WO2022073710A1

WO2022073710A1 - Heating device for heating an exhaust gas catalytic converter

Info

Publication number: WO2022073710A1
Application number: PCT/EP2021/074652
Authority: WO
Inventors: Dietmar Uhlenbrock
Original assignee: Robert Bosch Gmbh
Priority date: 2020-10-08
Filing date: 2021-09-08
Publication date: 2022-04-14
Also published as: DE102020212715A1

Abstract

A heating device (3) for heating an exhaust gas catalytic converter (4) comprises a burner chamber (3a); an air supply (8) which is configured to conduct air (7) into the burner chamber (3a); a fuel injection device (10) which is configured to inject fuel (11) into the burner chamber (3a); an ignition device (12) which is configured to ignite the fuel (11) which is introduced into the burner chamber (3a); and a gas outlet (3b) which is configured to discharge hot combustion gases (22) from the burner chamber (3a). An orifice plate (13) is arranged in the gas outlet (3b), which orifice plate (13) comprises an outer, substantially closed region (14) and an inner, substantially open region (20) which is arranged inside the outer region (14). The outer region extends along an outer circumference of the gas outlet (3b), and impedes or prevents the outflow of unburned fuel (11) through an outer region (14) of the gas outlet (3b). The open inner region (20) allows combustion gases (22) to flow out of the burner chamber (3a).

Description

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description

title

Heating device for heating up an exhaust gas catalytic converter

The invention relates to a heating device for heating up an exhaust gas catalytic converter which is arranged in an exhaust system of an internal combustion engine. The invention also includes an exhaust line with a heating device according to the invention.

State of the art

In order to reduce the pollutants in the exhaust gases from internal combustion engines, exhaust gas catalytic converters, in particular three-way catalytic converters, are used, which are arranged in the exhaust system of the respective internal combustion engine.

In order to efficiently reduce the pollutants in the exhaust gases, the exhaust gas catalytic converters must be operated at a certain operating temperature. The operating temperature required for a high efficiency of the exhaust gas catalytic converter is not reached immediately in the cold start phase of the internal combustion engine, in particular in the first 20 s to 40 s after starting the internal combustion engine. Until the operating temperature is reached, the catalytic converters do not work at all or only with a low level of efficiency. It is therefore advantageous to heat up exhaust gas catalytic converters in the cold start phase using a heating device so that the operating temperature required for efficient pollutant reduction is reached as quickly as possible.

It is an object of the invention to provide an efficient heating device for heating up an exhaust gas catalyst.

Disclosure of Invention

A heating device according to the invention for heating up an exhaust gas catalytic converter is designed as a burner with a combustion chamber. The heater includes an air supply configured to direct air into the combustion chamber; one Fuel injector configured to inject fuel into the combustion chamber; an ignition device configured to ignite a fuel-air mixture in the combustion chamber; and a gas outlet configured to exhaust from the combustion chamber hot combustion gases generated when the fuel-air mixture is combusted in the combustion chamber.

A screen is arranged in the gas outlet and comprises an outer, essentially closed area and an inner, essentially open area, which is arranged in the radial direction inside the outer area. The inner, substantially open area allows combustion gases to flow out through a radially central portion of the outlet.

"Substantially closed" in this context means that at least 80% of the area of the outer region is closed.

"Substantially open" in this context means that at least 80% of the area of the inner region is open.

The outer portion of the screen extends along an outer perimeter of the outlet. Because the outer portion is closed or substantially closed, the outer portion of the orifice impedes or prevents unburned fuel from flowing out through a radially outer portion of the outlet. In this way, unburned fuel residing in an outer region of the combustion chamber is given additional time to continue to heat, vaporize and ignite, creating additional hot combustion gases. Due to the fact that in a heating device according to the invention, due to the described effect of the orifice, a larger part of the fuel introduced into the combustion chamber is burned than in a heating device that is not equipped with such an orifice, the efficiency of the heating device can be significantly improved.

Due to the improved efficiency, the combustion chamber of a heating device according to the invention can be made relatively small. In particular, the combustion chamber can be made smaller than the combustion chamber of a conventional one Heating device not having a screen according to the invention. As a result, a heating device can be provided that requires only a small amount of space.

An orifice designed according to the invention causes only a small pressure loss in the gas outlet of the combustion chamber. A small and inexpensive conveying device (pump) can therefore be used to convey the combustion air into the combustion chamber.

A screen designed according to the invention makes it possible to efficiently dissipate the intense heat of the hot combustion gases, which is transferred to the screen, to the (possibly cooled) wall of the combustion chamber and thus prevent the screen from overheating. As a result, the life of the bezel can be extended and less heat-resistant and therefore less expensive materials can be used for the bezel.

In one embodiment, the outer area of the screen is ring-shaped and extends along the circumference of a cylinder-shaped combustion chamber. This allows unburned fuel that is in the outer area of the combustion chamber to be retained in the combustion chamber.

In one embodiment, the outer portion of the bezel has at least one off-center opening that allows combustion gases to flow through the outer portion of the bezel and exit the combustion chamber. At least one decentralized opening formed in the outer region of the orifice allows the flow resistance of the orifice and thus the pressure loss in the gas outlet of the combustion chamber caused by the orifice to be kept low.

In one embodiment, the outer portion of the orifice includes a plurality of segments extending radially inward from an outer perimeter of the outlet toward the center of the combustor. The individual segments are separated from one another by open areas, in particular by gaps or slits, which also extend in the radial direction. Such segments, which are separated from one another by open areas, create an area of the diaphragm which - retains unburned fuel in the combustion chamber without causing excessive flow resistance and pressure loss in the gas outlet of the combustion chamber.

In one embodiment, opposite edges of adjacent segments extend substantially parallel to one another. In such an embodiment, the openings in the screen create a strong air turbulence behind the screen, so that unburned fuel residues can react well.

In another embodiment, the open areas between adjacent segments are V-shaped with a narrower outer area and a wider inner area. In such an embodiment, too, the openings in the screen produce a particularly strong air turbulence behind the screen, so that unburned fuel residues can react well.

In one embodiment, the segments are each twisted helically, i.e., similar to the blades of a marine propeller, about an axis extending radially outward from the center of the outlet. Such twisted segments create a swirl in the combustion gases flowing through the orifice. Such a swirl results in better mixing of unburned or only partially burned fuel with unburned oxygen. Improved mixing results in more fuel being burned, so the efficiency of the heater can be improved even further.

In one embodiment, the segments are oriented at a right angle to the perimeter of the outlet. Such segments aligned at right angles to the outer boundary of the outlet can be produced in a particularly simple and cost-effective manner.

In an embodiment wherein the segments are inclined at an angle of between 7.5° and 30° to the perimeter of the outlet. The segments can be inclined in the flow direction of the combustion gases or against the flow direction. By tilting the segments of the iris, the efficiency of the iris can be further increased. An inclination angle of at least 7.5° ensures that the hot exhaust gases, after passing the inner/front edge where the hot exhaust gases first meet the respective segment, detach from the segment and do not flow along the segment in a laminar manner . By stalling the flow, the transfer of heat from the hot exhaust gases to the segments is kept low, so that the segments are not overheated.

In one embodiment, each of the segments has an outer portion oriented at a right angle to the perimeter of the outlet and a near-center portion oriented at an angle between 7.5° and 30° to the perimeter of the outlet is.

The inclined portions may be inclined in the direction of flow of the combustion gases or against the direction of flow.

In one embodiment, the baffle is formed increasingly curved, starting from the outer wall of the combustion chamber, so that the end of the baffle near the center extends almost parallel to the axial direction of the outlet, without the baffle having a sharp bend. A mechanically weak point (“predetermined breaking point”), such as that created by a sharp bend, can be avoided by means of a screen designed in this way.

Each of the segments has an inner end portion that faces the central portion of the outlet. In one embodiment, the inner end areas are formed with a smaller material thickness than the outer areas of the segments that border the perimeter of the outlet. In particular, the inner end portions are formed with a sharp edge facing the flow of hot combustion gases. Since the hot combustion gases strike the inner end areas of the segments in particular, the transfer of heat from the hot combustion gases to the segments is further reduced by the inner end areas which are particularly thin, in particular sharp-edged. In one embodiment, the segments have inner end portions that are at most 0.5 mm thick. Outside the inner end areas, the segments can be 2 mm to 3 mm thick, for example. Thicker outer areas of the segments have a higher thermal capacity than thinner areas and can therefore better transfer the absorbed heat to the (possibly cooled) wall of the combustion chamber.

Reduced heat transfer to the screen and good heat dissipation from the screen increases its service life and/or less heat-resistant and therefore less expensive materials can be used to manufacture the screen.

The screen can be made of CrNi steel or Ni-based steel, for example.

The invention also includes an exhaust system for an internal combustion engine with at least one exhaust gas catalytic converter, in particular a three-way catalytic converter, and a heating device according to the invention, which is arranged upstream of the at least one exhaust gas catalytic converter on the exhaust gas system.

Short description of the figures

Exemplary embodiments of a heating device according to the invention are described below with reference to the attached figures.

FIG. 1 shows a schematic view of an exhaust system of an internal combustion engine with a heating device according to the invention.

FIG. 2 shows a schematic sectional view of a heating device according to the invention.

FIGS. 3 to 8 show longitudinal sectional views of possible exemplary embodiments of a screen of a heating device according to the invention.

FIGS. 9 to 11 show cross-sectional views of possible exemplary embodiments of a screen of a heating device according to the invention. character description

Figure 1 shows a schematic view of an exhaust system 2 of an internal combustion engine 1. Downstream of the internal combustion engine 1 in the flow direction of the exhaust gases, the exhaust system 2 comprises a three-way catalytic converter 4, a particle filter 5 and a silencer 6.

A heating device 3 is located between the internal combustion engine 1 and the three-way catalytic converter 4. A gas outlet of the heating device 3 opens into the exhaust line 2.

The heating device 3 is designed as a burner 3 and is intended to feed hot combustion gases into the exhaust system 2 during operation, in particular during the cold start phase of the internal combustion engine 1, in order to heat the three-way catalytic converter 4 very quickly to the operating temperature required for efficient pollutant reduction .

Figure 2 shows a schematic longitudinal sectional view of a heating device 3 designed according to the invention.

The heating device 3 is designed as a burner 3 and has a combustion chamber 3a, which is designed in particular in the shape of a cylinder about a longitudinal axis A. The combustion chamber 3a has, for example, a diameter Do of 40 mm to 70 mm, in particular a diameter Do of between 50 mm and 60 mm.

A gas outlet 3b shown in Figure 2 on the right side of the combustion chamber 3a is connected to the exhaust line 2, so that the combustion chamber 3a is in fluid communication with the exhaust line 2 and combustion gases 22 can flow from the combustion chamber 3a into the exhaust line 2.

A fuel injection device 10 with an injection valve 10a is provided on the end face of the combustion chamber 3a shown on the left in FIG. The fuel injection device 10 is designed to inject fuel 11 into the combustion chamber 3a.

An air supply 8 is integrated into the burner casing 3d surrounding the combustion chamber 3a and is designed to guide fresh air 7 into the combustion chamber 3a. The fresh air 7 conducted into the combustion chamber 3a is wired through swirl grids 9 arranged in the air supply 8 and introduced into the combustion chamber 3a through the end face of the combustion chamber 3a opposite the gas outlet 3b.

The burner 3 also includes an ignition device 12 enabling the fuel-air mixture in the combustion chamber 3a to be ignited.

The combustion of the fuel-air mixture in the combustion chamber 3a produces hot combustion gases 22, which are introduced into the exhaust system 2 through the gas outlet 3b in order to heat the three-way catalytic converter 4.

In the gas outlet 3b of the combustion chamber 3a, an aperture 13, in particular an aperture 13 formed in a circle around the longitudinal axis A, is provided. The orifice 13 prevents unburned fuel 11, which is located in a radially outer area of the combustion chamber 3a outside of the particularly hot reaction zone in the center 3c of the combustion chamber 3a, from escaping through the gas outlet 3b from the combustion chamber 3a.

The screen 13 has a central opening 20, for example a circular opening 20 with a diameter Di of 25 mm to 50 mm, in particular with a diameter Di of 30 mm to 40 mm.

The orifice 13 may be inclined toward the fuel injector 10 such that the inner edge of the orifice 13 is closer to the fuel injector 10 than the outer portion of the orifice 13, as shown in FIG. The panel 13 can in particular be inclined in such a way that the panel is aligned at an angle of at least 7.5°, preferably at an angle of between 7.5° and 30°, to the longitudinal axis A.

By inclining the orifice 13 by at least 7.5° to the longitudinal axis A of the combustion chamber 3a, the hot combustion gas flow 22 is directed directly behind the front end region (the front edge) 23 of the orifice 13, which is the hot reaction zone in the center 3c of the combustion chamber 3a faces, tears off, so that the hot combustion gas flow 22 is not applied to the screen 13 and the screen 13 additionally heats up in this way. In order to further reduce the heat transfer from the hot combustion gases 22 to the screen 13, the inner end region 23 of the screen 13 facing the combustion chamber 3a is preferably designed to be as thin and sharp-edged as possible. Following the thin inner end region 23 of the screen 13, which is directly exposed to the hot combustion gas flow 22, the material of the screen 13 is preferably thicker, for example 2 mm to 3 mm thick, by the hot combustion gases 22 transferred to the screen 13 able to absorb and dissipate heat.

The panel 13 is preferably made of a particularly heat-resistant material, in particular a CrNi steel or a Ni-based steel.

Longitudinal sections through the combustion chamber 3a with alternative exemplary embodiments of the screen 13 are shown in FIGS.

The orifice 13 can, for example, be aligned orthogonally to the longitudinal axis A of the combustion chamber 3a (FIG. 3), or the orifice 13 can be inclined away from the fuel injector 10 towards the gas outlet 3b of the combustion chamber (FIG. 4).

The panel 13 can also be kinked. The screen 13 can in particular have a first area 13a, which is aligned orthogonally to the longitudinal axis A of the combustion chamber 3a, and a second area 13b, which is inclined towards the fuel injection device 10 or away from the fuel injection device 10, as shown in Figures 5 and 6 is shown. In this case too, the angle a between the inclined area 13b of the diaphragm and the outer boundary 3d of the combustion chamber 3a is preferably at least 7.5°, in particular between 7.5° and 30°.

The diaphragm 13 can also be designed to be increasingly curved, starting from the outer boundary 3d of the combustion chamber 3a (see FIG. 7), without having a sharp kink.

In a further exemplary embodiment, the orifice plate 13 is designed as a thread-shaped spiral lying against the outer boundary 3d of the outlet 3b, as is shown in FIG. By means of a diaphragm 13 which is designed in the form of a spiral, the fluid flowing through the diaphragm 13 becomes Combustion gases 22 are provided with an additional twist about the longitudinal axis A of the combustion chamber 3a. Such an additional mixing of the combustion gases 22, in particular of unburned fuel 11 contained in the combustion gases 22 and unburned oxygen, is achieved. In this way, the unburned fuel 11 can react with the unburned oxygen, whereby the efficiency of the heating device 3 can be further increased. The spiral formed by the diaphragm 13 can have Vi, 1, 2 or more turns.

FIGS. 9 to 11 show possible cross sections of screens 13 designed according to the invention.

Each exemplary embodiment of a screen 13 according to the invention has a closed or predominantly closed outer ring-shaped area ("outer ring") 14, which has a width d of 5 mm to 15 mm in the radial direction, for example, and with its outer circumference 14a on the outer boundary 3d of the (Not shown in Figures 9 to 11) combustion chamber 3a adjacent.

In this context, “predominantly closed” means that the closed area makes up at least 80% of the area of the outer area 14 .

Within the outer region 14 is a central opening 20, for example a circular central opening 20 with a diameter D1 of 25 mm to 50 mm, in particular with a diameter D1 of 30 mm to 40 mm.

One or more decentralized openings 16 can be formed in the outer region 14, as is shown in FIG. The decentralized openings 16 create additional flow paths for the hot combustion gases 22 and thus reduce the flow resistance of the screen 13.

In alternative exemplary embodiments, as shown in FIGS. 10 and 11, one or more segments or vanes 15 are formed on the inside of the outer region 14 facing the longitudinal axis A of the burner 3, - 77 - which, starting from the outer area 14, extend radially inwards into the central opening 20 of the diaphragm 13.

The segments or vanes 15 are designed in such a way that an open area with a diameter Di of 20 mm to 40 mm, in particular an open area with a diameter Di of 20 mm to 30 mm, remains between their inner end areas 23 .

Open areas 18 , in particular gaps or slits, are formed between segments/wings 15 which are adjacent to one another in the circumferential direction of the diaphragm 13 and which separate the segments/wings 15 which are adjacent to one another.

In the exemplary embodiment shown in FIG. 10, the mutually opposite edges 25 of adjacent segments or vanes 15 extend essentially parallel to one another in the radial direction. In this embodiment, the segments or wings 15 have a substantially rectangular shape.

In another embodiment shown in Figure 11, the opposing edges 25 of adjacent segments or wings 15 are formed such that the spacing of the opposing edges 25 is greater at the inner end portions 23 of the segments or wings 15 than at theirs outer ends. The open areas 18 between adjacent segments/wings 15 are thereby formed in a V-shape, and the segments/wings 15 have a trapezoidal shape.

The segments or vanes 15 may be helically twisted about axes B (see Figure 10) extending radially outward from the longitudinal axis A, similar to the vanes of a ship's propeller, to provide additional spin on the air flowing through the orifice 13 Apply combustion gases 22 and to achieve an even better mixing of the combustion gases 22 in this way.

The aperture shapes shown in Figures 9 to 11 have the common property that through the additional decentralized openings 16 in the outer area 14 or through the open areas 18, which are adjacent between - 72 - bold segments / vanes 15 are formed, additional flow paths are provided, which reduce the flow resistance of the orifice 13 and thus reduce the pressure loss caused by the orifice 13 in the outlet 3b of the combustion chamber 3a.

In addition, the flow velocity in the outer region of the outlet 3b close to the aperture is reduced by the aperture geometries described. In this way, inert carbon monoxide (CO), which has been produced as a product of incomplete combustion of the fuel 11, is kept in the vicinity of the hot reaction zone in the center 3c of the combustion chamber 3a for as long as possible in order to withstand the high temperatures of 1100 °C prevailing there up to 1400 °C to oxidize as completely as possible to carbon dioxide (CO2).

Claims

patent claims

A heating device (3) for heating up an exhaust gas catalyst (4), the heating device (3) comprising: a combustion chamber (3a); an air supply (8) adapted to supply air (7) into the combustion chamber (3a); a fuel injector (10) adapted to inject fuel (11) into the combustion chamber (3a); an ignition device (12) adapted to ignite a fuel-air mixture in the combustion chamber (3a); a gas outlet (3b) adapted to discharge hot combustion gases (22) from the combustion chamber (3a); characterized in that a screen (13) is arranged in the gas outlet (3b) and comprises an outer, essentially closed area (14) and an inner, essentially open area (20) which is inside the outer area (14) is arranged; the outer portion extending along an outer periphery of the gas outlet (3b) and impeding or preventing unburned fuel (11) from flowing out through an outer portion (14) of the gas outlet (3b); and wherein the inner portion (20) allows combustion gases (22) to flow out through a central portion of the gas outlet (3b). - - A heater (3) according to claim 1, wherein the outer portion (14) of the baffle (13) is annular and has at least one off-center opening (16) allowing combustion gases (22) to pass through the outer portion of the baffle (13) to stream. The heating device (3) according to claim 1 or 2, wherein the outer region (14) comprises a plurality of segments (15) which, starting from an outer boundary (3d) of the gas outlet (3b), extend inwards in the radial direction and through open regions ( 18), in particular by gaps or slits, are separated from one another. A heater (3) according to claim 3, wherein opposite edges (25) of adjacent segments (15) extend substantially parallel to each other, or wherein the open areas (18) between adjacent segments (15) are V-shaped with a narrower outer area and a further inner area are formed. A heater (3) according to claim 3 or 4, wherein the segments (15) are each helically twisted about an axis (B) extending radially outward from the center of the gas outlet (3b). A heater (3) as claimed in any one of claims 3 to 5, wherein the segments (15) are oriented at right angles to the perimeter (3d) of the gas outlet (3b). Heating device (3) according to one of Claims 3 to 5, the segments (15) or at least partial areas (13b) near the center of the segments (15) at an angle (□) of between 7.5° and 30° to the outer boundary (3d ) of the gas outlet (3b). ) which is oriented at an angle (□) between 7.5° and 30° to the outer boundary (3d) of the gas outlet (3b). - 75 - A heater (3) according to any one of claims 3 to 7, wherein each of the segments (15) has an inner end portion (23) facing the central portion of the gas outlet (3b), the inner end portions (23) having a small material thickness are formed as the outer regions of the segments (15), the inner end regions (23) being formed in particular with sharp edges. Heating device (3) according to one of the preceding claims, in which the diaphragm (13) is designed as a spiral which bears against the outer boundary (3d) of the gas outlet (3b). Exhaust system (2) for an internal combustion engine (1) with at least one exhaust gas catalytic converter (4), in particular a three-way catalytic converter (4), and a heating device (3) according to one of the preceding claims, the heating device (3) upstream of the at least a

Exhaust gas catalytic converter (4) is arranged on the exhaust system (2).