Abstract:
A microwave irradiation apparatus includes: an annular microwave transmission path; a first microwave generation circuit that is coupled with the microwave transmission path and generates a first microwave; and a second microwave generation circuit that is coupled with the microwave transmission path and generates a second microwave; wherein the first microwave and the second microwave have frequencies equal to each other but have phases different from each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-215112, filed on Oct. 30, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a microwave irradiation apparatus and an exhaust gas purification apparatus. 
       BACKGROUND 
       [0003]    Currently, an exhaust gas purification apparatus in which a diesel particulate filter (DPF) is used is practically used as an apparatus that collects fine particles such as particulate matter (PM) contained in the exhaust gas. Since, in such an exhaust gas purification apparatus, fine particles such as PM are deposited on the DPF through use thereof, regeneration of the DPF is demanded. As a method for regenerating the DPF, for example, a method is disclosed in which a high-frequency electromagnetic wave such as a microwave irradiated from a microwave irradiation apparatus is used. In particular, according to the method, regeneration of the DPF is performed by irradiating an electromagnetic wave such as a microwave on the DPF to heat and combust fine particles such as PM deposited on the DPF. 
         [0004]    A microwave irradiation apparatus is used also in a food heating apparatus for heating food, a chemical reaction apparatus or the like. 
         [0005]    In the exhaust gas purification apparatus described above, regeneration of a DPF is performed by irradiating an electromagnetic wave such as a microwave on the DPF to dielectrically heat fine particles such as PM to oxidize and decompress the fine particles such as PM. However, it is difficult to irradiate a microwave, which is to be irradiated on the DPF, with a uniform intensity in the DPF, and a high intensity region and a low intensity region of the microwave appear in the DPF, resulting in unevenness of the temperature in the DPF. Therefore, fine particles such as PM are removed in some region while fine particles are not removed very much in another region in the DPF, and the DPF is not regenerated sufficiently. The phenomenon that a region which the intensity of an irradiated microwave is high and another region in which the intensity of the irradiated microwave is low appear in this manner similarly occurs also with a food heating apparatus, a chemical reaction apparatus and so forth. 
         [0006]    Therefore, a microwave irradiation apparatus is demanded in which a region in which the intensity of an irradiated microwave is high and another region in which the intensity of the irradiated microwave is low are less likely to appear and a heating target may be heated uniformly. 
         [0007]    The followings are a reference documents. 
       [Document 1] Japanese Laid-open Patent Publication No. 2006-140063 
     [Document 2] Japanese Laid-open Patent Publication No. 4-179817 
     [Document 3] Japanese Patent No. 4995351 
     [Document 4] Japanese Laid-open Patent Publication No. 05-202733 
     [Document 5] Japanese Laid-open Patent Publication No. 2014-175122 
     SUMMARY 
       [0008]    According to an aspect of the embodiments, a microwave irradiation apparatus includes: an annular microwave transmission path; a first microwave generation circuit that is coupled with the microwave transmission path and generates a first microwave; and a second microwave generation circuit that is coupled with the microwave transmission path and generates a second microwave; wherein the first microwave and the second microwave have frequencies equal to each other but have phases different from each other. 
         [0009]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIGS. 1A and 1B  are schematic views depicting a structure of a microwave irradiation apparatus according to a first embodiment; 
           [0012]      FIG. 2  is a schematic view illustrating a standing wave generated in a circular ring waveguide according to the first embodiment; 
           [0013]      FIG. 3  is a schematic view depicting a structure of a microwave irradiation apparatus in which one microwave generation unit is coupled with a circular ring waveguide; 
           [0014]      FIGS. 4A and 4B  are intensity distribution diagrams of a microwave in the microwave irradiation apparatus depicted in  FIG. 3 ; 
           [0015]      FIGS. 5A and 5B  are intensity distribution diagrams of a microwave in the microwave irradiation apparatus according to the first embodiment; 
           [0016]      FIG. 6  is a schematic view depicting a structure (1) of a microwave irradiation apparatus according to a second embodiment; and 
           [0017]      FIG. 7  is a schematic view depicting another structure (2) of the microwave irradiation apparatus according to the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    In the following, embodiments for carrying out the technology are described. It is to be noted that like elements and so forth are denoted by like reference symbols and description of them is omitted herein. 
         [0019]    As an example of a filter regeneration apparatus for an internal combustion engine, a filter regeneration apparatus of a structure is available in which a peripheral region of a DPF that is a heating target is covered with a waveguide and a microwave is supplied to the waveguide such that the microwave leaks from holes provided at the inner side of the waveguide and is irradiated on the DPF. However, in a filter regeneration apparatus of such a structure as just described, since a standing wave is formed in the waveguide by the microwave supplied to the waveguide, bellies and knots by the standing wave are formed. Therefore, a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low appear. It is to be noted that, in the present application, the phenomenon that a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low appear is referred to sometimes as an intensity distribution of the microwave appears. 
       First Embodiment 
       [0020]    Now, a microwave irradiation apparatus according to a first embodiment is described with reference to  FIGS. 1A and 1B .  FIGS. 1A and 1B  depict an exhaust gas purification apparatus to which the microwave irradiation apparatus according to the present embodiment is attached. 
         [0021]      FIGS. 1A and 1B  are schematic views of a structure of the microwave irradiation apparatus according to the present embodiment. In particular,  FIG. 1A  is a perspective view of part of the exhaust gas purification apparatus to which the microwave irradiation apparatus according to the present embodiment is attached, and  FIG. 1B  is a sectional view taken along a direction in which exhaust gas flows in the exhaust gas purification apparatus. The exhaust gas purification apparatus includes a fine particle collection unit  10 , a housing  20 , a first microwave generation unit  41 , a second microwave generation unit  42 , a controller  60  and so forth. A circular ring waveguide  30  that is a ring-formed microwave transmission path is provided around the cylindrical housing  20 , and holes or the like not depicted are formed on the circular ring waveguide  30  at the housing  20  side that is an inner side of the circular ring waveguide  30  such that the microwave leaks to inside of the housing  20  and is irradiated on the fine particle collection unit  10 . 
         [0022]    The fine particle collection unit  10  is formed from a DPF or the like. The DPF is formed in a honeycomb structure in which vents adjacent each other are closed alternately, and exhaust gas is exhausted from vents different from vents that serve as entrances. 
         [0023]    The housing  20  is formed from a metal material such as stainless steel, and includes a housing main portion  20   a  that covers the periphery of the fine particle collection unit  10 , and an intake port  20   b  and a discharge port  20   c  coupled with the housing main portion  20   a.  In the exhaust gas purification apparatus according to the present embodiment, exhaust gas such as exhaust gas from an engine or the like is purified when it enters the housing  20  from the intake port  20   b  in a direction indicated by a broken line arrow mark A and passes the fine particle collection unit  10  installed in the housing main portion  20   a.  Thereafter, the exhaust gas purified in the fine particle collection unit  10  is exhausted in a direction indicated by a broken line arrow mark B from the discharge port  20   c.    
         [0024]    The first microwave generation unit  41  is coupled with the circular ring waveguide  30  by a first coupling waveguide  51 , and the second microwave generation unit  42  is coupled with the circular ring waveguide  30  by a second coupling waveguide  52 . A microwave generated by the first microwave generation unit  41  propagates in a direction indicated by a broken line arrow mark C in the first coupling waveguide  51  and is supplied into the circular ring waveguide  30 . Meanwhile, a microwave generated by the second microwave generation unit  42  propagates in a direction indicated by a broken line arrow mark D in the second coupling waveguide  52  and is supplied into the circular ring waveguide  30 . 
         [0025]    It is to be noted that the frequency of the microwave generated by the first microwave generation unit  41  and the frequency of the microwave generated by the second microwave generation unit  42  are equal to each other. The microwave irradiation apparatus according to the present embodiment includes the circular ring waveguide  30 , the first microwave generation unit  41 , the second microwave generation unit  42 , the first coupling waveguide  51 , the second coupling waveguide  52 , and the controller  60 . 
         [0026]    A distance L between a center  51   a  of the coupling portion between the circular ring waveguide  30  and the first coupling waveguide  51  and a center  52   a  of the coupling portion between the circular ring waveguide  30  and the second coupling waveguide  52  is formed so as to be equal to (2N−1)×λ/4. It is to be noted that λ is a wavelength of the microwave supplied to the circular ring waveguide  30  and N is a positive integer. Since preferably the distance L is not too long, it is preferable to set the distance L to λ/4, 3λ/4, 5λ/4, or 7λ/4. 
         [0027]    Further, the microwave supplied from the first microwave generation unit  41  to the circular ring waveguide  30  through the first coupling waveguide  51  and the microwave supplied from the second microwave generation unit  42  to the circular ring waveguide  30  through the second coupling waveguide  52  are displaced by π/2, namely, by λ/4, in phase from each other. Consequently, as depicted in  FIG. 2 , standing waves W 1  and W 2  are generated by the microwave generated by the first microwave generation unit  41  and the microwave generated by the second microwave generation unit  42  in the circular ring waveguide  30 . It is to be noted that  FIG. 2  is a sectional view taken along an alternate long and short dash line  1 A- 1 B in  FIG. 1B , and is a schematic view illustrating a standing wave generated in the circular ring waveguide according to the first embodiment. 
         [0028]    In the present embodiment, the standing wave W 1  generated by the microwave from the first microwave generation unit  41  and the standing wave W 2  generated by the microwave from the second microwave generation unit  42  are displaced by π/2 in phase from each other. Accordingly, bellies of the standing wave W 1  generated by the microwave from the first microwave generation unit  41  correspond to knots of the standing wave W 2  generated by the microwave from the second microwave generation unit  42 . Similarly, knots of the standing wave W 1  generated by the microwave from the first microwave generation unit  41  correspond to bellies of the standing wave W 2  generated by the microwave from the second microwave generation unit  42 . Consequently, since the position of a knot of one of the standing waves corresponds to the position of a belly of the other one of the standing waves and the standing waves complement each other, an intensity distribution of the microwaves can be suppressed from appearing in the circular ring waveguide  30 . In other words, such a situation may be suppressed that a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low appear in the circular ring waveguide  30 . The microwaves in the circular ring waveguide  30  leak from the holes not depicted provided on the circular ring waveguide  30  at the fine particle collection unit  10  side that is the inner side of the circular ring waveguide  30  and is irradiated on the fine particle collection unit  10 . Accordingly, in the present embodiment, since the intensity of the microwave irradiated on the fine particle collection unit  10  may be substantially uniformized, the fine particle collection unit  10  may be heated uniformly. 
         [0029]    Further, in the present embodiment, the center  51   a  of the coupling portion between the circular ring waveguide  30  and the first coupling waveguide  51  functions as a knot of the standing wave W 2  generated by the microwave from the second microwave generation unit  42 . Therefore, the microwave from the second microwave generation unit  42  does not advance into the first coupling waveguide  51 . Similarly, the center  52   a  of the coupling portion between the circular ring waveguide  30  and the second coupling waveguide  52  functions as a knot of the standing wave W 1  generated by the microwave from the first microwave generation unit  41 . Therefore, the microwave from the first microwave generation unit  41  does not advance into the first coupling waveguide  51 . 
         [0030]    The microwave irradiation apparatus according to the present embodiment may generate the microwaves at the same time from the first microwave generation unit  41  and the second microwave generation unit  42 , or may generate the microwaves alternately. The control where the microwaves are alternately generated by the first microwave generation unit  41  and the second microwave generation unit  42  is performed by the controller  60 . 
         [0031]    Now, intensity distributions of the microwave in the microwave irradiation apparatus according to the present embodiment depicted in  FIG. 1  and a microwave irradiation apparatus that is depicted in  FIG. 3  and includes a single microwave generation unit are described. The microwave irradiation apparatus depicted in  FIG. 3  and including a single microwave generation unit includes a fine particle collection unit  10 , a housing  20 , a microwave generation unit  941  and so forth. The circular ring waveguide  30  is provided around the cylindrical housing  20 , and a microwave generation unit  941  is coupled with the circular ring waveguide  30  by a coupling waveguide  951 . In particular, the microwave irradiation apparatus depicted in  FIG. 3  is structured such that the single microwave generation unit  941  is coupled with the circular ring waveguide  30  by the coupling waveguide  951 . 
         [0032]    A microwave generated by the microwave generation unit  941  propagates in a direction indicated by a broken line arrow mark E in the coupling waveguide  951  and is supplied into the circular ring waveguide  30 . The microwave supplied into the circular ring waveguide  30  forms a standing wave in the circular ring waveguide  30  and is irradiated on the fine particle collection unit  10 . 
         [0033]      FIGS. 4A and 4B  depict intensity distribution of the microwave irradiated by the microwave irradiation apparatus depicted in  FIG. 3  and including the single microwave generation unit. In particular,  FIG. 4A  depicts an intensity distribution of the microwave of the fine particle collection unit  10  in a direction perpendicular to a flowing direction of exhaust gas, and  FIG. 4B  depicts an intensity distribution of the microwave of the fine particle collection unit  10  in the flowing direction of exhaust gas indicated by a broken line arrow mark F. Further,  FIGS. 5A and 5B  depict intensity distribution of the microwave irradiated by the microwave irradiation apparatus according to the present embodiment. In particular,  FIG. 5A  depicts an intensity distribution of the microwave of the fine particle collection unit  10  in a direction perpendicular to a flowing direction of exhaust gas, and  FIG. 5B  depicts an intensity distribution of the microwave of the fine particle collection unit  10  in the flowing direction of exhaust gas indicated by a broken line arrow mark G. 
         [0034]    In the microwave irradiation apparatus depicted in  FIG. 3  and including a single microwave generation unit, the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low is great as depicted in  FIGS. 4A and 4B . In this manner, if the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low is great, then temperature unevenness occurs in the fine particle collection unit  10 . Therefore, a region in which fine particles such as PM are removed and another region in which fine particles are not removed very much appear and regeneration of the fine particle collection unit  10  may not be performed sufficiently. 
         [0035]    The reason why the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low is great in this manner is that a single microwave is supplied to the circular ring waveguide  30  and an intensity distribution of the microwave appears in response to bellies and knots of the standing wave generated by the supplied microwave. 
         [0036]    In contrast, as depicted in  FIGS. 5A and 5B , in the microwave irradiation apparatus according to the present embodiment, the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low is reduced. Where the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low is small in this manner, in the fine particle collection unit  10 , little temperature unevenness appears and heating is performed substantially uniformly. Consequently, removal of fine particles such as PM in the fine particle collection unit  10  may be performed uniformly and regeneration of the fine particle collection unit  10  may be performed sufficiently. 
         [0037]    The reason why the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low is reduced in the microwave irradiation apparatus according to the present embodiment in this manner is that two microwaves whose phases are displayed by π/2 from each other are supplied to the circular ring waveguide  30 . Consequently, in the circular ring waveguide  30 , knots of the standing wave generated by one of the microwaves correspond to bellies of the standing wave generated by the other one of the microwaves while knots of the standing wave generated by the other one of the microwaves correspond to bellies of the standing wave generated by one of the microwaves. In the present embodiment, the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low may be reduced as described above, and the fine particle collection unit  10  may be heated substantially uniformly by the irradiated microwaves. 
         [0038]    It is to be noted that the microwave irradiation apparatus according to the present embodiment may be applied not only for regeneration of the fine particle collection unit  10  but also to a heating apparatus that heats food or the like by a microwave, a chemical reaction apparatus and so forth. 
       Second Embodiment 
       [0039]    Now, a second embodiment is described.  FIG. 6  is a schematic view depicting a structure (1) of a microwave irradiation apparatus according to the second embodiment. The microwave irradiation apparatus according to the present embodiment includes, as depicted in  FIG. 6 , a microwave transmission path  130 , a first microwave generation unit  41 , a second microwave generation unit  42 , a first coupling waveguide  51 , a second coupling waveguide  52 , and a controller  60 . 
         [0040]    The microwave transmission path  130  is formed in a tubular shape having a quadrangular cross section and has reflection walls  131   a  and  131   b  provided at the opposite ends thereof such that they reflect a microwave. A plurality of opening holes  132  for radiating a microwave there through are provided in a wall of the tubular portion between the reflection wall  131   a  and the reflection wall  131   b.    
         [0041]    The first microwave generation unit  41  is coupled with the microwave transmission path  130  by the first coupling waveguide  51 , and the second microwave generation unit  42  is coupled with the microwave transmission path  130  by the second coupling waveguide  52 . A distance L between a center  51   a  of the coupling portion between the microwave transmission path  130  and the first coupling waveguide  51  and a center  52   a  of the coupling portion between the microwave transmission path  130  and the second coupling waveguide  52  is formed so as to be equal to (2N−1)×λ/4. It is to be noted that λ is a wavelength of the microwave supplied to the microwave transmission path  130  and N is a positive integer. Since preferably the distance L is not too long, preferably the distance L is set to λ/4, 3λ/4, 5λ/4, or 7λ/4. 
         [0042]    The microwave generated by the first microwave generation unit  41  propagates in a direction indicated by a broken line arrow mark H in the first coupling waveguide  51  and is supplied into the microwave transmission path  130 . Meanwhile, the microwave generated by the second microwave generation unit  42  propagates in the second coupling waveguide  52  in a direction indicated by a broken line arrow mark I and is supplied into the microwave transmission path  130 . 
         [0043]    In the present embodiment, the microwave supplied from the first microwave generation unit  41  to the microwave transmission path  130  through the first coupling waveguide  51  is reflected by the reflection wall  131   a  and the reflection wall  131   b  of the microwave transmission path  130  to form a standing wave. Similarly, the microwave supplied from the second microwave generation unit  42  to the microwave transmission path  130  through the second coupling waveguide  52  is reflected by the reflection wall  131   a  and the reflection wall  131   b  of the microwave transmission path  130  to form a standing wave. Since the microwave supplied from the first microwave generation unit  41  and the microwave supplied from the second microwave generation unit  42  are displaced by π/2, namely, by λ/4, in phase from each other, also the phases of the two standing waves generated in the microwave transmission path  130  are displaced by π/2 from each other. 
         [0044]    Accordingly, in the microwave transmission path  130 , knots of the standing wave generated by one of the microwaves correspond to bellies of the standing wave generated by the other one of the microwaves while knots of the standing wave generated by the other one of the microwaves correspond to bellies of the standing wave generated by the one of the microwaves. Consequently, the microwave irradiation apparatus according to the present embodiment may reduce the difference between a region in which the intensity of the microwave is high and another region in which the intensity of the microwave is low and may irradiate the microwave having a substantially uniform intensity in a direction indicated by a broken line arrow mark J through the opening holes  132 . Therefore, a heating target placed in the direction indicated by the broken line arrow mark J may be heated substantially uniformly. 
         [0045]      FIG. 7  is a schematic view depicting another structure (2) of the microwave irradiation apparatus according to the second embodiment. As described in  FIG. 7 , the microwave irradiation apparatus structured such that a plurality of microwave irradiation units, each of which may be the microwave irradiation apparatus of  FIG. 6  except the controller, are juxtaposed such that they may heat substantially uniformly over a wide area. In particular, the microwave irradiation units are installed in in a juxtaposed relationship in a lateral direction such that the orientations of opening portions in a plurality of microwave transmission paths  130   a,    130   b,    130   c,  and  130   d  are same as each other. Thus, the microwave irradiation units may heat a heating target  200 , which has a wide area and is placed at the side of the opening portions, substantially uniformly. 
         [0046]    It is to be noted that, in the microwave irradiation apparatus of  FIG. 7 , a first microwave generation unit  41   a  and a second microwave generation unit  42   a  are coupled with the microwave transmission path  130   a,  and another first microwave generation unit  41   b  and another second microwave generation unit  42   b  are coupled with the microwave transmission path  130   b.  Further, a first microwave generation unit  41   c  and a second microwave generation unit  42   c  are coupled with the microwave transmission path  130   c,  and another first microwave generation unit  41   d  and another second microwave generation unit  42   d  are coupled with the microwave transmission path  130   d.  It is to be noted that the first microwave generation units  41   a,    41   b,    41   c,  and  41   d  and the second microwave generation unit  42   a,    42   b,    42   c,  and  42   d  are coupled with the controller  60 . 
         [0047]    It is to be noted that the configuration of the other part of the microwave irradiation apparatus is similar to that of the first embodiment. 
         [0048]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.