JP2004076679A - Gas fuel addition method and gas fuel addition device for internal combustion engine - Google Patents

Gas fuel addition method and gas fuel addition device for internal combustion engine Download PDF

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JP2004076679A
JP2004076679A JP2002240119A JP2002240119A JP2004076679A JP 2004076679 A JP2004076679 A JP 2004076679A JP 2002240119 A JP2002240119 A JP 2002240119A JP 2002240119 A JP2002240119 A JP 2002240119A JP 2004076679 A JP2004076679 A JP 2004076679A
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gaseous fuel
fuel
addition
hydrogen
amount
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Tomohiro Shinagawa
品川　知広
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Toyota Motor Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0602—Control of components of the fuel supply system
    • F02D19/0607—Control of components of the fuel supply system to adjust the fuel mass or volume flow
    • F02D19/061—Control of components of the fuel supply system to adjust the fuel mass or volume flow by controlling fuel injectors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0639—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels
    • F02D19/0642—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels at least one fuel being gaseous, the other fuels being gaseous or liquid at standard conditions
    • F02D19/0644—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels at least one fuel being gaseous, the other fuels being gaseous or liquid at standard conditions the gaseous fuel being hydrogen, ammonia or carbon monoxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0663—Details on the fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
    • F02D19/0686—Injectors
    • F02D19/0689—Injectors for in-cylinder direct injection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0663—Details on the fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
    • F02D19/0686—Injectors
    • F02D19/0692—Arrangement of multiple injectors per combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/08—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed simultaneously using pluralities of fuels
    • F02D19/081—Adjusting the fuel composition or mixing ratio; Transitioning from one fuel to the other
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0027—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures the fuel being gaseous
    • 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
    • Y02T10/30—Use of alternative fuels, e.g. biofuels

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas fuel addition method for internal combustion engine capable of realizing the improvement in heat efficiency and the improvement in exhaust air by effectively utilizing a gas fuel such as hydrogen to extend the lean limit of fuel-air mixture. <P>SOLUTION: This gas fuel addition method for an internal combustion engine 1 for adding hydrogen into a cylinder 3 separately from a gasoline fuel for forming the fuel-air mixture comprises a first addition process for adding the hydrogen during an intake stroke, and a second addition process for adding the hydrogen during a compression stroke. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、内燃機関の筒内に形成される燃料混合気に水素等の気体燃料を添加する方法及び装置に関する。
【０００２】
【従来の技術】
ガソリン燃料と空気とによって形成された燃料混合気に水素を添加することにより、着火性を向上させて燃料混合気のリーンリミット（希薄限界）の向上とＮＯｘ（窒素酸化物）の排出量の低減とを図る技術が知られている。例えば特開平７−６３１２８号公報に記載された内燃機関では、点火プラグの周辺に水素を集中的に添加して着火性を向上させるとともに、ガソリンと空気との混合気については点火プラグから離れるほどリッチとなるように分布させて筒内の周辺部への火炎伝播の向上を図っている。
【０００３】
【発明が解決しようとする課題】
しかしながら、上記公報の内燃機関では水素を着火性の改善に利用しているだけであり、着火後の火炎伝播はガソリン燃料に依存している。従って、火炎の伝播には水素が殆ど関与せず、火炎伝播特性からみたリーンリミットはガソリン燃料のみを利用する場合と比較して殆ど変わらない。従って、リーンリミットを無理に拡大すれば火炎伝播不良による失火や運転状態の不安定化を招く。
【０００４】
一方、筒内に満遍なく水素を分散させた場合には火炎伝播特性が改善される。この改善度は水素の量が増加するほど向上し、水素の量が増加するに従いリーンリミットが拡大し、それに伴って熱効率が向上してＮＯｘの低減量は増加する。しかし、水素の供給に関する社会資本の整備等を考慮すると、ＮＯｘが完全に削減できるような大量の水素の添加は不可能である。従って、現実には、添加できる水素の量をできる限り少量に抑える必要がある。
【０００５】
しかし、少量の水素の添加では、燃料混合気の着火性に関してガソリンの影響が大きく、水素による着火性の向上は大きくない。従って、リーンリミットに関しては、ガソリン燃料のみを使用した場合と比較して全く拡大しないわけではないが、この程度のリーン域ではＮＯｘの生成を完全には排除できず触媒を利用せざるを得ないが、リーン領域であるためにＮＯｘ吸蔵触媒を利用してＮＯｘを処理することが必要不可欠である。このような触媒を使用した場合には性能の維持や保守点検に関して相当の配慮が必要となり、手間がかかる。
【０００６】
そこで、本発明は、水素等の気体燃料を有効に利用して燃料混合気のリーンリミットを拡大し、熱効率の向上と排気の改善とを実現可能であり、望ましくはＮＯｘ吸蔵触媒を不要とする程度まで排気を改善できる内燃機関の気体燃料添加方法及び装置を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の気体燃料添加方法は、燃料混合気を形成するための主燃料とは別の気体燃料を筒内に添加する内燃機関の気体燃料添加方法であって、前記気体燃料を吸気行程中に添加する第１の添加工程と、前記気体燃料を圧縮行程中に添加する第２の添加工程とを備えることにより、上述した課題を解決する（請求項１）。
【０００８】
本発明の気体燃料添加方法において、第１の添加工程で添加された気体燃料は吸気行程中における燃焼室の膨張に伴って主燃料や空気と十分に混合されて筒内に満遍なく分散される。一方、第２の添加工程で添加される気体燃料は点火の直前であり、筒内に拡散せず、部分的に気体燃料の濃度が高い領域を形成する。この気体燃料の濃度が高い領域を点火に利用することにより燃料混合気の着火性を向上させることができる。そして、着火後の火炎伝播に関しては、筒内に満遍なく気体燃料が分散されているので、主燃料のみを利用した場合よりも火炎伝播特性が向上する。
【０００９】
このように、本発明によれば、着火を含む初期燃焼と、火炎伝播を主体とする後期燃焼とのいずれに対しても気体燃料が有効に作用するので、主燃料に対する空気量を増加させてリーンリミットを拡大し、それにより熱効率の向上と排気の改善、特にＮＯｘの生成量の削減とを図ることができる。リーンリミットの拡大により燃焼時の筒内温度を十分に低下させてＮＯｘ生成量をほぼ０まで低下させることも不可能ではなく、その場合にはＮＯｘ吸蔵触媒をも不要とすることができる。
【００１０】
本発明の気体燃料添加方法において、前記第２の添加工程では、前記気体燃料が点火プラグの周りに集まるように添加することが望ましい（請求項２）。このような気体燃料の添加は、点火プラグに向かって前記気体燃料を噴射すること（請求項３）、あるいは、ピストンの頂面に前記気体燃料を前記点火プラグに向かって案内する案内部を形成し、その案内部に向かって気体燃料を噴射すること（請求項４）、によって実現することができる。このように圧縮行程で添加される気体燃料を点火プラグの周りに集めたならば、着火性を確実に向上させることができる。
【００１１】
本発明の気体燃料添加方法においては、第２の添加工程で添加される気体燃料は着火性を確保できれば十分であり、ごく僅かな量で足りるのに対して、第１の添加工程で添加される気体燃料は筒内に満遍なく分散される必要がある。従って、前記第１の添加工程における前記気体燃料の添加量よりも前記第２の添加工程における前記気体燃料の添加量を少なくすることが望ましい（請求項５）。より好ましくは、前記第２の添加工程における前記気体燃料の添加量を、前記点火プラグの付近に火炎核が形成されるために必要な最小限度に設定する（請求項６）。着火時に気体燃料の効果を利用して火炎核が形成できれば、それ以降は第１の添加工程で添加された気体燃料の助けを得て火炎がほぼ確実に伝播する。火炎核の形成に必要最小限度まで気体燃料の添加量を制限することにより、火炎核形成時のＮＯｘ生成量も減らすことができ、排気がさらに改善される。
【００１２】
また、本発明の気体燃料添加方法においては、一回の燃焼に備えて供給される前記主燃料の量を、実質的な燃焼が可能な最小限度に設定するとよい（請求項７）。このように主燃料の供給量を制限すれば主燃料のみでは実現し得ない希薄域で内燃機関を運転することができ、ＮＯｘ生成量を大幅に低減することができる。なお、実質的な燃焼とは、内燃機関を実用に供し得る程度に燃焼が成立すること意味し、燃焼の安定性に相関する物理量を指標としてこれを評価することができる。例えば、燃焼の不安定化に伴って内燃機関の出力トルクの変動量が拡大するため、トルク変動量に対して実用上の限界値を設定し、その限界値を超えるときに実質的な燃焼が成立していないと評価することができる。
【００１３】
さらに、本発明の気体燃料添加方法においては、吸気行程において筒内に吸気流動を形成してもよい（請求項８）。吸気流動を形成した場合には第１の添加工程で添加された気体燃料を主燃料や空気と効率よく混合させて筒内に均質に分散させることができる。吸気流動は、気筒の中心線の回りに旋回するスワール流でもよいし、気筒の中心線の方向に沿って旋回するタンブル流であってもよい。
【００１４】
次に、本発明の内燃機関の気体燃料添加装置は、燃料混合気を形成するための主燃料とは別の気体燃料を筒内に添加する気体燃料添加手段と、前記気体燃料が吸気行程及び圧縮行程でそれぞれ添加されるように前記気体燃料添加手段を制御する添加制御手段とを備えることにより、上述した課題を解決する（請求項１０）。
【００１５】
この気体燃料添加装置によれば、吸気行程及び圧縮行程でそれぞれ気体燃料を添加することにより、本発明の気体燃料添加方法の第１及び第２の添加工程を実現して上記の通りの作用効果を得ることができる。
【００１６】
上述した本発明の気体燃料添加方法の好ましい態様を実現するため、本発明の内燃機関の気体燃料添加装置も次のような態様を含むことができる。
【００１７】
前記気体燃料添加手段は、点火プラグに向かって前記気体燃料を噴射可能であってもよい（請求項１１）。ピストンには前記気体を前記点火プラグに向かって案内する案内部が形成され、前記気体燃料添加手段は前記案内部に向かって前記気体燃料を噴射可能であってもよい（請求項１２）。
【００１８】
前記添加制御手段は、吸気行程中における前記気体燃料の添加量よりも圧縮行程中における前記気体燃料の添加量が少なくなるように前記気体燃料添加手段を制御してもよい（請求項１３）。前記添加制御手段は、圧縮行程中の前記気体燃料の添加量が、前記点火プラグの付近に火炎核が形成されるために必要な最小限度となるように前記気体燃料添加手段を制御してもよい（請求項１４）。一回の燃焼に備えて供給される前記主燃料の量が、実質的な燃焼が可能な最小限度となるように前記主燃料の供給量を制御する燃料供給量制御手段を備えてもよい（請求項１５）。筒内に吸気流動を形成する吸気流動形成手段を備えてもよい（請求項１６）。吸気流動形成手段はスワール流又はタンブル流を形成するものでよく、これらの吸気流動は例えば吸気ポートの一部に配置されたスワールコントロールバルブやタンブルコントロールバルブ等の弁手段やヘリカルポート等により実現できる。
【００１９】
さらに、本発明の気体燃料添加装置においては、気筒の中心線の回りを旋回するスワール流を筒内に形成する吸気流動形成手段を備え、前記案内部は前記気体燃料を前記スワール流の方向に沿って湾曲させるように形成されてもよい（請求項１７）。この場合には、スワール流に沿って気体燃料が点火プラグ側に向かうので圧縮行程中の筒内に対してより少ない圧力で気体燃料を添加することができる利点がある。
【００２０】
本発明において、前記主燃料は例えばガソリンであり、その場合に前記気体燃料として水素を好適に使用することができる（請求項９，１８）。
【００２１】
本発明において、「添加」の語は、燃料混合気を形成するために内燃機関に加えられる主燃料に対して気体燃料が追加されることを意味し、気体燃料を加える量、速度、圧力等の態様により、添加の範囲が限定されるものではない。
【００２２】
【発明の実施の形態】
図１は本発明の一実施形態の気体燃料添加装置が組み込まれた内燃機関の要部を示している。内燃機関１は４サイクル式のガソリンエンジンとして構成されており、燃焼室２を形成するシリンダ（気筒）３、ピストン４及びシリンダヘッド５と、吸気ポート８及び排気ポート９をそれぞれ開閉する吸気バルブ６及び排気バルブ７と、吸気ポート８に主燃料としてのガソリンを噴射する燃料噴射弁１０と、その燃料噴射弁１０に所定圧の燃料を供給する燃料デリバリチューブ１１と、混合気点火用の火花を形成する点火プラグ１２とを備えている。さらに、シリンダヘッド５には気体燃料添加手段としての水素噴射弁１３が設けられている。水素噴射弁１３は水素供給装置１４から水素デリバリチューブ１５を介して供給される気体燃料としての水素をそのノズル１３ａからシリンダ３内に噴射する。水素の噴射方向は、シリンダ３の中心線ＣＬ１と直交する方向（以下、シリンダ横断方向と呼ぶ。）に対してピストン４側に幾らか傾けられている。水素供給装置１４は、水素タンクに蓄えられた高圧水素を所定圧力に調圧して供給するものでもよいし、ガソリン燃料を改質して水素を取り出すものでもよい。
【００２３】
ピストン４の頂面４ａにはその水素噴射弁１３から噴射された水素を点火プラグ１２の付近に案内するための案内部としてのキャビティ４ｂが形成されている。そのキャビティ４ｂの詳細を図２に示す。キャビティ４ｂは、直線状の第１の壁面４ｃと、湾曲した第２の壁面４ｄとを有している。第１の壁面４ｃはピストン頂面４ａとの交差部Ｐ１からシリンダ横断方向に対して一定の傾斜角βで下り勾配を描いて延びている。水素噴射弁１３から噴射される水素流２０の中心線ＣＬ２のシリンダ横断方向に対する傾斜角をα、シリンダ３の中心線ＣＬ１の方向に関する水素流２０の広がり角をθｖとしたとき、傾斜角βは次式を満たすように設定される。
【００２４】
【数１】
β＞α＋θｖ／２
このように傾斜角βを設定すれば、水素流２０が第１の壁面４ｃに接触せず、第１の壁面４ｃと水素流２０との衝突による水素の拡散を防止することができる。なお、ピストン頂面４ａと第１の壁面４ｃとの交差部Ｐ１の位置は、後述する圧縮行程中の水素の噴射時期において、水素流２０がピストン頂面４ａと衝突しないように定められる。
【００２５】
一方、第２の壁面４ｄは第１の壁面４ｃとの交差部Ｐ２から凹曲面を描きつつ点火プラグ１２側に向かって立ち上がる湾曲面に形成される。第１の壁面４ｄの湾曲は、圧縮行程中における水素の噴射時期において、水素流２０を点火プラグ１２の付近に集中させることができるように定められる。第２の壁面４ｄとピストン頂面４ａとの交差部Ｐ３は圧縮行程中に噴射される水素流２０の上端の延長線Ａよりも点火プラグ１２側に位置するように定められる。これにより、水素流２０を第２の壁面４ｄで漏れなく捉えて点火プラグ１２の周りに効率よく集中させることができる。
【００２６】
図１に戻って、内燃機関１の動作はエンジンコントロールユニット（ＥＣＵ１６）により制御される。ＥＣＵ１６はマイクロプロセッサ及びその動作に必要な主記憶装置としてのＲＡＭ、ＲＯＭ等の周辺装置を備えたコンピュータとして構成される周知の制御装置である。ＥＣＵ１６は、各種のセンサの出力信号に基づいて特定した内燃機関１の運転状態に応じて燃料噴射弁１０の燃料噴射時期、及び燃料噴射量を制御することにより、本発明の燃料供給制御手段として機能する。また、ＥＣＵ１６は、クランク角センサ１７から出力されるクランク角信号に基づいて水素噴射弁１３からの水素の噴射時期及び噴射量を制御することにより、本発明の添加制御手段として機能する。
【００２７】
図３はＥＣＵ１６によって制御される燃料噴射弁１０からの燃料噴射時期、水素噴射弁１３からの水素噴射時期及び点火プラグ１２による点火時期と、吸排気バルブ６，７の開弁時期と、筒内圧（シリンダ３の内部圧力）とをクランク角と対応付けて示したタイミングチャートである。なお、クランク角は圧縮ＴＤＣ（圧縮行程においてピストン４が上死点（ＴＤＣ）に達したとき）を０°とし、その圧縮ＴＤＣまでにクランク軸が回転すべき角度として示されている。
【００２８】
図３から明らかなように、燃料噴射弁１０による燃料噴射時期は吸気バルブ６が閉じている圧縮ＴＤＣから吸気ＴＤＣ（ピストン４が上死点に位置する吸気行程の始期）の直前迄の間に設定される。排気バルブ７は膨張行程の終期（ピストン４が下死点（ＢＴＤＣ）に位置する時期）付近から吸気ＴＤＣ付近まで開弁され、吸気バルブ６は吸気ＴＤＣ付近から吸気行程の終期付近まで開弁される。筒内圧は吸気バルブ６又は排気バルブ７のいずれかが開弁している期間において低下し、バルブ６，７が閉じられると上昇する。そして、水素噴射弁１３からの水素の噴射時期は吸気行程中の第１回目噴射期間（第１の添加工程）と、圧縮行程中の第２回目噴射期間（第２の添加工程）とに分けて設定されている。第２回目噴射期間は特に圧縮行程の後半、すなわち圧縮ＴＤＣまでのクランク角が９０°以下になった時期に設定される。そして、第２回目噴射期間は第１回目噴射期間よりも十分に短く設定される。
【００２９】
ＥＣＵ１６はクランク角センサ１７の出力信号に基づいてクランク角を常時監視し、図３のタイミングチャートに従って燃料噴射弁１０からの燃料噴射、水素噴射弁１３からの水素噴射、及び点火プラグ１２による点火時期を制御する。
【００３０】
図３に従って水素が噴射される様子を図４に示す。図４（ａ）は第１回目噴射期間の様子を示している。第１回目噴射期間においては吸気バルブ６が開弁しかつピストン４が下降することにより、吸気ポート８からガソリン燃料と空気とが燃料混合気を形成しつつシリンダ３内に吸入される。これらの吸入と並行して水素噴射弁１３から水素流２０が噴射され、その水素はピストン４の下降による燃焼室２の膨張に伴って拡散して燃料混合気と混ざり合う。
【００３１】
続く圧縮行程中の第２回目噴射期間においては、図４（ｂ）に示すように水素噴射弁１３から上昇過程のピストン４に向かって水素が噴射される。噴射された水素流２０は図２に示したようにキャビティ４ｂに沿って方向転換されて点火プラグ１２の付近に導かれる。従って、圧縮行程の後半には、図４（ｃ）に示すように、第１回目噴射期間に噴射された水素が想像線Ｌ１で示すようにシリンダ３内の広い範囲に亘ってほぼ均等に分散される一方、第２回目噴射期間に噴射された水素により、点火プラグ１２の付近には他の部分よりも水素濃度の高い領域Ｌ２が形成される。
【００３２】
これにより、点火プラグ１２による着火時には、水素の着火改善効果が十分に発揮され、ガソリン燃料のみを使用する場合や混合気に対して均質に水素を分散させるだけの場合と比較して着火性が改善されて良好な初期燃焼が実現される。そして、着火した火炎が伝播する後期燃焼においては、第１回目噴射期間に噴射された水素が燃焼室２内に十分に分散しているので火炎伝播特性が向上し、ガソリン成分が少なくても良好な燃焼状態が確保される。このように初期燃焼及び後期燃焼のいずれにおいても水素の燃焼改善効果を十分に発揮させることができるので、従来と比べてシリンダ３内に導入される空気量を増大させてリーンリミットを拡大することができる。例えば、水素をその熱量にしてガソリンの２０％添加するとした場合（但し、第１回目と第２回目の合計値）、従来であれば空気過剰率が２倍程度が限界であるが、本実施形態であれば空気過剰率を２．５〜３倍程度まで拡大しても燃焼状態を安定させることができる。この程度まで空気を増やすことができれば筒内の温度が大幅に低下してＮＯｘ生成量がほぼ０まで減少し、ＮＯｘ吸蔵触媒を使用する必要がなくなる。
【００３３】
以上の実施形態において、第２回目噴射期間に噴射されるべき水素の量は着火に必要な最小限度でよい。具体的には点火プラグ１２の近傍に、火炎伝播の起点となる火炎核が形成されるために必要な最小限度でよい。例えば第１回目の噴射量と第２回目の噴射量の合計を熱量にしてガソリンの２０％に設定する場合、第２回目の噴射量はガソリンの熱量の３％程度に相当する量で足りる。残りの１７％に相当する量は第１回目に噴射すればよい。火炎核の形成に必要な水素量を絞り込むことにより、火炎核の形成時におけるＮＯｘの生成量を最小限に抑えることができる。いずれにせよ、第２回目噴射期間における水素の噴射量は第１回目噴射期間における噴射量と比較して遙かに少ない値でよい。
【００３４】
また、一回の燃焼に備えて噴射されるガソリンの量は実質的な燃焼が可能な最小限度でよい。実質的な燃焼が可能か否かは例えばトルク変動によって評価することができる。すなわち、ガソリンの噴射量を減らして空燃比をリーン側に変化させると、リーンリミット近傍において空気の比率が増加するほど燃焼が徐々に不安定となり、その影響がトルク変動として出現する。従って、吸気、圧縮、膨張及び排気の４行程を一つの単位としたとき、一単位内におけるトルク変動量の限界値を０．４〜０．５Ｎｍに設定し、この限界値に達したときの空燃比をリーンリミットとして実質的な燃焼が可能な範囲を特定し、そのリーンリミット内で燃焼が行われるようにガソリン噴射量を設定すればよい。
【００３５】
なお、各噴射期間においては、水素を連続的に噴射してもよいし、複数回に分けて噴射してもよい。第１回目噴射期間及び第２回目噴射期間における水素の噴射量は、それぞれの噴射期間に対して予め定められた一定値に制御してもよいが、内燃機関１の運転状態に応じて第１回目噴射期間及び第２回目噴射期間の水素の噴射量をそれぞれ変化させてもよい。例えば、噴射されるガソリンの熱量に対して一定の比率で水素を噴射させる場合にはＥＣＵ１６が算出する燃料噴射量に基づいて第１回目及び第２回目のそれぞれ水素噴射量を演算し、その演算結果に従って水素噴射弁１３の開弁時期（デューティー比）を制御すればよい。第１回目噴射期間及び第２回目噴射期間の長さも必要に応じて適宜に調整してよい。
【００３６】
次に、図５〜図８を参照して上記の実施形態の幾つかの好ましい変形例を説明する。なお、各図において図１〜図４と共通する部分には同一符号を付してある。
【００３７】
まず、圧縮行程における水素噴射弁１３からの水素流２０の噴射方向については、図５に示すように水素噴射弁１３から点火プラグ１２の付近に向かって水素流２０を噴射してもよい。なお、圧縮行程に限らず、吸気行程及び圧縮行程の両者で点火プラグ１２に向かって水素を噴射してもよい。ピストン４のキャビティ４ｂは省略してもよい。吸気行程と圧縮行程とで異なる方向に水素を噴射させる場合には、水素噴射弁１３に噴射方向が異なる複数の噴孔を形成するとともに、実際に使用する噴孔を選択的に切り替える切替機構を水素噴射弁１３に内蔵させる。切替機構は、例えば各噴孔に通じる流路をスプール等の流路選択手段にて切り替えるように構成すればよい。
【００３８】
吸気ポート８については、図６に示すように２本の吸気バルブ６，６に１：１に対応させて分岐路８ａ，８ｂを形成し、一方の分岐路８ａにスワールコントロールバルブ３０を設けて分岐路８ａの開口面積を分岐路８ｂよりも減少させる（完全に閉じる場合も含む。）ことにより、シリンダ３内にスワール流３１が形成されるようにしてもよい。スワールコントロールバルブ３０に代え、図７に示すように他方の分岐路８ｂをヘリカルポート状に形成してスワール流３１を形成してもよい。以上のようにしてスワール流３１を形成した場合には、吸気行程で噴射される水素と、ガソリン及び空気とが効率よく混合されて水素の分布がより均質化される。
【００３９】
スワール流３１を形成する場合においては、図８に示すようにピストン４のキャビティ４ｂをスワール流３１の方向に沿って湾曲させてもよい。この場合にはキャビティ４ｂに沿って点火プラグ１２の付近に案内される水素流２０がスワール流３１に沿って流れるので、シリンダ３内の気流に逆らって水素を噴射する必要がない。従って、水素の噴射圧を低下させることができる。圧縮行程では筒内圧が上昇しているので、水素の圧力もそれに応じて高める必要があり、例えば第２回目噴射期間の筒内圧が２〜３ＭＰａ程度であれば、少なくとも１ＭＰａ以上高い圧力で水素を噴射する必要があると考えられる。しかし、キャビティ４ｂを図８のように形成すれば、筒内圧に対して１ＭＰａを超えない小さい範囲で水素の圧力を高めるだけでよいと考えられる。なお、スワール流に代え、又は追加してタンブル流を形成してガソリン、水素及び空気の混合を促進してもよい。
【００４０】
本発明はシリンダ内に直接燃料を噴射する筒内噴射式の内燃機関に対しても適用可能である。特に均質燃焼時に本発明を利用すれば、均質燃焼時のリーンリミットを拡大することができる。なお、ガソリン燃料を筒内に噴射する内燃機関においては、吸気行程で燃料を噴射して燃料混合気を筒内に均質に拡散させる均質燃焼と、圧縮行程で燃料を噴射して点火プラグの付近に燃料混合気を集中させる成層燃焼とを使い分けており、それらの燃焼モードの境界付近では、両者間の移行を円滑化するために吸気行程及び圧縮行程でそれぞれ燃料を噴射することもある。しかし、本発明はあくまで均質燃焼を実現するために気体燃料を吸気行程及び圧縮行程のそれぞれで噴射するものであり、ガソリン燃料の２回噴射とはその目的も作用も全く異なるものである。
【００４１】
なお、本発明において、主燃料はガソリンに限らず、内燃機関において燃焼混合気を形成するために使用される各種の燃料を主燃料として使用できる。気体燃料はその主燃料の着火性や火炎伝播特性を改善できる作用を有していれば使用できる可能性があり、主燃料との混合によって不所望の反応を生じないものであれば水素に限らず各種の気体燃料を使用してよい。
【００４２】
【発明の効果】
以上に説明したように、本発明の気体燃料添加方法及び装置によれば、吸気行程と圧縮行程のそれぞれで気体燃料を添加するようにしたので、燃焼室の膨張に伴って主燃料や空気と気体燃料とを十分に混合して筒内に満遍なく気体燃料を分散させて火炎伝播特性を向上させるとともに、圧縮行程中の筒内に部分的に気体燃料の濃度が高い領域を形成して燃料混合気の着火性を向上させることができる。すなわち、本発明によれば、着火を含む初期燃焼と、火炎伝播を主体とする後期燃焼とのいずれに対しても気体燃料を有効に作用させることができる。従って、主燃料に対する空気量を増加させてリーンリミットを拡大し、それにより熱効率の向上と排気の改善、特にＮＯｘの生成量の削減とを図ることができる。リーンリミットの拡大により燃焼時の筒内温度を十分に低下させてＮＯｘ生成量をほぼ０まで低下させることも不可能ではなく、その場合にはＮＯｘ吸蔵触媒をも不要とすることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態の気体燃料添加装置が組み込まれた内燃機関の要部を示す図。
【図２】ピストンの頂面に形成されたキャビティを示す図。
【図３】燃料噴射時期、水素噴射時期及び点火時期と、吸排気バルブの開弁時期と、筒内圧とをクランク角と対応付けて示したタイミングチャート。
【図４】本発明に従って筒内に水素が噴射される様子を示す図。
【図５】水素の噴射方向を変更した例を示す図。
【図６】スワール流を形成する例を示す図。
【図７】スワール流を形成する他の例を示す図。
【図８】スワール流に合わせてピストンのキャビティを湾曲させた例を示す図。
【符号の説明】
１　内燃機関
２　燃焼室
３　シリンダ
４　ピストン
４ａ　ピストンの頂面
４ｂ　ピストンのキャビティ（案内部）
５　シリンダヘッド
６　吸気バルブ
７　排気バルブ
８　吸気ポート
８ｂ　分岐路（吸気流動形成手段）
９　排気ポート
１０　燃料噴射弁
１２　点火プラグ
１３　水素噴射弁（気体燃料添加手段）
１６　エンジンコントロールユニット（添加制御手段、燃料供給制御手段）
２０　水素流
３０　スワールコントロールバルブ（吸気流動形成手段）
３１　スワール流（吸気流動）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for adding a gaseous fuel such as hydrogen to a fuel mixture formed in a cylinder of an internal combustion engine.
[0002]
[Prior art]
By adding hydrogen to the fuel mixture formed by gasoline fuel and air, the ignitability is improved, the lean limit (lean limit) of the fuel mixture is improved, and the emission of NOx (nitrogen oxide) is reduced. There is known a technique for achieving the above. For example, in the internal combustion engine described in JP-A-7-63128, ignitability is improved by intensively adding hydrogen to the periphery of the spark plug, and the mixture of gasoline and air increases as the distance from the spark plug increases. The distribution is made rich so as to improve the flame propagation to the peripheral portion in the cylinder.
[0003]
[Problems to be solved by the invention]
However, in the internal combustion engine disclosed in the above publication, only hydrogen is used for improving the ignitability, and flame propagation after ignition depends on gasoline fuel. Therefore, hydrogen is hardly involved in the flame propagation, and the lean limit viewed from the flame propagation characteristics is almost the same as in the case of using only gasoline fuel. Therefore, if the lean limit is forcibly expanded, a misfire or an unstable operation state due to poor flame propagation is caused.
[0004]
On the other hand, when hydrogen is uniformly dispersed in the cylinder, the flame propagation characteristics are improved. The degree of improvement increases as the amount of hydrogen increases, and as the amount of hydrogen increases, the lean limit increases, with the result that thermal efficiency improves and the amount of NOx reduction increases. However, considering the development of public capital related to the supply of hydrogen, it is impossible to add a large amount of hydrogen so that NOx can be completely reduced. Therefore, in reality, it is necessary to keep the amount of hydrogen that can be added as small as possible.
[0005]
However, when a small amount of hydrogen is added, the ignitability of the fuel mixture is greatly affected by gasoline, and the ignitability is not significantly improved by hydrogen. Accordingly, the lean limit is not necessarily not expanded at all compared to the case of using only gasoline fuel, but in such a lean region, the generation of NOx cannot be completely eliminated and the catalyst must be used. However, it is indispensable to treat NOx using a NOx storage catalyst because of the lean region. When such a catalyst is used, considerable care is required for maintenance of performance and maintenance and inspection, which is troublesome.
[0006]
Therefore, the present invention can effectively utilize a gaseous fuel such as hydrogen to extend the lean limit of the fuel mixture, improve heat efficiency and improve exhaust, and desirably eliminate the need for a NOx storage catalyst. It is an object of the present invention to provide a method and an apparatus for adding gaseous fuel to an internal combustion engine, which can improve exhaust gas to a certain extent.
[0007]
[Means for Solving the Problems]
The gaseous fuel addition method of the present invention is a gaseous fuel addition method for an internal combustion engine in which another gaseous fuel other than a main fuel for forming a fuel mixture is added into a cylinder, wherein the gaseous fuel is added during an intake stroke. The above-described problem is solved by providing a first addition step of adding and a second addition step of adding the gaseous fuel during a compression stroke (claim 1).
[0008]
In the gaseous fuel addition method of the present invention, the gaseous fuel added in the first addition step is sufficiently mixed with the main fuel and air with the expansion of the combustion chamber during the intake stroke, and is uniformly dispersed in the cylinder. On the other hand, the gaseous fuel added in the second addition step is immediately before ignition, does not diffuse into the cylinder, and partially forms a region where the concentration of the gaseous fuel is high. By utilizing the region where the concentration of the gaseous fuel is high for ignition, the ignitability of the fuel mixture can be improved. As for the flame propagation after ignition, the gaseous fuel is uniformly dispersed in the cylinder, so that the flame propagation characteristics are improved as compared with the case where only the main fuel is used.
[0009]
As described above, according to the present invention, the gaseous fuel effectively acts on both the initial combustion including the ignition and the late combustion mainly based on the flame propagation, so that the air amount with respect to the main fuel is increased. By increasing the lean limit, it is possible to improve the thermal efficiency and the exhaust gas, and in particular, to reduce the generation amount of NOx. It is not impossible to sufficiently reduce the in-cylinder temperature at the time of combustion to reduce the NOx generation amount to almost 0 by expanding the lean limit. In this case, the NOx storage catalyst can be dispensed with.
[0010]
In the gaseous fuel addition method of the present invention, it is preferable that in the second addition step, the gaseous fuel is added so as to gather around the spark plug (claim 2). In order to add such gaseous fuel, the gaseous fuel is injected toward the spark plug (Claim 3), or a guide portion for guiding the gaseous fuel toward the spark plug is formed on the top surface of the piston. Then, gas fuel can be injected toward the guide portion (claim 4). If the gaseous fuel added in the compression stroke is collected around the spark plug in this way, the ignitability can be reliably improved.
[0011]
In the gaseous fuel addition method of the present invention, the gaseous fuel added in the second addition step is sufficient as long as ignitability can be ensured, and a very small amount is sufficient, whereas the gaseous fuel added in the first addition step is sufficient. Gaseous fuel needs to be evenly dispersed in the cylinder. Therefore, it is desirable to make the amount of the gaseous fuel added in the second addition step smaller than the amount of the gaseous fuel added in the first addition step (claim 5). More preferably, the addition amount of the gaseous fuel in the second addition step is set to a minimum necessary for forming a flame kernel near the ignition plug (claim 6). If a flame nucleus can be formed using the effect of gaseous fuel at the time of ignition, thereafter, the flame will almost certainly propagate with the help of the gaseous fuel added in the first addition step. By limiting the amount of gaseous fuel added to the minimum required for flame kernel formation, the amount of NOx generated during flame kernel formation can also be reduced, further improving emissions.
[0012]
Further, in the gaseous fuel addition method of the present invention, the amount of the main fuel supplied in preparation for one combustion may be set to a minimum that allows substantial combustion (claim 7). If the supply amount of the main fuel is limited in this way, the internal combustion engine can be operated in a lean region that cannot be realized only with the main fuel, and the NOx generation amount can be greatly reduced. It should be noted that substantial combustion means that combustion is achieved to such an extent that the internal combustion engine can be put to practical use, and this can be evaluated using a physical quantity correlated with combustion stability as an index. For example, the fluctuation amount of the output torque of the internal combustion engine expands due to combustion instability, so a practical limit value is set for the torque fluctuation amount, and when the limit value is exceeded, substantial combustion occurs. It can be evaluated that it does not hold.
[0013]
Furthermore, in the gaseous fuel addition method of the present invention, an intake air flow may be formed in the cylinder during the intake stroke (claim 8). When the intake flow is formed, the gaseous fuel added in the first addition step can be efficiently mixed with the main fuel or air and uniformly dispersed in the cylinder. The intake flow may be a swirl flow turning around the center line of the cylinder or a tumble flow turning along the direction of the center line of the cylinder.
[0014]
Next, the gaseous fuel addition device for an internal combustion engine of the present invention is a gaseous fuel addition means for adding a gaseous fuel other than the main fuel for forming a fuel mixture into a cylinder, and the gaseous fuel is provided in an intake stroke and The above-mentioned problem is solved by providing an addition control means for controlling the gaseous fuel addition means so as to be added in each compression stroke (claim 10).
[0015]
According to this gaseous fuel addition device, the first and second addition steps of the gaseous fuel addition method of the present invention are realized by adding the gaseous fuel in the intake stroke and the compression stroke, respectively, to achieve the above-described effects. Can be obtained.
[0016]
In order to realize the above-described preferred embodiment of the gaseous fuel addition method of the present invention, the gaseous fuel addition device for an internal combustion engine of the present invention may include the following embodiments.
[0017]
The gaseous fuel adding means may be capable of injecting the gaseous fuel toward a spark plug (claim 11). A guide may be formed on the piston to guide the gas toward the spark plug, and the gaseous fuel adding means may be capable of injecting the gaseous fuel toward the guide (claim 12).
[0018]
The addition control means may control the gaseous fuel addition means so that the addition amount of the gaseous fuel during the compression stroke is smaller than the addition amount of the gaseous fuel during the intake stroke (claim 13). The addition control means may control the gaseous fuel addition means such that an addition amount of the gaseous fuel during a compression stroke is a minimum necessary for forming a flame kernel near the ignition plug. Good (claim 14). A fuel supply amount control means for controlling the supply amount of the main fuel such that the amount of the main fuel supplied for one combustion is a minimum at which substantial combustion can be performed may be provided ( Claim 15). An intake flow forming means for forming an intake flow in the cylinder may be provided. The intake flow forming means may form a swirl flow or a tumble flow, and these intake flows can be realized by a valve means such as a swirl control valve or a tumble control valve disposed at a part of the intake port, a helical port, or the like. .
[0019]
Furthermore, in the gaseous fuel adding device of the present invention, there is provided an intake flow forming means for forming a swirl flow swirling around the center line of the cylinder in the cylinder, and the guide unit is configured to transfer the gaseous fuel in a direction of the swirl flow. It may be formed to be curved along (claim 17). In this case, since the gaseous fuel flows toward the spark plug along the swirl flow, there is an advantage that the gaseous fuel can be added at a lower pressure into the cylinder during the compression stroke.
[0020]
In the present invention, the main fuel is gasoline, for example, and in that case, hydrogen can be suitably used as the gaseous fuel (claims 9 and 18).
[0021]
In the present invention, the term "addition" means that gaseous fuel is added to the main fuel added to the internal combustion engine to form a fuel mixture, and the amount, speed, pressure, etc., of gaseous fuel added. Does not limit the range of addition.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a main part of an internal combustion engine in which a gaseous fuel adding apparatus according to one embodiment of the present invention is incorporated. The internal combustion engine 1 is configured as a four-cycle gasoline engine, and includes an intake valve 6 that opens and closes a cylinder (cylinder) 3, a piston 4 and a cylinder head 5 that form a combustion chamber 2, and an intake port 8 and an exhaust port 9. And an exhaust valve 7, a fuel injection valve 10 for injecting gasoline as main fuel into the intake port 8, a fuel delivery tube 11 for supplying a predetermined pressure of fuel to the fuel injection valve 10, and a spark for mixture ignition. And a spark plug 12 to be formed. Further, the cylinder head 5 is provided with a hydrogen injection valve 13 as a gaseous fuel adding means. The hydrogen injection valve 13 injects hydrogen as a gaseous fuel supplied from a hydrogen supply device 14 via a hydrogen delivery tube 15 into the cylinder 3 from its nozzle 13a. The hydrogen injection direction is slightly inclined to the piston 4 side with respect to a direction orthogonal to the center line CL1 of the cylinder 3 (hereinafter, referred to as a cylinder transverse direction). The hydrogen supply device 14 may be a device that regulates and supplies high-pressure hydrogen stored in a hydrogen tank to a predetermined pressure, or may be a device that reforms gasoline fuel and extracts hydrogen.
[0023]
A cavity 4b is formed on the top surface 4a of the piston 4 as a guide for guiding the hydrogen injected from the hydrogen injection valve 13 to the vicinity of the ignition plug 12. FIG. 2 shows details of the cavity 4b. The cavity 4b has a linear first wall surface 4c and a curved second wall surface 4d. The first wall surface 4c extends downward from the intersection P1 with the piston top surface 4a at a constant inclination angle β with respect to the cylinder transverse direction. Assuming that the inclination angle of the center line CL2 of the hydrogen flow 20 injected from the hydrogen injection valve 13 with respect to the transverse direction of the cylinder is α, and the spread angle of the hydrogen flow 20 in the direction of the center line CL1 of the cylinder 3 is θv, It is set to satisfy the following equation.
[0024]
(Equation 1)
β> α + θv / 2
By setting the inclination angle β in this manner, the hydrogen flow 20 does not contact the first wall surface 4c, and the diffusion of hydrogen due to the collision between the first wall surface 4c and the hydrogen flow 20 can be prevented. The position of the intersection P1 between the piston top surface 4a and the first wall surface 4c is determined so that the hydrogen flow 20 does not collide with the piston top surface 4a at the injection timing of hydrogen during the compression stroke described later.
[0025]
On the other hand, the second wall surface 4d is formed as a curved surface that rises toward the spark plug 12 while drawing a concave curved surface from the intersection P2 with the first wall surface 4c. The curvature of the first wall surface 4d is determined so that the hydrogen flow 20 can be concentrated near the ignition plug 12 at the injection timing of hydrogen during the compression stroke. The intersection P3 between the second wall surface 4d and the piston top surface 4a is determined so as to be located closer to the ignition plug 12 than the extension line A at the upper end of the hydrogen flow 20 injected during the compression stroke. Thereby, the hydrogen flow 20 can be caught by the second wall surface 4d without leakage, and can be efficiently concentrated around the ignition plug 12.
[0026]
Returning to FIG. 1, the operation of the internal combustion engine 1 is controlled by an engine control unit (ECU 16). The ECU 16 is a well-known control device configured as a computer including a microprocessor and peripheral devices such as a RAM and a ROM as main storage devices necessary for the operation thereof. The ECU 16 controls the fuel injection timing and the fuel injection amount of the fuel injection valve 10 according to the operating state of the internal combustion engine 1 specified based on the output signals of various sensors, thereby serving as the fuel supply control means of the present invention. Function. Further, the ECU 16 functions as an addition control unit of the present invention by controlling the timing and amount of hydrogen injection from the hydrogen injection valve 13 based on the crank angle signal output from the crank angle sensor 17.
[0027]
FIG. 3 shows the fuel injection timing from the fuel injection valve 10 controlled by the ECU 16, the hydrogen injection timing from the hydrogen injection valve 13, the ignition timing by the spark plug 12, the valve opening timing of the intake and exhaust valves 6, 7, and the in-cylinder pressure. 6 is a timing chart showing (internal pressure of the cylinder 3) in association with a crank angle. Note that the crank angle is defined as an angle at which the crankshaft should rotate by the compression TDC (when the piston 4 reaches the top dead center (TDC) in the compression stroke) by 0 ° by the compression TDC.
[0028]
As is apparent from FIG. 3, the fuel injection timing by the fuel injection valve 10 is between the compression TDC in which the intake valve 6 is closed and immediately before the intake TDC (the start of the intake stroke in which the piston 4 is located at the top dead center). Is set. The exhaust valve 7 is opened from near the end of the expansion stroke (when the piston 4 is located at the bottom dead center (BTDC)) to near the intake TDC, and the intake valve 6 is opened from near the intake TDC to near the end of the intake stroke. You. The in-cylinder pressure decreases during a period in which either the intake valve 6 or the exhaust valve 7 is open, and increases when the valves 6 and 7 are closed. The injection timing of hydrogen from the hydrogen injection valve 13 is divided into a first injection period during the intake stroke (first addition step) and a second injection period during the compression stroke (second addition step). Is set. The second injection period is set particularly in the latter half of the compression stroke, that is, the time when the crank angle up to the compression TDC becomes 90 ° or less. Then, the second injection period is set sufficiently shorter than the first injection period.
[0029]
The ECU 16 constantly monitors the crank angle based on the output signal of the crank angle sensor 17, and in accordance with the timing chart of FIG. 3, the fuel injection from the fuel injection valve 10, the hydrogen injection from the hydrogen injection valve 13, and the ignition timing by the spark plug 12. Control.
[0030]
FIG. 4 shows how hydrogen is injected according to FIG. FIG. 4A shows a state during the first injection period. In the first injection period, the intake valve 6 opens and the piston 4 descends, so that gasoline fuel and air are drawn into the cylinder 3 from the intake port 8 while forming a fuel mixture. A hydrogen flow 20 is injected from the hydrogen injection valve 13 in parallel with the suction, and the hydrogen diffuses with the expansion of the combustion chamber 2 due to the lowering of the piston 4 and mixes with the fuel mixture.
[0031]
In the second injection period during the subsequent compression stroke, hydrogen is injected from the hydrogen injection valve 13 toward the ascending piston 4 as shown in FIG. The injected hydrogen flow 20 is diverted along the cavity 4b as shown in FIG. Accordingly, in the latter half of the compression stroke, as shown in FIG. 4C, the hydrogen injected during the first injection period is substantially evenly distributed over a wide range in the cylinder 3 as indicated by the imaginary line L1. On the other hand, due to the hydrogen injected during the second injection period, a region L2 having a higher hydrogen concentration than other portions is formed near the ignition plug 12.
[0032]
Thereby, at the time of ignition by the ignition plug 12, the effect of improving the ignition of hydrogen is sufficiently exhibited, and the ignitability is improved as compared with the case where only gasoline fuel is used or the case where only hydrogen is uniformly dispersed in the air-fuel mixture. Improved and better initial combustion is achieved. In the latter combustion in which the ignited flame propagates, the hydrogen injected in the first injection period is sufficiently dispersed in the combustion chamber 2, so that the flame propagation characteristics are improved, and even if the gasoline component is small, the gaseous component is good. A proper combustion state is ensured. As described above, the effect of improving the combustion of hydrogen can be sufficiently exhibited in both the initial combustion and the late combustion, so that the lean amount can be increased by increasing the amount of air introduced into the cylinder 3 as compared with the related art. Can be. For example, if hydrogen is added as the calorie and 20% of gasoline is added (however, the total value of the first and second times), the conventional method has a limit of about twice the excess air ratio. With this configuration, the combustion state can be stabilized even if the excess air ratio is increased to about 2.5 to 3 times. If the air can be increased to this extent, the temperature in the cylinder will be greatly reduced, the NOx generation amount will be reduced to almost 0, and it will not be necessary to use a NOx storage catalyst.
[0033]
In the above embodiment, the amount of hydrogen to be injected during the second injection period may be the minimum required for ignition. More specifically, it may be the minimum necessary for forming a flame kernel serving as a starting point of flame propagation near the ignition plug 12. For example, when the sum of the first injection amount and the second injection amount is set as the calorific value and set to 20% of the gasoline, the second injection amount is an amount corresponding to about 3% of the gasoline's heat amount. The remaining amount corresponding to 17% may be injected for the first time. By narrowing down the amount of hydrogen necessary for the formation of the flame nucleus, the amount of NOx generated during the formation of the flame nucleus can be minimized. In any case, the injection amount of hydrogen in the second injection period may be much smaller than the injection amount in the first injection period.
[0034]
Further, the amount of gasoline injected for one combustion may be the minimum that allows substantial combustion. Whether or not substantial combustion is possible can be evaluated by, for example, torque fluctuation. That is, if the air-fuel ratio is changed to the lean side by reducing the injection amount of gasoline, the combustion becomes gradually unstable as the air ratio increases near the lean limit, and the effect appears as torque fluctuation. Therefore, when the four strokes of intake, compression, expansion, and exhaust are defined as one unit, the limit value of the amount of torque fluctuation within one unit is set to 0.4 to 0.5 Nm. The air-fuel ratio may be set as a lean limit to specify a range in which substantial combustion is possible, and the gasoline injection amount may be set so that combustion is performed within the lean limit.
[0035]
Note that in each injection period, hydrogen may be injected continuously or may be injected a plurality of times. Although the injection amount of hydrogen in the first injection period and the second injection period may be controlled to a predetermined constant value for each injection period, the first injection amount may be controlled in accordance with the operation state of the internal combustion engine 1. The amount of hydrogen injected during the second injection period and the second injection period may be changed. For example, when injecting hydrogen at a fixed ratio with respect to the amount of heat of gasoline to be injected, the first and second hydrogen injection amounts are calculated based on the fuel injection amount calculated by the ECU 16, and the calculation is performed. The opening timing (duty ratio) of the hydrogen injection valve 13 may be controlled according to the result. The lengths of the first injection period and the second injection period may be appropriately adjusted as needed.
[0036]
Next, some preferred modifications of the above embodiment will be described with reference to FIGS. In each of the drawings, the same reference numerals are given to parts common to FIGS.
[0037]
First, regarding the injection direction of the hydrogen flow 20 from the hydrogen injection valve 13 in the compression stroke, the hydrogen flow 20 may be injected from the hydrogen injection valve 13 toward the vicinity of the spark plug 12 as shown in FIG. The hydrogen may be injected toward the ignition plug 12 not only in the compression stroke but also in the intake stroke and the compression stroke. The cavity 4b of the piston 4 may be omitted. When hydrogen is injected in different directions between the intake stroke and the compression stroke, a plurality of injection holes having different injection directions are formed in the hydrogen injection valve 13 and a switching mechanism for selectively switching the injection holes actually used is provided. It is built in the hydrogen injection valve 13. The switching mechanism may be configured, for example, to switch the flow path leading to each injection hole by flow path selection means such as a spool.
[0038]
As for the intake port 8, as shown in FIG. 6, branch paths 8a and 8b are formed in a one-to-one correspondence with the two intake valves 6 and 6, and a swirl control valve 30 is provided in one branch path 8a. The swirl flow 31 may be formed in the cylinder 3 by making the opening area of the branch passage 8a smaller than that of the branch passage 8b (including a case where the branch passage 8b is completely closed). Instead of the swirl control valve 30, the swirl flow 31 may be formed by forming the other branch passage 8b in a helical port shape as shown in FIG. When the swirl flow 31 is formed as described above, hydrogen injected in the intake stroke, gasoline and air are efficiently mixed, and the distribution of hydrogen is further homogenized.
[0039]
When the swirl flow 31 is formed, the cavity 4b of the piston 4 may be curved along the swirl flow 31 as shown in FIG. In this case, the hydrogen flow 20 guided to the vicinity of the ignition plug 12 along the cavity 4b flows along the swirl flow 31, so that there is no need to inject hydrogen against the air flow in the cylinder 3. Therefore, the injection pressure of hydrogen can be reduced. Since the in-cylinder pressure increases in the compression stroke, the hydrogen pressure also needs to be increased accordingly. For example, if the in-cylinder pressure during the second injection period is about 2 to 3 MPa, hydrogen is supplied at a pressure higher by at least 1 MPa. It is considered necessary to inject. However, if the cavity 4b is formed as shown in FIG. 8, it is considered that it is only necessary to increase the hydrogen pressure within a small range not exceeding 1 MPa with respect to the in-cylinder pressure. Instead of or in addition to the swirl flow, a tumble flow may be formed to promote the mixing of gasoline, hydrogen and air.
[0040]
The present invention is also applicable to an in-cylinder injection type internal combustion engine that directly injects fuel into a cylinder. In particular, if the present invention is used during homogeneous combustion, the lean limit during homogeneous combustion can be increased. In an internal combustion engine that injects gasoline fuel into a cylinder, homogeneous combustion in which fuel is injected during an intake stroke to uniformly diffuse a fuel mixture into the cylinder, and fuel near a spark plug that is injected during a compression stroke. In the vicinity of the boundary between the combustion modes, fuel may be injected in the intake stroke and the compression stroke, respectively, in order to smooth the transition between the two. However, the present invention injects gaseous fuel in each of the intake stroke and the compression stroke in order to achieve homogeneous combustion, and its purpose and operation are completely different from those of double injection of gasoline fuel.
[0041]
In the present invention, the main fuel is not limited to gasoline, and various fuels used for forming a combustion mixture in an internal combustion engine can be used as the main fuel. A gaseous fuel may be used if it has the effect of improving the ignitability and flame propagation characteristics of the main fuel, and is limited to hydrogen if it does not cause undesired reactions when mixed with the main fuel. Alternatively, various gaseous fuels may be used.
[0042]
【The invention's effect】
As described above, according to the gaseous fuel addition method and apparatus of the present invention, the gaseous fuel is added in each of the intake stroke and the compression stroke, so that the main fuel and the air are added together with the expansion of the combustion chamber. Gaseous fuel is mixed thoroughly to distribute the gaseous fuel evenly in the cylinder to improve the flame propagation characteristics, and to form a region with a high concentration of gaseous fuel partially in the cylinder during the compression stroke to mix the fuel. The ignitability of the air can be improved. That is, according to the present invention, the gaseous fuel can effectively act on both the initial combustion including ignition and the latter combustion mainly involving flame propagation. Therefore, it is possible to increase the lean limit by increasing the amount of air with respect to the main fuel, thereby improving the thermal efficiency and the exhaust, and in particular, reducing the amount of NOx generated. It is not impossible to sufficiently reduce the in-cylinder temperature at the time of combustion to reduce the NOx generation amount to almost 0 by expanding the lean limit. In this case, the NOx storage catalyst can be dispensed with.
[Brief description of the drawings]
FIG. 1 is a diagram showing a main part of an internal combustion engine in which a gaseous fuel adding apparatus according to an embodiment of the present invention is incorporated.
FIG. 2 is a diagram showing a cavity formed on a top surface of a piston.
FIG. 3 is a timing chart showing a fuel injection timing, a hydrogen injection timing, an ignition timing, a valve opening timing of an intake / exhaust valve, and an in-cylinder pressure in association with a crank angle.
FIG. 4 is a diagram showing how hydrogen is injected into a cylinder according to the present invention.
FIG. 5 is a diagram showing an example in which the injection direction of hydrogen is changed.
FIG. 6 is a diagram illustrating an example of forming a swirl flow.
FIG. 7 is a diagram showing another example of forming a swirl flow.
FIG. 8 is a diagram showing an example in which a cavity of a piston is curved in accordance with a swirl flow.
[Explanation of symbols]
1 Internal combustion engine
2 Combustion chamber
3 cylinder
4 piston
4a Top surface of piston
4b Piston cavity (guide)
5 Cylinder head
6 Intake valve
7 Exhaust valve
8 Intake port
8b fork (intake flow forming means)
9 Exhaust port
10 Fuel injection valve
12 Spark plug
13. Hydrogen injection valve (gas fuel addition means)
16. Engine control unit (addition control means, fuel supply control means)
20 Hydrogen flow
30 Swirl control valve (intake flow forming means)
31 swirl flow (intake flow)

Claims (18)

燃料混合気を形成するための主燃料とは別の気体燃料を筒内に添加する内燃機関の気体燃料添加方法であって、前記気体燃料を吸気行程中に添加する第１の添加工程と、前記気体燃料を圧縮行程中に添加する第２の添加工程とを備えることを特徴とする内燃機関の気体燃料添加方法。A gas fuel addition method for an internal combustion engine, wherein a gas fuel other than a main fuel for forming a fuel mixture is added into a cylinder, a first addition step of adding the gas fuel during an intake stroke, A second addition step of adding the gaseous fuel during a compression stroke. 前記第２の添加工程では、前記気体燃料が点火プラグの周りに集まるように添加することを特徴とする請求項１に記載の気体燃料添加方法。The gaseous fuel addition method according to claim 1, wherein in the second addition step, the gaseous fuel is added so as to gather around a spark plug. 前記第２の添加工程では、点火プラグに向かって前記気体燃料を噴射することを特徴とする請求項２に記載の気体燃料添加方法。The gaseous fuel addition method according to claim 2, wherein in the second addition step, the gaseous fuel is injected toward a spark plug. ピストンの頂面に前記気体燃料を前記点火プラグに向かって案内する案内部を形成し、前記第２の添加工程では前記案内部に向かって前記気体燃料を噴射することを特徴とする請求項２に記載の気体燃料添加方法。A guide for guiding the gaseous fuel toward the spark plug is formed on a top surface of the piston, and the gaseous fuel is injected toward the guide in the second adding step. The method for adding a gaseous fuel according to the above. 前記第１の添加工程における前記気体燃料の添加量よりも前記第２の添加工程における前記気体燃料の添加量を少なくしたことを特徴とする請求項１〜４のいずれか１項に記載の気体燃料添加方法。The gas according to any one of claims 1 to 4, wherein an addition amount of the gaseous fuel in the second addition step is smaller than an addition amount of the gaseous fuel in the first addition step. Fuel addition method. 前記第２の添加工程における前記気体燃料の添加量を、前記点火プラグの付近に火炎核が形成されるために必要な最小限度に設定することを特徴とする請求項１〜４のいずれか１項に記載の気体燃料添加方法。The amount of the gaseous fuel added in the second addition step is set to a minimum necessary for forming a flame kernel near the spark plug. The method for adding a gaseous fuel according to the above item. 一回の燃焼に備えて供給される前記主燃料の量を、実質的な燃焼が可能な最小限度に設定することを特徴とする請求項１〜６のいずれか１項に記載の気体燃料添加方法。The gaseous fuel addition according to any one of claims 1 to 6, wherein an amount of the main fuel supplied in preparation for one combustion is set to a minimum at which substantial combustion is possible. Method. 前記吸気行程において筒内に吸気流動を形成することを特徴とする請求項１〜７のいずれか１項に記載の気体燃料添加方法。The method according to any one of claims 1 to 7, wherein an intake flow is formed in the cylinder during the intake stroke. 前記主燃料がガソリンであり、前記気体燃料が水素であることを特徴とする請求項１〜８のいずれか１項に記載の気体燃料添加方法。The method according to any one of claims 1 to 8, wherein the main fuel is gasoline and the gaseous fuel is hydrogen. 燃料混合気を形成するための主燃料とは別の気体燃料を筒内に添加する気体燃料添加手段と、
前記気体燃料が吸気行程及び圧縮行程でそれぞれ添加されるように前記気体燃料添加手段を制御する添加制御手段と、
を備えたことを特徴とする内燃機関の気体燃料添加装置。Gaseous fuel adding means for adding a gaseous fuel different from the main fuel for forming a fuel mixture into the cylinder,
Addition control means for controlling the gaseous fuel addition means such that the gaseous fuel is added in each of an intake stroke and a compression stroke,
A gas fuel addition device for an internal combustion engine, comprising: 前記気体燃料添加手段は、点火プラグに向かって前記気体燃料を噴射可能であることを特徴とする請求項１０に記載の気体燃料添加装置。The gaseous fuel adding device according to claim 10, wherein the gaseous fuel adding means is capable of injecting the gaseous fuel toward an ignition plug. ピストンには前記気体を前記点火プラグに向かって案内する案内部が形成され、前記気体燃料添加手段は前記案内部に向かって前記気体燃料を噴射可能であることを特徴とする請求項１０に記載の気体燃料添加装置。11. The piston according to claim 10, wherein a guide portion for guiding the gas toward the spark plug is formed, and the gaseous fuel adding means is capable of injecting the gaseous fuel toward the guide portion. Gas fuel addition device. 前記添加制御手段は、吸気行程中における前記気体燃料の添加量よりも圧縮行程中における前記気体燃料の添加量が少なくなるように前記気体燃料添加手段を制御することを特徴とする請求項１０〜１２のいずれか１項に記載の気体燃料添加装置。The gas fuel adding means controls the gas fuel adding means so that the amount of the gaseous fuel added during the compression stroke is smaller than the amount of the gaseous fuel added during the intake stroke. 13. The gaseous fuel addition device according to any one of 12 above. 前記添加制御手段は、圧縮行程中の前記気体燃料の添加量が、前記点火プラグの付近に火炎核が形成されるために必要な最小限度となるように前記気体燃料添加手段を制御することを特徴とする請求項１０〜１２のいずれか１項に記載の気体燃料添加方法。The addition control means controls the gaseous fuel addition means such that an addition amount of the gaseous fuel during a compression stroke is a minimum necessary for forming a flame kernel near the ignition plug. The gaseous fuel addition method according to any one of claims 10 to 12, characterized in that: 一回の燃焼に備えて供給される前記主燃料の量が、実質的な燃焼が可能な最小限度となるように前記主燃料の供給量を制御する燃料供給制御手段を備えたことを特徴とする請求項１０〜１４のいずれか１項に記載の気体燃料添加装置。Fuel supply control means for controlling a supply amount of the main fuel such that an amount of the main fuel supplied for one combustion is a minimum at which substantial combustion is possible. The gaseous fuel adding device according to any one of claims 10 to 14. 筒内に吸気流動を形成する吸気流動形成手段を備えたことを特徴とする請求項１０〜１５のいずれか１項に記載の気体燃料添加装置。The gas fuel addition device according to any one of claims 10 to 15, further comprising an intake flow forming unit configured to form an intake flow in the cylinder. 気筒の中心線の回りを旋回するスワール流を筒内に形成する吸気流動形成手段を備え、前記案内部は前記気体燃料を前記スワール流の方向に沿って湾曲させるように形成されていることを特徴とする請求項１２に記載の気体燃料添加装置。An intake flow forming means for forming a swirl flow swirling around the center line of the cylinder in the cylinder, wherein the guide portion is formed so as to curve the gaseous fuel along the direction of the swirl flow. The gaseous fuel addition device according to claim 12, wherein 前記主燃料がガソリンであり、前記気体燃料が水素であることを特徴とする請求項１０〜１７のいずれか１項に記載の気体燃料添加装置。18. The gaseous fuel adding device according to claim 10, wherein the main fuel is gasoline, and the gaseous fuel is hydrogen.
JP2002240119A 2002-08-21 2002-08-21 Gas fuel addition method and gas fuel addition device for internal combustion engine Pending JP2004076679A (en)

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