JP5447009B2 - Internal combustion engine - Google Patents

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JP5447009B2
JP5447009B2 JP2010048132A JP2010048132A JP5447009B2 JP 5447009 B2 JP5447009 B2 JP 5447009B2 JP 2010048132 A JP2010048132 A JP 2010048132A JP 2010048132 A JP2010048132 A JP 2010048132A JP 5447009 B2 JP5447009 B2 JP 5447009B2
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oxygen
oxygen separation
intake
egr
passage
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亮 北畠
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Isuzu Motors Ltd
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    • YGENERAL 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

本発明は内燃機関に係り、特に、エンジン本体の燃焼室からのNOx排出量の抑制に好適な内燃機関に関する。   The present invention relates to an internal combustion engine, and more particularly, to an internal combustion engine suitable for suppressing NOx emission from a combustion chamber of an engine body.

空燃比がリーンな状態で燃焼が行われる内燃機関、主にディーゼルエンジンにおいては、その排ガス浄化技術の一つとして、排気ガスの一部を吸気に還流させるEGR(Exhaust Gas Recirculation)が知られている(例えば、特許文献1参照)。これは、不活性ガスの多い排気ガスを吸気に還流することで、エンジン本体の燃焼室に吸入される吸気ガスの酸素濃度を低下させ、燃焼時の筒内温度の上昇を抑制し、高温度場で生成される窒素酸化物NOxの生成を抑制することが可能となる。   As an exhaust gas purification technology, EGR (Exhaust Gas Recirculation) that recirculates a part of exhaust gas to intake air is known as an exhaust gas purification technique for internal combustion engines that mainly perform combustion with a lean air-fuel ratio. (For example, see Patent Document 1). This is because the exhaust gas with a large amount of inert gas is recirculated to the intake air, so that the oxygen concentration of the intake gas sucked into the combustion chamber of the engine body is reduced, and the increase in the in-cylinder temperature during combustion is suppressed. Generation of nitrogen oxides NOx generated in the field can be suppressed.

ディーゼルエンジンに対する排出ガス規制や燃費規制は年々厳しくなっており、排気通路に設置した後処理装置による排気の浄化のみならず、燃焼室からの排気ガスの改善が必要となっている。   Exhaust gas regulations and fuel economy regulations for diesel engines are becoming stricter year by year, and it is necessary to improve exhaust gas from the combustion chamber as well as purification of exhaust gas by an aftertreatment device installed in the exhaust passage.

燃焼室からのNOx排出量を抑制するため、上述のEGRは好適である。また、年々厳しくなる排出ガス規制等に対応して、エンジンの低負荷および中負荷領域のみならず、高負荷領域においても高いEGR率でEGRを行うことが好適である。   The above-mentioned EGR is suitable for suppressing the NOx emission amount from the combustion chamber. Further, in response to exhaust gas regulations that are becoming stricter year by year, it is preferable to perform EGR at a high EGR rate not only in the low and medium load regions of the engine but also in the high load region.

しかし、高負荷領域における高EGR率化には次のような問題がある。すなわち、EGRは高温の排気ガスを吸気側へ多量に還流するが、筒内への吸入空気(吸気)の充填効率悪化を回避すべく、EGRガスをEGRクーラにて十分に冷却する必要がある。ところで、低中負荷領域に比べ過給圧が高い高負荷領域においては、EGR率としては低中負荷時よりも低いものの、EGRガス量としては低中負荷時よりも増加し、EGRクーラにて多大なEGRガスの除熱を行わなければならない。EGRクーラがエンジン冷却水を用いてEGRガスの冷却を行う水冷式であると、除熱量が増した分、冷却水温度が上昇し、エンジン全体として熱効率が低下する虞がある。   However, increasing the EGR rate in the high load region has the following problems. That is, EGR recirculates a large amount of high-temperature exhaust gas to the intake side, but it is necessary to sufficiently cool the EGR gas with the EGR cooler in order to avoid deterioration of the charging efficiency of intake air (intake) into the cylinder. . By the way, in the high load region where the supercharging pressure is higher than that in the low and medium load region, the EGR rate is lower than that in the low and medium load, but the EGR gas amount increases than in the low and medium load. A great deal of heat must be removed from the EGR gas. If the EGR cooler is a water-cooled type that cools EGR gas using engine cooling water, the amount of heat removal increases, the cooling water temperature rises, and the overall efficiency of the engine may decrease.

このように、EGRのみでエンジン本体からのNOx排出量を抑制しようとしても、それには自ずと限界があり、EGRとは別の手法が待ち望まれているのが現状である。   As described above, even if it is attempted to suppress the NOx emission amount from the engine main body only by EGR, there is a limit in itself, and a method different from EGR is awaited at present.

そこで、本発明者は、排気ガスを多量に還流することなく、エンジン本体への吸入空気の酸素濃度を低下させる手段として酸素分離膜を適用し、新気自体を低酸素濃度化することができるようにした内燃機関を先に発明した(特願2000−198637号、未公開)。この発明によれば、熱効率の悪化を伴うことなく、NOxの低減を図ることが可能となる。   Therefore, the present inventor can apply the oxygen separation membrane as a means for reducing the oxygen concentration of the intake air to the engine body without recirculating the exhaust gas in a large amount, thereby reducing the oxygen concentration in the fresh air itself. The internal combustion engine thus made was first invented (Japanese Patent Application No. 2000-198637, unpublished). According to the present invention, it is possible to reduce NOx without deteriorating thermal efficiency.

酸素分離膜における気体分離は、下記に示す気体透過の基本式(1)に基いている。下記式(1)中の気体透過率P、膜厚L、膜面積Sは、エンジンの運転状態によらず、酸素分離膜のモジュールによって決定される。
F=(P/L)×ΔP×S ・・・(1)
Gas separation in the oxygen separation membrane is based on the basic equation (1) of gas permeation shown below. The gas permeability P, the film thickness L, and the membrane area S in the following formula (1) are determined by the oxygen separation membrane module regardless of the operating state of the engine.
F = (P / L) × ΔP × S (1)

ここでFは膜からの流出流量(cm3/s)、Pは気体透過率(Barrer=10-10cm3(STP)・cm/s・cm2・cmHg)、Lは膜厚(cm)、ΔPは膜内外差圧(分圧差)(cmHg)、Sは膜面積(cm2)である。 Where F is the flow rate out of the membrane (cm 3 / s), P is the gas permeability (Barrer = 10 -10 cm 3 (STP) · cm / s · cm 2 · cmHg), and L is the film thickness (cm) , ΔP is the transmembrane pressure difference (partial pressure difference) (cmHg), and S is the membrane area (cm 2 ).

従って、前記式(1)より酸素分離膜からの流出流量は、膜内外差圧(分圧差)ΔPに依存することになるため、酸素分離膜を適用したエンジンとしては、吸気行程中に過給機から吸気マニホールドまでの間に酸素分離膜を設置することが必要である。   Therefore, since the outflow flow rate from the oxygen separation membrane depends on the transmembrane pressure (partial pressure difference) ΔP according to the equation (1), the engine using the oxygen separation membrane is supercharged during the intake stroke. It is necessary to install an oxygen separation membrane between the machine and the intake manifold.

特開2005−291001号公報JP 2005-291001 A

ところで、前記エンジンにおいては、酸素分離膜から流出する酸素富化空気量が膜内外の差圧に依存するため、高過給化が高EGR化と同義になる。しかしながら、過度に高過給化を進めた場合、目標とする吸気酸素濃度を下回り、スモークの排出の悪化が懸念される。   By the way, in the engine, since the amount of oxygen-enriched air flowing out from the oxygen separation membrane depends on the differential pressure inside and outside the membrane, high supercharging is synonymous with high EGR. However, if excessive supercharging is promoted, the target intake oxygen concentration is below the target, and there is a concern that smoke emissions will deteriorate.

そこで、本発明はかかる事情を考慮してなされたものであり、酸素分離膜を用いてエンジン本体からのNOx排出量を抑制できると共に吸気酸素濃度の過度の低下を抑制できる内燃機関を提供することを目的とする。   Therefore, the present invention has been made in view of such circumstances, and provides an internal combustion engine that can suppress the NOx emission amount from the engine body using an oxygen separation membrane and suppress an excessive decrease in the intake oxygen concentration. With the goal.

前記目的を達成するために、本発明は、吸気が流れる吸気通路に設けられ、吸気に含まれる酸素の一部を酸素分離膜を透過させて前記吸気通路の外側に取り出して吸気を低酸素化する酸素分離装置と、該酸素分離装置により取り出された酸素を該酸素分離装置よりも上流の吸気通路に導入するか又は大気に放出するための切替弁と、前記酸素分離装置よりも下流の吸気通路に設けられ、吸気中の酸素濃度を検出する酸素濃度センサと、該酸素濃度センサにより検出された吸気中の酸素濃度が所定値以上のときは前記切替弁を大気放出側に開き、所定値未満のときは前記切替弁を吸気通路導入側に開くように制御する制御装置とを備えたことを特徴とする。   In order to achieve the above object, the present invention is provided in an intake passage through which intake air flows, and a part of oxygen contained in intake air passes through an oxygen separation membrane and is taken out of the intake passage to reduce the intake oxygen. An oxygen separation device, a switching valve for introducing oxygen taken out by the oxygen separation device into an intake passage upstream of the oxygen separation device or releasing it into the atmosphere, and intake air downstream of the oxygen separation device An oxygen concentration sensor provided in the passage for detecting the oxygen concentration in the intake air, and when the oxygen concentration in the intake air detected by the oxygen concentration sensor is greater than or equal to a predetermined value, the switching valve is opened to the atmospheric discharge side, and the predetermined value And a control device that controls the switching valve to open to the intake passage introduction side when less.

前記酸素分離装置は、前記吸気通路の一部を前記酸素分離膜で形成した酸素分離管路と、該酸素分離管路を収容するように設けられ、該酸素分離管路を介して分離された酸素を取り出すためのケーシングとを備えたことが好ましい。   The oxygen separation device is provided so as to accommodate an oxygen separation pipe having a part of the intake passage formed of the oxygen separation membrane and the oxygen separation pipe, and is separated through the oxygen separation pipe. It is preferable to include a casing for taking out oxygen.

排気ガスの一部を吸気側に還流するためのEGR通路と、該EGR通路に設けられたEGR弁と、排気ガスにより駆動されるタービンおよび吸気を過給するコンプレッサを有する過給機とを備え、前記酸素分装置は前記コンプレッサよりも下流側の吸気通路に設けられ、前記制御装置は、前記酸素濃度センサにより検出された吸気中の酸素濃度が所定値以上のときは前記切替弁を大気放出側に開くと共に前記EGR弁を開き、所定値を下回るときは前記切替弁を吸気通路導入側に開くと共に前記EGR弁を閉じるように制御することが好ましい。   An EGR passage for returning a part of the exhaust gas to the intake side, an EGR valve provided in the EGR passage, a turbine driven by the exhaust gas, and a supercharger having a compressor for supercharging the intake air The oxygen content device is provided in an intake passage downstream of the compressor, and the control device releases the switching valve to the atmosphere when the oxygen concentration in the intake air detected by the oxygen concentration sensor is equal to or higher than a predetermined value. It is preferable that the EGR valve is opened while the valve is opened to the side, and when the value falls below a predetermined value, the switching valve is opened to the intake passage introduction side and the EGR valve is closed.

本発明によれば、酸素分離膜を用いてエンジン本体からのNOx排出量を抑制できると共に吸気酸素濃度の過度の低下を抑制できる。   According to the present invention, it is possible to suppress the NOx emission amount from the engine body using the oxygen separation membrane and to suppress an excessive decrease in the intake oxygen concentration.

本発明の実施形態に係る内燃機関を概略的に示す図である。1 is a diagram schematically showing an internal combustion engine according to an embodiment of the present invention. 酸素分離管路を示す部分斜視図である。It is a fragmentary perspective view which shows an oxygen separation pipeline. 制御装置による制御方法を示すフローチャートである。It is a flowchart which shows the control method by a control apparatus. 酸素分離膜通過後のO2濃度と酸素富化空気還流割合の関係を示すグラフである。It is a graph showing the O 2 concentration and the oxygen-enriched air reflux ratio relationship of the oxygen separation membrane after passing.

以下に、本発明を実施するための形態を添付図面に基いて詳述する。   EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is explained in full detail based on an accompanying drawing.

図1に、本発明の実施形態に係る内燃機関(エンジン)を示す。本実施形態のエンジン1は、自動車用の多気筒の圧縮着火式内燃機関、即ちディーゼルエンジンである。エンジン1は、複数のシリンダ、ピストン、シリンダブロックおよびクランクシャフト等を含むエンジン本体2を有し、このエンジン本体2には吸気マニホールド3および排気マニホールド4が取り付けられている。吸気マニホールド3は、吸気が流れる吸気通路5の下流端部を形成する。同様に排気マニホールド4は、排気ガスが流れる排気通路6の上流端部を形成する。図1において、吸気の流れを白矢印で示し、排気の流れを黒矢印で示す。   FIG. 1 shows an internal combustion engine (engine) according to an embodiment of the present invention. The engine 1 of this embodiment is a multi-cylinder compression ignition type internal combustion engine for automobiles, that is, a diesel engine. The engine 1 has an engine body 2 including a plurality of cylinders, pistons, cylinder blocks, crankshafts, and the like, and an intake manifold 3 and an exhaust manifold 4 are attached to the engine body 2. The intake manifold 3 forms a downstream end portion of an intake passage 5 through which intake air flows. Similarly, the exhaust manifold 4 forms an upstream end portion of an exhaust passage 6 through which exhaust gas flows. In FIG. 1, the flow of intake air is indicated by white arrows, and the flow of exhaust gas is indicated by black arrows.

前記エンジン1は、吸気を過給するための過給機7を備えている。この過給機7は、排気通路6に設けられて排気ガスにより駆動されるタービン8と、吸気通路5に設けられてタービン8により駆動され、吸気を過給するコンプレッサ9とを有する。吸気通路5におけるコンプレッサ9の下流側には、コンプレッサ9により過給された吸気を冷却するインタークーラ10が設けられている。   The engine 1 includes a supercharger 7 for supercharging intake air. The supercharger 7 includes a turbine 8 provided in the exhaust passage 6 and driven by exhaust gas, and a compressor 9 provided in the intake passage 5 and driven by the turbine 8 to supercharge intake air. An intercooler 10 that cools the intake air supercharged by the compressor 9 is provided downstream of the compressor 9 in the intake passage 5.

一方、エンジン本体2には、排気ガスの一部すなわちEGRガスを吸気側に還流するためのEGR装置11が設けられている。このEGR装置11は、排気通路6内(特に排気マニホールド4内)の排気ガスの一部を吸気通路5内(特に吸気マニホールド3内)に還流させるためのEGR通路12と、このEGR通路12を流れるEGRガスを冷却するEGRクーラ13と、EGR通路12の下流側に設けられ、EGRガスの流量を調節するEGR弁14とを備える。EGRガスの流れを破線矢印で図中に示す。EGRクーラ13は、エンジン本体2の冷却水を用いてEGRガスの冷却を行うものであり、水冷式である。   On the other hand, the engine body 2 is provided with an EGR device 11 for returning a part of the exhaust gas, that is, EGR gas to the intake side. The EGR device 11 includes an EGR passage 12 for returning a part of exhaust gas in the exhaust passage 6 (particularly in the exhaust manifold 4) to the intake passage 5 (particularly in the intake manifold 3), and the EGR passage 12 through the EGR passage 12. An EGR cooler 13 that cools the flowing EGR gas, and an EGR valve 14 that is provided on the downstream side of the EGR passage 12 and adjusts the flow rate of the EGR gas are provided. The flow of EGR gas is indicated in the figure by broken line arrows. The EGR cooler 13 cools the EGR gas using the cooling water of the engine body 2 and is water-cooled.

特に、本実施形態のエンジン1では、吸気通路5の一部を酸素分離膜Mで形成し、吸気通路5内の吸気に含まれる酸素O2の一部を酸素分離膜Mを透過させて吸気通路5の外側に取り出して吸気を低酸素化する酸素分離装置15と、該酸素分離装置15により取り出された酸素を該酸素分離装置15よりも上流の吸気通路5に導入するか又は大気に放出するための3方電磁弁からなる切替弁19と、前記酸素分離装置15よりも下流の吸気通路5例えば吸気マニホールド3に設けられ、吸気中の酸素濃度を検出する酸素濃度センサ20と、該酸素濃度センサ20により検出された吸気中の酸素濃度が所定値C以上のときは前記切替弁19を大気放出側(好ましくは大気放出通路)21に開き、所定値C未満のときは前記切替弁19を吸気通路導入側(好ましくはコンプレッサ9の上流側の新気通路)5aに開くように制御する制御装置(ECU)22とを備えている。 In particular, in the engine 1 of the present embodiment, a part of the intake passage 5 is formed by the oxygen separation membrane M, and a portion of the oxygen O 2 contained in the intake air in the intake passage 5 is permeated through the oxygen separation membrane M to take in the air. An oxygen separator 15 that takes out the outside of the passage 5 to reduce the intake oxygen, and introduces oxygen extracted by the oxygen separator 15 into the intake passage 5 upstream of the oxygen separator 15 or releases it to the atmosphere. A switching valve 19 comprising a three-way solenoid valve, an oxygen concentration sensor 20 provided in the intake passage 5 downstream of the oxygen separation device 15, for example, the intake manifold 3, for detecting the oxygen concentration in the intake air, and the oxygen When the oxygen concentration in the intake air detected by the concentration sensor 20 is equal to or higher than the predetermined value C, the switching valve 19 is opened to the atmospheric discharge side (preferably the atmospheric discharge passage) 21, and when it is lower than the predetermined value C, the switching valve 19 is opened. The intake passage Entry side (preferably fresh air passage upstream of the compressor 9) and a control unit (ECU) 22 for controlling to open 5a.

この点について詳細に述べると、吸気通路5におけるインタークーラ10の下流側で且つ吸気マニホールド3の上流側には、吸気通路5の一部をなす酸素分離管路16を有する酸素分離装置15が設けられている。この酸素分離装置15は、空気通路の一部を酸素分離膜Mで形成した酸素分離管路16と、この酸素分離管路16を収容するよう設けられ、酸素分離管路16を介して分離された酸素を取り出すためのケーシング17とを備えている。   This point will be described in detail. An oxygen separation device 15 having an oxygen separation pipe 16 that forms part of the intake passage 5 is provided on the intake passage 5 downstream of the intercooler 10 and upstream of the intake manifold 3. It has been. This oxygen separation device 15 is provided so as to accommodate an oxygen separation conduit 16 in which a part of an air passage is formed by an oxygen separation membrane M, and this oxygen separation conduit 16, and is separated via the oxygen separation conduit 16. And a casing 17 for taking out oxygen.

図2は、酸素分離管路16(管壁)の長手方向の中間部が、部分的に、管状の酸素分離膜Mで形成されている例を示している。ここで、酸素分離管路16のうちどの部分をどのように酸素分離膜Mで形成するかについては、特に限定はない。酸素分離管路16の全体を酸素分離膜Mで形成してもよい。図2には円筒状の酸素分離管路16および酸素分離膜Mを示すが、これらの形状についても特に限定はない。また、図1には酸素分離管路16はU字状に形成されているが、直線状であってもよい。   FIG. 2 shows an example in which the intermediate portion in the longitudinal direction of the oxygen separation conduit 16 (tube wall) is partially formed of a tubular oxygen separation membrane M. Here, there is no particular limitation as to which part of the oxygen separation pipe 16 is formed by the oxygen separation membrane M. The entire oxygen separation conduit 16 may be formed of the oxygen separation membrane M. Although FIG. 2 shows the cylindrical oxygen separation pipe 16 and the oxygen separation membrane M, there is no particular limitation on these shapes. In FIG. 1, the oxygen separation pipe 16 is formed in a U shape, but it may be linear.

酸素分離膜Mは、その内表面を酸素分離管路16の内部に露出させており、その外表面をケーシング17内に露出させている。そして透過させた酸素がそのまま大気に放出されることなくケーシング17内に一旦収容されるようになっている。前記ケーシング17には内部に溜まった酸素を排出するための排出管18が設けられ、この排出管18の端部が切替弁19を介して前記吸気通路5の導入側(コンプレッサ9の上流側の新気通路)5aまたは大気に開放された大気放出側(大気放出通路)21に切換可能に接続されている。なお、前記切替弁19は、新気通路5a側又は大気放出通路21側に排出される酸素の流量を調節することも可能である。   The oxygen separation membrane M has its inner surface exposed to the inside of the oxygen separation conduit 16 and its outer surface exposed to the casing 17. The permeated oxygen is once accommodated in the casing 17 without being released to the atmosphere as it is. The casing 17 is provided with a discharge pipe 18 for discharging oxygen accumulated therein, and an end of the discharge pipe 18 is connected to the introduction side of the intake passage 5 (on the upstream side of the compressor 9) via a switching valve 19. A fresh air passage) 5a or an atmospheric discharge side (atmospheric discharge passage) 21 opened to the atmosphere is switchably connected. The switching valve 19 can also adjust the flow rate of oxygen discharged to the fresh air passage 5a side or the atmospheric discharge passage 21 side.

前記酸素分離管路16内に流入する吸気である新気は、大気と同じ酸素濃度を有し、その値は約21%である。この新気が、酸素分離膜Mでできた酸素分離管路16内を流れる過程で、新気に含まれる酸素の一部が選択的に酸素分離膜Mを透過する。なお、酸素以外の窒素N2も酸素分離膜Mを透過するが、酸素の透過速度が窒素の透過速度よりも早いため、あたかも酸素のみが選択的に透過するような状態となる。酸素透過の結果、吸気の酸素濃度は低下し、吸気は低酸素濃度空気となる。他方、酸素分離膜Mの外側表面付近では、透過酸素の混入による酸素富化空気が生成される。低酸素濃度空気は例えば19%の酸素濃度を有し、酸素富化空気は例えば30%の酸素濃度を有する。従って、吸気の酸素濃度は21%から19%に2%減少されることになる。 The fresh air that is the intake air flowing into the oxygen separation pipe 16 has the same oxygen concentration as the atmosphere, and its value is about 21%. In the process in which this fresh air flows through the oxygen separation conduit 16 made of the oxygen separation membrane M, a part of oxygen contained in the fresh air selectively permeates the oxygen separation membrane M. Nitrogen N 2 other than oxygen also permeates the oxygen separation membrane M, but the oxygen permeation rate is faster than the nitrogen permeation rate, so that only oxygen is selectively permeated. As a result of the oxygen permeation, the oxygen concentration of the intake air decreases, and the intake air becomes low oxygen concentration air. On the other hand, in the vicinity of the outer surface of the oxygen separation membrane M, oxygen-enriched air is generated due to mixing of permeated oxygen. Low oxygen concentration air has an oxygen concentration of 19%, for example, and oxygen enriched air has an oxygen concentration of 30%, for example. Therefore, the oxygen concentration in the intake air is reduced by 2% from 21% to 19%.

このように酸素分離膜Mの無い通常のエンジンと比較して、吸気の酸素濃度を低下させることができる。よって、エンジン本体2の燃焼室に吸入される吸気の酸素濃度を低下させることができ、このこと自体によって、すなわちEGRとは別の手法で、エンジン本体2からのNOx排出量を抑制することができる。   Thus, the oxygen concentration of the intake air can be reduced as compared with a normal engine without the oxygen separation membrane M. Therefore, the oxygen concentration of the intake air sucked into the combustion chamber of the engine main body 2 can be reduced, and by this, that is, the NOx emission amount from the engine main body 2 can be suppressed by a method different from EGR. it can.

そして、EGRを併用する場合、特に高負荷領域において、吸気の酸素濃度が低下した分、EGRガス量を減少することができる。よって、大量EGRを行うに際しても、通常のエンジンと比較してEGRクーラ13におけるEGRガスの除熱量を減少し、冷却水温度の上昇ひいてはエンジン全体の熱効率低下を抑制することができる。このように本実施形態は、EGRを補助することができるという利点も有する。   When EGR is used in combination, the amount of EGR gas can be reduced by the amount of reduced oxygen concentration in the intake air, particularly in the high load region. Therefore, even when performing a large amount of EGR, it is possible to reduce the amount of heat removed from the EGR gas in the EGR cooler 13 as compared with a normal engine, and to suppress an increase in the coolant temperature and hence a decrease in the thermal efficiency of the entire engine. Thus, this embodiment also has the advantage that EGR can be assisted.

ところで、エンジン本体2からのNOx排出量を抑制するには、次のような予混合燃焼を実行するのも効果的であり、本実施形態のエンジン1もこの予混合燃焼を実行するように構成することができる。予混合燃焼を実行する場合、燃料の噴射時期は圧縮上死点よりも早期の圧縮行程早期とされ、燃料の噴射終了時から着火までの間の予混合期間に、燃料と空気が十分に混合され、希薄・均一化される。そして、この混合気は、燃料の噴射終了後、ある程度の期間を経て着火する。このため、局所的な燃焼温度が下がり、NOx排出量が低減する。   By the way, in order to suppress the NOx emission amount from the engine body 2, it is also effective to execute the following premixed combustion, and the engine 1 of the present embodiment is also configured to execute this premixed combustion. can do. When performing premixed combustion, the fuel injection timing is set to an earlier compression stroke than the compression top dead center, and the fuel and air are sufficiently mixed during the premixing period from the end of fuel injection to ignition. Is diluted and homogenized. The air-fuel mixture is ignited after a certain period of time after the fuel injection is completed. For this reason, local combustion temperature falls and NOx emission amount reduces.

しかし、予混合燃焼は中高負荷領域での適用が困難であり、中高負荷領域でNOx排出量を抑制しようとした場合、EGRに頼らざるを得ないのが現状である。本実施形態では、こうした予混合燃焼が困難な運転領域でEGRを行う場合であっても、吸気の酸素濃度を低下させることでEGRを補助することができる。   However, premixed combustion is difficult to apply in the medium and high load region, and when trying to suppress the NOx emission amount in the medium and high load region, it is currently necessary to rely on EGR. In the present embodiment, even when EGR is performed in such an operation region where premixed combustion is difficult, EGR can be assisted by reducing the oxygen concentration of the intake air.

前記酸素分離膜Mは、高分子材料からなる膜であり、酸素と窒素の選択性および透過速度の差を利用して吸気の酸素濃度を低下させる。高分子材料はその種類に応じて気体選択透過性に違いがある。酸素分離膜Mとしては、気体選択透過性(PO2/PN2)の高い高分子材料を含むのが好ましい。酸素分離膜Mは、ポリイミド、ニトロセルロース、ポリ酢酸ビニル、ポリエーテルスルホン、ポリスルホンのうちの少なくとも一つを含むのが好ましい。 The oxygen separation membrane M is a membrane made of a polymer material, and lowers the oxygen concentration of the intake air by utilizing the difference between oxygen and nitrogen selectivity and permeation rate. The polymer material has a difference in gas permselectivity depending on its type. The oxygen separation membrane M preferably includes a polymer material having a high gas selective permeability (PO 2 / PN 2 ). The oxygen separation membrane M preferably contains at least one of polyimide, nitrocellulose, polyvinyl acetate, polyethersulfone, and polysulfone.

この酸素分離膜Mにおいては、高分子材料における酸素/窒素の気体選択透過性、および膜内外の差圧により、酸素が膜表面に染み出るような構造となる。このため、気体分離による圧力損失は、例えば公知の中空糸フィルタと比較して1/10程度に抑制可能と考えられる。   The oxygen separation membrane M has a structure in which oxygen oozes out to the membrane surface due to the selective permeability of oxygen / nitrogen in the polymer material and the differential pressure inside and outside the membrane. For this reason, it is thought that the pressure loss by gas separation can be suppressed to about 1/10 compared with, for example, a known hollow fiber filter.

前記式(1)から分かるように、酸素分離膜Mによる気体分離性能を確保するためには、膜内外に圧力差がなければならない。この点、本実施形態では、酸素分離膜Mを有する酸素分離管路16がコンプレッサ9の下流側、特にインタークーラ10の下流側に位置されている。また、前記酸素分離管路16を収容したケーシング17の排気通路18が切替弁19を介してコンプレッサ9の吸気通路5a側又は大気開放通路21側に開放されるため、コンプレッサ9で大気圧よりも高圧とされた吸気を酸素分離膜Mの内側に供給することができ、膜内外の圧力差を容易かつ確実に得ることができる。   As can be seen from the equation (1), in order to ensure gas separation performance by the oxygen separation membrane M, there must be a pressure difference between the inside and outside of the membrane. In this regard, in the present embodiment, the oxygen separation pipe 16 having the oxygen separation membrane M is located on the downstream side of the compressor 9, particularly on the downstream side of the intercooler 10. In addition, since the exhaust passage 18 of the casing 17 containing the oxygen separation pipe 16 is opened to the intake passage 5a side or the air release passage 21 side of the compressor 9 via the switching valve 19, the compressor 9 is under atmospheric pressure. The high-pressure intake air can be supplied to the inside of the oxygen separation membrane M, and the pressure difference between the inside and outside of the membrane can be obtained easily and reliably.

新気の酸素濃度は過給圧に拘わらず一定である。他方、過給圧の上昇に伴い酸素富化空気の酸素濃度は次第に増大し、低酸素濃度空気の酸素濃度は次第に減少する。これは、酸素分離膜Mの内圧が上昇して膜内外の圧力差が大きくなると、膜中の酸素透過量が増大し、酸素分離性能が向上することを意味する。EGR実行中の場合だと、過給圧の上昇はEGR率の増加と同義となる。過渡運転時(特に急加速時等)にあっては、EGR弁14の応答遅れによりNOxが瞬間的或いはスパイク的に悪化することがあるが、本実施形態によれば過渡運転時の過給圧上昇と同時に酸素透過量を増大し、吸気の酸素濃度をより低減できる。よって、そのようなNOx悪化を抑制することができる。   The fresh oxygen concentration is constant regardless of the supercharging pressure. On the other hand, as the supercharging pressure increases, the oxygen concentration of the oxygen-enriched air gradually increases, and the oxygen concentration of the low oxygen concentration air gradually decreases. This means that when the internal pressure of the oxygen separation membrane M rises and the pressure difference between the inside and outside of the membrane increases, the oxygen permeation amount in the membrane increases and the oxygen separation performance improves. When EGR is being executed, an increase in supercharging pressure is synonymous with an increase in EGR rate. During transient operation (particularly during rapid acceleration, etc.), NOx may deteriorate instantaneously or spiked due to a response delay of the EGR valve 14, but according to the present embodiment, the boost pressure during transient operation is increased. Simultaneously with the increase, the oxygen transmission amount can be increased, and the oxygen concentration in the intake air can be further reduced. Therefore, such NOx deterioration can be suppressed.

ところで、上述の膜内外の差圧とは、各気体分子の分圧差であるといえる。よって、酸素分離膜Mの内外における酸素分圧差が大きいほど、酸素分離膜Mを透過する酸素の流量は多くなり、吸気酸素濃度の低減効果が増大する。従って、吸気酸素濃度の低減効果を増大し、NOx抑制に寄与し得る点で有利である。   By the way, the above-mentioned differential pressure inside and outside the membrane can be said to be a partial pressure difference of each gas molecule. Therefore, as the oxygen partial pressure difference inside and outside the oxygen separation membrane M increases, the flow rate of oxygen that passes through the oxygen separation membrane M increases and the effect of reducing the intake oxygen concentration increases. Therefore, the effect of reducing the intake oxygen concentration is increased, which is advantageous in that it can contribute to NOx suppression.

酸素分離膜Mから排出した酸素により排気ガスの酸素濃度を増大することができる。また、酸素分離装置15は、酸素分離管路16とケーシング16とで構成されるため、構造が簡単でコンパクトになると共に酸素分離を効率的に行うことができる。   The oxygen concentration of the exhaust gas can be increased by the oxygen discharged from the oxygen separation membrane M. Further, since the oxygen separation device 15 is constituted by the oxygen separation conduit 16 and the casing 16, the structure is simple and compact, and oxygen separation can be performed efficiently.

ところで、式(1)によれば、膜面積Sが大きいほど酸素分離膜Mから流出する酸素の流量Fは多くなる。よって、酸素の流出流量を多くしたい場合には酸素分離膜Mの膜面積Sを大きくするのが好ましい。この場合、例えば酸素分離管路16の長手方向両端面を除いた周面部全体を、酸素分離膜Mで形成するのがよい。   By the way, according to the equation (1), the larger the membrane area S, the larger the flow rate F of oxygen flowing out from the oxygen separation membrane M. Therefore, it is preferable to increase the membrane area S of the oxygen separation membrane M when it is desired to increase the oxygen outflow rate. In this case, for example, the entire peripheral surface portion excluding both end surfaces in the longitudinal direction of the oxygen separation conduit 16 may be formed by the oxygen separation membrane M.

また、酸素分離膜Mは、上記実施形態の如く、EGRガスと吸気とが混合する混合部(吸気マニホールド3)よりも上流側の吸気通路5に設けるのが好ましい。混合部よりも下流側に設けると、EGRガスが混入して酸素濃度が低下した吸気からさらに酸素を排出するようになるため、膜内外の大きな酸素分圧差を得るのに不利だからである。   The oxygen separation membrane M is preferably provided in the intake passage 5 upstream of the mixing portion (intake manifold 3) where EGR gas and intake air are mixed, as in the above embodiment. If it is provided on the downstream side of the mixing portion, oxygen is further discharged from the intake air in which the EGR gas is mixed and the oxygen concentration is lowered, which is disadvantageous for obtaining a large difference in oxygen partial pressure inside and outside the membrane.

以上述べたように、本実施形態によれば、酸素分離膜Mによって吸気中の酸素を吸気通路5から排出し、吸気の酸素濃度を低下させることができる。よって、EGRとは別の手法で、エンジン本体からのNOx排出量を抑制することができる。   As described above, according to the present embodiment, oxygen in the intake air can be discharged from the intake passage 5 by the oxygen separation membrane M, and the oxygen concentration of the intake air can be reduced. Therefore, the NOx emission amount from the engine body can be suppressed by a method different from EGR.

また、EGRを併用する場合にあっては、EGRを補助することができ、特に高負荷領域においてEGRガス量を減少することができる。よって、EGRクーラ13におけるEGRガスの除熱量を減少し、エンジン全体の熱効率の低下を抑制することができる。   Further, when EGR is used in combination, EGR can be assisted, and the amount of EGR gas can be reduced particularly in a high load region. Therefore, the amount of heat removed from the EGR gas in the EGR cooler 13 can be reduced, and a decrease in the thermal efficiency of the entire engine can be suppressed.

さらに、酸素分離膜Mの外側に酸素を収容するケーシング17を設け、このケーシング17の排出通路18を切替弁19を介して新気通路5a側又は大気放出通路21側に接続するため、酸素分離膜Mの内外の酸素分圧差を増大して酸素分離効果を向上することができる。よって、NOx排出量の抑制等に一層効果的である。   Further, a casing 17 for storing oxygen is provided outside the oxygen separation membrane M, and the discharge passage 18 of the casing 17 is connected to the fresh air passage 5a side or the atmospheric discharge passage 21 side via the switching valve 19, so that oxygen separation is performed. The oxygen separation effect can be improved by increasing the oxygen partial pressure difference between the inside and outside of the membrane M. Therefore, it is more effective for suppressing NOx emissions.

特に、本制御においては、図3に示すように、吸気マニホールド3に設けられた酸素濃度センサ20により酸素濃度を検出し(S1)、その検出値を目標酸素濃度Cと比較し、検出値が目標酸素濃度C以上である場合には、切替弁19を大気開放通路21側(新気通路5a側は全閉)にすると共にEGR弁14を開き(S3)、酸素分離膜MとEGRの併用により目標酸素濃度Cを達成することができる。また、検出値が目標酸素濃度Cよりも低い場合には、EGR弁14を閉じる共に切替弁19を新気通路5a側に開き(S4)、その開度を調節することにより目標酸素濃度Cを達成することができる。酸素富化空気を過給機7前の新気通路5aへ戻した際の酸素分離膜M通過後の吸気酸素濃度の変化の一例は図4に示す通りである。   In particular, in this control, as shown in FIG. 3, the oxygen concentration is detected by the oxygen concentration sensor 20 provided in the intake manifold 3 (S1), and the detected value is compared with the target oxygen concentration C. When the target oxygen concentration C is equal to or higher than the target oxygen concentration C, the switching valve 19 is set to the atmosphere opening passage 21 side (the fresh air passage 5a side is fully closed) and the EGR valve 14 is opened (S3), and the oxygen separation membrane M and EGR are used together. Thus, the target oxygen concentration C can be achieved. When the detected value is lower than the target oxygen concentration C, the EGR valve 14 is closed and the switching valve 19 is opened to the fresh air passage 5a side (S4), and the target oxygen concentration C is set by adjusting the opening degree. Can be achieved. An example of the change in the intake oxygen concentration after passing through the oxygen separation membrane M when the oxygen-enriched air is returned to the fresh air passage 5a before the supercharger 7 is as shown in FIG.

本実施形態によれば、過度の低酸素濃度化を回避でき、運転領域全域で目標酸素濃度を達成することができ、スモーク及びNOxの排出の低減が可能となる。   According to this embodiment, excessively low oxygen concentration can be avoided, the target oxygen concentration can be achieved over the entire operation region, and smoke and NOx emissions can be reduced.

以上、本発明の実施形態を詳細に述べたが、本発明は他の実施形態を採用することも可能である。例えば、本発明は、EGR装置を備えていない内燃機関にも適用可能である。   As mentioned above, although embodiment of this invention was described in detail, this invention can also employ | adopt other embodiment. For example, the present invention is also applicable to an internal combustion engine that does not include an EGR device.

1 エンジン(内燃機関)
5 吸気通路
5a 新気通路(吸気通路導入側)
6 排気通路
7 過給機
8 タービン
9 コンプレッサ
11 EGR装置
14 EGR弁
15 酸素分離装置
16 酸素分離管路
17 ケーシング
M 酸素分離膜
19 切替弁
20 酸素濃度センサ
21 大気放出通路(大気放出側)
22 制御装置
1 engine (internal combustion engine)
5 Intake passage 5a Fresh air passage (intake passage introduction side)
6 Exhaust passage 7 Supercharger 8 Turbine 9 Compressor 11 EGR device 14 EGR valve 15 Oxygen separation device 16 Oxygen separation pipe 17 Casing M Oxygen separation membrane 19 Switching valve 20 Oxygen concentration sensor 21 Atmospheric discharge passage (atmospheric discharge side)
22 Control device

Claims (3)

吸気が流れる吸気通路に設けられ、吸気に含まれる酸素の一部を酸素分離膜を透過させて前記吸気通路の外側に取り出して吸気を低酸素化する酸素分離装置と、該酸素分離装置により取り出された酸素を該酸素分離装置よりも上流の吸気通路に導入するか又は大気に放出するための切替弁と、前記酸素分離装置よりも下流の吸気通路に設けられ、吸気中の酸素濃度を検出する酸素濃度センサと、該酸素濃度センサにより検出された吸気中の酸素濃度が所定値以上のときは前記切替弁を大気放出側に開き、所定値未満のときは前記切替弁を吸気通路導入側に開くように制御する制御装置とを備えたことを特徴とする内燃機関。   An oxygen separation device provided in an intake passage through which intake air flows, a part of oxygen contained in the intake air passes through an oxygen separation membrane and is taken out of the intake passage to reduce the intake air, and the oxygen separation device extracts the oxygen. A switch valve for introducing the released oxygen into the intake passage upstream of the oxygen separation device or releasing it into the atmosphere, and the intake passage downstream of the oxygen separation device, and detecting the oxygen concentration in the intake air And when the oxygen concentration in the intake air detected by the oxygen concentration sensor is equal to or higher than a predetermined value, the switching valve is opened to the atmosphere release side, and when the oxygen concentration is lower than the predetermined value, the switching valve is opened to the intake passage introduction side. An internal combustion engine comprising: a control device that controls to open to 前記酸素分離装置は、前記吸気通路の一部を前記酸素分離膜で形成した酸素分離管路と、該酸素分離管路を収容するように設けられ、該酸素分離管路を介して分離された酸素を取り出すためのケーシングとを備えたことを特徴とする請求項1に記載の内燃機関。   The oxygen separation device is provided so as to accommodate an oxygen separation pipe having a part of the intake passage formed of the oxygen separation membrane and the oxygen separation pipe, and is separated through the oxygen separation pipe. The internal combustion engine according to claim 1, further comprising a casing for taking out oxygen. 排気ガスの一部を吸気側に還流するためのEGR通路と、該EGR通路に設けられたEGR弁と、排気ガスにより駆動されるタービンおよび吸気を過給するコンプレッサを有する過給機とを備え、前記酸素分離装置は前記コンプレッサよりも下流側の吸気通路に設けられ、前記制御装置は、前記酸素濃度センサにより検出された吸気中の酸素濃度が所定値以上のときは前記切替弁を大気放出側に開くと共に前記EGR弁を開き、所定値未満のときは前記切替弁を吸気通路導入側に開くと共に前記EGR弁を閉じるように制御することを特徴とする請求項1又は2に記載の内燃機関。   An EGR passage for returning a part of the exhaust gas to the intake side, an EGR valve provided in the EGR passage, a turbine driven by the exhaust gas, and a supercharger having a compressor for supercharging the intake air The oxygen separation device is provided in an intake passage downstream of the compressor, and the control device releases the switching valve to the atmosphere when the oxygen concentration in the intake air detected by the oxygen concentration sensor is equal to or higher than a predetermined value. 3. The internal combustion engine according to claim 1, wherein the EGR valve is controlled to open to the side and open the EGR valve, and when less than a predetermined value, the switching valve is controlled to open to the intake passage introduction side and the EGR valve is closed. organ.
JP2010048132A 2010-03-04 2010-03-04 Internal combustion engine Expired - Fee Related JP5447009B2 (en)

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