Abstract:
An internal combustion engine is disclosed, comprising at least one first compression device and at least one second compression device which is connected in series relative to the first compression device. At least one bypass pipe bypasses at least one compression device. At least one controllable valve is arranged in the at least one bypass pipe such that the amount of fluid which can be recirculated around the compression device can be controlled.

Description:
This application is a Continuation of International application No. PCT/AT2010/000033, filed Feb. 2, 2010, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     (1) Field of the Invention 
     The invention concerns a method of regulating an internal combustion engine, involving a tracking setting to an engine regulating parameter, wherein the internal combustion engine has at least one first compressor device and at least one second compressor device arranged serially in relation to the first compressor device, which compress a fluid. The invention further concerns an internal combustion engine including at least one first compressor device and at least one second compressor device arranged serially in relation to the first compressor device. In addition the invention concerns a regulating device for carrying out the method and for an aforementioned internal combustion engine. 
     (2) Description of Related Art 
     To increase power it is known in internal combustion engines for compressor devices to be connected in series in the inlet tract so that the supplied compressed gas is raised to a high pressure in two compression steps. In that case intermediate cooling is usually effected between the compressors so that a greater amount of gas can be implemented in the second compressor. To have a certain regulating reserve available, it is already known, for example from EP 1 640 598 A1, for a branch arrangement to be provided upstream of the second compressor device, the so-called high-pressure compressor, in order to take the compressed gas past the high-pressure compressor. 
     Although it is possible in the state of the art to quickly counter changes in load at the internal combustion engine, the period of time for tracking adjustment to the engine regulating parameter is relatively long and it is possible to observe oscillations around the reference target value. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above, the object of the present invention is to provide a method of the general kind set forth in the opening part of this specification, in which those problems are alleviated. The invention also seeks to provide an internal combustion engine of the general kind set forth in the opening part of this specification and a regulating device which is provided for same, where those problems are alleviated. 
     That object is attained by a method of regulating an internal combustion engine to a substantially constant engine parameter, wherein the internal combustion engine has at least one first compressor device and at least one second compressor device arranged serially in relation to the first compressor device, which is characterised in that for tracking setting to the engine regulating parameter as a control parameter a given amount of fluid is returned around at least one of the at least two compressor devices by way of at least one bypass conduit. 
     In normal operation a certain compressed amount of fluid (in general compressed gas such as air or a fuel/air mixture) is continuously circulated around the compressor device, that is to say the entire compressed amount of fluid is not introduced into the combustion chamber of the internal combustion engine, but a given amount is recycled again upstream of the high-pressure compressor. When a change in load occurs, it is possible on the one hand to introduce a greater amount of compressed fluid into the combustion chamber by reducing the amount of fluid which is blown around the compressor, while on the other hand it is possible to introduce a smaller amount of compressed fluid into the combustion chamber by increasing the amount of fluid blown around the compressor. In contrast to the methods in which the compressed gas is taken past the compressor device, the method the subject-matter of this invention has the advantage that not only is the regulating reserve greater but also a tracking adjustment to the parameter to be regulated is effected more quickly. 
     In a preferred case it is provided that for tracking setting to the engine regulating parameter as the control parameter a given amount of fluid is returned around the at least two compressor devices by way of bypass conduits so that the regulating reserve and the level of regulating accuracy are increased. 
     In an internal combustion engine of the general kind set forth in the opening part of this specification that object is attained in that at least one bypass conduit passes around at least one compressor device and wherein at least one regulatable valve is arranged in the at least one bypass conduit so that the amount of fluid which can be recycled around the compressor device is regulatable, wherein at least one cooling device is arranged downstream of the at least one compressor device. The bypass conduits branch off in the direction of flow of the fluid downstream of the cooling device of the respective compressor device. The difference in density is increased by cooling of the fluid so that a larger amount of fluid can be recycled by way of the bypass conduit upstream of the compressor. 
     It is preferably provided in that respect that bypass conduits pass around the first compressor device and around the second compressor device and wherein regulatable valves are arranged in the bypass conduits so that the amount of fluid which can be recycled around each compressor device by means of the bypass conduits is separately regulatable. The cooling device after the respective compressor device, after which the bypass conduit branches off, leads to a greater density difference and thus permits a greater fluid recycling. 
     Desirably it is provided in the method that the amount of fluid returned around the first compressor device and the amount of fluid returned around the second compressor device are separately adapted. In the simplest case it can be provided that a bypass conduit passes around each compressor device. 
     In an embodiment it can be provided that a bypass conduit in which a regulatable valve is arranged passes around the first compressor device and a bypass conduit in which a regulatable valve is arranged passes around the second compressor device, wherein tracking setting to the engine regulating parameter is effected by regulating intervention at the at least two valves. 
     It can further be provided that tracking setting to the engine regulating parameter is additionally effected by regulating intervention at the throttle device. In order to still more refine the regulation action, it can finally be provided that the compressor devices are driven by an exhaust gas turbine, wherein a bypass conduit passes around at least one exhaust gas turbine, wherein for regulation to the engine regulating parameter the amount of fluid which is taken past the exhaust gas turbine is additionally regulated with a regulatable valve. 
     In a variant in the internal combustion engine it can be provided that the internal combustion engine is operable in at least two operating modes, wherein in the first operating mode a given amount of fluid can be recycled around each compressor device, and wherein in a second operating mode the ratio of the amount which can be recycled around the first compressor device is altered in relation to the amount which can be recycled around the second compressor device with respect to the first operating mode. In a further variant there can be provided a regulating device with which the internal combustion engine is trackingly adjusted to the engine regulating parameter, wherein for tracking setting to the engine regulating parameter in the operating mode by regulation of the regulatable valves arranged in the bypass conduits the amount of fluid which can be circulated around each compressor device can be separately altered. In the simplest case it can be provided in that respect that the first compressor device is bridged over by a bypass conduit with a regulatable valve arranged therein and the second compressor device is bridged over by a bypass conduit with a regulatable valve arranged therein. Bridging is effected in such a way that the compressor devices are bridged over in anti-parallel relationship in the flow direction, that is to say compressed fluid issuing from the compressor device is returned to the fluid inlet of the compressor device again. 
     In an alternative variant it can be provided that the first compressor device and the second compressor device are bridged over by a bypass conduit with two valves arranged serially therein, wherein branching off between the two valves is a conduit which opens between the two series-connected compressor devices and in which a controllable valve is arranged. Here too it is provided that the bypass conduits bridge over the compressor devices in anti-parallel relationship in the direction of flow of the compressor devices. 
     To improve the regulating characteristics it can further be provided that the compressor devices are driven by at least one exhaust gas turbine, wherein a bypass conduit passes around at least one exhaust gas turbine and wherein for tregulation to the engine regulating parameter in addition the amount of fluid which is taken past the exhaust gas turbine is regulated with a regulatable valve. In that case also it can be provided that there are provided two series-connected exhaust gas turbines which each drive a respective compressor device, wherein bypass conduits pass around the first exhaust gas turbine and around the second exhaust gas turbine, wherein regulatable valves are arranged in the bypass conduits so that the amount of fluid which can be taken around each exhaust gas turbine in the bypass conduits can be separately regulated. In the simplest case in that respect it can be provided that the first exhaust gas turbine is bridged over in parallel by a bypass conduit with a regulatable valve arranged therein and the second exhaust gas turbine is bridged over in parallel by a bypass conduit with a regulatable valve arranged therein. As an alternative thereto it can be provided that the first exhaust gas turbine and the second exhaust gas turbine are bridged over in parallel by a bypass conduit with two valves arranged serially therein, wherein branching off between the two valves is a conduit which opens between the two series-connected exhaust gas turbines and in which a controllable valve is arranged. In a variant it can be provided that there is provided a common regulating device for the valves. 
     In the preferred case the internal combustion engine is a stationary internal combustion engine of the type used, for example, in stationary power generating installations. Stationary power generating installations generally have an internal combustion engine and an electric generator for electrical power generation. 
     In addition the preferably stationary internal combustion engine can be a gas engine, that is to say a combustion engine which burns a gaseous fuel such as methane. Preferably this involves a mixture-charged gas engine. In mixture-charged gas engines it is not pure air but a fuel/air mixture that is compressed as the fluid in the compressor devices. For example in a variant this can involve an Otto-cycle, that is to say spark-ignition internal combustion engine. 
     In a variant it can be provided that the engine regulating parameter is a substantially constant engine parameter. That can be for example a constant rotary speed or a constant output power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and details of the invention are described by means of the specific description and the following Figures. 
         FIGS. 1 through 5  diagrammatically show five variants of internal combustion engines according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  diagrammatically shows an embodiment of an internal combustion engine  1  according to the invention for carrying out the method. The internal combustion engine  1  has the actual engine  2  which is for example a gas engine. That means that gaseous fuel such as for example methane or landfill gas or biogas is burnt in the respective combustion chambers of the internal combustion engine. It is preferably provided that the internal combustion engine  2  is a stationary internal combustion engine which for example serves for power generation by means of a generator  25 . 
     Firstly a gas mixer  7  is fed with air  10  by way of an air feed conduit  9  and a fuel gas  11 , for example methane, by way of a gas feed conduit  8 . Air  9  and fuel gas  11  are mixed in the gas mixer  7  to form a gas mixture and fed to the first compressor device  3  (‘low-pressure compressor’). In that case the gas mixture passes by way of a fluid inlet  3   a  into the compressor device  4 , is compressed therein and issues from the compressor device by way of a fluid outlet  3   b . Then the compressed fuel-air mixture is cooled in a cooling device  5  and passed to the second compressor device  4  (‘high-pressure compressor’). That is connected in series with the first compressor device  3 . The gas which is pre-compressed in the first compressor device  3  is now introduced by way of the fluid inlet  4   a  into the compressor device  4  (‘high-pressure compressor’), compressed there and issues from the compressor device  4  by way of the fluid outlet  4   b . The mixture which is now highly compressed (pressures above 6 bars are possible) is then cooled by way of a further cooling device  6 . The amount of gas mixture which is fed to the combustion engine  2  is now finally regulated by way of a throttle device  12 , for example a throttle flap. The description hitherto applies to all five embodiments so that attention is directed to the preceding specific description for the description of  FIGS. 2 through 5 . 
     In  FIG. 1  a first bypass conduit  13   a  in which a first valve  14   a , a so-called blow-around bypass valve  14   a  is arranged, passes around the first compressor device  3 . A certain amount of gas of the compressed gas-air mixture can be continuously blown around the compressor device  3 , that is to say recycled, through the bypass conduit  13   a . In specific terms therefore a part of the gas mixture compressed by the first compressor device  3  is passed from the fluid outlet  3   b  back to the fluid inlet  3   a  (by way of the cooling device or mixture cooler  5 ). 
     In  FIG. 2  in contrast to the variant in  FIG. 1  a first bypass conduit  13   b  in which a valve  14   b , a so-called blow-around bypass valve  14   b  is arranged, passes not around the first but around the second compressor device  4 . A certain amount of the compressed gas-air mixture can be continuously blown around the second compressor device  4 , that is to say recycled, through the bypass conduit  13   b . In this case therefore a part of the gas mixture compressed by the first compressor device  4  is passed from the fluid outlet  4   b  back to the fluid inlet  4   a  (by way of the cooling device or mixture cooler  6 ). 
       FIGS. 3   a  and  3   b  show further variants. In this case a common bypass conduit  13   a  in which the valve  14   b , once again a so-called blow-around bypass valve  14   b , is arranged passes around the first compressor device  3  and the second compressor device  4 . A certain amount of the compressed gas-air mixture can be constantly blown around both compressor devices  3 ,  4 , that is to say recycled, through the bypass conduit  13   a . A part of the gas mixture compressed by the first compressor device  3  and the second compressor device  4  is passed from the fluid outlet  4   b  back to the fluid inlet  3   a.    
     In the variant in  FIG. 4  a first bypass conduit  13   a  in which a first valve  14   a , a so-called blow-around bypass valve  14   a , is arranged passes around the first compressor device  3 . A second bypass conduit  13   b  with a second blow-around valve  14   b  passes around the second compressor device  4 . Therefore a certain amount of the compressed gas-air mixture can be continuously blown around the respective compressor device  3 ,  4 , that is to say recycled, through the bypass conduits  13   a ,  13   b . In specific terms therefore a part of the gas mixture compressed by the first compressor device  3  is passed from the fluid outlet  3   b  back to the fluid inlet  3   a  (by way of the mixture cooler  5 ). In addition a part of the gas mixture compressed by the second compressor device  4  is passed from the fluid outlet  4   b  back to the fluid inlet  4   a  (by way of the mixture cooler  6 ). 
     While  FIG. 4  shows two serial compressor devices  3 ,  4 , around which a respective bypass conduit  13   a  and  13   b  is passed (more specifically in an anti-parallel flow direction as can be seen from the flow arrows), each with a respective valve  14   a ,  14   b ,  FIG. 5  shows a variant in which two series-connected valves  14   a ,  14   b  are provided around the series-connected compressor devices  3 ,  4 . In the bypass conduit  13   a ,  13   b  there is a branching between the two valves  14   a ,  14   b  by way of the conduit  13   c  which opens in the inlet tract between the two compressor devices  3 ,  4 . 
     The most essential difference in comparison with the  FIG. 4  embodiment is that in the example in  FIG. 5 , it is possible to provide that the compressed fluid is blown around or recycled directly from the fluid outlet side  4   b  of the second compressor  4  in the direction of the fluid inlet  3   a  of the first compressor device  3 . In that case recycle blowing can be effected by way of both compressor devices or only by way of one by suitable actuation of the individual valves  14   a ,  14   b  and  14   c . As the other components are identical to the embodiment of the preceding Figures there is no need for them also to be discussed in greater detail here. 
     What is common to the illustrated embodiments in  FIGS. 1 through 5  is that the valves  14   a ,  14   b ,  14   c  (insofar as they are present) in the respective bypass conduit  13   a ,  13   b ,  13   c  (also insofar as present) are now connected to a regulator  15  of a regulating device. For the sake of clarity of the drawing an individual regulator  15  is shown in relation to each valve  14   a ,  14   b ,  14   c , the regulators jointly forming a regulating device. 
     The operating mode will be described in greater detail with reference to  FIG. 4 . As already mentioned air  9  and fuel gas  8  are mixed in the gas mixer  7 , compressed in the low-pressure compressor  3  and then cooled in the gas mixture cooler  5 . A part of the mixture is blown around by way of the bypass conduit  13   a , that is to say returned to the fluid inlet  3   a , while another part of the mixture is passed into the high-pressure compressor  4 . It is further compressed in the high-pressure compressor  4  and then cooled in the cooler  6  and a part of the mixture is by-passed with the bypass conduit  13   b  and recycled between the two compressor devices  3 ,  4  at the fluid inlet  4   a  of the second compressor device. The remaining part of the mixture is introduced into the combustion chamber of the internal combustion engine  2 . Final quantitative regulation of the mixture feed can be implemented by way of the throttle flap  12 . 
     Under modified conditions on the engine such as for example a change in load the supplied amount of fuel can now be adapted without further ado by way of a regulating intervention at the valves  14   a  and  14   b  in order to provide for regulation to a given engine regulating parameter (such as for example a constant engine parameter, for example a constant rotary speed n or a constant output power P). Upon very great changes in loads both valves  14   a  and  14   b  are actuated so that the amount of fluid which is bypassed or recycled around both compressor devices  3 ,  4  is altered. With less severe changes in load it is generally sufficient to actuate only one valve  14   a ,  14   b . Fluctuations can be particularly advantageously avoided by way of actuation of the valve  14   a  as here the bypassed amount is less so that the internal combustion engine  2  receives a feed of a larger or smaller amount of compressed gas more slowly. In comparison the valve  14   b  can react better to very fast changes in load. Individual regulation can be effected by way of the throttle flap  12  just like by way of regulation of the rotary speed of the compressor device  3 ,  4  insofar as an alteration is made at the exhaust gas turbine  16  or  17 . For that purpose a certain amount of exhaust gas can be continuously circulated in operation by way of the bypass conduits  20   a  and  20   b  respectively. Here too upon changes in load it is possible by actuation of the valves  21   a  and  21   b  to make changes to the engine such as for example an altered load or an altered rotary speed by bypassing more or less mixture around the compressor devices  16 ,  17 . 
     Regulation of the examples in  FIGS. 1 and 2  is effected in corresponding fashion in simplified form by regulating only the amount of mixture that is blown around a compressor device  3  ( FIG. 1 ) or  4  ( FIG. 2 ). Regulation can otherwise be effected in a similar manner. A similar consideration applies to the variants in  FIGS. 3   a  and  3   b  in which the mixture is passed around both compressor devices  3 ,  4  but no branching is provided therebetween so that only the fluid outlet  4   b  is ever connected to the fluid inlet  3   a . The embodiments of  FIGS. 3   a  and  3   b  are preferred embodiments of the invention. The difference between the examples of  FIGS. 3   a  and  3   b  is that  FIG. 3   a  has a bypass conduit in which a regulator  15  regulates a valve  14   b  while in the example of  FIG. 3   b  two valves  14   b ,  14   b ′ arranged in parallel are provided in the one bypass conduit  13   a . In that case a valve  14   b  is regulated in the example in  FIG. 3   a  by way of the regulator  15 . The second valve  14   b ′ is operated in the adjusting mode, that is to say it is to be operated only in the position open, and not continuously like the valve  14   b . That permits faster intervention upon changes in load on the internal combustion engine. 
     Regulation can also be effected for example in such a way that in the operating mode a given amount of gas is continuously blown around both compressor devices (see for example  FIG. 5 ), by for example the valves  14   a  and  24   b  being opened while the valve  14   c  is closed. Now for regulation purposes one of the two valves  14   a ,  14   b  can be closed and the valve  14   c  opened. Either the valve  14   a  or  14   b  is closed in dependence on the difference between the reference value and the actual value. The example of  FIG. 5  is particularly suitable as here the regulating strategies of the variants of  FIGS. 1 ,  2  and  3  can be additionally implemented. 
     Hitherto only the inlet tract has been described. Hereinafter the outlet tract will also be briefly described, and the regulating strategies arising therefrom explained. As can be seen from  FIGS. 1 through 5  the compressor devices  3 ,  4  are so-called turbochargers. They are driven by an exhaust gas turbine  16  and  17  respectively by exhaust gas from the internal combustion engine  2  entering at the fluid inlet  16   a  of the exhaust gas turbine  16 , rotating the turbine  16  and issuing at the fluid outlet  16   b  again. The turbine  16  which now rotates drives the high-pressure compressor  4  by way of the shaft  18 . The exhaust gas is now passed to the series-connected second exhaust gas turbine  17  where the exhaust gas fluid enters the exhaust gas turbine  17  at the fluid inlet  17   a  and is definitively expelled at the fluid outlet  17   b.    
     A bypass conduit  20   a  having a valve  21   a  now passes around the exhaust gas turbine  16 . A further bypass conduit  20   b  having a valve  21   b  passes around the compressor device  17 . The amount of exhaust gas which is passed around the exhaust gas turbine  16  and  17  respectively can be regulated by way of the two valves  21   a ,  21   b  (similarly to the bypass valves  14   a ,  14   b ). They are also connected to the regulating device by way of regulators  15  ( FIGS. 1 ,  2  and  4 ). 
     In the embodiments of  FIGS. 3   a  and  3   b  and  5  the arrangement of the valves  21   a  and  21   b  in the exhaust gas tract is modified and there is an additional valve  21   c  insofar therefore as the valves  21   a  and  21   b  are connected in series and a branching  20   c  is taken off between them, which opens between the two exhaust gas turbines  16 ,  17 . 
     In addition to regulation by way of the inlet tract, it is also possible to provide for regulation by way of the outlet tract, by way of suitable regulating interventions at the valves  21   a ,  21   b ,  21   c . A combination of the individual inlet tract variants of  FIGS. 1 ,  2  and  4  with the outlet tracts of  FIGS. 3 and 5  and the inlet tract variants of  FIGS. 3 and 5  with the outlet tracts of  FIGS. 1 ,  2  and  4  is obviously also provided in accordance with the invention and no longer needs to be discussed in detail here.