Patent Publication Number: US-2023151754-A1

Title: Exhaust gas turbine and method of operating the same

Description:
The invention relates to an exhaust gas turbine. Furthermore, the invention relates to a method for operating an exhaust gas turbine. 
     The basic structure of an exhaust gas turbocharger is known from DE 10 2016 125 189 A1. An exhaust gas turbocharger has an exhaust gas turbine for expanding exhaust gas of an internal combustion engine, wherein energy is obtained during the expansion of the exhaust gas. Further, the exhaust gas turbocharger comprises a compressor for compressing charge air to be supplied to the internal combustion engine, using the energy obtained when the exhaust gas is expanded. The exhaust gas turbine has a turbine housing and a turbine rotor. The compressor has a compressor housing and a compressor rotor. The turbine rotor and compressor rotor are coupled via a while, which is supported in a bearing housing. 
     From WO 2018/080371 A1 an exhaust gas turbine of an exhaust gas turbocharger is known, which has a dosing device for reducing agent or a precursor substance of a reducing agent. Via this metering device, the reducing agent or the precursor substance can be introduced into the exhaust gas expanded in the exhaust gas turbine, the metering device directing the reducing agent or the precursor substance onto a swirl atomizer which engages the turbine rotor at a hub-side section of the turbine rotor and rotates together with the turbine rotor. The swirl atomizer can be used to atomize the reducing agent or the precursor substance of the reducing agent in the expanded exhaust gas. The reducing agent is used to reduce nitrogen oxides in the exhaust gas, in particular in the region of an SCR catalytic converter which is arranged downstream of the exhaust gas turbine and to which the expanded exhaust gas can be fed together with the reducing agent atomized in the exhaust gas. 
     There is the problem that deposits of solid components of the reducing agent or of the precursor substance of the reducing agent form on assemblies of the exhaust gas turbine, for example on the swirl atomizer, the metering device or also on the turbine housing, such as deposits of urea decomposition products like cyanuric acid or melamine. This is disadvantageous. 
     There is therefore a need for an exhaust gas turbine in which the risk of deposits forming on components thereof from solid components of the reducing agent or the precursor substance of the reducing agent is reduced. 
     From this, the invention is based on the task of creating a novel exhaust gas turbine and a method for operating the same. 
     According to a first aspect, this task is solved by an exhaust gas turbine according to claim  1 . According to this, the exhaust gas turbine has, downstream of the turbine rotor in extension of the axis of rotation of the turbine rotor, an impingement body for the reducing agent or the precursor substance introduced into the exhaust gas and atomized, which impingement body is arranged at a defined distance from the swirl atomizer, the defined distance of the impingement body from the swirl atomizer corresponding to at most 7 times a diameter of the turbine rotor. 
     By providing the impingement body downstream of the turbine rotor in extension of the axis of rotation of the turbine rotor with a defined distance between the impingement body and the swirl atomizer in the direction of the axis of rotation, an effective atomization of the reducing agent or of the precursor substance of the reducing agent in the expanded exhaust gas can be ensured, which reduces the risk of deposits of solid components of the reducing agent or of the precursor substance forming on the swirl atomizer, the metering device and the turbine housing. 
     According to an advantageous further development of the first aspect, the distance between the swirl body and the swirl atomizer, as seen in the direction of the axis of rotation of the turbine rotor, corresponds to a maximum of 6 times, preferably a maximum of 5 times, particularly preferably a maximum of 4 times, the diameter of the turbine rotor. This distance between the impingement body and the swirl atomizer is particularly advantageous. 
     According to an advantageous further development of the first aspect, the impingement body is thermally decoupled from the turbine housing. Preferably, the impingement body is flowed against on a first side by exhaust gas expanded in the exhaust gas turbine with the reducing agent or the precursor substance atomized in the expanded exhaust gas and on an opposite second side by exhaust gas not expanded in the exhaust gas turbine. The thermal decoupling of the impingement body and turbine housing reduces the risk of deposits of solid components of the reducing agent or precursor substance forming on the impingement body. Then, when the second side of the impingement body is flowed against by non-expanded and thus hotter exhaust gas from upstream of the exhaust turbine, any such deposits that may form on the first side of the impingement body can be effectively thermally decomposed. 
     According to a second aspect, this task is solved by an exhaust gas turbine according to claim  11 . According to this aspect, the swirl atomizer has a cavity and, on a wall bounding the cavity and extending parallel to the axis of rotation of the turbine rotor or at an acute angle of at most 40° to the axis of rotation of the turbine rotor, openings through which the reducing agent or the precursor substance enters the expanded exhaust gas from the cavity. This design of the swirl atomizer can also reduce the risk of deposits of solid components of the reducing agent or the precursor substance of the reducing agent forming on assemblies of the exhaust gas turbine. This embodiment is further particularly preferred for effective atomization of the reducing agent or the precursor substance thereof. 
     According to an advantageous further development of the second aspect, the openings are arranged in at least two planes offset as viewed in the direction of the axis of rotation of the turbine rotor, with partition walls preferably being arranged between the offset planes and projecting inwardly into the swirl atomizer. This further development permits particularly effective atomization of the precursor substance of the reducing agent or of the reducing agent in the expanded exhaust gas. 
     According to an advantageous further development of the second aspect, at least one opening has a longitudinal central axis that differs from other openings. This further development also permits a particularly effective atomization of the precursor substance of the reducing agent or of the reducing agent in the expanded exhaust gas. 
     Preferably, both aspects are used in combination with each other on an exhaust gas turbine. 
     Methods according to the invention for operating an exhaust gas turbine are defined in claims  17  to  20 . 
    
    
     
       Preferred further embodiments of the invention are apparent from the subclaims and the following description. Examples of embodiments of the invention are explained in more detail, without being limited thereto, by reference to the drawing. 
       Thereby shows: 
         FIG.  1    a perspective view of an exhaust gas turbocharger comprising an exhaust gas turbine according to the invention, 
         FIG.  2    a perspective view of a further exhaust gas turbine according to the invention, 
         FIG.  3    a further development of  FIG.  1     
         FIG.  4    a further development of  FIG.  1     
         FIG.  5    a cross-section through a swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  6    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  7    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  8    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  9    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  10    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  11    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  12    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  13    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  14    a cross-section through a further swirl atomizer of an exhaust gas turbine according to the invention, 
         FIG.  15    assemblies of a further exhaust gas turbocharger comprising an exhaust gas turbine according to the invention, 
         FIG.  16    a further development of  FIG.  15     
         FIG.  17    assemblies of a further exhaust gas turbine according to the invention, 
         FIG.  18    assemblies of a further exhaust gas turbine according to the invention. 
     
    
    
     The invention relates to an exhaust gas turbine which is, in particular, a component of an exhaust gas turbocharger of an internal combustion engine, in particular an internal combustion engine operated with diesel fuel or heavy oil. 
       FIG.  1    shows an exhaust gas turbocharger  30  with an exhaust gas turbine  31  according to the invention, which serves to expand exhaust gas of an internal combustion engine. Furthermore, the exhaust gas turbocharger  30  comprises a compressor  32  for compressing charge air to be supplied to the internal combustion engine, in which case the energy obtained in the exhaust gas turbine  31  during the expansion of the exhaust gas is utilized. 
     The exhaust gas turbine  31  has a turbine housing  33  and a turbine rotor  34 , the turbine rotor  34  being rotatable about an axis of rotation R. The turbine housing  33  has a rotor  34 . The turbine housing  33  has an inflow housing section  35  and an outflow housing section  36 , wherein exhaust gas to be expanded can be supplied to the turbine rotor  34  via the inflow housing section  35 , and wherein exhaust gas expanded from the turbine rotor  34  can be discharged via the outflow housing section  36 . The exhaust gas turbine  31  shown in  FIG.  1    is a radial turbine in which the exhaust gas to be expanded flows radially against the turbine rotor  34  via the inflow housing section  35 . The expanded exhaust gas is discharged in the axial direction from the turbine rotor  34 . 
     The compressor  32  has a compressor housing  37  and a compressor rotor  38 . The compressor rotor  38  is coupled to the turbine rotor  34  via a shaft  39 , which is supported in a bearing housing  40  of the exhaust gas turbocharger  30 . The rotational axis R of the turbine rotor  34  corresponds to a rotational axis R of the compressor rotor  38  and the rotational axis of the shaft  39 . 
     The bearing housing  40  is connected to both the compressor housing  37  and the turbine housing  33 , namely the inflow housing portion  35  thereof. Furthermore,  FIG.  1    shows a muffler  41  connected to the compressor housing  37 , wherein the charge air is guided via the muffler  41 . 
     After leaving the exhaust gas turbocharger  30 , the exhaust gas expanded in the exhaust gas turbine  31  is directed toward a catalytic converter (not shown), in particular toward an SCR catalytic converter, in order to reduce the nitrogen oxide content in the exhaust gas. The reducing agent required for the selective catalytic reduction in the SCR catalytic converter or a precursor substance of the reducing agent can be introduced into the expanded exhaust gas in the region of the exhaust gas turbine  31  downstream of the turbine rotor  34  via a metering device  42  of the exhaust gas turbine  31 , wherein in  FIG.  1    the metering device  42  introduces the reducing agent or the precursor substance of the reducing agent into the exhaust gas in the direction opposite to the direction of flow of the expanded exhaust gas in the direction of the axis of rotation R of the turbine rotor  34 . 
     The exhaust gas turbine  31  according to the invention further has a swirl atomizer  43  for the reducing agent or the precursor substance of the reducing agent introduced into the expanded exhaust gas via the metering device  42 , the swirl atomizer  43  engaging the turbine rotor  34  at a downstream section of the turbine rotor  34 , as viewed in the flow direction of the exhaust gas, and rotating together with the turbine rotor  34 . Via the swirl atomizer  43 , the reducing agent or the precursor substance of the reducing agent, which is directed to the swirl atomizer  43  via the metering device  42 , can be atomized in the expanded exhaust gas. 
     According to a first aspect of the invention, the exhaust gas turbine  31  has, viewed in the direction of flow of the exhaust gas downstream of the turbine rotor  34  in extension of the axis of rotation R of the turbine rotor  34 , an impingement body  44  for the reducing agent or the precursor substance of the reducing agent, wherein, viewed in the direction of the axis of rotation R of the turbine rotor  34 , a distance X in the direction of the axis of rotation R (see  FIGS.  1 ,  2   ) between the impingement body  44  and the swirl atomizer  43  corresponds to a maximum of 7 times a diameter of the turbine rotor  34 . 
     In particular, the distance X of the impingement body  44  from the swirl atomizer  43 , viewed in the direction of the axis of rotation R of the turbine rotor  34 , corresponds to a maximum of 6 times the diameter of the turbine rotor  34 , preferably to a maximum of 5 times the diameter of the turbine rotor  34 , particularly preferably to a maximum of 4 times the diameter of the turbine rotor  34 . 
     The impingement body  44  is plate-like in the embodiment example of  FIG.  1   . 
     The impingement body  44  is an assembly separate from the turbine housing  33 , mounted on the turbine housing  33  and preferably thermally decoupled from the turbine housing  33 . Thus, it can be seen from  FIG.  1    that a gap  46  is formed between the impingement body  44  and a sealing body  45  of the discharge housing section  36  of the turbine housing  33 , which gap serves to thermally decouple the impingement body  44  from the turbine housing  33 . 
     The impingement body  44  is positioned in a deflection region  47  of the outflow housing section  36  of the turbine housing  33 , wherein in this deflection region  47  the expanded exhaust gas, which flows axially away from the turbine rotor  34 , is deflected, namely by at least 70°, preferably by at least 80°, particularly preferably by at least 89°, with respect to the axis of rotation R. 
     The baffle  44 , which is preferably thermally decoupled from the turbine housing  33 , can prevent reducing agent or the precursor substance of the reducing agent from reaching the turbine housing  33  and solid components of the reducing agent or the precursor substance of the reducing agent, in particular solid urea decomposition products such as cyanuric acid or melamine, from settling or depositing on the turbine housing  33 . 
     The impingement body  44 , which is preferably thermally decoupled from the turbine housing  33 , has a higher temperature than the turbine housing  33 , so that droplets of the reducing agent or precursor substance that reach the impingement body  44  can be effectively decomposed. In this context, the defined distance x of the impingement body  44  from the swirl atomizer  43  is of particular advantage in counteracting the formation of such deposits. 
       FIG.  2    shows a further development of the embodiment example of  FIG.  1   , in which the impingement body  44 , in contrast to  FIG.  1   , is not plate-like or flatly contoured, but rather trough-like or concavely curved as seen in the direction of flow of the exhaust gas downstream of the turbine rotor  34 . In this case, the impingement body  44  can be designed as a hollow sphere segment. 
       FIG.  3    shows a further development of the embodiment example of  FIG.  1   , in which exhaust gas is introduced into the gap  46  between the impingement body  44  and the sealing body  45  of the turbine housing  33  via a feed device  48 , namely relatively hot exhaust gas which has not been expanded in the exhaust gas turbine  31 . 
     In this case, the impingement body  44  is then flown against on a first side facing the turbine rotor  34  by the exhaust gas expanded in the exhaust gas turbine  31  with the reducing agent atomized in the expanded exhaust gas or the atomized precursor substance of the reducing agent, whereas the impingement body is flown against on an opposite second side facing away from the turbine rotor  34  by non-expanded exhaust gas which is hotter than the expanded exhaust gas. 
     The further embodiment of  FIG.  3    permits a particularly advantageous thermal decoupling of the impingement body  44  from the turbine housing  33  and a particularly effective decomposition of droplets of the reducing agent or the precursor substance of the reducing agent which reach the first side of the impingement body  44 . 
     Whereas in the embodiment of  FIG.  1    the thermal decoupling of the impingement body  44  and turbine housing  33  takes place via an air gap insulation, in the embodiment of  FIG.  3    it is additionally provided to flow hot exhaust gas to the impingement body  44  on the side facing away from the turbine rotor  34  and thus to heat the same from the back side. The exhaust gas, which can be fed to the impingement body  44  via the feed device  48 , can be branched off upstream of the turbine rotor  34 , for example from the feed housing section  35  of the turbine housing  33 . It is particularly advantageous to extract the exhaust gas supplied via the feed device  48  upstream of the exhaust rotor  34 , since a higher pressure level prevails there than downstream of the exhaust rotor or in the region of the impingement body  44 . This means that a conveying device for the hot exhaust gas can be dispensed with. 
       FIG.  4    shows a further advantageous further development of the exhaust gas turbine  31  of  FIG.  1   . 
     In the further development of  FIG.  4   , it is shown that the metering device  42  extends through the impingement body  44  and accordingly extends in the region of the turbine housing  33  exclusively in the axial direction of the axis of rotation R of the turbine rotor  34 . Thereby, the metering device  42  also extends through the sealing body  45  of the turbine housing  33 . 
     With the above features of the exhaust gas turbine  31  according to the invention, it can be avoided that deposits of solid decomposition products of the reducing agent or of the precursor substance of the reducing agent, such as, for example, cyanuric acid or melamine, are deposited in particular on the impingement body  44  and the turbine housing  33  and on the metering device  42  preferably also on the swirl atomizer  43 . 
     The effectiveness of atomizing the reducing agent or the precursor substance of the reducing agent in the exhaust gas can be increased if the swirl atomizer  43  is designed as shown in  FIGS.  5  to  14   . In this context,  FIGS.  5  to  14    show preferred design variants for the swirl atomizer  43  together with the metering device  42 , where in  FIGS.  5  to  14    arrows  49  visualize the flow of the expanded exhaust gas in the region of the swirl atomizer  43  and arrows  50  visualize the feed of the reducing agent or the precursor substance of the reducing agent to the swirl atomizer  43 . 
     The swirl atomizers  43  of  FIGS.  5  and  6    each have a cavity  51 , and the reducing agent  50  is introduced into this cavity  51  via the metering device  42  and then atomized via the swirl atomizer  43  and moved toward the impingement body  44 . In  FIG.  5   , the swirl atomizer  43  is bell-shaped or cup-shaped, with walls  52 ,  53  of the swirl atomizer  43  delimiting the cavity  51  thereof. Thus, the swirl atomizer  43  of  FIG.  5    has a bottom wall  52  which is completely closed in  FIG.  5    and which extends perpendicularly to the axis of rotation R of the turbine rotor  34  and thus to the axis of rotation of the swirl atomizer  43 . A tubular wall  53  extends from this bottom wall  52 , which extends parallel or with an acute angle  6  to the axis of rotation R of the turbine rotor  34  or swirl atomizer  43 , this acute angle  6  being a maximum of 40°, preferably a maximum of 30°, preferably a maximum of 20°, particularly preferably a maximum of 10°. This wall  53  extends from the bottom wall  52  in the direction of the swirl atomizer  44 . In order to ensure a particularly effective atomization of the reducing agent  50  or of the precursor substance of the reducing agent via the swirl atomizer  43 , it is provided in the embodiment example of  FIG.  5    that free ends of the wall  53 , which face the swirl atomizer  44 , enclose between a radially outer region and a radially inner region of the wall  53  an acute angle α which is at most 60°, preferably at most 45°, particularly preferably at most 35°. In  FIG.  5   , the swirl atomizer  43  is open at the end opposite the bottom wall  52 , and is thus designed in the form of an open cup or an open bell. 
       FIG.  7    shows a further development of the swirl atomizer  43  of  FIG.  5   , wherein in the embodiment example of  FIG.  7    according to a second aspect of the invention it is provided that the wall  53  of the swirl atomizer  43 , which extends parallel to the axis of rotation or with the acute angle β oblique to the axis of rotation R of the turbine rotor  34  or swirl atomizer  43 , has openings  54  through which the reducing agent or the precursor substance of the reducing agent enters the expanded exhaust gas from the cavity  51 . 
     Hereby, a particularly advantageous atomization of the reducing agent or the precursor substance of the reducing agent can be ensured, whereby the risk of deposits of decomposition products of the reducing agent or the precursor substance of the reducing agent forming on the impingement body  44  or on the turbine housing  36  or on the swirl atomizer  43  can be reduced. 
     It should be noted that this second aspect of the invention is preferably used in combination with the first aspect of the invention on an exhaust gas turbine  31 . However, the two aspects of the invention may also be used independently. 
       FIG.  9    shows a modification of the swirl atomizer  43  of  FIG.  7   , according to which the openings  54  shown in  FIG.  9    in the region of the wall  53  have orientations or longitudinal central axes that differ from one another. Hereby, the atomization of the reducing agent  50  or the precursor substance of the reducing agent  50  can be further improved. in  FIGS.  7  and  9   , the dashed arrows illustrate in which direction the atomized reducing agent  50  exits the cavity  51  of the respective swirl atomizer  43  and enters the exhaust gas  49 . In  FIGS.  7  and  9   , the exhaust gas can exit the cavity  51  of the swirl atomizer  43  on the one hand at the open end of the swirl atomizer  43  and on the other hand via the openings  54  in two planes offset as seen in the direction of the axis of rotation R of the turbine rotor  34  or swirl atomizer atomizer  43 . 
       FIG.  11    shows a further development of the swirl atomizer  43  of  FIG.  9   , in which partition walls  55  are formed between the outlet planes offset as viewed in the direction of the axis of rotation of the turbine rotor  34  or swirl atomizer  43 , which partition walls are directed inward into the cavity  51  starting from the wall  53 . 
     In the case of a relatively small quantity of reducing agent  50  introduced into the swirl atomizer  43 , these partition walls  55  ensure that all reducing agent  50  first exits the cavity  51  via the openings  54  and enters the exhaust gas  59 . 
     In the case of a larger quantity of reducing agent and/or in the case of low rotational speeds of the swirl atomizer  43 , the level of reducing agent to be atomized in the cavity  51  can increase to such an extent that the reducing agent to be atomized then overcomes the partition walls  55  and flows to the right in  FIG.  11   , in order to then also exit the cavity  51  of the swirl atomizer  43  via the open end of the latter and enter the exhaust gas  49 . For this purpose, it is significant that the outlet opening of the metering device  42  is positioned in the cavity  51  of the swirl atomizer  43  in such a way that the same lies between the bottom wall  52  and the partition walls  55 . 
       FIGS.  5 ,  7 ,  9  and  11    all show swirl atomizers  43  which are open at their end opposite the base wall  52 , i.e. which are contoured in the form of an open cup or an open bell. In contrast,  FIGS.  6 ,  8 ,  10  and  12    show variations of swirl atomizers  43  which are closed at their end opposite the bottom wall  52  by a further wall  56 , whereby in  FIGS.  6 ,  8 ,  10  and  12    the metering device  42  extends through this closed wall  56  opposite the bottom wall  52 . Accordingly, here the dosing device  43  is contoured in the form of a closed cup or a closed bell. 
     In the embodiment examples of  FIGS.  6 ,  8 ,  10  and  12   , the tubular wall  53  extending between the closed walls  52  and  56  extends parallel to the axis of rotation R of the turbine rotor  34  or swirl atomizer  43 , wherein in this tubular wall  53 , the openings  54  are made through which the reducing agent  50  or the precursor substance of the reducing agent  50  emerges from the cavity  51  of the respective swirl atomizer  43  and enters the exhaust gas  49 . The tube-like wall  53  extends parallel or at an acute angle β to the axis of rotation R of the turbine rotor  34  or swirl atomizer  43 , this acute angle β being a maximum of 40°, preferably a maximum of 30°, preferably a maximum of 20°, particularly preferably a maximum of 10°. 
     In  FIGS.  8 ,  10  and  12   , these openings  54  are positioned in different planes, namely in at least two planes offset as seen in the direction of the axis of rotation R of the turbine rotor  34  or swirl atomizer  43 . In  FIG.  12   , the partition walls  55  are again formed between these planes in accordance with  FIG.  11   , which extend from the wall  53  inwardly into the cavity  51  of the swirl atomizer  43 . 
     With all the swirl atomizers  43  shown, it is possible to atomize the reducing agent  50  or the precursor substance thereof in a particularly advantageous manner and to introduce it into the expanded exhaust gas  49 , avoiding a hollow spray cone of atomized reducing agent  50  or of atomized precursor substance of the reducing agent. Avoiding such a hollow spray cone ensures that no circular deposit line of reducing agent or precursor substance of reducing agent is formed on the baffle  44 , which is preferably used in combination with the swirl atomizer  43 . The openings  54  in the wall  53  of the respective swirl atomizer  43  are particularly effective in counteracting the formation of a hollow spray cone of atomized reducing agent or atomized precursor substance, and these openings  54  can have different orientations, i.e. can run with different orientations with respect to the axis of rotation R of the swirl atomizer  43 . Longitudinal central axes of the openings  54  may extend perpendicularly or inclinedly to the direction of flow of the expanded exhaust gas  49 . 
     While in  FIGS.  5  to  12    the swirl atomizers  43  shown are all rotationally symmetrical except for the orientation of the openings  54 ,  FIGS.  13  and  14    show variations of the swirl atomizer  43  of  FIG.  5    which are not rotationally symmetrical in the region of the open end and thus of a break-off edge of the swirl atomizer  43 . Here, too, the formation of a hollow spray cone of atomized reducing agent can be advantageously counteracted. In  FIG.  13   , the wall  53  is of different lengths when viewed in the axial direction of the wall  53 . In  FIG.  14   , different angles α are provided in the region of the tear-off edge or the free end of the wall  53  between the radially outer and the radially inner region of the wall  53 . 
     It may be provided that guide grooves or guide grooves for the reducing agent or the precursor substance of the reducing agent are formed on the wall  53 , namely a radially inner surface  58  of the wall  53 , adjacent to the cavity  51  of the respective swirl atomizer  54 , these guide grooves or guide grooves extending in the direction of the rotation of the wall  53 . guide grooves extend straight or helically in the direction of the axis of rotation R of the respective swirl atomizer  43  and guide the reducing agent  50  or the precursor substance of the reducing agent  50 , which is introduced into the cavity  51  of the respective swirl atomizer  43  via the metering device  42 , in the direction of the open end or the openings of the swirl atomizer  43 . Such guide grooves or guide grooves can be used in all swirl atomizers  43  of  FIGS.  5  to  14   . 
     In the embodiment examples of  FIGS.  1  to  14   , the metering device  42  feeds the reducing agent or precursor substance to the swirl atomizer  43  in the opposite direction to the flow direction of the expanded exhaust gas and in the direction of the rotational axis R of the turbine rotor  43 . In contrast,  FIGS.  15  and  16    show embodiments in which the respective metering device  42  feeds the reducing agent or the precursor substance to the respective swirl atomizer  43  in the direction of flow of the expanded exhaust gas and in the direction of the axis of rotation R of the turbine rotor  34  and thus swirl atomizer  43 . 
     In  FIGS.  15 ,  16   , the reducing agent or precursor substance is fed through the shaft  39  mounted in the bearing housing  40  and through the hub of the turbine rotor  34 . This has the advantage that assemblies of the feed device  42 , which are arranged downstream of the turbine rotor  43 , can be dispensed with completely. There is then no risk whatsoever of deposits of decomposition products of the reducing agent or the precursor substance of the reducing agent being deposited on the metering device  42 , which could lead to clogging of the metering device  42 . 
       FIG.  16    shows a further development of the embodiment of  FIG.  15   , in which the swirl atomizer  43  is surrounded radially on the outside by a guiding device  57 , at least in sections. Such a guiding device  57  allows the atomized reducing agent or the atomized precursor substance of the reducing agent to be concentrated in a narrower region within the expanded exhaust gas. Further, the reducing agent  50  is prevented from reaching the downstream housing section  36  of the turbine housing  33 . This embodiment is not limited to the supply of the reducing agent via the shaft  39 , but can also be applied in the embodiments shown in  FIGS.  1 - 14    of supplying the reducing agent in the opposite direction to the direction of flow. 
     Preferably, the guiding device  57  is designed such that the flow velocity of the exhaust gas in the region of deflection thereof, i.e., in the deflection region  47  of the exhaust housing section  36 , is higher than the average flow velocity of the exhaust gas in order to improve the deflection of the reducing agent  50  or the precursor substance of the reducing agent  50  in the deflection region  47 . In the embodiment shown, the baffle  57  tapers at an end facing the impingement body  44 . 
     The guiding device  57  is preferably fixedly connected to the turbine wheel  34  and rotates together with the turbine wheel  34  as well as together with the swirl atomizer  43 , thus minimizing flow losses. 
     Although the connection of the guiding device  57  to the turbine wheel  34  is preferred, it is also possible for the guiding device  57  to be fixed to the turbine housing  33 , i.e. to be of a fixed design. 
       FIGS.  17  and  18    show embodiments of an exhaust gas turbine  31  according to the invention, in which the metering device  42  supplies the reducing agent  50  or the precursor substance of the reducing agent  50  to the swirl atomizer  43  perpendicular to the direction of flow of the expanded exhaust gas or in the direction of flow of the exhaust gas to be expanded and perpendicular to the direction of the axis of rotation R of the turbine rotor  34  and thus of the swirl atomizer  43 . The swirl atomizers  43  of  FIGS.  17  and  18    do not require a cavity; rather, the reducing agent  50  or the precursor substance thereof is guided along an outer surface  58  of the swirl atomizer  43 , which is contoured in a truncated cone shape in  FIG.  17    and in a cone shape in  FIG.  18   . In  FIG.  17   , the diameter of the swirl atomizer  43 , which is contoured in the manner of a truncated cone, widens when viewed in the direction of flow of the expanded exhaust gas, whereas in  FIG.  18   , the diameter of the swirl atomizer  43 , which is contoured in the manner of a cone, tapers when viewed in the direction of flow of the expanded exhaust gas. 
     On the outer surface  58  of the swirl atomizer  43  guiding the reducing agent  50  or the precursor substance of the reducing agent  50 , guide grooves or guide grooves can in turn be formed which extend in the longitudinal direction or in the flow direction of the expanded exhaust gas and serve to guide the reducing agent  50  to be atomized or the precursor substance to be atomized. 
     In the embodiments of  FIGS.  15 ,  16 ,  17  and  18   , the details of the impingement body  44  described with reference to  FIGS.  1  to  4    are preferably used. 
     In all of the embodiments of the invention described above, it is possible that the swirl atomizer  43  and/or the metering device  42  and/or the impingement body  44  is coated with a hydrophobic coating and/or a catalytically active coating, at least in sections. 
     A hydrophobic coating may be a coating of nanoparticles consisting of TiO 2 , Al 2 O 3  and/or SiO 2 . Such a hydrophobic coating may simultaneously have catalytically active properties, and then comprise, for example, SiO 2 -stabilized TiO 2  or WO 3 . 
     Preferably, the metering device  42  and/or the swirl atomizer  43  and/or the impingement body  44  are made at least in sections of a stainless steel, in particular an austenitic stainless steel. In this way, corrosion of these assemblies can be prevented. 
     It is possible to manufacture these assemblies only in the area of their surfaces from stainless steel, preferably austenitic stainless steel, and to manufacture them in the interior from a material of lower value, for example from a cast steel or black steel. This can reduce manufacturing costs. 
     All of the above-described design details of the gas turbines  31  according to the invention serve the purpose of counteracting the formation of deposits of the reducing agent or the precursor substance of the reducing agent on assemblies of the exhaust gas turbine  31 , in particular on the swirl atomizer  43  and/or the metering device  42  and/or the baffle  44 . This risk can be further reduced if the exhaust gas turbine is operated as described below. 
     In a first embodiment according to the invention of a method for operating the gas turbines  31  described above, it is provided to adjust a viscosity of an aqueous reducing agent solution or an aqueous solution of the precursor substance of the reducing agent and water to at least 1.33 mPas, preferably to at least 1.35 mPas, particularly preferably to at least 1.38 mPas. This is preferably done by adjusting a concentration of the reducing agent in the aqueous reducing agent solution or of the precursor substance in the solution from the precursor substance to at least 35%, preferably to at least 37%, particularly preferably to at least 39%. 
     According to a further process aspect according to the invention, which can be used in combination or also alone, it is provided that the amount of the reducing agent  50  introduced into the expanded exhaust gas via the metering device  42  or the amount of the introduced precursor substance of the reducing agent is determined as a function of the rotational speed of the exhaust gas turbine  31  or as a function of a rotational speed of an internal combustion engine interacting therewith and/or as a function of a power of the exhaust gas turbine  31  or a power of the internal combustion engine interacting therewith and/or as a function of a temperature of the exhaust gas. In this context, it can be provided that if the rotational speed of the exhaust gas turbine or of the internal combustion engine and/or the power of the exhaust gas turbine or of the internal combustion engine and/or the exhaust gas temperature falls below a respective limit value, the introduction of the reducing agent or of the precursor substance of the reducing agent into the exhaust gas is stopped. Above the respective limit value, the amount of reducing agent or precursor substance introduced can be increased with increasing speed and/or power and/or exhaust gas temperature, in particular linearly or in steps. After stopping the introduction of reducing agent or precursor substance of the reducing agent, the metering device is preferably blown on and/or blown free with compressed air or exhaust gas in order to remove reducing agent or precursor substance of the reducing agent from the same. 
     LIST OF REFERENCE SIGNS 
     
         
           30  exhaust gas turbocharger 
           31  exhaust gas turbine 
           32  compressor 
           33  turbine housing 
           34  turbine rotor 
           35  inflow housing section 
           36  outflow housing section 
           37  compressor housing 
           38  compressor rotor 
           39  shaft 
           40  bearing housing 
           41  muffler 
           42  metering device 
           43  swirl atomizer 
           44  impingement body 
           45  sealing body 
           46  gap 
           47  deflection area 
           48  feed device 
           49  exhaust gas 
           50  reducing agent 
           51  cavity 
           52  wall 
           53  wall 
           54  opening 
           55  partition wall 
           56  wall 
           57  guiding device 
           58  surface