JP2015108298A - Spark ignition type engine and operation control method of the same - Google Patents

Spark ignition type engine and operation control method of the same Download PDF

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JP2015108298A
JP2015108298A JP2013250221A JP2013250221A JP2015108298A JP 2015108298 A JP2015108298 A JP 2015108298A JP 2013250221 A JP2013250221 A JP 2013250221A JP 2013250221 A JP2013250221 A JP 2013250221A JP 2015108298 A JP2015108298 A JP 2015108298A
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specific hydrocarbon
egr rate
hydrocarbon content
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egr
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大樹 田中
Daiki Tanaka
大樹 田中
俊介 染澤
Shunsuke Somezawa
俊介 染澤
孝弘 佐古
Takahiro Sako
孝弘 佐古
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Osaka Gas Co Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of suppressing deterioration of a combustion state in association with variations of an EGR ratio when EGR ratio control using EGR ratio adjustment means is performed in a spark ignition type engine adopted with an EGR.SOLUTION: In addition to EGR ratio control for activating EGR ratio adjustment means 40 and controlling an EGR ratio on the basis of driving conditions, specific hydrocarbon content control for activating specific hydrocarbon content adjustment means 60 and varying a specific hydrocarbon content in response to a state of the EGR ratio adjustment means 40 in a form that the specific hydrocarbon content being a content of specific hydrocarbon consisting of at least one of ethane and propane in an air-fuel mixture is increased as the EGR ratio is increased is executed.

Description

本発明は、燃焼室に吸気される新気に炭化水素系の主燃料を混合して混合気を形成し、当該混合気を燃焼室で圧縮して点火プラグにより火花点火し燃焼させる火花点火式エンジン及びその運転制御方法に関する。   The present invention relates to a spark ignition type in which a hydrocarbon-based main fuel is mixed with fresh air sucked into a combustion chamber to form an air-fuel mixture, and the air-fuel mixture is compressed in the combustion chamber and sparked by a spark plug and burned. The present invention relates to an engine and an operation control method thereof.

火花点火式エンジンの燃焼室では、ピストンの上昇により圧縮された混合気中で燃焼室の略中央に配置された点火プラグにより火花放電が行われることで火炎核が形成され、その火炎核を源とした火炎帯が混合気中を伝播し燃焼が進行する。このような火花点火による火炎伝播型の燃焼形態においては、火炎帯が比較的低温のシリンダ壁面に近づく火炎伝播後期において、当該シリンダ壁面の冷却作用により火炎帯が消炎することがある。更に、膨張行程では、体積増加に伴い燃焼室内の内部エネルギーが低下するために火炎帯の伝播が抑制される傾向にある。そのために、上記火炎伝播後期における火炎帯の消炎が助長される場合がある。そして、このような火炎伝播後期における火炎帯の消炎は、燃焼状態を不安定にしてエンジンのサイクル変動の悪化につながる。一方で、火炎伝播後期において、火炎帯の伝播方向前方の末端にある未燃混合気が急速に圧縮されて、火炎帯が到達する前に自己着火することによりノッキングが発生することがある。このようなノッキングが発生した際に生じる圧力波は構成部品の損傷の要因となる。   In the combustion chamber of a spark ignition type engine, a spark core is formed by spark discharge performed by an ignition plug disposed in the center of the combustion chamber in an air-fuel mixture compressed by the rise of the piston. The flame zone is propagated through the mixture and combustion proceeds. In such a flame propagation type combustion mode by spark ignition, the flame zone may extinguish due to the cooling action of the cylinder wall surface in the later stage of flame propagation when the flame zone approaches a relatively low temperature cylinder wall surface. Furthermore, in the expansion stroke, the propagation of the flame zone tends to be suppressed because the internal energy in the combustion chamber decreases as the volume increases. Therefore, extinction of the flame zone in the later stage of the flame propagation may be promoted. And extinction of the flame zone in the latter half of the flame propagation makes the combustion state unstable and leads to deterioration of engine cycle fluctuation. On the other hand, in the latter half of the flame propagation, the unburned air-fuel mixture at the front end in the propagation direction of the flame zone is rapidly compressed, and knocking may occur due to self-ignition before reaching the flame zone. Pressure waves generated when such knocking occurs cause damage to the components.

一方で、火花点火式エンジンにおいて、ＮＯｘ低減及び熱効率向上の目的で、燃焼室に排ガスを再循環させるＥＧＲを採用する場合がある（例えば、特許文献１及び２を参照。）。ＥＧＲを行えば、混合気の比熱が上昇するので、燃焼温度の上昇が抑制され、ＮＯｘの排出量が低減する。また、燃焼温度が低下すれば、シリンダ壁からの伝熱による熱損失が低減されるので、熱効率が向上する。また、このようなＥＧＲにおいて、エンジン負荷などの運転条件に基づいて燃焼室への排ガスの再循環率であるＥＧＲ率を制御する場合がある。   On the other hand, in a spark ignition engine, EGR that recirculates exhaust gas in a combustion chamber may be employed for the purpose of reducing NOx and improving thermal efficiency (see, for example, Patent Documents 1 and 2). If EGR is performed, the specific heat of the air-fuel mixture increases, so that the increase in combustion temperature is suppressed and the amount of NOx emission is reduced. Further, if the combustion temperature is lowered, heat loss due to heat transfer from the cylinder wall is reduced, so that thermal efficiency is improved. In such an EGR, there is a case where an EGR rate that is a recirculation rate of exhaust gas to the combustion chamber is controlled based on an operating condition such as an engine load.

特開２００９−２９９６６４号公報JP 2009-299664 A 特開平１０−３１８００５号公報Japanese Patent Laid-Open No. 10-31805

ＥＧＲを採用した火花点火式エンジンにおいて、ＥＧＲ率を制御するにあたり、ＥＧＲ率が増大しすぎると、大量の排ガスが新気に混入することで混合気中の酸素濃度が低下し、燃焼速度が低下する。燃焼速度の低下は、火炎伝播を不安定にし、エンジンのサイクル変動の悪化や失火につながる。特に、混合気に再循環される排ガスの分散状態によっては、燃焼室における混合気中の酸素濃度が空間的に不均一になり、結果、混合気の燃焼速度が空間的に不均一になって、燃焼室における燃焼状態が悪化する。そこで、従来技術では、ＥＧＲを行うにあたり、スワール、タンブル、スキッシュといった燃焼室の新気の流動に着目し、新気の流動を強化することで、燃焼速度の低下を抑制することが提案されているが、流動強化により点火プラグの冷却や火花放電の不安定化等の問題があり、その効果は限定的である。
本発明は、かかる点に着目してなされたものであり、その目的は、ＥＧＲを採用した火花点火式エンジンにおいて、ＥＧＲ率調整手段を用いたＥＧＲ率制御を行うにあたり、合理的な構成で、ＥＧＲ率の増加に伴う燃焼状態の悪化を抑制することができる技術を提供する点にある。 In a spark ignition engine that uses EGR, if the EGR rate increases too much when controlling the EGR rate, a large amount of exhaust gas is mixed with fresh air, resulting in a decrease in the oxygen concentration in the mixture and a reduction in the combustion speed To do. A decrease in the combustion speed makes flame propagation unstable, leading to deterioration of engine cycle fluctuations and misfire. In particular, depending on the dispersion state of the exhaust gas recirculated to the air-fuel mixture, the oxygen concentration in the air-fuel mixture in the combustion chamber becomes spatially non-uniform, and as a result, the combustion speed of the air-fuel mixture becomes spatially non-uniform. The combustion state in the combustion chamber is worsened. Therefore, in the prior art, when performing EGR, it has been proposed to focus on the flow of fresh air in the combustion chamber such as swirl, tumble, and squish, and to suppress the decrease in combustion speed by strengthening the flow of fresh air. However, there are problems such as cooling of the spark plug and instability of the spark discharge due to the flow enhancement, and the effect is limited.
The present invention has been made paying attention to such a point, and the purpose thereof is a rational configuration in performing EGR rate control using the EGR rate adjusting means in a spark ignition engine employing EGR. It exists in the point which provides the technique which can suppress the deterioration of the combustion state accompanying the increase in an EGR rate.

この目的を達成するための本発明に係る火花点火式エンジンは、
燃焼室に吸気される新気に炭化水素系の主燃料を混合して混合気を形成し、当該混合気を燃焼室で圧縮して点火プラグにより火花点火し燃焼させる火花点火式エンジンであって、
その特徴構成は、
燃焼室への排ガスの再循環率であるＥＧＲ率を調整可能なＥＧＲ率調整手段と、
エタン及びプロパンの少なくとも一方からなる特定炭化水素の混合気中の含有率である特定炭化水素含有率を調整可能な特定炭化水素含有率調整手段と、
運転条件に基づいて前記ＥＧＲ率調整手段を作動させてＥＧＲ率を制御するＥＧＲ率制御を実行する運転制御手段と、を備え
前記運転制御手段が、前記ＥＧＲ率制御に加えて、前記ＥＧＲ率の増加に伴って前記特定炭化水素含有率を増加させる形態で、前記ＥＧＲ率調整手段の状態に応じて前記特定炭化水素含有率調整手段を作動させて前記特定炭化水素含有率を変動させる特定炭化水素含有率制御を実行する点にある。 To achieve this object, a spark ignition engine according to the present invention includes:
A spark ignition engine in which a hydrocarbon-based main fuel is mixed with fresh air sucked into a combustion chamber to form an air-fuel mixture, and the air-fuel mixture is compressed in the combustion chamber and sparked by a spark plug to burn. ,
Its feature configuration is
An EGR rate adjusting means capable of adjusting an EGR rate that is a recirculation rate of exhaust gas to the combustion chamber;
A specific hydrocarbon content rate adjusting means capable of adjusting a specific hydrocarbon content rate, which is a content rate of a specific hydrocarbon content of at least one of ethane and propane,
Operating control means for executing EGR rate control for controlling the EGR rate by operating the EGR rate adjusting means based on operating conditions, in addition to the EGR rate control, the operation control unit is configured to control the EGR rate. A specific hydrocarbon that varies the specific hydrocarbon content by operating the specific hydrocarbon content adjusting means according to the state of the EGR rate adjusting means in a form that increases the specific hydrocarbon content with an increase. The content control is performed.

炭化水素系燃料の温度と着火遅れ時間は、通常、温度が低くなるほど着火遅れ時間が長くなるという相関関係を有するが、本発明者らは、炭化水素系燃料のうち、エタン及びプロパンの少なくとも一方からなる特定炭化水素、より好ましくはエタンが、メタンやブタンなどの他の炭化水素と比較して、その温度と着火遅れ時間との相関関係において酸素濃度の変動の影響をほとんど受けないという特性を発見し、その特性を利用して本発明を完成するに至った。
即ち、本特徴構成によれば、ＥＧＲ率制御を実行して、エンジン負荷などの運転条件に基づいてＥＧＲ率を制御するにあたり、ＥＧＲ率の増加により燃焼状態が悪化する傾向にあったとしても、ＥＧＲ率の増加に伴う混合気中の酸素濃度の不均一化の影響をほとんど受けない特定炭化水素の混合気中の含有率である特定炭化水素含有率、より好ましくはエタンの混合気中の含有率であるエタン含有率を、ＥＧＲ率の増加に応じて増加させることで、ＥＧＲ率の増加に伴う燃焼状態の悪化を抑制することができる。
具体的には、ＥＧＲ率の増加に伴って特定炭化水素含有率を増加させる形態で、ＥＧＲ率調整手段の状態に応じて特定炭化水素含有率調整手段を作動させて特定炭化水素含有率を変動させる。すると、ＥＧＲ率を増加させた場合には、混合気中の特定炭化水素含有率が増加することから、混合気の燃焼速度の不均一化が抑制され、結果、燃焼状態の悪化を抑制することができる。
一方、ＥＧＲ率が減少又はＥＧＲの実行が停止された場合には、特定炭化水素含有率が減少することから、混合気中の特定炭化水素含有率を増加するためのコストを節約することができる。
従って、本発明により、ＥＧＲを採用した火花点火式エンジンにおいて、ＥＧＲ率調整手段を用いたＥＧＲ率制御を行うにあたり、合理的な構成で、ＥＧＲ率の増加に伴う燃焼状態の悪化を抑制することができる技術を提供することができる。 The temperature of the hydrocarbon fuel and the ignition delay time usually have a correlation that the lower the temperature, the longer the ignition delay time.In the hydrocarbon fuel, the present inventors have at least one of ethane and propane. Compared to other hydrocarbons such as methane and butane, the specific hydrocarbon consisting of is characterized in that it is hardly affected by fluctuations in oxygen concentration in the correlation between its temperature and ignition delay time. It discovered and came to complete this invention using the characteristic.
That is, according to this characteristic configuration, when the EGR rate control is executed and the EGR rate is controlled based on the operating conditions such as the engine load, even if the combustion state tends to deteriorate due to the increase in the EGR rate, Specific hydrocarbon content, which is the content of the specific hydrocarbon in the gas mixture that is hardly affected by the heterogeneity of the oxygen concentration in the gas mixture with the increase in the EGR rate, more preferably ethane content in the gas mixture By increasing the ethane content rate, which is the rate, according to the increase in the EGR rate, it is possible to suppress the deterioration of the combustion state accompanying the increase in the EGR rate.
Specifically, the specific hydrocarbon content rate is increased by increasing the EGR rate, and the specific hydrocarbon content rate is changed by operating the specific hydrocarbon content rate adjusting unit according to the state of the EGR rate adjusting unit. Let Then, when the EGR rate is increased, the specific hydrocarbon content in the mixture increases, so that the non-uniform combustion rate of the mixture is suppressed, and as a result, the deterioration of the combustion state is suppressed. Can do.
On the other hand, when the EGR rate is reduced or the execution of EGR is stopped, the specific hydrocarbon content rate is reduced, so that the cost for increasing the specific hydrocarbon content rate in the air-fuel mixture can be saved. .
Therefore, according to the present invention, in the spark ignition engine employing EGR, when performing EGR rate control using the EGR rate adjusting means, the deterioration of the combustion state accompanying the increase in the EGR rate is suppressed with a rational configuration. It is possible to provide technology that can

本発明に係る火花点火式エンジンの更なる特徴構成は、
サイクル変動の悪化を検出するサイクル変動検出手段を備え、
前記運転制御手段が、前記特定炭化水素含有率制御において、前記サイクル変動検出手段で検出されるサイクル変動の悪化が抑制されるように前記特定炭化水素含有率調整手段を作動させて前記特定炭化水素含有率を変動させる形態で、前記特定炭化水素含有率を変動させる点にある。 Further features of the spark ignition engine according to the present invention are as follows:
A cycle fluctuation detecting means for detecting deterioration of cycle fluctuation is provided,
In the specific hydrocarbon content rate control, the operation control unit operates the specific hydrocarbon content rate adjusting unit so that deterioration of cycle fluctuation detected by the cycle fluctuation detection unit is suppressed. The specific hydrocarbon content is varied in a form in which the content is varied.

本特徴構成によれば、特定炭化水素含有率制御において、ＥＧＲ率を直接把握して特定炭化水素含有率を変動させるのではなく、サイクル変動検出手段で検出されるサイクル変動の悪化を抑制する形態で特定炭化水素含有率を変動させることでも、ＥＧＲ率の増加に伴う燃焼状態の悪化を抑制することができる。
即ち、サイクル変動検出手段でサイクル変動の悪化を検出すれば、ＥＧＲ率が増加したと判断して、特定炭化水素含有率制御により混合気中の特定炭化水素含有率を増加させることで、燃焼状態の悪化を抑制することができる。 According to this feature configuration, in the specific hydrocarbon content control, the EGR rate is not directly grasped and the specific hydrocarbon content is changed, but the deterioration of the cycle fluctuation detected by the cycle fluctuation detecting means is suppressed. Also, the deterioration of the combustion state accompanying the increase in the EGR rate can be suppressed by changing the specific hydrocarbon content.
That is, if deterioration of cycle fluctuation is detected by the cycle fluctuation detection means, it is determined that the EGR rate has increased, and the specific hydrocarbon content rate in the mixture is increased by controlling the specific hydrocarbon content rate, so that the combustion state Can be prevented.

本発明に係る火花点火式エンジンの更なる特徴構成は、
前記運転制御手段が、前記ＥＧＲ率制御において、エンジン負荷に基づいて前記ＥＧＲ率を変動させる点にある。 Further features of the spark ignition engine according to the present invention are as follows:
In the EGR rate control, the operation control means varies the EGR rate based on an engine load.

本特徴構成によれば、ＥＧＲ率制御では、エンジン負荷に基づいてＥＧＲ率を変動させて、ＮＯｘ低減及び熱効率向上を図ることができる。
具体的には、要求トルクの増加等に伴って運転条件としてエンジン負荷を増加させる場合には、ＥＧＲ率を増加させることでエンジン負荷の増加による燃焼温度の過剰な上昇を抑制して、ＮＯｘの生成を抑制することができる。逆に、要求トルクの減少等に伴ってエンジン負荷を減少させる場合には、ＥＧＲ率を減少させることでエンジン負荷の減少による燃焼温度の過剰な低下を抑制して、熱効率の低下を抑制することができる。
また、エンジン負荷を減少させる場合に、ＥＧＲ率を増加させることで、吸入混合気量を増加させ、それに伴ってスロットルバルブの開度を拡大させて、ポンプ損失の低減を図ることもできる。 According to this characteristic configuration, in the EGR rate control, the EGR rate can be varied based on the engine load to reduce NOx and improve the thermal efficiency.
Specifically, when the engine load is increased as an operating condition with an increase in the required torque, etc., an excessive increase in the combustion temperature due to the increase in the engine load is suppressed by increasing the EGR rate, and NOx is reduced. Generation can be suppressed. Conversely, when the engine load is reduced due to a decrease in the required torque, etc., the EGR rate is reduced to suppress an excessive decrease in the combustion temperature due to the decrease in the engine load, thereby suppressing a decrease in thermal efficiency. Can do.
Further, when the engine load is decreased, the EGR rate is increased, whereby the intake air-fuel mixture amount can be increased, and the throttle valve opening can be increased accordingly, thereby reducing the pump loss.

本発明に係る火花点火式エンジンの更なる特徴構成は、
前記特定炭化水素含有率調整手段が、燃焼室に対して添加量調整を伴って特定炭化水素を添加可能な特定炭化水素添加手段である点にある。 Further features of the spark ignition engine according to the present invention are as follows:
The specific hydrocarbon content rate adjusting means is a specific hydrocarbon addition means capable of adding the specific hydrocarbon with the addition amount adjustment to the combustion chamber.

本特徴構成によれば、上記特定炭化水素添加手段により、燃焼室に対して特定炭化水素を添加すると共にその添加量を調整する形態で、燃焼室における混合気中の特定炭化水素含有率を調整することができる。   According to this characteristic configuration, the specific hydrocarbon content in the air-fuel mixture in the combustion chamber is adjusted by adding the specific hydrocarbon to the combustion chamber and adjusting the addition amount by the specific hydrocarbon addition means. can do.

この目的を達成するための本発明に係る火花点火式エンジンの運転制御方法は、
燃焼室に吸気される新気に炭化水素系の主燃料を混合して混合気を形成し、当該混合気を燃焼室で圧縮して点火プラグにより火花点火し燃焼させる火花点火式エンジンの運転制御方法であって、
その特徴構成は、
前記火花点火式エンジンに、
燃焼室への排ガスの再循環率であるＥＧＲ率を調整可能なＥＧＲ率調整手段と、
エタン及びプロパンの少なくとも一方からなる特定炭化水素の混合気中の含有率である特定炭化水素含有率を調整可能な特定炭化水素含有率調整手段と、
を設け、
運転条件に基づいて前記ＥＧＲ率調整手段を作動させてＥＧＲ率を制御するＥＧＲ率制御を実行すると共に、当該ＥＧＲ率制御に加えて、前記ＥＧＲ率の増加に伴って前記特定炭化水素含有率を増加させる形態で、前記ＥＧＲ率調整手段の状態に応じて前記特定炭化水素含有率調整手段を作動させて前記特定炭化水素含有率を変動させる特定炭化水素含有率制御を実行する点にある。 In order to achieve this object, an operation control method for a spark ignition engine according to the present invention includes:
Operation control of a spark-ignition engine that mixes hydrocarbon-based main fuel with fresh air sucked into the combustion chamber to form an air-fuel mixture, compresses the air-fuel mixture in the combustion chamber, and ignites and burns with a spark plug A method,
Its feature configuration is
In the spark ignition engine,
An EGR rate adjusting means capable of adjusting an EGR rate that is a recirculation rate of exhaust gas to the combustion chamber;
A specific hydrocarbon content rate adjusting means capable of adjusting a specific hydrocarbon content rate, which is a content rate of a specific hydrocarbon content of at least one of ethane and propane,
Provided,
In addition to the EGR rate control, in addition to the EGR rate control, the specific hydrocarbon content rate is increased as the EGR rate is controlled by operating the EGR rate adjusting means based on operating conditions. In the form of increasing, the specific hydrocarbon content rate control is performed in which the specific hydrocarbon content rate adjusting means is operated to change the specific hydrocarbon content rate according to the state of the EGR rate adjusting means.

即ち、上記火花点火式エンジンの運転制御方法によれば、上述した本発明に係る火花点火式エンジンと同様に、ＥＧＲ率調整手段、及び、特定炭化水素含有率調整手段を設けた上で、ＥＧＲ率制御に加えて、特定炭化水素含有率調整制御を実行するので、当該本発明に係る火花点火式エンジンで説明したものと同様の作用効果を奏することができる。   That is, according to the operation control method for the spark ignition engine, the EGR rate adjusting means and the specific hydrocarbon content rate adjusting means are provided in the same manner as the spark ignition engine according to the present invention described above. Since the specific hydrocarbon content rate adjustment control is executed in addition to the rate control, the same effects as those described in the spark ignition engine according to the present invention can be achieved.

第１実施形態の火花点火式エンジンの概略構成図Schematic block diagram of the spark ignition engine of the first embodiment ＥＧＲ率制御におけるＥＧＲ率の調整状態を示すグラフ図The graph which shows the adjustment state of the EGR rate in EGR rate control ＥＧＲ率に対する特定炭化水素含有率の関係を示すグラフ図The graph which shows the relationship of specific hydrocarbon content rate with respect to EGR rate 特定炭化水素含有率制御におけるサイクル変動の悪化に対する特定炭化水素含有率の調整状態を示すグラフ図The graph which shows the adjustment state of the specific hydrocarbon content rate with respect to the deterioration of cycle fluctuation in specific hydrocarbon content rate control 炭化水素系燃料の着火遅れ時間を示すグラフ図Graph showing the ignition delay time of hydrocarbon fuels 第２実施形態の火花点火式エンジンの概略構成図Schematic block diagram of the spark ignition engine of the second embodiment

〔第一の実施形態〕
本発明に係る火花点火式エンジン及びその運転制御方法の第１実施形態について、図１〜図４に基づいて説明する。
図１に示すエンジン１は、燃焼室１０に吸気される新気に炭化水素系の主燃料を混合して混合気Ｍを形成し、当該混合気Ｍを燃焼室１０で圧縮して点火プラグ１１により火花点火し燃焼させる火花点火燃焼を行う火花点火式エンジンとして構成されている。
燃焼室１０は、シリンダ２の内面と、シリンダ２の上部に連結されたシリンダヘッド３の下面と、シリンダ２内において連結棒を介しクランク軸６に連結されて往復移動自在に収容されたピストン４の頂面とで形成されている。
そして、燃焼室１０には、吸気路２１及び排気路３１が開口され、燃焼室１０の吸気路２１側には吸気弁２０が、燃焼室１０の排気路３１側には排気弁３０が設けられている。 [First embodiment]
A first embodiment of a spark ignition engine and its operation control method according to the present invention will be described with reference to FIGS.
The engine 1 shown in FIG. 1 mixes hydrocarbon-based main fuel with fresh air sucked into a combustion chamber 10 to form an air-fuel mixture M, which is compressed in the combustion chamber 10 and spark plug 11. Thus, the spark ignition engine is configured to perform spark ignition combustion.
The combustion chamber 10 includes an inner surface of the cylinder 2, a lower surface of the cylinder head 3 connected to the upper portion of the cylinder 2, and a piston 4 that is connected to the crankshaft 6 through a connecting rod in the cylinder 2 and is reciprocally accommodated. And the top surface of the.
An intake passage 21 and an exhaust passage 31 are opened in the combustion chamber 10, an intake valve 20 is provided on the intake passage 21 side of the combustion chamber 10, and an exhaust valve 30 is provided on the exhaust passage 31 side of the combustion chamber 10. ing.

吸気路２１には、吸気路２１を流通する新気（空気）に、外部から供給されたメタンを主成分とする天然ガス系都市ガス１３Ａである主燃料を、主燃料供給弁２４による供給量調整を伴って混合して、混合気Ｍを形成するミキサ２３が設けられている。また、吸気路２１におけるミキサ２３の下流側には、開度調整により燃焼室１０への混合気Ｍの吸気量を調整可能なスロットルバルブ２２が設けられている。そして、このスロットルバルブ２２を通過した混合気Ｍが燃焼室１０に吸気される。
また、一般的な火花点火式エンジンと同様に、各種センサとして、クランク軸６の角度であるクランク角を計測するクランク角センサ７や、燃焼室１０の圧力である筒内圧を計測する筒内圧力センサ８や、シリンダ２の振動状態を検出する加速度センサ９等が設けられている。 A main fuel supply valve 24 supplies main fuel, which is natural gas city gas 13 </ b> A mainly composed of methane, supplied from outside to fresh air (air) flowing through the intake passage 21. A mixer 23 that mixes with adjustment to form an air-fuel mixture M is provided. A throttle valve 22 is provided on the downstream side of the mixer 23 in the intake passage 21 so that the intake amount of the air-fuel mixture M to the combustion chamber 10 can be adjusted by adjusting the opening. Then, the air-fuel mixture M that has passed through the throttle valve 22 is sucked into the combustion chamber 10.
Similarly to a general spark ignition engine, as various sensors, a crank angle sensor 7 that measures the crank angle that is the angle of the crankshaft 6 and an in-cylinder pressure that measures the in-cylinder pressure that is the pressure of the combustion chamber 10. A sensor 8 and an acceleration sensor 9 for detecting the vibration state of the cylinder 2 are provided.

エンジン１は、吸気行程、圧縮行程、膨張行程、排気行程の順に各行程を行う一連の動作を繰り返し行う。
詳しくは、吸気弁２０を開動作させた状態でピストン４が上死点から下降することにより、吸気路２１から燃焼室１０に混合気Ｍを吸気する吸気行程が行われ、次に、吸気弁２０を閉動作させた状態でピストン４が上昇することにより、燃焼室１０の混合気Ｍを圧縮する圧縮行程が行われる。
この圧縮行程の後期では、予め設定された所望の点火時期（例えば、ピストン４が上死点に達する直前）に、点火プラグ１１が火花放電を行い燃焼室１０の混合気Ｍが点火され、火炎核が形成される。
圧縮行程に続く膨張行程では、火炎核を源とした火炎帯が伝播することで燃焼室１０の混合気Ｍが燃焼され、燃焼室１０の容積増加によりピストン４が降下し、それに続く排気行程では、排気弁３０を開動作させた状態でピストン４が上昇することにより、燃焼室１０の排ガスが排気路３１に排出される。 The engine 1 repeatedly performs a series of operations for performing each stroke in the order of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.
Specifically, when the intake valve 20 is opened, the piston 4 descends from the top dead center, whereby an intake stroke for intake of the air-fuel mixture M from the intake passage 21 to the combustion chamber 10 is performed. When the piston 4 rises in a state in which 20 is closed, a compression stroke for compressing the air-fuel mixture M in the combustion chamber 10 is performed.
In the latter stage of the compression stroke, the spark plug 11 performs a spark discharge at a desired ignition timing set in advance (for example, immediately before the piston 4 reaches top dead center), and the mixture M in the combustion chamber 10 is ignited. Nuclei are formed.
In the expansion stroke that follows the compression stroke, the flame zone originating from the flame kernel propagates, so that the mixture M in the combustion chamber 10 is combusted, and the piston 4 descends due to the increase in the volume of the combustion chamber 10, and in the subsequent exhaust stroke The exhaust gas in the combustion chamber 10 is discharged to the exhaust passage 31 by raising the piston 4 with the exhaust valve 30 opened.

エンジン１は、燃焼室１０に排ガスを再循環させるＥＧＲとして、排気弁３０を上死点よりも進角側又は遅角側で閉弁して燃焼室１０に排ガスを残留させる又は吸い戻す内部ＥＧＲを行う。そして、その内部ＥＧＲにおけるＥＧＲ率を調整するＥＧＲ率調整手段として、当該排気弁３０の閉弁タイミングを調整してＥＧＲ率を調整する内部ＥＧＲ率調整手段４０が設けられている。また、内部ＥＧＲ率調整手段４０は、吸気弁２０及び排気弁３０の開閉時期を調整可能なバルブタイミング可変機構４１で構成されており、このバルブタイミング可変機構４１は、クランク角センサ７によるクランク軸６のクランク角検出を伴って制御されて、吸気弁２０及び排気弁３０の開閉タイミングをクランク角に対する所定の時期に設定することができる。
即ち、排気弁３０の閉タイミングを下死点よりも進角した時点に設定する形態で内部ＥＧＲを行えば、燃焼室１０に排ガスを残留させることができ、一方、排気弁３０の閉時期を下死点よりも遅角した時点に設定する形態で内部ＥＧＲを行えば、排気路３１から燃焼室１０に排ガスを吸い戻すことができる。
このように内部ＥＧＲにより燃焼室１０に排ガスを残留又は吸い戻すと、燃焼室１０では、新気（空気）と比べて比熱が大きい二酸化炭素や水分が多く含まれている排ガスが、燃焼室１０に再循環されることになる。
このように内部ＥＧＲにより比熱が大きい排ガスを燃焼室１０に再循環させると、燃焼室１０では、その排ガスが混合気Ｍに混入され、膨張行程における火花点火後の燃焼温度の上昇が抑制され、ＮＯｘの排出量が低減することになる。また、燃焼温度が低下すれば、シリンダ２壁からの伝熱による熱損失が低減されるので、熱効率が向上することになる。 The engine 1 is an EGR that recirculates exhaust gas into the combustion chamber 10, and closes the exhaust valve 30 on the advance side or the retard side from the top dead center so that the exhaust gas remains in the combustion chamber 10 or sucks it back. I do. And as an EGR rate adjusting means for adjusting the EGR rate in the internal EGR, an internal EGR rate adjusting means 40 for adjusting the EGR rate by adjusting the closing timing of the exhaust valve 30 is provided. The internal EGR rate adjusting means 40 includes a variable valve timing mechanism 41 that can adjust the opening / closing timing of the intake valve 20 and the exhaust valve 30. The variable valve timing mechanism 41 is a crankshaft formed by the crank angle sensor 7. 6 is controlled with crank angle detection, and the opening / closing timing of the intake valve 20 and the exhaust valve 30 can be set to a predetermined timing with respect to the crank angle.
That is, if the internal EGR is performed in such a manner that the closing timing of the exhaust valve 30 is set at a time advanced from the bottom dead center, the exhaust gas can be left in the combustion chamber 10, while the closing timing of the exhaust valve 30 is set. If the internal EGR is performed in a mode set at a time delayed from the bottom dead center, the exhaust gas can be sucked back into the combustion chamber 10 from the exhaust passage 31.
When exhaust gas remains or sucks back into the combustion chamber 10 by the internal EGR in this way, in the combustion chamber 10, the exhaust gas containing a large amount of carbon dioxide and water having a larger specific heat than fresh air (air) is contained in the combustion chamber 10. Will be recycled.
When the exhaust gas having a large specific heat is recirculated to the combustion chamber 10 by the internal EGR in this way, in the combustion chamber 10, the exhaust gas is mixed into the air-fuel mixture M, and an increase in combustion temperature after spark ignition in the expansion stroke is suppressed. The amount of NOx emission is reduced. Further, if the combustion temperature is lowered, heat loss due to heat transfer from the cylinder 2 wall is reduced, so that the thermal efficiency is improved.

エンジン１の各種制御は、ＥＣＵ（エンジン・コントロール・ユニット）５０によって行われ、かかるＥＣＵ５０は、所定のコンピュータープログラムを実行することにより、サイクル変動の悪化を検出するサイクル変動検出手段５１、エンジン１の運転制御を実行する運転制御手段５２等として機能する。   Various controls of the engine 1 are performed by an ECU (engine control unit) 50. The ECU 50 executes a predetermined computer program, thereby detecting cycle fluctuation detection means 51 for detecting deterioration of cycle fluctuation, and the engine 1. It functions as the operation control means 52 etc. which performs operation control.

運転制御手段５２は、後述するＥＧＲ率制御及び特定炭化水素含有率制御を実行すると共に、クランク角センサ７で検出されるクランク角を参照しながら所望のタイミングで点火プラグ１１に火花放電をさせる点火制御や、酸素センサ（図示省略）で検出された排ガスの酸素濃度に基づいて主燃料供給弁２４の開度を制御することによって、ミキサ２３で生成される混合気Ｍの当量比（空燃比）を火花点火燃焼に適した理論当量比近傍の所望の目標当量比に維持する空燃比制御や、クランク角センサ７の検出結果から求められるクランク軸６の回転速度が所望の回転速度に維持されるようにスロットルバルブ２２の開度を制御する回転速度維持制御などの各種制御を実行するように構成されている。   The operation control means 52 performs an EGR rate control and a specific hydrocarbon content rate control, which will be described later, and causes the spark plug 11 to spark discharge at a desired timing while referring to the crank angle detected by the crank angle sensor 7. Equivalent ratio (air-fuel ratio) of the air-fuel mixture M generated by the mixer 23 by controlling the opening degree of the main fuel supply valve 24 based on the oxygen concentration of the exhaust gas detected by the control or an oxygen sensor (not shown) Is maintained at a desired target equivalent ratio in the vicinity of the theoretical equivalent ratio suitable for spark ignition combustion, and the rotational speed of the crankshaft 6 obtained from the detection result of the crank angle sensor 7 is maintained at the desired rotational speed. Thus, various controls such as a rotation speed maintenance control for controlling the opening degree of the throttle valve 22 are executed.

更に、運転制御手段５２は、エンジン負荷などの運転条件に基づいて内部ＥＧＲ率調整手段４０として機能するバルブタイミング可変機構４１を作動させてＥＧＲ率を変動させる形態で、ＥＧＲ率を制御するＥＧＲ制御を実行する。
具体的には、図２に示すように、運転制御手段５２によるＥＧＲ制御では、エンジン負荷の増加を伴う要求トルクの増加に対して、ＥＧＲ率を増加させる形態で、ＥＧＲ率を制御する。
即ち、要求トルクの増加等に伴って運転条件としてエンジン負荷を増加させる場合には、ＥＧＲ制御によりＥＧＲ率を増加させる。すると、エンジン負荷の増加による燃焼温度の過剰な上昇が抑制されて、ＮＯｘの生成が抑制される。逆に、要求トルクの減少等に伴ってエンジン負荷を減少させる場合には、ＥＧＲ制御によりＥＧＲ率を減少させる。すると、エンジン負荷の減少による燃焼温度の過剰な低下が抑制されて、熱効率の低下が抑制される。 Further, the operation control means 52 operates the valve timing variable mechanism 41 that functions as the internal EGR rate adjustment means 40 based on the operation conditions such as the engine load to vary the EGR rate, thereby controlling the EGR rate. Execute.
Specifically, as shown in FIG. 2, in the EGR control by the operation control means 52, the EGR rate is controlled in such a manner that the EGR rate is increased with respect to an increase in required torque accompanying an increase in engine load.
That is, when the engine load is increased as an operating condition with an increase in the required torque or the like, the EGR rate is increased by EGR control. Then, an excessive increase in the combustion temperature due to an increase in engine load is suppressed, and generation of NOx is suppressed. Conversely, when the engine load is reduced as the required torque is reduced, the EGR rate is reduced by EGR control. Then, an excessive decrease in combustion temperature due to a decrease in engine load is suppressed, and a decrease in thermal efficiency is suppressed.

以上がエンジン１の基本構成であるが、更に、このエンジン１は、内部ＥＧＲ率調整手段４０を用いたＥＧＲ制御を行うにあたり、ＥＧＲ率の変動に伴う燃焼状態の悪化を抑制するために、燃焼室１０における混合気Ｍの特定炭化水素含有率を調整可能な特定炭化水素含有率調整手段６０を備えると共に、運転制御手段５２が、ＥＧＲ率制御に加えて、燃焼室１０における混合気Ｍの燃焼状態に基づいて特定炭化水素含有率調整手段６０を作動させて特定炭化水素含有率を制御する特定炭化水素含有率制御を実行するように構成されている。
以下、その詳細構成について説明を加える。 The basic configuration of the engine 1 is as described above. Further, when performing the EGR control using the internal EGR rate adjusting means 40, the engine 1 is used to suppress the deterioration of the combustion state due to the fluctuation of the EGR rate. The specific hydrocarbon content rate adjusting means 60 capable of adjusting the specific hydrocarbon content rate of the air-fuel mixture M in the chamber 10 is provided, and the operation control means 52 performs combustion of the air-fuel mixture M in the combustion chamber 10 in addition to the EGR rate control. The specific hydrocarbon content rate control means for operating the specific hydrocarbon content rate adjusting means 60 based on the state to control the specific hydrocarbon content rate is executed.
The detailed configuration will be described below.

図１に示すように、特定炭化水素含有率調整手段６０は、燃焼室１０に対して添加量調整を伴って特定炭化水素を添加可能な特定炭化水素添加部（特定炭化水素添加手段の一例）６１で構成されている。
具体的に、天然ガスの蒸留過程などで得られたエタンやプロパンの少なくとも一方の特定炭化水素が可搬式の高圧ガス容器６３に加圧状態で蓄えられており、この特定炭化水素添加部６１は、その高圧ガス容器６３に貯留されている特定炭化水素を、ミキサ２３に供給される主燃料に対して、特定炭化水素添加量調整弁６２による添加量調整を伴って混合するように構成されている。
そして、運転制御手段５２は、特定炭化水素含有率制御において特定炭化水素含有率を変動させるにあたり、混合気Ｍの特定炭化水素含有率を増加させる場合には特定炭化水素添加量調整弁６２の開度を拡大させ、混合気Ｍの特定炭化水素含有率を減少させる場合には特定炭化水素添加量調整弁６２の開度を縮小させる。 As shown in FIG. 1, the specific hydrocarbon content rate adjusting means 60 is a specific hydrocarbon addition section (an example of a specific hydrocarbon addition means) that can add specific hydrocarbons to the combustion chamber 10 by adjusting the addition amount. 61.
Specifically, at least one specific hydrocarbon of ethane or propane obtained in a natural gas distillation process or the like is stored in a pressurized state in a portable high-pressure gas container 63, and the specific hydrocarbon addition unit 61 The specific hydrocarbon stored in the high-pressure gas container 63 is mixed with the main fuel supplied to the mixer 23 with the addition amount adjustment by the specific hydrocarbon addition amount adjustment valve 62. Yes.
Then, the operation control means 52 opens the specific hydrocarbon addition amount adjustment valve 62 when increasing the specific hydrocarbon content of the air-fuel mixture M in changing the specific hydrocarbon content in the specific hydrocarbon content control. The degree of opening of the specific hydrocarbon addition amount adjusting valve 62 is reduced when the degree is increased to reduce the specific hydrocarbon content of the mixture M.

このような特定炭化水素としてのエタンやプロパンは、メタンやブタンなどの他の炭化水素と比較して、その温度と着火遅れ時間との相関関係において酸素濃度の変動の影響が少ないという特性を有しており、その特定について以下に説明を加える。
図５は、メタン（ＣＨ4）、エタン（Ｃ2Ｈ6）、プロパン（Ｃ3Ｈ8）、イソブタン（ｉｓｏ−Ｃ4Ｈ10）、及びノルマルブタン（ｎ−Ｃ4Ｈ10）の夫々の炭化水素系燃料について、密閉定容系の詳細化学反応計算により、着火遅れ時間の酸素濃度依存性について解析した結果を示している。
特定炭化水素としてのエタンやプロパン以外の炭化水素系燃料（図５（ａ）、（ｄ）、及び（ｅ）参照）については、酸素濃度が１０．５％、２１％、及び４２％の順に増加するほど、温度上昇に対する着火遅れ時間の短縮度合いが増加している。一方、エタンやプロパン（図５（ｂ）、（ｃ）参照）については、酸素濃度が１０．５％、２１％、及び４２％と変化した場合でも、温度上昇に対する着火遅れ時間の短縮度合いが略一定である。即ち、この解析結果から、炭化水素系燃料のうち、エタンやプロパンが、他の炭化水素と比較して、着火遅れ時間に対する酸素濃度の変動の影響が少ないことがわかる。即ち、エタンやプロパンは、混合気中の酸素濃度が不均一になった場合でも、その影響をあまり受けることなく着火すると言える。
更に、エタン（図５（ｂ））については、プロパン（図５（ｃ））と比較しても、着火遅れ時間が酸素濃度の変動の影響をほとんど受けないことがわかる。よって、エタンは、混合気中の酸素濃度が不均一になった場合でも、その影響をほとんど受けることなく着火すると言える。 Ethane and propane as such specific hydrocarbons have the characteristic that the influence of fluctuations in oxygen concentration is less in the correlation between the temperature and the ignition delay time than other hydrocarbons such as methane and butane. The specifics will be described below.
FIG. 5 shows methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), isobutane (iso-C 4 H 10 ), and normal butane (n-C 4 H 10 ). The result of analyzing the dependence of the ignition delay time on the oxygen concentration by the detailed chemical reaction calculation of the sealed constant volume system for the hydrocarbon fuel is shown.
For hydrocarbon fuels other than ethane and propane as specific hydrocarbons (see FIGS. 5 (a), (d), and (e)), the oxygen concentration is in the order of 10.5%, 21%, and 42%. As the number increases, the degree of shortening of the ignition delay time with respect to the temperature rise increases. On the other hand, for ethane and propane (see FIGS. 5B and 5C), even when the oxygen concentration changes to 10.5%, 21%, and 42%, the degree of reduction in the ignition delay time with respect to the temperature rise is small. It is almost constant. That is, from this analysis result, it can be seen that, among hydrocarbon fuels, ethane and propane are less affected by fluctuations in the oxygen concentration on the ignition delay time than other hydrocarbons. That is, it can be said that ethane and propane are ignited without much influence even when the oxygen concentration in the air-fuel mixture becomes uneven.
Furthermore, it can be seen that ethane (FIG. 5 (b)) is hardly affected by fluctuations in oxygen concentration even when compared with propane (FIG. 5 (c)). Therefore, it can be said that ethane is ignited with almost no influence even when the oxygen concentration in the air-fuel mixture becomes uneven.

そして、運転制御手段５２は、ＥＧＲ率制御を実行して、要求トルクに連動するエンジン負荷などの運転条件に基づいてＥＧＲ率を制御するにあたり、ＥＧＲ率の増加により混合気Ｍの酸素濃度が不均一になってサイクル変動が悪化する傾向にあったとしても、そのＥＧＲ率の増加に伴ってエタンやプロパンの混合気中の含有率である特定炭化水素含有率を増加させる形態で、内部ＥＧＲ率調整手段４０の状態に応じて特定炭化水素含有率調整手段６０を作動させて特定炭化水素含有率を変動させることで、ＥＧＲ率の増加に伴う燃焼状態の悪化を抑制する。
具体的に、特定炭化水素含有率制御では、図３のグラフ図に示すように、要求トルクの増加等に伴う内部ＥＧＲにおけるＥＧＲ率の増加に対しては、略比例的に特定炭化水素含有率を増加させることで、ＥＧＲ率の増加に伴う燃焼状態の悪化を抑制し、逆に、要求トルクの増加等に伴う内部ＥＧＲにおけるＥＧＲ率の減少に対しては、略比例的に特定炭化水素含有率を減少させることで、特定炭化水素の消費を節約することができる。 Then, the operation control means 52 executes the EGR rate control and controls the EGR rate based on the operating conditions such as the engine load linked to the required torque. When the EGR rate increases, the oxygen concentration of the air-fuel mixture M does not increase. Even if the cycle fluctuation tends to be uniform, the internal EGR rate is increased in the form of increasing the specific hydrocarbon content, which is the content of ethane or propane in the gas mixture, as the EGR rate increases. The deterioration of the combustion state accompanying the increase in the EGR rate is suppressed by operating the specific hydrocarbon content rate adjusting unit 60 according to the state of the adjusting unit 40 to vary the specific hydrocarbon content rate.
Specifically, in the specific hydrocarbon content rate control, as shown in the graph of FIG. 3, the specific hydrocarbon content rate is approximately proportional to the increase in the EGR rate in the internal EGR accompanying an increase in the required torque or the like. By increasing the EGR, the deterioration of the combustion state accompanying the increase in the EGR rate is suppressed, and conversely, the specific EGR ratio is contained approximately proportionally to the decrease in the EGR rate in the internal EGR due to the increase in the required torque, etc. By reducing the rate, consumption of specific hydrocarbons can be saved.

更に、運転制御手段５２は、特定炭化水素含有率制御を実行するにあたり、燃焼時期の調整のために変更されるＥＧＲ率に基づいて特定炭化水素含有率を決定するように構成しても構わないが、本実施形態では、燃焼時期の調整に伴って変化するサイクル変動の状態に基づいて特定炭化水素含有率を決定するように構成される。以下、その詳細について説明を加える。
ＥＣＵ５０は、サイクル変動の悪化を検出するサイクル変動検出手段５１として機能する。
上記サイクル変動検出手段５１は、クランク角センサ７で検出されるクランク角を参照しながら筒内圧力センサ８で検出された筒内圧力を分析して、図示平均有効圧力を算出し、その図示平均有効圧力の標準偏差を同圧力の平均値で除算した値を、所定のサイクル数における変動係数ＣＯＶとして求め、その変動係数ＣＯＶが許容範囲を超えて増大した状態を、サイクル変動の悪化として検出する。
そして、運転制御手段５２は、特定炭化水素含有率制御において、サイクル変動検出手段５１で検出されるサイクル変動の悪化が抑制されるように特定炭化水素含有率調整手段６０により特定炭化水素含有率を変動させる形態で、混合気Ｍの特定炭化水素含有率を変動させる。
具体的に、要求トルクの増加等に伴って内部ＥＧＲにおけるＥＧＲ率を増加側へ調整することで、燃焼室１０における酸素濃度が時間的に不均一になり、サイクル変動検出手段５１でサイクル変動の悪化が検出される。この場合、特定炭化水素含有率制御により混合気Ｍの特定炭化水素含有率を増加させることで、混合気Ｍの燃焼速度に対する酸素濃度の不均一化の影響が小さくなり、結果、サイクル変動の悪化が抑制されることになる。 Further, the operation control means 52 may be configured to determine the specific hydrocarbon content based on the EGR rate changed for adjustment of the combustion timing when executing the specific hydrocarbon content control. However, the present embodiment is configured to determine the specific hydrocarbon content based on the state of cycle fluctuation that varies with adjustment of the combustion timing. The details will be described below.
The ECU 50 functions as cycle fluctuation detection means 51 that detects deterioration of cycle fluctuation.
The cycle fluctuation detecting means 51 analyzes the in-cylinder pressure detected by the in-cylinder pressure sensor 8 while referring to the crank angle detected by the crank angle sensor 7, and calculates the indicated mean effective pressure. A value obtained by dividing the standard deviation of the effective pressure by the average value of the same pressure is obtained as a coefficient of variation COV in a predetermined number of cycles, and a state in which the coefficient of variation COV increases beyond an allowable range is detected as deterioration of cycle fluctuation. .
Then, the operation control unit 52 controls the specific hydrocarbon content rate by the specific hydrocarbon content rate adjusting unit 60 so that the deterioration of the cycle variation detected by the cycle variation detection unit 51 is suppressed in the specific hydrocarbon content rate control. The specific hydrocarbon content of the air-fuel mixture M is changed in such a manner that it is changed.
Specifically, by adjusting the EGR rate in the internal EGR to the increasing side as the required torque increases, the oxygen concentration in the combustion chamber 10 becomes non-uniform in time, and the cycle fluctuation detecting means 51 Deterioration is detected. In this case, by increasing the specific hydrocarbon content of the mixture M by controlling the specific hydrocarbon content, the influence of non-uniform oxygen concentration on the combustion rate of the mixture M is reduced, resulting in worse cycle fluctuations. Will be suppressed.

〔第２実施形態〕
本発明に係る火花点火式エンジン及びその運転制御方法の第２実施形態について、図６に基づいて説明する。尚、上記第１実施形態と同様の構成については、説明を割愛する場合がある。
図６に示すエンジン１００は、ＥＧＲの形態並びにＥＧＲ率を調整するＥＧＲ率調整手段以外の構成において、第１実施形態と略同様の基本構成を有する火花点火式エンジンとして構成されている。
即ち、エンジン１００は、燃焼室１０に排ガスを再循環させるＥＧＲとして、排気路３１と吸気路２１とを接続するＥＧＲ路４３を介して燃焼室１０に排ガスを再循環させる外部ＥＧＲを行う。そして、その外部ＥＧＲにおけるＥＧＲ率を調整するＥＧＲ率調整手段といて、当該ＥＧＲ路４３に設けられたＥＧＲ弁４４の開度を調整してＥＧＲ率を調整する外部ＥＧＲ率調整手段４２が設けられている。
即ち、ＥＧＲ弁４４を開弁する形態で外部ＥＧＲを行えば、新気（空気）と比べて比熱が大きい二酸化炭素や水分が多く含まれている排ガスが、排気路３１からＥＧＲ路４３に取り出され、吸気路２１を通流してある程度冷却された後に、燃焼室１０に再循環されることになる。
このように外部ＥＧＲにより比熱が大きく比較的低温の排ガスを燃焼室１０に再循環させると、上記第１実施形態と同様に、ＮＯｘの排出量の低減と熱効率の向上が実現される。
よって、上記運転制御手段５２が実行するＥＧＲ制御では、上記第１実施形態と同様に、図２に示すように、エンジン負荷の増加を伴う要求トルクの増加に対して、ＥＧＲ率を増加させる形態で、ＥＧＲ率を制御する。
更に、上記運転制御手段５２が実行する特定炭化水素含有率制御においても、上記第１実施形態と同様に、図３及び図４に示すように、外部ＥＧＲにおけるＥＧＲ率を増加したとき、又は、サイクル変動検出手段５１でサイクル変動の悪化を検出したときには、混合気Ｍの特定炭化水素含有率を増加させることで、サイクル変動の悪化を抑制することができ、逆に、外部ＥＧＲにおけるＥＧＲ率を減少したとき、又は、サイクル変動検出手段５１でサイクル変動の悪化を検出しなくなったときには、混合気Ｍの特定炭化水素含有率を減少させることで、特定炭化水素の消費を節約することができる。 [Second Embodiment]
A second embodiment of the spark ignition engine and the operation control method thereof according to the present invention will be described with reference to FIG. In addition, about the structure similar to the said 1st Embodiment, description may be omitted.
The engine 100 shown in FIG. 6 is configured as a spark ignition engine having a basic configuration substantially the same as that of the first embodiment except for the EGR mode and the configuration other than the EGR rate adjusting means for adjusting the EGR rate.
That is, the engine 100 performs external EGR for recirculating exhaust gas to the combustion chamber 10 via the EGR passage 43 connecting the exhaust passage 31 and the intake passage 21 as EGR for recirculating exhaust gas to the combustion chamber 10. And as an EGR rate adjusting means for adjusting the EGR rate in the external EGR, an external EGR rate adjusting means 42 for adjusting the EGR rate by adjusting the opening degree of the EGR valve 44 provided in the EGR path 43 is provided. ing.
That is, if external EGR is performed in a form in which the EGR valve 44 is opened, exhaust gas containing a large amount of carbon dioxide and moisture having a larger specific heat than fresh air (air) is extracted from the exhaust passage 31 to the EGR passage 43. Then, after flowing through the intake passage 21 and being cooled to some extent, it is recirculated to the combustion chamber 10.
Thus, when the exhaust gas having a large specific heat and a relatively low temperature is recirculated to the combustion chamber 10 by the external EGR, the NOx emission amount is reduced and the thermal efficiency is improved as in the first embodiment.
Therefore, in the EGR control executed by the operation control means 52, as in the first embodiment, as shown in FIG. 2, the EGR rate is increased with respect to the increase in the required torque accompanying the increase in the engine load. Thus, the EGR rate is controlled.
Furthermore, also in the specific hydrocarbon content rate control executed by the operation control means 52, as shown in FIGS. 3 and 4, when the EGR rate in the external EGR is increased, as in the first embodiment, or When the cycle fluctuation detection means 51 detects the deterioration of the cycle fluctuation, the cycle fluctuation deterioration can be suppressed by increasing the specific hydrocarbon content of the mixture M, and conversely, the EGR rate in the external EGR is reduced. When it decreases or when the cycle fluctuation detecting means 51 no longer detects the deterioration of the cycle fluctuation, the consumption of the specific hydrocarbon can be saved by reducing the specific hydrocarbon content of the mixture M.

〔その他の実施形態〕
最後に、本発明のその他の実施形態について説明する。尚、以下に説明する各実施形態の構成は、それぞれ単独で適用されるものに限られず、矛盾が生じない限り、他の実施形態の構成と組み合わせて適用することも可能である。
（１）上記実施形態では、特定炭化水素含有率調整手段６０を、燃焼室１０に対して添加量調整を伴って特定炭化水素を添加可能な特定炭化水素添加部６１として構成したが、例えば、特定炭化水素含有率調整手段６０を、燃焼室１０に供給される主燃料から分離量調整を伴って特定炭化水素を分離することで、燃焼室１０における混合気Ｍの特定炭化水素含有率の調整を行っても構わない。 [Other Embodiments]
Finally, other embodiments of the present invention will be described. Note that the configuration of each embodiment described below is not limited to being applied independently, and can be applied in combination with the configuration of other embodiments as long as no contradiction arises.
(1) In the above-described embodiment, the specific hydrocarbon content rate adjusting means 60 is configured as the specific hydrocarbon addition unit 61 that can add the specific hydrocarbon with the addition amount adjustment to the combustion chamber 10. The specific hydrocarbon content adjusting means 60 separates the specific hydrocarbon from the main fuel supplied to the combustion chamber 10 with adjustment of the separation amount, thereby adjusting the specific hydrocarbon content of the mixture M in the combustion chamber 10. You may do.

（２）上記実施形態では、特定炭化水素添加部６１は、高圧ガス容器６３に蓄えられた特定炭化水素を添加するように構成したが、主燃料即ち天然ガスの一部を取り出し、その天然ガスから、公知の酸化カップリング法（例えば特開平０５−０７０３７２号公報参照）や、膜分離法及び加圧凝縮法などの精製法（例えば特開２００９−１６７４１１号公報参照）などにより特定炭化水素を分離して、特定炭化水素添加部６１に供給するように構成しても構わない。
また、主燃料以外の原料を外部から供給し、その原料を合成して特定炭化水素を得るように構成しても構わない。尚、この場合、原料としてのエチレンの水素化反応により特定炭化水素としてのエタンを得ることができ、更に、そのエチレンをエタノールの脱水処理により得ることもできる。
また、特定炭化水素添加部６１から供給される特定炭化水素は、必ずしも特定炭化水素１００％でなくてもよく、例えば主燃料よりも特定炭化水素の濃度が高く、それを燃焼室１０に添加することで当該燃焼室１０における混合気Ｍの特定炭化水素含有率を上昇せる程度に特定炭化水素を含むものであればよい。 (2) In the above embodiment, the specific hydrocarbon addition unit 61 is configured to add the specific hydrocarbon stored in the high-pressure gas vessel 63. However, the main fuel, that is, a part of the natural gas is taken out and the natural gas is extracted. From a known oxidative coupling method (for example, see JP-A No. 05-070372) or a purification method such as a membrane separation method or a pressure condensation method (for example, see JP-A No. 2009-167411). You may comprise so that it may isolate | separate and it may supply to the specific hydrocarbon addition part 61. FIG.
In addition, a raw material other than the main fuel may be supplied from the outside, and the raw material may be synthesized to obtain the specific hydrocarbon. In this case, ethane as a specific hydrocarbon can be obtained by a hydrogenation reaction of ethylene as a raw material, and further, the ethylene can be obtained by a dehydration treatment of ethanol.
Further, the specific hydrocarbon supplied from the specific hydrocarbon addition unit 61 does not necessarily have to be 100% of the specific hydrocarbon. For example, the concentration of the specific hydrocarbon is higher than that of the main fuel, and the specific hydrocarbon is added to the combustion chamber 10. As long as the specific hydrocarbon content of the air-fuel mixture M in the combustion chamber 10 is increased, the specific hydrocarbon may be included.

（３）上記実施形態では、図３に示すように、特定炭化水素含有率制御において、ＥＧＲ率の増減に対して略比例的に特定炭化水素含有率を増減させたが、別に、ＥＧＲ率の増減に対して例えば特定炭化水素含有率を段階的に増減させるなど、特定炭化水素含有率の増減方法については適宜変更可能である。
例えば、ＥＧＲ率が０を含む所定値を超えた場合には、燃焼室１０に対する特定炭化水素の添加を実行して、所定の特定炭化水素含有率の混合気Ｍを燃焼室１０に吸気し、ＥＧＲ率が所定値以下になった場合には、燃焼室１０に対する特定炭化水素の添加を停止して、特定炭化水素が添加されていない混合気Ｍ、即ち特定炭化水素含有率が０の混合気Ｍを燃焼室１０に吸気するように構成しても構わない。 (3) In the above embodiment, as shown in FIG. 3, in the specific hydrocarbon content control, the specific hydrocarbon content is increased or decreased approximately proportionally to the increase or decrease of the EGR rate. The method for increasing or decreasing the specific hydrocarbon content can be changed as appropriate, for example, by increasing or decreasing the specific hydrocarbon content in stages.
For example, when the EGR rate exceeds a predetermined value including 0, the addition of specific hydrocarbons to the combustion chamber 10 is executed, and the mixture M having a predetermined specific hydrocarbon content rate is sucked into the combustion chamber 10. When the EGR rate becomes equal to or less than a predetermined value, the addition of the specific hydrocarbon to the combustion chamber 10 is stopped, and the mixture M to which the specific hydrocarbon is not added, that is, the mixture having the specific hydrocarbon content of 0. You may comprise so that M may be sucked into the combustion chamber 10.

（４）上記実施形態では、ＥＧＲ率制御において、エンジン負荷が増加した場合にＥＧＲ率を増加することで、ＮＯｘの生成を抑制するように構成したが、逆に、エンジン負荷が減少した場合にＥＧＲ率を増加することで、吸入混合気量を増加させ、それに伴ってスロットルバルブの開度を拡大させて、ポンプ損失の低減を図るように構成することもできる。
また、このようにエンジン負荷の減少に伴ってＥＧＲ率を増加させる場合においても、そのようなＥＧＲ率の増加に伴って混合気中の特定炭化水素含有率を増加させることで、ＥＧＲ率増加に伴うサイクル変動の悪化を抑制することができる。 (4) In the above embodiment, the EGR rate control is configured to suppress the generation of NOx by increasing the EGR rate when the engine load increases, but conversely, when the engine load decreases. By increasing the EGR rate, the amount of intake air-fuel mixture can be increased, and the opening of the throttle valve can be increased accordingly, so that the pump loss can be reduced.
In addition, even when the EGR rate is increased as the engine load decreases in this way, the EGR rate can be increased by increasing the specific hydrocarbon content in the air-fuel mixture as the EGR rate increases. The accompanying deterioration of cycle fluctuation can be suppressed.

（５）上記実施形態では、本発明に係る火花点火式エンジンを、単気筒型に構成したが、当然多気筒型に構成しても構わない。 (5) In the above-described embodiment, the spark ignition engine according to the present invention is configured as a single cylinder type.

本発明は、燃焼室に吸気される新気に炭化水素系の主燃料を混合して混合気を形成し、当該混合気を燃焼室で圧縮して点火プラグにより火花点火し燃焼させる火花点火式エンジン及びその運転制御方法として好適に利用可能である。   The present invention relates to a spark ignition type in which a hydrocarbon-based main fuel is mixed with fresh air sucked into a combustion chamber to form an air-fuel mixture, and the air-fuel mixture is compressed in the combustion chamber and sparked by a spark plug and burned. It can be suitably used as an engine and its operation control method.

１，１００：エンジン
１０ ：燃焼室
１１ ：点火プラグ
４０ ：内部ＥＧＲ率調整手段（ＥＧＲ率調整手段）
４２ ：外部ＥＧＲ率調整手段（ＥＧＲ率調整手段）
５１ ：サイクル変動検出手段
５２ ：運転制御手段
６０ ：特定炭化水素含有率調整手段
１００ ：エンジン
Ｍ ：混合気 1, 100: Engine 10: Combustion chamber 11: Spark plug 40: Internal EGR rate adjusting means (EGR rate adjusting means)
42: External EGR rate adjusting means (EGR rate adjusting means)
51: Cycle fluctuation detecting means 52: Operation control means 60: Specific hydrocarbon content rate adjusting means 100: Engine M: Air-fuel mixture

Claims (5)

燃焼室に吸気される新気に炭化水素系の主燃料を混合して混合気を形成し、当該混合気を燃焼室で圧縮して点火プラグにより火花点火し燃焼させる火花点火式エンジンであって、
燃焼室への排ガスの再循環率であるＥＧＲ率を調整可能なＥＧＲ率調整手段と、
エタン及びプロパンの少なくとも一方からなる特定炭化水素の混合気中の含有率である特定炭化水素含有率を調整可能な特定炭化水素含有率調整手段と、
運転条件に基づいて前記ＥＧＲ率調整手段を作動させてＥＧＲ率を制御するＥＧＲ率制御を実行する運転制御手段と、を備え
前記運転制御手段が、前記ＥＧＲ率制御に加えて、前記ＥＧＲ率の増加に伴って前記特定炭化水素含有率を増加させる形態で、前記ＥＧＲ率調整手段の状態に応じて前記特定炭化水素含有率調整手段を作動させて前記特定炭化水素含有率を変動させる特定炭化水素含有率制御を実行する火花点火式エンジン。 A spark ignition engine in which a hydrocarbon-based main fuel is mixed with fresh air sucked into a combustion chamber to form an air-fuel mixture, and the air-fuel mixture is compressed in the combustion chamber and sparked by a spark plug to burn. ,
An EGR rate adjusting means capable of adjusting an EGR rate that is a recirculation rate of exhaust gas to the combustion chamber;
A specific hydrocarbon content rate adjusting means capable of adjusting a specific hydrocarbon content rate, which is a content rate of a specific hydrocarbon content of at least one of ethane and propane,
Operating control means for executing EGR rate control for controlling the EGR rate by operating the EGR rate adjusting means based on operating conditions, in addition to the EGR rate control, the operation control unit is configured to control the EGR rate. A specific hydrocarbon that varies the specific hydrocarbon content by operating the specific hydrocarbon content adjusting means according to the state of the EGR rate adjusting means in a form that increases the specific hydrocarbon content with an increase. A spark ignition engine that performs content control. サイクル変動の悪化を検出するサイクル変動検出手段を備え、
前記運転制御手段が、前記特定炭化水素含有率制御において、前記サイクル変動検出手段で検出されるサイクル変動の悪化が抑制されるように前記特定炭化水素含有率調整手段を作動させて前記特定炭化水素含有率を変動させる形態で、前記特定炭化水素含有率を変動させる請求項１に記載の火花点火式エンジン。 A cycle fluctuation detecting means for detecting deterioration of cycle fluctuation is provided,
In the specific hydrocarbon content rate control, the operation control unit operates the specific hydrocarbon content rate adjusting unit so that deterioration of cycle fluctuation detected by the cycle fluctuation detection unit is suppressed. The spark ignition engine according to claim 1, wherein the specific hydrocarbon content is changed in a form in which the content is changed. 前記運転制御手段が、前記ＥＧＲ率制御において、エンジン負荷に基づいて前記ＥＧＲ率を変動させる請求項１又は２に記載の火花点火式エンジン。   The spark ignition engine according to claim 1 or 2, wherein the operation control means varies the EGR rate based on an engine load in the EGR rate control. 前記特定炭化水素含有率調整手段が、燃焼室に対して添加量調整を伴って特定炭化水素を添加可能な特定炭化水素添加手段である請求項１〜３の何れか１項に記載の火花点火式エンジン。   The spark ignition according to any one of claims 1 to 3, wherein the specific hydrocarbon content rate adjusting means is a specific hydrocarbon addition means capable of adding the specific hydrocarbon with the addition amount adjustment to the combustion chamber. Expression engine. 燃焼室に吸気される新気に炭化水素系の主燃料を混合して混合気を形成し、当該混合気を燃焼室で圧縮して点火プラグにより火花点火し燃焼させる火花点火式エンジンの運転制御方法であって、
前記火花点火式エンジンに、
燃焼室への排ガスの再循環率であるＥＧＲ率を調整可能なＥＧＲ率調整手段と、
エタン及びプロパンの少なくとも一方からなる特定炭化水素の混合気中の含有率である特定炭化水素含有率を調整可能な特定炭化水素含有率調整手段と、
を設け、
運転条件に基づいて前記ＥＧＲ率調整手段を作動させてＥＧＲ率を制御するＥＧＲ率制御を実行すると共に、当該ＥＧＲ率制御に加えて、前記ＥＧＲ率の増加に伴って前記特定炭化水素含有率を増加させる形態で、前記ＥＧＲ率調整手段の状態に応じて前記特定炭化水素含有率調整手段を作動させて前記特定炭化水素含有率を変動させる特定炭化水素含有率制御を実行する前記火花点火式エンジンの運転制御方法。 Operation control of a spark-ignition engine that mixes hydrocarbon-based main fuel with fresh air sucked into the combustion chamber to form an air-fuel mixture, compresses the air-fuel mixture in the combustion chamber, and ignites and burns with a spark plug A method,
In the spark ignition engine,
An EGR rate adjusting means capable of adjusting an EGR rate that is a recirculation rate of exhaust gas to the combustion chamber;
A specific hydrocarbon content rate adjusting means capable of adjusting a specific hydrocarbon content rate, which is a content rate of a specific hydrocarbon content of at least one of ethane and propane,
Provided,
In addition to the EGR rate control, in addition to the EGR rate control, the specific hydrocarbon content rate is increased as the EGR rate is controlled by operating the EGR rate adjusting means based on operating conditions. The spark-ignition engine that performs specific hydrocarbon content control to vary the specific hydrocarbon content by operating the specific hydrocarbon content adjustment in accordance with the state of the EGR rate adjustment Operation control method.
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JP2009138567A (en) * 2007-12-04 2009-06-25 Toyota Motor Corp Control device of internal combustion engine
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JP2011026144A (en) * 2009-07-21 2011-02-10 Tokyo Gas Co Ltd Activated carbon for suppressing heat quantity fluctuation of fuel gas, and method and system for suppressing heat quantity fluctuation

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH10121070A (en) * 1996-10-22 1998-05-12 Cosmo Sogo Kenkyusho:Kk Gas composition
JP2009138567A (en) * 2007-12-04 2009-06-25 Toyota Motor Corp Control device of internal combustion engine
JP2009299664A (en) * 2008-06-17 2009-12-24 Osaka Gas Co Ltd Energy system
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JP2011026144A (en) * 2009-07-21 2011-02-10 Tokyo Gas Co Ltd Activated carbon for suppressing heat quantity fluctuation of fuel gas, and method and system for suppressing heat quantity fluctuation

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