JP5549809B2 - Diesel engine open toroidal combustion chamber - Google Patents

Diesel engine open toroidal combustion chamber Download PDF

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JP5549809B2
JP5549809B2 JP2010139421A JP2010139421A JP5549809B2 JP 5549809 B2 JP5549809 B2 JP 5549809B2 JP 2010139421 A JP2010139421 A JP 2010139421A JP 2010139421 A JP2010139421 A JP 2010139421A JP 5549809 B2 JP5549809 B2 JP 5549809B2
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cavity
combustion chamber
fuel
diesel engine
side wall
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JP2012002167A (en
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徳昭 小野
猛 森屋
英行 ▲高▼橋
康徳 醍醐
純一 山田
健次 佐々木
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Mitsubishi Fuso Truck and Bus Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

本発明は、ピストンの頂面に、上部を外側へ曲成させて拡げたオープン形状のキャビティを形成したディーゼルエンジンのオープントロイダル燃焼室に関する。   The present invention relates to an open toroidal combustion chamber of a diesel engine in which an open-shaped cavity is formed on the top surface of a piston by bending the upper part outward.

トラックなど車両に搭載される直噴形ディーゼルエンジンのピストンの頂面には、噴霧された燃料を燃焼させるため窪み形の燃焼室が形成されている。
この燃焼室には、下部（底部）に噴霧燃料を受ける円弧状の曲面をもつ皿状や同じく円環状のキャビティが用いられる。多くは、キャビティの上部開口端をすぼませた燃焼室、直線状の側壁面を用いて上部開口端をキャビティの底部からストレートに開口させた燃焼室、特許文献１にも開示されているような上部開口の縁部を若干、外側に円弧状に拡げさせたオープントロイダル形の燃焼室が用いられている。 A hollow combustion chamber is formed on the top surface of a piston of a direct injection diesel engine mounted on a vehicle such as a truck for burning sprayed fuel.
In this combustion chamber, a dish-like or circular-shaped cavity having an arcuate curved surface that receives the sprayed fuel at the lower part (bottom part) is used. Many of them are also disclosed in Japanese Patent Application Laid-Open No. 2003-260260, a combustion chamber in which the upper open end of the cavity is recessed, a combustion chamber in which the upper open end is opened straight from the bottom of the cavity using a straight side wall surface. An open toroidal combustion chamber is used in which the edge of the upper opening is slightly expanded outward in a circular arc shape.

ところで、車両のディーゼルエンジンでは、排ガス規制（ＮＯｘ規制など）に対応するために排ガスの一部を燃焼室に還流させるＥＧＲ（Exhaust Gas Recirculation）が行われている。近年では、厳しい排ガス規制の対応のために、大量のＥＧＲを実施することが主流となる。
ところが、上部開口をすぼませた燃焼室、上部開口を底部から直線状に開口させた燃焼室、上部開口の縁部を若干拡げただけのオープントロイダル形の燃焼室は、いずれも燃焼室内の酸素だけで燃焼を行うことを目的として形成された燃焼室であるため、大量のＥＧＲ下での燃焼には適さない。 Incidentally, EGR (Exhaust Gas Recirculation) in which a part of exhaust gas is recirculated to a combustion chamber is performed in a vehicle diesel engine in order to comply with exhaust gas regulations (NOx regulations and the like). In recent years, it has become mainstream to implement a large amount of EGR in order to comply with strict exhaust gas regulations.
However, the combustion chamber with the top opening sunk, the combustion chamber with the top opening opened linearly from the bottom, and the open toroidal combustion chamber with a slightly widened edge of the top opening are all in the combustion chamber. Since it is a combustion chamber formed for the purpose of performing combustion only with oxygen, it is not suitable for combustion under a large amount of EGR.

すなわち、大量のＥＧＲは、燃焼室内の酸素量が少なくなるため、燃焼室内の空気過剰率（以下、λという）が低下するので、主に燃焼室内部の酸素だけで燃焼させることを目的とした燃焼室だと、燃焼に求められる酸素量の不足が生じる。このため、燃焼初期や燃焼中期における燃焼は損なわれ、排煙濃度が増加するなど排ガスが悪化したり、燃費が低下したりする。特にディーゼルエンジンは、λが１．３より低下すると、著しく排煙濃度や燃費が著しく増加する傾向が見られる。   That is, since a large amount of EGR reduces the amount of oxygen in the combustion chamber, the excess air ratio (hereinafter referred to as λ) in the combustion chamber is reduced, so that the purpose is to burn mainly with oxygen in the combustion chamber. In the combustion chamber, the amount of oxygen required for combustion is insufficient. For this reason, the combustion in the early stage of combustion or the middle stage of combustion is impaired, and the exhaust gas is deteriorated, for example, the smoke concentration is increased, or the fuel consumption is lowered. In particular, in the diesel engine, when λ is lower than 1.3, the smoke concentration and the fuel consumption tend to increase remarkably.

そこで、近時では特許文献２〜４に開示されているように燃焼室の開口側を、突起や段部を介在させて、階段状に拡げる構造が提案されている。特許文献２〜４は、燃焼室の開口側を拡げることにより、燃焼室外側のスキッシュエリアに有る酸素を燃焼に積極的に用い、酸素不足を対応するものとしている。   Therefore, recently, as disclosed in Patent Documents 2 to 4, a structure has been proposed in which the opening side of the combustion chamber is expanded in a stepped manner with protrusions and stepped portions interposed. In Patent Documents 2 to 4, oxygen in the squish area outside the combustion chamber is actively used for combustion by expanding the opening side of the combustion chamber to cope with oxygen shortage.

特開平５−３１２１０４号公報JP-A-5-312104 特開２００７−２１１６４４号公報JP 2007-21644 A 特開２００８−１５１０８９号公報JP 2008-151089 A 特開２００９−５３５５６１号公報JP 2009-535561 A

ところが、階段状の燃焼室は、ディーゼルエンジンの運転領域の全体（低回転領域〜高回転領域、低負荷領域〜高負荷領域）には対応できない難点がある。
すなわち、ディーゼルエンジンの燃料噴射時期は、エンジンの回転数や負荷など運転状態に応じて異なる。しかも、排ガス規制の対応のために、メイン噴射より早い時期に、噴射するというパイロット噴射を行うこともある。 However, the staircase-like combustion chamber has a drawback that it cannot cope with the entire operation region of the diesel engine (low rotation region to high rotation region, low load region to high load region).
That is, the fuel injection timing of the diesel engine varies depending on the operating state such as the engine speed and load. Moreover, in order to comply with exhaust gas regulations, pilot injection may be performed in which injection is performed earlier than main injection.

燃料噴射時期が異なると、それに応じてピストンは上死点（圧縮）からの位置、すなわち燃焼室の位置が変化する。しかし、階段状の燃焼室は、突起や段部が有るために、燃料噴射時期が変化すると、燃料が衝突する地点が、段部付近だったり、段部からキャビティ開口側へ離れた地点であったり、段部からキャビティ下部（底部）側へ離れた地点であったりするなど、段部を境にずれる。このため、階段状の燃焼室だと、ディーゼルエンジンの運転状態により突起や段部を境に、多くの燃料が上側へ偏って噴射され、下側へは極少量しか到達しなかったり、逆に多くの燃料が下側へ偏って噴射され、上側へは極少量しか到達しなかったりするなど、上下で極端に偏った燃料噴射が生じやすく、スキッシュエリアを活用しても燃焼が安定しないことがある。つまり、階段状の燃焼室は、スキッシュエリアの酸素を用いて、一部の運転領域については良好な燃焼となるものの、大部分の運転領域に対応できるものではなかった。   If the fuel injection timing is different, the position of the piston from the top dead center (compression), that is, the position of the combustion chamber changes accordingly. However, since the stepped combustion chamber has protrusions and steps, the point of fuel collision when the fuel injection timing changes is near the step or the point away from the step toward the cavity opening. Or a point away from the step to the cavity lower part (bottom) side. For this reason, in the case of a staircase-shaped combustion chamber, a large amount of fuel is injected in an upward direction with a projection or step portion as a boundary depending on the operating state of the diesel engine, and only a very small amount reaches the lower side. Many fuels are injected in a biased manner on the lower side and only a very small amount is reached on the upper side. is there. In other words, the staircase-shaped combustion chamber uses the oxygen in the squish area, and the combustion is good in a part of the operation region, but it cannot cope with the most operation region.

そこで、本発明の目的は、ディーゼルエンジンの運転領域全体における低空気過剰率下で良好な燃焼を実現可能としたディーゼルエンジンのオープントロイダル燃焼室を提供することにある。   Accordingly, an object of the present invention is to provide an open toroidal combustion chamber of a diesel engine capable of realizing good combustion under a low excess air ratio in the entire operation range of the diesel engine.

請求項１に記載の発明は、上記目的を達成するために、オープントロイダル燃焼室をなすピストンの頂面と前記キャビティの側壁面とをつなぐキャビティ上部の円弧状の曲成部は、キャビティの側壁面の一部であるとともに、ピストンの頂面とキャビティの側壁面とを曲線状につなぎ、かつ、キャビティの側壁面とキャビティの底面とつなぐキャビティ下部の円弧状の曲面部より大きい半径寸法で形成したことにある。 In order to achieve the above object, the invention according to claim 1 is characterized in that the arc-shaped bent portion at the upper part of the cavity connecting the top surface of the piston forming the open toroidal combustion chamber and the side wall surface of the cavity is provided on the side of the cavity. It is a part of the wall surface, and it is connected with the top surface of the piston and the side wall surface of the cavity in a curved line, and has a larger radius than the arcuate curved surface at the bottom of the cavity connecting the side wall surface of the cavity and the bottom surface of the cavity It is to have done.

同構成によると、キャビティ上部の曲成部の円弧面の大きさを利用して、燃焼は、キャビティ（燃焼室）内部の酸素だけでなく、キャビティ（燃焼室外）外のスキッシュエリアの酸素も用いて行われ、低空気過剰率（λ）下での酸素不足が改善される。しかも、曲成部は、キャビティ下部（底部）の円弧状の曲面部よりも大きくしただけなので、たとえ燃料噴射時期によりピストン位置が変動しても、噴射燃料は、若干、ずれるだけで、キャビティ開口側、キャビティ下部（底部）側へ大きく偏らずに噴射される。このため、燃料衝突位置のずれに対して寛容となり、ディーゼルエンジンの運転領域の全体で安定した良好な燃焼が得られる。   According to the same configuration, the combustion uses not only the oxygen inside the cavity (combustion chamber) but also oxygen in the squish area outside the cavity (outside of the combustion chamber) by utilizing the size of the arc surface of the curved portion at the top of the cavity. The oxygen deficiency under a low excess air ratio (λ) is improved. Moreover, since the bent portion is only larger than the arcuate curved portion at the bottom (bottom) of the cavity, even if the piston position fluctuates due to the fuel injection timing, the injected fuel is only slightly displaced, and the cavity opening Injected to the side and cavity lower (bottom) side without significant deviation. For this reason, it becomes tolerant to the shift of the fuel collision position, and stable and good combustion can be obtained in the entire operation region of the diesel engine.

請求項２に記載の発明は、側壁面が、曲成部と曲面部、及び、曲成部と曲面部の間の変曲点で構成されるものとした。
請求項３に記載の発明は、噴霧燃料が、燃料噴射ノズルのノズル先端から側壁面に向かって噴射されるものとした。 In the invention described in claim 2, the side wall surface is configured by a bent portion and a curved surface portion, and an inflection point between the bent portion and the curved surface portion .
According to a third aspect of the present invention, the sprayed fuel is injected from the nozzle tip of the fuel injection nozzle toward the side wall surface .

請求項１の発明によれば、燃焼は、キャビティ上部の大きな円弧状の曲成部により、キャビティ（燃焼室）内部の酸素だけでなく、キャビティ（燃焼室外）外のスキッシュエリアの酸素を用いて行われ、低空気過剰率（λ）下での酸素不足が改善できる。しかも、同曲成部は、燃料がキャビティ開口側、キャビティ下部（底部）側へ大きく偏らずに噴射されずにすむから、燃料噴射時期の変化がもたらす燃料衝突位置のずれに対して寛容であり、ディーゼルエンジンの運転領域の全体において良好な燃焼を行わせることができる。
したがって、ディーゼルエンジンの運転領域全体における低空気過剰率下で安定した良好な燃焼が実現できる。 According to the first aspect of the present invention, combustion is performed using not only oxygen inside the cavity (combustion chamber) but also oxygen in the squish area outside the cavity (outside of the combustion chamber) by a large arc-shaped bent portion at the top of the cavity. Oxygen deficiency under a low excess air ratio (λ) can be improved. In addition, the bent portion is tolerant of a fuel collision position shift caused by a change in fuel injection timing because the fuel is not injected without being largely biased toward the cavity opening side and the cavity lower part (bottom) side. Thus, good combustion can be performed in the entire operation region of the diesel engine.
Therefore, stable good combustion can be realized under a low excess air ratio in the entire operation range of the diesel engine.

請求項２の発明によれば、極力、キャビティの上部の曲成部は、大きい半径寸法で形成でき、良好な燃焼の実現に貢献する。
請求項３の発明によれば、最も燃料衝突位置のずれに対する寛容度を高めることができ、良好な燃焼の実現に貢献する。 According to the invention of claim 2, the bent portion at the upper part of the cavity can be formed with a large radial dimension as much as possible, and contributes to the realization of good combustion.
According to the invention of claim 3, the tolerance for the deviation of the fuel collision position can be increased most, and this contributes to the realization of good combustion.

本発明の一実施形態の要部となるオープントロイダル燃焼室を示す一部断面した斜視図。The perspective view which carried out the partial cross section which shows the open toroidal combustion chamber used as the principal part of one Embodiment of this invention. 上死点近くにピストンが位置するときにおける燃料噴射状態を示す断面図。Sectional drawing which shows the fuel-injection state when a piston is located near a top dead center. 上死点からピストンが離れた位置にあるときにおける燃料噴射状態を示す断面図。Sectional drawing which shows a fuel-injection state when a piston exists in the position away from the top dead center. （ａ）は観察窓を通してスキッシュエリア付近を観察したときの燃焼初期の火炎の発生状況を示す図、（ｂ）は同じく燃焼後期の火炎の発生状況を示す図。(A) is a figure which shows the generation | occurrence | production state of the flame of the early stage of combustion when observing the squish area vicinity through an observation window, (b) is a figure which similarly shows the generation | occurrence | production state of the flame of a late combustion stage. キャビティ上部の曲成部の半径とキャビティ底部の曲面部の半径との比に応じた燃費の状況を示す線図。The diagram which shows the condition of the fuel consumption according to ratio of the radius of the bending part of a cavity upper part, and the radius of the curved surface part of a cavity bottom part. 同じくスモークの状況を示す図。The figure which similarly shows the condition of smoke. 燃焼室の形状に違いによるＳＯＯＴ（すす）、ＣＯの改善状況を示す図。The figure which shows the improvement condition of SOOT (soot) and CO by a difference in the shape of a combustion chamber. 同じくトルク、燃費、スモーク、ＨＣの改善状況を示す図。The figure which similarly shows the improvement condition of torque, fuel consumption, smoke, and HC.

以下、本発明を図１ないし図８に示す一実施形態にもとづいて説明する。
図１は、直噴式ディーゼルエンジンのピストン周辺を示す断面図を示し、図２および図３は同ピストンの断面図を示している。図中１は気筒を示す。 Hereinafter, the present invention will be described based on an embodiment shown in FIGS.
FIG. 1 is a sectional view showing the periphery of a piston of a direct injection diesel engine, and FIGS. 2 and 3 are sectional views of the piston. In the figure, 1 indicates a cylinder.

ここで、気筒１は、シリンダヘッド２（図２，３に図示）、シリンダブロック（図示しない）に設けた筒形のシリンダライナ４で囲まれた円筒状の空間で形成される。気筒１の頭部の中央には燃料を噴射する燃料噴射ノズル５が設けられる。その両側には吸気を導入する吸気弁、燃焼を終えたガスを導出させる排気弁（いずれも図示しない）が設けられる。この気筒１内にピストン７が往復動可能に収められている。   Here, the cylinder 1 is formed in a cylindrical space surrounded by a cylindrical cylinder liner 4 provided in a cylinder head 2 (shown in FIGS. 2 and 3) and a cylinder block (not shown). A fuel injection nozzle 5 for injecting fuel is provided at the center of the head of the cylinder 1. On both sides thereof, there are provided an intake valve for introducing intake air and an exhaust valve (both not shown) for deriving the burned gas. A piston 7 is accommodated in the cylinder 1 so as to be able to reciprocate.

このピストン７の頂面中央には、上部を外側に拡げたオープントロイダル燃焼室８（以下、単に燃焼室８という）が設けられている。すなわち、燃焼室８は、図１〜図３に示されるように円環状（または皿状）のキャビティ１１を有している。このキャビティ１１のうち底面１２と側壁面１３とをつなぐ下側のコーナー部は、半径寸法Ｒ２でなす円弧形の曲面部１５で形成される。この曲面部１５は、燃料噴射ノズル５から噴霧した燃料を受ける機能をもつ。この曲面部１５が、底面中央から円錐状に突き出た突起部１６と連ねてある。ピストン７の頂面７ａと側壁面１３とをつなぐキャビティ１１の開口縁部は、半径寸法Ｒ１でなす円弧形の曲成面１８で形成されている。このキャビティ１１の開口側の曲成面１８は、キャビティ１１の底面（下部）側の曲面部１５よりも大きい円弧形としている。つまり、開口（上部）側に形成される曲成面１８の半径寸法Ｒ１は、底面（底部）側に形成される曲面部１５の半径寸法Ｒ２より大きくしてある（Ｒ１＞Ｒ２、Ｒ１／Ｒ２が１．０より大）。この大きな曲成面１８から、上部が外側に大きく拡がるオープントロイダル形の燃焼室８を形成している。この燃焼室８により、燃焼室８の開口周囲のスキッシュエリア１９に存する酸素（空気）を積極的に活用した燃焼が行えるようにしている。   In the center of the top surface of the piston 7, an open toroidal combustion chamber 8 (hereinafter simply referred to as the combustion chamber 8) having an upper portion extended outward is provided. That is, the combustion chamber 8 has an annular (or dish-shaped) cavity 11 as shown in FIGS. A lower corner portion connecting the bottom surface 12 and the side wall surface 13 of the cavity 11 is formed by an arcuate curved surface portion 15 having a radius R2. The curved surface portion 15 has a function of receiving fuel sprayed from the fuel injection nozzle 5. The curved surface portion 15 is connected to a projection portion 16 protruding in a conical shape from the center of the bottom surface. The opening edge of the cavity 11 connecting the top surface 7a of the piston 7 and the side wall surface 13 is formed by an arcuate curved surface 18 having a radial dimension R1. The curved surface 18 on the opening side of the cavity 11 has a larger arc shape than the curved surface portion 15 on the bottom (lower) side of the cavity 11. That is, the radius R1 of the curved surface 18 formed on the opening (top) side is larger than the radius R2 of the curved surface portion 15 formed on the bottom (bottom) side (R1> R2, R1 / R2). Is greater than 1.0). The large curved surface 18 forms an open toroidal combustion chamber 8 whose upper portion extends greatly outward. The combustion chamber 8 enables combustion that actively utilizes oxygen (air) existing in the squish area 19 around the opening of the combustion chamber 8.

特に燃焼に、燃焼室８外のスキッシュエリア１９の酸素ができる限り多く活用されるよう、曲成部１８は、直線部を介在させずに、円弧の向きが異なるキャビティ底部（下部）の曲面部１５と、曲面同士を接線連続させて連ねてあり、極力、大きい半径寸法Ｒ１とし、できる限り外側に大きく拡がる円弧形としている。   In particular, the curved portion 18 has a curved bottom portion (lower portion) in which the direction of the arc is different without interposing a straight portion so that oxygen in the squish area 19 outside the combustion chamber 8 is utilized as much as possible for combustion. 15 and the curved surfaces are connected in a tangential manner, and have a large radius R1 as much as possible, and have an arc shape that expands as much as possible.

またキャビティ上部の曲成部１８とキャビティ底部（下部）の曲面部１５の間、具体的には異なる円弧の向きで連続する曲成部１８と曲面部１５間の曲がりが変わる変曲点Ｐ付近が、図１に示されるように燃料噴射ノズル５から噴射される噴霧燃料の中心Ｓと衝突する衝突点Ｎ（噴霧の中心衝突点）にしてある。
特に噴霧燃料の中心衝突点Ｎは、キャビティ底部（下部）の曲面部１５内で、良好に燃料の旋回流が生成されるよう、キャビティ１１の底面中央から突き出た突起部１６とほぼ同じ高さ位置に設定してある。 Further, in the vicinity of the inflection point P where the bending between the curved portion 18 at the upper part of the cavity and the curved portion 15 at the bottom (lower) portion of the cavity, specifically, the curved portion 18 and the curved portion 15 that continue in different arc directions changes. However, as shown in FIG. 1, a collision point N (a center collision point of the spray) that collides with the center S of the sprayed fuel injected from the fuel injection nozzle 5 is used.
In particular, the center collision point N of the sprayed fuel is almost the same height as the protrusion 16 protruding from the center of the bottom surface of the cavity 11 so that the swirling flow of fuel is generated well in the curved surface portion 15 at the bottom (lower part) of the cavity. Set to position.

こうしたオープントロイダル形の燃焼室８の特徴は、多量のＥＧＲによって低λ（空気過剰率）となるディーゼルエンジンの運転のときに発揮する。
すなわち、ディーゼルエンジンの運転に伴い燃料噴射ノズル５からは、圧縮上死点に近づくピストン７の燃焼室８内へ向け燃料が噴射される。具体的には燃料は、ノズル先端から燃焼室８の側壁面１３に向かって噴射される。 Such characteristics of the open toroidal combustion chamber 8 are exhibited during operation of a diesel engine having a low λ (excess air ratio) due to a large amount of EGR.
That is, with the operation of the diesel engine, fuel is injected from the fuel injection nozzle 5 into the combustion chamber 8 of the piston 7 that approaches the compression top dead center. Specifically, the fuel is injected from the nozzle tip toward the side wall surface 13 of the combustion chamber 8.

このとき、キャビティ１１の開口縁部は、燃料を受ける曲面部１５よりも半径寸法の大きい円弧を描く曲成部１８で形成され、当該縁部をキャビティ１１の開口周囲に存するスキッシュエリア１９に大きく開口させているから、図１中の矢印αに示されるように開口側へ向かう燃料は曲成部１８の円弧面にならってスキッシュエリア１９へ導かれる。すると、スキッシュエリア１９に至る噴霧燃料は、スキッシュエリア１９からの酸素（空気）の供給を受けながら燃焼する（自己着火による）。またキャビティ１１の底部に至る燃料は、キャビティ１１内の酸素の供給を受けて燃焼する（自己着火による）。   At this time, the opening edge portion of the cavity 11 is formed by a bent portion 18 that draws an arc having a larger radius than the curved surface portion 15 that receives the fuel, and the edge portion is larger in the squish area 19 around the opening of the cavity 11. Since the opening is made, the fuel traveling toward the opening side is guided to the squish area 19 along the arc surface of the bent portion 18 as indicated by an arrow α in FIG. Then, the sprayed fuel that reaches the squish area 19 burns while being supplied with oxygen (air) from the squish area 19 (by self-ignition). Further, the fuel reaching the bottom of the cavity 11 is burned by the supply of oxygen in the cavity 11 (by self-ignition).

これにより、多量のＥＧＲにより燃焼室８内が低λとなっても、燃焼室８外のスキッシュエリア１９の活用により酸素不足が解消されるために、燃料は燃焼初期から活発に燃焼する。燃焼の実験を行い、観察窓を通してスキッシュエリア１９付近を観察した結果、図４（ａ）に示されるように燃焼初期となるＡＴＤＣ５°や、図４（ｂ）に示されるように燃焼中期となるＡＴＤＣ１２°において、スキッシュエリア１９の酸素を活用して燃料が良好に燃焼していることが確認された。   Thereby, even if the inside of the combustion chamber 8 becomes low λ due to a large amount of EGR, the lack of oxygen is eliminated by utilizing the squish area 19 outside the combustion chamber 8, so that the fuel burns actively from the beginning of combustion. As a result of conducting an experiment of combustion and observing the vicinity of the squish area 19 through the observation window, ATDC 5 °, which is the initial stage of combustion as shown in FIG. 4 (a), and middle stage of combustion as shown in FIG. 4 (b). At ATDC 12 °, it was confirmed that the fuel burned well by utilizing oxygen in the squish area 19.

しかも、曲成部１８は、キャビティ底部の曲面部１５よりも円弧を大きくしただけなので（Ｒ１＞Ｒ２、Ｒ１／Ｒ２が１．０より大）、ディーゼルエンジンの運転状態に応じた燃料噴射時期により、ピストン位置が変動（圧縮上死点からの変化）しても、スキッシュエリア１９の酸素を活用した燃焼は行える。   In addition, the bent portion 18 has a larger arc than the curved surface portion 15 at the bottom of the cavity (R1> R2, R1 / R2 is greater than 1.0), so that it depends on the fuel injection timing according to the operating state of the diesel engine. Even if the piston position fluctuates (change from the compression top dead center), combustion using oxygen in the squish area 19 can be performed.

すなわち、例えば図２に示されるように燃料噴射時期が遅く、ピストン７が圧縮上死点に接近した位置から燃料噴射が行われた場合、若干、噴射する領域がキャビティ１１の底部（下部）側にずれるだけで、噴射した燃料の上側の領域は、曲成部１８の円弧面と衝突して、同曲成部１８の円弧面（曲面）を経てスキッシュエリア１９に向かうから、スキッシュエリア１９の酸素を用いた燃焼が行われる。また例えば図３に示されるように燃料噴射時期が早く、ピストン７が圧縮上死点から遠い位置にあるとき燃料噴射が行われた場合、若干、噴射する領域がキャビティ１１の開口（上部）側にずれるだけで、噴射した燃料の上側の領域は、同様に曲成部１８の円弧面と衝突して、同曲成部１８の円弧面（曲面）を経てスキッシュエリア１９に向かい、同様にスキッシュエリア１９の酸素を用いて燃焼されるだけで、噴射位置のずれに関わらず、スキッシュアリア１９側やキャビティ１１側でも、安定した良好な燃焼が継続される。   That is, for example, as shown in FIG. 2, when the fuel injection timing is late and the fuel injection is performed from the position where the piston 7 approaches the compression top dead center, the injection region is slightly on the bottom (lower) side of the cavity 11. The upper region of the injected fuel just collides with the arc surface of the bent portion 18 and travels to the squish area 19 through the arc surface (curved surface) of the bent portion 18. Combustion using oxygen is performed. For example, as shown in FIG. 3, when fuel injection is performed when the fuel injection timing is early and the piston 7 is far from the compression top dead center, the injection region is slightly on the opening (upper) side of the cavity 11. Just by shifting, the upper region of the injected fuel similarly collides with the arc surface of the bent portion 18, passes through the arc surface (curved surface) of the bent portion 18, and goes to the squish area 19. Only by using the oxygen in the area 19, stable and good combustion is continued on the squish area 19 side and the cavity 11 side regardless of the deviation of the injection position.

つまり、たとえ燃料噴射時期のよりピストン位置が変わることがあっても、燃料の噴射領域が、若干、キャビティ１１の開口側や底部側にずれるだけで、キャビティ１１の開口側、キャビティ１１の底部側へ大きく偏らずに噴射されるから、燃料衝突位置のずれに対する燃料の偏りは寛容である。そのため、ディーゼルエンジンの運転領域の全体で、スキッシュエリア１０を積極的に活用した安定した良好な燃焼を得ることができる。   That is, even if the piston position changes depending on the fuel injection timing, the fuel injection region is slightly shifted to the opening side or the bottom side of the cavity 11, so that the opening side of the cavity 11 and the bottom side of the cavity 11 are Since the fuel is injected without a large deviation, the deviation of the fuel with respect to the deviation of the fuel collision position is tolerant. Therefore, it is possible to obtain stable and good combustion that actively uses the squish area 10 in the entire operation range of the diesel engine.

こうした利点は、キャビティ上部の曲成部１８を、直線部を介在させずに曲面同士の接線連続で、キャビティ１１の曲面部１５と連ねて、曲成部１８を、極力、大きい半径寸法をもつ円弧形としたり、曲成部１８と曲面部１５との間の変曲点Ｐ近傍を、噴霧燃料の中心Ｓが衝突する衝突点Ｎとしたりすることにより、顕著に表れる。   Such an advantage is that the curved portion 18 at the upper part of the cavity is connected to the curved surface portion 15 of the cavity 11 in a continuous tangent line between the curved surfaces without interposing a straight portion, so that the curved portion 18 has a large radial dimension as much as possible. It becomes prominent by making it an arc shape, or by setting the vicinity of the inflection point P between the bent portion 18 and the curved surface portion 15 as the collision point N where the center S of the sprayed fuel collides.

小型ディーゼルエンジンや大型ディーゼルエンジンなど、キャビティ１１の深さ寸法が異なるオープントロイダル燃焼室８を用いて、実験により同エンジンの燃費やスモークの発生を調べた結果、いずれのエンジンにおいても図５および図６に示されるようにＲ１／Ｒ２の比が「１．０」を超える付近（Ｒ１＞Ｒ２）から、スモークの減少と燃費の向上との双方が改善することが見られた。   As a result of investigating the fuel consumption and smoke generation of the engine using an open toroidal combustion chamber 8 having different cavities 11 such as a small diesel engine and a large diesel engine, FIG. 5 and FIG. As shown in FIG. 6, from the vicinity where the ratio of R1 / R2 exceeds “1.0” (R1> R2), it was observed that both the reduction of smoke and the improvement of fuel consumption were improved.

また燃焼室形状の違いからもオープントロイダル燃焼室８が、図７（ａ），（ｂ）に示されるように大量のＥＧＲにより著しく排煙濃度が増加するとされる低λのとき、特にλが１．３より低くなる領域においてＳＯＯＴ（すす）、ＣＯ、トルク、燃費、スモーク、ＨＣのいずれに対して、他の形状の燃焼室よりも優れていることが確認された。   Also, due to the difference in the shape of the combustion chamber, when the open toroidal combustion chamber 8 is low λ, where the flue gas concentration is remarkably increased by a large amount of EGR as shown in FIGS. In the region lower than 1.3, it was confirmed that it was superior to other shapes of combustion chambers for any of SOOT, CO, torque, fuel consumption, smoke, and HC.

すなわち、図７（ａ）〜（ｄ）、図８（ａ）〜（ｄ）は、開口をすぼめた円環状の燃焼室（ひし形で表記）、ストレートに開口する円環状の燃焼室（四角形で表記）、上述の開口が曲成により外側に大きく開口するオープントロイダル燃焼室８（三角で表記）を用いてディーゼルエンジンを運転したときの、ＳＯＯＴ（すす）、ＣＯ、トルク、燃費、スモーク、ＨＣの挙動を線図化したものである。これら線図からは、特にλが１．３より低くなる運転領域の大部分で、三角で表記したオープントロイダル燃焼室が、他の形状の燃焼室を用いたときよりも、著しくＳＯＯＴやＣＯやスモークやＨＣなど排ガスの点で改善が見られ、その分、トルクや燃費が向上したことが見られ、オープントロイダル燃焼室８が他の形状の燃焼室よりも優れていることが確認された。   7 (a) to 7 (d) and 8 (a) to 8 (d), an annular combustion chamber (represented by rhombus) with a narrowed opening, and an annular combustion chamber (rectangular shape) that opens straight. Notation), SOOT (soot), CO, torque, fuel consumption, smoke, HC when the diesel engine is operated using the open toroidal combustion chamber 8 (indicated by a triangle) whose opening is greatly opened outward by bending. Is a diagram of the behavior of. From these graphs, the open toroidal combustion chamber indicated by a triangle is significantly more soot, CO, and so on than in the case of using a combustion chamber of another shape, particularly in most of the operation region where λ is lower than 1.3. Improvements were seen in terms of exhaust gas such as smoke and HC, and it was found that torque and fuel consumption were improved accordingly, and it was confirmed that the open toroidal combustion chamber 8 was superior to combustion chambers of other shapes.

なお、本発明は上述した一実施形態に限定されるものではなく、本発明の主旨を逸脱しない範囲内で種々可変して実施しても構わない。例えば一実施形態では円環状のキャビティを用いた例を挙げたが、皿状のキャビティを用いた燃焼室でもよく、一実施形態と同様の効果を奏する。   Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the spirit of the present invention. For example, in one embodiment, an example using an annular cavity has been described. However, a combustion chamber using a dish-like cavity may be used, and the same effect as that of the embodiment is achieved.

７ ピストン
８ オープントロイダル燃焼室
１１ キャビティ
１５ 曲面部
１８ 曲成部 7 Piston 8 Open toroidal combustion chamber 11 Cavity 15 Curved section 18 Curved section

Claims (3)

ピストンに、上部を外側に円弧状に曲成させて拡げ、下部に噴霧燃料を受ける円弧状の曲面を有するオープン形状のキャビティを形成したディーゼルエンジンのオープントロイダル燃焼室であって、
前記ピストンの頂面と前記キャビティの側壁面とをつなぐ前記キャビティ上部の円弧状の曲成部は、前記キャビティの側壁面の一部であるとともに、前記ピストンの頂面と前記キャビティの側壁面とを曲線状につなぎ、かつ、前記キャビティの側壁面と前記キャビティの底面とつなぐ前記キャビティ下部の円弧状の曲面部より大きい半径寸法で形成される
ことを特徴とするディーゼルエンジンのオープントロイダル燃焼室。 The piston, spread by bent arcuately top outwardly, and an open toroidal combustion chamber of a diesel engine to form a cavity of an open shape having an arcuate curved surface to receive the fuel spray at the bottom,
An arcuate bend at the top of the cavity connecting the top surface of the piston and the side wall surface of the cavity is a part of the side wall surface of the cavity, and the top surface of the piston and the side wall surface of the cavity the connecting curved and open toroidal combustion chamber of a diesel engine, characterized in that it is formed by the greater radius than the arc-shaped curved surface portion of the cavity bottom connecting the side wall surface of the cavity and the bottom surface of the cavity. 前記側壁面は、前記曲成部と前記曲面部、及び、前記曲成部と前記曲面部の間の変曲点で構成されることを特徴とする請求項１に記載のディーゼルエンジンのオープントロイダル燃焼室。 2. The diesel engine open toroidal according to claim 1, wherein the side wall surface includes the bent portion and the curved portion, and an inflection point between the bent portion and the curved portion. Combustion chamber. 前記噴霧燃料は、燃料噴射ノズルのノズル先端から前記側壁面に向かって噴射されることを特徴とする請求項１または請求項２に記載のディーゼルエンジンのオープントロイダル燃焼室。 3. The open toroidal combustion chamber of a diesel engine according to claim 1 , wherein the sprayed fuel is injected from a nozzle tip of a fuel injection nozzle toward the side wall surface . 4.
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