Abstract:
A gas mixer for mixing a first gas and a second gas, having a first, outer gas housing part, having an inlet for the first gas in a longitudinal axis and an inlet for the second gas in a transverse axis, a second, interior gas housing part set into the first gas housing part to form an annular space for a second gas, having a mixing space into which the first gas and the second gas are introduced for mixing. The first and second gas housing parts and the annular space are aligned along the longitudinal axis and the mixing space is aligned cylindrically along the longitudinal axis. A mixing device having a plurality of hollow rods is arranged in the mixing space. A hollow space of a hollow rod is in fluid communication on both sides with the annular space. The number of hollow rods extends transverse to the longitudinal axis and the transverse axis and at least one hollow rod has a plurality of openings for the second gas, so that the hollow space is in fluid communication with the cylindrical mixing space.

Description:
The present application is a 371 of International application PCT/EP2012/004450, filed Oct. 25, 2012, which claims priority of DE 10 2011 086 321.4, filed Nov. 14, 2011, the priority of these applications is hereby claimed and these applications are incorporated herein by reference 
     BACKGROUND OF THE INVENTION 
     The invention pertains to a gas mixer comprising: a first, external gas housing part with a feed line for the first gas in a longitudinal axis and a feed line for the second gas in a transverse axis; a second, internal gas housing part, which is inserted into the first gas housing part to form an annular space for a second gas, with a mixing space, into which the first gas and the second gas can be introduced so that they can be mixed to form a gas mixture; wherein the first gas housing part, the second gas housing part, and the annular space are oriented along the longitudinal axis, while the mixing space is oriented cylindrically along the longitudinal axis; and wherein a mixing arrangement consisting of a number of hollow bars is arranged in the mixing space; wherein a hollow space of a hollow bar is fluidically connected at both ends to the annular space. The invention also pertains to a gas mixing system with a gas engine. 
     A gas mixer of the type described above serves to mix together a first gas and a second gas. Especially in the case of a gas engine, the first gas is in the form of combustion air, that is, fresh air or a lean air/gas mixture—also called “charge air”, and the second gas is in the form of a fuel gas. The gas mixer provides an air/fuel gas mixture, consisting of combustion air into which a fuel gas is mixed, suitable for the gas engine. Especially for a lean gas engine, it has been found important to adjust the lambda ratio, namely, the ratio of fuel gas to combustion air—to suit the power demand of the lean gas engine, for example. A gas mixer is described in EP 0 898 064 A1, for example, where it appears in the form of a venturi mixer, which is positioned in a gas mixing system upstream of a lean gas engine to add fuel gas to the combustion air or a lean gas mixture and to mix these two components together. 
     To increase the mixing quality of the air/fuel gas mixture, it is possible in principle to work with a venturi mixer with different cross sections; EP 2 258 983 A2, for example, describes a mixing section of a venturi mixer provided with different cross sections. GB 154,920 describes a gas mixer of the type previously mentioned with a movable displacement body in a venturi tube, as a result of which a mixing gap can be set to different values. A venturi mixer works on the basis of the venturi principle, on which the mixing of the gases depends; that is, what is essential is to reduce the overall backpressure in the flow by increasing the flow velocity in the area of a displacement body, this displacement body being arranged centrally in the flow to reduce the overall size of the flow cross section. This essential “global” venturi principle is thus based on the use of a central displacement body, which influences, i.e., accelerates, the flow over the entire flow cross section. 
     EP 2016 994 A describes a gas mixer of the type indicated above, in which a venturi tube comprises inlet openings for the fuel gas in the area of a narrowed cross section; the size of these openings can be varied by control elements during the mixing process. The control elements comprise here a control sleeve, which surrounds the narrowed cross section and has fuel control openings, wherein the size of the pass-through cross sections for the fuel gas can be changed by shifting the position of the fuel control openings with respect to the position of the inlet openings for the fuel gas. The narrowed cross section is formed by a displacement body arranged in the venturi tube. Although it is possible in this way achieve a comparatively precise adjustment of the pass-through cross section, it takes a comparatively long time to execute the corresponding control process, and the maximum allowable actuating force is also limited. In addition, the mechanical design of the previously mentioned control elements is comparatively complicated, which means that the precision with which adjustments can be made will deteriorate over the service life of the gas mixer as a result of wear and possibly the accumulation of dirt. 
     In addition to a displacement body, which is usually torpedo-shaped, all of the previously mentioned solutions are characterized by an increasingly narrow flow-through opening extending around the displacement body, which is arranged on the center axis. This leads to the maximum possible acceleration of the combustion air in the area of the narrowed flow-through opening and thus produces a high negative pressure across the entire cross section of the narrowed flow-through opening, sufficient to allow the admixture of the fuel gas. This mixing principle, called here the “global” venturi principle, makes use of the venturi effect across the entire cross section of the narrowed flow-through opening, thus making it the primary and essential principle of the mixing process. 
     The venturi principle generally offers the basic advantage that the quantities of fuel gas and combustion air remain at the same ratio to each other, even if, for the purpose of changing the power output, a throttle valve is adjusted to change the central mass rate-of-flow of the first gas, i.e., the air. 
     Theoretically, the venturi principle also works loss-free; that is, theoretically, it works without a loss of total pressure. In reality, however, it is found that, in the case of a venturi nozzle, a negative pressure gradient, that is, a pressure difference between the feed of the second gas and the feed of the first gas, attributable to the use of the “global venturi principle”, depends on the number of cylinders of the gas engine connected to the gas mixer or on the equivalent volume of the system making use of the gas. For example, it is to be observed that a gas engine with more than a double-digit number of cylinders can cause a total pressure loss at the gas mixer in the double-digit mbars range. A total pressure loss of this type must be compensated regularly by the compressor of an exhaust gas turbocharger, usually installed downstream from the gas mixer; this means that the power produced by the compressor changes with the variation of the total pressure loss, which impairs the overall efficiency of an internal combustion engine equipped with the gas mixer, especially a gas mixing system with a gas engine or the like. This proves to be especially disadvantageous when the second gas is a combustible gas such as natural gas, biogas, or similar type of fuel gas with a highly variable CO 2  component and the first gas is charge air or similar type of combustion air. 
     It is desirable to design a gas mixer in such a way that the compressor of the internal combustion engine is relieved of this load. It is also desirable to have a gas mixer of comparatively simple design which offers a long and reliable service life. 
     SUMMARY OF THE INVENTION 
     It is at this point that the invention enters the picture, its goal being to provide a gas mixer which is superior to that according to the prior art. In particular, a gas mixer is to be designed in such a way that it is improved with respect to its total pressure loss. In particular, the total pressure loss of the gas mixer is to remain almost completely immune to changes—even when the number of cylinders connected to it changes or when some other working volume of a downstream combustion system changes. The goal of the invention is also to provide an improved system with a gas mixer, especially a gas engine or other type of internal combustion engine equipped with a gas mixer. 
     The goal with respect to the gas mixer is achieved by a gas mixer of the type indicated above, in which, according to the invention, the set of hollow bars extends transversely to the longitudinal axis and transversely to the transverse axis, and at least one hollow bar comprises a plurality of through-openings for the second gas so that the hollow space. 
     In concrete terms, the invention proceeds from a gas mixer in which, in the mixing space, a mixing arrangement consisting of a number of hollow bars is arranged, wherein the hollow space of the hollow bar is fluidically connected at both ends to the annular space. The invention is based on the reasoning that, in a departure from the globally applied venturi principle for the mixing process, a local mixing principle has proven to yield better results in the sense that it makes the gas mixer largely immune to total pressure losses. The invention has recognized that, to achieve the goal, a concept can be more successful which—in contrast to the global venturi principle explained above—accepts a higher backpressure but also makes available a larger cross section for the inflow of the second gas into the flow of the first gas. The invention has recognized that this concept, based on the “local venturi principle”, significantly reduces inflow losses, especially the losses which occur on the transfer of the second gas into the first gas; that is, the loss coefficient of the gas mixer is reduced. The invention has recognized that, in a real-world application, a considerable portion of the total pressure loss, i.e., a considerable loss of efficiency, is attributable not primarily to an insufficient decrease in the static pressure but rather, on the contrary, to the excessive transfer loss which occurs when the global mixing principle is optimized, which therefore outweighs the advantages. To implement the concept of a local mixing principle, it is provided according to the invention that at least one hollow bar comprises a plurality of pass-through openings for the second gas, so that the hollow space is fluidically connected to the cylindrical mixing-space fluid. All of the hollow bars of the set of hollow bars preferably extend transversely to the longitudinal axis and transversely to the transverse axis. 
     According to the concept of the invention, the set of hollow bars is used to construct a mixing arrangement, by means of which a plurality of pass-through openings can be distributed over the entire flow cross section in the mixing space of the housing part. The hollow bars of the mixing arrangement are not meant to exert a global influence on the flow; quite the reverse: they have only a small inflow cross section facing the flow, which therefore has only a local effect on the flow. Because of this local restriction, the venturi principle goes into effect only locally. Because of this “local venturi principle” in the area of the plurality of through-openings in the hollow bar, only a local scavenging gradient is made available, which is enough to ensure sufficient mixing of the second gas with the flow of the first gas but at the same time makes the mixer less susceptible to the pressure losses resulting from a downstream combustion chamber or the like. As a result of the local venturi principle, there is little global acceleration of the combustion air, because the flow-through opening is narrowed in practice to only an in significant degree by the hollow bars or is narrowed only theoretically, which excludes the occurrence of a significant global influence on the flow velocity. Nevertheless, the venturi principle acts locally in the immediate vicinity of the inflow surface of the hollow bar and of the plurality of pass-through openings provided near the inflow surface. 
     According to the concept of the mixing arrangement, the “local venturi principle” realized in this way as a mixing principle offers the advantage—arising from the inflow surfaces distributed over practically the entire cross section of a mixing space with adjacent venturi nozzle-like pass-through openings—that the blending of the second gas into the flow of the first gas proceeds in a highly homogeneous manner. The advantageous result is the homogeneous blending of the second gas into the first gas and thus the production of an especially homogeneous gas mixture in a mixing space which is nevertheless small and simple in design. 
     The concept of the invention increases the overall surface area of the through-openings for the second gas into the first gas, even though they are distributed in a decentralized manner, which is to say that the surface area of pass-through openings leading from the annular space into the mixing space can be increased and adapted to the concrete application. At the same time, as a result of a considerably lower scavenging gradient and a practically insignificant restriction of the flow-through cross sections in the mixing space, the backpressure is greater than that observed when the “global venturi principle” is applied. This solution makes the total pressure loss of the gas mixer much less vulnerable to outside influences and leads to a much more homogeneous gas mixture. The concept is comparatively easy to realize and proves to be less expensive than a gas mixer with a central venturi nozzle. In comparison to a global venturi mixing principle, the concept of the invention can provide mixing sections which are comparatively short but still large in cross section. 
     Advantageous elaborations of the invention can be derived from the subclaims, which describe in detail additional preferred possibilities for elaborating the concept of the invention which offer additional advantages within the scope of problem to be solved. 
     It is especially preferable for the mixing arrangement to be mirror-symmetric with respect to a first central plane containing the transverse axis and the longitudinal axis and also mirror-symmetric with respect to a second central plane perpendicular to the transverse axis. In other words, it has been found advantageous to design the mixing arrangement without point symmetry. The elaboration achieves the advantageous result that, when the second gas is being supplied from the direction of the transverse axis, the second gas has the same pressure amplitude at both ends of the fluid connection of the hollow bar to the annular space. This leads advantageously to a uniform inflow of the second gas into the hollow bar at both ends, i.e. with the same flow and pressure amplitude at both ends. It has turned out to be especially advantageous for the hollow bar to be oriented so that it is perpendicular to the transverse axis. In this case, the pressure amplitudes at the two ends of the hollow bar will be especially well balanced. Nevertheless, depending on the application, it can also prove to be suitable for the hollow bar to be tilted out of the perpendicular orientation but still be basically transverse to the transverse axis. It is preferable for the deviation from the perpendicular orientation to the transverse axis not to exceed 30°. 
     A straight hollow bar has been found to be especially advantageous. According to a modified elaboration, however, it can also be advantageous for the hollow bar to have a design which deviates from an exclusively straight line. 
     At least one hollow bar of the set of hollow bars preferably extends through the mixing space along a secant, which means that it is thus off-center from a diameter. Depending on the number of hollow bars, this can apply preferably to two hollow bars, especially to at least two hollows rods of the set. Within the scope of an especially preferred elaboration, all of the hollow bars are off-center from a diameter of the mixing space and thus extend along secants through the mixing space. 
     Under consideration of the especially preferred two-fold mirror symmetry of the mixing arrangement described above, the previously mentioned variant of an elaboration has been found to be especially advantageous, especially when an even number of hollow bars is present. In particular, the mixing arrangement has no hollow bar in the center in this case. 
     In another variant of an elaboration, especially in the case of an odd number of hollow bars, it has been found advantageous for only a single, central hollow bar of the set of hollow bars to extend transversely to the longitudinal axis and transversely to the transverse axis and centrally along a diameter of the mixing space. Within the scope of this other variant, it is possible, for example, to provide only a single, central hollow bar or—under consideration of the previously mentioned two-fold mirror symmetry—an odd number of hollow bars such as three, five, six, seven hollow bars, etc. 
     In principle, the number of hollow bars in the gas mixer can be determined ahead of time as a function of the number of cylinders of the gas engine or similar type of working or internal combustion machine. Overall it has proven to be advantageous for the number of hollow bars to be between four and twelve. In particular it has been found advantageous for the number of hollow bars to increase with the number of cylinders of the gas engine; in other words, the larger the working volumes connected to the gas mixer, the larger the number of hollow bars. It has been found advantageous for the overall surface area of the through-openings for the second gas between the cylindrical mixing space and the annular space to be comparatively large in order to keep the inlet pressure, that is, a pressure level of the second gas being supplied to the gas mixer, as low as possible. Whereas it is therefore basically advantageous to increase the backpressure of the first gas and the inflow surface for the second gas, it has also been found to be advantageous according to this elaboration for the inlet pressure of the supplied second gas to be kept as low as possible. 
     It has also been found to be advantageous for the hollow bar to comprise a first plurality of through-openings on the top side and a second plurality of the through-openings on the bottom side. This advantageously increases the flow-through surface area for the second gas. At the same time, the spacing of the through-openings for the second gas is decreased. Reducing the spacing between the openings leads to an especially advantageous, homogeneous mixing of the first and second gases. This elaboration is based on the idea of the molecular mixing section, which is defined as the shortest free path between, for example, a molecule of the fuel gas (second gas) and, for example, a molecule of charge air (first gas); the shorter the distance between adjacent through-openings, the more likely it is that it will be only insignificantly larger than the molecular mixing section. In other words, the closer the spacing of the through-openings to the size of the molecular mixing section, the more homogeneous the gas mixing and the smaller the space occupied by the gas mixer. 
     Following the concept of this elaboration, it has been found to be especially advantageous for a plurality of through-openings to be distributed along the entire length of the hollow bar, preferably with equal spacing. In other words, it is advantageous to use the entire length of the hollow bar to accommodate the plurality of through-openings. For example, a plurality of through-openings can be distributed in a single row or in several rows, and the openings could also be offset from each other, as needed. 
     Within the scope of a mixing arrangement supporting the uniform mixing of the first and second gases, it has been found to be especially advantageous for at least one first and one second hollow bar to be oriented in the same direction, especially in plane-parallel fashion. In other words, a geometrically exact plane-parallel orientation has proven to be especially preferred; slight deviations from this exact geometric arrangement within the scope of a basically similar orientation of the hollow bars has also proven possible, depending on the purpose of the application. It has been found to be especially advantageous for all of the hollow bars of the set of hollow bars to have the same orientation or to be arranged in plane-parallel fashion. 
     The annular space, arranged in particular downstream of an inlet orifice to supply the second gas to the mixing space, can preferably be connected directly to the mixing space by additional through-openings for the second gas. In particular, the additional through-openings can be arranged upstream of the plurality of through-openings in the hollow bars. These elaborations advantageously increase the total flow-through surface area for the second gas flowing to the mixing space. In particular, an upstream arrangement of these additional through-openings in front of a downstream arrangement of through-openings in the hollow bars takes advantage of the combination of the mixing behavior from a radial direction and the mixing behavior from a secant direction in the cross section of the flow. 
     Within the scope of an especially preferred elaboration, the placement of the plurality of through-openings for the second gas and the geometric design of the hollow bars can both be improved with respect to the flow behavior and the mixing behavior. 
     In particular, the hollow bar of the set of hollow bars can be designed in the form of a flat bar; a flat bar with the profile of a box can be manufactured comparatively easily. One of the narrow sides of the flat bar preferably has an inflow cross section which preferably has only a local effect on the flow behavior. The flat side of the flat bar is preferably parallel to the longitudinal axis. 
     The size of the narrow side of the flat bar is designed to produce a sufficiently small amount of displacement, so that, according to the previously explained general concept, a high backpressure can be maintained. The narrow side of the flat bar is not at the service of a “global venturi principle”. Instead, the narrow, upstream side of the hollow bar with an inflow surface in the form of, for example, a half-rounded shape serves to create a flow stagnation point, which to this extent is able to realize only a “local venturi principle”; in particular, the inflow surface is free of through-openings. For example, a hollow bar can comprise a rectangular profile with a half-round leading edge. 
     A flow guide surface proceeding from the narrow, upstream side of the hollow bar to the flat side and adjoining the inflow surface should preferably comprise the plurality of through-openings. In the area of the flow guide surface, it can be assumed, namely, that the gas is still flowing directly over a surface of the flat bar; therefore, given the plurality of through-openings, a local venturi principle comes into play, and thus the inflow surface is capable of producing a local negative pressure in the flow guide surface, that is, in the area of the plurality of through-openings. 
     It is also preferable for a flow separation surface, which proceeds further downstream along the flat side of the hollow bar and adjoins the flow guide surface, to be free of through-openings. The absence of through-openings from both the inflow surface and the flow separation surface offers the advantage that the first gas is reliably prevented from penetrating into the area where the second gas is being introduced into the mixing space. 
     In concrete terms, the plurality of through-openings can be arranged advantageously in an area of the flow guide surface of the flat side located upstream of a center line perpendicular to the flat side. For example, the plurality of through-openings can be arranged in a row, e.g., essentially close to and at equal distances from each other, parallel to an upstream side edge (e.g., the boundary between the narrow, upstream side and the flat side) of the hollow bar. The exact number and surface area of a through-opening—and thus also the spacing of the openings—can be adjusted according to the total inflow surface area to be achieved for the second gas and according to the extent to which it is desired to reduce the transfer losses of the second gas into the first gas. A “side edge” is to be understood as the boundary line between the half-rounded portion and the planar surface of the flat side of the hollow bar. 
     Exemplary embodiments of the invention are now described below on the basis of the drawing and in comparison with the prior art, some of which is also illustrated. The drawing does not necessarily represent the exemplary embodiments to scale; on the contrary, where useful for the purpose of explanation, it is executed in schematized and/or slightly distorted form. With respect to information going beyond the teachings directly derivable from the drawing, reference is made to the relevant prior art. In this regard, it should be kept in mind that many different modifications and changes pertaining to the form and the details of an embodiment can be made without departing from the general idea of the invention. The features of the invention disclosed in the description, in the drawing, and in the claims can be essential both individually and in any desired combination to the elaboration of the invention. In addition, all combinations of at least two of the features disclosed in the description, the drawing, and/or the claims fall within the scope of the invention. The general idea of the invention is not limited to the exact shape or to the details of the preferred embodiment illustrated and described below, nor is it limited to an object which might be limited in comparison to the object claimed in the claims. In the case of the stated dimensional ranges, values lying within the stated limits are also to be disclosed as boundary values and usable and claimable as desired. Additional advantages, features, and details of the invention can be derived from the following description of the preferred exemplary embodiments and from the drawing: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a perspective partial view of a gas mixing system with a gas engine and a gas mixer of a preferred embodiment, which comprises a mixing arrangement designed according to the concept of the invention in a mixing space; and 
         FIG. 2  shows a perspective partial cross section, in perspective, of the gas mixer and a detailed view illustrating the local venturi principle serving as the functional principle of the mixer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a gas mixing system  1000  with a gas mixer  100  for mixing a first gas G 1 —in the present case, charge air LL—and a second gas G 2 —in the present case a fuel gas BG for a gas engine  400 . The gas mixture G 3  formed by the first gas G 1  and the second gas G 2 —here the fuel gas mixture BGGM—is sent to a compressor  300  and then finally in compressed form to an internal combustion engine, which in the present case is illustrated symbolically by the gas engine  400  with its cylinders  1 ,  2 ,  3 ,  4 . The fuel gas mixture BGGM burned in the gas engine  400  to produce work is discharged as exhaust gas AG into an exhaust gas return line and then into the environment, possibly via an exhaust gas post-treatment unit, not shown. In the present embodiment, it is shown that the gas mixer  100  is part of a high-pressure return line  310 . A pressure regulator  320  serves here to manage the output of the gas engine  400  and, in a manner not shown in detail, branches off a compressed portion of the compressed fuel gas mixture BGGM-VD downstream from the compressor  300  into the high-pressure return line  310  and thus back to the gas mixer  100 . The compressed fuel gas mixture BGGM-VD can be supplied via the gas mixer  100  back to the fuel gas mixture BGGM again upstream of the compressor  300 . 
     The housing of the gas mixer  100  has a first, outer housing part  110  and a second, inner housing part  120 . The first and second housing parts  110 ,  120  are connected to each other by screw joints  130  and positive-locking connections  131  in such a way that the second housing part  120  is firmly seated in the first housing part  110 . The charge air LL is introduced in the direction of the longitudinal axis LA of the gas mixer  100  from a first feed line Z 1  into a mixing space  20 , which is formed in the first housing part. The first gas G 1 , furthermore, is supplied through a feed part  112  arranged on the first housing part  110  upstream of the mixing space  20 , wherein the first feed part  112  merges smoothly and continuously with a second feed part  122  of the second housing part  120 . The feed orifice  132  formed by the first and second feed parts  112 ,  122 , finally, is connected to the geometrically cylindrical mixing space  20  in the second housing part  120  by way of an edge  133 . 
     Between the first and second housing parts  110 ,  120  there is an annular space  11 , which surrounds the mixing space  20 , is separated from it, and is fluidically connected to it by fluid connections. The second gas G 2  in the form of the fuel gas BG can be introduced into this annular space from a second feed line Z 2 . The connection of the second feed line Z 2  to the first housing part  10  is achieved by way of a ring flange  113 . The second gas G 2  is introduced along a transverse axis QA, arriving first in the previously mentioned annular space  11 , from which it proceeds via the fluid connections, formed as through-openings, into the mixing space  20 . In the present case, both the annular space  11  and the mixing space  20  are oriented along the longitudinal axis LA, wherein the mixing space is cylindrical in shape and is surrounded in a ring-like manner by the annular space  11 . The annular space  11  extends along the longitudinal axis LA over only a part of the length of the mixing space  20 . 
     The mixing space  20  itself is formed geometrically as a straight cylinder with a circular cross section  23 , oriented along the longitudinal axis LA. The surface area of the cross section  23 , drawn here at the entrance to the mixing space  20 , does not change as one proceeds along the longitudinal axis LA from the entrance of the mixing space  20  to a cross section  24  at the exit; along the longitudinal axis LA, the mixing space  20  therefore has an essentially constant diameter. The cross sections  23 ,  24  along the longitudinal axis LA are bounded by a wall  121  of the second housing part  120 . In the present case, the second housing part  120  is assembled from a first cylindrical sleeve, which forms the first part  21  of the mixing space  20 , and a second cylindrical sleeve, which forms the second part  22  of the mixing space  20 , wherein the cylindrical sleeves abut each other in positive fashion at an annular shoulder  134 . The cross section is constant over both the first part  21  of the mixing space  20  and the second part  22  of the mixing space. The second part of the mixing space serves to supply the compressed fuel gas mixture BGGM-VD from a second annular space  12 , which is connected to the high-pressure return line  310 . Downstream from the mixing space  20 , the first housing part  110  forms a discharge orifice  111 , which, in the present case, forms the boundary of a cross section  24 , which is neither constricted nor expanded, at the exit from the mixing space  20 . The cross section  24  at the exit therefore merges smoothly and continuously with the downstream guide for the gas mixture G 3 , that is, the fuel gas mixture BGGM, in the second part  22  of the mixing space  20 . 
     The returned portion of the compressed fuel gas mixture BGGM-VD is supplied to the second part  22  of the mixing space  20  by way of an essentially circumferential fluid connection in the wall  121  of the second cylindrical sleeve of the second housing part  120 —here a circumferential slot in the form of an elongated hole  36 . The feed of the fuel gas BG from the annular space  11  to the first part  21  of the mixing space  20  proceeds by way of circumferential bores in the form of round holes  35 . Through the oblong holes  36  and the round holes  35 , the compressed fuel gas BGGM-VD and the fuel gas BG can be supplied in the radial direction to the mixing space  20 . The slot-like design of the fluid feed openings in the second part  22  of the mixing space  20 , that is, the oblong holes  36 , serves to expand the compressed fuel gas mixture BGGM-VD as it is being introduced. The smaller design of the round holes  35  arranged around the circumference of the first part  21  ensures that the fuel gas BG will be injected radially into the mixing space  20  at a sufficiently high pressure. The annular space  11  for supplying the second gas G 2  to the mixing space  20  arranged downstream of the feed orifice  132  is connected directly to the mixing space  20  by way of the additional pass-through openings  25  for the second gas G 2  designed as round holes  35 . 
     As can be seen in  FIG. 2 , the additional through-openings—designated here by the number  25 —are formed upstream of a plurality of through-openings  26 ,  27 , the function of which is illustrated in  FIG. 2  and also in detail X of  FIG. 2 . 
       FIG. 2  shows that a mixing arrangement  30  consisting of a set of hollow bars  31 ,  32 ,  33 ,  34 , all of which extend transversely to the longitudinal axis LA and transversely to the transverse axis QA, is arranged in the mixing space  20 , namely, in the first part  21  of the mixing space  20 . In the present case, these are the hollow bars  31 ,  32 ,  33 ,  34 , which together form the mixing arrangement  30 . With respect to the arrangement of the hollow bars  31 ,  32 ,  33 ,  4 , the mixing arrangement  30  is mirror-symmetric to a first central plane ZA 1  containing the transverse axis QA and the longitudinal axis LA and also mirror-symmetric to a second central plane ZA 2  perpendicular to the transverse axis. In particular, each of the hollow bars  31 ,  32 ,  33 ,  34  is formed as a flat, hollow section with a rounded leading edge, the “leading edge” being the narrow, upstream side  53 , the inflow surface  41  of which faces the incoming flow S. Each of the hollow bars  31 ,  32 ,  33 ,  34  with its flat design also comprises a top flat side OF and a bottom flat side UF, all of these sides being plane-parallel to the second central plane ZA 2 . A trailing edge HK of a hollow bar  31 ,  32 ,  33 ,  34  is essentially rectangular in design in conformity with the rectangular profile. The leading edge VK comprises the inflow surface  41  with a half-round configuration, as shown more clearly in detail X. 
       FIG. 2  shows only the gas mixer  100  of the gas mixing system  1000 , wherein the same reference symbols are used to designate parts which are the same or similar and also to designate parts which have the same or a similar function; the mixing arrangement  30  according to the “local venturi principle” explained above, furthermore, is designed as the essential mixing principle of the gas mixer  100  and is described on the basis of  FIG. 2 . In regard to the other parts of  FIG. 2 , reference is made to the description of the identical parts shown in  FIG. 1 . 
     The leading edge VK of the narrow side  53  of a hollow bar  31 ,  32 ,  33 ,  34  with its flat design is provided with an inflow surface  41 , which has only a local influence on the course of the flow of the charge air LL. Adjoining the inflow surface  41  of the hollow bar  32 —which is shown in detail X by way of example for all of the rods as a symmetrical cross section through its profile—is a flow guide surface  42  and, further downstream, a flow separation surface  43 . The flow S of the charge air LL along the surface of the hollow bar  32  with its flat design is shown by way of example in the detailed drawing. It can be seen from this that a first part S 1  of the flow S arrives at the inflow surface  41 , and a second part S 2  of the flow S, theoretically laminar, proceeds closely along the flow guide surface  42 . Depending on the details of how the profile of the flat bar is designed and on the concrete flow parameters of the flow S, a flow separation surface  43  for a separated flow S 3  is formed in the downstream part of the profile. Under consideration of the “local venturi principle”, the flow guide surface  42  is especially suitable for producing a local negative pressure in the flow S 2  in the area of a through-opening  27 , shown here by way of example. Whereas a pressure P 2  is therefore present in the hollow space  52  of the hollow bar  32 , a pressure P 1  is present at the immediate outside surface of the hollow bar. Pressure P 2  is less than pressure P 1 , which therefore ensures that the fuel gas BG will enter the air flow of the charge air LL through the opening  27  (and not vice versa). 
     As can be seen in detail in  FIG. 2 , each of the hollow bars  31 ,  32 ,  33 ,  34  is provided with a first plurality of through-openings  26  on the top flat side OF and with a second plurality of through-openings  27  on the bottom flat side UF. The through-openings  26 ,  27  are distributed in a single rows along the entire length of the hollow bar  31 ,  32 ,  33 ,  34  and in the present case are spaced equally apart. The rows of through-openings  26 ,  27 —as can be seen in Detail X—are arranged in the area of the flow guide surface  42 . When the axes ÖA of the through-openings  26 ,  27  are compared to the center axis MA of the hollow bar  32 , it can be seen that the through-openings  26 ,  27  are arranged in the area of the flow guide surfaces  42  of the flat sides  54 —specifically the sides OF, UF—which lies upstream of the center perpendicular MA to the flat sides  54 . In the present embodiment, the axes ÖA of the openings of the plurality of through-openings  26 ,  27  are located approximately in the middle, i.e., between the side edge  28  (the side edge  28  between the flat side  54  and the narrow side  53 ) and the center perpendicular MA of the hollow bar  31 ,  32 ,  33 ,  34 . This placement has been found to be especially advantageous for the present embodiment as a way of realizing the “local venturi principle”, because the flow S 2  is still being guided by the profile of the hollow bar  32 ; that is, it has still not been separated, as part S 3  of the flow S has become in the area of the flow separation surface  43 . A negative pressure is thus produced especially effectively in the area of the partial surface S 2   
     According to the present embodiment with the plurality of n through-openings  25 ,  26 ,  27 , the end result is that the total surface area A BG  of all the individual outlet opening areas A Ö  for the fuel gas BG proceeding from the annular space  11  to the mixing space  20  is comparatively large; the flow pressure p S  at the mixing arrangement  30  is very high in comparison to that observed in connection with a global venturi principle. This leads to a comparatively low total pressure loss of the mixing arrangement  30  in the gas mixer  30 , which is considerably below that of a gas mixer operating on the global venturi principle. The reason for this is that the present embodiment does not make any attempt to exert a global influence on the flow S—such as by means of a central displacement body acting as a venturi element. It is found that, with the present mixing arrangement  30  in the gas mixer  100 , it is also possible to achieve an improvement in the knocking behavior and emissions behavior of an internal combustion engine, especially a gas engine  400 . The design of the mixing arrangement  30  in the gas mixer  100  also has the effect of creating a gas mixture G 3  in which the first and second gases G 1 , G 2  are mixed in an especially homogeneous way, which advantageously influences the operating bandwidth of the gas mixer  100  and thus the load switching capacity of the gas engine  400 . In particular, the number of hollow bars—four hollow bars  31 ,  32 ,  33 ,  34  in the present case—can be selected as a function of the number of cylinders  1 ,  2 ,  3 ,  4  of the gas engine  400 . The ratio—here it is 1:1—of the number n of hollow bars to the number of cylinders is to be understood in the present case only as an example and in a real-world application is usually less than 1:1; that is, the number of cylinders usually is greater than the number n of hollow bars. Another advantage is that the spacing A of the hollow bars  31 ,  33 ,  33 ,  34  can be selected in such a way that, under the assumption that the fuel gas BG is injected suitably through the through-openings  26 ,  27  with spacing A, the distance between openings comes relatively close to the dimensions of a real mixing section (understood as the shortest distance between the molecules of the fuel gas BG and the molecules of the charge air LL under the given flow conditions), or is only slightly larger. In other words, the spacing A can be reduced in such a way that the length of the mixing space  20  along the longitudinal axis LA can be relatively short while still being able to guarantee a homogeneous and especially good mixing of the fuel gas BG and the charge air LL. 
     The gas mixer  100  presented here is advantageously comparatively simple in design and is therefore suitable for a wide variety of different applications with a wide operating bandwidth. In particular, it has been found to be unnecessary in the case of the present embodiment to provide additional control elements for regulating the gas flow rates. These elements—such as those known from the prior art described above—turn out to have a limiting effect on the operating safety and long-term operational reliability of a gas mixer  100 . At the same time, modifications (not shown here) are also possible according to which an orifice design or a different fuel gas control design can be provided to regulate the rate at which the fuel gas BG is supplied via the feed line Z 2 ; a control design could also be applied to regulate the flow rate in the annular space  11  or to regulate the flow rate of the fuel gas BG as it passes through the through-openings  25 ,  26 ,  27 . 
     LIST OF REFERENCE SYMBOLS 
     
         
           11  annular space 
           12  second annular space 
           20  mixing space 
           21  first part of the mixing space 
           22  second part of the mixing space 
           22 ,  24  cross section 
           25 ,  26 ,  27  through-opening 
           28  side edge 
           30  mixing arrangement 
           31 ,  32 ,  33 ,  34  hollow bar, especially a flat bar 
           35  round hole 
           36  oblong hole 
           41  inflow surface 
           42  flow guide surface 
           43  flow separation surface 
           52  hollow space 
           53  narrow side 
           54  flat side 
           100  gas mixer 
           110  first outer housing part 
           111  discharge orifice 
           112  first entrance part 
           113  ring flange 
           120  second inner housing part 
           121  wall 
           122  second entrance part 
           130  screw joints 
           131  positive-locking connection 
           132  entrance orifice 
           133  edge 
           134  annular shoulder 
           300  compressor 
           310  high-pressure return line 
           320  pressure regulator 
           400  gas engine 
           1000  gas mixing system 
         A spacing 
         AG exhaust gas 
         BG fuel gas 
         BGGM fuel gas mixture 
         BGGM-VD compressed fuel gas mixture 
         G 1  first gas 
         G 2  second gas 
         G 3  gas mixture 
         HK trailing edge 
         LA longitudinal axis 
         LL charge air 
         MA center perpendicular 
         n number 
         OF top flat side 
         UF bottom flat side 
         ÖA axis of the opening 
         P 1  pressure 
         P 2  pressure 
         p S  flow pressure 
         QA transverse axis 
         S flow 
         S 1  first part of the flow 
         S 2  second part of the flow 
         S 3  separated flow 
         UF bottom flat side 
         VK leading edge 
         Z 1  feed line 
         Z 2  feed line 
         ZA 1  first central plane 
         ZA 2  second central plane