking of the SCR main catalyst 18 At low exhaust gas temperatures, therefore, that in the dynamic operation of the internal combustion engine, such as in a motor vehicle in the inner city area, the SCR main catalyst 18 is heated during the high load phases of the internal combustion engine and in the operating phases of the internal combustion engine, which show very low exhaust gas temperatures, not so far cool that he would have to warm up again at a subsequent high load phase until it reaches its functionality. This significantly increases the efficiency of the overall system during dynamic operation.

2 shows to illustrate the relationships described above, an exemplary time profile of the exhaust gas temperature and the temperature of an SCR catalyst 18 with and without locking device 26 ,

In a first phase 1 in 2 is the exhaust gas temperature in the SCR catalyst unit 10 For example, in high-load operation of the internal combustion engine above the light-off temperature of the SCR main catalyst 18 , The locking device 26 is open, the hot exhaust gases flow through the SCR main catalyst 18 and also the temperature of the SCR main catalyst 18 is above its light-off temperature, so it shows its full functionality.

In dynamic operation of the internal combustion engine, the motor vehicle is operated in a subsequent phase 2 at low load. The exhaust gas temperature falls below the light-off temperature of the SCR main catalyst 18 why, in the case of the present invention, the locking device 26 through the control device 28 closed and the exhaust gas mass flow through the SCR main catalyst 18 is locked. The SCR main catalyst 18 can thus keep its temperature substantially unchanged, since heat is released exclusively by heat conduction and radiation to the outside.

In phase 3, the light-off temperature of the main SCR catalyst becomes 18 exceeded by the exhaust gas temperature again. The locking device 26 is opened and the entire exhaust gas mass flow flows through the SCR main catalyst again 18 , As the temperature of the SCR main catalyst 18 is always above its light-off temperature, it is immediately functional and reduces the nitrogen oxides in the exhaust gas mass flow.

For comparison, in 2 also the case of a conventional SCR catalyst without blocking device shown.

If the SCR catalyst is not closed in phase 2, the lower temperature exhaust gases continue to flow through the SCR catalyst and Its temperature falls below the light-off temperature after a short time. If the exhaust gas temperature in phase 3 again exceeds the light-off temperature of the SCR catalytic converter, then the conventional SCR catalytic converter requires a certain time until its temperature again reaches the light-off temperature. During this time, although the hot exhaust gases flow through the SCR catalyst, this can not effectively reduce the nitrogen oxides, since its temperature is still below the light-off temperature.

Claims (21)

Exhaust after-treatment device for an internal combustion engine, with an SCR catalyst unit ( 10 ) for the selective catalytic reduction of nitrogen oxides with an exhaust gas inlet ( 12 ) and an exhaust outlet ( 14 ), characterized in that the SCR catalyst unit ( 10 ) comprises: a parallel connection of a main SCR catalytic converter ( 18 ) and an SCR by-pass catalyst ( 20 ), the SCR main catalyst ( 18 ) for the entire exhaust gas mass flow through the SCR catalyst unit ( 10 ) and the SCR by-pass catalyst ( 20 ) for a lower exhaust gas mass flow than the SCR main catalytic converter ( 18 ) is designed; A locking device ( 26 ) for blocking the exhaust gas mass flow through the SCR main catalytic converter ( 18 ); and a control device ( 28 ) for controlling the operation of the locking device ( 26 ) such that the exhaust gas mass flow through the SCR main catalytic converter ( 18 ) is blocked when the exhaust gas temperature falls below a predetermined temperature, which with a light-off temperature of the SCR main catalyst ( 18 ) is related. Exhaust after-treatment device for an internal combustion engine according to claim 1, characterized in that the locking device ( 26 ) at the inlet or outlet of the main SCR catalytic converter ( 18 ) is provided. Exhaust after-treatment device for an internal combustion engine according to claim 1 or 2, characterized in that further comprises a temperature sensing device ( 22 - 25 ) for detecting a temperature of the exhaust gas mass flow through the SCR catalyst unit ( 10 ) is provided. Exhaust after-treatment device for an internal combustion engine according to claim 1 or 2, characterized in that further comprises a volume detecting device for detecting a volume of the exhaust gas mass flow through the SCR catalyst unit (14). 10 ) is provided. Exhaust after-treatment device for an internal combustion engine according to Claim 1 or 2, characterized in that further comprises a load detection device provided for detecting a load state of the internal combustion engine is. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the SCR secondary catalytic converter ( 20 ) a lower light-off temperature than the SCR main catalyst ( 18 ) owns. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the SCR secondary catalytic converter ( 20 ) is designed for exhaust gas temperatures below about 250 ° C, preferably below about 200 ° C. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the SCR secondary catalytic converter ( 20 ) for exhaust gas mass flows of about 10-20% of that of the SCR main catalyst ( 18 ) is designed. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the SCR secondary catalytic converter ( 20 ) is provided with a nitrogen oxide storage coating. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the SCR catalyst unit ( 10 ) further comprises a flow guiding device ( 30 ) for conducting substantially all of the exhaust mass flow through the main SCR catalyst ( 18 ) with the locking device open ( 26 ). Exhaust after-treatment device for an internal combustion engine according to claim 10, characterized in that the flow guiding device ( 30 ) is formed as a fixed guide element or an adjustable flap element. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the locking device ( 26 ) by the control device ( 28 ) is actuated by compressed air, by electric actuators or by an exhaust gas back pressure. Exhaust after-treatment device for an internal combustion engine according to one of the preceding claims, characterized in that the temperature sensing device ( 22 - 25 ) upstream, downstream and / or within the SCR catalyst unit ( 10 ) is arranged. Exhaust after-treatment device for a Internal combustion engine according to one of the preceding claims, characterized in that upstream of the SCR catalyst unit ( 10 ) a reducing agent adding device ( 16 ) is provided for adding a reducing agent in the exhaust gas mass flow. Exhaust gas aftertreatment process for an internal combustion engine with an SCR catalyst unit ( 10 ) for the selective catalytic reduction of nitrogen oxides, characterized in that the SCR catalyst unit ( 10 ) a parallel connection of a SCR main catalytic converter ( 18 ) and an SCR by-pass catalyst ( 20 ), wherein the main SCR catalyst ( 18 ) for the entire exhaust gas mass flow through the SCR catalyst unit ( 10 ) and the SCR by-pass catalyst ( 20 ) for a lower exhaust gas mass flow than the SCR main catalytic converter ( 18 ) is designed; and the exhaust gas mass flow through the SCR main catalyst ( 18 ) is blocked when the exhaust gas temperature falls below a predetermined temperature, which with a light-off temperature of the SCR main catalyst ( 18 ) is related. Exhaust gas aftertreatment method for an internal combustion engine according to claim 15, characterized in that a temperature of the exhaust gas mass flow through the SCR catalyst unit ( 10 ) is detected as a measure of the exhaust gas temperature. An exhaust aftertreatment process for an internal combustion engine according to claim 15, characterized in that a volume of the exhaust gas mass flow through the SCR catalyst unit ( 10 ) is detected as a measure of the exhaust gas temperature. Exhaust after-treatment process for an internal combustion engine according to Claim 15, characterized in that a load state of the internal combustion engine as a measure of the exhaust gas temperature is detected. An exhaust aftertreatment process for an internal combustion engine according to any one of claims 15 to 18, characterized in that the exhaust gas mass flow through the SCR main catalyst ( 18 ) is blocked when the exhaust gas temperature is the light-off temperature of the SCR main catalyst ( 18 ) falls below. Exhaust gas aftertreatment method for an internal combustion engine according to any one of claims 15 to 19, characterized in that above the predetermined temperature substantially the entire exhaust gas mass flow through the SCR main catalyst ( 18 ). An exhaust gas after-treatment method for an internal combustion engine according to any one of claims 15 to 20, characterized in that the temperature of the exhaust gas mass flow upstream, downstream and / or within the SCR catalyst unit ( 10 ) is detected.