JP4304238B2

JP4304238B2 - Method and apparatus for exhaust gas purification of internal combustion engine

Info

Publication number: JP4304238B2
Application number: JP2003086936A
Authority: JP
Inventors: 純一河西; 逸男宮永; 哲也藤田; 彰水野; 健太内藤; 茂樹大八木; 暁千林
Original assignee: Isuzu Motors Ltd
Current assignee: Isuzu Motors Ltd
Priority date: 2003-03-27
Filing date: 2003-03-27
Publication date: 2009-07-29
Anticipated expiration: 2023-03-27
Also published as: JP2004293416A

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車等の内燃機関から排出される排気ガス中の粒子状物質を、その後段で浄化する内燃機関の排気ガス浄化方法及びその装置に関する。
【０００２】
【従来の技術】
ディーゼルエンジンの排気ガスに含まれる粒子状物質（ＰＭ：パティキュレート・マター：以下ＰＭとする）の除去に、ディーゼルパティキュレートフィルタ（ＤＰＦ：Diesel Particulate Filter ：以下ＤＰＦとする）と呼ばれるフィルタで捕集して、外部へ排出されるＰＭの量を低減する技術が開発されている。
【０００３】
このＰＭは主に黒煙（煤）とＳＯＦと呼ばれる燃え残った燃料や潤滑油の成分からなり、ＤＰＦを使用する場合には、通常、ＰＭの粒径が小さいため、フィルタの目を細かくする必要があり、そのため、捕集したＰＭによりＤＰＦが短時間で閉塞する。この閉塞を防ぐために、捕集したＰＭを電気ヒータやバーナ等によって燃焼除去しているが、ＰＭの成分の煤の燃焼温度は通常では５００℃を超えるので、高温発生によるＤＰＦの損傷という問題がある。
【０００４】
つまり、ＰＭは酸素が存在し、燃焼温度以上に維持できれば、自己燃焼してフィルタ部分から除去できて、堆積ムラが無いようにＰＭを均等にＤＰＦに捕集（トラップ）できればＤＰＦにおける燃焼温度を制御し易いが、捕集で蓄積された煤の量が多く不均等になると、ＤＰＦにおける燃焼温度を完全に制御することができなくなり、局部的に高温部分が生じ、ＤＰＦが溶損してしまう。
【０００５】
そのため、Ｏ₂（酸素）による煤の酸化よりも、ＮＯ₂（二酸化窒素）による煤の酸化の方が低い温度で酸化できることを利用して、より低温で捕集した煤を焼却できるように、ＤＰＦの上流側に設けた酸化触媒により排気ガス中のＮＯｘの主成分であるＮＯ（一酸化窒素）を酸化してＮＯ₂とし、このＮＯ₂を下流側のＤＰＦで煤と接触させることにより、２５０℃〜３５０℃前後から燃焼開始させるＰＭの浄化方法及びその装置等が開発されている。また、ＤＰＦの材料表面に酸化触媒を付与したＤＰＦも開発されている。
【０００６】
これらのＰＭの浄化方法及び装置は、高負荷時のエンジンから排出される高温の排気ガスで、捕集した煤が自動的に燃焼するので、連続再生式と呼ばれている。
【０００７】
しかし、これらのＤＰＦは、ＰＭを多く捕集するためには目地を細かくする必要があるが、細かくすると背圧が上昇し、また、目地を粗くしても、使用中にＰＭが堆積してくると、目地を細かくしたのと同様に背圧が上昇する。
【０００８】
この背圧の上昇が生じると、排気に負荷がかかり燃料消費効率や動力性能に著しい悪影響が生じ、更にＤＰＦの目詰まりが進行するとエンジンの停止を余儀なくされ、車両は走行不能となる。そのため、実用上、捕集効率に限界があるという問題がある。
【０００９】
そして、連続再生式のＤＰＦにおいても、捕集により堆積したＰＭを低い温度で焼却処理できるが、３００℃前後までであり、ＤＰＦで連続処理できる温度領域に限界がある。つまり、始動時や低負荷における走行時は十分に排気ガス温度が上昇しないため、燃料噴射におけるポスト噴射や吸気絞り等の手段で排気ガス温度を上昇させてＤＰＦを強制的に再生させるための追加機能が必要となり、幾つかの方法及び装置が提案されている。
【００１０】
この方法及び装置の一つとして、ＤＰＦに電気のプラズマ放電を利用した装置があり、この装置では、特定のプラズマ誘起体をＤＰＦの上流に設置した箇所にマイクロ波を照射することにより効果的にプラズマを発生させ、このプラズマによってフィルター上に補足した黒鉛微粒子（ＰＭ）等を３００℃〜６００℃の範囲で焼却処理するエンジン排ガスの処理方法及びその装置が提案されている（例えば、特許文献１参照。）。
【００１１】
【特許文献１】
特開２００２−３３９７３１号公報
【００１２】
【発明が解決しようとする課題】
一方、図１３に示すように、燃焼炉などの排ガス中の煤を集塵する装置として、線状の高圧電極（コロナ電極）５１と平板状の集塵電極（非コロナ電極）５２が排ガスＧの流れと平行に配置され、コロナ放電等によって帯電した排ガス中の浮遊微粒子は、両電極５１，５２間の不平等電界によって、ドリフトさせられて集塵電極５２に引き寄せられて集塵電極５２上で捕捉される構成になっている電気集塵装置５０がある。
【００１３】
このような構成では、電極間距離を広げると、ドリフト量が大きくなり、捕集されるまでの時間が長くなるため、滞留時間を長くする必要が生じて装置が大きくなったり、これを避けるためにドリフト力を強めて短時間で捕集できるようにしようとすると、非常に高い電圧が必要になったりする。また、装置を小型化するために、電極間距離を狭めると安定なコロナ放電の発生を確保するのが困難となる。つまり、集塵を効率よく行うためには、電界による帯電粒子のドリフト速度と、電極間距離、装置内における帯電粒子滞留時間等を適切に選定する必要があり、車載搭載用の集塵装置とすることが難しいという問題がある。
【００１４】
これらの問題を解決するために、本発明者らは、線状又は通気性を有する面状体のコロナ電極と、このコロナ電極の下流側に間隔を有してコロナ電極に対向して設けた通気性を有する面状体の集塵電極を、排気ガスが通過する方向と交差する方向、好ましくは垂直方向に設けて、コロナ電極と集塵電極との間に発生させたコロナ放電を利用して、排気ガス中のＰＭの捕集する内燃機関の排気ガス浄化方法及びその装置を開発した。
【００１５】
この排気ガス浄化方法及びその装置では、背圧上昇を殆ど伴わずにＰＭを捕集でき、しかも、コロナ電極、集塵電極を排気ガスの流通方向と交差する方向、好ましくは、垂直方向に配置しているので、コロナ電極の近傍で帯電したＰＭを下流側の集塵電極に流れ込ませて、この集塵電極に効率よく捕集する。
【００１６】
この集塵電極としてはメッシュ状金網、パンチングメタル、エキスパンダメタル、コイル状ワイヤ、または、これら集塵電極材料の上流側表面にＤＰＦより１０倍程度以上大きな孔径を有する誘電体材料を配置したもので構成され、ＤＰＦに比べると孔径と開孔率が大きくて目詰まりし難く、また、集塵電極に捕集されたＰＭも排気ガス温度が高くなると燃焼を開始して燃焼除去されるが、排気ガスの低温状態が長時間連続するような場合には、集塵電極にＰＭが堆積して、目詰まりに至る可能性があり、実用上に際しては、この危険性を回避しておく必要があるという問題がある。
【００１７】
本発明は、上述の問題を解決するためになされたものであり、その目的は、電気集塵機の原理を用いて、小型で低電力、且つ、高効率で内燃機関の排気ガス中のＰＭを捕集でき、しかも、集塵電極に捕集及び堆積されたＰＭを、非常に簡単な構成で、且つ、低電力消費で効率よく燃焼除去できる内燃機関の排気ガス浄化方法及びその装置を提供することにある。
【００１８】
【課題を解決するための手段】
以上のような目的を達成するための内燃機関の排気ガス浄化方法は、内燃機関の排気ガス中の粒子状物質を除去する排気ガス浄化方法であって、排気ガスの流れと交差する方向に設けた線状のコロナ電極、又は、排気ガスの流れと交差する方向に設けた通気性を有する面状体のコロナ電極に高電圧を印加すると共に、該コロナ電極の下流側に間隔を有して該コロナ電極に対向して設けられ、かつ、直径が０．１ｍｍ以上１０ｍｍ以下である排気ガスを通過させる孔部を有して通気性を有する面状体のメッシュ状金網で形成され、かつ、排気ガスの流れと交差する方向に設けられた集塵電極の面内に、排気ガスを通過させて、コロナ放電により帯電した排気ガス中の粒子状物質を、前記集塵電極で捕集して排気ガスを浄化し、更に、前記集塵電極の近傍に設けられ、前記集塵電極よりもメッシュが粗くて開孔率が大きいメッシュ状金網で形成され、排気ガスの流れと交差する方向に設けられた燃焼用電極に通電して、該燃焼用電極と前記集塵電極との間に電圧を印加することによって、前記集塵電極に捕集された粒子状物質の捕集量が増加して粒子状物質と前記燃焼用電極との距離が狭まると両者の間に電気的な短絡を発生させて、前記集塵電極に捕集された粒子状物質に電流を流して燃焼除去すると共に、前記集塵電極と前記燃焼用電極の間隙に排気ガス通過性を有する誘電材料を充填したことを特徴とする。
【００１９】
そして、上記の内燃機関の排気ガス浄化方法を実施するための装置は、内燃機関の排気ガス中の粒子状物質を除去する排気ガス浄化装置であって、排気ガスの流れと交差する方向に設けた線状のコロナ電極、又は、排気ガスの流れと交差する方向に設けた通気性を有する面状体のコロナ電極と、該コロナ電極の下流側に間隔を有して該コロナ電極に対向して設けられ、かつ、直径が０．１ｍｍ以上１０ｍｍ以下である排気ガスを通過させる孔部を有して通気性を有する面状体のメッシュ状金網で形成され、かつ、排気ガスの流れと交差する方向に設けられた集塵電極と、該集塵電極の近傍に設けられ、前記集塵電極よりもメッシュが粗くて開孔率が大きいメッシュ状金網で形成され、排気ガスの流れと交差する方向に設けられた燃焼用電極を有して形成されると共に、前記コロナ電極にコロナ放電用の高圧電圧を供給する高電圧供給装置と、前記集塵電極に捕集された粒子状物質の捕集量が増加して粒子状物質と前記燃焼用電極との距離が狭まると両者の間に電気的な短絡を発生させて捕集された粒子状物質に電流を流して燃焼除去するための電流を前記燃焼用電極に供給して、前記燃焼用電極と前記集塵電極との間に電圧を印加する燃焼用電流供給装置を備えると共に、前記集塵電極と前記燃焼用電極の間隙に排気ガス通過性を有する誘電材料を充填したことを特徴として構成される。
【００２０】
排気ガスの流れと交差する方向に設けたとは、排気ガスの主流方向と平行ではないとの意味であり、排気ガスの主流方向を横切って線状のコロナ電極と通気性を有する面状体の集塵電極とが設けられることを意味する。
【００２１】
また、上記の内燃機関の排気ガス浄化装置において、前記燃焼用電極を前記集塵電極の前記コロナ電極側の近傍に設けると共に、前記燃焼用電極の開孔率を、前記集塵電極の開孔率よりも大きくして構成される。なお、この開孔率とは、排気ガス主流方向に垂直な断面において、集塵電極（又は燃焼用電極）のガス通過部断面積が集塵電極（又は燃焼用電極）の全断面積（ガス通過部を含む）に占める割合をいう。
【００２２】
そして、この線状のコロナ電極と通気性を有する面状体の集塵電極及び燃焼用電極の組合せで構成される集塵ユニットとしては、単数又は複数の直線状又は曲線状のコロナ電極と、該コロナ電極と実質的に平行な平面形状の集塵電極及び燃焼用電極の組合せで構成される平面型集塵ユニット、同心円筒面上に配置された複数の直線状又は曲線状のコロナ電極の集合と、該同心円筒と中心を同じくした同心円筒面状の集塵電極及び燃焼用電極との組合せで構成される同心円型集塵ユニット、単数の線状コロナ電極と、該線状コロナ電極を軸とする円筒面状の集塵電極及び燃焼用電極との組合せで構成される同軸円筒型集塵ユニット等がある。
【００２３】
これらの集塵ユニットを単数又は複数組み合わせて排気ガス浄化装置のケース内に組み入れて排気ガス浄化装置を構成する。なお、これらの集塵ユニットにおいて、複数の線状コロナ電極を相互に連結して通気性を有する面状体としてもよい。
【００２４】
また、上記の内燃機関の排気ガス浄化装置において、前記コロナ電極、前記集塵電極、又は、前記燃焼用電極の少なくとも一つを、メッシュ状金網、パンチングメタル、エキスパンダメタル、コイル状ワイヤ、金属繊維の集合体の何れか一つ、又は、これらの組合せで形成する。また、前記集塵電極表面にガス通過用の主たる孔径がＤＰＦよりも１０倍程度以上大きい（孔径０．１ｍｍ以上）ガス通過性のセラミック等誘電材料を配置したもので形成してもよい。
【００２５】
そして、前記集塵電極と前記燃焼用電極の間隙に排気ガス通過性を有する誘電材料を充填したり、前記集塵電極が排気ガスを通過させる孔部を有し、前記孔部の直径が０．１ｍｍ以上１０ｍｍ以下となるように、また、前記誘電材料の排気ガス通過用孔径が０．１ｍｍ以上１０ｍｍ以下となるようにして構成する。また、前記集塵電極と前記燃焼用電極間に印加する電圧の波高値をＶとし、前記集塵電極と前記燃焼用電極間の距離をｄとして、前記集塵電極と前記燃焼用電極間距離の平均電解強度Ｅ＝Ｖ／ｄが３ｋＶ／ｃｍ以上３０ｋＶ／ｃｍ以下となるようにして構成する。
【００２６】
上記の内燃機関の排気ガス浄化方法及びその装置によれば、コロナ電極と集塵電極との間に発生させたコロナ放電を利用して、ガス通過用の主たる孔径がＤＰＦよりも１０倍程度以上大きい集塵電極を用いて、排気ガス中のＰＭを捕集するので、背圧上昇を殆ど伴わずにＰＭを捕集でき、しかも、コロナ電極、集塵電極、燃焼用電極を排気ガスの流通方向と交差する方向、好ましくは、垂直方向に配置しているので、コロナ電極と集塵電極間で形成されるコロナ放電によって帯電したＰＭが直接下流側の集塵電極に流れ込み、この集塵電極に効率よく捕集できる。また、集塵電極の上流側表面にＤＰＦよりも孔径の大きいガス通過性のセラミック等誘電材料を配置することで、誘電材料の分極効果と集塵面積の増大により集塵電極に流れ込むＰＭの捕集効率をさらに改善することができる。
【００２７】
その上、集塵電極の近傍に設けた燃焼用電極に加電することによって、集塵電極もしくは集塵電極表面のガス通過性誘電材料に捕集された粒子状物質を燃焼除去できるので、捕集されたＰＭの燃焼除去のための、電気ヒータ、石油バーナによるＰＭへの直接加熱や、燃料の後噴射等による排気ガスの昇温や、エンジンの性能チューニングや吸気絞り等による排気ガスの昇温等が不用となる。
【００２８】
また、集塵電極表面に、ガス通過性誘電材料（ガス通過用の孔径がＤＰＦより１０倍程度以上大きい誘電材料）を用いた場合、燃焼用電極に加電することによって誘電材料内部に電界が形成され、誘電材料内部に帯電したＰＭがより捕集され易くなる。誘電材料表面及び内表面に捕集されたＰＭが堆積し、燃焼用電極と集塵用電極間で電気的短絡状態となれば、堆積したＰＭを通じて電流が流れて通電加熱によってＰＭが昇温・燃焼開始し、誘電材料内部からＰＭが燃焼除去される。
【００２９】
そして、燃焼用電極に燃焼用電流供給装置から３００Ｖ〜１ｋＶ程度の直流電圧、交流電圧、パルス電圧のいずれかを常時印加しておき、集塵電極に捕集されたＰＭの捕集量が増加してくると、この捕集されたＰＭと燃焼用電極との距離が狭まり、両者の間に電気的な短絡（ショート）状態が生じてＰＭに電流が流れ、この電流によりＰＭは昇温し燃焼（ＰＭの通電加熱燃焼）を開始する。ここで、前記の電気的な短絡状態は、必ずしも集塵電極全面で均質に発生する必要はない。局所的にでも一旦ＰＭの燃焼（通電加熱燃焼）が生じると、ＰＭの燃焼熱により隣接したＰＭが燃焼を開始するので、連鎖的に捕集されたＰＭが燃焼する。そして、捕集されたＰＭが燃焼除去されるとショート状態が解消される。
【００３０】
この装置では、燃焼用電極が常時加電された状態であっても、ＰＭの捕集量の増加によりショートしてＰＭの燃焼を開始した時のみ電力の消費が発生し、燃焼により直ぐにショート状態が解除されると電力の消費も中断されるので、ＰＭ燃焼に使用される電力は極めて僅かで済むことになる。また、ＰＭの捕集量の局所的な増加により、自動的にショート及びＰＭの燃焼除去が行われるので、捕集されたＰＭを燃焼除去させるための制御も不要となる。
【００３１】
しかも、このＰＭの燃焼除去の場合、集塵電極に捕捉されたＰＭは、コロナ放電場に曝されているために、１５０℃〜２００℃といった低温から燃焼を開始できるので、高温燃焼による損傷は生じない。
【００３２】
このように、低い投入電力でＰＭを高い効率で大量に捕集でき、かつ捕集したＰＭを低電力で燃焼除去できるので燃費の悪化も殆ど無い。
【００３３】
【発明の実施の形態】
以下、本発明に係る実施の形態の内燃機関の排気ガス浄化方法及びその装置について、図面を参照しながら説明する。
【００３４】
最初に、本発明に係る実施の形態の排気ガス浄化装置の構成要素となる集塵ユニットについて説明する。図１〜図６に示すように、この集塵ユニット１０，２０は、コロナ放電を発生させるための高電圧を印加するコロナ電極１１，２１と、非コロナ電極である集塵電極１２，２２と、燃焼用電極１３，２３とからなる。
【００３５】
このコロナ電極１１，２１、集塵電極１２，２２、燃焼用電極１３，２３は、通常の金属、特に耐腐食性が要求される場合にはステンレス等を材料として形成される。
【００３６】
このコロナ電極１１，２１は導電性の線状の電極（ワイヤ状電極）で形成され、集塵電極１２，２２は排気ガスＧを通過させると共にコロナ放電で帯電したＰＭを捕集するために、通気性と集塵の利便性を考慮して、図１〜図３に示すような平面状メッシュ体や、図４〜図６に示すような円筒面状メッシュ体等の導電性の通気性を有する面状体で形成される。
【００３７】
また、集塵電極１１，２１としては、メッシュ状金網やパンチングメタル等の穴開き板やエキスパンダメタルを板状、筒状、その他の形状に形成したもの、コイル状ワイヤを加工して板状、筒状、その他の形状にしたもの、ステンレスウール等の金属繊維を集合体にしたもの等、及び、これらの複合体や積層体を用いることができる。
【００３８】
燃焼用電極１３，２３は、集塵電極１２，２２に捕集されたＰＭを通電により燃焼除去するためのものであり、集塵電極１２，２２の近傍に隣接して設けられる。そして、ＰＭは集塵電極１２，２２のコロナ電極側１１，２１に多く堆積するので、この燃焼用電極１３，２３もコロナ電極側１１，２１に設ける。即ち、この燃焼用電極１３，２３は、コロナ電極１１，２１と集塵電極１２，２２の間に配置される。言い換えれば、集塵電極１２，２２と燃焼用電極１３，２３で、互いに絶縁されたＰＭ燃焼用の二重構造を形成する。
【００３９】
そして、燃焼用電極１３，２３は、集塵電極１１，２１と同様にメッシュ状金網等で形成できるが、その開孔率は、集塵電極１２，２２の開孔率より大きく形成する。つまり、燃焼用電極１３，２３は、集塵電極１２，２２よりメッシュを粗く形成する。
【００４０】
このコロナ電極１１，２１と集塵電極１２，２２と燃焼用電極１３，２３を互いに電気的に絶縁状態で一組にして、集塵電極１２，２２をコロナ電極１１，２１の下流側に間隔を有してこのコロナ電極１１，２１に対向して設けた状態で、排気ガス浄化装置のケース内に配置し、しかも、このコロナ電極１１，２１と集塵電極１２，２２は、排気ガスＧの主流方向と交差する方向、好ましくは垂直方向になるように配置する。即ち、排気ガスＧがコロナ電極１１，２１を横切って集塵電極１２，２２の面内に流入及び面内を通過するように配置する。そして、更に、燃焼用電極１３，２３を集塵電極１２，２２の近傍、例えば、１〜２ｍｍ程度の間隔を有して配置して設ける。
【００４１】
図７に、線状コロナ電極１１と、このコロナ電極１１と平行な平面状メッシュ体の集塵電極１２及び燃焼用電極１３で形成される平面型集塵ユニット１０Ａを排気ガス浄化装置１Ａに組み込んだ例を示す。
【００４２】
図８に、金網等の平面状メッシュ体のコロナ電極１１と、このコロナ電極１１と平行な平面状メッシュ体の集塵電極１２及び燃焼用電極１３で形成される平面型集塵ユニット１０Ｂを排気ガス浄化装置１Ｂに組み込んだ例を示す。
【００４３】
また、図９に、同心円筒面上に配置された複数の線状コロナ電極１１の集合と、この同心円筒と中心を同じくした同心円筒面状の円筒面状メッシュ体の集塵電極１２及び燃焼用電極１３，２３との組合せで構成される同心円型集塵ユニット１０Ｃを排気ガス浄化装置１Ｃに組み込んだ例を示す。
【００４４】
この図９の構成の場合には、排気ガスＧは、排気ガス入口２から中央の通路を通り、放射方向に流れて浄化区画３を通過して、同心円型集塵ユニット１０ＣでＰＭを捕集された後、外側通路６を経由して排気ガス出口４に至る。
【００４５】
なお、平面型集塵ユニット１０Ａや同心円型集塵ユニット１０Ｃにおいて、複数の線状コロナ電極１１を相互に連結した通気性を有する面状体で形成してもよく、この面状体は、集塵電極１２，２２と同様に、メッシュ状金網等で形成できるが、コロナ放電用であるので目は粗くてよく、そのメッシュ間隔や開孔率は集塵電極１２，２２より大きくして、より通気抵抗の少ないものとする。
【００４６】
また、図１０及び図１１に、単数の線状コロナ電極２１と、この線状コロナ電極２１を軸とする円筒面状の円筒面状メッシュ体の集塵電極２２及び燃焼用電極２３との組合せで構成される同軸円筒型集塵ユニット２０を排気ガス浄化装置１Ｅ，１Ｆに組み込んだ例を示す。この図１１の場合も、図９と同様に、排気ガスＧは、排気ガス入口２から中央の通路を通り、放射方向に流れて浄化区画３を通過して外側通路６を経由して、排気ガス出口４に至る。
【００４７】
例えば、車載用としては、図８、図９、図１１の排気ガス浄化装置１Ｂ，１Ｃ，１Ｆは、通常のマフラー（消音装置）と同じ円筒形状にでき、車載時のレイアウトや取付構造面で実用性の高い装置となる。
【００４８】
そして、図１２に示すように、この排気ガス浄化装置１Ａ〜１Ｆを車両用ディーゼルエンジンに適用する場合は、ディーゼルエンジン３１の排気通路３２のマフラー３３の上流側に配置され、ディーゼルエンジンの制御系３４からの信号で制御され、バッテリー３５から電力の供給を受ける電力供給装置３６から電力供給される。この電力供給装置３６は高電圧供給装置３６ａと燃焼用電流供給装置３６ｂを有して構成される。
【００４９】
排気ガス浄化装置１Ａ〜１Ｆのコロナ電極１１，２１には、この高電圧供給装置３６ａから直流電圧、交流電圧、パルス電圧等のいずれかの高電圧を印加し、一方の集塵電極１２，２２をアースすることにより、コロナ電極１１，２１と集塵電極１２，２２との間に不平等電界を形成する。この交流電圧の周波数としては５０Ｈｚ〜１０ｋＨｚのものが適しているが、特に正弦波状である必要はなく、矩形状のものであってもよい。印加電圧の種類としては、直流電圧が投入電力あたりのＰＭ捕集率で優れており、電気系の構成装置も比較的簡略化できる。直流電圧としては負電圧でも正電圧でも十分な効果が得られるが、概して正電圧にしたほうが投入電力あたりのＰＭ捕集率で優れている。なお、周辺装置の仕様等によっては総合的な判断で交流電圧やパルス電圧のほうが良い場合もある。
【００５０】
印加電圧の波高値Ｖとしては、コロナ電極１１，２１にコロナ放電を形成するに足る電圧であればよく、コロナ電極１１，２１と接地電極１２，２２の形状と空間的配置から決定されるコロナ開始電圧をもとに設定すればよい。車載用排気ガス浄化装置であれば５ｋＶ〜４０ｋＶ程度、固定排出源用排気ガス浄化装置であれば５ｋＶ〜１００ｋＶ程度の範囲が適当である。
【００５１】
この高電圧の印加により、コロナ電極１１，２１の近傍に不平等電界が形成され、コロナ電極１１，２１を中心として、局所的にガスが非破壊放電すなわちコロナ放電空間が形成される。このコロナ放電によって、ガス中には高速電子と高速電子が衝突して電離された正イオンや電子付着による負イオンが多数形成される。このコロナ放電空間にＰＭが含まれた排気ガスＧを流通させると、電子・正イオン・負イオンとＰＭが衝突することによってＰＭは殆ど瞬間的に荷電され、帯電したＰＭはクーロン力によって集塵電極１２，２２に捕集される。
【００５２】
このとき、処理する排気ガスＧの流れをコロナ電極１１，２１や集塵電極１２，２２が遮る方向に、これらの電極１１，２１，１２，２２を配置し、コロナ電極１１，２１の下流側に通気性を有する面状体の集塵電極１２，２２が配置されているので、帯電されたＰＭは電界及びクローン力によるドリフト効果が小さくても、集塵電極１２，２２に捕集される確率が高くなり、効率よく集塵電極１２，２２に捕集されることになる。そのため、低い消費電力でＰＭを高効率で除去できる。
【００５３】
また、図１４のように集塵電極１２，２２と燃焼用電極１３間にガス通過性を有する誘電材料２５を配置してもよい。図１４（ａ）は図１〜図３に示すような平面型集塵ユニットを代表例として、燃焼用電極１３と集塵電極１２の間にガス通過性誘電材料２５を挟み込んだものである。図１４（ｂ）は、集塵電極１２の上流側にも下流側にも燃焼用電極１３を配置し、下流側の燃焼用電極１３と集塵電極１２の間にガス通過性誘電材料２５を配置したものであり、上流側の集塵電極１２表面で捕集しきれなかったＰＭを再度捕集させる構造となっている。図１４（ｃ）は、集塵電極１２の上流側にも下流側にも燃焼用電極１３を配置し、両方の燃焼用電極１３と集塵電極１２間にガス通過性誘電材料２５を挟み込んだものである。
【００５４】
このような構成において、集塵電極１２と燃焼用電極１３間に電圧を印加すれば誘電材料２５内部に電界が形成され、ＰＭ捕集効率が更に向上する。図１４の例では、燃焼用電極１３に印加する電圧は捕集ＰＭの燃焼用のみならず、ガス通過性誘電材料２５へのＰＭ捕集効率向上の役割も兼ねる。ガス通過性誘電材料２５は集塵電極１２、燃焼用電極１３に直接接触していてもよいし、適当なスペーサを介して数ｍｍ程度以下の空間を挟んで集塵電極１２、燃焼用電極１３間に配置されていてもよい。
【００５５】
ガス通過性誘電材料２５としては、ＤＰＦよりも孔径が１０倍程度大きい、より具体的には孔径が０．１ｍｍ程度以上の材料を用いればよいが、ＰＭ燃焼による損傷を避けるため、融点が高く耐熱性に優れた材料が好適であり、図１５に示すようなセラミック粒子の集合体２５Ａ、多孔質セラミック又はセラミック繊維の集合体のセラミックフィルタ２５Ｂ、セラミックハニカム２５Ｃ等が適している。
【００５６】
このコロナ放電を利用して電気集塵作用で捕集されたＰＭは、通常の物理的なフィルタで機械的にトラップする場合に比べ、より繊細なＰＭの粒子を選択的に捕集することができ、かなり長時間連続運転しても目詰まりの恐れがない。
【００５７】
また、コロナ電極１１，２１は線状又は通気性を有する面状体の電極で形成され、集塵電極１２，２２及び燃焼用電極１３，２３は、通気性を有する面状体で形成されるが、この面状体はメッシュ体のように、孔径と開孔率が大きく、その孔径はＤＰＦの１０倍程度以上でよいので、排気ガスＧの流れの方向と交差する方向（通常は垂直な方向）に配置されても、排気ガスＧの流路を大きく塞がないので、排気ガス抵抗が著しく小さく、背圧上昇を殆ど伴わない。
【００５８】
その上、電極間距離、所要電圧（消費電力）、排気ガス滞留時間をほぼ独立に選定することができ、また、スペース等の制約がある場合でも安定的なコロナ放電を形成できるので、排気ガス浄化装置のコンパクト化を図ることができる。
【００５９】
そして、この集塵電極１２，２２に捕集されたＰＭを燃焼除去するために燃焼用電極１３，２３に、燃焼用電流供給装置３６ｂから３００Ｖ〜１ｋＶ程度の直流電圧、交流電圧、パルス電圧を常時連続的に印加する。印加する電圧波高値Ｖは、燃焼用電極１３，２３と集塵電極１２，２２の間隙ｄに依存し、電圧波高値Ｖを間隙ｄで除した平均電界強度Ｅ（＝Ｖ／ｄ）を３ｋＶ／ｃｍ以上とすればＰＭの燃焼除去を速やかに行うことができることを実験的に見出している。傾向として、電圧波高値Ｖが高い程ＰＭ燃焼が速やかに行われることがわかっており、例えば、ＰＭ堆積量に応じて電圧を制御してもよい。
【００６０】
より具体的には直流電圧印加の場合は電圧波高値Ｖを、交流電圧印加の場合は電圧波高値Ｖ若しくは周波数を、パルス電圧印加の場合は電圧波高値Ｖ若しくは繰り返し率を変化させることによって、ＰＭ堆積量が多いときには平均電圧が高くなるように制御してやればよい。ＰＭ堆積量の評価としては、エンジンモード等で予めわかっている場合にはプログラム制御で対応することもできるし、集塵電極１２，２２前後の圧力損失をモニタリングすることでフィードバック制御をすることも可能である。
【００６１】
また、印加する電圧波高値ＶをＥ＝２０〜２５ｋＶ／ｃｍ以上となるようにすると、燃焼用電極１３，２３と集塵電極１２，２２間の空間で火花放電が発生するようになる。この特性は、燃焼用電極１３，２３と集塵電極１２，２２間の空間にガス通過性誘電材料２５を挟み込んだ場合でも略同様である。この火花放電をもって、堆積したＰＭの着火燃焼除去するここも可能である。常時火花放電を発生させるような電圧を印加することは燃焼用電極１３，２３、集塵電極１２，２２、ガス通過性誘電材料２５の損傷、並びに消費電力の点で好ましくないが、例えば、図１６のように、一時的に電圧波高値Ｖを火花発生電圧レベルに上げたようなパターンの電圧を印加してもよい。電圧波高値Ｖを一時的に火花発生電圧レベルに上げる時間及び時間的頻度は、ＰＭ堆積量に応じて制御してやればよい。
【００６２】
この電圧の印加及び電流の供給により、集塵電極１２，２２に捕集されたＰＭの捕集量が増加してくると、この捕集されたＰＭとこの集塵電極１２，２２に近接して設けられた燃焼用電極１３，２３との間の電気的な短絡（ショート）が生じてＰＭに電流が流れ、ＰＭはこの電流により昇温し燃焼を開始する。
【００６３】
一旦ＰＭの燃焼が生じると、ＰＭの燃焼熱により隣接したＰＭが昇温して燃焼を開始し、連鎖的に捕集されたＰＭが燃焼する。また、この捕集されたＰＭが燃焼除去されるとショート状態が解消され、電力消費も止まる。
【００６４】
この場合に、燃焼用電極１３，２３が常時通電された状態であっても、ＰＭの捕集が少ない場合には捕集されたＰＭと集塵電極１２，２２の間には絶縁状態が維持され電力の消費は生じないので、また、ＰＭの捕集量の増加によりショートしてＰＭの燃焼を開始すると、燃焼により直ちにショート状態が解除されるので、ＰＭ燃焼に使用される電力は極めて僅かで済むことになる。
【００６５】
また、ＰＭの捕集量の局所的な増加により、自動的にショート及びＰＭの燃焼除去が行われるので、捕集されたＰＭを燃焼除去させるための制御も不要となる。
【００６６】
しかも、このＰＭの燃焼除去の場合、集塵電極１２，２２に捕捉されたＰＭは、コロナ放電場に曝されているために、１５０℃〜２００℃といった低温から燃焼を開始できるので、高温燃焼による損傷は生じない。
【００６７】
そして、更に、コロナ電極１１，２１や集塵電極１２，２２や燃焼用電極１３，２３に白金や酸化チタン等の酸化力をもった触媒成分を担持又は塗布することによりＰＭの燃焼を促進できる。この場合に各電極ともコロナ放電場に曝されているため、触媒が相乗効果を発揮して、より低温でもＰＭを燃焼させることが可能となる。そのため、排気ガス温度を感知又はモニターするＯＮ／ＯＦＦ制御機能を追加して、排気ガス温度が触媒が機能する高温領域の場合には、燃焼用電極１３，２３への通電をＯＦＦにして、触媒機能が低下する低温領域の場合のみ通電をＯＮにすればよいことになる。
【００６８】
なお、本発明は、燃料の性状や燃焼方式、また、その普及率から、軽油を燃料とするディーゼルエンジンが主要な対象となるが、これに限定されず、また、自動車搭載の内燃機関のみならず、各種産業用機械や定置式の内燃機関にも適用可能である。
【００６９】
【発明の効果】
以上の説明したように、本発明の排気ガス浄化方法及びその装置によれば、コロナ電極と集塵電極との間に発生させたコロナ放電を利用して、排気ガス中のＰＭの捕集するので、背圧上昇を殆ど伴わずにＰＭを捕集でき、しかも、コロナ電極、集塵電極、燃焼用電極を排気ガスの流通方向と交差する方向に配置しているので、コロナ電極の近傍で帯電したＰＭを下流側の集塵電極に流れ込ませて、この集塵電極に効率よく捕集させることができる。
【００７０】
そして、集塵電極に捕集されたＰＭの量が増加してくると、この捕集されたＰＭと燃焼用電極との距離が狭まり、両者の間に電気的な短絡（ショート）が生じてＰＭに電流が流れる。この電流によりＰＭは昇温し燃焼を開始し、一旦ＰＭの燃焼が生じると、ＰＭの燃焼熱により隣接したＰＭが昇温し燃焼を開始するので、連鎖的に捕集されたＰＭを燃焼除去できる。
【００７１】
この場合に、燃焼用電極が常時通電された状態であっても、ＰＭの捕集量の増加によるショートでＰＭの燃焼を開始した時のみ電力の消費が発生し、燃焼により直ぐにショート状態が解除され、電力の消費も中断されるので、極めて僅か電力でＰＭ燃焼を効率よく行うことができる。
【００７２】
また、ＰＭの捕集量の局所的な増加により、自動的にショート及びＰＭの燃焼除去が行われるので、捕集されたＰＭを燃焼除去させるための制御も不要となる。
【００７３】
従って、低い投入電力でＰＭを高い効率で捕集でき、しかも、捕集したＰＭを燃焼用電極という非常に簡単な機構と少ない電力消費で自動的に燃焼除去できる。また、投入電力が低くて済むので燃費の悪化も殆ど無い。
【図面の簡単な説明】
【図１】本発明に係る実施の形態の内燃機関の排気ガス浄化装置の構成要素である平面型集塵ユニットの構成を示す模式的な斜視図である。
【図２】図１の平面型集塵ユニットの側面図である。
【図３】図１の平面型集塵ユニットの平面図である。
【図４】本発明に係る実施の形態の内燃機関の排気ガス浄化装置の構成要素である同軸円筒型集塵ユニットの構成を示す模式的な斜視図である。
【図５】図４の平面型集塵ユニットの側面図である。
【図６】図５の平面型集塵ユニットの平面図である。
【図７】本発明に係る第１の実施の形態の内燃機関の排気ガス浄化装置の構成を示す模式的な側断面図である。
【図８】本発明に係る第２の実施の形態の内燃機関の排気ガス浄化装置の構成を示す模式的な側断面図である。
【図９】本発明に係る第３の実施の形態の内燃機関の排気ガス浄化装置の構成を示す模式的な図で、（ａ）は横断面図で、（ｂ）は側断面図である。
【図１０】本発明に係る第４の実施の形態の内燃機関の排気ガス浄化装置の構成を示す模式的な図で、（ａ）は側断面図で、（ｂ）は平断面図である。
【図１１】本発明に係る第５の実施の形態の内燃機関の排気ガス浄化装置の構成を示す模式的な図で、（ａ）は横断面図で、（ｂ）は側断面図である。
【図１２】本発明に係るの内燃機関の排気ガス浄化装置を車載した場合の構成例を示す図である。
【図１３】従来技術の電気集塵装置の構造を模式的に示す平断面図である。
【図１４】本発明に係る第６の実施の形態の内燃機関の排気ガス浄化装置の構成を示す模式的な図で、燃焼用電極と集塵電極の間にガス通過性誘電材料を挟み込む代表的構造を示す模式的な図で、（ａ）は三層構造を示す図で、（ｂ）は四層構造を示す図で、（ｃ）は五層構造を示す図である。
【図１５】図１４のガス通過性誘電材料の代表的な例を示す模式図で、（ａ）はセラミック粒子を示す図で、（ｂ）は多孔質セラミック又はセラミック繊維集合体を示す図で、（ｃ）はハニカム状セラミクフィルタを示す図である。
【図１６】燃焼用電極に印加する電圧波形の一例を示す図である。
【符号の説明】
１Ａ〜１Ｆ排気ガス浄化装置
１０平面型集塵ユニット
１０Ｃ同心円型集塵ユニット
１１コロナ電極
１２集塵電極（平面状メッシュ体）
１２Ｃ集塵電極（円筒面状メッシュ体）
１３燃焼用電極
２０同軸円筒型集塵ユニット
２１コロナ電極
２２集塵電極（円筒面状メッシュ体）
２３燃焼用電極
２５ガス通過性誘電材料
２５Ａセラミック粒子
２５Ｂ多孔質セラミック又はセラミック繊維の集合体
２５Ｃハニカム状セラミックフィルタ
３６ａ高電圧供給装置
３６ｂ燃焼用電流供給装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification method for an internal combustion engine and an apparatus therefor, which purifies particulate matter in exhaust gas discharged from an internal combustion engine such as an automobile at a subsequent stage.
[0002]
[Prior art]
To remove particulate matter (PM: particulate matter: hereinafter referred to as PM) contained in exhaust gas from diesel engines, it is collected with a filter called diesel particulate filter (hereinafter referred to as DPF). Thus, a technique for reducing the amount of PM discharged to the outside has been developed.
[0003]
This PM is mainly composed of black smoke (soot) and unburned fuel and lubricating oil components called SOF. When DPF is used, the particle size of the PM is usually small, so the eyes of the filter are made finer. Therefore, the DPF is blocked by the collected PM in a short time. In order to prevent this blockage, the collected PM is burned and removed by an electric heater, a burner or the like, but the burning temperature of soot as a component of the PM usually exceeds 500 ° C. Therefore, there is a problem of DPF damage due to high temperature generation. is there.
[0004]
In other words, if there is oxygen in the PM and it can be maintained above the combustion temperature, it can be self-combusted and removed from the filter part. If PM can be evenly collected (trapped) in the DPF so that there is no accumulation unevenness, the combustion temperature in the DPF can be increased. Although it is easy to control, if the amount of soot accumulated by collection is large and uneven, the combustion temperature in the DPF cannot be completely controlled, a high temperature portion is locally generated, and the DPF is melted.
[0005]
Therefore, O₂Rather than oxidation of soot by oxygen₂Utilizing the fact that soot oxidation with (nitrogen dioxide) can be oxidized at a lower temperature, so that the soot collected at a lower temperature can be incinerated, the oxidation catalyst provided on the upstream side of the DPF can reduce the NOx in the exhaust gas. NO (nitrogen monoxide), the main component, is oxidized to NO₂And this NO₂A PM purification method and apparatus for starting combustion from around 250 ° C. to 350 ° C. by bringing the slag into contact with the soot at the downstream DPF have been developed. A DPF having an oxidation catalyst applied to the surface of the DPF material has also been developed.
[0006]
These PM purification methods and devices are called continuous regeneration because the soot collected is automatically burned by high-temperature exhaust gas discharged from the engine under high load.
[0007]
However, these DPFs require fine joints to collect a large amount of PM, but if they are made fine, the back pressure increases, and even if the joints are rough, PM accumulates during use. When it comes, the back pressure rises as if the joints were made finer.
[0008]
When this back pressure rises, exhaust is loaded and fuel consumption efficiency and power performance are significantly adversely affected. Further, when the clogging of the DPF progresses, the engine is forced to stop and the vehicle cannot run. Therefore, there is a problem that there is a limit to the collection efficiency in practical use.
[0009]
Even in a continuous regeneration type DPF, PM deposited by collection can be incinerated at a low temperature, but is up to around 300 ° C., and there is a limit to the temperature range in which DPF can be continuously processed. In other words, since the exhaust gas temperature does not rise sufficiently during start-up or when running at low load, additional DPF is forcibly regenerated by increasing the exhaust gas temperature by means such as post-injection or intake throttle in fuel injection. Functionality is required and several methods and devices have been proposed.
[0010]
As one of this method and apparatus, there is an apparatus using an electric plasma discharge in the DPF. In this apparatus, it is effective to irradiate a portion where a specific plasma inducer is installed upstream of the DPF with microwaves. There has been proposed an engine exhaust gas treatment method and apparatus for generating plasma and incinerating graphite fine particles (PM) and the like captured on the filter by the plasma in a range of 300 ° C. to 600 ° C. (for example, Patent Document 1). reference.).
[0011]
[Patent Document 1]
JP 2002-339931 A
[0012]
[Problems to be solved by the invention]
On the other hand, as shown in FIG. 13, as a device for collecting soot in exhaust gas such as a combustion furnace, a linear high voltage electrode (corona electrode) 51 and a flat dust collection electrode (non-corona electrode) 52 are exhaust gas G. The suspended fine particles in the exhaust gas, which are arranged in parallel with the flow of the gas and are charged by corona discharge or the like, are caused to drift by the unequal electric field between the electrodes 51, 52 and are attracted to the dust collecting electrode 52. There is an electrostatic precipitator 50 configured to be captured by the
[0013]
In such a configuration, if the distance between the electrodes is increased, the amount of drift increases and the time until collection is increased, so that it is necessary to lengthen the residence time, and the apparatus becomes larger and this is avoided. If you try to increase the drift force and make it possible to collect in a short time, a very high voltage will be required. In addition, if the distance between the electrodes is reduced in order to reduce the size of the device, it is difficult to ensure stable generation of corona discharge. In other words, in order to efficiently collect dust, it is necessary to appropriately select the drift velocity of the charged particles due to the electric field, the distance between the electrodes, the charged particle residence time in the device, and the like. There is a problem that it is difficult to do.
[0014]
In order to solve these problems, the present inventors have provided a corona electrode having a linear or air-permeable planar body and a gap on the downstream side of the corona electrode so as to face the corona electrode. Use a corona discharge generated between the corona electrode and the dust collecting electrode by providing a planar dust collecting electrode with air permeability in a direction intersecting the exhaust gas passage direction, preferably in the vertical direction. Thus, an exhaust gas purification method and apparatus for an internal combustion engine that collects PM in the exhaust gas have been developed.
[0015]
In this exhaust gas purification method and apparatus, PM can be collected with little increase in back pressure, and the corona electrode and the dust collection electrode are arranged in a direction intersecting with the exhaust gas flow direction, preferably in a vertical direction. Therefore, PM charged in the vicinity of the corona electrode flows into the dust collecting electrode on the downstream side, and is efficiently collected by the dust collecting electrode.
[0016]
As this dust collecting electrode, a mesh wire mesh, punching metal, expander metal, coiled wire, or a dielectric material having a hole diameter about 10 times larger than DPF on the upstream surface of these dust collecting electrode materials is arranged. Compared to DPF, the hole diameter and the hole area ratio are large and clogging is difficult, and PM collected by the dust collecting electrode starts to burn and is removed by combustion when the exhaust gas temperature rises. When the low temperature state of the exhaust gas continues for a long time, PM may accumulate on the dust collecting electrode and lead to clogging. In practical use, it is necessary to avoid this danger. There is a problem that there is.
[0017]
The present invention has been made to solve the above-described problems, and its purpose is to capture PM in the exhaust gas of an internal combustion engine with a small size, low power, and high efficiency using the principle of an electrostatic precipitator. To provide an exhaust gas purification method and apparatus for an internal combustion engine that can collect and collect and collect PM collected and deposited on a dust collection electrode with a very simple configuration and with low power consumption. It is in.
[0018]
[Means for Solving the Problems]
An exhaust gas purification method for an internal combustion engine for achieving the above object is an exhaust gas purification method for removing particulate matter in the exhaust gas of an internal combustion engine, and is provided in a direction crossing the flow of the exhaust gas. LinearA high voltage is applied to the corona electrode of the sheet or a planar corona electrode having air permeability provided in a direction crossing the flow of the exhaust gas, and the corona electrode is spaced downstream from the corona electrode. And is formed of a mesh-like metal mesh having a planar body having a hole having a diameter of 0.1 mm or more and 10 mm or less for allowing exhaust gas to pass therethrough, and of exhaust gas. Exhaust gas is allowed to pass through the surface of the dust collecting electrode provided in the direction intersecting the flow, and particulate matter in the exhaust gas charged by corona discharge is collected by the dust collecting electrode to collect the exhaust gas. Purified, and further provided in the vicinity of the dust collecting electrode, formed of a mesh metal mesh having a coarser mesh and a larger porosity than the dust collecting electrode, and a combustion provided in a direction intersecting with the flow of exhaust gas Energizing the electrode for combustion and the electrode for combustion When a voltage is applied between the dust collecting electrode and the collected amount of the particulate matter collected by the dust collecting electrode is increased, the distance between the particulate matter and the combustion electrode is reduced. An electric short circuit is generated between the dust collection electrode and the particulate matter collected by the dust collection electrode is burned and removed by passing an electric current, and an exhaust gas passage property is provided between the dust collection electrode and the combustion electrode. It is characterized by being filled with a dielectric material having
[0019]
An apparatus for carrying out the above exhaust gas purification method for an internal combustion engine is an exhaust gas purification apparatus that removes particulate matter in the exhaust gas of the internal combustion engine, and is provided in a direction crossing the flow of the exhaust gas. LinearA corona electrode having air permeability provided in a direction intersecting the flow of exhaust gas, and facing the corona electrode with a space downstream of the corona electrode. And is formed of a mesh-like metal mesh of a planar body having a hole having a diameter of 0.1 mm or more and 10 mm or less for allowing exhaust gas to pass therethrough and crossing the flow of the exhaust gas. Provided in the direction that intersects the flow of exhaust gas, and is formed in the vicinity of the dust collection electrode, and is formed of a mesh wire mesh with a coarser mesh and a larger porosity than the dust collection electrode. A high voltage supply device for supplying a high voltage for corona discharge to the corona electrode, and a collection amount of particulate matter collected by the dust collection electrode. Between the particulate matter and the combustion electrode When the separation is narrowed, an electric short circuit is generated between the two, and a current is supplied to the combustion electrode by flowing an electric current through the collected particulate matter, and the combustion electrode and the combustion electrode are supplied. A combustion current supply device for applying a voltage between the dust collection electrode and the dust collection electrode is provided, and a gap between the dust collection electrode and the combustion electrode is filled with a dielectric material having an exhaust gas permeability.It is configured as a feature.
[0020]
Providing in a direction intersecting with the flow of exhaust gas means that it is not parallel to the main flow direction of exhaust gas, and a linear corona electrode and a planar body having air permeability across the main flow direction of exhaust gas. It means that a dust collecting electrode is provided.
[0021]
Further, in the above exhaust gas purifying apparatus for an internal combustion engine, the combustion electrode is provided in the vicinity of the corona electrode side of the dust collection electrode, and the aperture ratio of the combustion electrode is set to the opening of the dust collection electrode. It is configured to be larger than the rate. The open area ratio means that the cross-sectional area of the gas passage part of the dust collection electrode (or combustion electrode) is the total cross-sectional area (gas) of the dust collection electrode (or combustion electrode) in the cross section perpendicular to the exhaust gas mainstream direction. The percentage of the total (including the passing part).
[0022]
And, as a dust collection unit composed of a combination of this linear corona electrode and a dust-collecting electrode having a breathable planar body and a combustion electrode, a single or a plurality of linear or curved corona electrodes, A planar dust collection unit comprising a combination of a planar dust collection electrode and a combustion electrode substantially parallel to the corona electrode, and a plurality of linear or curved corona electrodes arranged on a concentric cylindrical surface A concentric circular dust collecting unit composed of a set, a concentric cylindrical surface-shaped dust collecting electrode having the same center as the concentric cylinder, and a combustion electrode, a single linear corona electrode, and the linear corona electrode There is a coaxial cylindrical dust collection unit constituted by a combination of a cylindrical surface-shaped dust collection electrode and a combustion electrode.
[0023]
One or a plurality of these dust collection units are combined and incorporated in the case of the exhaust gas purification device to constitute the exhaust gas purification device. In these dust collecting units, a plurality of linear corona electrodes may be connected to each other to form a planar body having air permeability.
[0024]
Further, in the exhaust gas purifying apparatus for an internal combustion engine, at least one of the corona electrode, the dust collecting electrode, or the combustion electrode may be a mesh wire mesh, punching metal, expander metal, coiled wire, metal It is formed of any one of the fiber aggregates or a combination thereof. Alternatively, the dust collecting electrode may be formed by disposing a dielectric material such as a gas-permeable ceramic whose main hole diameter for passing gas is about 10 times or more larger than DPF (hole diameter: 0.1 mm or more).
[0025]
The gap between the dust collection electrode and the combustion electrode is filled with a dielectric material having exhaust gas permeability, or the dust collection electrode has a hole through which exhaust gas passes, and the diameter of the hole is 0. The exhaust gas passage hole diameter of the dielectric material is 0.1 mm or more and 10 mm or less so that it is 1 mm or more and 10 mm or less. The peak value of the voltage applied between the dust collection electrode and the combustion electrode is V, and the distance between the dust collection electrode and the combustion electrode is d, and the distance between the dust collection electrode and the combustion electrode. The average electrolysis strength E = V / d is 3 kV / cm or more and 30 kV / cm or less.
[0026]
According to the above exhaust gas purification method and apparatus for an internal combustion engine, the main hole diameter for gas passage is about 10 times or more than DPF by using corona discharge generated between the corona electrode and the dust collecting electrode. Since PM in exhaust gas is collected using a large dust collection electrode, PM can be collected with almost no increase in back pressure, and exhaust gas flows through the corona electrode, dust collection electrode, and combustion electrode. Since it is arranged in a direction crossing the direction, preferably in the vertical direction, PM charged by corona discharge formed between the corona electrode and the dust collecting electrode flows directly into the dust collecting electrode on the downstream side, and this dust collecting electrode Can be collected efficiently. In addition, by disposing a dielectric material such as a gas-permeable ceramic having a larger pore diameter than the DPF on the upstream surface of the dust collection electrode, the PM flowing into the dust collection electrode due to the polarization effect of the dielectric material and the increase in the dust collection area can be captured. The collection efficiency can be further improved.
[0027]
In addition, by applying electricity to the combustion electrode provided in the vicinity of the dust collection electrode, particulate matter collected on the dust collection electrode or the gas-permeable dielectric material on the surface of the dust collection electrode can be removed by combustion. For the purpose of burning and removing the collected PM, direct heating of the PM by an electric heater or oil burner, temperature rise of exhaust gas by post-injection of fuel, etc., exhaust gas rise by engine performance tuning, intake throttle, etc. Temperature etc. are unnecessary.
[0028]
In addition, when a gas-permeable dielectric material (a dielectric material whose gas passage hole diameter is about 10 times or more than DPF) is used on the surface of the dust collection electrode, an electric field is generated inside the dielectric material by applying electric power to the combustion electrode. The PM that is formed and charged inside the dielectric material is more easily collected. If PM collected on the dielectric material surface and the inner surface is deposited and an electrical short circuit occurs between the combustion electrode and the dust collection electrode, a current flows through the deposited PM, and the temperature of the PM rises due to current heating. Combustion starts, and PM is burned and removed from inside the dielectric material.
[0029]
Then, any of DC voltage, AC voltage, and pulse voltage of about 300 V to 1 kV is always applied to the combustion electrode from the combustion current supply device, and the amount of PM collected on the dust collection electrode increases. As a result, the distance between the collected PM and the combustion electrode is reduced, an electrical short circuit occurs between the two, and a current flows through the PM. Combustion (PM energization heating combustion) is started. Here, the electrical short circuit state does not necessarily have to occur uniformly on the entire surface of the dust collection electrode. Even if locally, once PM combustion (electrically heated combustion) occurs, adjacent PMs start to combust due to the combustion heat of PM, and thus the PM collected in a chain is combusted. Then, when the collected PM is removed by combustion, the short state is eliminated.
[0030]
In this device, even when the combustion electrode is constantly energized, power is consumed only when the PM is short-circuited due to an increase in the amount of PM collected and combustion of the PM is started. When is released, power consumption is also interrupted, so very little power is used for PM combustion. Moreover, since the short circuit and PM combustion removal are automatically performed due to the local increase in the amount of collected PM, control for burning and removing the collected PM becomes unnecessary.
[0031]
In addition, in the case of this PM removal by combustion, the PM trapped by the dust collecting electrode is exposed to the corona discharge field, so combustion can be started from a low temperature of 150 ° C. to 200 ° C. Does not occur.
[0032]
In this way, a large amount of PM can be collected with high efficiency with low input power, and the collected PM can be burned and removed with low power, so there is almost no deterioration in fuel consumption.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an exhaust gas purification method and apparatus for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings.
[0034]
Initially, the dust collection unit used as the component of the exhaust-gas purification apparatus of embodiment which concerns on this invention is demonstrated. As shown in FIGS. 1 to 6, the dust collection units 10 and 20 include corona electrodes 11 and 21 that apply a high voltage for generating corona discharge, and dust collection electrodes 12 and 22 that are non-corona electrodes. And the combustion electrodes 13 and 23.
[0035]
The corona electrodes 11, 21, dust collecting electrodes 12 and 22, and combustion electrodes 13 and 23 are made of a normal metal, particularly stainless steel or the like when corrosion resistance is required.
[0036]
The corona electrodes 11 and 21 are formed of conductive linear electrodes (wire-like electrodes), and the dust collection electrodes 12 and 22 pass exhaust gas G and collect PM charged by corona discharge. In consideration of air permeability and convenience of dust collection, conductive air permeability such as a planar mesh body as shown in FIGS. 1 to 3 and a cylindrical surface mesh body as shown in FIGS. It is formed with the planar body which has.
[0037]
Also, as the dust collecting electrodes 11 and 21, a perforated plate such as a mesh metal mesh or punching metal or an expander metal formed into a plate shape, a cylindrical shape, or other shapes, or a plate shape obtained by processing a coiled wire A cylindrical shape, other shapes, aggregates of metal fibers such as stainless wool, and composites and laminates thereof can be used.
[0038]
The combustion electrodes 13 and 23 are used for burning and removing the PM collected by the dust collection electrodes 12 and 22 by energization, and are provided adjacent to the vicinity of the dust collection electrodes 12 and 22. Since a large amount of PM is deposited on the corona electrode sides 11 and 21 of the dust collecting electrodes 12 and 22, the combustion electrodes 13 and 23 are also provided on the corona electrode sides 11 and 21, respectively. That is, the combustion electrodes 13 and 23 are disposed between the corona electrodes 11 and 21 and the dust collection electrodes 12 and 22. In other words, the dust collecting electrodes 12 and 22 and the combustion electrodes 13 and 23 form a double structure for PM combustion that is insulated from each other.
[0039]
The combustion electrodes 13 and 23 can be formed of a mesh-like wire net or the like, similar to the dust collection electrodes 11 and 21, but the porosity is larger than that of the dust collection electrodes 12 and 22. That is, the combustion electrodes 13 and 23 form a coarser mesh than the dust collection electrodes 12 and 22.
[0040]
The corona electrodes 11, 21, the dust collecting electrodes 12, 22 and the combustion electrodes 13, 23 are paired in an electrically insulated state, and the dust collecting electrodes 12, 22 are spaced downstream of the corona electrodes 11, 21. The corona electrodes 11 and 21 and the dust collecting electrodes 12 and 22 are disposed in the case of the exhaust gas purifying device in a state of being provided facing the corona electrodes 11 and 21. It is arranged so as to be in a direction intersecting with the mainstream direction, preferably a vertical direction. That is, the exhaust gas G is arranged so as to cross the corona electrodes 11 and 21 and to flow into and through the surfaces of the dust collecting electrodes 12 and 22. Further, the combustion electrodes 13 and 23 are provided in the vicinity of the dust collection electrodes 12 and 22, for example, with an interval of about 1 to 2 mm.
[0041]
In FIG. 7, a flat dust collecting unit 10A formed of a linear corona electrode 11, a dust collecting electrode 12 having a planar mesh body parallel to the corona electrode 11, and a combustion electrode 13 is incorporated in the exhaust gas purifying apparatus 1A. Here is an example.
[0042]
In FIG. 8, a planar dust collecting unit 10 </ b> B formed by a corona electrode 11 having a planar mesh body such as a wire mesh, a dust collecting electrode 12 and a combustion electrode 13 having a planar mesh body parallel to the corona electrode 11 is exhausted. The example incorporated in the gas purification apparatus 1B is shown.
[0043]
FIG. 9 shows a collection of a plurality of linear corona electrodes 11 arranged on a concentric cylindrical surface, a dust collecting electrode 12 of a cylindrical surface mesh body with a concentric cylindrical surface having the same center as the concentric cylinder, and combustion. An example in which a concentric dust collecting unit 10C configured by a combination with the electrodes 13 and 23 for use is incorporated in the exhaust gas purification device 1C is shown.
[0044]
In the case of the configuration of FIG. 9, the exhaust gas G passes through the central passage from the exhaust gas inlet 2, flows in the radial direction, passes through the purification section 3, and collects PM by the concentric circular dust collection unit 10C. After that, the exhaust gas outlet 4 is reached via the outer passage 6.
[0045]
In the planar dust collection unit 10A and the concentric dust collection unit 10C, a plurality of linear corona electrodes 11 may be formed by a planar body having air permeability, and the planar body may be a collector. Similar to the dust electrodes 12 and 22, it can be formed with a mesh wire mesh or the like, but since it is for corona discharge, the eyes may be rough, and the mesh interval and the porosity are larger than those of the dust collection electrodes 12 and 22. The ventilation resistance shall be low.
[0046]
FIGS. 10 and 11 show a combination of a single linear corona electrode 21 and a dust collecting electrode 22 and a combustion electrode 23 of a cylindrical cylindrical mesh body having the linear corona electrode 21 as an axis. An example in which the coaxial cylindrical dust collecting unit 20 configured by the above is incorporated in the exhaust gas purifying apparatuses 1E and 1F is shown. Also in the case of FIG. 11, as in FIG. 9, the exhaust gas G passes through the central passage from the exhaust gas inlet 2, flows in the radial direction, passes through the purification section 3, passes through the outer passage 6, and is exhausted. The gas outlet 4 is reached.
[0047]
For example, for in-vehicle use, the exhaust gas purification devices 1B, 1C, and 1F in FIGS. 8, 9, and 11 can be formed in the same cylindrical shape as a normal muffler (silencer), and in terms of layout and mounting structure when mounted on the vehicle It becomes a highly practical device.
[0048]
And as shown in FIG. 12, when applying this exhaust-gas purification apparatus 1A-1F to the diesel engine for vehicles, it arrange | positions in the upstream of the muffler 33 of the exhaust passage 32 of the diesel engine 31, and is a control system of a diesel engine. Power is supplied from a power supply device 36 that is controlled by a signal from 34 and receives power from the battery 35. The power supply device 36 includes a high voltage supply device 36a and a combustion current supply device 36b.
[0049]
A high voltage such as a DC voltage, an AC voltage, a pulse voltage, or the like is applied from the high voltage supply device 36a to the corona electrodes 11 and 21 of the exhaust gas purification devices 1A to 1F, and one dust collection electrode 12, 22 is applied. Is grounded to form an unequal electric field between the corona electrodes 11 and 21 and the dust collecting electrodes 12 and 22. As the frequency of the AC voltage, a frequency of 50 Hz to 10 kHz is suitable, but it is not particularly necessary to have a sine wave shape and may be a rectangular shape. As the type of applied voltage, a DC voltage is excellent in the PM collection rate per input power, and the electrical component device can be relatively simplified. A sufficient effect can be obtained by using either a negative voltage or a positive voltage as the DC voltage. However, a positive voltage is generally superior in PM collection rate per input power. Depending on the specifications of the peripheral device, etc., an AC voltage or a pulse voltage may be better for comprehensive judgment.
[0050]
The peak value V of the applied voltage may be a voltage sufficient to form corona discharge on the corona electrodes 11 and 21, and is determined from the shape and spatial arrangement of the corona electrodes 11 and 21 and the ground electrodes 12 and 22. It may be set based on the start voltage. In the case of an in-vehicle exhaust gas purification device, a range of about 5 kV to 40 kV is appropriate, and in the case of a fixed exhaust source exhaust gas purification device, a range of about 5 kV to 100 kV is appropriate.
[0051]
By applying this high voltage, an unequal electric field is formed in the vicinity of the corona electrodes 11 and 21, and a non-destructive discharge, that is, a corona discharge space is locally formed around the corona electrodes 11 and 21. By this corona discharge, a large number of positive ions ionized by collision of fast electrons and fast electrons and negative ions due to electron attachment are formed in the gas. When exhaust gas G containing PM is circulated in this corona discharge space, PM collides with electrons, positive ions, negative ions and PM, and PM is charged almost instantaneously. The charged PM is collected by Coulomb force. Collected by the electrodes 12 and 22.
[0052]
At this time, these electrodes 11, 21, 12, 22 are arranged in a direction in which the flow of the exhaust gas G to be processed is blocked by the corona electrodes 11, 21 and the dust collecting electrodes 12, 22, and downstream of the corona electrodes 11, 21. Since the planar dust collecting electrodes 12 and 22 having air permeability are arranged in the sphere, the charged PM is collected by the dust collecting electrodes 12 and 22 even if the drift effect due to the electric field and the clonal force is small. The probability increases and the dust is collected by the dust collecting electrodes 12 and 22 efficiently. Therefore, PM can be removed with high efficiency with low power consumption.
[0053]
Further, as shown in FIG. 14, a dielectric material 25 having gas permeability may be disposed between the dust collecting electrodes 12 and 22 and the combustion electrode 13. FIG. 14A shows a planar dust collecting unit as shown in FIGS. 1 to 3 as a representative example, in which a gas-permeable dielectric material 25 is sandwiched between the combustion electrode 13 and the dust collecting electrode 12. In FIG. 14B, the combustion electrode 13 is disposed on both the upstream side and the downstream side of the dust collection electrode 12, and the gas-permeable dielectric material 25 is disposed between the downstream combustion electrode 13 and the dust collection electrode 12. It is arranged, and has a structure in which PM that could not be collected on the surface of the dust collection electrode 12 on the upstream side is collected again. In FIG. 14C, the combustion electrode 13 is arranged on both the upstream side and the downstream side of the dust collection electrode 12, and the gas-permeable dielectric material 25 is sandwiched between both the combustion electrode 13 and the dust collection electrode 12. Is.
[0054]
In such a configuration, when a voltage is applied between the dust collection electrode 12 and the combustion electrode 13, an electric field is formed inside the dielectric material 25, and PM collection efficiency is further improved. In the example of FIG. 14, the voltage applied to the combustion electrode 13 serves not only for burning the collected PM, but also for improving the efficiency of collecting PM to the gas-permeable dielectric material 25. The gas-permeable dielectric material 25 may be in direct contact with the dust collection electrode 12 and the combustion electrode 13, or the dust collection electrode 12 and the combustion electrode 13 with a space of about several millimeters or less sandwiched between appropriate spacers. You may arrange | position between.
[0055]
As the gas-permeable dielectric material 25, a material having a hole diameter about 10 times larger than that of the DPF, more specifically, a material having a hole diameter of about 0.1 mm or more may be used. However, in order to avoid damage due to PM combustion, the melting point is high. A material having excellent heat resistance is suitable, and ceramic particle aggregate 25A, porous ceramic or ceramic fiber aggregate ceramic filter 25B, ceramic honeycomb 25C and the like as shown in FIG. 15 are suitable.
[0056]
The PM collected by the electric dust collection using this corona discharge can selectively collect finer PM particles than when mechanically trapped by a normal physical filter. And there is no risk of clogging even after continuous operation for quite a long time.
[0057]
The corona electrodes 11 and 21 are formed of linear or breathable planar electrodes, and the dust collection electrodes 12 and 22 and the combustion electrodes 13 and 23 are formed of breathable planar bodies. However, since the planar body has a large hole diameter and an open area ratio like the mesh body, and the hole diameter may be about 10 times or more that of the DPF, it is in a direction intersecting with the flow direction of the exhaust gas G (usually vertical). Even if it is disposed in the direction), the flow path of the exhaust gas G is not greatly blocked, so the exhaust gas resistance is remarkably small and the back pressure hardly increases.
[0058]
In addition, the distance between the electrodes, the required voltage (power consumption), and the exhaust gas residence time can be selected almost independently, and a stable corona discharge can be formed even when there are space constraints, etc. The purification device can be made compact.
[0059]
Then, in order to burn and remove the PM collected by the dust collection electrodes 12 and 22, the combustion electrodes 13 and 23 are supplied with a DC voltage, an AC voltage, and a pulse voltage of about 300 V to 1 kV from the combustion current supply device 36b. Always apply continuously. The voltage peak value V to be applied depends on the gap d between the combustion electrodes 13 and 23 and the dust collecting electrodes 12 and 22, and the average electric field strength E (= V / d) obtained by dividing the voltage peak value V by the gap d is 3 kV. It has been experimentally found that if it is at least / cm, PM can be burnt and removed quickly. As a tendency, it is known that the higher the voltage peak value V is, the faster PM combustion is performed. For example, the voltage may be controlled in accordance with the PM deposition amount.
[0060]
More specifically, by changing the voltage peak value V in the case of applying a DC voltage, the voltage peak value V or frequency in the case of applying an AC voltage, and changing the voltage peak value V or the repetition rate in the case of applying a pulse voltage, What is necessary is just to control so that an average voltage becomes high when there is much PM deposition amount. The PM accumulation amount can be evaluated by program control if it is known in advance in the engine mode or the like, or feedback control can be performed by monitoring the pressure loss before and after the dust collection electrodes 12 and 22. Is possible.
[0061]
Further, when the applied voltage peak value V is set to E = 20 to 25 kV / cm or more, a spark discharge is generated in the space between the combustion electrodes 13 and 23 and the dust collection electrodes 12 and 22. This characteristic is substantially the same even when the gas-permeable dielectric material 25 is sandwiched between the combustion electrodes 13 and 23 and the dust collection electrodes 12 and 22. It is also possible to ignite and remove the deposited PM with this spark discharge. It is not preferable to apply a voltage that always generates a spark discharge in terms of damage to the combustion electrodes 13 and 23, the dust collection electrodes 12 and 22, and the gas-permeable dielectric material 25, and power consumption. As in 16, a voltage having a pattern in which the voltage peak value V is temporarily raised to the spark generation voltage level may be applied. The time and frequency with which the voltage peak value V is temporarily raised to the spark generation voltage level may be controlled according to the PM deposition amount.
[0062]
When the collected amount of PM collected by the dust collecting electrodes 12 and 22 increases due to the application of this voltage and the supply of current, the collected PM and the dust collecting electrodes 12 and 22 come close to each other. An electrical short circuit occurs between the combustion electrodes 13 and 23 provided, and a current flows through the PM. The PM is heated by this current and starts to burn.
[0063]
Once PM combustion occurs, the adjacent PM rises in temperature due to the combustion heat of PM and starts combustion, and the PM collected in a chain is burned. Further, when the collected PM is burned and removed, the short-circuit state is eliminated and power consumption is also stopped.
[0064]
In this case, even if the combustion electrodes 13 and 23 are always energized, an insulation state is maintained between the collected PM and the dust collection electrodes 12 and 22 when the amount of PM collected is small. In addition, since power consumption does not occur, and when short-circuiting is started due to an increase in the amount of collected PM and combustion of PM is started, the short-circuit state is immediately released by combustion, so the power used for PM combustion is very small. Will be enough.
[0065]
Moreover, since the short circuit and PM combustion removal are automatically performed due to the local increase in the amount of collected PM, control for burning and removing the collected PM becomes unnecessary.
[0066]
In addition, in the case of this PM removal by combustion, since the PM trapped by the dust collecting electrodes 12 and 22 is exposed to the corona discharge field, combustion can be started from a low temperature of 150 ° C. to 200 ° C. Will not cause damage.
[0067]
Further, the combustion of PM can be promoted by supporting or applying a catalyst component having an oxidizing power such as platinum or titanium oxide on the corona electrodes 11, 21, the dust collection electrodes 12, 22 and the combustion electrodes 13, 23. . In this case, since each electrode is exposed to the corona discharge field, the catalyst exhibits a synergistic effect and PM can be burned even at a lower temperature. Therefore, an ON / OFF control function for sensing or monitoring the exhaust gas temperature is added. When the exhaust gas temperature is in a high temperature range where the catalyst functions, the power to the combustion electrodes 13 and 23 is turned off to It is only necessary to turn on the energization only in the low temperature region where the function is lowered.
[0068]
Note that the present invention is mainly intended for diesel engines that use light oil as fuel because of the nature of the fuel, the combustion method, and the prevalence of the fuel. However, the present invention is not limited to this. It can also be applied to various industrial machines and stationary internal combustion engines.
[0069]
【The invention's effect】
As described above, according to the exhaust gas purification method and apparatus of the present invention, PM in the exhaust gas is collected by using the corona discharge generated between the corona electrode and the dust collecting electrode. Therefore, PM can be collected with almost no increase in back pressure, and the corona electrode, dust collection electrode, and combustion electrode are arranged in a direction intersecting with the exhaust gas flow direction. The charged PM can be caused to flow into the dust collecting electrode on the downstream side and be efficiently collected by the dust collecting electrode.
[0070]
When the amount of PM collected by the dust collecting electrode increases, the distance between the collected PM and the combustion electrode is reduced, and an electrical short circuit occurs between the two. Current flows through PM. This current raises the temperature of the PM and starts combustion. Once combustion of the PM occurs, the adjacent PM rises in temperature due to the combustion heat of the PM and starts combustion, so the PM collected in a chain is burned and removed. it can.
[0071]
In this case, even if the combustion electrode is always energized, power is consumed only when PM combustion starts due to a short circuit due to an increase in the amount of PM collected, and the short circuit is immediately released by combustion. Since power consumption is also interrupted, PM combustion can be performed efficiently with very little power.
[0072]
Moreover, since the short circuit and PM combustion removal are automatically performed due to the local increase in the amount of collected PM, control for burning and removing the collected PM becomes unnecessary.
[0073]
Therefore, PM can be collected with high efficiency with low input power, and the collected PM can be automatically burned and removed with a very simple mechanism called a combustion electrode and low power consumption. Also, since the input power can be low, there is almost no deterioration in fuel consumption.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing a configuration of a planar dust collection unit that is a component of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a side view of the planar dust collecting unit of FIG.
3 is a plan view of the planar dust collection unit of FIG. 1. FIG.
FIG. 4 is a schematic perspective view showing the configuration of a coaxial cylindrical dust collection unit that is a component of the exhaust gas purifying device for an internal combustion engine according to the embodiment of the present invention.
5 is a side view of the planar dust collection unit of FIG.
6 is a plan view of the planar dust collection unit of FIG. 5. FIG.
FIG. 7 is a schematic sectional side view showing the configuration of the exhaust gas purifying apparatus for the internal combustion engine according to the first embodiment of the present invention.
FIG. 8 is a schematic cross-sectional side view showing a configuration of an exhaust gas purification apparatus for an internal combustion engine according to a second embodiment of the present invention.
FIGS. 9A and 9B are schematic views showing the configuration of an exhaust gas purifying apparatus for an internal combustion engine according to a third embodiment of the present invention, wherein FIG. 9A is a cross-sectional view and FIG. 9B is a side cross-sectional view. .
FIGS. 10A and 10B are schematic views showing the configuration of an exhaust gas purification apparatus for an internal combustion engine according to a fourth embodiment of the present invention, where FIG. 10A is a side sectional view and FIG. 10B is a plan sectional view; .
FIGS. 11A and 11B are schematic views showing the configuration of an exhaust gas purification apparatus for an internal combustion engine according to a fifth embodiment of the present invention, where FIG. 11A is a cross-sectional view and FIG. 11B is a side cross-sectional view. .
FIG. 12 is a diagram showing a configuration example when the exhaust gas purifying apparatus for an internal combustion engine according to the present invention is mounted on a vehicle.
FIG. 13 is a plan sectional view schematically showing the structure of a conventional electrostatic precipitator.
FIG. 14 is a schematic diagram showing the configuration of an exhaust gas purification apparatus for an internal combustion engine according to a sixth embodiment of the present invention, which is representative of sandwiching a gas-permeable dielectric material between a combustion electrode and a dust collecting electrode. It is a schematic diagram showing a general structure, (a) is a diagram showing a three-layer structure, (b) is a diagram showing a four-layer structure, (c) is a diagram showing a five-layer structure.
15 is a schematic view showing a typical example of the gas-permeable dielectric material of FIG. 14, wherein (a) shows ceramic particles, and (b) shows a porous ceramic or ceramic fiber aggregate. (C) is a figure which shows a honeycomb-like ceramic filter.
FIG. 16 is a diagram illustrating an example of a voltage waveform applied to a combustion electrode.
[Explanation of symbols]
1A-1F Exhaust gas purification device
10 Flat type dust collection unit
10C Concentric Dust Collection Unit
11 Corona electrode
12 Dust collection electrode (planar mesh body)
12C Dust collection electrode (cylindrical mesh)
13 Combustion electrode
20 Coaxial cylindrical dust collection unit
21 Corona electrode
22 Dust collecting electrode (cylindrical mesh)
23 Combustion electrode
25 Gas-permeable dielectric material
25A ceramic particles
25B Porous ceramic or aggregate of ceramic fibers
25C Honeycomb ceramic filter
36a High voltage supply device
36b Current supply device for combustion

Claims

An exhaust gas purification method for removing particulate matter in exhaust gas of an internal combustion engine, which is provided in a direction that intersects a flow of exhaust gas with a linear corona electrode provided in a direction intersecting with the flow of exhaust gas In addition, a high voltage is applied to the corona electrode of the planar body having air permeability, the gap is provided on the downstream side of the corona electrode so as to face the corona electrode, and the diameter is 0.1 mm or more and 10 mm. In the surface of a dust collecting electrode formed of a mesh-like metal mesh of a planar material having air permeability and having a hole for allowing exhaust gas to pass through , and provided in a direction intersecting with the flow of exhaust gas The particulate matter in the exhaust gas charged by corona discharge through the exhaust gas is collected by the dust collection electrode to purify the exhaust gas, and further provided in the vicinity of the dust collection electrode , The mesh is coarser than the dust collection electrode, and the hole area ratio is Formed by listening meshed wire net, by energizing the combustion electrode provided in a direction intersecting the flow of the exhaust gases, by applying a voltage between the combustion electrode and the dust collecting electrode, said current When the amount of particulate matter collected by the dust electrode increases and the distance between the particulate matter and the combustion electrode decreases, an electrical short circuit occurs between the two and the dust collection electrode An exhaust gas for an internal combustion engine, wherein an electric current is passed through the collected particulate matter for combustion removal, and a gap between the dust collection electrode and the combustion electrode is filled with a dielectric material having exhaust gas permeability Purification method.

The peak value of the voltage applied between the dust collection electrode and the combustion electrode is V, the distance between the dust collection electrode and the combustion electrode is d, and the average distance between the dust collection electrode and the combustion electrode 2. The exhaust gas purification method for an internal combustion engine according to claim 1, wherein the electric field strength E = V / d is 3 kV / cm or more and 30 kV / cm or less.

An exhaust gas purifying device for removing particulate matter in exhaust gas of an internal combustion engine, provided with a linear corona electrode provided in a direction intersecting with the flow of exhaust gas, or provided in a direction intersecting with the flow of exhaust gas A corona electrode having a planar surface with air permeability and an exhaust gas having a diameter downstream from the corona electrode and facing the corona electrode, and having a diameter of 0.1 mm to 10 mm. It has a hole for passing formed by the meshed metal net of the planar member having gas permeability and a dust collecting electrode provided in a direction intersecting the flow of exhaust gas, provided in the vicinity of the dust collecting electrode And is formed of a mesh wire mesh having a mesh larger than that of the dust collecting electrode and having a larger opening ratio, and having a combustion electrode provided in a direction crossing the flow of exhaust gas, and the corona High voltage for corona discharge on the electrode A high voltage supply device for supplying an electrical short circuit between the two when the distance between the particulate matter and the combustion electrode collecting quantity of the current particulate matter trapped in the dust electrode is increased narrows It is supplied to the combustion electrode current for burning off by applying a current to the collected particulate matter by generating and applying a voltage between the dust collecting electrode and the combustion electrode combustion An exhaust gas purifying device for an internal combustion engine, characterized in that a dielectric material having exhaust gas permeability is filled in a gap between the dust collecting electrode and the combustion electrode.

4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein the combustion electrode is provided in the vicinity of the dust collecting electrode on the corona electrode side.

The exhaust gas purifying device for an internal combustion engine according to claim 3, wherein the dielectric material has an exhaust gas passage hole diameter of not less than 0.1 mm and not more than 10 mm.

The peak value of the voltage applied between the dust collection electrode and the combustion electrode is V, the distance between the dust collection electrode and the combustion electrode is d, and the average distance between the dust collection electrode and the combustion electrode 6. The exhaust gas purifying device for an internal combustion engine according to claim 3, wherein the electric field intensity E = V / d is 3 kV / cm or more and 30 kV / cm or less.