EXHAUST DUCT WITH BYPASS

Description

[0001] The invention relates to an exhaust duct for guiding the exhaust gas of an internal combustion engine, wherein the exhaust duct has at least one main flow duct and a bypass as well as an adjustable throttle valve in the main flow duct, wherein the throttle valve can be pivoted from an open position in which the main flow duct is released and a closed position in which the main flow duct is blocked, wherein a bypass valve is kinematically connected to the throttle valve in such a way that when the bypass is closed the throttle valve is in its open position and that when the bypass is completely released the throttle valve is in its closed position.

[0002] Such exhaust ducts are known from JP 5 256239 B2 and JP 2008 101496 A. DE 10 2010 049 957 A1 discloses a device by means of which fuel can be decomposed into shorter carbon chains through pyrolysis, and through whose subsequent oxidation the exhaust gases can be heated in order to provide the exhaust gas temperature level required for effective nitrogen oxide reduction during a cold start of the internal combustion engine. Such devices are typically arranged in a bypass parallel to the exhaust system of the internal combustion engine, and a partial mass flow of the exhaust gas is directed through the device.

[0003] Selective catalytic reduction (SCR) catalysts are used to reduce nitrogen oxide emissions from diesel engines, combustion plants, waste incineration plants, industrial facilities, and the like. A reducing agent is injected into the exhaust system using a dosing device. The reducing agent is ammonia, an ammonia solution, or another reducing agent.

[0004] Since carrying ammonia in vehicles is safety-critical, urea is used in an aqueous solution, typically with a 32.5% urea content, particularly in accordance with DIN 70070. In the exhaust gas, the urea decomposes into gaseous ammonia and CO2 at temperatures above 150°C. The parameters for urea decomposition are essentially time (evaporation and reaction time), temperature, and droplet size of the injected urea solution. In these SCR catalysts, nitrogen oxide emissions are reduced by approximately 90% through selective catalytic reduction.

[0005] The term reducing agent solution or reducing agent includes any reducing agent suitable for selective catalytic reduction; preferably, a urea solution according to DIN 70070 is used for this purpose.

[0006] In the known exhaust gas aftertreatment systems for selective catalytic reduction, the relatively low temperatures of the exhaust gases, for example during a cold start of the combustion engine, i.e. before the operating temperature of the combustion engine is reached, can have an adverse effect on the functioning of an SCR catalyst.

[0007] After the urea is injected in aqueous solution into the exhaust system, ammonia (NH 3 ) must first be formed for the SCR reaction. The reducing ammonia is released through the thermal decomposition of urea (thermolysis) and the hydrolysis of the resulting isocyanic acid. In the first reaction, thermolysis, the temperature influences the conversion of urea into ammonia (NH 3 ) and isocyanic acid (HNCO). In the second step, hydrolysis takes place in the presence of water; in this step, the isocyanic acid is also converted into ammonia to form carbon dioxide (CO 2 ). Relatively low temperatures, such as those encountered during a cold start of an internal combustion engine, can slow down these reactions.

[0008] In order to ensure the effectiveness of the selective catalytic reduction in the exhaust system, the temperature level of the exhaust gas must be raised as quickly as possible to a certain temperature level of approximately 200°C during a cold start.

[0009] A disadvantage of the known devices is that the entire reaction chamber is first electrically heated in order to heat the pyrolysis reactor located therein to a temperature level at which oxidation of the introduced fuel can occur automatically. For evaporation, the fleece must be heated by radiant heat, which the pyrolysis reactor must provide. This requires a very high temperature in the pyrolysis reactor. This requires a very high electrical power. The very high currents flowing through the honeycomb structure of the pyrolysis reactor can damage the honeycomb structure and the electrical connection of the pyrolysis reactor in the reaction chamber.

[0010] A further disadvantage of the prior art is that it is not possible, or only insufficiently possible, to keep the partial mass flow of the exhaust gas that is passed through the device constant by means of the throttle valve that is usually used in the bypass that accommodates the device, which is, however, necessary for the effective use of the device.

[0011] A further disadvantage of the known devices is that they require a large installation space, since a bypass with the device for exhaust gas heating must be arranged next to the main exhaust line.

[0012] The object of the invention is therefore to further develop an exhaust gas duct, in particular with a device for heating the exhaust gases of an internal combustion engine with a pyrolysis reactor, in such a way that the aforementioned disadvantages are overcome and the required installation space is reduced.

[0013] This object is achieved according to the invention by an exhaust duct according to claim 1. Advantageous developments of the invention are specified in the dependent claims.

[0014] Particularly advantageous in the exhaust duct for guiding the exhaust gas of an internal combustion engine, wherein the exhaust duct has at least one main flow duct and a bypass as well as an adjustable throttle valve in the main flow duct, wherein the throttle valve can be pivoted from an open position in which the main flow duct is released and a closed position in which the main flow duct is blocked, is that a bypass valve is kinematically connected to the throttle valve in such a way that when the bypass is closed the throttle valve is in its open position and that when the bypass is completely released the throttle valve is in its closed position.

[0015] The term “closed position” in which the main flow channel is blocked includes, in the sense of the invention, both a complete blocking of the main flow channel and a maximum throttling effect, in which a gas-tight closure of the main flow channel is not necessarily present.

[0016] Preferably, the throttle valve and the bypass valve are formed by a single component, in particular by a cast part or injection-molded part made of the same material.

[0017] Particularly preferably, the throttle valve and the bypass valve can be pivoted synchronously around a common axis of rotation relative to one another in a rotationally fixed manner.

[0018] Preferably, a servomotor is provided, by means of which the throttle valve and the bypass valve are pivoted. This servomotor therefore serves to adjust the throttle valve and the kinematically coupled bypass valve.

[0019] According to the invention, the bypass is formed by an integral component of the main flow channel. Preferably, the bypass is formed by a flow channel whose cross-section forms a sub-sector of the exhaust duct, in particular a circular segment of an exhaust duct with a circular cross-section. The channel to the pyrolysis reactor can be realized by a simple sheet metal or an additional pipe in or on the exhaust pipe.

[0020] According to the invention, the bypass opens into a device for exhaust gas heating with at least one pyrolysis reactor, into which at least a partial mass flow of the exhaust gas of the internal combustion engine is introduced via the bypass, wherein at least one fleece is connected upstream of the pyrolysis reactor, which fleece is supplied with fuel, wherein the fuel evaporates and at least partially reacts exothermically in the pyrolysis reactor with an oxygen component of the exhaust gas mass flow introduced into the pyrolysis reactor by oxidation, in particular in order to provide a sufficiently high temperature for pyrolysis, wherein the exhaust gas heated by means of the device is introduced into the main flow channel downstream of the device for exhaust gas heating

[0021] Fuel, particularly vehicle fuel or diesel fuel, is fed into the system. The fuel decomposes in the pyrolysis reactor and, as long as sufficient oxygen is present, completely oxidizes. The gas exits the pyrolysis reactor at a temperature of approximately 750°C. At higher fuel feed rates, the system operates under oxygen deficiency. The reaction products are essentially CO and H2, as well as unburned hydrocarbons. H2 and CO have a very low ignition temperature, the so-called "light-off temperature," at the downstream oxidation catalyst in the overall exhaust system. This allows heat to be released at the oxidation catalyst even at exhaust temperatures as low as 200°C, keeping the overall temperature above 200°C.

[0022] As a result, the temperature of the SCR system remains above 200°C even in operating ranges of the combustion engine below 200°C, so that high denitrification efficiencies can be achieved.

[0023] Two different modes are required for heating the exhaust system and the main oxidation catalyst (main DOC). A lean "Lambda>>1" mode is used, on the one hand, as a heating mode to warm the main DOC to the ignition temperature of the pyrolysis gases, and, on the other hand, as a holding mode for a) the pyrolysis reactor itself and b) the main DOC and SCR to a sufficiently high reaction temperature for effective denitrification. A rich "Lambda<<1" mode is used to generate the pyrolysis gases, which are then oxidized in the main DOC and release heat there, which is many times the energy of "Lambda>>1" mode. This allows the entire exhaust system to be heated up very quickly, so that denitrification can begin as soon as possible after engine start.

[0024] Lambda denotes the air ratio.

[0025] In "Lambda<<1" operation (rich operation, also referred to as heating operation), the oxidation in the pyrolysis reactor itself is very distributed over a wide area. This means that the internal catalyst receives far too much fuel locally, over a large area, or even across the entire area. However, this fuel cannot be completely combusted locally because the exhaust gas supplied to the pyrolysis reactor is distributed through many holes in the internal pyrolysis reactor. This means that only as much fuel can be oxidized locally as the oxygen present locally in the exhaust gas. In "Lambda = 0.1" operation with 25 kW heating power per pyrolysis reactor, only 10% of the fuel is oxidized in the pyrolysis reactor; the remaining 90% is converted into shorter carbon chains through pyrolysis.

[0026] Too little exhaust gas mass flow will cool the pyrolysis reactor, and too much (lambda>0.3 or even 1.0) would cause the pyrolysis reactor to overheat and melt. For this very low exhaust gas mass flow, the bypass must have a high flow resistance, meaning the bypass must have a higher flow resistance than the fully open exhaust flap in the main exhaust system parallel to the pyrolysis reactor.

[0027] In "Lambda>>1" operation (lean operation, also known as DOC operation), all of the fuel is oxidized in the pyrolysis reactor. Depending on the operating conditions, lambda values ​​from 1.5 to 10 can be achieved. An excess of oxygen is present. The fuel is fed to the top of the mat, which is located directly upstream of the pyrolysis reactor, then spreads across the mat and is vaporized during this process. Because of the excess oxygen, almost all of the fuel is converted into heat through oxidation. The correct cooling capacity is adjusted by the supplied exhaust gas mass flow. Here, the situation is exactly the opposite: Too much exhaust gas mass flow cools the pyrolysis reactor, while too little (Lambda<1.5 or even 1.0) would overheat and melt the pyrolysis reactor. For this relatively high exhaust gas mass flow, the bypass must have a relatively low flow resistance so that the engine does not experience excessive exhaust backpressure.

[0028] The bypass mass flow is fed to the pyrolysis reactor inside the main exhaust pipe via an internally "gas-tight" separated channel, which is enabled and can be controlled by the combined throttle valve with bypass valve.

[0029] With the inventive dual-acting exhaust valve, the bypass exhaust flow can be reliably adjusted for both operating modes using this valve alone. The engine does not experience high backpressure, and the bypass through the pyrolysis reactor maintains low flow resistance.

[0030] With the combined throttle valve in the main exhaust pipe, the flow can be smoothly directed into both systems, using only the single existing exhaust valve. This means that only one valve needs to be controlled and regulated. Various continuously adjustable angles of the combined throttle valve with bypass valve in the secondary flow now create different distributions of the exhaust flows.

[0031] A particularly advantageous feature is that the mass flow through the pyrolysis reactor can be set to zero by completely closing the bypass valve. This provides an emergency shutdown function in the event of overheating of the pyrolysis reactor. This reduces the oxygen content in the pyrolysis reactor to almost zero, allowing the fuel in the pyrolysis reactor to evaporate, but no heat is generated through oxidation.

[0032] The bypass flap on the throttle valve can be spring-loaded and attached to the valve spindle, so that the spindle remains stationary when the bypass is completely closed, allowing only the throttle valve to continue rotating. This rotation can continue until the main exhaust system is almost completely closed. This function can be used as a brake flap or exhaust backpressure flap.

[0033] This attached bypass flap allows for a large amount of clearance between the bypass flap and the exhaust flap housing pipe. By positioning the bypass flap below the beginning of the internal bypass channel and simultaneously creating a gap between the bypass and the bypass flap, the high flow there below the bypass flap creates a suction above the bypass flap. This virtually eliminates the mass flow caused by the leakage, preventing any mass flow to the pyrolysis reactor.

[0034] Particularly advantageous are the compact overall system design and less space required in the vehicle, simpler thermal insulation of the entire system, and less heat loss, as the entire bypass piping and the corresponding surface area to the cooling environment are eliminated. Another advantage is faster heating of the pyrolysis reactor, as the supplied bypass mass flow is not cooled by the environment.

[0035] The invention is applicable to all diesel engines, particularly commercial vehicles, passenger cars, combined heat and power plants, power generators, and emergency power units, although this list is not exhaustive. The invention is particularly advantageous for all diesel engines with very low exhaust temperatures, caused by cold starts, very short running times such as "stop-and-go," high idle times, use only in the low load range, or with high engine efficiency with correspondingly low exhaust temperatures.

[0036] Preferably, the bypass opens into an inlet chamber, wherein two pyrolysis reactors are connected downstream of the inlet chamber, which are preferably arranged symmetrically to the exhaust gas duct.

[0037] The double-sided pyrolysis reactor is "pulled apart" so that it does not sit on top of the main exhaust pipe as in the prior art, but can be essentially slipped over the main exhaust pipe. This frees up the installation space above the main exhaust pipe and significantly reduces the overall system's installation space. The bypass mass flow is fed to the pyrolysis reactors inside the main exhaust pipe via an internally "gas-tight" separated channel. By pulling the inlet chamber apart, internal installation space is created within the inlet chamber. A channel is integrated into the main exhaust pipe downstream of the throttle valve, through which the bypass mass flow is fed to the pyrolysis reactors. This eliminates all external piping and the inlet / outlet cones and flanges. This internal channel can be realized, for example, with an inserted and welded sheet metal.Alternatively, the channel can be realized by an appropriately shaped pipe, which is simply tacked into the main exhaust pipe.

[0038] The fuel-exhaust gas mixture is formed in the inlet chamber before entering the pyrolysis reactors.

[0039] Preferably, the bypass opens into a device for exhaust gas heating with at least one pyrolysis reactor, wherein the device for exhaust gas heating has at least one heat source by means of which the fleece can be heated and the fuel introduced into the fleece can be at least partially locally vaporized and / or heated to a temperature above the ignition temperature of the fuel and / or by means of which the exhaust gas introduced into the inlet chamber can be heated to a temperature above the vaporization temperature and / or above the ignition temperature of the fuel, in particular at least one flame glow plug can be arranged upstream of the pyrolysis reactor(s) in the flow direction of the exhaust gas.

[0040] A particularly advantageous feature is that ceramic catalysts can be used as pyrolysis reactors. The ceramic catalysts can be fixed, for example, using expanded mats and / or wire mesh.

[0041] Preferably, the bypass opens into a device for exhaust gas heating with at least one pyrolysis reactor, wherein each pyrolysis reactor has a baffle with a plurality of through-bores downstream of the inlet chamber, through which a fuel-exhaust gas mixture is introduced into the pyrolysis reactor in an evenly distributed manner.

[0042] Preferably, the bypass opens into a device for exhaust gas heating with at least one pyrolysis reactor, wherein the device for exhaust gas heating has two metering pumps for metering fuel, wherein fuel is conveyed and metered to the fleece by means of the first metering pump and wherein fuel is conveyed and metered to a flame glow plug by means of the second metering pump.

[0043] When operating with an air / fuel ratio of lambda>>1, referred to as heating operation, the exact equal distribution of fuel to exhaust gas within the area of ​​the pyrolysis reactor or the area of ​​the pyrolysis reactor into which the exhaust gas is fed is ensured in lambda>>1 mode by evaporating the fuel in front of the holes and then feeding it through the holes into the pyrolysis reactor together with the exhaust gas. This ensures that there is never too much fuel locally in the pyrolysis reactor, and thus the heat generation through oxidation also corresponds to the "cooling capacity" of the exhaust gas mass fed locally through the holes. The local temperatures in the pyrolysis reactor are thus almost identical.

[0044] The fuel evaporates in the inlet chamber of the pyrolysis reactor. To provide sufficient heat for fuel evaporation, a flame glow plug is positioned in the inlet chamber or in the bypass channel upstream of the inlet chamber. With a flame glow plug, heating outputs of up to 10 kW, for example, can be achieved. The small power range up to 10 kW can be provided with the flame glow plug alone; for higher power outputs, fuel is also fed to the fleece in the inlet chamber. This fuel evaporates there, is mixed with the exhaust gas flowing into the inlet chamber, and is transported through the holes to the pyrolysis reactors, where the fuel vapors are oxidized. Appropriate flow-related internals in the inlet chamber can provide a uniform lambda across all holes.It is then irrelevant whether more or less gas mixture flows through a hole; the oxidation to cooling ratio is fixed, and thus this local pyrolysis reactor temperature is the same as the temperatures at all other points in the pyrolysis reactor where exhaust gas is fed into the pyrolysis reactor. In order to reduce the area of ​​the pyrolysis reactor where no holes are located and thus achieve a more uniform thermal load on the pyrolysis reactor, the holes can now be made smaller in diameter again, thereby increasing the number of holes. This improves the even distribution of heat input and temperature in the pyrolysis reactor. Smaller holes and a slightly greater pressure drop result in a higher flow velocity through the pyrolysis reactor. This promotes recirculation in the pyrolysis reactor and improves the oxidation behavior of the pyrolysis reactor.

[0045] In order to prevent coking or to reduce coking in the inlet chamber, the fleece and the holes, only the flame glow plug is operated with a lambda that is not too lean, so that sufficient heat and a high temperature are available from the flame glow plug.

[0046] When operating with an air / fuel ratio of lambda <<1, referred to as DOC operation, the fuel is fed directly onto the mat. There is no risk of damage due to uneven vapor distribution in DOC operation. The flame glow plug only needs to provide a low power output of less than 2 kW.

[0047] The starting process is particularly advantageous, as the flame glow plug heats the fleece in the inlet chamber more quickly and reliably than was possible with conventional systems. Since the bypass mass flow is not cooled by the environment, the desired temperature level is also reached more quickly.

[0048] Another particularly advantageous feature during the start-up process is that the flame glow plug heats not only the fleece but also the two pyrolysis reactors. This makes it possible to use simple ceramic catalysts and fix them with foam mats or wire mesh.

[0049] A further advantage during start-up and operation is that no radiant heat is required from the pyrolysis reactors. A chemical start-up process, i.e., fuel supply to the mat, its evaporation, and transfer to the pyrolysis reactors, can therefore take place at a pyrolysis reactor temperature of approximately 270°C, because at this temperature, fuel vapors can oxidize sufficiently well.

[0050] Because the fleece is positioned in the inlet chamber, a high temperature can be provided by the flame glow plug. To reduce any carbon buildup that may have occurred, the following procedures can be performed: No more fuel is metered into this new mat, meaning no cooling by the fuel itself and no evaporation that cools the mat. Additionally, to reduce the cooling of the mat, the exhaust gas mass flow through the pyrolysis reactor can be significantly reduced. Setting a lambda range using only the flame glow plug is required to provide a sufficiently high temperature while still remaining in the lean range so that the coking can oxidize. This mode is required every time the system is started anyway to heat the pyrolysis reactors. When the engine is turned off, the pyrolysis reactor is still hot internally; the heat is distributed, and thus the mat in the inlet chamber also becomes very hot.

[0051] During a driving cycle, sufficient time periods can be created in which any coking on the fleece and also on the inside of the perforated plate in the inlet chamber and in the holes themselves can be reduced.

[0052] Due to the uniform distribution and local allocation of fuel to the oxygen-containing exhaust gas (uniform lambda) in the inlet chamber, the exhaust gas is heated by oxidation behind each feed hole. This ensures that it does not lead to localized high fuel loading or to local overheating, which could destroy the pyrolysis reactor.

[0053] Because the pyrolysis reactors now receive an oxidizable mixture evenly behind the holes, there is no local cooling of the pyrolysis reactors; any HC or CO that may be produced can be completely oxidized at any local point in the pyrolysis reactor, since the pyrolysis reactors are hot everywhere.

[0054] Local or surface evaporation of the fuel on the fleece has no influence on the uniform distribution of oxidation in the pyrolysis reactor.

[0055] Any droplets spraying out of the fleece in the direction of the pyrolysis reactor due to the exhaust gas flow velocity from the holes are no longer present, since droplets spraying out of the fleece do not reach the surface of the pyrolysis reactor, but are first evaporated in the inlet chamber before flowing as a mixture to the pyrolysis reactor.

[0056] Due to the selected position of the fleece in the inlet chamber, there is hardly any cooling through the outer walls and the flame glow plug can provide sufficient heat / temperature to reduce any coking that may have occurred.

[0057] The pyrolysis reactor, whether in heating mode or DOC mode, is preferably operated with two dosing pumps: one for the flame glow plug and the second for the fleece. Both meter into the inlet chamber, and the equal distribution between the left and right pyrolysis reactors is ensured solely by the inlet chamber. Two separate temperature sensors for the left and right pyrolysis reactors are thus no longer required.

[0058] The outlet temperature of this new pyrolysis reactor is higher in "Lambda>>1" operation due to the good uniform distribution than with an unevenly distributed fuel / exhaust gas mixture, since the air ratio can be shifted closer to Lambda=1 without having to fear local overheating.

[0059] More heat output can be achieved with the pyrolysis reactor in heating mode because the temperature is more uniform. The highest local temperature reduces the overall output. If there is no local hot spot, the entire pyrolysis reactor can be operated at higher temperatures, thus achieving higher overall output. This allows for more oxidation heat to be released at the same maximum temperature in the pyrolysis reactor. A larger temperature difference can be achieved across the pyrolysis reactor.

[0060] Preferably, at least one catalyst for selective catalytic reduction of nitrogen oxides, a so-called SCR catalyst, is arranged downstream of the exhaust gas heating device. Furthermore, at least one oxidation catalyst can be arranged downstream of the exhaust gas heating device.

[0061] An embodiment of the invention is illustrated in the figures and explained below. They show: Fig. 1A perspective view of an exhaust duct; Fig. 2A side view of the exhaust duct according to Figure 1 ; Fig. 3 a section of the side view of the exhaust duct according to Fig. 1 ; Fig. 4 the section A - A according to Figure 3 ; Fig. 5 the section B - B according to Figure 4 ; Figures 6 to 10 each show a section of the area of ​​the throttle valve and the bypass valve in a side view and in a perspective view in different angular positions of the throttle valve.

[0062] Figure 1 shows a perspective view of the overall system with the exhaust duct 1 for guiding the exhaust gas of a combustion engine (not shown) and the exhaust gas heating device 2. An adjustable throttle valve 3 is arranged at the inlet to the exhaust duct 1, which can be actuated by the servomotor 4 and adjusted to the desired setting.

[0063] Figure 2 shows a side view of the entire system and Figure 3shows a section of the side view of the entire system with the exhaust duct 1 for guiding the exhaust gas of a combustion engine (not shown) and the device 2 for exhaust gas heating as well as the servo motor 4 for actuating and adjusting the throttle valve 3.

[0064] The exhaust duct 1 is shown in the illustrations according to the Figures 2 and 3 in the image plane from left to right, through which flows the exhaust gas of the combustion engine (not shown). The exhaust duct is divided into the main flow duct 11 and the bypass 12. The flow through the main flow duct 11 and the bypass 12 is regulated by the throttle valve 3, the function of which is determined by the Figures 6 to 10 is explained.

[0065] The bypass 12 leads into the device 2 for exhaust gas heating, the structure and function of which are described below with reference to the Figures 4 and 5 is explained.

[0066] Figure 4 shows the section A - A according to Figure 3by the exhaust gas heating device 2. Shown in Figure 4 is only the left half of the exhaust gas heating device 2, which is constructed symmetrically to the centerline 13 of the exhaust duct 1. As explained, the exhaust duct 1 is divided into the main flow channel 11 and the bypass 12. The bypass 12 opens via the exhaust inlet 14 into the inlet chamber 21 of the exhaust gas heating device 2. Fuel 23 is supplied to the inlet chamber 21 via the fleece 22 by means of a metering pump (not shown).

[0067] The device 2 for exhaust gas heating is, as explained, constructed mirror-symmetrically to the center line 13 of the exhaust duct 1 and sits on the exhaust duct 1 similar to a headphone, as shown in Figure 1 as can be seen in the perspective view. This results in a very space-saving arrangement of the device 2 for exhaust gas heating on the exhaust duct 1.

[0068] The fuel 23 is vaporized in the inlet chamber 21 and mixed with the exhaust gas before the mixture flows through the holes 24 of the perforated plate 25 to the pyrolysis reactor 26. In addition to or as an alternative to the perforated plate 25, mixers, baffles, or sieves can be used to ensure homogeneous distribution. The heat required for vaporization is provided here by a flame glow plug (not shown). At these high temperatures, possible coking in the holes 24 or on the fleece 22 can be reduced by reducing the exhaust gas mass flow through the device 2 and shutting off the diesel supply to this fleece 22. As explained above, the fuel-exhaust gas mixture is further heated in the pyrolysis reactor 26 before being passed over the surface 27 to the outlet 28 and reintroduced into the main flow channel 11 of the exhaust channel 1. The separation between the inlet chamber 21 and the outlet 28 is effected by means of a partition wall 29.

[0069] The perforated plate or aperture 25 serves to direct the exhaust gas mass flow towards the pyrolysis reactor 26 and to bring about a uniform velocity distribution over the cross section of the pyrolysis reactor 26.

[0070] Due to the prior evaporation of the fuel introduced into the pyrolysis reactor 26, the oxidation of the fuel with the oxygen content of the exhaust gas mass flow introduced into the pyrolysis reactor 26 begins and the device 2 thereby continues to heat up automatically.

[0071] In Figure 5 is the section B - B after Figure 4 The perforated plate 25 with the holes 24 is shown, through which the fuel-exhaust gas mixture formed in the inlet chamber 21 is fed into the Figure 5The flow is introduced into the pyrolysis reactor 26, which is not visible. The uniform distribution of the supplied fuel-exhaust gas mixture in the exhaust gas heating device 2 via the holes 24 of the exhaust gas supply is evident. The oxygen-rich exhaust gas, including the previously vaporized fuel, is supplied evenly distributed over the marked area 25' of the perforated plate 25. The heated fuel-exhaust gas mixture is returned to the exhaust duct 1 via the outlet 28.

[0072] Regardless of low or high fuel dosage, i.e., whether the required heating output of the exhaust gas heating device 2 is low or high in heating mode, the fuel 23 evaporates within the inlet chamber 21, i.e., the exhaust gas feed. The distribution and mixing of the fuel vapor occurs in the inlet chamber 21, so that fuel and exhaust gas mass flow are supplied evenly through the holes 24. The air ratio is thus uniform throughout the area 25', over which uniform, complete oxidation takes place. Zones with excessively high temperatures are thus excluded. Thus, the temperature of the pyrolysis reactor 26 can now be precisely adjusted.

[0073] Locally excess oxygen cannot be incorporated into oxidation, since locally there is no more fuel available than is evenly distributed across the holes 24. It does not matter whether more or less mixture flows through a hole 24; the resulting temperature in the pyrolysis reactor 26 remains constant. Therefore, the pyrolysis reactor 26 is not locally overheated at any point. On the contrary, the temperature can be set well below the endurance temperature of the pyrolysis reactor 26. This significantly increases the stability of the system.

[0074] In the Figures 6 to 10A section of the area of ​​the throttle valve 3 and the bypass valve 31 is shown in a side view and a perspective view in different angular positions of the throttle valve 3. The flow through the main flow channel 11 and the bypass 12 is regulated by means of the throttle valve 3 and the bypass valve 31, the function of which is explained below. The adjustment of the throttle valve 3 by rotating the throttle valve 3 about the rotation axis 32 is carried out by means of the servo motor 4.

[0075] As shown in the Figures 6 to 10 As can be seen, the throttle valve 3 is opened from an open position according to Figure 6 , in which the main flow channel 11 is released, and a closed position according to Figure 10 , in which the main flow channel 11 is blocked, can be pivoted around the axis of rotation 32 by means of the servo motor 4.

[0076] The bypass valve 31 is kinematically connected to the throttle valve 3 in such a way that when the bypass 12 is closed, the throttle valve 3 is in its open position according to Figure 6 and when the bypass 12 is fully released, the throttle valve 3 is in its closed position according to Figure 10 In the position according to Figure 10 the main flow channel 11 is blocked and the bypass 12 is fully open, so that in this position of throttle valve 3 and bypass valve 31 the exhaust gas mass flow is completely directed via the bypass 12. In the position according to Figure 6 the main flow channel 11 is opened and the bypass 12 is closed by means of the bypass flap 31, so that in this position of the throttle valve 3 and the bypass flap 31 the exhaust gas mass flow is completely directed via the main flow channel 11.

[0077] The other Figures 7 to 9show intermediate positions of the throttle valve 3 and the bypass valve 31, by means of which the desired distribution of the exhaust gas mass flow between the main flow channel 11 and the bypass 12 can be continuously adjusted.

[0078] The throttle valve 3 and the bypass valve 31 are constructed in one piece and thus constitute a single component. The throttle valve 3 and the bypass valve 31 can be pivoted synchronously and in a rotationally fixed manner relative to each other about the common axis of rotation 32. The pivoting of the throttle valve 3 and the bypass valve 31 is achieved, as explained, by means of the actuator 4.

Claims

1. Exhaust duct (1) for conducting the exhaust of an internal combustion engine, wherein the exhaust duct (1) has at least one main flow duct (11) and a bypass (12) as well as an adjustable throttle valve (3) in the main flow duct (11), wherein the throttle valve (3) is pivotable from an open position, in which the main flow duct (11) is open, and a closed position, in which the main flow duct (11) is closed, wherein a bypass valve (31) is kinematically connected to the throttle valve (3) in such a way that when the bypass (12) is closed the throttle valve (3) is in its open position and that when the bypass (12) is fully open the throttle valve (3) is in its closed position, characterized in that the bypass (12) is formed by an integral component of the main flow duct (11), wherein the bypass (12) opens into a device (2) for heating the exhaust with at least one pyrolysis reactor (26), into which at least a partial mass flow of the exhaust of the internal combustion engine is introduced via the bypass (12), wherein at least one fleece (22), which is charged with fuel, is arranged upstream of the pyrolysis reactor (26), wherein the fuel vaporizes and reacts exothermically at least partially in the pyrolysis reactor (26) with an oxygen content of the exhaust mass flow introduced into the pyrolysis reactor (26) by oxidation, in particular in order to provide a sufficiently high temperature for pyrolysis, wherein the exhaust heated by means of the device (2) is introduced into the main flow duct (11) for heating exhaust downstream of the device (2).

2. Exhaust duct (1) according to claim 1, characterized in that the throttle valve (3) and the bypass valve (31) are formed by a single component, in particular by a cast part or injection-moulded part of the same material.

3. Exhaust duct (1) according to claim 1 or claim 2, characterized in that the throttle valve (3) and the bypass valve (31) can be pivoted synchronously in a rotationally fixed manner about a common axis of rotation (32).

4. Exhaust duct (1) according to any one of the preceding claims, characterized in that a servomotor (4) is arranged, by means of which the throttle valve (3) and the bypass valve (31) are pivoted.

5. Exhaust duct (1) according to any one of the preceding claims, characterized in that the bypass (12) is formed by a flow duct, which in cross-section forms a sub-sector of the exhaust duct (1), in particular a circular section of an exhaust duct (1) which is circular in cross-section.

6. Exhaust duct (1) according to any one of the preceding claims, characterized in that the bypass (12) opens into an inlet chamber (21), wherein two pyrolysis reactors (26) are connected downstream of the inlet chamber (21), which are arranged in particular to be symmetrical to the exhaust duct (1).

7. Exhaust duct (1) according to any one of the previous claims, characterized in that the bypass (12) opens into a device (2) for heating the exhaust with at least one pyrolysis reactor (26), wherein the device (2) for heating the exhaust has at least one heat source, by means of which the fleece (22) can be heated and the fuel introduced into the fleece (22) can be at least partially vaporized locally and / or can be heated to a temperature above the ignition temperature of the fuel and / or by means of which the exhaust introduced into the inlet chamber (21) can be heated to a temperature above the vaporization temperature and / or above the ignition temperature of the fuel, in particular in that a flame glow plug is provided.

8. Exhaust duct (1) according to any one of the preceding claims, characterized in that the bypass (12) opens into a device (2) for heating exhaust with at least one pyrolysis reactor (26), each pyrolysis reactor (26) having, downstream of the inlet chamber (21), an orifice (25) with multiple through-holes (24), through which a fuel / exhaust mixture is introduced into the pyrolysis reactor (26) in a uniformly distributed manner.

9. Exhaust duct (1) according to any one of the preceding claims, characterized in that the bypass (12) opens into a device (2) for heating exhaust with at least one pyrolysis reactor (26), wherein the device (2) for heating exhaust has two metering pumps for metering fuel, wherein fuel is conveyed and metered to a fleece (22) by means of the first metering pump and wherein fuel is conveyed and metered to a flame glow plug by means of the second metering pump.