Combustion chamber assembly

Abstract

Combustion chamber assembly (10) for a fuel-operated vehicle heater, comprising a combustion chamber housing (12) surrounding a combustion chamber (18) and, downstream of the combustion chamber housing (12), an exhaust gas flow path (26) leading to an exhaust gas outlet (42), further comprising a flame tube (20) and a heat exchanger housing (30) surrounding the flame tube (20), wherein a first exhaust gas flow path region (24) of the exhaust gas flow path (26) receiving a combustion exhaust gas (A) from the combustion chamber (18) is provided in the flame tube (20), and a second exhaust gas flow path region (36) of the exhaust gas flow path (26) is provided between the flame tube (20) and the heat exchanger housing (30), adjoining the first exhaust gas flow path region (24) and leading to the exhaust gas outlet (42), wherein on an inner side of the Heat exchanger housing (30) is provided with heat transfer fins (50) extending in the second exhaust gas flow path region (36),wherein a catalyst arrangement (52) is provided in the exhaust gas flow path (26) in the second exhaust gas flow path region (36) downstream of the heat transfer fins (50), and wherein a heating device (54) for heating the catalyst arrangement (52) is assigned to the catalyst arrangement (52), characterized in that the heating device (54) comprises a coupling region (58) with a coupling volume (60) for coupling electromagnetic radiation (S) generated by at least one radiation source (56) separated from the exhaust gas flow path (26) by the coupling volume (60) into the exhaust gas flow path (26) for heating the catalyst arrangement (52) by means of the electromagnetic radiation (S) generated by the at least one radiation source (56).

Description

[0001] The present invention relates to a combustion chamber assembly for a fuel-operated vehicle heater according to the preamble of claim 1. The combustion chamber assembly comprises a combustion chamber housing defining a combustion chamber and, downstream of the combustion chamber housing, an exhaust gas flow path leading to an exhaust gas outlet, wherein a catalyst arrangement is provided in the exhaust gas flow path, optionally also in the exhaust gas outlet, and wherein a heating device for heating the catalyst arrangement is assigned to the catalyst arrangement.

[0002] Such a combustion chamber assembly is known from DE 10 2018 100 216 B3. In this known combustion chamber assembly, a catalyst assembly is provided in a region of an exhaust gas flow path formed between a flame tube and a heat exchanger housing surrounding it, adjacent to a downstream end of heat transfer fins provided on the heat exchanger housing. In order to avoid excessive pollutant emissions even in operating phases in which the catalyst assembly is not heated by the exhaust gas flowing through it to such an extent that the temperature required to carry out the catalytic reaction is reached, a heating device is assigned to the catalyst assembly for heating the same. The heating device comprises an electrically excitable heating conductor arranged on an upstream side of the catalyst assembly facing the heat transfer fins.When the heating element is energized, it is heated and the heat generated by the heating element is transferred to the catalyst arrangement by thermal conduction.

[0003] DE 696 05 055 T2 discloses a catalyst system with a catalyst block arranged in a cavity providing a resonator volume. Microwave radiation is coupled into the cavity via a waveguide, heating the catalyst block arranged in the cavity. For this purpose, the cavity is defined by walls designed to resonate the electromagnetic energy coupled in the form of the microwave radiation.

[0004] US 2018 / 0291786 A1 discloses a catalyst system with a catalyst block arranged in a housing. A radiant heating element is provided on an upstream end face of the catalyst block, through which the exhaust gas flowing toward the catalyst block can flow. This radiant heating element emits infrared radiation to heat the catalyst block.

[0005] It is the object of the present invention to further develop a generic combustion chamber assembly in such a way that improved heating of the catalyst arrangement can be achieved with reduced impairment of the exhaust gas flow.

[0006] According to the invention, this object is achieved by a combustion chamber assembly for a fuel-operated vehicle heater according to claim 1. This comprises a combustion chamber housing defining a combustion chamber and, downstream of the combustion chamber housing, an exhaust gas flow path leading to an exhaust gas outlet, wherein a catalyst arrangement is provided in the exhaust gas flow path, and wherein at least one catalyst arrangement is assigned a heating device for heating the catalyst arrangement.

[0007] The combustion chamber assembly includes a flame tube and a heat exchanger housing surrounding the flame tube. A first exhaust gas flow path region receiving combustion exhaust gas from the combustion chamber is provided in the flame tube, and a second exhaust gas flow path region is provided between the flame tube and the heat exchanger housing. The second exhaust gas flow path region adjoins the first exhaust gas flow path region and leads to the exhaust gas outlet. For improved thermal interaction of exhaust gas flowing in the exhaust gas flow path, heat transfer fins extending in the second exhaust gas flow path region are provided on an inner side of the heat exchanger housing facing the second exhaust gas flow path region. The catalyst arrangement is arranged downstream of the heat transfer fins in the second exhaust gas flow path region.

[0008] In this combustion chamber assembly, the heating device is designed to heat the catalyst arrangement using electromagnetic radiation. The heating device comprises at least one radiation source for generating electromagnetic radiation and a coupling region for coupling the electromagnetic radiation generated by the at least one radiation source into the exhaust gas flow path. Efficient irradiation of the catalyst arrangement is supported by the coupling region comprising a coupling volume separating at least one radiation source from the exhaust gas flow path or the exhaust gas outlet. In the coupling volume, the electromagnetic radiation emitted by one or more radiation sources can, for example, be reflected multiple times, so that the electromagnetic radiation is specifically directed onto the catalyst arrangement to be heated.

[0009] Heating the catalyst assembly using electromagnetic radiation avoids the need for direct physical interaction between a heating device positioned in the exhaust gas flow path and the catalyst assembly. Therefore, there are no areas of the catalyst assembly that are shielded by the heating device and thus cannot be penetrated by exhaust gas or can only be penetrated with difficulty. Since the system area of ​​the heating device intended to generate the electromagnetic radiation is not, or does not need to be, positioned directly in the area of ​​the catalyst assembly, the exhaust gas flow path, or the exhaust outlet, this system area is not exposed to the exhaust gas and the thermal or chemical stress it generates.This system area can be positioned in such a way that a large-area irradiation of the catalyst arrangement is achieved, so that a more uniform and thus more intensive heating of the same can be achieved.

[0010] For efficient heating, it is further proposed that at least one, preferably each radiation source is designed to generate infrared radiation.

[0011] A configuration has proven particularly effective in which at least one, preferably each radiation source is designed to generate electromagnetic radiation in the frequency range from 300 MHz to 300 GHz.

[0012] In order to avoid shielding the catalyst arrangement to be heated by radiation against the electromagnetic radiation, it is proposed that at least one, preferably each coupling region comprises at least one coupling window permeable to electromagnetic radiation generated by the at least one radiation source.

[0013] In a thermally, chemically and mechanically stable design, at least one, preferably each coupling window can be formed with quartz glass.

[0014] At least one, preferably each coupling volume can be separated from the exhaust gas flow path or exhaust gas outlet by at least one coupling window.

[0015] In order to be able to irradiate the catalyst arrangement efficiently without being impaired by the heat transfer fins when the catalyst arrangement is designed or positioned in this way, it is proposed that at least one, preferably each, radiation source is arranged to direct the electromagnetic radiation emitted by it onto a downstream side of the catalyst arrangement facing away from the heat transfer fins.

[0016] The electromagnetic radiation can be efficiently directed onto the catalyst arrangement if at least one, preferably each, radiation source is arranged for coupling the electromagnetic radiation emitted by it into the exhaust gas flow path through an end wall delimiting the second exhaust gas flow path region at its downstream end.

[0017] In a further embodiment, it can be provided that at least one, preferably each, radiation source is arranged for coupling the electromagnetic radiation emitted by it into the exhaust gas flow path through the exhaust gas outlet. This positioning is suitable when other system regions of the combustion chamber assembly, for example, a combustion air blower or a volume conducting combustion air to the combustion chamber, do not permit the positioning of one or more radiation sources at the downstream end region of the second exhaust gas flow path region.

[0018] In a further embodiment, at least one, preferably each, radiation source can be arranged to direct the electromagnetic radiation emitted by it to an upstream side of the catalyst arrangement facing the heat transfer fins. In this embodiment, the heat transfer fins can be used to specifically direct the electromagnetic radiation to the upstream side of the catalyst arrangement by single or multiple reflections.

[0019] This can be achieved, for example, by arranging at least one, preferably each, radiation source in the region of a bottom wall of the heat exchanger housing formed with a peripheral wall and the bottom wall adjoining this.

[0020] The present invention is described in detail below with reference to the accompanying figures. They show: Fig. 1 is a schematic longitudinal sectional view of a combustion chamber assembly of a fuel-fired vehicle heater; Fig. 2 one of the Fig. 1 corresponding representation of an alternative design of a combustion chamber assembly; Fig. 3 one of the Fig. 1 corresponding representation of an alternative design of a combustion chamber assembly; Fig. 4 one of the Fig. 1 corresponding representation of a combustion chamber assembly not constructed according to the principles of the present invention.

[0021] In Fig. 1 shows a combustion chamber assembly for a fuel-operated vehicle heater, generally designated 10. The combustion chamber assembly 10 comprises a combustion chamber housing 12 with a peripheral wall 14 and a bottom wall 16. The peripheral wall 14 and the bottom wall 16 define a combustion chamber 18, into which combustion air is fed by a combustion air blower (not shown), and into which fuel is fed by a fuel pump (not shown). The fuel can, for example, be vaporized in the combustion chamber and mixed with the combustion air to produce or burn a combustible mixture.

[0022] In a flame tube 20, which adjoins, for example, the peripheral wall 14 of the combustion chamber housing 12, a first exhaust gas flow path region 24 of an exhaust gas flow path, generally designated 26, is formed, separated from the combustion chamber 18 in the region of a flame baffle 22. Exhaust gas A generated during combustion flows essentially in the direction of a housing longitudinal axis L in the first exhaust gas flow path region 24 to an axially open end 28 of the flame tube 20.

[0023] The flame tube 20 is surrounded on its outside by a pot-shaped heat exchanger housing 30. The heat exchanger housing 30 has a bottom wall 32 opposite the axially open end 28 of the flame tube 20 and an adjoining peripheral wall 34. The peripheral wall 34 can extend, for example, into the region of the peripheral wall 14 of the combustion chamber housing 12. A second exhaust gas flow path region 36 is formed between the peripheral wall 34 and the flame tube 20, which thus has an annular structure surrounding the housing longitudinal axis L. From the flame tube 20 orExhaust gas A emerging from the first exhaust gas flow path region 24 formed therein in the region of the axially open end 28 is deflected radially outwards on the bottom wall 32 and thus flows into the second exhaust gas flow path region 36, in which it flows essentially in a flow direction opposite to the flow direction in the first exhaust gas flow path region 24 and in the process transfers heat to the heat transfer medium to be heated on its outside, for example air or a liquid.

[0024] At its axial end 38 remote from the bottom wall 32 of the heat exchanger housing 30, the second exhaust gas flow path region 36 is delimited by an end wall 40. In the region of the end wall 40, the exhaust gas A flowing in the second exhaust gas flow path region 36 is deflected in the circumferential direction to an exhaust gas outlet generally designated 42. The exhaust gas outlet 42 comprises an outlet line 44, which can, for example, comprise an outlet nozzle 46 extending from the heat exchanger housing 30 or its peripheral wall 34 and an outlet pipe 48 adjoining it. The exhaust gas leaving the exhaust gas flow path 26 is discharged to the environment via the outlet line 44, for example via a silencer or the like.

[0025] On an inner side of the heat exchanger housing 30 facing the exhaust gas flow path 26, heat transfer fins 50 are provided in the second exhaust gas flow path region 36. These fins increase the surface area available for heat transfer. Adjacent to the heat transfer fins 50, a catalyst arrangement, generally designated 52, is provided in the second exhaust gas flow path region 36. The catalyst arrangement 52 is held between the peripheral wall 34 of the heat exchanger housing 30 and, for example, the peripheral wall 14 of the combustion chamber housing 12 and / or the flame tube 20, so that the exhaust gas A flowing in the second exhaust gas flow path region 36 flows through the catalyst arrangement 52.The catalyst assembly 52, designed, for example, as an oxidation catalyst, comprises a substrate constructed, for example, with a metal mesh or metal mesh, which is coated with a catalytically active material on its surface formed by the pore structure. A monolithic, porous substrate, e.g., constructed with a foamed material, can also be used to construct the catalyst assembly 52.

[0026] The exhaust gas A flowing through the catalyst arrangement 52 leaves the second exhaust gas flow path region 36 to the exhaust gas outlet 42.

[0027] A heating device, generally designated 54, is provided in association with the catalytic converter arrangement 52. By means of the heating device 54, the catalytic converter arrangement 52 can be brought to this temperature or kept at this temperature, particularly in operating phases in which it is not heated by the exhaust gas A flowing through the catalytic converter arrangement 52 in order to obtain or maintain the temperature required for the catalytic reaction, so that, particularly at the start of combustion operation, there is essentially no phase in which exhaust gas A flowing through the exhaust gas flow path 26 is not subjected to a catalytic reaction. The heating device 54 associated with the catalytic converter arrangement 52 is designed to heat the catalytic converter arrangement 52 by irradiation with electromagnetic radiation S.For efficient heating operation, the electromagnetic radiation can be infrared radiation, with the frequency being in the range between 300 MHz and 300 GHz.

[0028] The heating device 54 comprises a radiation source 56 positioned outside the exhaust gas flow path 26 or also outside the exhaust gas outlet 42, which is designed to generate radiation at the desired frequency or with the desired frequency spectrum. Such a radiation source 56, which is designed in particular to generate or emit infrared radiation, can be provided with a very compact size, approximately the size of a credit card, and thus can be arranged in the area of ​​the combustion chamber assembly.

[0029] In order to be able to guide the electromagnetic radiation emitted by the radiation source 56 to the catalyst arrangement 52, a coupling region, generally designated 58, is provided. The coupling region 58 comprises a coupling volume 60, which is surrounded by a wall 61 which reflects the radiation S and is constructed, for example, of metal material and carries the radiation source 56, and further comprises in the Fig. 1, a coupling window 62 is provided in the region of the exhaust outlet 42. The coupling window 62 is constructed, for example, with quartz glass and inserted into a wall of the exhaust line 44. The electromagnetic radiation S emitted by the radiation source 56 passes through the coupling window 62 into the region of the exhaust outlet 42 and the second exhaust flow path region 36. Since the exhaust outlet 42 and the heat exchanger housing 30, as well as the peripheral wall 14 of the combustion chamber housing 12 and the flame tube 20, are generally constructed of metal material, the radiation S is also reflected at these system regions and thus reaches the region of the downstream side 64 of the catalyst arrangement 52, which is positioned facing away from the heat transfer fins 50.On this downstream side 64, the catalyst arrangement 52 is heated over a large area and very evenly by the electromagnetic radiation S, without the flowability of the catalyst arrangement 52 being impaired by any system regions of the heating device 54. All system regions of the heating device 54, in particular those that are thermally sensitive, are located outside the exhaust gas flow path 26 or the exhaust gas outlet 42 and are thus not exposed to the thermally and chemically highly polluting exhaust gas A. Also, no components are required that, for example, conduct electrical energy through the exhaust gas flow path 26 or the exhaust gas outlet 42 toward the catalyst arrangement 52.

[0030] By heating the catalyst arrangement 52 by means of electromagnetic radiation S, not only a very uniform but also a very intensive heating of the catalyst arrangement 52 is achieved due to the achievable heat flux density, whereby this heating begins almost instantaneously upon activation of the heating device 54. Due to the possibility of achieving a very high energy density or introducing it into the catalyst arrangement 52, it is also possible to heat the catalyst arrangement 52 so intensely by means of the heating device 54 that soot deposits formed therein can be sufficiently heated and thus burned off.

[0031] An alternative embodiment of the combustion chamber assembly 10 is shown in Fig. 2. This corresponds in terms of the basic structure and also the positioning of the catalyst arrangement 52 to the above with reference to the Fig. 1, so that reference can be made to these explanations.

[0032] A difference can be seen in the design and positioning of the heating device 54. This is designed to couple the electromagnetic radiation via the end wall 40 axially delimiting the second exhaust gas flow path region 36 in the direction of the catalyst arrangement 52. Furthermore, the heating device 54 has a plurality of radiation sources 56 distributed in the circumferential direction. Each radiation source 56 is assigned a coupling region 58, each with a coupling volume 60 and a coupling window 62. By means of the plurality of radiation sources 56, it is possible to ensure even more uniform irradiation of the catalyst arrangement 52 on its downstream side 64, distributed over the circumference.

[0033] A further modification of the combustion chamber assembly is in Fig. 3. This combustion chamber assembly 10 also corresponds in terms of its basic structure to that described above with reference to the Fig. 1 described structure. Unlike the designs of the Fig. 1 and Fig. 2, is in the form of the Fig. 3 the heating device 54 is arranged and designed such that the catalyst arrangement 52 is irradiated on its upstream side 66 facing the heat transfer fins 50. For this purpose, a coupling volume 60 of the coupling region 58 can be provided on the bottom wall 32, for example completely covering the bottom wall 32, in association with the single radiation source 56, for example. A coupling window 62 of the coupling region 58 can be provided between each two heat transfer fins 50 arranged one after the other in the circumferential direction, so that in the area between immediately adjacent heat transfer fins 50 the radiation S can be coupled into the exhaust gas flow path 26 and, by reflection on the opposing surfaces of the heat transfer fins 50 or also the inner circumferential surface of the circumferential wall 34 orthe outer circumferential surface of the flame tube 20 in the direction of the upstream side 66 of the catalyst arrangement 52, wherein the opposing surfaces reflecting the electromagnetic radiation S guide the possibly multiply reflected electromagnetic radiation S to the catalyst arrangement 52 in the manner of a waveguide.

[0034] A combustion chamber assembly 10 not constructed according to the principles of the present invention is shown in Fig. 4. In this embodiment, the catalyst arrangement 52 is arranged in the exhaust outlet 42, in particular the outlet pipe 48 of the outlet line 44 adjoining the outlet connection 46. A coupling window 62 of the coupling region 58 associated with the radiation source 56 is provided in the outlet line 44, so that the electromagnetic radiation S coupled through the coupling volume 60 into the exhaust outlet 42 is directed onto the upstream side 66 of the catalyst arrangement 52, thus efficiently heating the catalyst arrangement 52.This embodiment, in which the heating device 54 is to be activated, for example depending on the ambient temperature, even during normal combustion operation in order to keep the catalyst arrangement 52 sufficiently warm, is particularly suitable for use in hybrid vehicles or in fuel-operated vehicle heaters in fully electric vehicles, which have a higher battery capacity to also supply the heating device 54 with electrical energy.

[0035] Finally, it should be noted that, of course, various embodiments described above can be combined with one another. For example, radiation sources 56 of the heating device 54 can be positioned such that the catalyst arrangement 52 is heated on both its upstream side 66 and its downstream side 64. For example, the Fig. 3 can be combined with the embodiment of 1 and / or the embodiment of Fig. 2. It is also possible that a catalyst arrangement 52 is arranged both in the second exhaust gas flow path area 36 and in the exhaust gas outlet 42, so that, for example, the design of the Fig. 4 with one or more of the forms of the Fig. 1 to 3 can be combined. In this case, functionally different catalyst arrangements 52 can be used to carry out different catalytic reactions. One of the catalyst arrangements 52 could also be designed in the form of a soot particle filter or provide a soot particle filter.

[0036] When the combustion chamber assembly 10 is constructed with multiple catalyst assemblies 52, for example, only one of the catalyst assemblies 52 can be assigned a heating device 54, so that, for example, in the start-up phase of combustion operation, heating of this catalyst assembly 52 ensures the implementation of a catalytic reaction of the exhaust gas A produced in this operating phase. One or more catalyst assemblies 52 not provided in cooperation with a heating device 54 can develop their catalytic effectiveness when their temperature has been sufficiently raised during combustion operation by the exhaust gas A flowing through them.

[0037] The invention also relates to a vehicle heater constructed with a combustion chamber assembly 10 according to the invention.

Claims

[1] Combustion chamber assembly (10) for a fuel-operated vehicle heater, comprising a combustion chamber housing (12) surrounding a combustion chamber (18) and, downstream of the combustion chamber housing (12), an exhaust gas flow path (26) leading to an exhaust gas outlet (42), further comprising a flame tube (20) and a heat exchanger housing (30) surrounding the flame tube (20), wherein a first exhaust gas flow path region (24) of the exhaust gas flow path (26) receiving a combustion exhaust gas (A) from the combustion chamber (18) is provided in the flame tube (20), and a second exhaust gas flow path region (36) of the exhaust gas flow path (26) is provided between the flame tube (20) and the heat exchanger housing (30), adjoining the first exhaust gas flow path region (24) and leading to the exhaust gas outlet (42), wherein on an inner side of the Heat exchanger housing (30) is provided with heat transfer fins (50) extending in the second exhaust gas flow path region (36),wherein a catalyst arrangement (52) is provided in the exhaust gas flow path (26) in the second exhaust gas flow path region (36) downstream of the heat transfer fins (50), and wherein a heating device (54) for heating the catalyst arrangement (52) is assigned to the catalyst arrangement (52), , characterized by that the heating device (54) comprises a coupling region (58) with a coupling volume (60) for coupling electromagnetic radiation (S) generated by means of at least one radiation source (56) separated from the exhaust gas flow path (26) by the coupling volume (60) into the exhaust gas flow path (26) for heating the catalyst arrangement (52) by means of the electromagnetic radiation (S) generated by the at least one radiation source (56). [2] Combustion chamber assembly (10) according to claim 1, characterized by that at least one, preferably each radiation source (56) is designed to generate infrared radiation. [3] Combustion chamber assembly (10) according to claim 1 or 2, characterized by that at least one, preferably each radiation source (56) is designed to generate electromagnetic radiation (S) in the frequency range from 300 MHz to 300 GHz. [4] Combustion chamber assembly (10) according to one of claims 1-3, characterized by that at least one, preferably each coupling region (58) comprises at least one coupling window (62) which is permeable to electromagnetic radiation (S) generated by the at least one radiation source (56). [5] Combustion chamber assembly (10) according to claim 4, characterized by that at least one, preferably each coupling window (62) is formed with quartz glass. [6] Combustion chamber assembly (10) according to claim 4 or 5, characterized by that at least one, preferably each coupling volume (60) is separated from the exhaust gas flow path (26) or from the exhaust gas outlet (42) by at least one coupling window (62). [7] Combustion chamber assembly (10) according to one of the preceding claims, characterized by that at least one, preferably each radiation source (56) is arranged to direct the electromagnetic radiation (S) emitted thereby onto a downstream side (64) of the catalyst arrangement (52) facing away from the heat transfer fins (50). [8] Combustion chamber assembly (10) according to claim 7, characterized by that at least one, preferably each radiation source (56) is arranged for coupling the electromagnetic radiation (S) emitted by it into the exhaust gas flow path (26) through an end wall (40) delimiting the second exhaust gas flow path region (36) at its downstream end (38). [9] Combustion chamber assembly (10) according to claim 7 or 8, characterized bythat at least one, preferably each radiation source (56) is arranged for coupling the electromagnetic radiation (S) emitted thereby into the exhaust gas flow path (26) through the exhaust gas outlet (42). [10] Combustion chamber assembly (10) according to one of the preceding claims, characterized by that at least one, preferably each radiation source (56) is arranged to direct the electromagnetic radiation (S) emitted thereby onto an upstream side (66) of the catalyst arrangement (52) facing the heat transfer fins (50). [11] Combustion chamber assembly (10) according to claim 10, characterized by that at least one, preferably each radiation source (56) is arranged in the region of a bottom wall (32) of the heat exchanger housing (30) formed with a peripheral wall (34) and the bottom wall (32) adjoining this. [12] Vehicle heater comprising a combustion chamber assembly (10) according to any one of the preceding claims.

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