JP3842047B2 - Intake stratification method in a direct injection internal combustion engine - Google Patents

Intake stratification method in a direct injection internal combustion engine Download PDF

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JP3842047B2
JP3842047B2 JP2001015617A JP2001015617A JP3842047B2 JP 3842047 B2 JP3842047 B2 JP 3842047B2 JP 2001015617 A JP2001015617 A JP 2001015617A JP 2001015617 A JP2001015617 A JP 2001015617A JP 3842047 B2 JP3842047 B2 JP 3842047B2
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intake
combustion chamber
intake air
region
stratification
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JP2001280139A (en
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清己 中北
孝之 冬頭
和久 稲垣
義博 堀田
一弘 秋浜
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Toyota Motor Corp
Toyota Central R&D Labs Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
    • F02B23/02—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition
    • F02B23/06—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition the combustion space being arranged in working piston
    • F02B23/0672—Omega-piston bowl, i.e. the combustion space having a central projection pointing towards the cylinder head and the surrounding wall being inclined towards the cylinder center axis
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B2275/00—Other engines, components or details, not provided for in other groups of this subclass
    • F02B2275/14—Direct injection into combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
    • F02B23/02—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition
    • F02B23/06—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition the combustion space being arranged in working piston
    • F02B23/0618—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition the combustion space being arranged in working piston having in-cylinder means to influence the charge motion
    • F02B23/0621—Squish flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
    • F02B23/02—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition
    • F02B23/06—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition the combustion space being arranged in working piston
    • F02B23/0618—Other engines characterised by special shape or construction of combustion chambers to improve operation with compression ignition the combustion space being arranged in working piston having in-cylinder means to influence the charge motion
    • F02B23/0624—Swirl flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F1/00—Cylinders; Cylinder heads 
    • F02F1/24—Cylinder heads
    • F02F2001/244—Arrangement of valve stems in cylinder heads
    • F02F2001/247—Arrangement of valve stems in cylinder heads the valve stems being orientated in parallel with the cylinder axis
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Combustion Methods Of Internal-Combustion Engines (AREA)
  • Exhaust-Gas Circulating Devices (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、燃料を燃焼室に噴射する直接噴射式内燃機関において、燃焼室の吸気を成層化する方法に関する。
【０００２】
【従来の技術】
排気還流装置を備えた直接噴射式圧縮着火内燃機関において、特開平１１−１４８４２９号公報に開示されているように、排気中の有害物質を低減するため、燃焼室の吸気を成層化する技術が提案されている。
【０００３】
燃焼室は、同一方向のスワール流を同心状に形成する２個の吸気ポートを設け、スワール流の上流側の吸気ポートでは、燃焼室の中心部に小径のスワール流を、下流側の吸気ポートでは、燃焼室の周辺部に大径のスワール流を形成する。
【０００４】
上流側の吸気ポートを通過する吸気には還流排気を混入し、下流側の吸気ポートを通過する吸気には還流排気を混入せず、燃焼室中心部の円柱状領域には、還流排気を混入した吸気を、燃焼室周辺部の円環状領域には、還流排気を混入しない吸気を配置する。
【０００５】
【発明が解決しようとする課題】
ところが、上記の従来技術においては、燃焼室に小径のスワール流と大径のスワール流を内外に形成するとしているが、スワール流は、径を拡大させる遠心力があるので、小径のスワール流は、遠心力によって外側に拡大し、燃焼室の周壁によって径が拡大しない大径のスワール流と衝突して混合することになる。従って、燃焼室の中心部の円柱状領域と周辺部の円環状領域に、組成の異なる吸気を配置することは困難である。
【０００６】
また、吸気行程において、燃焼室に小径と大径のスワール流が内外に形成されたとしても、次の圧縮行程には、ピストン頂面の周辺部上の吸気がピストン頂面の中央部のキャビティに流入するスキッシュ流が発生するので、燃焼室周辺部の大径のスワール流は、スキッシュ流によって燃焼室中心側に運ばれ、燃焼室中心部の小径のスワール流と衝突して混合することになる。従って、吸気行程において形成した吸気の内外の成層状態を圧縮行程の終期近傍まで維持することは困難である。
【０００７】
結局、燃料が燃焼室に噴霧されて燃焼を開始する圧縮行程の終期近傍の時点では、組成の異なる吸気が燃焼室の中心部の円柱状領域と周辺部の円環状領域に配置されているものとは認められない。
【０００８】
燃焼室の吸気が燃料の燃焼開始時に所望の状態に成層化されていなければ、燃焼室における燃料の燃焼を所望の通りに制御することができない。
【０００９】
【課題を解決するための着眼と研究】
１）直接噴射式圧縮着火内燃機関において、燃焼室の吸気中に燃料噴射弁から噴射された燃料流は、根元側部分では、その周囲の空気を燃料流内部に巻き込むと共に、その周囲の空気を燃料流外周に連行し、燃料流に随伴する空気流を誘起する。
【００１０】
また、燃焼室の吸気中に噴射された燃料流は、高速で飛翔しながら、分裂して微粒化し、蒸気になり、蒸気になる先端側部分で燃焼して火炎を生ずる。なお、燃料流は、先端側部分より根元側で燃焼して火炎を生ずる場合もあるが、高温の火炎が大規模に発生する部分は、燃料流の先端側部分である。
【００１１】
燃焼室は、燃料を噴射して燃焼している間、燃料流の根元側に、燃料と空気を混合して混合気を形成する混合気形成領域が形成されると共に、燃料流の先端側に、混合気が激しく燃焼して高温の火炎が大規模に発生する火炎発生領域が形成され、混合気形成領域と火炎発生領域に大別される。
【００１２】
燃焼室の混合気形成領域において形成される混合気の組成は、燃料噴射時ないし燃焼開始時に、混合気形成領域に存在する吸気の組成に影響される。
【００１３】
また、燃焼室の混合気形成領域で形成された混合気は、燃料流ないし混合気流によって燃焼室の火炎発生領域に運ばれる。燃焼室の火炎発生領域は、混合気形成領域から火炎発生領域に運ばれた混合気と、燃焼開始前から火炎発生領域に存在した吸気、及び、火炎発生領域で燃料の燃焼により発生した気体が存在することになり、それらが混在した状態の中で燃料の燃焼が行われる。燃焼室の燃料の燃焼状態は、燃焼開始時に、火炎発生領域に存在する気体の組成に影響される。
【００１４】
換言すると、燃料噴射時ないし燃焼開始時に燃焼室の混合気形成領域に存在する気体に、所望の混合気を形成するのに適した組成の気体を選択すると共に、燃焼開始時に燃焼室の火炎発生領域に存在する気体に、所望の燃焼状態を発生させるのに適した組成の気体を選択すると、燃焼室の燃料の燃焼状態を所望の通りに制御することができる。
【００１５】
即ち、燃焼室の吸気を混合気形成領域と火炎発生領域に成層化することにより、燃焼室の燃料の燃焼状態を制御することができる。
【００１６】
２）燃料流の先端側部分において大規模な高温火炎の発生が始まる火炎発生開始位置は、燃料噴射弁の噴口から燃料流の分裂開始位置までの距離を噴霧分裂距離とすると、燃料噴射弁噴口位置から噴霧分裂距離の１〜１．５倍位離れた位置になる。なお、噴霧分裂距離＝１５．８（燃料密度／空気密度）1/2・（燃料噴射弁噴口径）である。
【００１７】
また、燃料噴射弁は、ピストン頂面と対面する燃焼室天井面の中心部に多数の噴口を配置し、噴射方向は、多数であって放射方向であり、燃焼室の半径方向からピストン頂面側に傾斜し、圧縮行程の終期近傍においてピストン頂面中央部のキャビティの周辺部に向かう。
【００１８】
従って、燃焼室の火炎発生領域は、各燃料噴射方向には燃焼室の燃料噴射弁噴口位置から噴霧分裂距離の約１〜１．５倍以上離れた領域になり、燃焼室の中心軸に対してほぼ対称になる。混合気形成領域は、各燃料噴射方向には燃焼室の燃料噴射弁噴口位置から噴霧分裂距離の約１〜１．５倍以内の領域になり、燃焼室の中心軸に対してほぼ対称になる。
【００１９】
これらのことから、燃料が燃焼を開始する圧縮行程の終期近傍において、燃料が噴射される燃焼室の天井面中心部を中心とする概略半球面ないし概略扁平半球面の内側の領域と外側の領域に燃焼室の吸気を成層化することができると、上記の内側の領域と外側の領域にそれぞれ所望の組成の吸気を配置することにより、燃料の燃焼状態を制御することができる。
【００２０】
３）複数の吸気ポートで燃焼室に複数の同一方向の吸気スワール流を形成し、燃料を燃焼室にその天井面の中心部からピストン頂面中央部のキャビティの周辺部に向けて噴射する直接噴射式圧縮着火内燃機関において、燃焼室や吸気ポートの形状、従って、吸気のスキッシュ流やスワール流の流動特性を選択して吸気成層化装置を構成すると、吸気を次のように成層化することができる。
【００２１】
吸気行程において、図２に例示するように、スワール流の下流側の吸気ポート３では、燃焼室１の上部にその周壁に沿う第１吸気１１のスワール流を、上流側の吸気ポート４では、燃焼室１の下部にその周壁に沿う第２吸気１２のスワール流を形成する。図４と図５に例示するように、燃焼室１において組成の異なる第１吸気１１のスワール流と第２吸気１２のスワール流が上下に配置された状態は、圧縮行程の中程まで継続される。
【００２２】
スキッシュ流が発生する圧縮行程の後半において、ピストン頂面の周辺部上のスワール流は、スキッシュ流によってピストン頂面の中央部のキャビティ内に運ばれ、径の縮小に伴うスワール方向速度の増加による遠心力によって、キャビティの中心に向かわず、キャビティの周壁に沿って流れ、キャビティの底面に向かう。キャビティは、スキッシュ流の発生前には、全域に第２吸気が存在するが、スキッシュ流が発生すると、図６（ａ）（ｂ）（ｃ）に時間経過順に例示するように、中央領域に第１吸気１１が流入し、周辺領域と底部領域のみに第２吸気１２が存在することになる。
【００２３】
燃料が燃焼を開始する圧縮行程の終期近傍においては、図１に例示するように、燃焼室１は、燃料が噴射される天井面中心位置を中心とする概略扁平半球面１３内の領域には、第１吸気１１が主に存在し、その外側の領域には、第２吸気１２が主に存在することになる。燃料の燃焼開始時に燃焼室の燃料噴射位置を中心とする概略半球面ないし概略扁平半球面の内側の領域と外側の領域に、組成の異なる吸気１１、１２が成層化されることになる。
【００２４】
４）排気還流装置を備えた直接噴射式圧縮着火内燃機関において、燃焼期間中に、燃料噴射弁から噴射される燃料流の根元側部分の周囲に、還流排気を分布させずに、新鮮空気を分布させると、燃料流ないし混合気流によってその先端部に新鮮空気が運ばれ、酸素不足状態で燃焼する燃料流先端部ないしキャビティ谷部に酸素が供給され、酸素濃度がスート（すす）生成抑制値以上に増加して、スートの生成が減少する。だだし、この時、酸素濃度がＮOx（窒素酸化物）生成値までには上昇しないように制御する。また、理論空燃比近傍のリーン側領域で高温燃焼してＮOxが発生する燃焼室のスキッシュエリアとキャビティ周辺部に、還流排気を混入した吸気を分布させると、酸素濃度、燃焼温度が低下して、ＮOxの生成が減少する。
【００２５】
内燃機関の負荷が多くて燃料の噴射終了時期が遅いとき、又は、内燃機関の回転数が高くて逆スキッシュ流が強いときには、燃料は、燃焼室のキャビティ外に流出する割合が高くなり、キャビティ外で酸素不足状態で燃焼し、キャビティ内で酸素過剰状態で燃焼する。すると、キャビティ外で主にスートが発生し、キャビティ内で主にＮOxが発生する。
【００２６】
このようなときには、燃焼室の成層パターンを逆にし、燃料噴射位置を中心とする概略半球面ないし概略扁平半球面の内側の領域に、還流排気が混入している吸気又は還流排気濃度が濃い吸気を、その外側の領域に、還流排気が混入していない吸気又は還流排気濃度が薄い吸気を配置する。すると、燃焼室のキャビティ外、スキッシュエリアでは、酸素濃度が増加し、スートの生成が抑制されると同時にスートの酸化が促進されて、スートが減少する。だだし、この時、酸素濃度がＮOx生成値までには上昇しないように制御して、ＮOxの増加を防ぐ。
【００２７】
即ち、内燃機関の運転条件に応じて、燃焼室１の成層パターンを変更する必要がある。燃焼室１の成層度も変更する必要がある。
【００２８】
図１〜図６に例示する内燃機関において、運転条件に応じて、スワール流の下流側の吸気ポート３を通過する第１吸気に混入される還流排気の量と、上流側の吸気ポート４を通過する第２吸気に混入される還流排気の量をそれぞれ増減すると、燃焼室１の成層パターンは、変更される。燃焼室１の概略扁平半球面１３内の領域でその外側の領域より還流排気の濃度が低くなる正成層パターンになる。また、燃焼室１の概略扁平半球面１３内の領域でその外側の領域より還流排気の濃度が高くなる逆成層パターンになる。更に、燃焼室１の概略扁平半球面１３内の領域とその外側の領域で還流排気の濃度が等しくなる均質パターンになる。
【００２９】
また、内燃機関の運転条件に応じて、第１吸気に混入される還流排気の量と、第２吸気に混入される還流排気の量をそれぞれ増減すると、燃焼室１の成層度が変更される。概略扁平半球面１３内の還流排気濃度に対する、概略扁平半球面１３外の還流排気濃度の比、成層度が増減する。
【００３０】
【課題を解決するための手段】
１）複数の吸気ポートで燃焼室に複数の同一方向の吸気スワール流を形成し、燃料を燃焼室にそのピストン頂面と対面する天井面の中心部からピストン頂面中央部のキャビティの周辺部に向けて噴射する直接噴射式内燃機関において、
複数の吸気スワール流は、特定成分の濃度が異なる第１吸気と第２吸気にし、
吸気行程において、燃焼室の上部にその周壁に沿う第１吸気のスワール流を形成し、燃焼室の下部にその周壁に沿うスワール流を形成し、圧縮行程の中程まで、燃焼室において第１吸気のスワール流と第２吸気のスワール流が上下に配置された状態を継続し、
スキッシュ流が発生する圧縮行程の後半に、ピストン頂面中央部のキャビティにおいて、中央領域に第１吸気を流入させ、周辺領域と底部領域に第２吸気を残存させ、
燃料が燃焼を開始する圧縮行程の終期近傍において、燃焼室の燃料噴射位置を中心とする概略半球面ないし概略扁平半球面の内側の領域に第１吸気を、外側の領域に第２吸気を主に配置し、内側の領域と外側の領域に、特定成分の濃度が異なる吸気を配置することを特徴とする吸気成層化方法。
【００３１】
２）上記の吸気成層化方法において、
直接噴射式内燃機関の運転条件に応じて、燃焼室の成層パターンを、上記の内側の領域で上記の外側の領域より吸気の特定成分の濃度が低くなる正成層パターン、上記の内側の領域で上記の外側の領域より吸気の特定成分の濃度が高くなる逆成層パターン、又は、上記の内側の領域と上記の外側の領域で吸気の特定成分の濃度が等しくなる均質パターンに変更することを特徴とする。
【００３２】
３）上記の吸気成層化方法において、
直接噴射式内燃機関の運転条件に応じて、燃焼室の成層度、上記の内側の領域における吸気の特定成分の濃度に対する、上記の外側の領域における吸気の特定成分の濃度の比を変更することを特徴とする。
【００３４】
４）上記の吸気成層化方法において、
燃焼室の燃料噴射位置を中心とする概略半球面ないし概略扁平半球面は、燃料の噴射方向には燃焼室の燃料噴射位置から噴霧分裂距離の１〜１．５倍位離れていることを特徴とする。
【００３５】
【発明の効果】
圧縮行程終期近傍の燃料の燃焼開始時に、燃焼室の燃料噴射位置を中心とする概略半球面ないし概略扁平半球面の内側の領域と外側の領域に、それぞれ、所望の組成の吸気、所望の成分濃度の吸気を配置し、燃料の燃焼状態を制御することができる。
【００３６】
【発明の実施の形態】
［第１例（図１〜図８参照）］
本例の吸気成層化装置を備えた直接噴射式圧縮着火内燃機関は、図１に示すように、燃焼室１の天井面の中心部に燃料噴射弁２の多数の噴口を配置し、燃焼室１の天井面の一側側に２個の吸気ポート３、４と吸気弁５、６を、他側側に２個の排気ポート７と排気弁８を設け、ピストン頂面の中央部に中心軸対称形状のキャビティ９を形成し、キャビティ９の底面中央部に山部１０を設けている。
【００３７】
燃料噴射弁２は、圧縮行程の終期近傍において、燃料を多数の噴口から放射方向にキャビティ９の周辺部に向けて噴射する。
【００３８】
２個の吸気ポート３、４は、吸気行程において、図２に示すように、燃焼室１に吸気のスワール流１１、１２を同一方向に形成する。スワール流の下流側の吸気ポート３は、図２と図３に示すように、ヘリカルポート形状であり、吸気がほぼ燃焼室１天井面に沿う向きに流出し、燃焼室１の天井面側の上部にその周壁に沿う強い第１吸気のスワール流１１を形成する。上流側の吸気ポート４は、タンジェンシャルポート形状であり、第１吸気のスワール流１１との衝突を避けるため、吸気が斜め下向きに流出し、燃焼室１のピストン頂面側の下部にその周壁に沿う第２吸気のスワール流１２を形成する。
【００３９】
本例の吸気成層化装置においては、吸気行程に、図２に示すように、燃焼室１の上部と下部に、それぞれ、その周壁に沿う第１吸気のスワール流１１、第２吸気のスワール流１２を形成すると、吸気行程の終期に、図４に示すように、燃焼室１に第１吸気のスワール流１１と第２吸気のスワール流１２が上下に成層化される。吸気行程の終期には、上流側の吸気ポート４から最後に流入した第２吸気１２の最後尾部分が燃焼室１の上部に存在するため、第１吸気１１と第２吸気１２の境界面１３は、ピストン頂面に平行する平面にならず、傾斜した凹凸曲面になる。
【００４０】
燃焼室１の組成の異なる第１吸気１１と第２吸気１２は、時間の経過に従って混ざり合い、一方の吸気にのみ含まれていた成分が他方の吸気にも含まれるようになり、その成分の濃度が連続して変化する状態になるので、その成分の濃度がほぼ中間値になる面を第１吸気１１と第２吸気１２の境界面１３とする。
【００４１】
圧縮行程になると、第２吸気１２の最後尾部分が燃焼室１の下部に移動し、第１吸気１１と第２吸気１２の混合が進行し、圧縮行程の中程には、図５に示すように、第１吸気１１と第２吸気１２の境界面１３は、ピストン頂面に平行する平面に近づく。燃焼室１に第１吸気スワール流１１と第２吸気スワール流１２が上下に成層化された状態は、圧縮行程の中程まで継続する。
【００４２】
スキッシュ流が発生する圧縮行程の後半には、ピストン頂面の周辺部上のスワール流は、スキッシュ流によってピストン頂面の中央部のキャビティ９内に運ばれ、径の縮小に伴うスワール方向速度の増加による遠心力によって、キャビティ９の中心に向かわず、キャビティ９の周壁に沿って流れ、キャビティ９の底面に向かう。キャビティ９内は、図６（ａ）（ｂ）（ｃ）に時間経過順に示すように、燃焼室１下部の第２吸気１２が充満した状態から、中央領域に燃焼室１上部の第１吸気１１が流入し、周辺領域と底部領域のみに第２吸気１２が残る。
【００４３】
燃料が燃料噴射弁２から噴射されて燃焼を開始する圧縮行程の終期近傍には、図１に示すように、燃焼室１の燃料が噴射される天井面中心部を中心とする概略扁平半球面１３の内側の領域には、第１吸気１１が主に存在し、その外側の領域には、第２吸気１２が主に存在する。燃料の燃焼開始時に、燃焼室１の燃料噴射位置を中心とする概略扁平半球面１３の内側の領域と外側の領域に吸気１１、１２が成層化される。
【００４４】
上記の概略扁平半球面１３は、燃料噴射方向の半径を噴霧分裂距離の１〜１．５倍位にすると、燃焼室１の混合気形成領域と火炎発生領域に吸気１１、１２が成層化される。
【００４５】
圧縮行程の終期近傍において、第１吸気１１のスワール流が強過ぎると、図７（ａ）に示すように、第１吸気１１は、スキッシュ流によってキャビティ９の底面に運ばれる際、キャビティ９の周壁を下る逆トロイダル流になり、キャビティ９の底面に流入し、キャビティ９の周壁と底面に存在した第２吸気１２をキャビティ９の中央部に押し退ける。
【００４６】
本例においては、吸気１１、１２のスワール流とスキッシュ流が適度であるので、図７（ｂ）に示すように、第１吸気１１は、キャビティ９の山部１０と周壁の中間部を下るトロイダル流になり、その中間部に存在した第２吸気１２をキャビティ９の周辺領域と底部領域に押し退け、燃焼室１の燃料噴射位置を中心とする概略扁平半球面１３の内外に吸気１１、１２が成層化される。
【００４７】
本例の吸気成層化装置は、吸気１１、１２がこのように成層化されるように、吸気１１、１２のスキッシュ流やスワール流の流動特性を決定する燃焼室１や吸気ポート３、４の形状を選択している。これらの形状によって吸気１１、１２の成層の度合いや境界面１３の形状寸法を制御することができる。
【００４８】
上記の形状には、燃焼室１のキャビティ９形状、ピストン頂面周辺部と天井面周辺部との間の間隔や、天井面からの吸気弁５、６下面の凹み量が例示される。
【００４９】
模擬実験例
本例の吸気成層化装置において、燃焼室１に下流側の吸気ポート３から流入する第１吸気１１を新鮮空気１００％にし、上流側の吸気ポート４から流入する第２吸気１２を新鮮空気５０％と還流排気５０％にした場合について、圧縮行程の終期における燃焼室１の還流排気濃度の分布を数値計算により求めた。
【００５０】
図８はその結果を示し、同図（ｂ）は下流側と上流側の吸気ポート３、４の間を通る燃焼室１の中央縦断面、同図（ａ）はその中央縦断面に直交する中央縦断面における還流排気濃度（ＥＧＲ率）の分布を明度で示す。
【００５１】
これらの図から明らかなように、圧縮行程の終期に、燃焼室１の還流排気濃度分布の等高面が燃料噴射位置を中心とする概略扁平半球面状に現れ、燃料噴射位置に近付くに従って還流排気濃度が薄くなり、還流排気濃度の分布がほぼ軸対称になる。燃焼室１の吸気は、燃料噴射位置を中心とする概略扁平半球面の内外に吸気１１、１２が成層化されることを示している。
【００５２】
［第２例（図９参照）］
本例の吸気成層化装置は、第１例のそれにおいて、吸気の成層度を高めるため、下流側と上流側の吸気ポート３、４で吸気弁５、６の開放期間をずらす。
【００５３】
燃焼室１の上部に第１吸気１１を流入させる下流側の吸気ポート３では、図９に示すように、吸気弁５を遅い時期に開いて遅い時期に閉じる。燃焼室１の下部に第２吸気１２を流入させる上流側の吸気ポート４では、吸気弁６を早い時期に開いて早い時期に閉じる。
【００５４】
吸気行程の前期には、上流側の吸気ポート４の吸気弁６のみが開放し、燃焼室１の下部に配置する第２吸気１２のみが燃焼室１に流入する。吸気行程の中期には、両者の吸気ポート３、４の吸気弁５、６が開放して第１吸気１１と第２吸気１２が燃焼室１に流入する。吸気行程の後期には、下流側の吸気ポート３の吸気弁５のみが開放し、燃焼室１の上部に配置する第１吸気１１のみが燃焼室１に流入する。
【００５５】
下流側と上流側の吸気ポート３、４で吸気弁５、６の開放期間が一致する第１例の場合に比較して、吸気行程の終期に第１吸気１１と第２吸気１２が上下に成層化される度合いが高くなり、圧縮行程の終期に吸気１１、１２が燃料噴射位置を中心とする概略扁平半球面１３の内外に成層化される度合いが高くなる。
【００５６】
その他の点は、第１例におけるのと同様である。
【００５７】
［第３例（図１０参照）］
本例の吸気成層化装置は、第１例のそれにおいて、吸気の成層度を高めるため、上流側の吸気ポート４の片側のみから第２吸気１２を燃焼室１に流入させる。
【００５８】
上流側の吸気ポート４においては、吸気が斜め下向きに流出して燃焼室１の周壁に斜めに衝突し、燃焼室１下部の周壁に沿うスワール流になる。タンジェンシャルポート形状の吸気ポート４の燃焼室１周壁側部分を流出する吸気の方が、燃焼室１中心側部分を流出する吸気より、燃焼室１の周壁に衝突するまでの距離が短く、燃焼室１の下部に流入し易い。
【００５９】
そこで、上流側の吸気ポート４は、図１０に示すように、燃焼室１の周壁側部分と中心側部分に２分割する仕切り壁２１を設け、吸気ポート４の燃焼室１周壁側部分に、還流排気のような特定成分の濃度を高くした第２吸気１２を流し、吸気ポート４の燃焼室１周壁側部分から第２吸気１２を燃焼室１の下部に流入させる。吸気ポート４の燃焼室１中心側部分には、上流側の吸気ポート３と同様に第１吸気１１を流し、吸気ポート４の燃焼室１中心側部分から第１吸気１１を燃焼室１に流入させる。
【００６０】
吸気ポート４の燃焼室１周壁側部分から燃焼室１に流入する第２吸気１２は、気流が細くなって、第１吸気１１と混合し難くなる。
【００６１】
上流側の吸気ポート４の全体から第２吸気１２を燃焼室１に流入させる第１例の場合に比較して、吸気行程の終期に第１吸気１１と第２吸気１２が上下に成層化される度合いが高くなり、圧縮行程の終期に吸気１１、１２が燃料噴射位置を中心とする概略扁平半球面１３の内外に成層化される度合いが高くなる。
【００６２】
その他の点は、第１例におけるのと同様である。
【００６３】
［第４例］
本例の吸気成層化装置は、第１例のそれにおいて、吸気の成層度を高めるため、燃焼室１の下部又は上部に吸気が流入し易いサブポートを設ける。
【００６４】
第３例における、燃焼室１の下部に吸気が流入し易い吸気ポート４の燃焼室１周壁側部分と同様な補助吸気ポートを設け、補助吸気ポートから燃焼室１の下部に、特定成分の濃度を高くした第２吸気１２を流入させる。
【００６５】
［第５例（図１１参照）］
本例の吸気成層化装置は、第１例のそれにおいて、内燃機関の運転条件に応じて、燃焼室１の吸気の成層パターンと成層度を変更する。
【００６６】
第１例の内燃機関において、スワール流の下流側の吸気ポート３に接続した第１吸気通路２３に、図１１に示すように、第１流量制御弁２４を介して第１排気還流通路２５を接続し、また、上流側の吸気ポート４に接続した第２吸気通路２６に、第２流量制御弁２７を介して第２排気還流通路２８を接続する。第１流量制御弁２４の開度と第２流量制御弁２７の開度をそれぞれ内燃機関の運転条件に応じて制御する装置２９を設ける。
【００６７】
内燃機関の運転条件に応じて、第１流量制御弁２４の開度と第２流量制御弁２７の開度をそれぞれ制御すると、下流側の吸気ポート３を通過する第１吸気に混入される還流排気の量と、上流側の吸気ポート４を通過する第２吸気に混入される還流排気の量がそれぞれ増減し、燃焼室１の成層パターンは、変更される。燃焼室１の概略扁平半球面１３内の領域でその外側の領域より還流排気の濃度が低くなる正成層パターンになる。また、燃焼室１の概略扁平半球面１３内の領域でその外側の領域より還流排気の濃度が高くなる逆成層パターンになる。更に、燃焼室１の概略扁平半球面１３内の領域とその外側の領域で還流排気の濃度が等しくなる均質パターンになる。
【００６８】
また、内燃機関の運転条件に応じて、第１流量制御弁２４の開度と第２流量制御弁２７の開度をそれぞれ制御すると、燃焼室１の成層度が変更される。概略扁平半球面１３内の還流排気濃度に対する、概略扁平半球面１３外の還流排気濃度の比、具体的には、概略扁平半球面１３内の燃料噴射位置の還流排気濃度に対する、概略扁平半球面１３外のキャビティ底部周辺領域の還流排気濃度の比、成層度が増減する。
【図面の簡単な説明】
【図１】本発明の実施形態の第１例における吸気成層化装置を備えた直接噴射式圧縮着火内燃機関の概略縦断面図。
【図２】同内燃機関における吸気行程中程の燃焼室の概略斜視図。
【図３】同内燃機関における燃焼室の概略平面図。
【図４】同内燃機関における吸気行程終期の燃焼室の概略斜視図。
【図５】同内燃機関における圧縮行程中程の燃焼室の概略斜視図。
【図６】同内燃機関における圧縮行程終期近傍の燃焼室の概略縦断面図で、吸気の流動状態を示す図。
【図７】内燃機関における圧縮行程終期の燃焼室の概略縦断面図で、吸気の流動状態を示す図。
【図８】同内燃機関における模擬実験例の圧縮行程終期の吸気成層化状態を示す図。
【図９】実施形態の第２例における吸気成層化装置を備えた直接噴射式圧縮着火内燃機関の吸気弁揚程図。
【図１０】第３例における吸気成層化装置を備えた直接噴射式圧縮着火内燃機関の燃焼室の概略平面図。
【図１１】第５例における吸気成層化装置を備えた直接噴射式圧縮着火内燃機関の吸気通路部分の概略図。
【符号の説明】
１ 燃焼室
２ 燃料噴射弁
３ スワール流の下流側の吸気ポート
４ スワール流の上流側の吸気ポート
５ スワール流の下流側の吸気弁
６ スワール流の上流側の吸気弁
９ キャビティ
１１ 第１吸気
１２ 第２吸気
１３ 第１吸気と第２吸気の境界面、概略扁平半球面[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for stratifying intake air in a combustion chamber in a direct injection internal combustion engine that injects fuel into the combustion chamber.To the lawRelated.
[0002]
[Prior art]
In a direct injection compression ignition internal combustion engine equipped with an exhaust gas recirculation device, as disclosed in Japanese Patent Laid-Open No. 11-148429, there is a technique for stratifying intake air in a combustion chamber in order to reduce harmful substances in exhaust gas. Proposed.
[0003]
The combustion chamber is provided with two intake ports that concentrically form a swirl flow in the same direction. In the intake port on the upstream side of the swirl flow, a small-diameter swirl flow is provided at the center of the combustion chamber, and the intake port on the downstream side. Then, a large-diameter swirl flow is formed in the periphery of the combustion chamber.
[0004]
Recirculation exhaust is mixed into the intake air passing through the upstream intake port, recirculation exhaust is not mixed into the intake air passing through the downstream intake port, and recirculation exhaust is mixed into the cylindrical region in the center of the combustion chamber. The intake air that does not mix the recirculated exhaust gas is disposed in the annular region around the combustion chamber.
[0005]
[Problems to be solved by the invention]
However, in the above prior art, a small-diameter swirl flow and a large-diameter swirl flow are formed inside and outside in the combustion chamber. However, since the swirl flow has a centrifugal force that expands the diameter, the small-diameter swirl flow Then, it expands outward due to centrifugal force, and collides with and mixes with a large-diameter swirl flow whose diameter does not expand due to the peripheral wall of the combustion chamber. Therefore, it is difficult to arrange intake air having different compositions in the cylindrical region at the center of the combustion chamber and the annular region at the periphery.
[0006]
In addition, even if a small diameter and large diameter swirl flow is formed inside and outside in the combustion chamber during the intake stroke, the intake air on the periphery of the piston top surface is in the center of the piston top surface in the next compression stroke. Therefore, the large-diameter swirl flow around the combustion chamber is transported to the combustion chamber center side by the squish flow and collides with the small-diameter swirl flow at the combustion chamber central portion. Become. Therefore, it is difficult to maintain the stratified state inside and outside the intake air formed in the intake stroke to the vicinity of the end of the compression stroke.
[0007]
Eventually, near the end of the compression stroke in which fuel is sprayed into the combustion chamber and starts combustion, intake air of different composition is arranged in the cylindrical region in the center of the combustion chamber and the annular region in the periphery It is not accepted.
[0008]
If the intake air in the combustion chamber is not stratified to a desired state at the start of fuel combustion, fuel combustion in the combustion chamber cannot be controlled as desired.
[0009]
[Focus and research to solve problems]
1) In a direct injection type compression ignition internal combustion engine, the fuel flow injected from the fuel injection valve during intake of the combustion chamber entrains the surrounding air inside the fuel flow at the base portion and Entrains the fuel flow perimeter and induces an air flow associated with the fuel flow.
[0010]
In addition, the fuel flow injected into the intake air of the combustion chamber flies at a high speed, breaks up and atomizes, becomes steam, and burns at the tip side portion that becomes steam, generating a flame. In some cases, the fuel flow burns closer to the root side than the tip side portion to generate a flame, but the portion where the high temperature flame is generated on a large scale is the tip side portion of the fuel flow.
[0011]
The combustion chamber is formed with an air-fuel mixture formation region in which fuel and air are mixed to form an air-fuel mixture on the base side of the fuel flow while fuel is injected and burned, and at the front end side of the fuel flow. In addition, a flame generation region is formed in which the air-fuel mixture burns vigorously and a high-temperature flame is generated on a large scale, and is broadly divided into a mixture generation region and a flame generation region.
[0012]
The composition of the air-fuel mixture formed in the air-fuel mixture formation region of the combustion chamber is affected by the composition of the intake air existing in the air-fuel mixture formation region at the time of fuel injection or combustion start.
[0013]
Further, the air-fuel mixture formed in the air-fuel mixture formation region of the combustion chamber is conveyed to the flame generation region of the combustion chamber by the fuel flow or the mixed air flow. The flame generation area of the combustion chamber consists of the air-fuel mixture carried from the mixture formation area to the flame generation area, the intake air existing in the flame generation area before the start of combustion, and the gas generated by the combustion of fuel in the flame generation area The fuel is burned in a state in which they exist. The combustion state of the fuel in the combustion chamber is affected by the composition of the gas present in the flame generation region at the start of combustion.
[0014]
In other words, a gas having a composition suitable for forming a desired air-fuel mixture is selected as the gas existing in the air-fuel mixture formation region of the combustion chamber at the time of fuel injection or at the start of combustion, and flame is generated in the combustion chamber at the start of combustion. When a gas having a composition suitable for generating a desired combustion state is selected as the gas existing in the region, the combustion state of the fuel in the combustion chamber can be controlled as desired.
[0015]
That is, the combustion state of the fuel in the combustion chamber can be controlled by stratifying the intake air in the combustion chamber into the mixture formation region and the flame generation region.
[0016]
2) The flame generation start position where the generation of a large-scale high-temperature flame starts at the front end portion of the fuel flow is defined as the fuel injection valve nozzle, where the distance from the fuel injection valve nozzle to the fuel flow split start position is the spray splitting distance. The position is 1 to 1.5 times the spray splitting distance from the position. Spray splitting distance = 15.8 (fuel density / air density)1/2-(Fuel injection valve nozzle diameter).
[0017]
In addition, the fuel injection valve has a large number of injection holes arranged at the center of the combustion chamber ceiling surface facing the piston top surface, and the injection directions are many and radial, and the piston top surface from the radial direction of the combustion chamber. In the vicinity of the end of the compression stroke, the piston heads toward the periphery of the cavity at the center of the top surface of the piston.
[0018]
Therefore, the flame generation region of the combustion chamber is a region separated from the fuel injection valve nozzle position of the combustion chamber by about 1 to 1.5 times or more of the spray splitting distance in each fuel injection direction, with respect to the central axis of the combustion chamber. Almost symmetrical. The air-fuel mixture formation region is a region within about 1 to 1.5 times the spray splitting distance from the fuel injection valve nozzle position of the combustion chamber in each fuel injection direction, and is substantially symmetric with respect to the central axis of the combustion chamber .
[0019]
Therefore, in the vicinity of the end of the compression stroke in which the fuel starts to burn, the inner and outer regions of the substantially hemispherical surface or the generally flat hemispherical surface centered on the center of the ceiling surface of the combustion chamber into which the fuel is injected. If the intake air in the combustion chamber can be stratified, the combustion state of the fuel can be controlled by disposing the intake air having a desired composition in the inner region and the outer region.
[0020]
3) A plurality of intake swirl flows in the same direction are formed in the combustion chamber by a plurality of intake ports, and fuel is directly injected into the combustion chamber from the center of the ceiling surface toward the periphery of the cavity at the center of the piston top surface. In an injection compression ignition internal combustion engine, when the intake stratification device is configured by selecting the shape of the combustion chamber and intake port, and thus the flow characteristics of the intake squish flow and swirl flow, the intake is stratified as follows: Can do.
[0021]
In the intake stroke, as illustrated in FIG. 2, at the intake port 3 on the downstream side of the swirl flow, the swirl flow of the first intake air 11 along the peripheral wall at the upper portion of the combustion chamber 1, and at the intake port 4 on the upstream side, A swirl flow of the second intake air 12 along the peripheral wall is formed in the lower part of the combustion chamber 1. As illustrated in FIGS. 4 and 5, the state in which the swirl flow of the first intake air 11 and the swirl flow of the second intake air 12 having different compositions in the combustion chamber 1 are arranged up and down continues to the middle of the compression stroke. The
[0022]
In the latter half of the compression stroke in which the squish flow is generated, the swirl flow on the periphery of the piston top surface is carried by the squish flow into the cavity at the center of the piston top surface, and due to the increase in swirl speed as the diameter decreases. The centrifugal force does not go to the center of the cavity, but flows along the peripheral wall of the cavity and goes to the bottom surface of the cavity. Before the squish flow occurs, the second intake air exists in the entire area of the cavity. However, when the squish flow occurs, the cavities enter the central region as illustrated in the order of time passage in FIGS. 6 (a), 6 (b), and 6 (c). The first intake air 11 flows in, and the second intake air 12 exists only in the peripheral region and the bottom region.
[0023]
In the vicinity of the end of the compression stroke in which the fuel starts to burn, as shown in FIG. 1, the combustion chamber 1 is located in a region in the substantially flat hemispherical surface 13 centered on the center position of the ceiling surface where the fuel is injected. The first intake air 11 is mainly present, and the second intake air 12 is mainly present in the outer region. At the start of fuel combustion, intake air 11 and 12 having different compositions are stratified in an inner region and an outer region of a substantially hemispherical surface or a generally flat hemispherical surface centered on the fuel injection position of the combustion chamber.
[0024]
4) In a direct injection compression ignition internal combustion engine equipped with an exhaust gas recirculation device, fresh air is distributed without distributing the recirculated exhaust gas around the base portion of the fuel flow injected from the fuel injection valve during the combustion period. When distributed, fresh air is carried to the tip by the fuel flow or mixed air flow, oxygen is supplied to the fuel flow tip or cavity valley that burns in an oxygen-deficient state, and the oxygen concentration is the soot generation suppression value. With this increase, soot generation decreases. However, at this time, control is performed so that the oxygen concentration does not rise to the NOx (nitrogen oxide) generation value. In addition, if the intake air mixed with the recirculated exhaust gas is distributed in the squish area of the combustion chamber where the NOx is generated by high-temperature combustion in the lean region near the stoichiometric air-fuel ratio and the cavity periphery, the oxygen concentration and the combustion temperature decrease. , NOx production is reduced.
[0025]
When the load of the internal combustion engine is heavy and the fuel injection end time is late, or when the internal combustion engine has a high rotational speed and a strong reverse squish flow, the ratio of the fuel flowing out of the cavity of the combustion chamber increases. It burns in an oxygen-deficient condition outside and burns in an oxygen-excess condition in the cavity. Then, soot is mainly generated outside the cavity, and NOx is mainly generated inside the cavity.
[0026]
In such a case, the stratification pattern of the combustion chamber is reversed, and the intake air in which the recirculated exhaust gas is mixed or the intake air having a high recirculated exhaust gas concentration in the region inside the substantially hemispherical surface or the generally flat hemispherical surface centered on the fuel injection position. In the region outside the intake air, the intake air in which the recirculated exhaust gas is not mixed or the intake air having a low recirculated exhaust gas concentration is arranged. Then, outside the cavity of the combustion chamber and in the squish area, the oxygen concentration increases, soot generation is suppressed, and at the same time, soot oxidation is promoted and soot is reduced. However, at this time, control is performed so that the oxygen concentration does not rise to the NOx generation value, thereby preventing an increase in NOx.
[0027]
That is, it is necessary to change the stratification pattern of the combustion chamber 1 according to the operating conditions of the internal combustion engine. It is also necessary to change the stratification degree of the combustion chamber 1.
[0028]
In the internal combustion engine illustrated in FIGS. 1 to 6, the amount of the recirculated exhaust gas mixed into the first intake air passing through the intake port 3 on the downstream side of the swirl flow and the intake port 4 on the upstream side according to the operating conditions. When the amount of the recirculated exhaust gas mixed into the second intake air passing through is increased or decreased, the stratification pattern of the combustion chamber 1 is changed. It becomes a normal stratified pattern in which the concentration of the recirculated exhaust gas is lower in the region in the generally flat hemispherical surface 13 of the combustion chamber 1 than in the outer region. Further, the reverse stratification pattern is such that the concentration of the recirculated exhaust gas is higher in the region in the generally flat hemispherical surface 13 of the combustion chamber 1 than in the outer region. Furthermore, a uniform pattern is obtained in which the concentration of the recirculated exhaust gas becomes equal in the region in the substantially flat hemispherical surface 13 of the combustion chamber 1 and the region outside the region.
[0029]
Further, when the amount of the recirculated exhaust gas mixed into the first intake air and the amount of the recirculated exhaust gas mixed into the second intake air are increased or decreased according to the operating conditions of the internal combustion engine, the stratification degree of the combustion chamber 1 is changed. . The ratio of the recirculation exhaust concentration outside the general flat hemisphere 13 to the recirculation exhaust concentration in the general flat hemisphere 13 and the degree of stratification increase or decrease.
[0030]
[Means for Solving the Problems]
  1)A plurality of intake ports form the same swirl flow in the same direction in the combustion chamber,Fuel into the combustion chamberFrom the center of the ceiling facing the piston top to the periphery of the cavity at the center of the piston topIn a direct injection internal combustion engine for injection,
  The plurality of intake swirl flows are the first intake and the second intake with different concentrations of specific components,
  In the intake stroke, a swirl flow of the first intake along the peripheral wall is formed in the upper portion of the combustion chamber, a swirl flow along the peripheral wall is formed in the lower portion of the combustion chamber, and the first in the combustion chamber until the middle of the compression stroke. The state in which the swirl flow of the intake air and the swirl flow of the second intake air are arranged up and down continues,
  In the latter half of the compression stroke in which the squish flow is generated, in the cavity at the central portion of the top surface of the piston, the first intake air is caused to flow into the central region and the second intake air is left in the peripheral region and the bottom region.,
  Near the end of the compression stroke when the fuel begins to burn, A region inside a substantially hemispherical surface or a generally flat hemispherical surface centered on the fuel injection position of the combustion chamberThe first intake,In the outer areaThe second intake is mainly arranged, and intakes having different concentrations of specific components are arranged in the inner region and the outer region.Inhalation stratification characterized byMethod.
[0031]
2) In the above intake stratification method,
Depending on the operating conditions of the direct injection internal combustion engine, the stratification pattern of the combustion chamber is a positive stratification pattern in which the concentration of the specific component of the intake air is lower in the inner region than in the outer region. A reverse stratification pattern in which the concentration of the specific component of the intake air is higher than that in the outer region, or a uniform pattern in which the concentration of the specific component of the intake air is equal in the inner region and the outer region. And
[0032]
3) In the above intake stratification method,
The ratio of the concentration of the specific component of the intake air in the outer region to the concentration of the specific component of the intake air in the inner region is changed according to the operating conditions of the direct injection internal combustion engine. It is characterized by.
[0034]
  4) The above intake stratification methodTo the lawLeave
  The substantially hemispherical surface or the generally flat hemispheric surface centering on the fuel injection position of the combustion chamber is characterized by being 1 to 1.5 times the spray splitting distance from the fuel injection position of the combustion chamber in the fuel injection direction. And
[0035]
【The invention's effect】
  At the start of combustion of fuel near the end of the compression stroke, intake of a desired composition is applied to the inner and outer regions of the approximately hemispherical surface to the generally flat hemispherical surface centered on the fuel injection position of the combustion chamber.Inhalation of the desired component concentrationAnd the combustion state of the fuel can be controlled.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
[First example (see FIGS. 1 to 8)]
As shown in FIG. 1, the direct injection compression ignition internal combustion engine provided with the intake stratification device of this example has a large number of injection holes of a fuel injection valve 2 disposed at the center of the ceiling surface of the combustion chamber 1. 1 is provided with two intake ports 3 and 4 and intake valves 5 and 6 on one side of the ceiling surface, and two exhaust ports 7 and exhaust valves 8 on the other side, with the center at the center of the piston top surface. An axisymmetric cavity 9 is formed, and a peak 10 is provided at the center of the bottom surface of the cavity 9.
[0037]
The fuel injection valve 2 injects fuel from a number of injection holes in the radial direction toward the periphery of the cavity 9 in the vicinity of the end of the compression stroke.
[0038]
The two intake ports 3 and 4 form, in the intake stroke, intake swirl flows 11 and 12 in the same direction in the combustion chamber 1 as shown in FIG. As shown in FIGS. 2 and 3, the intake port 3 on the downstream side of the swirl flow has a helical port shape, and the intake air flows out in a direction substantially along the ceiling surface of the combustion chamber 1. A strong first intake swirl flow 11 along the peripheral wall is formed at the top. The upstream intake port 4 has a tangential port shape, and in order to avoid collision with the swirl flow 11 of the first intake air, the intake air flows out obliquely downward, and its peripheral wall is formed at the lower part of the piston top surface side of the combustion chamber 1. The second intake swirl flow 12 is formed along
[0039]
In the intake stratification apparatus of this example, as shown in FIG. 2, in the intake stroke, the swirl flow 11 of the first intake air and the swirl flow of the second intake air along the peripheral wall are respectively provided at the upper and lower portions of the combustion chamber 1. As shown in FIG. 4, the swirl flow 11 of the first intake air and the swirl flow 12 of the second intake air are vertically stratified in the combustion chamber 1 at the end of the intake stroke. At the end of the intake stroke, the rearmost portion of the second intake air 12 that has finally flowed in from the intake port 4 on the upstream side exists at the upper part of the combustion chamber 1, and therefore, the boundary surface 13 between the first intake air 11 and the second intake air 12. Is not a plane parallel to the top surface of the piston, but an inclined uneven curved surface.
[0040]
The first intake air 11 and the second intake air 12 having different compositions in the combustion chamber 1 are mixed with the passage of time, and the component included in only one intake air is also included in the other intake air. Since the concentration continuously changes, the surface where the concentration of the component is approximately an intermediate value is defined as a boundary surface 13 between the first intake air 11 and the second intake air 12.
[0041]
In the compression stroke, the rearmost portion of the second intake air 12 moves to the lower portion of the combustion chamber 1 and mixing of the first intake air 11 and the second intake air 12 proceeds. Thus, the boundary surface 13 between the first intake air 11 and the second intake air 12 approaches a plane parallel to the piston top surface. The state in which the first intake swirl flow 11 and the second intake swirl flow 12 are vertically stratified in the combustion chamber 1 continues to the middle of the compression stroke.
[0042]
In the latter half of the compression stroke in which the squish flow is generated, the swirl flow on the periphery of the piston top surface is carried by the squish flow into the cavity 9 in the center of the piston top surface, and the swirl velocity of the swirl flow accompanying the reduction in diameter is increased. The centrifugal force due to the increase does not move toward the center of the cavity 9 but flows along the peripheral wall of the cavity 9 and toward the bottom surface of the cavity 9. As shown in FIGS. 6A, 6B, and 6C in the order of time passage, the cavity 9 is filled with the second intake air 12 at the lower part of the combustion chamber 1 and the first intake air at the upper part of the combustion chamber 1 in the central region. 11 flows in, and the second intake air 12 remains only in the peripheral region and the bottom region.
[0043]
In the vicinity of the end of the compression stroke in which the fuel is injected from the fuel injection valve 2 and starts combustion, as shown in FIG. 1, a substantially flat hemispherical surface centered on the center of the ceiling surface where the fuel in the combustion chamber 1 is injected. 13, the first intake air 11 mainly exists in the inner region, and the second intake air 12 mainly exists in the outer region. At the start of fuel combustion, intake air 11 and 12 are stratified in an inner region and an outer region of a substantially flat hemispherical surface 13 centering on the fuel injection position of the combustion chamber 1.
[0044]
When the radius in the fuel injection direction is about 1 to 1.5 times the spray splitting distance, the intake air 11, 12 is stratified in the mixture formation region and the flame generation region of the combustion chamber 1. The
[0045]
If the swirl flow of the first intake air 11 is too strong near the end of the compression stroke, the first intake air 11 is transported to the bottom surface of the cavity 9 by the squish flow as shown in FIG. It becomes a reverse toroidal flow down the peripheral wall, flows into the bottom surface of the cavity 9, and pushes the second intake air 12 existing on the peripheral wall and the bottom surface of the cavity 9 toward the center of the cavity 9.
[0046]
In this example, since the swirl flow and squish flow of the intake air 11 and 12 are moderate, the first intake air 11 descends the peak portion 10 of the cavity 9 and the middle portion of the peripheral wall as shown in FIG. The second intake air 12, which has a toroidal flow and is present in the middle portion thereof, is pushed away to the peripheral region and the bottom region of the cavity 9, and the intake air 11, 12 enters and exits the substantially flat hemispherical surface 13 centered on the fuel injection position of the combustion chamber 1. Is stratified.
[0047]
The intake stratification device of this example is configured so that the combustion chamber 1 and the intake ports 3 and 4 determine flow characteristics of the squish flow and the swirl flow of the intake air 11 and 12 so that the intake air 11 and 12 are stratified in this way. The shape is selected. By these shapes, the degree of stratification of the intake air 11 and 12 and the shape and size of the boundary surface 13 can be controlled.
[0048]
Examples of the shape include the shape of the cavity 9 of the combustion chamber 1, the distance between the piston top surface peripheral portion and the ceiling surface peripheral portion, and the amount of recess in the lower surfaces of the intake valves 5 and 6 from the ceiling surface.
[0049]
Simulation experiment example
In the intake stratification apparatus of this example, the first intake air 11 flowing into the combustion chamber 1 from the downstream intake port 3 is made 100% fresh air, and the second intake air 12 flowing from the upstream intake port 4 is made fresh air 50. % And recirculation exhaust 50%, the distribution of the recirculation exhaust concentration in the combustion chamber 1 at the end of the compression stroke was obtained by numerical calculation.
[0050]
FIG. 8 shows the result. FIG. 8B is a central longitudinal section of the combustion chamber 1 passing between the intake ports 3 and 4 on the downstream side and the upstream side, and FIG. 8A is orthogonal to the central longitudinal section. The distribution of the recirculated exhaust gas concentration (EGR rate) in the central vertical section is shown by lightness.
[0051]
As is clear from these figures, at the end of the compression stroke, the contour surface of the recirculated exhaust gas concentration distribution in the combustion chamber 1 appears in a generally flat hemispherical shape centered on the fuel injection position, and recirculates as it approaches the fuel injection position. The exhaust gas concentration is reduced, and the distribution of the recirculated exhaust gas concentration is almost axisymmetric. The intake air in the combustion chamber 1 indicates that the intake air 11 and 12 are stratified inside and outside a substantially flat hemisphere centered on the fuel injection position.
[0052]
[Second example (see FIG. 9)]
In the intake stratification device of this example, in order to increase the stratification degree of intake air in the first example, the opening periods of the intake valves 5 and 6 are shifted between the intake ports 3 and 4 on the downstream side and the upstream side.
[0053]
As shown in FIG. 9, in the intake port 3 on the downstream side where the first intake air 11 flows into the upper part of the combustion chamber 1, the intake valve 5 is opened at a later time and closed at a later time. In the upstream intake port 4 through which the second intake air 12 flows into the lower portion of the combustion chamber 1, the intake valve 6 is opened early and closed early.
[0054]
In the first half of the intake stroke, only the intake valve 6 of the intake port 4 on the upstream side is opened, and only the second intake air 12 arranged at the lower part of the combustion chamber 1 flows into the combustion chamber 1. In the middle of the intake stroke, the intake valves 5 and 6 of both intake ports 3 and 4 are opened, and the first intake air 11 and the second intake air 12 flow into the combustion chamber 1. In the latter stage of the intake stroke, only the intake valve 5 of the intake port 3 on the downstream side is opened, and only the first intake air 11 arranged at the upper part of the combustion chamber 1 flows into the combustion chamber 1.
[0055]
Compared to the case of the first example in which the opening periods of the intake valves 5 and 6 coincide in the intake ports 3 and 4 on the downstream side and the upstream side, the first intake air 11 and the second intake air 12 are moved up and down at the end of the intake stroke. The degree of stratification increases, and the degree of stratification of the intake air 11, 12 at the end of the compression stroke on the inside and outside of the generally flat hemispherical surface 13 centered on the fuel injection position increases.
[0056]
Other points are the same as in the first example.
[0057]
[Third example (see FIG. 10)]
The intake stratification device of this example is the same as that of the first example, and in order to increase the stratification of intake air, the second intake air 12 flows into the combustion chamber 1 from only one side of the intake port 4 on the upstream side.
[0058]
In the intake port 4 on the upstream side, the intake air flows obliquely downward and collides obliquely with the peripheral wall of the combustion chamber 1 to form a swirl flow along the peripheral wall of the lower portion of the combustion chamber 1. The intake air flowing out of the combustion chamber 1 peripheral wall side portion of the tangential port-shaped intake port 4 has a shorter distance until it collides with the peripheral wall of the combustion chamber 1 than the intake air flowing out of the combustion chamber 1 center side portion. It tends to flow into the lower part of the chamber 1.
[0059]
Therefore, as shown in FIG. 10, the upstream intake port 4 is provided with a partition wall 21 that is divided into a peripheral wall side portion and a central side portion of the combustion chamber 1, and a combustion chamber 1 peripheral wall side portion of the intake port 4. The second intake air 12 having a higher concentration of a specific component such as recirculation exhaust is flowed, and the second intake air 12 is caused to flow into the lower portion of the combustion chamber 1 from the combustion chamber 1 peripheral wall side portion of the intake port 4. The first intake air 11 flows into the combustion chamber 1 center portion of the intake port 4 as in the upstream intake port 3, and the first intake air 11 flows into the combustion chamber 1 from the combustion chamber 1 center portion of the intake port 4. Let
[0060]
The second intake air 12 that flows into the combustion chamber 1 from the combustion chamber 1 peripheral wall side portion of the intake port 4 becomes narrower in airflow and is difficult to mix with the first intake air 11.
[0061]
Compared to the case of the first example in which the second intake air 12 flows into the combustion chamber 1 from the entire intake port 4 on the upstream side, the first intake air 11 and the second intake air 12 are stratified vertically at the end of the intake stroke. The degree to which the intake air 11 and 12 is stratified inside and outside the substantially flat hemispherical surface 13 centered on the fuel injection position at the end of the compression stroke is increased.
[0062]
Other points are the same as in the first example.
[0063]
[Fourth example]
The intake stratification apparatus of this example is similar to that of the first example, and a subport is provided at the lower or upper part of the combustion chamber 1 where the intake air easily flows to increase the stratification of the intake air.
[0064]
In the third example, an auxiliary intake port similar to the combustion chamber 1 peripheral wall side portion of the intake port 4 where intake air easily flows into the lower portion of the combustion chamber 1 is provided, and the concentration of the specific component is provided from the auxiliary intake port to the lower portion of the combustion chamber 1. The second intake air 12 having a higher value is introduced.
[0065]
[Fifth example (see FIG. 11)]
The intake stratification apparatus of this example is the same as that of the first example, and changes the stratification pattern and degree of stratification of the intake air in the combustion chamber 1 in accordance with the operating conditions of the internal combustion engine.
[0066]
In the internal combustion engine of the first example, a first exhaust gas recirculation passage 25 is connected to a first intake passage 23 connected to the intake port 3 on the downstream side of the swirl flow via a first flow control valve 24 as shown in FIG. The second exhaust gas recirculation passage 28 is connected to the second intake passage 26 connected to the upstream intake port 4 via the second flow rate control valve 27. A device 29 is provided for controlling the opening of the first flow control valve 24 and the opening of the second flow control valve 27 according to the operating conditions of the internal combustion engine.
[0067]
When the opening degree of the first flow rate control valve 24 and the opening degree of the second flow rate control valve 27 are respectively controlled according to the operating conditions of the internal combustion engine, the recirculation mixed into the first intake air passing through the downstream intake port 3 The amount of exhaust gas and the amount of recirculated exhaust gas mixed into the second intake air that passes through the upstream intake port 4 increase and decrease, respectively, and the stratification pattern of the combustion chamber 1 is changed. It becomes a normal stratified pattern in which the concentration of the recirculated exhaust gas is lower in the region in the generally flat hemispherical surface 13 of the combustion chamber 1 than in the outer region. Further, the reverse stratification pattern is such that the concentration of the recirculated exhaust gas is higher in the region in the generally flat hemispherical surface 13 of the combustion chamber 1 than in the outer region. Furthermore, a uniform pattern is obtained in which the concentration of the recirculated exhaust gas becomes equal in the region in the substantially flat hemispherical surface 13 of the combustion chamber 1 and the region outside the region.
[0068]
Further, when the opening degree of the first flow rate control valve 24 and the opening degree of the second flow rate control valve 27 are respectively controlled according to the operating conditions of the internal combustion engine, the stratification degree of the combustion chamber 1 is changed. The ratio of the recirculation exhaust concentration outside the general flat hemisphere 13 to the recirculation exhaust concentration in the general flat hemisphere 13, specifically, the general flat hemisphere with respect to the recirculation exhaust concentration at the fuel injection position in the general flat hemisphere 13. The ratio of the reflux exhaust concentration and the degree of stratification in the outer peripheral region of the cavity bottom 13 are increased or decreased.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a direct injection compression ignition internal combustion engine equipped with an intake stratification device in a first example of an embodiment of the present invention.
FIG. 2 is a schematic perspective view of a combustion chamber in the middle of an intake stroke in the internal combustion engine.
FIG. 3 is a schematic plan view of a combustion chamber in the internal combustion engine.
FIG. 4 is a schematic perspective view of a combustion chamber at the end of an intake stroke in the internal combustion engine.
FIG. 5 is a schematic perspective view of a combustion chamber in the middle of a compression stroke in the internal combustion engine.
FIG. 6 is a schematic longitudinal sectional view of a combustion chamber near the end of a compression stroke in the internal combustion engine, showing a flow state of intake air.
FIG. 7 is a schematic longitudinal sectional view of a combustion chamber at the end of a compression stroke in an internal combustion engine, showing a flow state of intake air.
FIG. 8 is a view showing an intake stratification state at the end of a compression stroke in a simulation experiment example in the internal combustion engine.
FIG. 9 is an intake valve lift diagram of a direct injection compression ignition internal combustion engine equipped with an intake stratification device according to a second example of the embodiment.
FIG. 10 is a schematic plan view of a combustion chamber of a direct injection compression ignition internal combustion engine equipped with an intake stratification device in a third example.
FIG. 11 is a schematic view of an intake passage portion of a direct injection compression ignition internal combustion engine equipped with an intake stratification device in a fifth example.
[Explanation of symbols]
1 Combustion chamber
2 Fuel injection valve
3 Inlet port on the downstream side of the swirl flow
4 Inlet port upstream of swirl flow
5 Inlet valve downstream of swirl flow
6 Inlet valve upstream of swirl flow
9 cavity
11 First intake
12 Second intake
13 Boundary surface between first intake air and second intake air, roughly flat hemispherical surface

Claims (7)

複数の吸気ポートで燃焼室に複数の同一方向の吸気スワール流を形成し、燃料を燃焼室にそのピストン頂面と対面する天井面の中心部からピストン頂面中央部のキャビティの周辺部に向けて噴射する直接噴射式内燃機関において、
複数の吸気スワール流は、特定成分の濃度が異なる第１吸気と第２吸気にし、
吸気行程において、燃焼室の上部にその周壁に沿う第１吸気のスワール流を形成し、燃焼室の下部にその周壁に沿うスワール流を形成し、圧縮行程の中程まで、燃焼室において第１吸気のスワール流と第２吸気のスワール流が上下に配置された状態を継続し、
スキッシュ流が発生する圧縮行程の後半に、ピストン頂面中央部のキャビティにおいて、中央領域に第１吸気を流入させ、周辺領域と底部領域に第２吸気を残存させ、
燃料が燃焼を開始する圧縮行程の終期近傍において、燃焼室の燃料噴射位置を中心とする概略半球面ないし概略扁平半球面の内側の領域に第１吸気を、外側の領域に第２吸気を主に配置し、内側の領域と外側の領域に、特定成分の濃度が異なる吸気を配置することを特徴とする吸気成層化方法。A plurality of intake ports form a plurality of intake swirl flows in the same direction in the combustion chamber, and fuel is directed from the center of the ceiling surface facing the piston top surface to the periphery of the cavity at the center of the piston top surface. In a direct injection internal combustion engine that injects
The plurality of intake swirl flows are the first intake and the second intake with different concentrations of specific components,
In inspiratory stroke, forming a first intake swirl flow along the peripheral wall at the top of the combustion chamber, forming a swirl flow along the peripheral wall in the lower part of the combustion chamber, to the middle of the compression stroke, the in the combustion chamber the state where the first intake swirl flow and a swirl flow of the second intake of are arranged vertically continuously,
In the latter half of the compression stroke of the squish flow is generated in the cavity of the piston top center, allowed to flow into the first intake in the central region, thereby leaving a second intake in the peripheral region and a bottom region,
In the vicinity of the end of the compression stroke at which the fuel starts to burn, the first intake air is mainly in the region inside the substantially hemispherical surface or the generally flat hemisphere centered on the fuel injection position in the combustion chamber, and the second intake air is mainly in the outer region. The intake stratification method is characterized by disposing intake air having different concentrations of specific components in the inner region and the outer region . 直接噴射式内燃機関の運転条件に応じて、燃焼室の成層パターンを、上記の内側の領域で上記の外側の領域より吸気の特定成分の濃度が低くなる正成層パターン、上記の内側の領域で上記の外側の領域より吸気の特定成分の濃度が高くなる逆成層パターン、又は、上記の内側の領域と上記の外側の領域で吸気の特定成分の濃度が等しくなる均質パターンに変更することを特徴とする請求項１に記載の吸気成層化方法。  Depending on the operating conditions of the direct injection internal combustion engine, the stratification pattern of the combustion chamber is a positive stratification pattern in which the concentration of the specific component of the intake air is lower in the inner region than in the outer region. A reverse stratification pattern in which the concentration of the specific component of the intake air is higher than that in the outer region, or a uniform pattern in which the concentration of the specific component of the intake air is equal in the inner region and the outer region. The intake stratification method according to claim 1. 直接噴射式内燃機関の運転条件に応じて、上記の内側の領域における吸気の特定成分の濃度に対する、上記の外側の領域における吸気の特定成分の濃度の比を変更することを特徴とする請求項１又は２に記載の吸気成層化方法。  The ratio of the concentration of the specific component of intake air in the outer region to the concentration of the specific component of intake air in the inner region is changed according to operating conditions of the direct injection internal combustion engine. 3. The intake stratification method according to 1 or 2. 燃焼室の燃料噴射位置を中心とする概略半球面ないし概略扁平半球面は、燃料の噴射方向には燃焼室の燃料噴射位置から噴霧分裂距離の１〜１．５倍位離れていることを特徴とする請求項１〜３のいずれかに記載の吸気成層化方法。The substantially hemispherical surface or the generally flat hemispheric surface centering on the fuel injection position of the combustion chamber is characterized by being 1 to 1.5 times the spray splitting distance from the fuel injection position of the combustion chamber in the fuel injection direction. The intake stratification method according to any one of claims 1 to 3 . 直接噴射式内燃機関は、圧縮着火内燃機関であることを特徴とする請求項１〜４のいずれかに記載の吸気成層化方法。The intake stratification method according to any one of claims 1 to 4 , wherein the direct injection internal combustion engine is a compression ignition internal combustion engine. 燃焼室の上部に第１吸気のスワール流を形成する吸気ポートと、燃焼室の下部に第２吸気のスワール流を形成する吸気ポートとで吸気弁の開放期間をずらし、吸気行程の前期には、後者の吸気ポートの吸気弁のみが開放して第２吸気のみが燃焼室に流入し、吸気行程の中期には、両者の吸気ポートの吸気弁が開放して第１吸気と第２吸気が燃焼室に流入し、吸気行程の後期には、前者の吸気ポートの吸気弁のみが開放して第１吸気のみが燃焼室に流入することを特徴とする請求項１〜５のいずれかに記載の吸気成層化方法。The intake valve opening period is shifted between the intake port that forms the swirl flow of the first intake air in the upper part of the combustion chamber and the intake port that forms the swirl flow of the second intake air in the lower part of the combustion chamber. Only the intake valve of the latter intake port is opened and only the second intake air flows into the combustion chamber. In the middle of the intake stroke, the intake valves of both intake ports are opened and the first intake air and the second intake air are discharged. flows into the combustion chamber, the late intake stroke, one of the claims 1 to 5 only the intake valve of the former intake port only first intake open is characterized by a Turkey to flow into the combustion chamber The intake stratification method as described in 2. 吸気の特定成分は、吸気に混入した還流排気であることを特徴とする請求項１〜６のいずれかに記載の吸気成層化方法。 The intake stratification method according to claim 1, wherein the specific component of the intake air is recirculated exhaust gas mixed in the intake air .
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JP4715804B2 (en) * 2007-05-09 2011-07-06 トヨタ自動車株式会社 Exhaust gas recirculation device for internal combustion engine
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