JP4131784B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

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JP4131784B2
JP4131784B2 JP2001138393A JP2001138393A JP4131784B2 JP 4131784 B2 JP4131784 B2 JP 4131784B2 JP 2001138393 A JP2001138393 A JP 2001138393A JP 2001138393 A JP2001138393 A JP 2001138393A JP 4131784 B2 JP4131784 B2 JP 4131784B2
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reducing agent
exhaust
internal combustion
combustion engine
injection valve
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JP2002332827A (en
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裕司 矢島
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UD Trucks Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関の排気浄化装置において、特に、窒素酸化物の浄化効率を向上させる技術に関する。
【０００２】
【従来の技術】
内燃機関から排出される排気中には、無害な二酸化炭素（ＣＯ2），水（Ｈ2Ｏ），窒素（Ｎ2）の他に、有害な一酸化炭素（ＣＯ），炭化水素（ＨＣ），窒素酸化物（ＮＯｘ）が含まれていることは知られている。このため、有害物質であるＮＯｘを浄化することを目的として、例えば、特開平６−１３７１３６号公報に開示されるような排気浄化装置が提案されている。かかる排気浄化装置は、酸素過剰雰囲気でＮＯｘを無害なＮ2，酸素（Ｏ2）等に転化すべく、内燃機関の排気通路にＮＯｘ還元触媒が介装されている。また、ＮＯｘ還元触媒におけるＮＯｘ浄化効率を高めるべく、その上流側の排気通路に、還元剤としてのＨＣを含む軽油等を添加する構成が採用されている。さらに、還元剤として、ＨＣの代わりに尿素（(ＮＨ2)2ＣＯ）水溶液を用いる技術も提案されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、軽油、尿素水溶液等の液体還元剤をそのまま排気通路に添加すると、還元剤が液滴状態で排気と混合するため、気化熱により排気温度が低下し、ＮＯｘ還元触媒の活性が低下してしまうおそれがあった。また、還元剤が液滴状態で添加されるため、ＮＯｘ還元触媒に対する還元剤の供給にむらが生じ、還元剤の拡散が不十分になり易いという問題もあった。このため、従来技術においては、液体還元剤を添加しても、ＮＯｘ還元触媒によるＮＯｘ浄化効率が期待したほど向上しなかった。
【０００４】
そこで、本発明は以上のような従来の問題点に鑑み、液体還元剤添加による排気温度の低下を防止すると共に、還元剤の拡散性を高めることで、ＮＯｘ還元触媒によるＮＯｘ浄化効率を向上させた内燃機関の排気浄化装置を提供することを目的とする。
【０００５】
【課題を解決するための手段】
このため、請求項１記載の発明では、内燃機関の排気通路に介装され、排気中の窒素酸化物を還元反応により無害物質に転化させる窒素酸化物還元触媒と、液体還元剤を加熱しつつ、前記窒素酸化物還元触媒の上流側に添加する還元剤噴射弁と、を含んで構成された内燃機関の排気浄化装置において、前記還元剤噴射弁は、軸方向に延びつつ略同心に配設される２つの発熱体の間に還元剤流路が形成されると共に、該還元剤流路の横断面において還元剤導入口が軸中心に対してオフセットした位置に開口していることを特徴とする。
【０００６】
かかる構成によれば、窒素酸化物還元触媒の上流側には、液体還元剤が加熱されてから添加されるため、その液滴が排気と混合しても、排気温度の低下が抑制される。また、液体還元剤が加熱されることで、その気化が促進されるので、窒素酸化物還元触媒に対する還元剤の供給分布が均一化され、還元剤の拡散性が向上される。
さらに、還元剤噴射弁は、軸方向に延びつつ略同心に配設される２つの発熱体の間に還元剤流路が形成されると共に、還元剤流路の横断面において還元剤導入口が軸中心に対してオフセットした位置に開口しているため、還元剤流路内に旋回流が生じる。このため、液体還元剤の加熱が効果的に行なわれるようになる。
【０００７】
請求項２記載の発明では、前記還元剤噴射弁の還元剤流路内壁面には、液体還元剤としての尿素（（ＮＨ2）2ＣＯ）をアンモニア（ＮＨ3）に改質する改質触媒が塗布されたことを特徴とする。
かかる構成によれば、還元剤流路内に旋回流が生じているため、液体還元剤が還元剤流路を通るときに、ここで、尿素がアンモニアに効果的に改質される。そして、還元剤としてのアンモニアが窒素酸化物還元触媒の上流側に添加されるため、窒素酸化物の還元反応が促進され、窒素酸化物の浄化効率が一層向上される。
【０００８】
請求項３記載の発明では、前記改質触媒は、酸化チタン（ＴｉＯ2），アルミナ（Ａｌ2Ｏ3）及びシリカ（ＳｉＯ2）からなることを特徴とする。
かかる構成によれば、改質触媒として酸化チタン，アルミナ及びシリカからなるものが用いられることで、還元剤としての尿素がアンモニアに効果的に改質される。
【００１０】
請求項４記載の発明では、機関運転状態を検出する運転状態検出手段と、前記液体還元剤の温度を検出する還元剤温度検出手段と、前記運転状態検出手段及び還元剤温度検出手段により夫々検出された機関運転状態及び還元剤温度に基づいて、前記還元剤噴射弁による液体還元剤の加熱量を制御する加熱量制御手段と、を含んだ構成であることを特徴とする。
【００１１】
かかる構成によれば、液体還元剤の加熱量は、機関運転状態及び還元剤温度に基づいて制御されるため、加熱量を必要最小限とすることができ、液体還元剤の加熱に要する消費電力及び発熱体の熱劣化が極力抑制される。
【００１２】
【発明の実施の形態】
以下、添付された図面を参照して本発明を詳述する。
図１は、本発明に係る内燃機関の排気浄化装置（以下「排気浄化装置」という）を備えたディーゼル機関の全体構成を示す。
ディーゼル機関１０の排気通路１２には、排気流通方向に沿って、粒子状物質（ＰＭ）を捕集除去するディーゼルパティキュレートフィルタ（ＤＰＦ）１４と、ＮＯｘを還元浄化するＮＯｘ還元触媒１６と、が介装される。
【００１３】
ＤＰＦ１４は、セラミック等の多孔性部材からなる隔壁により排気流と略平行なセルが多数形成され、各セルの入口と出口とが目封材により互い違いに千鳥格子状に目封じされた構成をなす。そして、出口が塞がれたセル内の排気が、隔壁を介して入口が塞がれている隣接するセルに流入するとき、排気中のＰＭが隔壁を形成する多孔性部材により捕集除去される。
【００１４】
一方、ＮＯｘ還元触媒１６は、セラミックのコーディライトやＦｅ−Ｃｒ−Ａｌ系の耐熱鋼からなるハニカム形状の横断面を有するモノリスタイプの触媒担体に、例えば、ゼオライト系の活性成分が担持された構成をなす。そして、触媒担体に担持された活性成分は、添加剤としての炭化水素（ＨＣ）又は尿素（(ＮＨ2)2ＣＯ）等の供給を受けて活性化し、ＮＯｘを効果的に無害物質に転化させる。
【００１５】
ＮＯｘ還元触媒１６の上流側の排気通路１２には、軽油，尿素水溶液等の液体還元剤を噴射添加する還元剤噴射弁１８が介装される。還元剤噴射弁１８には、定圧圧送ポンプ２０が介装された還元剤導入路２２を介して、燃料タンク等の還元剤貯蔵タンク２４に貯蔵される液体還元剤が加圧供給される。還元剤導入路２２には、還元剤流量を制御すべく、マイクロコンピュータを内蔵したコントロールユニット２６によりデューティ制御される還元剤流量制御弁２８が介装される。
【００１６】
還元剤噴射弁１８は、図２に示すように、排気通路１２に添加される液体還元剤の温度を高めるべく、軸方向に延びつつ略同心に配設された２つの発熱体１８Ａ，１８Ｂの間に、還元剤流路１８Ｃが形成された構成をなす。ここで、発熱体１８Ａ，１８Ｂは、還元剤を短時間で加熱可能な低熱容量の電気ヒータで構成されることが望ましい。発熱体１８Ｂの外周には、熱が外部に放散されることを抑制すべく、遮熱材１８Ｄが配設される。なお、還元剤導入口１８Ｅは、還元剤流路１８Ｃ内に旋回流が生じるように、還元剤噴射弁１８の軸中心に対してオフセットした位置に開口することが望ましい（図２（Ｂ）参照）。また、発熱体１８Ａ，１８Ｂは、必ずしも、その両方が配設される必要はなく、少なくとも一方が配設されるようにしてもよい。
【００１７】
ところで、液体還元剤として尿素水溶液を用いる場合には、還元剤流路１８Ｃの内壁面、即ち、中央に配設される発熱体１８Ａの外周面及びその周囲に配設される発熱体１８Ｂの内周面には、還元剤を改質させる改質触媒が塗布されることが望ましい。改質触媒としては、次式のように、尿素（（ＮＨ2）2ＣＯ）と水（Ｈ2Ｏ）とを反応させて、アンモニア（ＮＨ3）と二酸化炭素（ＣＯ2）とに転化すべく、酸化チタン（ＴｉＯ2），アルミナ（Ａｌ2Ｏ3）及びシリカ（ＳｉＯ2）からなるものが用いられる。
【００１８】
(ＮＨ2)2ＣＯ＋Ｈ2Ｏ→２ＮＨ3＋ＣＯ2
また、排気浄化装置の制御を行なうために、機関運転状態，還元剤状態などを検出する種々のセンサが配設される。即ち、ＤＰＦ１４の下流側の排気通路１２には、排気中のＮＯｘ濃度ＣNOxを検出するＮＯｘセンサ３０、及び、排気温度Ｔeを検出する排気温度センサ３２が夫々介装される。ディーゼル機関１０には、吸気流量Ｑを検出する吸気流量センサ３４、機関回転速度Ｎを検出する回転速度センサ３６、及び、機関負荷Ｌを検出する負荷センサ３８が夫々配設される。なお、ＮＯｘセンサ３０，排気温度センサ３２，吸気流量センサ３４，回転速度センサ３６及び負荷センサ３８により、運転状態検出手段が構成される。定圧圧送ポンプ２０の下流側の還元剤導入路２２には、還元剤温度Ｔrを検出する還元剤温度センサ４０（還元剤温度検出手段）が介装される。
【００１９】
そして、コントロールユニット２６では、図３に示す処理が所定時間毎に繰り返し実行され、還元剤噴射弁１８の発熱体１８Ａ，１８Ｂ及び還元剤流量制御弁２８が夫々制御される。なお、発熱体１８Ａ，１８Ｂに対する電力供給制御が、加熱量制御手段に該当する。
ステップ１（図では「Ｓ１」と略記する。以下同様）では、機関運転状態として、ＮＯｘセンサ３０，排気温度センサ３２，吸気流量センサ３４，回転速度センサ３６及び負荷センサ３８から、夫々、ＮＯｘ濃度ＣNOx，排気温度Ｔe，吸気流量Ｑ，回転速度Ｎ及び機関負荷Ｌが検出される。また、還元剤温度センサ４０から、還元剤温度Ｔrが検出される。
【００２０】
ステップ２では、例えば、還元剤添加量マップ及び還元剤添加流量マップが参照され、機関運転状態に応じた還元剤添加量及び還元剤添加流量（単位時間当りの還元剤添加量）が夫々演算される。
ステップ３では、還元剤添加流量，排気温度Ｔe及び還元剤温度Ｔrに基づいて、還元剤噴射弁１８の発熱体１８Ａ，１８Ｂへの供給電力が演算される。即ち、発熱体１８Ａ，１８Ｂへの供給電力は、図４に示すように、還元剤添加流量に比例すると共に、排気温度Ｔe及び還元剤温度Ｔrに依存する。このため、例えば、排気温度Ｔe及び還元剤温度Ｔrに基づいて、マップから図４に示す直線の傾きを求め、簡単な演算により発熱体１８Ａ，１８Ｂへの供給電力を求めることができる。
【００２１】
ステップ４では、還元剤の加熱及び噴射が開始される。即ち、演算された供給電力に基づいて、例えば、発熱体１８Ａ，１８Ｂに印加する電圧又は／及び電流が制御され、還元剤噴射弁１８に供給された液体還元剤が加熱される。また、演算された還元剤添加流量に基づいて、還元剤流量制御弁２８の開度がデューティ制御され、還元剤噴射弁１８から排気通路１２内に、加熱昇温された液体還元剤が噴射される。
【００２２】
ステップ５では、液体還元剤の噴射が終了、即ち、演算された還元剤添加量が排気通路１２内に噴射されたか否かが判定される。還元剤の噴射が終了したか否かは、例えば、液体還元剤の噴射開始から、還元剤添加量を還元剤添加流量で除算して求められる噴射時間が経過したか否かで判定することができる。そして、液体還元剤の噴射が終了したならばステップ６へと進み（Ｙｅｓ）、液体還元剤の噴射が終了していなければステップ５における判定が繰り返される（Ｎｏ）。
【００２３】
ステップ６では、液体還元剤の加熱を停止すべく、発熱体１８Ａ，１８Ｂへの通電が遮断されると共に、液体還元剤の噴射を停止すべく、還元剤流量制御弁２８が閉弁制御される。
かかる構成によれば、ＮＯｘ還元触媒１６の上流側には、液体還元剤が加熱されてから噴射添加されるので、その液滴が排気と混合しても、排気温度の低下を抑制することができる。また、液体還元剤が加熱されることで、その気化が促進されるので、ＮＯｘ還元触媒１６に対する還元剤の供給分布が均一化され、還元剤の拡散性を向上させることができる。そして、排気温度の低下抑制と還元剤の拡散性向上との相乗作用により、最小限の液体還元剤を用いて、ＮＯｘ還元触媒１６によるＮＯｘ浄化効率を向上させることができる。
【００２４】
また、液体還元剤として尿素水溶液を用いることを前提として、還元剤噴射弁１８の還元剤流路１８Ｃの内壁面に改質触媒を塗布した場合には、ここで、尿素（(ＮＨ2)2ＣＯ）がアンモニア（ＮＨ3）に改質される。そして、還元剤噴射弁１８からアンモニアが排気通路１２内に噴射添加されるため、ＮＯｘ還元触媒１６によるＮＯｘの還元反応が促進され、ＮＯｘ浄化効率を一層向上させることができる。なお、還元剤として炭化水素（ＨＣ）を用いた場合には、改質触媒を塗布する必要はないことは言うまでもない。
【００２５】
ここで、改質触媒として、酸化チタン（ＴｉＯ2），アルミナ（Ａｌ2Ｏ3）及びシリカ（ＳｉＯ2）からなるものを用いているので、還元剤としての尿素をアンモニアに効果的に改質することができる。
さらに、還元剤噴射弁１８は、還元剤流路１８Ｃが軸方向に延び、かつ、その横断面において還元剤導入口１８Ｅが軸中心に対してオフセットした位置に開口しているため、還元剤流路１８Ｃ内に旋回流が発生する。このため、液体還元剤の加熱が効果的に行なわれるようになり、ＮＯｘ浄化触媒１６によるＮＯｘ浄化効率を一層向上させることができる。還元剤流路１８Ｃの内壁面に改質触媒が塗布されている場合には、旋回流により還元剤の改質を効果的に行なうことができる。
【００２６】
この他、還元剤噴射弁１８における還元剤の加熱量は、還元剤噴射流量，排気温度Ｔe及び還元剤温度Ｔrに基づいて制御されるため、加熱量を必要最小限とすることができ、加熱に要する消費電力及び発熱体１８Ａ，１８Ｂの熱劣化を極力抑制することができる。
なお、還元剤噴射弁１８の発熱体１８Ａ，１８Ｂは、コントロールユニット２６により制御される他、自己温度調整型のものを使用してもよい。また、本発明の排気浄化装置は、ディーゼル機関に限らず、ガソリン機関などの内燃機関にも適用可能であることは言うまでもない。
【００２７】
【発明の効果】
以上説明したように、請求項１記載の発明によれば、排気温度の低下抑制と還元剤の拡散性向上との相乗作用により、最小限の液体還元剤を用いて、窒素酸化物還元触媒による窒素酸化物の浄化効率を向上させることができる。また、還元剤流路内に生じた旋回流により、液体還元剤の加熱を効果的に行なうことができる。
請求項２記載の発明によれば、還元剤流路内に旋回流が生じているため、還元剤としての尿素がアンモニアに効果的に改質されるので、窒素酸化物の還元反応が促進され、窒素酸化物の浄化効率を一層向上することができる。
【００２８】
請求項３記載の発明によれば、改質触媒として酸化チタン，アルミナ及びシリカからなるものが用いられることで、還元剤としての尿素をアンモニアに効果的に改質することができる。
【００２９】
請求項４記載の発明によれば、液体還元剤の加熱量が必要最小限となるので、液体還元剤の加熱に要する消費電力及び発熱体の熱劣化を極力抑制することができる。
【図面の簡単な説明】
【図１】本発明に係る排気浄化装置を備えたディーゼル機関の全体構成図
【図２】還元剤噴射弁の詳細を示し、（Ａ）は縦断面図、（Ｂ）は横断面図
【図３】排気浄化装置の制御内容を示すフローチャート
【図４】発熱体への供給電力を演算する原理の説明図
【符号の説明】
１０ ディーゼル機関
１２ 排気通路
１６ ＮＯｘ還元触媒
１８ 還元剤噴射弁
１８Ａ 発熱体
１８Ｂ 発熱体
１８Ｃ 還元剤流路
１８Ｅ 還元剤導入口
２０ 定圧圧送ポンプ
２２ 還元剤導入路
２４ 還元剤貯蔵タンク
２６ コントロールユニット
２８ 還元剤流量制御弁
３０ ＮＯｘセンサ
３２ 排気温度センサ
３４ 吸気流量センサ
３６ 回転速度センサ
３８ 負荷センサ
４０ 還元剤温度センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for improving the purification efficiency of nitrogen oxides, particularly in an exhaust gas purification apparatus for an internal combustion engine.
[0002]
[Prior art]
In the exhaust discharged from the internal combustion engine, harmful carbon dioxide (CO 2 ), water (H 2 O), nitrogen (N 2 ), harmful carbon monoxide (CO), hydrocarbon (HC) It is known that nitrogen oxides (NOx) are contained. For this reason, for the purpose of purifying NOx, which is a harmful substance, for example, an exhaust purification device as disclosed in JP-A-6-137136 has been proposed. In such an exhaust purification device, a NOx reduction catalyst is interposed in the exhaust passage of the internal combustion engine in order to convert NOx into harmless N 2 , oxygen (O 2 ), etc. in an oxygen excess atmosphere. Further, in order to increase the NOx purification efficiency in the NOx reduction catalyst, a configuration is adopted in which light oil containing HC as a reducing agent is added to the upstream exhaust passage. Furthermore, a technique using a urea ((NH 2 ) 2 CO) aqueous solution instead of HC as a reducing agent has been proposed.
[0003]
[Problems to be solved by the invention]
However, if a liquid reducing agent such as light oil or urea aqueous solution is added to the exhaust passage as it is, the reducing agent mixes with the exhaust in the form of droplets, so the exhaust temperature decreases due to the heat of vaporization and the activity of the NOx reduction catalyst decreases. There was a risk of it. In addition, since the reducing agent is added in the form of droplets, there is a problem that unevenness in the supply of the reducing agent to the NOx reduction catalyst occurs and the diffusion of the reducing agent tends to be insufficient. For this reason, in the prior art, even when a liquid reducing agent was added, the NOx purification efficiency by the NOx reduction catalyst was not improved as expected.
[0004]
Therefore, in view of the conventional problems as described above, the present invention improves the NOx purification efficiency by the NOx reduction catalyst by preventing the exhaust temperature from decreasing due to the addition of the liquid reducing agent and increasing the diffusibility of the reducing agent. Another object of the present invention is to provide an exhaust purification device for an internal combustion engine.
[0005]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, a nitrogen oxide reduction catalyst that is interposed in the exhaust passage of the internal combustion engine and converts the nitrogen oxide in the exhaust gas into a harmless substance by a reduction reaction, and the liquid reducing agent are heated. In the exhaust gas purification apparatus for an internal combustion engine configured to include a reducing agent injection valve added to the upstream side of the nitrogen oxide reduction catalyst , the reducing agent injection valves are disposed substantially concentrically while extending in the axial direction. A reducing agent passage is formed between the two heating elements, and a reducing agent introduction port is opened at a position offset with respect to the axial center in a cross section of the reducing agent passage. To do.
[0006]
According to such a configuration, since the liquid reducing agent is added to the upstream side of the nitrogen oxide reduction catalyst after being heated, even if the liquid droplets are mixed with the exhaust gas, the exhaust gas temperature is prevented from lowering. Moreover, since the liquid reducing agent is heated to promote its vaporization, the supply distribution of the reducing agent to the nitrogen oxide reduction catalyst is made uniform, and the diffusibility of the reducing agent is improved.
Further, the reducing agent injection valve has a reducing agent passage formed between two heating elements that extend in the axial direction and are substantially concentric, and a reducing agent introduction port in the cross section of the reducing agent passage. Since the opening is made at a position offset with respect to the axial center, a swirling flow is generated in the reducing agent flow path. For this reason, heating of a liquid reducing agent comes to be performed effectively.
[0007]
According to a second aspect of the present invention, a reforming catalyst for reforming urea ((NH 2 ) 2 CO) as a liquid reducing agent to ammonia (NH 3 ) is formed on the inner wall surface of the reducing agent flow path of the reducing agent injection valve. Is applied.
According to such a configuration, since a swirl flow is generated in the reducing agent channel, urea is effectively reformed to ammonia here when the liquid reducing agent passes through the reducing agent channel. Since ammonia as a reducing agent is added to the upstream side of the nitrogen oxide reduction catalyst, the reduction reaction of nitrogen oxide is promoted, and the purification efficiency of nitrogen oxide is further improved.
[0008]
The invention according to claim 3 is characterized in that the reforming catalyst comprises titanium oxide (TiO 2 ), alumina (Al 2 O 3 ), and silica (SiO 2 ).
According to such a configuration, by using the reforming catalyst made of titanium oxide, alumina, and silica, urea as the reducing agent is effectively reformed to ammonia.
[0010]
According to a fourth aspect of the present invention, the operation state detecting means for detecting the engine operation state, the reducing agent temperature detecting means for detecting the temperature of the liquid reducing agent, and the operation state detecting means and the reducing agent temperature detecting means are respectively detected. And a heating amount control means for controlling the heating amount of the liquid reducing agent by the reducing agent injection valve based on the engine operating state and the reducing agent temperature.
[0011]
According to such a configuration, since the heating amount of the liquid reducing agent is controlled based on the engine operating state and the reducing agent temperature, the heating amount can be minimized and the power consumption required for heating the liquid reducing agent. In addition, thermal deterioration of the heating element is suppressed as much as possible.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an overall configuration of a diesel engine equipped with an exhaust gas purification device for an internal combustion engine (hereinafter referred to as “exhaust gas purification device”) according to the present invention.
A diesel particulate filter (DPF) 14 that collects and removes particulate matter (PM) and a NOx reduction catalyst 16 that reduces and purifies NOx are disposed in the exhaust passage 12 of the diesel engine 10 along the exhaust flow direction. Intervened.
[0013]
The DPF 14 has a structure in which a large number of cells substantially parallel to the exhaust flow are formed by partition walls made of a porous member such as ceramic, and the inlets and outlets of each cell are alternately sealed in a staggered pattern by a plugging material. Eggplant. When the exhaust gas in the cell whose outlet is blocked flows into the adjacent cell whose inlet is blocked via the partition wall, PM in the exhaust gas is collected and removed by the porous member forming the partition wall. The
[0014]
On the other hand, the NOx reduction catalyst 16 has a configuration in which, for example, a zeolite-based active component is supported on a monolith type catalyst carrier having a honeycomb-shaped cross section made of ceramic cordierite or Fe-Cr-Al heat-resistant steel. Make. The active component supported on the catalyst carrier is activated upon receiving supply of hydrocarbon (HC) or urea ((NH 2 ) 2 CO) as an additive, and effectively converts NOx into a harmless substance. .
[0015]
A reducing agent injection valve 18 for injecting and adding a liquid reducing agent such as light oil or aqueous urea solution is interposed in the exhaust passage 12 upstream of the NOx reduction catalyst 16. A liquid reducing agent stored in a reducing agent storage tank 24 such as a fuel tank is pressurized and supplied to the reducing agent injection valve 18 through a reducing agent introduction passage 22 in which a constant pressure pump 20 is interposed. The reducing agent introduction path 22 is provided with a reducing agent flow rate control valve 28 that is duty-controlled by a control unit 26 incorporating a microcomputer in order to control the reducing agent flow rate.
[0016]
As shown in FIG. 2, the reducing agent injection valve 18 includes two heating elements 18 </ b> A and 18 </ b> B that extend in the axial direction and are substantially concentrically arranged to increase the temperature of the liquid reducing agent added to the exhaust passage 12. There is a configuration in which a reducing agent flow path 18C is formed therebetween. Here, it is desirable that the heating elements 18A and 18B are constituted by low-heat capacity electric heaters capable of heating the reducing agent in a short time. A heat shield 18D is disposed on the outer periphery of the heating element 18B in order to suppress heat from being dissipated to the outside. The reducing agent introduction port 18E is preferably opened at a position offset with respect to the axial center of the reducing agent injection valve 18 so that a swirling flow is generated in the reducing agent flow path 18C (see FIG. 2B). ). Further, both of the heating elements 18A and 18B are not necessarily arranged, and at least one of them may be arranged.
[0017]
By the way, when the urea aqueous solution is used as the liquid reducing agent, the inner wall surface of the reducing agent channel 18C, that is, the outer peripheral surface of the heating element 18A disposed in the center and the heating element 18B disposed in the periphery thereof. It is desirable to apply a reforming catalyst for reforming the reducing agent on the peripheral surface. As a reforming catalyst, urea ((NH 2 ) 2 CO) and water (H 2 O) are reacted as shown in the following formula and converted into ammonia (NH 3 ) and carbon dioxide (CO 2 ). Accordingly, those made of titanium oxide (TiO 2 ), alumina (Al 2 O 3 ), and silica (SiO 2 ) are used.
[0018]
(NH 2 ) 2 CO + H 2 O → 2NH 3 + CO 2
In order to control the exhaust emission control device, various sensors for detecting the engine operating state, the reducing agent state, and the like are provided. That is, the NOx sensor 30 for detecting the NOx concentration C NOx in the exhaust and the exhaust temperature sensor 32 for detecting the exhaust temperature Te are interposed in the exhaust passage 12 on the downstream side of the DPF 14, respectively. The diesel engine 10 is provided with an intake flow sensor 34 for detecting the intake flow rate Q, a rotational speed sensor 36 for detecting the engine rotational speed N, and a load sensor 38 for detecting the engine load L. The NOx sensor 30, the exhaust gas temperature sensor 32, the intake air flow rate sensor 34, the rotation speed sensor 36, and the load sensor 38 constitute an operating state detection means. A reducing agent temperature sensor 40 (reducing agent temperature detecting means) for detecting the reducing agent temperature Tr is interposed in the reducing agent introduction path 22 on the downstream side of the constant pressure pump 20.
[0019]
Then, in the control unit 26, the processing shown in FIG. 3 is repeatedly executed every predetermined time, and the heating elements 18A and 18B and the reducing agent flow rate control valve 28 of the reducing agent injection valve 18 are controlled. The power supply control for the heating elements 18A and 18B corresponds to the heating amount control means.
In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the NOx concentration is determined from the NOx sensor 30, the exhaust temperature sensor 32, the intake flow rate sensor 34, the rotational speed sensor 36, and the load sensor 38 as engine operating states. C NOx , exhaust temperature Te, intake air flow rate Q, rotational speed N and engine load L are detected. Further, the reducing agent temperature Tr is detected from the reducing agent temperature sensor 40.
[0020]
In step 2, for example, the reducing agent addition amount map and the reducing agent addition flow rate map are referred to, and the reducing agent addition amount and the reducing agent addition flow rate (reducing agent addition amount per unit time) corresponding to the engine operating state are respectively calculated. The
In step 3, the power supplied to the heating elements 18A and 18B of the reducing agent injection valve 18 is calculated based on the reducing agent addition flow rate, the exhaust gas temperature Te, and the reducing agent temperature Tr. That is, as shown in FIG. 4, the power supplied to the heating elements 18A and 18B is proportional to the reducing agent addition flow rate and depends on the exhaust gas temperature Te and the reducing agent temperature Tr. Therefore, for example, the slope of the straight line shown in FIG. 4 can be obtained from the map based on the exhaust temperature Te and the reducing agent temperature Tr, and the power supplied to the heating elements 18A and 18B can be obtained by a simple calculation.
[0021]
In step 4, heating and injection of the reducing agent are started. That is, based on the calculated supply power, for example, the voltage or / and current applied to the heating elements 18A and 18B is controlled, and the liquid reducing agent supplied to the reducing agent injection valve 18 is heated. Further, the opening degree of the reducing agent flow rate control valve 28 is duty-controlled based on the calculated reducing agent addition flow rate, and the liquid reducing agent heated and heated is injected from the reducing agent injection valve 18 into the exhaust passage 12. The
[0022]
In step 5, it is determined whether or not the injection of the liquid reducing agent has been completed, that is, whether or not the calculated reducing agent addition amount has been injected into the exhaust passage 12. Whether or not the injection of the reducing agent has ended can be determined, for example, based on whether or not the injection time determined by dividing the reducing agent addition amount by the reducing agent addition flow rate has elapsed since the start of the injection of the liquid reducing agent. it can. If the injection of the liquid reducing agent is completed, the process proceeds to step 6 (Yes), and if the injection of the liquid reducing agent is not completed, the determination in step 5 is repeated (No).
[0023]
In step 6, energization of the heating elements 18A and 18B is interrupted to stop the heating of the liquid reducing agent, and the reducing agent flow rate control valve 28 is controlled to close to stop the injection of the liquid reducing agent. .
According to such a configuration, since the liquid reducing agent is injected and added to the upstream side of the NOx reduction catalyst 16 after being heated, even if the droplets are mixed with the exhaust, it is possible to suppress a decrease in the exhaust temperature. it can. In addition, since the vaporization of the liquid reducing agent is promoted by heating, the supply distribution of the reducing agent to the NOx reduction catalyst 16 is made uniform, and the diffusibility of the reducing agent can be improved. The NOx purification efficiency of the NOx reduction catalyst 16 can be improved by using the minimum liquid reducing agent by the synergistic effect of suppressing the decrease in the exhaust temperature and improving the diffusibility of the reducing agent.
[0024]
In addition, when a reforming catalyst is applied to the inner wall surface of the reducing agent flow path 18C of the reducing agent injection valve 18 on the assumption that an aqueous urea solution is used as the liquid reducing agent, urea ((NH 2 ) 2 is used here. CO) is reformed to ammonia (NH 3 ). Since ammonia is injected and added from the reducing agent injection valve 18 into the exhaust passage 12, the NOx reduction reaction by the NOx reduction catalyst 16 is promoted, and the NOx purification efficiency can be further improved. Needless to say, when hydrocarbon (HC) is used as the reducing agent, it is not necessary to apply the reforming catalyst.
[0025]
Here, since the catalyst made of titanium oxide (TiO 2 ), alumina (Al 2 O 3 ) and silica (SiO 2 ) is used as the reforming catalyst, urea as a reducing agent is effectively reformed to ammonia. can do.
Further, since the reducing agent flow path 18C extends in the axial direction and the reducing agent introduction port 18E is opened at a position offset with respect to the axial center in the cross section, the reducing agent injection valve 18 has a reducing agent flow. A swirling flow is generated in the path 18C. Therefore, the liquid reducing agent is effectively heated, and the NOx purification efficiency by the NOx purification catalyst 16 can be further improved. When the reforming catalyst is applied to the inner wall surface of the reducing agent channel 18C, the reducing agent can be effectively reformed by the swirling flow.
[0026]
In addition, since the heating amount of the reducing agent in the reducing agent injection valve 18 is controlled based on the reducing agent injection flow rate, the exhaust temperature Te, and the reducing agent temperature Tr, the heating amount can be minimized and the heating is performed. Power consumption and heat deterioration of the heating elements 18A and 18B can be suppressed as much as possible.
In addition, the heating elements 18A and 18B of the reducing agent injection valve 18 may be controlled by the control unit 26, or a self-temperature adjusting type may be used. Needless to say, the exhaust emission control device of the present invention is not limited to a diesel engine, but can also be applied to an internal combustion engine such as a gasoline engine.
[0027]
【The invention's effect】
As described above, according to the first aspect of the present invention, by the synergistic effect of suppressing the decrease in the exhaust temperature and improving the diffusibility of the reducing agent, the minimum amount of liquid reducing agent is used and the nitrogen oxide reduction catalyst is used. The purification efficiency of nitrogen oxides can be improved. Moreover, the liquid reducing agent can be effectively heated by the swirling flow generated in the reducing agent channel.
According to the second aspect of the present invention, since the swirling flow is generated in the reducing agent flow path, urea as the reducing agent is effectively reformed to ammonia, so that the reduction reaction of nitrogen oxides is promoted. Moreover, the purification efficiency of nitrogen oxides can be further improved.
[0028]
According to the invention described in claim 3, by using the reforming catalyst made of titanium oxide, alumina and silica, urea as the reducing agent can be effectively reformed to ammonia .
[0029]
According to the fourth aspect of the present invention, since the heating amount of the liquid reducing agent becomes the minimum necessary, the power consumption required for heating the liquid reducing agent and the thermal deterioration of the heating element can be suppressed as much as possible.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a diesel engine equipped with an exhaust purification device according to the present invention. FIG. 2 shows details of a reducing agent injection valve, (A) is a longitudinal sectional view, and (B) is a transverse sectional view. 3] Flow chart showing the control contents of the exhaust purification device [FIG. 4] Explanatory diagram of the principle for calculating the power supplied to the heating element
10 diesel engine 12 exhaust passage 16 NOx reduction catalyst 18 reducing agent injection valve 18A heating element 18B heating element 18C reducing agent passage 18E reducing agent introduction port 20 constant pressure pump 22 reducing agent introduction path 24 reducing agent storage tank 26 control unit 28 reduction Agent flow rate control valve 30 NOx sensor 32 Exhaust temperature sensor 34 Intake flow rate sensor 36 Rotational speed sensor 38 Load sensor 40 Reductant temperature sensor

Claims (4)

内燃機関の排気通路に介装され、排気中の窒素酸化物を還元反応により無害物質に転化させる窒素酸化物還元触媒と、
液体還元剤を加熱しつつ、前記窒素酸化物還元触媒の上流側に添加する還元剤噴射弁と、
を含んで構成され、
前記還元剤噴射弁は、軸方向に延びつつ略同心に配設される２つの発熱体の間に還元剤流路が形成されると共に、該還元剤流路の横断面において還元剤導入口が軸中心に対してオフセットした位置に開口していることを特徴とする内燃機関の排気浄化装置。A nitrogen oxide reduction catalyst that is interposed in the exhaust passage of the internal combustion engine and converts the nitrogen oxide in the exhaust gas into a harmless substance by a reduction reaction;
A reducing agent injection valve that is added to the upstream side of the nitrogen oxide reduction catalyst while heating the liquid reducing agent;
It is configured to include a,
In the reducing agent injection valve, a reducing agent flow path is formed between two heating elements that extend in the axial direction and are substantially concentric, and a reducing agent introduction port is formed in a cross section of the reducing agent flow path. An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas purification apparatus is opened at a position offset with respect to a shaft center . 前記還元剤噴射弁の還元剤流路内壁面には、液体還元剤としての尿素（（ＮＨ2）2ＣＯ）をアンモニア（ＮＨ3）に改質する改質触媒が塗布されたことを特徴とする請求項１記載の内燃機関の排気浄化装置。A reforming catalyst for reforming urea ((NH 2 ) 2 CO) as a liquid reducing agent to ammonia (NH 3 ) is applied to the inner wall surface of the reducing agent flow path of the reducing agent injection valve. The exhaust emission control device for an internal combustion engine according to claim 1. 前記改質触媒は、酸化チタン（ＴｉＯ2），アルミナ（Ａｌ2Ｏ3）及びシリカ（ＳｉＯ2）からなることを特徴とする請求項２記載の内燃機関の排気浄化装置。The reforming catalyst is titanium oxide (TiO 2), alumina (Al 2 O 3) and silica exhaust purification system of an internal combustion engine according to claim 2, characterized in that it consists of (SiO 2). 機関運転状態を検出する運転状態検出手段と、
前記液体還元剤の温度を検出する還元剤温度検出手段と、
前記運転状態検出手段及び還元剤温度検出手段により夫々検出された機関運転状態及び還元剤温度に基づいて、前記還元剤噴射弁による液体還元剤の加熱量を制御する加熱量制御手段と、
を含んだ構成であることを特徴とする請求項１〜請求項３のいずれか１つに記載の内燃機関の排気浄化装置。 An operating state detecting means for detecting an engine operating state;
Reducing agent temperature detecting means for detecting the temperature of the liquid reducing agent;
A heating amount control means for controlling the heating amount of the liquid reducing agent by the reducing agent injection valve based on the engine operating state and the reducing agent temperature detected by the operating state detecting means and the reducing agent temperature detecting means, respectively;
It is inclusive constitute an exhaust purification system of an internal combustion engine according to any one of claims 1 to 3, characterized in.
JP2001138393A 2001-05-09 2001-05-09 Exhaust gas purification device for internal combustion engine Expired - Fee Related JP4131784B2 (en)

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JP4262522B2 (en) 2003-05-28 2009-05-13 株式会社日立ハイテクノロジーズ Exhaust gas treatment device for engine and exhaust gas treatment method
WO2006025110A1 (en) * 2004-09-02 2006-03-09 Nissan Diesel Motor Co., Ltd. Exhaust gas purifier
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