Exhaust-gas aftertreatment system

Abstract

The invention relates to an exhaust-gas aftertreatment system (1) designed to treat an exhaust-gas stream that results from the combustion in an internal combustion engine. The invention is characterized in that a first dosing device (2) is included which is designed to add a first additive into the exhaust-gas stream, wherein a heating device (3) is included which is arranged downstream and is designed to introduce thermal energy, and an oxidation catalytic converter (4) is included which is situated further downstream and is designed to oxidize compounds of nitrogen, carbon and hydrogen that are contained in the exhaust gases. 

Description

[0001] exhaust aftertreatment system

[0002] The invention relates to an exhaust gas aftertreatment system designed to treat an exhaust gas flow resulting from the combustion of an internal combustion engine.

[0003] The exhaust gases emitted by internal combustion engines consist of a heterogeneous mixture containing, for example, gaseous emissions of carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx), as well as condensed-phase materials that can form particulate matter. Therefore, catalyst systems are provided in an engine exhaust system, such as a diesel engine, to convert and filter certain or all of these exhaust components into non-restricted exhaust components.

[0004] Common exhaust aftertreatment systems typically consist of an oxidation catalyst (DOC), a particulate filter (DPF), and a selective reduction catalyst (SRC), arranged in that order. The elements can also be arranged in the reverse order, for example.

[0005] For example, DE 102012 209 197 B4 shows an exhaust aftertreatment system comprising an electrically heated catalyst device, an oxidation catalyst device, a hydrocarbon absorber and a control module.

[0006] EP 3 111 067 B1 describes an exhaust gas aftertreatment system comprising a first oxidation catalyst for oxidizing compounds such as nitrogen, carbon, and hydrogen, and a first metering device arranged downstream of the first oxidation catalyst and configured to deliver a first additive into the exhaust gas stream. Furthermore, a reduction catalyst device is included, which is arranged downstream of the first metering device and reduces nitrogen oxides in the exhaust gas stream by means of the first additive. The same arrangement is arranged again downstream of the first reduction catalyst device, wherein a second additive is used instead of the first additive.

[0007] DE 10 2008 026 191 A1 describes an exhaust gas aftertreatment system and a method for reducing particulate matter and nitrogen oxide emissions. The exhaust gas aftertreatment system comprises a particulate filter, a NOx adsorber, and an SCR catalyst located downstream of the NOx adsorber in the direction of exhaust flow. By supplying heated exhaust gas to the NOx adsorber, the SCR catalyst reaches its light-off temperature earlier than the NOx adsorber reaches its desorption temperature.

[0008] US 2008 / 0264042 A1 discloses a method for reducing NOx in exhaust gases produced by an internal combustion engine. The method comprises activating a heat source when the exhaust gases are below a certain temperature. Furthermore, this method comprises injecting a reducing agent into the segment of the exhaust path upstream of the SCR catalyst to react with NOx in the exhaust gases in that segment.

[0009] DE 102014 105 043 A1 discloses an exhaust aftertreatment system for an internal combustion engine, which comprises an exhaust line, a first injection device in fluid communication with the exhaust line, which is configured to selectively inject fuel containing unburned hydrocarbon (HC) into the exhaust line, and an oxidation catalyst arranged in the exhaust line downstream of the first injection device. The system includes a hydrocarbon selective catalytic reduction (HC-SCR) catalyst applied to the oxidation catalyst, a heating device positioned on an upstream side of the oxidation catalyst and configured to heat the oxidation catalyst and the HC-SCR catalyst.

[0010] According to current standards, exhaust aftertreatment systems must comply with Euro VI legislation. Even lower emission limits are being discussed for future standards, such as Euro VII and higher. Therefore, significant performance improvements are required for existing exhaust aftertreatment systems, particularly during cold starts. Future aftertreatment systems must therefore ensure compliance with the prescribed emission parameters, which particularly affect NOx, NO2, NH3, and PN values.

[0011] The object of the present invention is to provide an exhaust gas aftertreatment system which can meet the aforementioned requirements.

[0012] According to the invention, this object is achieved by an exhaust gas aftertreatment system having the features in claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments emerge from the dependent claims.

[0013] The core of the exhaust gas aftertreatment system according to the invention is formed by a first metering device which is designed to add a first additive to the exhaust gas stream, comprising a downstream heating device which is designed to introduce thermal energy, and further downstream an oxidation catalyst which is designed to oxidize nitrogen, carbon and hydrogen compounds contained in the exhaust gases.

[0014] The exhaust gas aftertreatment system serves to treat the exhaust gas stream resulting from the combustion of an internal combustion engine and can, for example, comply with upcoming emissions regulations, such as Euro VII. Particularly during a cold start, the exhaust gas aftertreatment system according to the invention can achieve a significant increase in performance compared to known systems. This can be achieved in particular by the arrangement of the elements, i.e., the first metering device, the heating device, and the oxidation catalyst, arranged downstream in this order.

[0015] The heating device is an electric heater or an electrically heated oxidation catalyst. If the heating device is designed as an electric heater, the NO2 / NOx ratio, the HC light-off, the SCR light-off, and the urea treatment can be improved, for example. Instead of an electric heater, an electrically heated oxidation catalyst can also be used. The previously mentioned oxidation catalyst can be used here. This can also release thermal energy. Furthermore, the electrically heated oxidation catalyst can be used to oxidize compounds of nitrogen, carbon, and hydrogen in the exhaust gas. The invention significantly improves cold-start emissions performance while simultaneously requiring minimal installation space. The core is therefore the arrangement and positioning of heating, dosing, and catalyst devices to achieve maximum overall system performance.Overall, an exhaust aftertreatment system is proposed that enables rapid warm-up of all components during a cold start. This can, in particular, achieve NOx reduction. Advantageously, low PN values ​​and low secondary emissions, particularly NH3 and NO2, can be maintained at the same time.

[0016] The first additive could be, for example, a hydrocarbon. Other substances or mixtures of substances are also conceivable.

[0017] In an advantageous embodiment, the electrically heated oxidation catalyst can additionally or alternatively serve as a poison scavenger, whereby in particular chemical elements can be accumulated which can lead to a deactivation of the catalytic surface.

[0018] According to a very advantageous development of the concept, a second dosing device can be provided downstream of the oxidation catalyst, which is designed to supply a second additive to the exhaust gas stream. The second additive can be, for example, a urea solution. Other solutions, substances, or mixtures of substances are also conceivable.

[0019] According to an advantageous embodiment, a first selective reduction catalyst can be arranged downstream of the second metering device. The first selective reduction catalyst can be used to reduce nitrogen oxides (NOx) in the exhaust gas stream, in particular using a urea solution as a second additive.

[0020] According to a very advantageous development of the concept, it can be provided that a first slip catalyst is arranged downstream of the first selective reduction catalyst, which serves to oxidize additive residues and / or to support the first reduction catalyst. For example, NH3 slip can be oxidized by the first slip catalyst. The oxidation of additive residues and / or the support of the first reduction catalyst can be achieved by additional reduction of nitrogen oxides (NOx) in the exhaust gas stream. According to an advantageous embodiment, it can be provided that the second additive is supplied as a function of a diesel particulate filter temperature. This allows sufficient NO2 to be provided, in particular for passive regeneration.

[0021] According to a very advantageous development of the concept, a particulate filter designed to retain and / or oxidize soot particles can be arranged downstream of the first slip catalyst. For example, an oxidation layer applied to the particulate filter can lead to an exothermic reaction leading to soot regeneration and / or desulfurization of the downstream catalysts. Advantageously, a sufficient NO2 / NOx ratio is provided for NO2-based soot regeneration and / or NOx reduction on any downstream SCR catalysts.

[0022] According to an advantageous embodiment, a third dosing device can be arranged downstream of the particulate filter, which is configured to supply a third additive to the exhaust stream. The third additive can be a urea solution. Other solutions, substances, or mixtures of substances are also conceivable.

[0023] According to a very advantageous development of the concept, a second selective reduction catalyst can be arranged downstream of the third dosing device. This makes it possible to achieve a reduction of nitrogen oxides (NOx) in the exhaust stream, particularly by using the second and / or third additive.

[0024] According to an advantageous embodiment, a second slip catalyst can be arranged downstream of the second selective reduction catalyst, which serves to oxidize additive residues and / or to support the first reduction catalyst. This advantageously allows NH3 slip to be oxidized.

[0025] Further advantageous embodiments of the exhaust gas aftertreatment system according to the invention also emerge from the exemplary embodiment which is illustrated in more detail below with reference to the figures.

[0026] Showing:

[0027] Fig. 1 is a schematic representation of a possible embodiment of the exhaust gas aftertreatment system; Fig. 2 is a further schematic representation of a possible embodiment of the exhaust gas aftertreatment system.

[0028] The illustration in Fig. 1 shows a schematic representation of a possible embodiment of the exhaust gas aftertreatment system 1. The exhaust gas aftertreatment system 1 is designed to treat an exhaust gas stream resulting from the combustion of an internal combustion engine 20. For this purpose, a first metering device 2 is provided, which serves to deliver a first additive into the exhaust gas stream. A heating device 3 is provided downstream to supply thermal energy to the system and, in particular, to improve the NO2 / NOx ratio, the HC light-off, the SRC light-off, and / or the urea preparation.

[0029] Further downstream, an oxidation catalyst 4 is provided, which serves to oxidize nitrogen, carbon, and hydrogen compounds in the exhaust gas. The oxidation catalyst 4 can also be used as a toxic trap to collect chemical elements, which can lead to deactivation of the catalytic surface.

[0030] A second metering device 5 can be arranged further downstream, specifically after the first oxidation catalyst 4. The second metering device 5 is used in particular to supply a second additive to the exhaust gas stream. The second additive can be, for example, a urea solution. Other substances, solutions, or compositions are also conceivable as the second additive.

[0031] Further downstream, a first selective reduction catalyst 6 can be arranged, specifically after the second dosing device 5. The first selective reduction catalyst 6 serves to reduce nitrogen oxides (NOx) in the exhaust stream using a second additive. The second additive can also contain a urea solution or another solution.

[0032] A first slip catalyst 7 can be arranged further downstream, in particular to oxidize NH3 slip. The slip catalyst 7 serves in particular to oxidize an additive residue and / or to assist the first reduction catalyst 6 by additionally reducing nitrogen oxides in the exhaust gas stream. Furthermore, control of the addition of the second additive can be provided as a function of a diesel particulate filter (DPF) temperature in order to provide sufficient NO2 for passive regeneration. According to the illustrated embodiment, a particulate filter 8 can also be arranged downstream of the first slip catalyst 7. This is designed in particular to retain and / or oxidize soot particles. Furthermore, an oxidizing coating can be applied to the particulate filter 8 in order to generate an exothermic reaction for soot regeneration and desulfurization of the downstream catalysts.Advantageously, this can also provide a sufficient NO2 / NOx ratio for NO2-based soot regeneration and / or NOx reduction at the following SCR catalysts.

[0033] Further downstream, a third dosing device 9 can be provided to deliver a third additive into the exhaust gas stream. The third additive can also be a urea solution, or another solution or composition.

[0034] A second selective reduction catalyst 10 can be arranged downstream of the third metering device 9. This serves in particular to reduce nitrogen oxides in the exhaust gas stream using the second and / or third additive.

[0035] Further downstream, a second slip catalyst 11 may be provided to oxidize NH3 slip. The second slip catalyst 11 is provided, in particular, to oxidize additive residues and / or to assist the second reduction catalyst 10 by additionally reducing nitrogen oxides (NOx) in the exhaust gas stream.

[0036] Another embodiment of the exhaust gas aftertreatment system 1 can be seen in Fig. 2. The same elements are provided with the same reference numerals, so they need not be discussed in detail. In contrast to Fig. 1, an electrically heated oxidation catalyst is provided here as the heating device 3, instead of an electric heater and an oxidation catalyst 4. This electrically heated oxidation catalyst can also be used as a poison trap to collect chemical elements, which can lead to deactivation of the catalytic surface.

[0037] Of course, the described embodiments of the exhaust gas aftertreatment system 1 in Figures 1 and 2 can also be modified in accordance with the invention, so that various possibilities arise that enable rapid heating of the exhaust gas aftertreatment system 1 during a cold start.

Claims

Exhaust gas aftertreatment system (1) which is designed to treat an exhaust gas flow resulting from the combustion of an internal combustion engine, wherein a first metering device (2) is included which is designed to add a first additive to the exhaust gas flow, wherein a heating device (3) arranged downstream is included which is designed to introduce thermal energy, and further downstream an oxidation catalyst (4) which is designed to oxidize nitrogen, carbon and hydrogen compounds contained in the exhaust gases, characterized in that the heating device (3) is an electric heater which is arranged directly upstream of an oxidation catalyst (4), or is an electrically heatable oxidation catalyst.Exhaust gas aftertreatment system (1) according to claim 1, characterized in that a second metering device (5) is arranged downstream of the oxidation catalyst (4), which is configured to supply a second additive to the exhaust gas stream. Exhaust gas aftertreatment system (1) according to claim 2, characterized in that a first selective reduction catalyst (6) is arranged downstream of the second metering device (5). Exhaust gas aftertreatment system (1) according to claim 3, characterized in that a first slip catalyst (7) after the first selective reduction catalyst (6) is arranged, which serves to oxidize additive residues and / or to support the first reduction catalyst (6). Exhaust gas aftertreatment system (1) according to one of claims 2 to 4, characterized in that a supply of the second additive takes place as a function of a diesel particulate filter temperature. Exhaust gas aftertreatment system (1) according to one of claims 4 or 5, characterized in that a particulate filter (8) is arranged downstream of the first slip catalyst (7), which particulate filter is designed to retain and / or oxidize soot particles. Exhaust gas aftertreatment system (1) according to claim 6, characterized in that an oxidation layer is applied to the particulate filter (8), the exothermic reaction leading to soot regeneration and / or to desulfurization of the downstream catalysts.Exhaust gas aftertreatment system (1) according to one of claims 6 or 7, characterized in that a third metering device (9) is arranged downstream of the particulate filter (8), which third metering device is designed to supply a third additive to the exhaust gas flow. Exhaust gas aftertreatment system (1) according to claim 8, characterized in that a second selective reduction catalyst (10) is arranged downstream of the third metering device (9). Exhaust gas aftertreatment system (1) according to claim 9, characterized in that a second slip catalyst (11) is arranged downstream of the second selective reduction catalyst. Reduction catalyst (10) is arranged, which serves to oxidize additive residues and / or to support the first reduction catalyst (6).

Images