Catalyst heater for exhaust gas device for internal combustion engine, exhaust gas device, and method for operating exhaust gas device

Abstract

To provide a heater for an exhaust gas device for an internal combustion engine that enables efficient heating of a component of the exhaust gas device while reducing energy consumption, the exhaust gas device including the heater, and a method for operating the exhaust gas device.SOLUTION: A catalyst heater for an exhaust gas device for an internal combustion engine includes: at least one heating element (14) that can be electrically excited; a hydrocarbon release device (20) for releasing liquid hydrocarbon (K) to the at least one heating element that can be electrically excited; and an oxidation catalyst device (26) for oxidizing the hydrocarbon heated by the at least one heating element that can be electrically excited.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a catalyst heater for an exhaust gas device of an internal combustion engine such as a vehicle, an exhaust gas device including such a catalyst heater, and a method for operating such an exhaust gas device.

[0002] When starting an internal combustion engine of a vehicle, in order to shorten the period during which the content of harmful substances in the exhaust gas of the internal combustion engine cannot be substantially reduced due to the too low temperature of the exhaust gas treatment assembly such as a catalyst provided in the exhaust gas device, it is known to use an electric heater that generates heat when a voltage is applied and transfers this heat to the exhaust gas discharged from the internal combustion engine. The exhaust gas thus further heated results in faster heating of the exhaust gas treatment assembly located downstream of such a heater, and thus shortens the period until the start of efficient exhaust gas treatment after starting the internal combustion engine.

[0003] The object of the present invention is to provide a heater for an exhaust gas device of an internal combustion engine, an exhaust gas device including such a heater, and a method for operating such an exhaust gas device, which achieve efficient heating of the components of the exhaust gas device while reducing the energy consumption.

[0004] According to a first aspect of the present invention, this object is solved by a catalyst heater for an exhaust gas device of an internal combustion engine, comprising - at least one electrically excitable heating element, - a hydrocarbon release device for releasing a liquid hydrocarbon to the at least one electrically excitable heating element, - an oxidation catalyst device for oxidizing the hydrocarbon heated by the at least one electrically excitable heating element provided in the catalyst heater.

[0005] By means of a catalytic heater configured according to the invention, most of the heat transmitted to the exhaust gas flowing in the exhaust gas device or to the components of the exhaust gas device is generated not by the electrical excitation of at least one heating element, but via catalytic oxidation and the energy released thereby. This results in, on the one hand, a reduction in the load on the on-board voltage system of the vehicle, and on the other hand, the heating of the system area conditioned for the operation of the exhaust gas device, such as an internal combustion engine or a catalyst, becomes significantly faster and stronger.

[0006] In order to be able to provide a large surface area for the catalytic oxidation of hydrocarbons carried out in the catalytic heater, the oxidation catalyst device may comprise an oxidation catalyst block for receiving and oxidizing hydrocarbons vaporized by at least one electrically excitable heating element, which is arranged on the outflow side of at least one electrically excitable heating element.

[0007] Regarding the efficient utilization of the heat released by at least one electrically excitable heating element, it is proposed that the oxidation catalyst device comprises an oxidation catalyst material coating of at least one electrically excitable heating element. Thus, the oxidation catalyst material coating can reach the operating temperature required for the catalytic oxidation of hydrocarbons extremely quickly even at relatively low ambient temperatures by direct physical contact and the heat conduction enabled thereby.

[0008] According to a further aspect of the invention, the object is achieved by an exhaust gas device for an internal combustion engine, comprising at least one exhaust gas treatment assembly and, upstream of at least one exhaust gas treatment assembly in the exhaust gas flow direction, a catalytic heater having the structure according to the invention.

[0009] At least one exhaust gas treatment assembly may include a first exhaust gas treatment assembly having an oxidation catalyst and / or a particulate filter. Depending on the type of internal combustion engine used in connection with the exhaust gas device, i.e., a diesel engine or an Otto engine, and thus also depending on the type of hydrocarbon used in the catalyst heater, the oxidation catalyst may be formed as a diesel oxidation catalyst or as a three-way catalyst.

[0010] For even more efficient exhaust gas purification, especially when the internal combustion engine is configured as a diesel engine, at least one exhaust gas treatment assembly may include a second exhaust gas treatment assembly having an SCR catalyst.

[0011] In this case, the first exhaust gas treatment assembly may be arranged upstream of the second exhaust gas treatment assembly in the exhaust gas flow direction.

[0012] The catalyst heater may be arranged, for example, downstream of an exhaust gas turbocharger in the exhaust gas flow direction. If the catalyst heater is arranged downstream of a third exhaust gas treatment assembly in the exhaust gas flow direction, for example, when the third exhaust gas treatment assembly comprises an SCR catalyst, a significant reduction in the proportion of nitrogen oxides in the exhaust gas discharged from the internal combustion engine can be achieved.

[0013] In cases where the operation of the catalyst heater is no longer necessary in a sufficiently warmed-up exhaust gas device, it has been proposed that a selectively cut-off bypass flow path be provided in parallel with the catalyst heater in order to compensate for the inevitable increase in the flow resistance of the exhaust gas device caused by this catalyst heater.

[0014] Depending on the type of vehicle in which the exhaust gas device is incorporated, - the catalyst heater may be arranged within an exhaust gas device section that extends away downward and / or laterally in the height direction from the internal combustion engine, or - The catalytic heater may extend under the underbody of the vehicle or be arranged within an exhaust gas device section located in the side area of the vehicle.

[0015] According to a further aspect of the invention, the problem described at the beginning is a method for operating an exhaust gas device configured by the invention, which heats the liquid hydrocarbons impinging on the surface of at least one electrically excitable heating element of the catalytic heater, oxidizes them in an oxidation catalyst device, and operates at least one electrically excitable heating element so as to generate heat.

[0016] In order to ensure that the hydrocarbons injected in the direction of at least one electrically excitable heating element are substantially completely converted by catalytic oxidation, and thus the release of unoxidized hydrocarbons into the environment is avoided, after the start of excitation of at least one electrically excitable heating element, the oxidation catalyst device starts injecting hydrocarbons into at least one electrically excitable heating element when it has a predetermined temperature, preferably a temperature enabling catalytic oxidation of hydrocarbons in the oxidation catalyst arrangement, or / and when a predetermined period has elapsed since the start of excitation of at least one electrically excitable heating element.

[0017] The period during which the exhaust gas emitted by the internal combustion engine cannot or cannot efficiently be processed in the exhaust gas device to reduce the harmful substance ratio can be further shortened, for example, when the excitation of at least one electrically excitable heating element starts before the start of the internal combustion engine.

[0018] In the method according to the invention, when the injection of hydrocarbons into at least one electrically excitable heating element starts together with or after the start of the internal combustion engine, it is ensured that the hydrocarbons vaporized by at least one electrically excitable heating element are conveyed through the exhaust gas already flowing in the exhaust gas device, for example, to a downstream oxidation catalyst block.

[0019] In an alternative method, the injection of hydrocarbons into at least one electrically excitable heating element may already be started before the start of the internal combustion engine. This method has an oxidation catalyst material coating formed on at least one electrically excitable heating element, and thus, in such a coated heating element, when heat is already directly released by the oxidation of the heated hydrocarbons, it provides particularly fast and efficient heating.

[0020] In this case, for efficient heating, a) before starting the internal combustion engine, in a pre-injection process, inject hydrocarbons in a predetermined amount and / or for a predetermined period, b) after the end of the pre-injection process, rotationally drive the internal combustion engine without ignition, c) before starting the internal combustion engine, in the last pre-injection process, inject hydrocarbons in a predetermined amount and / or for a predetermined period may be specified.

[0021] During the intermediate rotation of the internal combustion engine, i.e., by the movement of the crankshaft and the piston of the internal combustion engine without ignition occurring in the cylinder, in a subsequent further pre-injection process, air and thus oxygen is conveyed to the exhaust gas device to provide oxygen for the oxidation of hydrocarbons.

[0022] Before the implementation of measure c), measures a) and b) may be repeated at least once. Since the last pre-injection process is carried out by measure c), the internal combustion engine may be operated after or during the implementation of measure c).

[0023] If the exhaust gas device is already sufficiently heated by repeating such a pre-injection process a plurality of times, the injection of hydrocarbons may be terminated upon completion of measure c). For example, if the ambient temperature is relatively low and correspondingly the exhaust gas device is cold, it may be advantageous for the injection of hydrocarbons to be restarted or continued after the completion of measure c) and after the start of the internal combustion engine for sufficient and rapid heating of the exhaust gas device. This means, for example, that upon completion of measure c), the injection of hydrocarbons can be continued without interruption when the internal combustion engine is subsequently operating, or that after the completion of measure c), the injection of hydrocarbons is temporarily interrupted, and then, for example, if it is determined that different system regions of the exhaust gas device are not yet sufficiently warmed up, the injection of hydrocarbons is started again and heat is released by its catalytic oxidation.

[0024] To ensure that the injected hydrocarbons can be substantially completely converted in the oxidation catalyst device and heat can be released, the hydrocarbon injection rate may be determined according to the temperature of the oxidation catalyst device and / or according to the exhaust gas volume flow rate in the exhaust gas device. The higher the temperature of the oxidation catalyst device, the more efficiently the oxidation catalyst device can convert hydrocarbons. Therefore, as the temperature of the oxidation catalyst device increases, it is possible to increase the amount of energy released per unit time by increasing the hydrocarbon injection rate. A higher exhaust gas volume flow rate means a higher flow velocity, and correspondingly, a shorter residence time, or it also means that the probability that the vaporized hydrocarbons transported in the exhaust gas stream contact the surface of the oxidation catalyst device and are oxidized there is lower. Therefore, in order to avoid the release of unoxidized hydrocarbons, it is advantageous to reduce the amount of hydrocarbons injected per unit time at a higher exhaust gas volume flow rate. For example, quantities such as the temperature of the oxidation catalyst device, for example the temperature in its different regions, and the exhaust gas volume flow rate can be considered as input quantities in a characteristic map defining the hydrocarbon injection rate.

[0025] In this case, in particular, it may be specified that the hydrocarbon injection rate increases as the temperature of the oxidation catalyst device increases, and / or the hydrocarbon injection rate decreases as the exhaust gas volume flow rate increases.

[0026] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

[0028] FIG. 1 shows a schematic longitudinal sectional view of a catalyst heater generally designated by reference numeral 10 within an exhaust gas device 12 for an internal combustion engine.

[0029] The catalyst heater 10 includes, as an essential component, an electrically excitable heating element 14 that can be connected via a connection contact 16 to a voltage source, for example, an on-board voltage system of a vehicle. The electrically excitable heating element 14 may be formed as a heating conductor made of a strip-shaped flat material, such as a jacket heater, and may be arranged, for example, in a helical winding structure, a meandering winding structure, or bent into other forms. For example, the exhaust gas A flowing within a tubular exhaust gas guiding component 18 can flow around the heating element 14 and absorb heat therein. Upstream of the heating element 14 is located a hydrocarbon release device 20, which is also generally shown as an injector. Thereby, a liquid hydrocarbon K, such as diesel or gasoline, is released in a spray form or a droplet form, for example, in the direction of the inflow side 22 of the electrically excitable heating element 14.

[0030] On the outflow side 23 of the heating element 14, an oxidation catalyst block 24 of an oxidation catalyst device, generally denoted by reference numeral 26, is supported, for example, by a fiber mat 28 in the exhaust gas guiding component 18. The oxidation catalyst block 24 is composed of, for example, a substrate through which the exhaust gas A can flow, and this substrate has an oxidation catalyst material on its surface. Depending on the type of internal combustion engine used in connection with the exhaust gas device 12, this oxidation catalyst material may be a diesel oxidation catalyst material in the case of a diesel engine or a three-way catalyst material in the case of an Otto engine.

[0031] The oxidation catalyst device 26 optionally comprises an oxidation catalyst material coating 30 on the electrically excitable heating element 14. This can also completely cover or only partially cover the surface of the electrically excitable heating element, and may also include, for example, a diesel oxidation catalyst material or a three-way catalyst material depending on the type of internal combustion engine and thus the type of hydrocarbon K used.

[0032] The hydrocarbon release device 20 used in the catalyst heater 10 may, for example, comprise an injector that releases the hydrocarbon K symmetrically, i.e., in the form of a uniform spray cone, or an injector that releases the hydrocarbon K asymmetrically, i.e., more on one side. As can be recognized in FIG. 1, instead of being inclined with respect to the exhaust gas flow direction within the substantially linearly extending exhaust gas guiding component 18, the hydrocarbon release device 20 may be located in the arc region of the exhaust gas guiding component 18 upstream of the heating element 14 such that the main release direction of the hydrocarbon release device 20 substantially corresponds to the flow direction of the exhaust gas A immediately upstream of the heating element 14. Thereby, a compact structural form of the catalyst heater 10 or the exhaust gas device 12 configured using the same can be achieved.

[0033] Figure 2 shows an exhaust gas device 12 used in connection with an internal combustion engine 32. An exhaust gas turbocharger 34 is provided in the exhaust gas device 12 upstream of the catalyst heater 10. Downstream of the catalyst heater 10, there are provided a first exhaust gas treatment assembly 40 including, for example, a diesel oxidation catalyst 36 and a particulate filter 38, and a second exhaust gas treatment assembly 46 including an SCR catalyst 42 to which an injector 44 is assigned. Such a configuration of the two exhaust gas treatment assemblies 44, 46 is provided in particular in connection with an internal combustion engine 32 formed as a diesel engine.

[0034] If the dimensions of the oxidation catalyst block 24 of the catalyst heater 10 are sufficiently large, for example, the diesel oxidation catalyst 36 of the first exhaust gas treatment assembly 40 can be omitted. Further, optionally, a third exhaust gas treatment assembly 48 may be provided upstream of the catalyst heater 10 or downstream of the exhaust gas turbocharger 34, which may include, for example, a pre-SCR catalyst 50 to which an injector 52 is assigned.

[0035] Furthermore, Figure 2 advantageously shows that a bypass flow path 54 may be provided, assigned to the catalyst heater 10 and parallel to this catalyst heater 10, and this bypass flow path 54 can be selectively opened and allowed to flow through or blocked against the flow by a valve 56 assigned to the catalyst heater 10. In a state where the operation of the catalyst heater 10 is not required, the bypass flow path 54 is opened and allowed to flow through, so that an increase in flow resistance caused by the catalyst heater 10 can be compensated. When the bypass flow path 54 is opened and allowed to flow through, for example, most of the exhaust gas A discharged from the internal combustion engine 32 can flow through this bypass flow path 54.

[0036] In the heating operation of the catalytic heater 10, the bypass flow path 54 is blocked by the valve 56. Therefore, the entire exhaust gas flow is guided through the catalytic heater 10, and thus heat may be transferred from the catalytic heater 10 to the system region downstream. In this case, if the heating operation of the catalytic heater 10 starts almost simultaneously with the start of the operation of the internal combustion engine 32, the valve 56 is opened, and thus it may also be specified that most of the exhaust gas A discharged from the internal combustion engine 32 flows through the bypass flow path 54 in the heating stage of the heating element 14. Thereby, a relatively small portion of the heat generated by the excitation of the heating element 14 is released by the exhaust gas A flowing around the heating element 14, whereby the heating element 14 is heated more rapidly, and thereby the state in which the hydrocarbon K is vaporized on the surface of the heating element 14 is achieved more rapidly.

[0037] Figures 3 and 4 show options for different arrangements of the catalytic heater 10 within the exhaust gas device 12. The exhaust gas device 12 may basically be configured to have an exhaust gas device section 58, shown generally as a downpipe, that follows the internal combustion engine 32 or the exhaust gas turbocharger 34 and extends away from the internal combustion engine 32, for example downward and / or laterally. This exhaust gas device section 58 that extends downward and / or laterally can be connected to an exhaust gas device section 60 that extends, for example, under the underbody of the vehicle. Also, the section 58 may lead to an exhaust gas treatment assembly located, for example, in the lateral region of the truck.

[0038] In the embodiment shown in Figure 3, the catalytic heater 10 is located within the section 58 of the exhaust gas device 12 that extends downward and / or laterally with respect to the internal combustion engine 32. Therefore, this installation space is utilized efficiently. Therefore, the catalytic heater 10 is located extremely close to the internal combustion engine 32, and thus the exhaust gas A that flows through this catalytic heater 10 and is further heated, as described below, can efficiently contribute to the heating of the exhaust gas treatment assembly located further downstream.

[0039] In an alternative configuration, for example, if the installation space for this purpose is not available, the catalytic heater 10 is not located within the section 58 of the exhaust gas device 12 that connects downward or laterally, but within the section 60 of the exhaust gas device 12 located under the underbody of the vehicle or in a region on the side of the vehicle.

[0040] It should be noted that each configuration variation of the exhaust gas device 12 shown in FIGS. 3 and 4 may be specified in relation to various different further system regions shown in detail in FIG. 2, namely, various different exhaust gas treatment assemblies 40, 46, 48 and / or bypass channels 54.

[0041] The operation of the catalytic heater 10 in the exhaust gas device 12 to promote the heating of the system regions following the exhaust gas flow path, namely, in particular the exhaust gas treatment assemblies 40, 46, will be described below.

[0042] In the operation of the catalytic heater 10, the hydrocarbon K that collides with the heating element 14 in liquid form is heated and in this case vaporized by the excitation of the heating element 14, that is, by applying a voltage to the heating element 14 and by the heat generated by the heating element 14 at that time. At the same time, heat is transmitted mainly by thermal radiation to the upstream end region of the oxidation catalyst block 24, and this upstream end region is heated even if the exhaust gas flow does not exist in some cases. The temperature of the oxidation catalyst block 24 in its upstream end region can be detected by the temperature sensor 62 and used in the control unit that controls the catalytic heater 10 to control or operate the catalytic heater 10 and, optionally, further system regions of the exhaust gas device 12 according to this temperature.

[0043] The hydrocarbon K heated and vaporized by the heating element 14 is further conveyed in the direction of the oxidation catalyst block 24 by the method described in more detail below, and on its surface, it can be oxidized by the oxygen also present in the exhaust gas device 12. Heat is released during this catalytic oxidation reaction, and this heat also contributes to the further heating of the oxidation catalyst block 26 and thus to the heating of the exhaust gas A flowing through this oxidation catalyst block 26 during the operation of the internal combustion engine 32. The exhaust gas A conveys the heat absorbed by the catalyst heater 10 in the downstream direction to the subsequent exhaust gas treatment assemblies 40, 46 and transfers at least a part of the heat to these exhaust gas treatment assemblies 40, 46. Thereby, the exhaust gas treatment assemblies 40, 46 are heated more rapidly, especially at the start-up stage of the operation of the internal combustion engine 32, which enables the catalytic reaction optionally carried out in this exhaust gas treatment assembly 40, 46 to be started earlier, and thus the period during which the exhaust gas A is discharged substantially untreated is significantly shortened.

[0044] When an oxidation catalyst material coating 30 is also provided on the heating element 14, at least a part of the hydrocarbon K that has collided with the heating element 14 and thereby vaporized may be oxidized by the catalytic reaction in the heating element 14 already. Heat is also released here, and this heat contributes, on the one hand, to the more rapid and intense heating of the heating element 14 and, on the other hand, also to the more rapid heating of the oxidation catalyst block 24 or the exhaust gas A flowing through the exhaust gas device 12.

[0045] When using such a catalyst heater 10, not only is the system area of the exhaust gas or the subsequent exhaust gas device 12 further downstream heated by the heat generated by the electrical excitation of the heating element 14, but also a significant part of the thermal energy released within the area of the catalyst heater 10 is supplied by the catalytic oxidation reaction of the hydrocarbon K, so that it is possible to achieve a significantly stronger and more rapid heating of different system areas of the exhaust gas device 12 while significantly reducing the use of electrical energy. Thereby, for example, it becomes possible to operate the heating element 14 at a lower operating voltage, for example, a voltage of 24V supplied by an on-board voltage network.

[0046] The following describes various operating modes of the exhaust gas device 12 or the catalyst heater 10 that can bring about efficient heating of the system regions present in the exhaust gas device 12 for exhaust gas purification, particularly the exhaust gas treatment assemblies 40, 46.

[0047] When starting the vehicle or the internal combustion engine 32, it is also possible to excite the heating element 14, that is, to apply a voltage to this heating element 14 to start generating heat in this region. Along with the start of the operation of the internal combustion engine 32, the release of the exhaust gas A from this internal combustion engine 32 also begins. Therefore, a part of the heat generated in the heating element 14 is carried to the oxidation catalyst block 24 in the downstream direction through the exhaust gas flow. Also, a part of the heat may be directly transmitted from the heating element 14 to the upstream end region of the oxidation catalyst block 24 by heat radiation.

[0048] For example, based on the output signal of the temperature sensor 62, when it is recognized that the oxidation catalyst block 24 has a temperature sufficient for carrying out the catalytic oxidation of hydrocarbons K, for example, at least in its upstream end region, it may be 250 °C or higher, the injection of the liquid hydrocarbon K in the direction of the heating element 14 can be started. The liquid hydrocarbon K vaporizes on the surface of the heated heating element 14 and is conveyed in the direction of the oxidation catalyst block 24 through the exhaust gas flow. Then, in the oxidation catalyst block 24, the oxidation of the hydrocarbon K occurs by the oxygen contained in the exhaust gas device 12 in this state or conveyed in the exhaust gas A. Heat is released during this oxidation, and this heat not only heats the exhaust gas A flowing in the further downstream direction in addition to the heat released by the excitation of the heating element 14, but also contributes to the faster heating of the oxidation catalyst block 24, particularly in the direction of its downstream region. As a result, relatively quickly after the oxidation reaction starts in the oxidation catalyst block 24, the entire oxidation catalyst block 24 reaches the temperature required for carrying out the catalytic oxidation of hydrocarbons K.

[0049] In order to reach this temperature even faster or to be able to contribute even faster to heating the exhaust gas A for heating the system area of the exhaust gas device 12 further downstream, the excitation of the heating element 14 may already be started, for example, 5 to 20 seconds before the start of the internal combustion engine 32. As a trigger for this, an event within the vehicle can be utilized, which suggests that it is very likely to operate the internal combustion engine 32 in the near future. For example, unlocking the vehicle door or inserting the ignition key into the ignition lock can be utilized as such an event that triggers the excitation of the heating element 14.

[0050] The injection of hydrocarbons can start, for example, when the heating element reaches a sufficiently high temperature, for example, in the range of 200 to 400 °C, preferably at least 350 °C. This temperature can be detected by a temperature sensor assigned to the heating element 14 or determined empirically and associated with a certain period from the start of the excitation of the heating element 14, so that the injection of hydrocarbons can start a certain period after the start of the excitation of the heating element 14. If the excitation of the heating element 14 already starts before the start of the operation of the internal combustion engine 32, an even faster heating of the heating element 14 to the desired temperature can be achieved because there is no exhaust gas flow yet at this stage.

[0051] When the heating element 14 has the oxidation catalyst material coating 30, similarly, the excitation of the heating element 14 may be started together with or slightly before the start of the internal combustion engine 32, and the injection of the hydrocarbon K may be started together with the start of the internal combustion engine 32. In such a configuration of the heating element 14 having the oxidation catalyst material coating 30, since a part of the hydrocarbon K that has been heated and vaporized in the heating element 14 has already been oxidized in the oxidation catalyst material coating 30, the heating element 14 is heated at a higher speed and more heat is supplied, and this amount of heat is transmitted to the oxidation catalyst block 24 by heat radiation and convection. The exhaust gas A flowing in the exhaust gas device 12 from the start of the operation of the internal combustion engine 32 also strongly absorbs heat in the region of the heating element 14, and this heat can also be conveyed to the regions of the system regions following further downstream of the exhaust gas device 12.

[0052] Therefore, by strengthening the generation of heat in the region of the heating element 14, not only stronger vaporization of the liquid hydrocarbon K but also faster heating of all the subsequent downstream system regions is brought about, so that the oxidation catalyst block 24 reaches the maximum capacity of the catalytic oxidation of the hydrocarbon K at a higher speed, and the system regions following further downstream in the exhaust gas device 12 reach the operating temperature required for each of their exhaust gas purification functions at a higher speed.

[0053] In a further alternative approach, both the excitation of the heating element 14 and the injection of the hydrocarbon K may be carried out already before the start of the operation of the internal combustion engine 32. For example, first, when the internal combustion engine 32 is not yet operating, the heating element 14 provided with the oxidation catalyst material coating 30 can be excited until it reaches a target temperature in the range of at least 300°C, preferably at least 400°C. This temperature can be detected by a sensor or determined in combination with an empirically determined period, and this temperature is assumed to be present after a period of, for example, 5 to 20 seconds, which depends on the structural form of the heating element 14. At this stage, since no exhaust gas is flowing in the exhaust gas device 12, this period can be relatively short.

[0054] After reaching the desired temperature or after the elapse of a given period, a predetermined amount of fuel can be injected into the heating element 14 or the oxidation catalyst material coating 30. The liquid hydrocarbon K is heated at the surface of the heating element 14 or the oxidation catalyst material coating 30, vaporized in some cases, and oxidized by the oxygen present around the heating element 14 in the exhaust gas device 12. During this oxidation, relatively more heat is released compared to the heat released by the excitation of the heating element 14, and this heat strengthens the heating of the heating element 14 itself and also already strongly heats the upstream region of the oxidation catalyst material block 24, mainly by thermal radiation. The heating element 14 can reach a temperature of 600 °C to 800 °C at this stage.

[0055] Thereafter, the internal combustion engine 32 can be operated and the injection of the hydrocarbon K can be continued. Therefore, on the one hand, heat is also conveyed from the region of the heating element 14 in the downstream direction, especially to the oxidation catalyst block 24, by the exhaust gas flow used in the same way. From the exhaust gas A flowing in the exhaust gas device 12, the vaporized hydrocarbon K is conveyed to the region of the oxidation catalyst block 24, and then, in at least its already heated upstream region as well, catalytic oxidation of the vaporized hydrocarbon K can occur. With the start of the internal combustion engine 12 and the use of the exhaust gas flow, complete conversion of the hydrocarbon K occurs not only in the oxidation catalyst material coating 30 but also, similarly or mainly, on the surface of the oxidation catalyst block 24. Therefore, for example, the amount of the injected hydrocarbon K can also be increased. When the oxidation of the hydrocarbon K starts in the oxidation catalyst block 24, relatively rapid heating of the downstream end region of the oxidation catalyst block 24 is also brought about, so that the period until the maximum oxidation capacity of the oxidation catalyst block 24 is reached can be further shortened by the injection of the hydrocarbon K that starts even before the start of the internal combustion engine 32.

[0056] By utilizing the injection of the liquid hydrocarbon K even before the start of the internal combustion engine 12, in the range of one or more pilot injections, the temperature in the region of the heating element 14 and especially in the upstream region of the oxidation catalyst block 24 can be raised to the desired temperature more rapidly.

[0057] In this case, first, after excitation of the heating element 14 and heating thereof to a temperature of at least 300°C, preferably at least 400°C, in the pre-injection process, it is possible to inject the hydrocarbon K in the direction of the heated heating element 14, or correspondingly, to inject the heated oxidation catalyst material coating 30. The hydrocarbon K is heated upon impact on the surface of the heating element 14 or the oxidation catalyst material coating 30, vaporized in some cases, and oxidized by a contact reaction with oxygen present in this region of the exhaust gas device 12. The heat generated here contributes to stronger and faster heating of the heating element 14 or, similarly, the upstream region of the oxidation catalyst block 24. After the end of this pre-injection process and substantially complete catalytic oxidation of the injected hydrocarbon K, the internal combustion engine 32 is rotationally driven by a starting device, a starter / generator, etc., without ignition occurring in its cylinders at that time. By the piston moving during this rotation of the crankshaft of the internal combustion engine 12, air and thus oxygen are discharged from the cylinders of the internal combustion engine 32 in the direction of the upstream region of the exhaust gas device 12, i.e., this region where the catalyst heater 10 is also located. Thus, it is ensured that sufficient oxygen is made available again for a further pre-injection process and that the hydrocarbon K injected within the scope of this further pre-injection process can be completely oxidized.

[0058] Depending on the length of the period available for carrying out such a pre-injection process, this process of alternately injecting the hydrocarbon K and rotating the internal combustion engine 32 can be repeated a plurality of times.

[0059] After performing the last pre-injection process and ending the injection of hydrocarbon K, the internal combustion engine 32 can be started. Alternatively, the internal combustion engine 32 can also be started already during the performance of the last pre-injection process. If the downstream system area of the exhaust gas device 12 is already sufficiently heated, the injection of hydrocarbon K can be adjusted by ending the last pre-injection process. However, generally, it is considered that the entire exhaust gas device 12 is not sufficiently heated by pilot injection, so it is necessary to inject hydrocarbon K after or immediately following the performance of the last pre-injection process in some cases, and the heat released in the oxidation catalyst block 24 or similarly in the oxidation catalyst material coating 30 needs to be conveyed by the exhaust gas A to a thermally conditioned system area in a region further downstream in the exhaust gas device 12.

[0060] The degree of rotation of the crankshaft of the internal combustion engine 32 performed within the range of such pilot injection mainly depends on how many cylinders the internal combustion engine 32 has or how large the volume of the cylinders is. The degree of rotation should be adapted to the amount of hydrocarbon K injected within the range of each pre-injection process so as to ensure that sufficient oxygen is available to completely oxidize the hydrocarbon K injected during the pre-injection process within the exhaust gas device 12, especially around the heating element 14.

[0061] For the start of such pilot injection, an event indicating that the internal combustion engine 32 starts operating immediately can be utilized. For example, a signal indicating the opening of a vehicle door can be accessed. Alternatively or additionally, it is also possible for a vehicle user to preset the point in time of a planned start of the vehicle, similar to what is practiced in relation to an auxiliary heater, so that, for example, depending on the ambient temperature and thus also depending on the temperature of different system areas thermally conditioned in the exhaust gas device 12, pilot injection can be started in a sufficient period before the planned start of use of the vehicle. Accordingly, it is ensured that the oxidation catalyst block 24 is already sufficiently heated along with the start of the internal combustion engine 32, and efficient catalytic oxidation and thus also efficient heat release can be achieved during the injection of hydrocarbons used or continued along with the start of the internal combustion engine 32.

[0062] The amount of hydrocarbons injected during or after the excitation of the heating element 14 can be adjusted according to various parameters. Parameters essential for the catalytic conversion of hydrocarbons K are, for example, the temperature of the oxidation catalyst block 24 and the exhaust gas volume flow rate, that is, the amount of exhaust gas A entraining vaporized hydrocarbons K flowing through the oxidation catalyst block 24 per unit time. The higher the temperature of the oxidation catalyst block 24, especially the temperature in its downstream end region, the more efficiently this oxidation catalyst block 24 can oxidize hydrocarbons K colliding on its surface. This means that the hydrocarbon injection rate can be increased, for example, up to the maximum value of the hydrocarbon injection rate as the temperature of the oxidation catalyst block 24 increases. The greater the exhaust gas volume flow rate, that is, the greater the amount of exhaust gas flowing through the oxidation catalyst block 24 per unit time, the result is that the residence time of hydrocarbons K conveyed in the exhaust gas A in the oxidation catalyst block 24 becomes correspondingly shorter. In order to avoid the release of unoxidized hydrocarbons K, it may be specified that the hydrocarbon injection rate decreases, for example, to a minimum value as the exhaust gas volume flow rate increases.

[0063] Such an amount of influence, for example, not only the temperature of the oxidation catalyst block 24 and the exhaust gas volume flow rate, but also, for example, the exhaust gas temperature, the target temperature that the exhaust gas should have after passing through the oxidation catalyst block 24, and the electric heating output of the heating element 14 are considered. On the one hand, a characteristic map can be defined that can release the maximum amount of heat, and on the other hand, the hydrocarbon injection rate is preset according to such an input amount of power so as to avoid the release of unoxidized hydrocarbons K.

Claims

1. A catalytic heater for an exhaust gas system of an internal combustion engine, comprising: at least one electrically excitable heating element (14), a hydrocarbon discharge device (20) for discharging liquid hydrocarbons (K) into said at least one electrically excitable heating element (14); - an oxidation catalytic device (26) for oxidizing the hydrocarbons (K) heated by said at least one electrically excitable heating element (14); A catalytic heater comprising:

2. 2. The catalytic heater according to claim 1, characterized in that the oxidation catalyst device (26) comprises an oxidation catalyst block (24) arranged on the outlet side (23) of the at least one electrically excitable heating element (14) for receiving and oxidizing the hydrocarbons (K) vaporized by the at least one electrically excitable heating element (14).

3. The catalytic heater of claim 1 or 2, characterized in that the oxidation catalytic device (26) comprises an oxidation catalytic material coating (30) of the at least one electrically excitable heating element (14).

4. 4. An exhaust gas system for an internal combustion engine, comprising at least one exhaust gas treatment assembly (40, 46) and, upstream of the at least one exhaust gas treatment assembly (40, 46) in an exhaust gas flow direction, a catalytic heater (10) according to any one of claims 1 to 3.

5. The exhaust gas system of claim 4, wherein the at least one exhaust gas treatment assembly (40, 46) includes a first exhaust gas treatment assembly (40) having an oxidation catalyst (36) or / and a particulate filter (38).

6. The exhaust gas system of claim 4 or 5, wherein the at least one exhaust gas treatment assembly (40, 46) includes a second exhaust gas treatment assembly (46) having an SCR catalyst (42).

7. 7. Exhaust gas system according to claim 5 and 6, characterized in that the first exhaust gas treatment assembly (40) is arranged upstream in the exhaust gas flow direction with respect to the second exhaust gas treatment assembly (46).

8. 8. An exhaust gas system according to claim 4, characterized in that the catalytic heater (10) is arranged downstream of an exhaust gas turbocharger (34) or / and a third exhaust gas treatment assembly (48) in the exhaust gas flow direction.

9. The exhaust system of claim 8, wherein the third exhaust treatment assembly (48) comprises an SCR catalyst (50).

10. 10. An exhaust gas system according to claim 4, further comprising a selectively shut-off bypass passage (54) arranged parallel to the catalytic heater (10).

11. the catalytic heater (10) is arranged in an exhaust system section (58) which extends downward and / or laterally away from the internal combustion engine (32) in the height direction, or the catalytic heater (10) is arranged in an exhaust system section (60) which extends under the underbody of the vehicle or is located in the lateral region of the vehicle; 11. Exhaust gas system according to claim 4, characterized in that it comprises a first exhaust gas supply means.

12. 12. A method for operating an exhaust gas system according to any one of claims 4 to 11, comprising operating the at least one electrically excitable heating element (14) of the catalytic heater (10) to heat liquid hydrocarbons (K) impinging on a surface of the at least one electrically excitable heating element (14) and oxidizing the liquid hydrocarbons (K) in the oxidation catalytic device (26) to generate heat.

13. 13. The method according to claim 12, characterized in that the injection of hydrocarbons (K) into the at least one electrically excitable heating element (14) is started if, after the start of excitation of the at least one electrically excitable heating element (14), the oxidation catalyst arrangement (26) has a predetermined temperature, preferably a temperature which allows catalytic oxidation of hydrocarbons (K) in the oxidation catalyst arrangement (26) and / or if a predetermined period of time has elapsed since the start of excitation of the at least one electrically excitable heating element (14).

14. 14. The method according to claim 12 or 13, characterized in that the excitation of the at least one electrically excitable heating element (14) begins before starting the internal combustion engine (32).

15. 15. The method according to claim 14, characterized in that the injection of hydrocarbons (K) into the at least one electrically excitable heating element (14) is initiated together with or after the start-up of the internal combustion engine (32).

16. 15. The method according to claim 14, when dependent on claim 3, characterized in that the injection of hydrocarbons (K) into the at least one electrically excitable heating element (14) is initiated before starting the internal combustion engine (32).

17. a) injecting a hydrocarbon (K) in a pre-injection process in a predetermined amount and / or for a predetermined duration before starting the internal combustion engine (32); b) after completion of the pre-injection process, driving the internal combustion engine (32) into rotation without ignition; c) injecting a hydrocarbon (K) in a predetermined amount and / or for a predetermined duration in a final pre-injection process before starting the internal combustion engine (32).

17. The method according to claim 16, characterized in that

18. 18. The method according to claim 17, characterized in that before performing step c), steps a) and b) are repeated at least once and / or after or during performing step c), the internal combustion engine (32) is operated.

19. - by ending the said measure c), the injection of the hydrocarbons (K) is ended, or - resuming or continuing the injection of hydrocarbons (K) after the end of said measure c) and after starting said internal combustion engine (32), 20. The method of claim 18,

20. 20. The method according to claim 12, further comprising determining the hydrocarbon injection rate as a function of the temperature of the oxidation catalyst device and / or as a function of the exhaust gas volume flow rate in the exhaust gas system after starting of the internal combustion engine.

21. 21. The method of claim 20, characterized in that the hydrocarbon injection rate increases as the temperature of the oxidation catalyst device (26) increases and / or the hydrocarbon injection rate decreases as the exhaust gas volume flow rate increases.

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