Abstract:
The present disclosure relates to a system for recirculating engine exhaust gas, and more particularly, to a system for recirculating engine exhaust gas, which mixes a part of exhaust gas discharged from an engine with air for combustion, and recirculates the mixture, thereby inhibiting nitrogen oxide (NOx) from being generated. Therefore, a technical problem to be achieved in the present disclosure is to provide a system for recirculating engine exhaust gas which may have a simplified structure. In addition, another object of the present disclosure is to provide a system for recirculating engine exhaust gas, which improves output of an engine by increasing an amount of intake air, and further improves fuel efficiency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This Application is a Section 371 National Stage Application of International Application No. PCT/KR2013/002818, filed Apr. 4, 2013 and published, not in English, as WO 2013/151356 on Oct. 10, 2013. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to a system for recirculating engine exhaust gas, and more particularly, to a system for recirculating engine exhaust gas, which mixes a part of exhaust gas discharged from an engine with air for combustion, and recirculates the mixture, thereby inhibiting nitrogen oxide (NOx) from being generated. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    In general, an engine uses gasoline or diesel as fuel, nitrogen oxide (NOx) is included in exhaust gas and discharged when fuel is combusted and exhaust gas is discharged. 
         [0004]    Because nitrogen oxide causes environmental pollution, a technology for inhibiting the nitrogen oxide from being generated is being developed, and as the technology, there is an exhaust gas recirculation (EGR) system. 
         [0005]    The exhaust gas recirculation system is known as a technology which reduces a concentration of oxygen by mixing a part of exhaust gas with air for combustion, and prevents a flame temperature from being rapidly raised, thereby inhibiting the nitrogen oxide from being generated. 
         [0006]    Meanwhile, a turbocharger may be installed in the engine. In the turbocharger, a turbine and a compressor are connected to each other by a single shaft, the turbine of the turbocharger is rotated by energy (temperature and pressure) of exhaust gas, and the compressor is driven by rotational force of the turbine. The compressed air is mixed with a larger amount of fuel, thereby improving efficiency of the engine. 
         [0007]    On the other hand, a pressure wave (or pressure pulse), which is propagated when an exhaust valve of a cylinder is opened, may act as back pressure for other cylinders. There is a problem in that the aforementioned back pressure interference action degrades performance of the exhaust gas recirculation system. 
         [0008]    In order to inhibit the exhaust gas interference, a twin-entry layout, which has two independent passages at a portion where exhaust gas flows into the turbine from an exhaust manifold, is known to be applied. 
         [0009]    In the exhaust gas recirculation system, when recirculating gas is obtained from only one exhaust manifold, imbalance in pressure and flow rate between two lines leading to the turbine is caused, which degrades overall performance of the turbine and the engine system. 
         [0010]    On the other hand, in a case in which the turbocharger, to which the twin-entry layout is applied, and the exhaust gas recirculation system are applied together, the recirculating gas is generally obtained from both the exhaust manifolds. However, in a case in which a phenomenon that exhaust pressures waves are exchanged through both the exhaust manifolds is not effectively inhibited, there is a problem in that back pressure is increased such that performance of the exhaust gas recirculation system deteriorates. 
         [0011]    On the other hand, there is an example in which the twin-entry layout is applied to the exhaust gas recirculation system, and recirculating gas is obtained from two recirculation lines. Valves are installed in the two recirculation lines, respectively, thereby inhibiting the back pressure exchange phenomenon. However, in this example, since additional valves need to be installed and designed, there is a problem in that costs are increased. 
         [0012]    There is another exhaust gas recirculation system for solving the aforementioned problem, and the exhaust gas recirculation system in the related art will be described with reference to the attached  FIG. 1 . 
         [0013]    A plurality of cylinders is disposed in an engine  10 , and the cylinders may be designated as a first cylinder group  12   a  and a second cylinder group  12   b.  First and second exhaust manifolds  21  and  22  are connected to the first cylinder group  12   a  and the second cylinder group  12   b,  respectively. The first and second exhaust manifolds  21  and  22  are connected to a turbine  30  of a turbocharger. 
         [0014]    That is, exhaust gas discharged from the first and second cylinder groups  12   a  and  12   b  is provided to the turbine  30  through the first and second exhaust manifolds  21  and  22 . 
         [0015]    The turbine  30  is connected to a compressor  40 , the turbine is driven by energy of exhaust gas, and driving power drives the compressor  40  to compress air. 
         [0016]    Meanwhile, a first recirculation line  51  and a second recirculation line  52  are connected to the first exhaust manifold  21  and the second exhaust manifold  22 , respectively, such that a part of exhaust gas is obtained. 
         [0017]    The other side of each of the first and second recirculation lines  51  and  52  is connected to a pulse converter unit  60 . The pulse converter unit  60  serves to shut off a reverse flow and an exchange phenomenon of the exhaust pressure wave. 
         [0018]    That is, exhaust gas, which circulates through the first recirculation line  51 , and exhaust gas, which circulates through the second recirculation line  52 , are combined in the pulse converter unit  60 . 
         [0019]    A combining recirculation line  70  is connected to the pulse converter unit  60 , a cooler  90  is connected to the other side of the combining recirculation line  70 , and a valve  80  is provided on the combining recirculation line  70 . The valve  80  inhibits a back pressure exchange phenomenon. The cooler  90  cools high-temperature exhaust gas. 
         [0020]    The exhaust gas cooled by the cooler  90  is sent to a mixer where air and fuel are mixed. 
         [0021]    However, the exhaust gas recirculation system in the related art illustrated in  FIG. 1  has a complicated structure, and as a result, there is a problem in that manufacturing costs are increased. 
         [0022]    In addition, in order to improve efficiency of the engine, it is necessary to additionally increase an amount of intake air, and it is necessary to further improve fuel efficiency. 
         [0023]    The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
       SUMMARY 
       [0024]    This summary and the abstract are provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. The summary and the abstract are not intended to identify key features or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0025]    Therefore, a technical problem to be achieved in some embodiments of the present disclosure is to provide a system for recirculating engine exhaust gas which may have a simplified structure. 
         [0026]    In addition, another object of some embodiments of the present disclosure is to provide a system for recirculating engine exhaust gas, which improves output of an engine by increasing an amount of intake air, and further improves fuel efficiency. 
         [0027]    A technical problem to be achieved in some embodiments of the present disclosure is not limited to the aforementioned technical problem, and any other not-mentioned technical problem will be obviously understood from the description below by those skilled in the technical field to which the present disclosure pertains. 
         [0028]    In order to achieve the objects, a system for recirculating engine exhaust gas according to an exemplary embodiment of the present disclosure includes: first and second cylinder groups ( 12   a,    12   b ) which include cylinders selected from cylinders of an engine; a first manifold ( 21 ) which is connected to the first cylinder group ( 12   a ), and combines and discharges exhaust gas discharged from the cylinders of the first cylinder group ( 12   a ); a second manifold ( 22 ) which is connected to the second cylinder group ( 12   b ), and combines and discharges exhaust gas discharged from the cylinders of the second cylinder group ( 12   b ); a branching unit ( 100 ) which is connected to the first manifold ( 21 ) and the second manifold ( 22 ), and at which exhaust gas discharged from both sides is combined; first and second exhaust lines ( 23 ,  24 ) which have one side that branches off from the branching unit ( 100 ), and the other side that is connected to a turbine ( 30 ) of a turbocharger as a pair, and provide a part of the exhaust gas to the turbine ( 30 ); and a combining recirculation line ( 70 ) which branches off from the branching unit ( 100 ). 
         [0029]    In addition, the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure may further include a valve ( 80 ) which is installed on the combining recirculation line ( 70 ), and inhibits a back pressure exchange phenomenon. 
         [0030]    In addition, the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure may further include a cooler ( 90 ) which is connected to the combining recirculation line ( 70 ), cools the exhaust gas flowing from the combining recirculation line ( 70 ), and supplies the cooled exhaust gas to a mixer of the engine. 
         [0031]    The branching unit ( 100 ) of the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure may communicate with the first manifold ( 21 ), the second manifold ( 22 ), and the combining recirculation line ( 70 ) at one point. 
         [0032]    Specific items of other exemplary embodiments are included in the detailed description and the drawings. 
         [0033]    [Advantageous Effects] 
         [0034]    The system for recirculating engine exhaust gas according to an exemplary embodiment of the present disclosure, which is configured as described above, may remarkably reduce manufacturing costs by simplifying a structure of the system for recirculating exhaust gas. 
         [0035]    In addition, the system for recirculating engine exhaust gas according to an exemplary embodiment of the present disclosure may increase an amount of intake air, thereby improving output of the engine, and further improving fuel efficiency. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a view for explaining a system for recirculating engine exhaust gas in the related art. 
           [0037]      FIG. 2  is a view for explaining a system for recirculating engine exhaust gas according to an exemplary embodiment of the present disclosure. 
           [0038]      FIGS. 3 to 5  are comparative graphs for explaining an effect of the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure, which illustrate authorized fuel efficiency, pressure waveform, and a fuel consumption rate, respectively. 
       
    
    
     DESCRIPTION OF MAIN REFERENCE NUMERALS OF DRAWINGS 
       [0039]      10 : Engine 
         [0040]      12   a,    12   b:  First and second cylinder groups 
         [0041]      21 ,  22 : First and second exhaust manifolds 
         [0042]      23 ,  24 : First and second exhaust gas lines 
         [0043]      30 : Turbine 
         [0044]      40 : Compressor 
         [0045]      51 ,  52 : First and second recirculation lines 
         [0046]      60 : Pulse converter unit 
         [0047]      70 : Combining recirculation line 
         [0048]      80 : Valve 
         [0049]      90 : Cooler 
         [0050]      100 : Branching unit 
       DETAILED DESCRIPTION 
       [0051]    Advantages and features of the present disclosure and methods of achieving the advantages and features will be clear with reference to an exemplary embodiment described in detail below together with the accompanying drawings. 
         [0052]    Like reference numerals indicate like elements throughout the specification, constituent elements identical to constitute elements in the related art will be indicated by the same reference numerals, and duplicated descriptions thereof will be omitted. 
         [0053]    Meanwhile, the terms used in the description are defined considering the functions of the present disclosure and may vary depending on the intention or usual practice of a manufacturer. Therefore, the definitions should be made based on the entire contents of the present specification. 
         [0054]    Hereinafter, a system for recirculating engine exhaust gas according to an exemplary embodiment of the present disclosure will be described with reference to  FIG. 2 . 
         [0055]    The attached  FIG. 2  is a view for explaining the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure. 
         [0056]    The system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure sends a part of the exhaust gas discharged from cylinders of an engine to a turbocharger, and cools the remaining part, and recirculates the remaining part. 
         [0057]    A plurality of cylinders is provided in the engine, and several cylinders selected from the plurality of cylinders are defined as first and second cylinder groups  12   a  and  12   b,  respectively. 
         [0058]    First and second manifolds  21  and  22  are provided in the first and second cylinder groups  12   a  and  12   b,  respectively. 
         [0059]    The first manifold  21  is connected to the first cylinder group  12   a,  and combines and discharges exhaust gas discharged from the cylinders of the first cylinder group  12   a.    
         [0060]    In addition, the second manifold  22  is connected to the second cylinder group  12   b,  and combines and discharges exhaust gas discharged from the cylinders of the second cylinder group  12   b.    
         [0061]    A branching unit  100  is disposed between the first manifold  21  and the second manifold  22 . 
         [0062]    The exhaust gas discharged from the first and second manifolds  21  and  22  is combined by the branching unit  100 . 
         [0063]    In addition, first and second exhaust lines  23  and  24 , which form a pair, are connected to the branching unit  100 . The other side of each of the first and second exhaust lines  23  and  24 , which form a pair, is connected to a turbine  30  of a turbocharger. 
         [0064]    That is, the first and second exhaust lines  23  and  24  provide a part of the exhaust gas, which has been combined by the branching unit  100 , to the turbine  30 . 
         [0065]    In addition, a combining recirculation line  70  is connected to the branching unit  100 , such that a part of the combined exhaust gas branches off and is discharged. 
         [0066]    When describing the branching unit  100  in more detail, the branching unit  100  may communicate with the first manifold  21 , the second manifold  22 , and the combining recirculation line  70  at one point. 
         [0067]    In a case in which pressure in the first manifold  21  is high, and pressure in the second manifold  22  is low, the high pressure in the first manifold  21  may act as back pressure to the second manifold  22 , but with the aforementioned configuration, the combining recirculation line  70  communicates with the first and second manifolds  21  and  22 , thereby reducing back pressure. 
         [0068]    In addition, in the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure, a valve  80  may be further installed on the combining recirculation line  70 . The valve  80  inhibits a back pressure exchange phenomenon. 
         [0069]    In addition, in the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure, a cooler  90  may be further installed on the combining recirculation line  70 . The cooler  90  cools the exhaust gas flowing from the combining recirculation line  70 , and supplies the cooled exhaust gas to a mixer of the engine. 
         [0070]    The system for recirculating engine exhaust gas (EGR system) according to the exemplary embodiment of the present disclosure, which is configured as described above, has a structure which is more simplified than a structure of an exhaust gas recirculation system in the related art, such that the system for recirculating engine exhaust gas may be easily manufactured, and manufacturing costs may be reduced. 
         [0071]    Meanwhile, since the first manifold  21  joins the second manifold  22  at the branching unit  100 , there may be a risk that a back pressure interference phenomenon occurs, but the back pressure interference may be solved by adjusting the valve  80 . 
         [0072]    In addition, a portion where back pressure is exchanged may be a communication point of the branching unit  100 , but because the exhaust gas to be recirculated is obtained at the communication point, the back pressure interference effect is reduced, and as a result, the exhaust gas recirculation system is stabilized. 
         [0073]    In addition, in the system for recirculating exhaust gas according to the exemplary embodiment of the present disclosure, an amount of intake air is increased, and fuel efficiency is improved, and these effects will be described with reference to the attached  FIGS. 3 to 5 . 
         [0074]    The attached  FIGS. 3 to 5  are comparative graphs for explaining an effect of the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure, which illustrate authorized fuel efficiency, pressure waveform, and a fuel consumption rate, respectively. 
         [0075]      FIG. 3  illustrates a result of an air to fuel ratio (AFR) that is a criterion for performance in sucking fresh air, and more particularly, illustrates a result of comparing a Comparative Example in the related art and the present disclosure. 
         [0076]    Here, it can be understood that the higher the air to fuel ratio, the better the performance in sucking fresh air. The better performance in sucking fresh air advantageously acts upon the performance of an engine. 
         [0077]    In addition, the same ratio of an amount of exhaust gas to be recirculated to an overall amount of exhaust gas, that is, the same exhaust gas recirculation ratio is set to the Comparative Example and the present disclosure, and then the tests are performed. 
         [0078]    As can be seen from  FIG. 3 , it can be seen that the system for recirculating exhaust gas according to the exemplary embodiment of the present disclosure is better than the Comparative Example in terms of performance in sucking air, and this means that improved engine performance may be achieved in comparison with the related art. 
         [0079]    In addition, it can be seen that the system for recirculating exhaust gas according to the exemplary embodiment of the present disclosure has relatively excellent performance at a high engine speed rather than at a low engine speed. 
         [0080]    In addition, it can be seen that performance in sucking fresh air similar to that of the Comparative Example is achieved even in the vicinity of a maximum torque point. 
         [0081]    That is, the present disclosure has a structure that is more simplified than a structure in the related art, but can achieve the same or better performance in sucking fresh air, and an improvement in engine performance can be expected. 
         [0082]      FIG. 4  illustrates a result of measuring a pressure waveform at an exhaust port. 
         [0083]    When the engine is driven, pressure is varied based on a displacement angle at which a crankshaft is rotated, and the number of cylinders, and the variation in pressure may be indicated as a pressure waveform as illustrated in  FIG. 4 . 
         [0084]    Peaks and valleys are formed in the pressure waveform as many as the number of cylinders, and performance is better when a smooth waveform is formed at the peak portion. 
         [0085]    Referring to  FIG. 4 , when comparing the present disclosure with the Comparative Example, it can be seen that the Comparative Example has a sharp waveform having deep valleys in some sections, but the present disclosure has a smoother waveform, which has valleys that are not relatively deep, than the Comparative Example. 
         [0086]    In addition, the present disclosure has an exhaust pressure value that is generally greater than that of the Comparative Example, which means that the present disclosure may suck a larger amount of fresh air under the same fresh air suction condition, and it can be understood that performance in sucking fresh air is improved. 
         [0087]    That is, the present disclosure has a structure that is more simplified than a structure in the related art, but can achieve the same or better performance in sucking fresh air, and an improvement in engine performance may be expected. 
         [0088]      FIG. 5  is a graph illustrating a fuel consumption rate. 
         [0089]    As illustrated in  FIG. 5 , the present disclosure has a relatively low fuel consumption ratio in comparison with the Comparative Example, and as a result, it can be seen that the fuel efficiency of the present disclosure is better than that of the Comparative Example. 
         [0090]    That is, the present disclosure has a structure that is more simplified than a structure in the related art, but can achieve the same or better fuel efficiency. 
         [0091]    As described above, the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure may remarkably reduce manufacturing costs by simplifying a structure of the system for recirculating exhaust gas. 
         [0092]    In addition, the system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure has a simplified structure, but may increase an amount of intake air, thereby improving output of the engine, and further improving fuel efficiency. 
         [0093]    The exemplary embodiments of the present disclosure have been described with reference to the accompanying drawings, but those skilled in the art will understand that the present disclosure may be implemented in any other specific form without changing the technical spirit or an essential feature thereof. 
         [0094]    Accordingly, it should be understood that the aforementioned exemplary embodiment is described for illustration in all aspects and are not limited, and the scope of the present disclosure shall be represented by the claims to be described below, and it should be construed that all of the changes or modified forms induced from the meaning and the scope of the claims, and an equivalent concept thereto are included in the scope of the present disclosure. 
         [0095]    The system for recirculating engine exhaust gas according to the exemplary embodiment of the present disclosure may be used to inhibit nitrogen oxide from being generated.