Abstract:
A compression-ignition type internal combustion engine that burns a gaseous fuel, improves an ignition performance not only at a center part of the combustion chamber but also at an outer edge part. The compression-ignition engine comprises an electromagnetic wave generator configured to generate an electromagnetic wave, a controller configured to control the electromagnetic wave generator, and a plasma generator comprising a boosting circuit that constitutes a resonator configured to boost the electromagnetic wave, a first electrode configured to receive an output from the boosting circuit, and a second electrode provided to a vicinity of the first electrode, and the plasma generator is configured such that the first electrode is extruded and exposed toward a combustion chamber of the internal combustion engine, and a plurality of plasma generators are provided.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an internal combustion engine, specifically, a compression-ignition engine such as a diesel engine that burns a gaseous fuel such as CNG, i.e., Compressed Natural Gas, and a spark ignition engine such as a gasoline engine. 
       BACKGROUND ART 
       [0002]    The diesel engine that is one kind of the compression-ignition engines ignites by injecting liquid fuel into air becoming in high temperature at the compression process. The diesel engine is excellent in efficiency and applied to various fuels such as petroleum fuel, for example, diesel oil and fuel oil, or liquid fuel such as squalene and ester. Further, the diesel engine has an advantage that it can be applied to various kind of engines widely from small sized engine in high speed through gigantic sized ship engine in low speed. 
         [0003]    However, in the case of the diesel engine, there are defects such as occurrence of NOx exhaust gas or soot. On the other hand. CNG draws public strong attention as the fuel for being able to reduce the diesel exhaust gas. However CNG has the ignition temperature in high compared to the diesel oil. Therefore, since it is impossible to operate the conventional diesel engine by CNG fuel, it has been suggested that the diesel oil as an example is adopted as the pilot fuel, or the ignition means such as the ignition plug is adopted (No-Patent Document 1). 
       PRIOR ART DOCUMENT 
     Patent Document(s) 
       [0000]    
       
         Patent Document: Japanese unexamined patent application publication No. 2013-057279 
         Patent Document: U.S. Pat. No. 7,963,262 
         Non-Patent Document 1: “Development of Large Gas Engine with High Efficiency, Mitsui Engineering &amp; Shipbuilding Co., Ltd. (MES), technical review No. 191 (2007-6). Page 19-25) 
       
     
       SUMMARY OF INVENTION 
     Problems to be Solved 
       [0007]    However, as indicated in Patent Document 1, for example, the flame propagation speed in the diesel engine is slower than that of the gasoline engine. Accordingly, although the center part of the combustion chamber can be ignited by the ignition plug, the ignition at the outer edge part may not be performed sufficiently. In the spark ignition engine, similar problem is also indicated. 
         [0008]    The present invention is made from the viewpoint of the above. 
         [0009]    A compression-ignition type internal combustion engine that burns a gaseous fuel comprises an electromagnetic wave generator configured to generate an electromagnetic wave, a controller configured to control the electromagnetic wave generator, and a plasma generator comprising a boosting circuit that constitutes a resonator configured to boost the electromagnetic wave, a first electrode configured to receive an output from the boosting circuit, and a second electrode provided to a vicinity of the first electrode, and the plasma generator is configured such that the first electrode is extruded and exposed toward a combustion chamber of the internal combustion engine, and a plurality of plasma generators are provided. 
       Effect of Invention 
       [0010]    According to the present invention, an ignition performance not only at a center part of the combustion chamber but also at an outer edge part can be improved in a compression-ignition engine that burns a gaseous fuel. 
     
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates a structure of a diesel engine  10 . 
           [0012]      FIG. 2  illustrates a bottom view of a cylinder head of the diesel engine  10 . 
           [0013]      FIG. 3  illustrates a front view of a partial cross section that shows a structure of an igniter  3 . 
           [0014]      FIG. 4  is an equivalent circuit of the igniter  3 . 
           [0015]      FIG. 5  is a time chart that explains a control performed by a controller  41 . 
           [0016]      FIG. 6  is a view that illustrates a structure of a diesel engine  100 . 
           [0017]      FIG. 7  is a view that illustrates a structure of an injector unit  6 . 
           [0018]      FIG. 8  is a bottom view of a cylinder head of the diesel engine  100 . 
           [0019]      FIG. 9  is a time chart that explains the control performed by the controller  41 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    In below, embodiments of the present invention are illustrated in details, based on figures. Note that, the following embodiments are essentially desirable examples, and the scope of the present invention, the application product, or the use thereof does not intend to be limited. 
       (First Embodiment) Ignition Device 
       [0021]      FIG. 1  illustrates a diesel engine  10  structure. The diesel engine  10  illustrates one example of a compression-ignition type internal combustion engine of the present invention. Regarding an engine main body part.  FIG. 1  illustrates a front cross sectional view of a partial cross section. Into a cylinder head  21  of the diesel engine  10 , an injector  1  configured to inject CNG fuel toward a combustion chamber  28  is inserted 
         [0022]    Moreover, a plurality of igniters  3 , specifically,  3 A through  3 D, are respectively inserted into each insert hole of the cylinder head  21 . As illustrated in a bottom view of the cylinder head  21  of  FIG. 2 , an igniter  3 A is arranged an a point A between intake ports  24 , an igniter  3 B is arranged on a point B between exhaust ports  26 , an igniter  3 C and  3 D are respectively arranged on a point C and a point D between the intake port  24  and the exhaust port  26 , i.e., a total of four igniters are arranged. By arranging four igniters at a location that is distant away from the injector  1 , multi-points ignition can be achieved, a flame propagation distance can be reduced, an initial combustion period of time and a main combustion period of time can be shortened, and a stabilization can be achieved. Moreover, the flame propagation is completed before reaching to an auto-ignition by reduction of the flame propagation distance, and therefore. “knocking” phenomenon can be suppressed. It is also expected of obtaining an effect that the flame propagates toward a center of the combustion chamber, and a heat loss at a cylinder wall surface at a low temperature can be reduced, and a thermal efficiency improvement can be achieved. Moreover, NOx emission can also be suppressed. 
         [0023]    By referring to  FIG. 3 , a structure of an igniter  3  is explained in details. The igniter  3  divides into three parts, an input part  3   a , a coupling part  3   b , and an amplification/discharge part  3   c . The input part  3   a  is configured to input a microwave, the coupling part  3   b  is configured to perform a capacitive coupling in order to, for example, attain an impedance matching between the inputted microwave and the igniter  3 , and the amplification/discharge part  3   c  is configured to amplify a voltage and perform a discharge. Respective parts of the igniter  3  are housed inside a casing  31  that is composed of a conductive metal. 
         [0024]    The input part  3   a  includes an input terminal  32  configured to input a microwave generated at an outside oscillation circuit and a first center electrode  33 . The first center electrode  33  transmits the microwave. A dielectric  39   a  composed of for example, ceramics, is provided between the first center electrode  33  and the casing  31 . 
         [0025]    The coupling part  3   b  includes the first center electrode  33  and a second center electrode  34 . The coupling part  3   b  specializes in attaining an impedance matching between the oscillation circuit and the igniter  3 . The second center electrode  34  has a cylindrical structure with a bottom at the amplification/discharge part  3   c  side, and the cylindrical part surrounds the first center electrode  33 . The first center electrode  33  with stick type and the inner wall of the cylindrical part of the second center electrode  34  oppose to each other, and the microwave from the first center electrode  33  is transmitted to the second center electrode  34  at the opposing part by the capacitive coupling. At the cylindrical part of the second center electrode  34 , a dielectric  39   b  such as ceramics is filled with, and a dielectric  39   c  such as ceramics is provided between the second center electrode  34  and the casing  31 . 
         [0026]    The amplification/discharge part  3   c  includes a third center electrode  35  and a discharge electrode  36 . The third center electrode  35  is connected to the second center electrode  34 , and the microwave in the second center electrode  34  is transmitted from the second center electrode  34  to the third center electrode  35 . The discharge electrode  36  is mounted to a distal end of the third center electrode  35 . The third center electrode  35  has a coil element, and the microwave potential gradually becomes higher with passage through the third center electrode  35 . As a result, high voltage, some tens of KV, is generated between the discharge electrode  36  and the casing  31 , and eventually, the discharge is caused between the discharge electrode  36  and the casing  31 . 
         [0027]      FIG. 4  illustrates an equivalent circuit of the igniter  3 . The microwave inputted from the outside oscillation circuit MW, voltage V 1 , frequency 2.45 GHz, is connected to a resonance circuit that is constituted of a capacitor C 3 , a reactance L, and a capacitor C 2 , via a capacitor C 1 . Further, the discharger is provided aligning in parallel with the capacitor C 3 . 
         [0028]    Here, C 1  corresponds to a coupling capacitor, and C 1  is determined mainly by a positional relation between the second center electrode  34  and the first center electrode  33 , i.e., distance between both the electrodes and an opposing area therebetween, and a filler that fills between the electrodes, in the present embodiment, the ceramic type dielectric  39   b . The first center electrode  33  may be constituted slidably in an axial direction in order to adjust the impedance easily. 
         [0029]    The capacitor C 2  is a grounding (earth) capacitor that is formed by the second center electrode  34  and the casing  31 . C 2  is determined by the distance between the second center electrode  34  and the casing  31 , the opposing area therebetween, and also a constant of the dielectric  39   c . The casing  31  is composed of the conductive metal, and functions as a ground electrode. 
         [0030]    Reactance L corresponds to a coil element of the third center electrode  35 . 
         [0031]    The capacitor C 3  is a discharge capacitor that is formed by the third center electrode  35 , the discharge electrode  36 , and the casing  31 . C 3  is determined by such as (1) shape and size of the discharge electrode  36 , and distance from to the casing  31 . (2) distance between the third center electrode  35  and the casing  31 , and (3) cavity (air)  37  formed between the third center electrode  35  and the casing  31  and a thickness of a dielectric  39   d . If C 2 &gt;&gt;C 3 , the potential difference of both the ends of the capacitor C 3  can significantly become larger than V 1 , and as a result, the discharge electrode  36  can be introduced to a high potential. Moreover, C 3  can become sized in small, and therefore, the capacitor area also can be made smaller Note that, of the third center electrode  35  and the casing  31 , in fact, the capacitor C 3  is determined by the opposing part that sandwiches the dielectric  39 . Conversely, the capacitor C 3  can be adjusted by changing a length of the cavity (air)  37  in the axial direction. 
         [0032]    If the coupling capacitor C 1  is deemed to be small enough, the capacitor C 3 , the reactance L, and the capacitor C 2  form a series-resonance-circuit, and a resonance frequency f is expressed in a mathematical formula 1. 
         [0000]    
       
         
           
             
               
                 
                   f 
                   = 
                   
                     1 
                     
                       2 
                        
                       π 
                        
                       
                         LC 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    In the formula, 
         [0000]    
       
         
           
             
               1 
               C 
             
             = 
             
               
                 1 
                 
                   C 
                   2 
                 
               
               + 
               
                 1 
                 
                   C 
                   3 
                 
               
             
           
         
       
     
         [0033]    In other words, if f=2.45 GHz, the igniter  3  is designed such that the discharge capacitor C 3 , the coil reactance L, and the grounding capacitor C 2  satisfy the relation of the formula 1. 
         [0034]    As described above, the igniter  3  generates a voltage Vc 3  higher than a power source voltage, V 1  of the microwave inputted into the igniter  3  by a boosting system via resonator Thereby, the discharge is caused between the discharge electrode  36  and the ground electrode (casing  31 ). If the discharge voltage exceeds a breakdown voltage of gaseous molecules in the vicinity thereof electrons are released from gaseous molecules, on-equilibrium plasma is generated, and fuel is ignited. 
         [0035]    Since the frequency with 2.45 GHz band is adopted, large capacitance of the capacitor is not required, i.e., it is sufficient with smaller capacitor, and the igniter  3  is effective in the whole device downsize. Moreover, the boosting system is adopted, and as result, only the vicinity of the discharge electrode  36  of the igniter  3  becomes high potential. Therefore, an isolation performance is also excellent. Front these viewpoints, the igniter of the present invention is more excellent than the conventional igniter with resonator, for example, Patent Document 2. 
         [0036]    Again, referring to  FIG. 1 , a controller  41  controls an injection timing and an injection pressure (an injection size) of the injector  1 , and also controls a microwave generator  42 . The microwave generator  42  includes an oscillator configured to oscillate an AC signal, alternating current signal with 2.45 GHz, a circuit configured to control ON/OFF the microwave, and an amplification circuit configured to amplify the microwave generated at a power source of automotive battery, for example, direct current 12V so as to match with an input voltage specification of the igniter  3 . In other words, the controller  41  indirectly controls the igniter  3  by controlling the microwave generator  42 . Conversely, a discharge timing of the igniter  3  can freely be controlled by controlling a microwave generation timing of the microwave generator  42 . In the generally-used spark plug that uses the ignition coil having a large reactance, a first response in speed is difficult in performance, and a continuous discharge performance is also difficult. On the other hand, in the igniter  3  of the present invention, the first response in speed can be possible in performance since the igniter  3  is driven by the microwave. Further, by controlling the microwave generator  42  freely, exactly like a continuous discharge can be caused in high frequency at an arbitral timing. Accordingly, below described various controls can be performed, and in that point, the igniter  3  differs from the conventional spark plug. 
         [0037]    Here, next, referring to  FIG. 5 , a control example performed by the controller  41  is explained. The controller  41  controls the injector  1  such that the CNG fuel injection is started at a timing of a crank angle of a piston  27  reaching to around over −90 degree. It is controlled such that the igniter  3 A firstly performs a discharge after starting of injection performance by the injector  1 . The vicinity of the igniter  3 A, i.e., the point A is earlier ignited. Next, similarly with that, discharge is performed in the order of  3 B,  3 C, and  3 D and accordingly ignited at the point B, C, and D sequentially in this order. Four igniters may be discharged simultaneously, but in this case, four microwave generators  42  are required, and the cost performance for system is totally expensive. Here, giving a thought for a discharge time period, the period of time for performing the discharge necessary for ignition is not long term. Therefore, in the present embodiment, one microwave generator  42  is used, and the igniter to discharge is switched sequentially starting from first to fourth. 
         [0038]    A method of switching the igniter is considered for example by switching sequentially, another by sweeping the oscillation frequency of the microwave generator  42  by taking into consideration of a characteristic that the igniter has an independent different resonance frequency, or further another by using a reflection wave that is generated inside the igniter  3  as a signal source for other igniter  3 . 
         [0039]    The igniter  3  is driven by the microwave, and therefore, the discharge is performed at a cycle of microwave (GHz). Accordingly, next timing discharge is performed before generated radicals are destructed, and therefore, generated OH radicals and etc. are maintained without destruction. On the other hand, in the conventional spark plug, spark ON/OFF at high frequency cannot be performed, and therefore, once generated radicals soon go to destruct. Accordingly, if the conventional spark plug is used, the above described effect cannot be obtained. In the present embodiment, by use of the igniter  3 , the above described multi-points ignition can be achieved. 
       Second Embodiment 
       [0040]      FIG. 6  illustrates a diesel engine  100  structure regarding the second embodiment. A front cross sectional view of a partial cross section regarding the engine main body part is illustrated. Into the cylinder head  21  of the diesel engine  100 , an injector unit  6  that includes an injector configured to inject CNG fuel to the combustion chamber  28  and an igniter configured to ignite the fuel is inserted. 
         [0041]      FIG. 7  is a front view of a partial cross section that illustrates a structure of the injector unit  6 . The injector unit  6  includes injectors  61 , the igniter  3 , and a casing  64  housing them inside. 
         [0042]    The igniter  3  is arranged on a center axis of the casing  64 , and two injectors  61  are arranged adjacent to the igniter  3 . 
         [0043]    The injectors  61  are built together with the igniter  3 , and therefore, a downsized type one is selected. By the downsize, a fuel injected amount is reduced. Therefore, so as to compensate the reduced amount, the injector unit  6  uses a plurality of (two) injectors. 
         [0044]    Again, turning back to  FIG. 6 , in the diesel engine  10 , in addition to the igniter  3  housed inside the injector unit  6 , further more igniters are inserted into insert holes of the cylinder head  21 . As illustrated in a bottom view of the cylinder head  21  of  FIG. 8 , in addition to the igniter  3  (injector unit  6 ) in the center part, an igniter  3 A at the point A between the intake ports  24 , an igniter  3 B at the point B between the exhaust ports  26 , igniter  3 C,  3 D at the points C and D between the intake port  24  and the exhaust port  26 , i.e., a total of five igniters are arranged. 
         [0045]      FIG. 9  illustrates a control example performed by the controller  41 . The controller  41  controls such that firstly the igniter  3  performs the discharge, and the center part of the combustion chamber  28  where is a part provided with the injector  1  is earlier ignited. Next, other igniters perform discharge sequentially in the order of igniter  3 A, the igniter  3 B, the igniter  3 C, and the igniter  3 D, and ignited at the point A, B, C, and D sequentially in this order. 
         [0046]    Multi-points ignition can be achieved also in the present embodiment, the flame propagation distance can be reduced, the initial combustion period of time and the main combustion period of time can be shortened, and the stabilization can be achieved. 
       Third Embodiment 
       [0047]    In the above embodiments, each igniter takes turn for ignition according to the control of the controller  41 . On the other hand, reflection wave from the igniter  3  may be utilized to ignite sequentially among the respective injectors. If the discharge is performed at the discharge electrode  36  of the igniter  3 , at that moment, the impedance matching inside the igniter  3  falls out of phase, i.e., deformed, and the reflection wave is generated. In other words, the microwave flows in a reversed direction from the tip part, i.e., the amplification/discharge pan  3   c , to the rear part, i.e., the input part  3   a . By the characteristic, the reflection wave is successively introduced to the igniter  3 , and the reflection wave can efficiently be utilized. In other words, the igniters  3 A,  3 B,  3 C, and  3 D are electrically connected in series, the igniter  3 B uses the reflection microwave from the igniter  3 A as the power source, and the igniter  3 C uses the reflection microwave from the igniter  3 B as the power source, and thereby, the timing control by the controller  4  becomes unnecessary. Moreover, if the control of the igniter  3  is tried to be performed by using a single power source, switching in first speed is difficult; however by using the above-mentioned characteristic, the igniter for ignition can be switched in first speed. Note that, the present embodiments can be applied to not only compression-ignition engine but also the spark ignition engine such as gasoline engine. 
         [0048]    As above, the present embodiments are described. The scope of the present invention is determined based on inventions described in the claims. The scope of the present invention should not be limited to the present embodiments. 
         [0049]    For example, the igniter  3  is not limited to the above, and other type plug such as a corona discharge plug, for example, “EcoFlash”®, registered trademark in US owned by BorgWarner Inc. may be utilized. Note that, continuous-discharge-possible-igniter in high frequency is preferably to used in order to obtain an effect illustrated in the above embodiments. 
         [0050]    Moreover, the igniter  3  is operated by the microwave; however, the electromagnetic wave that has other band may be used. 
       EXPLANATION OF REFERENCES 
       [0000]    
       
           1  Injector 
           3  Igniter 
           3   a  Input Part 
           3   b  Coupling Part 
           3   c  Amplification/Discharge Part 
           31  Casing (Ground Electrode) 
           32  Microwave Input Terminal 
           33  First Center Electrode 
           34  Second Center Electrode 
           35  Third Center Electrode 
           36  Discharge Electrode 
           37  Cavity 
           39  Dielectric 
           6  Injector Unit 
           61  Injector 
           64  Casing 
           10  Diesel Engine 
           41  Controller 
           42  Microwave Generator 
           100  Diesel Engine