EXHAUST EMISSION CONTROL DEVICE, INTERNAL COMBUSTION ENGINE EQUIPPED THEREWITH AND METHOD FOR EXHAUST EMISSION CONTROL

Abstract

An exhaust emission control device has at least one exhaust gas line, at least one particulate filter and/or at least one exhaust gas catalytic converter connected to the exhaust gas line, and a heated catalyst assembly arranged upstream of the particulate filter and/or the exhaust gas catalytic converter. The heated catalyst assembly is designed to react fuel with exhaust gas, and has a housing provided with an inlet and an outlet connected to the exhaust gas line such that a partial flow of the exhaust gas flowing in the exhaust gas line can be fed through the inlet into the housing and can be discharged from the housing through the outlet back into the exhaust gas line downstream of the inlet. An exhaust emission control device of this type may be used in conjunction with an internal combustion engine, and may be used for emission control of exhaust gas.

Claims

1. An exhaust emission control device (1), comprising: at least one exhaust gas line (3) configured to convey exhaust gases; a heated catalyst assembly (2) configured to receive and react a portion of the exhaust gases with a fuel supplied thereto, the heated catalyst assembly (2) comprising a housing (25) having an inlet (21) and an outlet (22), wherein: said portion of the exhaust gases in said at least one exhaust gas line (3) is fed into the housing (25) through the inlet (21); and reaction products formed by the reaction of said portion of the exhaust gases with said fuel, are discharged from the housing (25) through the outlet (22) and back into the at least one exhaust gas line (3), downstream of the inlet (21); and a particulate filter (31) and/or an exhaust gas catalytic converter (32) connected to the at least one exhaust line (3) downstream of the heated catalyst assembly (2).

2. The exhaust emission control device according to claim 1, wherein the heated catalyst assembly (2) further comprises an electrically heatable support (5).

3. The exhaust emission control device according to claim 1, further comprising a perforated plate (4) arranged on a first side of the heated catalyst assembly (2) and configured to permit said portion of the exhaust gases to pass therethrough.

4. The exhaust emission control device according to claim 3, further comprising: a fuel plate (6) arranged on a second side of the heated catalyst assembly (2) that is opposite the first side where the perforated plate (4) is arranged.

5. The exhaust emission control device according to claim 4, further comprising a pump (65) configured to supply fuel to the heated catalyst assembly (2), via the fuel plate (6).

6. The exhaust emission control device according to claim 4, wherein the fuel plate (6) has a capillary transport arrangement configured to distribute fuel in a thin film over a surface of the fuel plate (6).

7. The exhaust emission control device according to claim 1, further comprising an air supply device configured to supply ambient air to the heated catalyst assembly (2).

8. The exhaust emission control device according to claim 1, further comprising: a pressure reduction device (7) positioned in the exhaust gas line (3) between the inlet (21) and the outlet (22) of the heated catalyst assembly (2).

9. The exhaust emission control device according to claim 8, wherein the pressure reduction device (7) is at least one from the group consisting of: a throttle valve, a mixer and a turbine (861) of a turbocharger (86).

10. The exhaust emission control device according to claim 1, wherein the housing (25) of the heated catalyst (2) is fully arranged inside the exhaust gas line (3).

11. The exhaust emission control device according to claim 1, wherein the housing (25) of the heated catalyst (2) is external to the exhaust gas line (3).

12. The exhaust emission control device according to claim 1, further comprising: an electrically heatable support (5) provided within the heated catalyst assembly (2); a perforated plate (4) arranged on a first side of the heated catalyst assembly (2) and configured to permit said portion of the exhaust gases to pass therethrough. a fuel plate (6) arranged on a second side of the heated catalyst assembly (2); and a pump (65) configured to supply fuel to the heated catalyst assembly (2), via the fuel plate (6);

13. The exhaust emission control device according to claim 12, further comprising: a pressure reduction device (7) positioned in the exhaust gas line (3) between the inlet (21) and the outlet (22) of the heated catalyst assembly (2), wherein: the pressure reduction device (7) comprises at least one from the group consisting of: a throttle valve, a mixer and a turbine (861) of a turbocharger (86).

14. An internal combustion engine (8) comprising an exhaust emission control device (1) according to claim 1.

15. A method of reducing nitrogen oxides in exhaust gases output by an internal combustion engine, the method, comprising: providing an exhaust emission control device (1) in accordance with claim 1; reacting a fuel with a portion of said exhaust gases in the heated catalyst assembly (2) to create reaction products for heating exhaust gases flowing downstream in the exhaust gas line (3); and supplying the heated exhaust gases to said particulate filter (31) and/or said exhaust gas catalytic converter (32) to reduce a level of nitrogen oxides in the exhaust gases.

16. A method for exhaust emission control, wherein exhaust gas is supplied with at least one exhaust gas line (3) to at least one particulate filter (31) and/or at least one exhaust gas catalytic converter (32, 33), the method comprising: arranging a heated catalyst assembly (2) upstream of the particulate filter (31) or the exhaust gas catalytic converter (32, 33), the heated catalyst assembly (2) having a housing (25) which has an inlet (21) and an outlet (22) and which is connected to the exhaust gas line (3) in such a way that a partial flow of the exhaust gas flowing in the exhaust gas line (3) is supplied through the inlet (21) into the housing (25) and is discharged from the housing (25) through the outlet (22) back into the exhaust gas line (3) downstream of the inlet (21); supplying the heated catalyst assembly (2) with fuel and a portion of said exhaust gas, and at least partially reacting said fuel with said portion of the exhaust gas to create reaction products for heating exhaust gas flowing downstream in the exhaust gas line (3); and supplying the heated exhaust gas to the particulate filter (31) or the exhaust gas catalytic converter (32, 33).

17. The method according to claim 16, comprising: at least temporarily electrically heating a catalyst support (5) of the heated catalyst assembly (2).

18. The method according to claim 16, comprising: in a first operating state, predominantly oxidizing the fuel with the exhaust gas; and in a second operating state, predominantly reacting the fuel to form a reformate.

19. The method according to claim 16, comprising: supplying said portion of the exhaust gas to the heated catalyst assembly (2) via at least one perforated plate (4) arranged on a first side of the heated catalyst assembly (2).

20. The method according to claim 19, comprising: applying the fuel to a fuel plate (6) which is arranged on a second side of the heated catalyst assembly (2) that is opposite to the first side where the perforated plate (4) is arranged.

21. The method according to claim 16, comprising: introducing said portion of said exhaust gas into the heated catalyst assembly (2) upstream of a pressure reduction device (7) and discharging said reaction products from the heated catalyst assembly (2) back into the exhaust gas line (3) downstream of the pressure reduction device (7).

22. The method according to according to claim 16, wherein: the pressure reduction device (7) is at least one from the group consisting of a throttle valve, a mixer and a turbine (861) of a turbocharger (86).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The invention shall be explained in more detail below by means of embodiments and drawings without limiting the general concept of the invention, wherein:

[0045] FIG. 1 shows a view of a first embodiment of a heated catalyst assembly according to the invention.

[0046] FIG. 2 shows the cross-section through the heated catalyst assembly according to the first embodiment.

[0047] FIG. 3 shows an exploded drawing of a heated catalyst assembly according to the first embodiment.

[0048] FIG. 4 illustrates exhaust emission control devices according to the invention by means of an internal combustion engine.

[0049] FIG. 5 illustrates different installation variants of the heated catalyst assembly according to the invention.

[0050] FIG. 6 shows a longitudinal section of a heated catalyst assembly according to the invention in a second embodiment.

[0051] FIG. 7 shows a cross-section of a heated catalyst assembly according to the invention in a second embodiment.

[0052] FIG. 8 shows a longitudinal section of a heated catalyst assembly according to the invention in a third embodiment.

[0053] FIG. 9 shows a cross-section of a heated catalyst assembly according to the invention in a third embodiment.

[0054] FIG. 10 shows the mass flows supplied to the heated catalyst assembly and the composition of the reformate generated in the heated catalyst assembly.

[0055] FIG. 11 shows the temperature of an oxidation catalyst and of a particulate filter after a cold start against time.

[0056] FIG. 12 shows the entire exhaust gas mass flow, the thermal power supplied to the exhaust gas after-treatment system and the resulting SCR temperature against time.

[0057] FIG. 13 shows the thermal power supplied to the exhaust gas after-treatment system and the resulting SCR temperature against time for the first 480 seconds of a WHTC measurement cycle.

[0058] FIG. 14 shows the integral of the heating power for electrical heating devices and the heated catalyst assembly according to the invention when heating an SCR catalyst in the WHTC cycle as well as the fuel amount respectively used for heating.

[0059] FIG. 15 shows a test stand for testing the heated catalyst assembly according to the invention.

[0060] FIG. 16 shows the entire exhaust gas mass flow, the exhaust gas mass flow supplied to the heated catalyst assembly according to the invention, and the oxygen concentration contained therein against time.

[0061] FIG. 17 shows the power supplied from the heated catalyst assembly, the oxygen concentration contained in the supplied exhaust gas mass flow and the temperature of the heated catalyst assembly against time.

[0062] FIG. 18 shows the temperature of the heated catalyst assembly against time in the case of varying supplied exhaust gas mass flow and oxygen concentration.

[0063] FIG. 19 shows a fourth embodiment of a heated catalyst assembly according to the invention.

DETAILED DESCRIPTION

[0064] FIGS. 1, 2 and 3 illustrate a first embodiment of the heated catalyst assembly according to the invention. FIGS. 1 and 2 here show a part of an exhaust gas line 3. The exhaust gas line 3 is designed to receive an exhaust gas stream 35, which originates e.g. from an internal combustion engine.

[0065] As can is also clear from FIGS. 1 and 2, the exhaust gas stream 35 is passed substantially in a straight line through the exhaust gas line 3. Only a partial flow 351 is passed into the housing 25 of the heated catalyst assembly 2 via the inlet 21. The partial flow 351 branched off in this way can be between about 10% and about 50% or between about 15% and about 30% of the total exhaust gas stream flowing in the exhaust gas line 3.

[0066] As shown in particular in FIG. 2, the exhaust gas stream 351 entering through the inlet 21 is supplied to the catalyst support 5 via a perforated plate 4. The perforated plate 4 can contain or consist of a ceramic material, a metal or an alloy. The perforated plate 4 further has a plurality of holes 41 through which the exhaust gas can enter. The number, size and distribution of the holes 41 can be determined in a computer simulation so as to distribute as homogeneously as possible the exhaust gas in the catalyst support 5.

[0067] In a manner known per se, the catalyst support 5 can be, for example, a sintered body, a honeycomb body, a foam or another porous molded body that is permeable to exhaust gas. For this purpose, the catalyst support 5 can be made of a metal, an alloy or a ceramic material. The catalyst support 5 can be provided with an electrical heating device so that it can be heated with a heating power between about 500 W and about 1500 W. For this purpose, an electrical connection 51 is used through which electrical heating energy can be introduced into the catalyst support 5. The temperature of the catalyst support 5 can be detected and controlled in open-loop or closed-loop fashion by means of a temperature sensor 50.

[0068] Finally, a fuel plate 6 is located on the side of the catalyst support 5 opposite the perforated plate. The fuel plate 6 can contain or consist of a metal or an alloy and optionally is provided with a capillary transport device. As a transport device, for example, channels can be introduced into the surface of the fuel plate 6 which allow a capillary transport of the fuel so that it is distributed as homogeneously as possible in a thin film over the surface of the fuel plate 6 facing the catalyst support 5. The supply of the fuel can be controlled in an open-loop or closed-loop fashion by a pump 65. In some embodiments of the invention, the fuel applied to the fuel plate 6 is taken from the main tank of the internal combustion engine. For example, the fuel can be gasoline or diesel fuel or natural gas or LPG. In other embodiments of the invention, a fuel specifically provided for heating the exhaust gas after-treatment system can be applied to the fuel plate 6, e.g. an alcohol or white spirit.

[0069] Heat is introduced into the fuel plate 6 by the exhaust gas flowing through the catalyst support 5 by convection and radiation. This causes the fuel to vaporize. The fuel vapor then rises into the catalyst support 5 where it is reacted exothermically with the exhaust gas. The resulting heat is partially supplied to the exhaust gas, so that the exhaust gas stream 352 flowing from the outlet 22 into the exhaust gas line 3 is heated relative to the incoming exhaust gas stream 351. In addition, the exhaust gas stream 352 introduced into the exhaust gas line 3 contains components of the fuel reacted at the catalyst support 5, for example a reformate.

[0070] In some embodiments of the invention, it is possible to initially select, after a cold start, a first operating state in which the fuel is predominantly oxidized with the exhaust gas. This generates primarily heat by exothermic reaction, which is used to heat the exhaust gas after-treatment system. In this first operating state, the catalyst support 5 can optionally be electrically heated at least at times. The air ratio λ of the heated catalyst assembly can be selected between about 0.7 and about 1, and in some embodiments also greater than 1.

[0071] In a second operating state of the heated catalyst assembly, the fuel can be predominantly reacted to a reformate containing or consisting of a mixture of predominantly short-chain alkenes and/or carbon monoxide and/or hydrogen. This reformate is subsequently oxidized at a particulate filter and/or an exhaust gas catalytic converter, the resulting heat being introduced directly into these components. For this purpose, the heated catalyst within the heat catalyst assembly 2 is operated substoichiometrically, i.e. the air ratio λ of the heated catalyst is between about 0.05 and about 0.7 or between about 0.1 and about 0.4.

[0072] Switching between the first and second operating state can be accomplished by adjusting the supplied fuel amount and/or by adjusting the exhaust gas composition and/or by supplying ambient air. The exhaust gas composition can be influenced by, among other things, selection of the injected fuel amount, the boost pressure, the throttle valve position, the number and duration of the individual injections, the injection or ignition timing, the opening duration of the intake and exhaust valves, the opening stroke, and/or the position of an exhaust gas recirculation valve. Preferably, but not necessarily, switching between the first and second operating state is performed by adjusting the supplied fuel amount, which is selected for this purpose on the basis of the exhaust gas composition. The exhaust gas composition can be measured at least in part, for example by a lambda probe. Alternatively or additionally, the exhaust gas composition can be extrapolated from the characteristic maps of the internal combustion engine, so that as a result the fuel amount supplied to the heated catalyst assembly can be determined from the characteristic maps or ranges of characteristic maps present in the respective operating state of the internal combustion engine.

[0073] In some embodiments of the invention, the switching between the first and the second operating state can be cyclic so that there are multiple changes between heat input and reformate generation.

[0074] In some embodiments of the invention, a plurality of heated catalyst assemblies can be provided so that the first and second operating state can also be applied simultaneously.

[0075] In some embodiments of the invention, the temperature of the fuel plate 6 can be used to control the flow rate of the pump 65, which is detected by an optional temperature sensor 60.

[0076] FIG. 2 also shows a pressure reduction device 7, which in the illustrated example contains a throttle valve, the angle of attack of which can be influenced by an actuator 70. Therefore, the pressure reduction device can be closed after the cold start so that a sufficiently large pressure difference is established between the inlet 21 and the outlet 22 so that a partial flow 351 of the exhaust gas flow 35 flows through the housing 25 of the heated catalyst assembly 2. The pressure reduction device 7 can also have the effect that turbulent wake vortices are formed downstream of the pressure reduction device, which ensures efficient mixing of the partial flow 352 leaving the housing 25 of the heated catalyst assembly 2 with the main flow flowing in the exhaust gas line 3. If the exhaust gas temperature is so high that additional heating of the exhaust emission control device is not required, the throttle valve 7 can be fully open. As a result, approximately the same exhaust gas pressure is present at the inlet 21 and at the outlet 22 so that the exhaust gas does not flow, or only flows to a small extent, through the heated catalyst assembly 2. The device according to the invention then does not have an exhaust gas back-pressure that is significantly higher than that of known exhaust gas systems without a heated catalyst assembly, which can result in a power and/or consumption advantage under full load or near-full load operating states.

[0077] Finally, FIG. 2 shows temperature sensors 88 that determine the exhaust gas temperature upstream and downstream of the pressure reduction device 7. This can ensure that no excessively hot exhaust gas is introduced into the catalyst support 5, which could lead to the destruction of the heated catalyst assembly 2. Furthermore, it is ensured that not so much energy is supplied in the heated catalyst assembly that the exhaust gas flow exceeds a predeterminable maximum temperature.

[0078] The pressure reduction device 7, the fuel supply via the pump 65, and the electrical heating energy of the catalyst support 5 can be controlled via an open-loop or closed-loop control device 87 in such a way that the heated catalyst assembly is controlled in open-loop or closed-loop fashion in an optimum way on the basis of the operating state.

[0079] FIG. 3 again shows the housing 25 of a heated catalyst assembly 2 in an exploded drawing. The fuel plate 6 on the underside and the perforated plate 4 on the upper side of the catalyst support 5 can be identified. Electric heating energy and fuel can be supplied via the connections 62 and 51. The upper side of the approximately cylindrical housing includes the inlet 21 and the outlet 22, through which the exhaust gas flow 351 enters the housing 25 and the modified exhaust gas flow 352 leaves the housing of the heated catalyst assembly 2.

[0080] The heated catalyst assembly 2 has a compact design and a high power density between about 30 kW/l and about 60 kW/l. In addition, the thermal power output can be adjusted in a wide range, for example between about 1 kW and about 18 kW, so that the modulation range is between about 1:16 and about 1:20.

[0081] With reference to FIG. 4, an internal combustion engine 8 with its external mounting parts is shown by way of diagram. In the illustrated exemplary embodiment, the internal combustion engine 8 has four cylinders 815. The number of cylinders can, of course, be larger or also smaller in other embodiments of the invention. The invention is suitable for all conventional designs, for example in-line engines, boxer engines or V-engines. The illustrated 4-cylinder in-line engine is thus to be understood merely as an example. Furthermore, it may be a spark-ignition internal combustion engine or a self-ignition internal combustion engine.

[0082] Fuel is supplied to the internal combustion engine 8 via a line 81. The line 81 can, for example, be part of a common rail system or any other mixture preparation system known per se. Furthermore, the internal combustion engine 8 has an intake section 811, via which fresh air is supplied to the internal combustion engine 8. The exhaust gases are collected via an exhaust manifold 812 and supplied to the exhaust gas line 3.

[0083] FIG. 4 also shows an optional high-pressure exhaust gas recirculation system. It contains an exhaust gas recirculation valve 835, which controls in open-loop or closed-loop manner the recirculated exhaust gas amount, and an exhaust gas cooler 83, which extracts thermal energy from the recirculated exhaust gas and thus lowers its temperature. The high-pressure exhaust gas recirculation system discharges a partial flow of the exhaust gas from the exhaust gas line 3 and supplies it back into the intake section 811 in a cooled state.

[0084] The main flow of the exhaust gas is passed from the exhaust gas line 3 via the turbine 861 of an optional turbocharger 86. Of course, the turbocharger 86 can also be omitted in other embodiments of the invention. The exhaust gas is expanded in the turbine 861, thereby driving a compressor 862 via a shaft. The compressor 862 compresses the fresh air drawn in via an inlet 85 after it has been passed through an air filter 855 where it is cleaned of dirt particles.

[0085] The compressed air leaving the compressor 862 reaches an optional charge air cooler 82 before the compressed and cooled intake air is supplied to the internal combustion engine 8 via the intake section 811.

[0086] The exhaust gas leaving the turbine 861 reaches an exhaust gas after-treatment system which has three stages in the illustrated exemplary embodiment. It contains an oxidation catalyst 32 that oxidizes unburned fuel components and carbon monoxide so that substantially CO.sub.2 and H.sub.2O escape from the oxidation catalyst 32.

[0087] The exhaust gas then reaches a particulate filter 31, which can be, for example, a diesel particulate filter known per se or a gasoline particulate filter. Soot particles produced by incomplete combustion in the cylinders 815 of the internal combustion engine 8 are retained in the particulate filter 31. When the particulate filter 31 is sufficiently loaded, the soot particles can be oxidized to form CO.sub.2. This requires exhaust gas temperatures between 350° C. and 600° C.

[0088] Finally, FIG. 4 shows an optional SCR catalyst 33, in which nitrogen oxides from the exhaust gas flow are reduced with urea. The reaction of the nitrogen oxides requires temperatures above 200° C., preferably above 250° C.

[0089] Finally, FIG. 4 shows an also optional low-pressure exhaust gas recirculation system, which branches off exhaust gas downstream of the particulate filter 31, lowers the temperature via an optional exhaust gas cooler 84, and feeds the cooled exhaust gas to the low-pressure side of the compressor 862. Another exhaust gas recirculation valve 845 is available to control the recirculated mass flow.

[0090] It is understood that FIG. 4 shows the maximum configuration with peripheral devices. In other embodiments of the invention, individual peripheral devices can also be omitted; for example, a turbocharger 86, a charge air cooler 82, an exhaust gas recirculation system 83 and 84 or a multistage exhaust emission control 31, 32 and 33 need not be provided in every case. Individual elements can also be omitted.

[0091] The object of the invention is now to rapidly bring the oxidation catalyst 32 and/or the particulate filter 31 and/or the SCR catalyst 33 to the required operating temperature even in part-load operation and/or after a cold start. For this purpose, the heated catalyst assembly according to the invention can be used at the points designated by reference sign 2. The heated catalyst assembly can thus be inserted into the exhaust gas line 3 either upstream or downstream of the turbine 861 of the turbocharger 86. In other embodiments of the invention, the heated catalyst assembly 2 can be integrated into the exhaust gas line 3 upstream or downstream of the turbocharger 86.

[0092] Various installation situations of the heated catalyst assembly 2 are explained in more detail with reference to FIG. 5. The design of the heated catalyst is assembly here substantially based on the three different embodiments of the invention, which are shown in FIGS. 1, 2 and 3 or FIGS. 6 and 7 or FIGS. 8 and 9.

[0093] FIG. 5a shows the installation of a heated catalyst assembly 2 parallel to the turbine 861 of turbocharger 86. In this case, the pressure loss occurring in turbine 861 ensures that an exhaust gas pressure present at the inlet 21 of the heated catalyst assembly 2 is higher than that at the outlet 22. As a result, a partial flow 351 of the exhaust gas is conveyed through the heated catalyst assembly 2. The turbulence of the exhaust gas after leaving the turbine 861 also ensures sufficiently good mixing of the fuel vapor or reformate generated in the heated catalyst assembly 2 with the main stream of the exhaust gas flowing through the turbine 861.

[0094] FIG. 5b shows an installation variant of the heated catalyst assembly 2 on the low-pressure side of the exhaust gas stream, i.e. after leaving the turbine 861 of the turbocharger 86. The embodiment of the invention shown in section in FIG. 2 and using a mixer is suitable for this purpose, for example. An advantage is the universal usability of the heated catalyst assembly for a plurality of vehicle types.

[0095] FIG. 5c shows the installation of a heated catalyst assembly 2 on the high-pressure side of the exhaust gas set, i.e. upstream of the turbine 861 of the turbocharger 86. This has the advantage that the turbine of the turbocharger 861 allows good mixing of the main stream with the partial stream leaving the heated catalyst assembly 2 and containing fuel vapor.

[0096] Finally, FIG. 5d shows the integration of the heated catalyst assembly 2 into the exhaust gas line directly upstream of the exhaust gas after-treatment system to be heated. The embodiment shown in FIGS. 6 to 9 is particularly suitable for this purpose. In this embodiment, the heated catalyst assembly 2 is arranged completely inside the exhaust gas line 3 and, being protected from damage, can thus also be arranged on the vehicle floor.

[0097] FIGS. 6 and 7 show a second embodiment of the heated catalyst assembly according to the invention. Equal components of the invention are provided with equal reference signs so that the description is limited to the essential differences. FIG. 6 shows a longitudinal section and FIG. 7 a cross-section.

[0098] As is clear from the drawings, the heated catalyst assembly 2 is again arranged in an approximately cylindrical housing. The housing is arranged approximately concentrically to the exhaust gas line 3. For this purpose, the diameter of the exhaust gas line 3 in the area of the heated catalyst assembly 2 can be larger than in other longitudinal sections of the exhaust gas line 3. The inlet 21 and the outlet 22 of the housing 25 are arranged on opposite ends of the cylindrical housing 25. Therefore, the exhaust gas flows into the housing 25 through the front side thereof and out again through the rear side thereof. As a result, the exhaust gas always flows through the housing 25 when the internal combustion engine is in operation. Due to the largely homogeneous flow of exhaust gas, the perforated plate 4 can also be omitted in these embodiments. As shown in FIGS. 6 and 7 as an example of an exhaust pipe, the heated catalyst assembly can also be integrated into the housing of an exhaust gas catalytic converter or a particulate filter.

[0099] With reference to FIGS. 8 and 9, a third embodiment of the invention is explained in more detail. Equal components of the invention are provided with equal reference signs so that the description is limited to the essential differences. Again, the longitudinal section is shown in FIG. 8 and the cross-section in FIG. 9.

[0100] As can be seen, the housing of the heated catalyst assembly 2 is not located approximately concentrically in the center of the exhaust gas line 3, but at its edge where it is separated from the remaining free cross-section of the exhaust gas line 3 by a flat or curved partition 251. This embodiment has the advantage that the connecting contacts 51 of an electrical heating device and the fuel supply 62 do not have to be passed through the hot exhaust gas zone. In this case, too, a perforated plate 4 can be omitted under certain circumstances since the catalyst support 5 already has a homogeneous flow anyway. As shown in FIGS. 8 and 9 by way of example for an exhaust gas pipe, the heated catalyst assembly can also be integrated into the housing of an exhaust gas catalytic converter or a particulate filter.

[0101] FIG. 19 shows a fourth embodiment of a heated catalyst assembly according to the invention. Equal components of the invention are provided with equal reference signs so that the description is limited to the essential differences.

[0102] As is clear from FIG. 19, the heated catalyst assembly has an approximately cylindrical housing 25, the inlet 21 and the outlet 22 being arranged axially. As also shown in FIG. 19, the exhaust gas stream 351 entering through the inlet 21 is supplied to the catalyst support 5 via a perforated plate 4 in the form of a cylinder jacket surface. The perforated plate 4 can contain or consist of a ceramic material, a metal or an alloy. In some embodiments of the invention, the perforated plate 4 can be formed by a longitudinal section of the pipe forming the inlet 21. The perforated plate 4 further includes a plurality of holes or openings 41 through which the exhaust gas can pass. The number, size and distribution of the holes 41 can be determined in an optional computer simulation in such a way that the exhaust gas is distributed as homogeneously as possible in the catalyst support 5. In some embodiments of the invention, the end of the pipe forming the inlet 21 can be closed so that the exhaust gas only exits through the openings 41.

[0103] In a manner known per se, the catalyst support 5 can be, for example, a sintered body, a honeycomb body, a foam or another porous shaped body which is permeable to exhaust gas. For this purpose, the catalyst support 5 can be made of a metal, an alloy or a ceramic material. The catalyst support 5 also has the form of a cylinder jacket surface and is arranged approximately concentrically around the cylindrical perforated plate 4 and/or approximately concentrically to the housing 25.

[0104] Finally, the side of the catalyst support 5 opposite the perforated plate includes a fuel plate which is also concentric and to which fuel is applied via a fuel supply 62.

[0105] In some embodiments of the invention, a fuel plate can also be omitted if the fuel is applied directly to the catalyst support 5. When fuel is applied directly to the catalyst support 5, the fuel can be introduced in gaseous form. For this purpose, a liquid fuel can be introduced into the heated catalyst assembly via an evaporator (not shown). This avoids or reduces undesirable cooling of the catalyst support 5 due to the enthalpy of vaporization of the fuel.

[0106] In some embodiments, the fuel supply 62 can be available multiple times so that fuel can be introduced at multiple locations along the circumference and/or along the longitudinal extension. The merely schematic illustration of only one fuel supply 62 should only be understood as explanatory.

[0107] The following comparative examples illustrate the invention, but should not be understood to the effect that the invention is limited thereto. In the following examples, an exhaust emission control device is used as described in FIGS. 1 to 4.

[0108] As already described above, the heated catalyst assembly according to the invention can have a first operating state in which fuel with comparatively long-chain hydrocarbons is reacted in the heated catalyst assembly. The resulting reformate can already be reacted at lower temperatures on a component of an exhaust gas after-treatment system, e.g. an oxidation catalyst, and thus generate heat directly in the exhaust gas set or the exhaust gas after-treatment system. In addition, the heated catalyst assembly according to the invention can be operated in a second operating state in which the fuel is largely or completely oxidized in order to introduce heat into the exhaust gas by exothermic reaction.

[0109] FIG. 10 shows on the positive ordinate the composition of the reformate generated by the heated catalyst assembly in the first operating state. The negative ordinate shows the composition of the mass flows supplied to the heated catalyst assembly.

[0110] FIG. 10 shows the results of a test operation in which the exhaust gas stream is simulated by a mixture of 14% oxygen and 84.7% nitrogen. This simulated exhaust gas stream is supplied to the heated catalyst assembly in the manner described above. In addition, commercially available diesel fuel is supplied to the heated catalyst assembly and consists essentially of a mixture of alkanes, alkenes, aromatics and oxygenated hydrocarbons. At room temperature, the alkanes consist of gaseous components having about 1 to 5 carbon atoms and liquid alkanes having more than 6 carbon atoms.

[0111] Inside the heated catalyst assembly, the diesel fuel is reacted with the exhaust gas. This produces heat and oxidation products, such as hydrogen and carbon monoxide. In addition, the fuel is cracked into short-chain alkenes, such as propane and ethylene. The resulting reformate contains almost no liquid alkanes that can be condensed at room temperature. As a result, the ignition temperature on an oxidation catalyst of an exhaust gas after-treatment system is reduced. Thus, heat can be generated directly in the exhaust gas after-treatment system by oxidation of the reformate, which heats the downstream components of the exhaust gas after-treatment system, e.g. a particulate filter. The heating power thus produced can be greater than about 10 kW or greater than about 15 kW or greater than about 20 kW or greater than about 25 kW or greater than about 30 kW.

[0112] FIG. 11 shows the temperature of a particulate filter 31 in curve B and the temperature of an oxidation catalyst 32 in curve A of an exhaust gas after-treatment system of a passenger car with diesel engine. The exhaust gas stream was set to 50 kg/h and a constant temperature of 140° C. FIG. 11 shows the temperature curve against time. After about 40 seconds, the reformate described above on the basis of FIG. 10 was introduced into the exhaust gas set. The temperature of the oxidation catalyst then rises to a value of over 200° C. within about 35 seconds. Over the course of another two minutes, the oxidation catalyst continues to heat to temperatures of about 450° C.

[0113] Heat is released from the oxidation catalyst 32 into the downstream particulate filter 31. As FIG. 11 shows, the particulate filter already reaches a temperature of more than 200° C. about 3 minutes after the cold start and about 140 seconds after the reformate addition. The heating power generated in this way by the heated catalyst assembly according to the invention is about 6 kW.

[0114] FIG. 12 shows the exhaust gas mass flow in curve 10. The heating power supplied to the exhaust gas after-treatment system is shown in the middle part of the drawing. Here, curve D denotes the heating power provided by the heated catalyst assembly according to the invention. As a comparative example, the heating power of electric heating with 4 kW is shown in curve E, and electric heating with 8 kW in curve F. Finally, FIG. 12 shows the temperature of an SCR catalyst against time. Curve H shows the temperature curve for heating with a heated catalyst assembly according to the invention, curve G shows the temperature curve for electric heating with 4 kW, curve I shows the temperature curve for an electric heating with 8 kW, and curve J shows the temperature curve without further heating measures. In each case, the time curve is shown for the first 30 minutes after the cold start during a WHTC test cycle. FIG. 13 shows an enlarged view of the first 480 seconds of the test cycle shown in FIG. 12.

[0115] As is clear from curve D, the heated catalyst assembly according to the invention provides, in the second operating state, a heating power of about 9 kW from the start. After a few tens of seconds, the oxidation catalyst of the exhaust gas after-treatment system is heated to such an extent that the heated catalyst assembly can switch to the first operating state. In the first operating state, a heating power of about 36 kW is output. The heating power is then reduced within the next two minutes. This sometimes results in fluctuations due to the fluctuating exhaust gas mass flow which is supplied to the heated catalyst assembly.

[0116] As is clear from figure H, the high heating power of the heated catalyst assembly according to the invention results in a temperature of more than 200° C. being reached at the SCR catalyst after just 70 seconds, which allows an efficient cleaning of nitrogen oxides in the exhaust gas.

[0117] By comparison, the same temperature or cleaning effect is only achieved after more than two minutes with an electric heating power of 8 kW. If the electric heating power is reduced further to 4 kW, which is already the limit of a 12-volt on-board power supply, the SCR catalyst reaches a temperature of 200° only after 180 seconds. A temperature of 250° is reached only after 420 seconds. In contrast, the heated catalyst assembly according to the invention allows a temperature of more than 250° C. at the SCR catalyst already after about 80 seconds. Compared with electric heating at 4 kW, the full function of the SCR catalyst thus starts more than five minutes earlier when the heated catalyst assembly according to the invention is used.

[0118] As FIG. 12 further shows in curve J, an SCR catalyst does not reach its full operating temperature of 250° C. until after a 30-minute ride if no heating device is used. In other words, the nitrogen oxide reduction in the exhaust gas is not possible at all during the first 30 minutes of a ride and thus in short-distance driving.

[0119] FIG. 14 shows the integrated heating power of the three heating devices compared in FIGS. 12 and 13 with one another over the entire WHTC test cycle. The heated catalyst assembly according to the invention was here operated in such a way that the SCR catalyst was heated up to operating temperature as quickly as possible. The fastest possible heating results from an operating control that operates the heated catalyst assembly in the second operating state until an oxidation catalyst arranged upstream of the SCR catalyst has reached a temperature of about 160° C. and subsequent switching to the first operating state, as explained in FIG. 13 by means of curve D.

[0120] As can be seen in FIG. 14, the heated catalyst assembly according to the invention here generates an average heating power of 2.9 kW over the entire WHTC test cycle. An additional fuel amount of 123 g is used for this purpose.

[0121] By comparison, an electrical heating device with a nominal output of 4 kW requires a fuel amount of 315 g during the WHTC test cycle for the operation to provide an average thermal output of 1.8 kW. If the electric heating power is doubled to nominally 8 kW, an average electric heating power of 2.5 kW is generated during the entire WHTC test cycle; however, a fuel amount of 447 g is required for this purse. Therefore, the fuel amount required to heat the exhaust gas after-treatment system is reduced by over 70% or over 60% when the heated catalyst assembly according to the invention is used compared to an electric heater, although the released heating power is considerably greater. This is due to the fact that the electric heating power in the motor vehicle must be provided by the driving engine and generator, which have a comparatively low efficiency.

[0122] As described above for an SCR catalyst, the heated catalyst assembly according to the invention can also be used to provide the heating power required for the regeneration of a particulate filter in all operating states, in particular also in operating states with low load.

[0123] With reference to FIG. 15, a test stand is explained in more detail with which the heated catalyst assembly 2 according to the invention can be tested under highly dynamic operating states such as occur in real operation in a motor vehicle.

[0124] Equal components of the invention are provided with equal reference signs so that the following description can be limited to the essential differences.

[0125] On the one hand, the exhaust gas of an internal combustion engine contains combustion gases, such as H.sub.2O and CO.sub.2, which can be approximately regarded as inert gases. In the simulated, synthetic exhaust gas, this part is formed by nitrogen. In addition, the exhaust gas stream contains a varying proportion of oxygen, which is available for oxidation in the exhaust gas set. In order to simulate an exhaust gas stream in the test mode, the test stand has a reservoir 92a containing nitrogen and a reservoir 92b containing air. Both components can be metered via mass flow control 93 so that a gas stream with varying oxygen content between 0% and 21% is available as synthetic exhaust gas at the inlet 21 of the heated catalyst assembly 2.

[0126] This gas stream flows through the heated catalyst assembly 2 and leaves the heated catalyst assembly 2 via the outlet 22. Furthermore, the heated catalyst assembly 2 is supplied with commercially available diesel fuel via the connection 62, which fuel is delivered from a tank 90 by means of a metering pump 91.

[0127] Depending on the operating state of the heated catalyst assembly 2, the gas stream discharged at the outlet 22 essentially contains a hot inert gas stream or a reformate, as described above.

[0128] In order to analyze the reformate, a partial flow of the exhaust gas is supplied via line 94 to an analysis device which, in the illustrated exemplary embodiment, includes a Fourier transform infrared spectrometer 941 and a gas chromatograph 942. The remaining exhaust gas stream is cooled by an exhaust gas cooler 95 and discharged via an exhaust gas line 3. The heat of the exhaust gas is here at least partially transferred to a coolant stream 96, which can comprise, for example, a cooling gas stream and/or liquid cooling. By measuring the temperatures and mass flows of the exhaust gas stream and of the coolant stream, the heating power delivered by the heated catalyst assembly 2 can be determined.

[0129] FIGS. 16, 17 and 18 illustrate experimental results of the characterization of a heated catalyst assembly according to the present invention. They show the total exhaust gas mass flow in curve C, the partial flow supplied to the heated catalyst assembly with an uncontrolled pressure reduction device 7 in curve S, the partial flow supplied to the heated catalyst assembly with a controlled pressure reduction device 7 in curve R, the oxygen content of the exhaust gas in curve O, the temperature of an SCR catalyst in curve H, the temperature of the heated catalyst assembly in curve K, the air ratio X of the heated catalyst assembly in curve M, and the heating power delivered by the heated catalyst assembly in curve D. Here, FIG. 16 shows the progression of these variables over 300 seconds. FIG. 17 shows an enlarged view of the first two minutes. FIG. 18 shows the course during the third to the tenth minute.

[0130] As is clear from FIG. 16 and in particular FIG. 17, the heated catalyst assembly is operated in the second operating state during the first 80 seconds. The second operating state is characterized by a large excess of air so that the supplied fuel is completely oxidized and converted exothermically. As shown in curve D, the heating power is about 12 kW in this case. The supplied partial flow of the exhaust gas is about 40 kg/h.

[0131] After 80 seconds, the supplied exhaust gas mass flow is reduced to about 14 kg/h. The heated catalyst assembly is then located in the first operating state, in which a lower thermal power is generated directly in the heated catalyst assembly. However, the reformate generated in the heated catalyst assembly in this operating state causes, when reacted at an oxidation catalyst of the exhaust gas after-treatment system, the heat amount effectively supplied to an exhaust gas after-treatment system to increase to 36 kW. After about 110 seconds, the SCR catalyst has reached its operating temperature, rendering possible efficient exhaust emission control of nitrogen oxides.

[0132] As curve K in FIG. 17 shows, the outlet temperature at the outlet 22 of the heated catalyst assembly 2 responds very quickly to changing the operating state. Furthermore, FIGS. 16, 17 and 18 show that the heated catalyst assembly according to the invention is very resistant to variations in the exhaust gas mass flow and to variations in the oxygen concentration. With a supplied mass flow S between about 30 kg/h and about 90 kg/h and variations of the oxygen concentration between 7% and 20.5%, there are no adverse effects on the heating power supplied to the exhaust gas after-treatment system.

[0133] The above described application examples demonstrate that the heated catalyst assembly according to the invention can provide high heating power in the short term, with which an exhaust gas after-treatment system can be brought to operating temperature within very short times of, for example, less than 120 seconds or less than 100 seconds or less than 80 seconds. Compared with electrical heating devices, the fuel requirement for heating the exhaust gas after-treatment systems is reduced.

[0134] Of course, the invention is not limited to the illustrated embodiments. Therefore, the above description should not be regarded as restrictive but as explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the claims and the above description define “first” and “second” embodiments, this designation is used to distinguish between two similar embodiments without determining a ranking order.