JP5224265B2

JP5224265B2 - Engine exhaust purification system

Info

Publication number: JP5224265B2
Application number: JP2007280298A
Authority: JP
Inventors: 康子鈴木; 博昭藤田; 智平沼; 真一斎藤; 琢也北清; 周一羽田
Original assignee: Mitsubishi Fuso Truck and Bus Corp
Current assignee: Mitsubishi Fuso Truck and Bus Corp
Priority date: 2007-10-29
Filing date: 2007-10-29
Publication date: 2013-07-03
Anticipated expiration: 2027-10-29
Also published as: JP2009108724A

Description

本発明はエンジンの排気浄化装置に係り、詳しくは排気通路を流通する排ガスに還元剤を噴射してベンチュリ状のミキシング室を流通させて撹拌しながら下流側の後処理装置に供給するエンジンの排気浄化装置に関するものである。 TECHNICAL FIELD The present invention relates to an engine exhaust purification device, and more specifically, engine exhaust supplied to a downstream aftertreatment device while injecting a reducing agent into exhaust gas flowing through an exhaust passage and flowing through a venturi-like mixing chamber and stirring. The present invention relates to a purification device.

近年の排ガス規制の強化に対応すべく、エンジンの排気通路には排気浄化装置を構成する様々な後処理装置が搭載されている。これらの後処理装置の中には還元剤の供給により浄化作用を発揮するものがあり、例えば選択還元型ＮＯx触媒は、アンモニア（ＮＨ_３）を還元剤として排ガス中のＮＯxを選択還元することから、アンモニアの生成のために尿素水溶液の供給を要し、吸蔵型ＮＯxは、吸蔵したＮＯxを放出還元するために未燃燃料等の還元剤の供給を要する。そして、これらの後処理装置の浄化作用を最大限に発揮させるには、後処理装置の各部位に均等に還元剤を供給することが必須条件であり、排ガス中に還元剤を均一に拡散させるために排気通路にベンチュリ状のミキシング室を設けた対策が提案されている（例えば、特許文献１参照）。 In order to respond to the recent tightening of exhaust gas regulations, various aftertreatment devices constituting an exhaust purification device are mounted in the exhaust passage of the engine. Some of these post-treatment devices exhibit a purification action by supplying a reducing agent. For example, a selective reduction type NOx catalyst selectively reduces NOx in exhaust gas using ammonia (NH ₃ ) as a reducing agent. In order to generate ammonia, it is necessary to supply an aqueous urea solution, and occlusion type NOx requires supply of a reducing agent such as unburned fuel in order to release and reduce the occluded NOx. In order to maximize the purifying effect of these post-treatment devices, it is an essential condition that the reducing agent is uniformly supplied to each part of the post-treatment device, and the reducing agent is uniformly diffused in the exhaust gas. For this reason, a countermeasure has been proposed in which a venturi-like mixing chamber is provided in the exhaust passage (see, for example, Patent Document 1).

特許文献１の技術は選択還元型ＮＯx触媒を対象としたものであるが、ＮＯx触媒の上流側の排気通路にミキシング室を形成し、そのミキシング室内の上流に設置した噴射ノズルから尿素水溶液を噴射して、尿素水溶液を含んだ排ガスをミキシング室により一旦絞ることにより排ガスへの尿素水溶液の拡散を促進している。
特開２００５−１０５９１４号公報 The technique of Patent Document 1 is directed to a selective reduction type NOx catalyst, but a mixing chamber is formed in the exhaust passage upstream of the NOx catalyst, and an aqueous urea solution is injected from an injection nozzle installed upstream in the mixing chamber. Then, once the exhaust gas containing the urea aqueous solution is squeezed by the mixing chamber, the diffusion of the urea aqueous solution into the exhaust gas is promoted.
JP 2005-105914 A

しかしながら、上記特許文献１の技術では、ミキシング室の最小径に相当する絞り部からその直下流側の拡大部にかけて尿素水溶液が結晶化して堆積するという問題があった。
図７は特許文献１に記載された排気浄化装置のミキシング室の詳細を示す部分拡大断面図であるが、ミキシング室１３は、下流側に向けてコーン状に縮径する縮径部１３ａ、縮径部１３ａから最小径を保って下流側に連続する絞り部１３ｂ、及び絞り部１３ｂから下流側に向けてコーン状に拡径してＮＯx触媒１６を収容するケーシング１２に接続される拡径部１３ｃから構成されている。 However, the technique disclosed in Patent Document 1 has a problem that the urea aqueous solution crystallizes and deposits from the throttle portion corresponding to the minimum diameter of the mixing chamber to the enlarged portion on the downstream side.
FIG. 7 is a partially enlarged cross-sectional view showing details of the mixing chamber of the exhaust gas purification device described in Patent Document 1. The mixing chamber 13 includes a reduced diameter portion 13a that is reduced in diameter toward the downstream side in a cone shape. A narrowed portion 13b that keeps the minimum diameter from the diameter portion 13a and continues downstream, and a diameter-expanded portion that expands in a cone shape toward the downstream side from the narrowed portion 13b and is connected to the casing 12 that houses the NOx catalyst 16. 13c.

ミキシング室１３内の中心部では排ガスがほぼ直線状に移送されるのに対し、ミキシング室１３内の外周部では縮径部１３ａ、絞り部１３ｂ及び拡径部１３ｃの内壁に沿いながら排ガスが移送される。外周部において、排ガスは自己の慣性力で内壁の形状変化に倣って瞬時に移送方向を変化できないことから、縮径部１３ａの内壁に沿って絞り部１３ｂに到達したときに内壁から剥離して渦や淀みを生じ、同じく絞り部１３ｂの内壁に沿って拡径部１３ｃに到達したときに内壁から剥離して渦や淀みを生じ、その後に排ガスは拡径部１３ｃの内壁に再付着するものの、ケーシング１２の入口で渦や淀みを生じて再び内壁から剥離する。 Exhaust gas is transferred substantially linearly in the central portion of the mixing chamber 13, whereas the exhaust gas is transferred along the inner walls of the reduced diameter portion 13 a, the throttle portion 13 b, and the enlarged diameter portion 13 c in the outer peripheral portion of the mixing chamber 13. Is done. At the outer periphery, the exhaust gas cannot change the transfer direction instantaneously following the change in the shape of the inner wall due to its own inertial force. Therefore, when the exhaust gas reaches the throttle portion 13b along the inner wall of the reduced diameter portion 13a, it peels off from the inner wall. Although vortices and stagnation occur, when the diameter reaches the enlarged diameter portion 13c along the inner wall of the narrowed portion 13b, the eddy and stagnation occur after peeling off from the inner wall, and then the exhaust gas reattaches to the inner wall of the enlarged diameter portion 13c. Then, a vortex or a stagnation is generated at the inlet of the casing 12 and peeled off from the inner wall again.

従って、縮径部１３ａと絞り部１３ｂとの境界、絞り部１３ｂと拡径部１３ｃとの境界、及び拡径部１３ｃとケーシング１２との境界には、それぞれ排ガスの剥離域Ａが形成される。このような排ガスの剥離域Ａでは、排ガスに含まれている尿素水溶液がミキシング室１３の内壁に付着した後に結晶化して堆積するため、次第にミキシング室１３の通路断面積が縮小し、排圧の増大によりエンジン性能が低下してしまうという問題があった。 Accordingly, an exhaust gas separation region A is formed at the boundary between the reduced diameter portion 13a and the throttle portion 13b, the boundary between the throttle portion 13b and the enlarged diameter portion 13c, and the boundary between the enlarged diameter portion 13c and the casing 12, respectively. . In such a flue gas separation zone A, the urea aqueous solution contained in the flue gas crystallizes and deposits after adhering to the inner wall of the mixing chamber 13, so that the passage cross-sectional area of the mixing chamber 13 gradually decreases and the exhaust pressure is reduced. There has been a problem that the engine performance deteriorates due to the increase.

また、ミキシング室１３の内壁への尿素水溶液の堆積分だけ実際のＮＯx触媒へのアンモニア供給量が低下することから、見かけ上のＮＯx触媒の浄化性能が低下してしまう問題もあり、さらに尿素水溶液がＮＯx触媒に付着して結晶化する際にＮＯx触媒が破壊される場合もあり、これらの点で改良の余地があった。
本発明はこのような問題点を解決するためになされたもので、その目的とするところは、ベンチュリ状をなすミキシング室の内壁への還元剤の堆積を抑制し、もって、排圧増大に起因するエンジン性能の低下を未然に防止できると共に、堆積による無駄な還元剤の消費を抑制して後処理装置に最大限の浄化性能を発揮させることができるエンジンの排気浄化装置を提供することにある。 In addition, since the actual amount of ammonia supplied to the NOx catalyst is reduced by the amount of urea aqueous solution deposited on the inner wall of the mixing chamber 13, there is also a problem that the apparent purification performance of the NOx catalyst is reduced. When the NOx catalyst is crystallized by adhering to the NOx catalyst, the NOx catalyst may be destroyed, and there is room for improvement in these respects.
The present invention has been made to solve such a problem, and the object of the present invention is to suppress the deposition of the reducing agent on the inner wall of the Venturi-like mixing chamber, thereby increasing the exhaust pressure. It is to provide an engine exhaust gas purification device that can prevent the engine performance from being deteriorated and suppress the use of unnecessary reducing agent due to accumulation and allow the post-treatment device to exhibit the maximum purification performance. .

上記目的を達成するため、請求項１の発明は、エンジンの排気通路に配設されて排気流通方向にほぼ同一径をなすケーシング内に収容され、還元剤の供給により上記エンジンの排ガスを浄化する後処理装置と、排気通路の後処理装置の上流側に設けられ、下流側に縮径する縮径部から最小径の絞り部を経て下流側に拡径する拡径部へと連続するベンチュリ状をなし、拡径部をケーシングの上流端に接続されたミキシング室と、ミキシング室内に還元剤を噴射する還元剤噴射手段とを備えたエンジンの排気浄化装置において、拡径部とケーシングとの境界を、排気流通方向に沿った所定曲率半径の断面形状に形成し、ケーシングの半径をＲ、拡径部とケーシングとの境界の曲率半径をｒ3としたときに、0.05≦ｒ3／Ｒ≦1.0を満足するものである。 In order to achieve the above object, the invention of claim 1 is housed in a casing that is disposed in the exhaust passage of the engine and has substantially the same diameter in the exhaust circulation direction, and purifies the exhaust gas of the engine by supplying a reducing agent. Venturi shape that is provided on the upstream side of the aftertreatment device and the exhaust passage aftertreatment device, and continues from the reduced diameter portion that is reduced in diameter downstream to the enlarged diameter portion that is increased in diameter downstream through the narrowed-down portion. In an exhaust emission control device for an engine, comprising a mixing chamber having an enlarged diameter portion connected to the upstream end of the casing, and a reducing agent injection means for injecting a reducing agent into the mixing chamber, the boundary between the enlarged diameter portion and the casing When the boundary is formed in a cross-sectional shape having a predetermined radius of curvature along the exhaust flow direction, the radius of the casing is R, and the radius of curvature of the boundary between the expanded portion and the casing is r3, 0.05≤r3 / R≤1.0. Is satisfied .

従って、縮径部、絞り部及び拡径部で構成されてケーシングの上流端に接続されたミキシング室内は、縮径部と絞り部との境界、絞り部と拡径部との境界、及び拡径部とケーシングとの境界において排気流通方向への断面形状が急激に変化するが、拡径部とケーシングとの境界は排気流通方向に沿って所定曲率半径の断面形状に形成されているため、ミキシング室内の断面変化が緩やかとなる。 Thus, reduced diameter portion, the throttle portion and consists of the enlarged diameter portion within chamber mixing connected to the upstream end of the casing, a boundary between the reduced diameter portion and the diaphragm portion, the boundary between the throttle portion and the enlarged diameter portion, and cone part and a cross-sectional shape of the Oite exhaust flow direction at the boundary between the casing changes abruptly, but the boundary between the enlarged diameter portion and the casing are formed in a radial cross-sectional shape predetermined curvature along the exhaust flow direction Therefore, the cross-sectional change in the mixing chamber becomes gradual.

このため、拡径部とケーシングとの境界の箇所において、排ガスはミキシング室の内壁から剥離したり渦や淀みを生じたりすることなく断面形状に倣って移送方向を変更され、排ガスの剥離域の形成が未然に防止され、排ガスに含まれる還元剤の内壁への付着が最小限に抑制される。よって、結晶化した還元剤がミキシング室の内壁に堆積したときの通路断面積の縮小が抑制されると共に、堆積による無駄な還元剤の消費が抑制される。
また、拡径部とケーシングとの境界は、比ｒ3／Ｒが0.05〜1.0の範囲内となる曲率半径ｒ3の断面形状に形成される。図３に示すように、比ｒ3／Ｒが0.05以上のときには、排ガスの剥離状況と相関する絞り部の入口外周の排気流速Ｖが上限値Ｖ0未満となるため排ガスの剥離域の形成が抑制され、一方、比ｒ3／Ｒが1.0以下のときには、幾何学的な矛盾を生じることなくミキシング室を形成可能となり、これによりミキシング室内での排ガスの剥離域の形成が未然に防止される。 Therefore, in the boundary of the portion of the enlarged diameter portion and the casing, the exhaust gas is changed the transport direction following the cross-sectional shape without or cause a vortex or stagnation peeled off from the inner wall of the mixing chamber, separation of the exhaust gas Formation of the zone is prevented in advance, and adhesion of the reducing agent contained in the exhaust gas to the inner wall is minimized. Therefore, the reduction of the cross-sectional area of the passage when the crystallized reducing agent is deposited on the inner wall of the mixing chamber is suppressed, and unnecessary consumption of the reducing agent due to the deposition is suppressed.
The boundary between the enlarged diameter portion and the casing is formed in a cross-sectional shape having a radius of curvature r3 in which the ratio r3 / R is in the range of 0.05 to 1.0. As shown in FIG. 3, when the ratio r3 / R is 0.05 or more, the exhaust flow velocity V on the outer periphery of the inlet of the throttle portion correlating with the state of exhaust gas separation is less than the upper limit value V0, so the formation of the exhaust gas separation region is suppressed. On the other hand, when the ratio r3 / R is 1.0 or less, it is possible to form a mixing chamber without causing a geometric contradiction, thereby preventing the formation of an exhaust gas separation region in the mixing chamber.

請求項２の発明は、請求項１において、拡径部とケーシングとの境界に加えて、絞り部と拡径部との境界が所定曲率半径の断面形状に形成され、絞り部と拡径部との境界の曲率半径を、拡径部とケーシングとの境界の曲率半径より大きくしたものである。
拡径部とケーシングとの境界に比較して絞り部と拡径部との境界では排気流速が高くて排ガスの剥離が発生し易いことから、より剥離を抑制する必要がある絞り部と拡径部との境界の曲率半径を、拡径部とケーシングとの境界の曲率半径より大きくすることにより、剥離域の形成による不具合を効果的に防止可能となる。 The invention according to claim 2, in claim 1, in addition to the boundary between the enlarged diameter portion and the casing, the boundary between the throttle portion and the enlarged diameter portion is formed on the cross-sectional shape of a predetermined curvature radius, the throttle portion and the expansion the boundary radius of curvature of the diameter, is made larger than the radius of curvature of the boundary between the enlarged diameter portion and the casing.
Compared to the boundary between the enlarged diameter part and the casing, the exhaust gas flow rate is higher at the boundary between the throttle part and the enlarged diameter part and the flue gas is more likely to be separated. the boundary curvature radius of the parts, by larger than the radius of curvature of the boundary between the enlarged diameter portion and the casing becomes possible to effectively prevent a problem due to the formation of the peeling zone.

請求項３の発明は、請求項１において、拡径部とケーシングとの境界に加えて、絞り部と拡径部との境界が所定曲率半径の断面形状に形成され、ケーシングの半径をＲ、絞り部と拡径部との境界の曲率半径をｒ2、拡径部とケーシングとの境界の曲率半径をｒ3としたときに、0.07≦ｒ2／Ｒ≦1.0，0.05≦ｒ3／Ｒ≦1.0を満足するものである。 The invention according to claim 3, in claim 1, in addition to the boundary between the enlarged diameter portion and the casing, the boundary between the throttle portion and the enlarged diameter portion is formed on the cross-sectional shape of a predetermined curvature radius, the radius of the casing R, a curvature radius of the boundary between the throttle portion and the enlarged diameter portion r2, the radius of curvature of the boundary between the enlarged diameter portion and the casing when the r3, 0.07 ≦ r2 / R ≦ 1.0,0.05 ≦ r3 / R ≦ 1.0 is satisfied.

従って、絞り部と拡径部との境界は、比ｒ2／Ｒが0.07〜1.0の範囲内となる曲率半径ｒ1，ｒ2の断面形状に形成され、拡径部とケーシングとの境界は、比ｒ3／Ｒが0.05〜1.0の範囲内となる曲率半径ｒ3の断面形状に形成される。図３に示すように、比ｒ2／Ｒが0.07以上のときには、排ガスの剥離状況と相関する絞り部の入口外周の排気流速Ｖが上限値Ｖ0未満となるため排ガスの剥離域の形成が抑制され、比ｒ3／Ｒが0.05以上のときには、排ガスの剥離状況と相関する絞り部の入口外周の排気流速Ｖが上限値Ｖ0未満となるため排ガスの剥離域の形成が抑制され、一方、比ｒ1／Ｒ，ｒ3／Ｒが1.0以下のときには、幾何学的な矛盾を生じることなくミキシング室を形成可能となり、これによりミキシング室内での排ガスの剥離域の形成が未然に防止される。 Therefore, the boundary between the throttle portion and the enlarged diameter portion, the ratio r2 / R is formed in a sectional shape of a radius of curvature r1, r2 comprised in the range of 0.07 to 1.0, the boundary between the enlarged diameter portion and the casing, It is formed in a cross-sectional shape having a radius of curvature r3 in which the ratio r3 / R is in the range of 0.05 to 1.0. As shown in FIG. 3, when the ratio r2 / R is 0.07 or more, the exhaust gas flow velocity V on the outer periphery of the throttle portion correlating with the state of exhaust gas separation is less than the upper limit value V0, so the formation of the exhaust gas separation region is suppressed. When the ratio r3 / R is 0.05 or more, the exhaust gas flow velocity V on the outer periphery of the inlet of the throttle portion, which correlates with the state of exhaust gas separation, is less than the upper limit value V0, so that the formation of the exhaust gas separation region is suppressed, while the ratio r1 / When R and r3 / R are 1.0 or less, a mixing chamber can be formed without causing a geometric contradiction, thereby preventing the formation of an exhaust gas separation region in the mixing chamber.

以上説明したように請求項１の発明のエンジンの排気浄化装置によれば、拡径部とケーシングとの境界を最適な曲率半径ｒ3の断面形状に形成することにより、拡径部とケーシングとの境界での排ガスの剥離域の形成を確実に防止できることから、拡径部とケーシングとの境界の箇所において、ベンチュリ状をなすミキシング室の内壁への還元剤の堆積を抑制し、もって、排圧増大に起因するエンジン性能の低下を未然に防止できると共に、堆積による無駄な還元剤の消費を抑制して後処理装置に最大限の浄化性能を発揮させることができる。
請求項２の発明のエンジンの排気浄化装置によれば、請求項１に加えて、より排ガスが剥離し易い絞り部と拡径部との境界の曲率半径を、拡径部とケーシングとの境界の曲率半径より大きくすることにより、剥離域の形成による不具合を効果的に防止することができる。 As described above, according to the exhaust emission control device for an engine of the first aspect of the present invention, the boundary between the enlarged diameter portion and the casing is formed in a cross-sectional shape having the optimum curvature radius r3, thereby because it can reliably prevent the formation of the peeling zone exhaust gas at the border, in the boundary of the portion of the enlarged diameter portion and the casing, to suppress deposition of the reducing agent to the inner wall of the mixing chamber forming a venturi, with, exhaust A reduction in engine performance due to an increase in pressure can be prevented in advance, and consumption of useless reducing agent due to deposition can be suppressed, and the maximum purification performance can be exerted on the aftertreatment device.
According to the exhaust purification system of an engine according to a second aspect of the invention, in addition to claim 1, further a boundary radius of curvature of the exhaust gas stripping easily narrowed portion and the enlarged diameter portion, the enlarged diameter portion and the casing by larger than the radius of curvature of the boundary, it is possible to effectively prevent problems due to the formation of the peeling zone.

請求項３の発明のエンジンの排気浄化装置によれば、請求項１に加えて、絞り部と拡径部との境界及び拡径部とケーシングとの境界を最適な曲率半径ｒ2，ｒ3の断面形状に形成することにより、それぞれの境界での排ガスの剥離域の形成を確実に防止することができる。 According to the engine exhaust gas purification apparatus of the third aspect of the present invention, in addition to the first aspect, the boundary between the throttle portion and the enlarged diameter portion and the boundary between the enlarged diameter portion and the casing are cross sections having optimum curvature radii r2, r3. By forming it in a shape, it is possible to reliably prevent formation of a flue gas separation region at each boundary .

以下、本発明を排気通路に選択還元型のＮＯx触媒を備えたディーゼルエンジンの排気浄化装置に具体化した一実施形態を説明する。
図１は本実施形態のディーゼルエンジンの排気浄化装置を示す全体構成図であり、エンジン１は直列６気筒機関として構成されている。エンジン１の各気筒には燃料噴射弁２が設けられ、各燃料噴射弁２は共通のコモンレール３から加圧燃料を供給され、機関の運転状態に応じたタイミングで開弁して各気筒の筒内に燃料を噴射する。 Hereinafter, an embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine provided with a selective reduction type NOx catalyst in an exhaust passage will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to this embodiment. The engine 1 is configured as an in-line 6-cylinder engine. Each cylinder of the engine 1 is provided with a fuel injection valve 2, and each fuel injection valve 2 is supplied with pressurized fuel from a common common rail 3 and is opened at a timing according to the operating state of the engine. The fuel is injected into the inside.

エンジン１の吸気側には吸気マニホールド４が装着され、吸気マニホールド４に接続された吸気通路５には、上流側よりエアクリーナ６、ターボチャージャ７のコンプレッサ７ａ、インタクーラ８が設けられている。また、エンジン１の排気側には排気マニホールド９が装着され、排気マニホールド９には上記コンプレッサ７ａと同軸上に連結されたターボチャージャ７のタービン７ｂを介して排気通路１０が接続されている。 An intake manifold 4 is mounted on the intake side of the engine 1, and an intake passage 5 connected to the intake manifold 4 is provided with an air cleaner 6, a compressor 7 a of a turbocharger 7, and an intercooler 8 from the upstream side. An exhaust manifold 9 is mounted on the exhaust side of the engine 1, and an exhaust passage 10 is connected to the exhaust manifold 9 via a turbine 7b of a turbocharger 7 coaxially connected to the compressor 7a.

エンジン１の運転中においてエアクリーナ６を経て吸気通路５内に導入された吸気はターボチャージャ７のコンプレッサ７ａにより加圧された後にインタクーラ８、吸気マニホールド４を経て各気筒に分配され、各気筒の吸気行程で筒内に導入される。筒内では所定のタイミングで燃料噴射弁２から燃料が噴射されて圧縮上死点近傍で着火・燃焼し、燃焼後の排ガスは排気マニホールド９を経てタービン７ｂを回転駆動した後に排気通路１０を経て外部に排出される。 The intake air introduced into the intake passage 5 through the air cleaner 6 during operation of the engine 1 is pressurized by the compressor 7a of the turbocharger 7 and then distributed to each cylinder through the intercooler 8 and the intake manifold 4, and the intake air of each cylinder It is introduced into the cylinder in the process. In the cylinder, fuel is injected from the fuel injection valve 2 at a predetermined timing and ignited and combusted in the vicinity of the compression top dead center. The exhaust gas after combustion rotates the turbine 7b through the exhaust manifold 9, and then passes through the exhaust passage 10. It is discharged outside.

上記排気通路１０には本発明の排気浄化装置が設けられ、排気浄化装置は上流側ケーシング１１、下流側ケーシング１２、及び両ケーシング１１，１２間に形成されたミキシング室１３を備えている。上流側ケーシング１１内には上流側より前段酸化触媒１４及びＤＰＦ（ディーゼルパティキュレートフィルタ）１５が収容され、下流側ケーシング１２内には上流側より選択還元型ＮＯx触媒１６（後処理装置）及び後段酸化触媒１７が収容されている。 The exhaust passage 10 is provided with the exhaust purification apparatus of the present invention, and the exhaust purification apparatus includes an upstream casing 11, a downstream casing 12, and a mixing chamber 13 formed between the casings 11 and 12. A pre-stage oxidation catalyst 14 and a DPF (diesel particulate filter) 15 are accommodated in the upstream casing 11 from the upstream side, and a selective reduction type NOx catalyst 16 (post-treatment device) and a post-stage are disposed in the downstream casing 12 from the upstream side. An oxidation catalyst 17 is accommodated.

全体としてミキシング室１３は排ガス流通方向の中間を縮径させたベンチュリ状をなし、上流側ケーシング１１の後部から下流側に向けてコーン状に縮径する縮径部１３ａ、縮径部１３ａの最小径を保って下流側に連続する絞り部１３ｂ、及び絞り部１３ｂから下流側に向けてコーン状に拡径して下流側ケーシング１２の上流端に接続される拡径部１３ｃから構成されている。これらの上流側ケーシング１１、下流側ケーシング１２、ミキシング室１３の各部１３ａ〜１３ｃの排気流通方向と直交する断面形状は、全て円形状に設定されている。 As a whole, the mixing chamber 13 has a venturi shape in which the diameter in the exhaust gas flow direction is reduced, and the diameter of the diameter-reduced portion 13a and the diameter-reduced portion 13a are reduced to a cone shape from the rear side of the upstream casing 11 toward the downstream side. A narrowed portion 13b that keeps a small diameter and continues downstream, and a widened portion 13c that expands in a cone shape toward the downstream side from the narrowed portion 13b and is connected to the upstream end of the downstream casing 12. . The cross-sectional shapes orthogonal to the exhaust flow direction of each of the portions 13a to 13c of the upstream casing 11, the downstream casing 12, and the mixing chamber 13 are all set to be circular.

ミキシング室１３の縮径部１３ａ内の最上流位置にはフィン装置１８が設けられている。詳細は説明しないがフィン装置１８は、スチール製の円形状をなすベース板１８ａをプレス成形することにより多数枚のフィン１８ｂが周方向に折曲されている。ベース板１８ａ上には各フィン１８ｂに対応して流通孔が貫設され、フィン装置１８はＤＰＦ１５からの排ガスを各流通孔を経て流通させると共に、流通直後に各フィン１８ｂにより排ガスの流通方向を変更して縮径部１３ａの下流側に旋回流を生起させる。縮径部１３ａのフィン装置１８の下流側には噴射ノズル１９（還元剤噴射手段）が配設されており、この噴射ノズル１９は縮径部１３ａの外周一側から中心に向けて延設され、その先端２４ａを縮径部１３ａの中心で排気下流側に指向させている。 A fin device 18 is provided at the most upstream position in the reduced diameter portion 13 a of the mixing chamber 13. Although not described in detail, the fin device 18 has a large number of fins 18b bent in the circumferential direction by press-forming a base plate 18a having a circular shape made of steel. On the base plate 18a, through holes are formed corresponding to the fins 18b. The fin device 18 distributes the exhaust gas from the DPF 15 through the through holes, and immediately after the distribution, the fins 18b change the distribution direction of the exhaust gas. The swirling flow is generated on the downstream side of the reduced diameter portion 13a by changing. An injection nozzle 19 (reducing agent injection means) is disposed on the downstream side of the fin device 18 of the reduced diameter portion 13a. The injection nozzle 19 extends from the outer peripheral side of the reduced diameter portion 13a toward the center. The tip 24a is directed to the exhaust downstream side at the center of the reduced diameter portion 13a.

噴射ノズル１９にはミキシング室１３の外周に設置された電磁弁２０を介して図示しない尿素タンクから所定圧の尿素水溶液が供給されており、電磁弁２０の開閉に応じて噴射ノズル１９の先端に貫設された図示しない噴射孔からミキシング室１３の外周に向けて放射状に尿素水溶液が噴射される。
一方、上記燃料噴射弁２及び噴射ノズル１９の電磁弁２０はＥＣＵ３１（電子コントロールユニット）に接続され、ＥＣＵ３１にはその他にもセンサ類やデバイス類が接続されている。例えばＥＣＵ３１は、エンジン回転速度Ｎe及びアクセル操作量θaccから図示しないマップに従って燃料噴射量を設定し、エンジン回転速度Ｎe及び燃料噴射量から図示しないマップに従って燃料噴射時期を設定し、これらの燃料噴射量及び燃料噴射時期に基づいて燃料噴射弁２を駆動制御してエンジン１を運転する。また、ＥＣＵ３１はＮＯx触媒１６上にアンモニア（ＮＨ_３）を供給してＮＯx浄化作用を発揮させるべく、ミキシング室１３の一側に設置した図示しない温度センサにより検出された排ガス温度に基づいて尿素水溶液の目標噴射量を決定し、目標噴射量に基づき電磁弁２０を駆動制御して噴射ノズル１９から尿素水溶液を噴射する。 The injection nozzle 19 is supplied with a urea aqueous solution having a predetermined pressure from a urea tank (not shown) via an electromagnetic valve 20 installed on the outer periphery of the mixing chamber 13. Aqueous urea solution is sprayed radially from the injection hole (not shown) provided to the outer periphery of the mixing chamber 13.
On the other hand, the fuel injection valve 2 and the solenoid valve 20 of the injection nozzle 19 are connected to an ECU 31 (electronic control unit), and other sensors and devices are connected to the ECU 31. For example, the ECU 31 sets a fuel injection amount according to a map (not shown) from the engine rotation speed Ne and the accelerator operation amount θacc, sets a fuel injection timing according to a map (not shown) from the engine rotation speed Ne and the fuel injection amount, and these fuel injection amounts. The engine 1 is operated by drivingly controlling the fuel injection valve 2 based on the fuel injection timing. Further, the ECU 31 supplies aqueous ammonia (NH ₃ ) onto the NOx catalyst 16 so as to exert a NOx purification action, based on an exhaust gas temperature detected by a temperature sensor (not shown) installed on one side of the mixing chamber 13. The target injection amount is determined, the solenoid valve 20 is driven and controlled based on the target injection amount, and the urea aqueous solution is injected from the injection nozzle 19.

エンジン１の運転中において、エンジン１から排出された排ガスは排気マニホールド９及び排気通路１０を経て上流側ケーシング１１内に導入され、前段酸化触媒１４を経てＤＰＦ１５を流通する際に含有しているパティキュレートを捕集される。その後、排ガスはミキシング室１３内に導入されてフィン装置１８により旋回流を生起し、この排ガス中に噴射ノズル１９から尿素水溶液が噴射される。排ガスは縮径部１３ａから絞り部１３ｂに移行する過程で次第に絞られることにより旋回半径を縮小して流速を速め、その後に絞り部１３ｂから拡径部１３ｃに移行する過程では旋回半径を次第に拡大しながら流速を低め、これにより尿素水溶液は排ガス中に拡散して排気熱及び排ガス中の水蒸気により加水分解されてアンモニアを生成する。そして、生成されたアンモニアによりＮＯX触媒１６上で排ガス中のＮＯxが無害なＮ_２に選択還元されてＮＯxの浄化が行われる一方、このときの余剰アンモニアが後段酸化触媒１７によりＮＯに酸化されて処理される。 During operation of the engine 1, exhaust gas discharged from the engine 1 is introduced into the upstream casing 11 through the exhaust manifold 9 and the exhaust passage 10, and is contained in the DPF 15 that flows through the upstream oxidation catalyst 14. Curate is collected. Thereafter, the exhaust gas is introduced into the mixing chamber 13 to generate a swirling flow by the fin device 18, and an aqueous urea solution is injected from the injection nozzle 19 into the exhaust gas. The exhaust gas is gradually throttled in the process of moving from the reduced diameter part 13a to the throttle part 13b, thereby reducing the turning radius to increase the flow velocity, and then gradually increasing the turning radius in the process of moving from the throttle part 13b to the enlarged diameter part 13c. The flow rate is lowered while the urea aqueous solution diffuses into the exhaust gas and is hydrolyzed by the exhaust heat and the water vapor in the exhaust gas to produce ammonia. The generated ammonia selectively reduces NOx in the exhaust gas to harmless N ₂ on the NOx catalyst 16 to purify NOx, while the excess ammonia at this time is oxidized to NO by the post-stage oxidation catalyst 17. It is processed.

［発明が解決しようとする課題］において説明したように、ミキシング室１３内を流通する過程で内壁との間に排ガスの剥離域が形成されると、尿素水溶液が内壁に堆積して不具合を生じることから、本実施形態では、その対策としてミキシング室１３の形状に工夫を講じており、以下、このミキシング室１３の形状について詳述する。
図２はミキシング室１３の詳細を示す部分拡大断面図である。 As described in [Problems to be Solved by the Invention], if an exhaust gas separation region is formed between the inner wall and the inner wall in the process of flowing through the mixing chamber 13, an aqueous urea solution accumulates on the inner wall, causing a problem. Therefore, in the present embodiment, as a countermeasure, the shape of the mixing chamber 13 is devised. Hereinafter, the shape of the mixing chamber 13 will be described in detail.
FIG. 2 is a partially enlarged sectional view showing details of the mixing chamber 13.

本実施形態では、排ガスの剥離現象がミキシング室１３内の排気流通方向への急激な断面変化に起因して発生するとの観点の基に、排ガスの剥離域が形成されるミキシング室１３内の縮径部１３ａと絞り部１３ｂとの境界（以下、第１境界部４１と称する）、絞り部１３ｂと拡径部１３ｃとの境界（以下、第２境界部４２と称する）、及び拡径部１３ｃと下流側ケーシング１２との境界（以下、第３境界部４３と称する）を、従来の単純な角部から排気流通方向に所定曲率半径をなす断面形状（即ち、断面Ｒ状）に変更している。なお、図２ではミキシング室１３の外周上の１点を示しているが、言うまでもなく、各境界部４１〜４３は外周上のどの箇所においても同一断面形状をなしている。 In the present embodiment, the shrinkage in the mixing chamber 13 in which the flue gas separation region is formed is based on the viewpoint that the flue gas separation phenomenon occurs due to an abrupt cross-sectional change in the exhaust flow direction in the mixing chamber 13. A boundary between the diameter portion 13a and the narrowed portion 13b (hereinafter referred to as a first boundary portion 41), a boundary between the narrowed portion 13b and the expanded diameter portion 13c (hereinafter referred to as a second boundary portion 42), and the expanded diameter portion 13c And the downstream casing 12 (hereinafter referred to as the third boundary portion 43) is changed from a conventional simple corner to a cross-sectional shape having a predetermined radius of curvature in the exhaust flow direction (that is, a cross-sectional R shape). Yes. In FIG. 2, one point on the outer periphery of the mixing chamber 13 is shown. Needless to say, each of the boundary portions 41 to 43 has the same cross-sectional shape at any location on the outer periphery.

即ち、図７に示す特許文献１の従来技術では、第１から第３境界部４１〜４３に相当する箇所の断面形状が上流側と下流側との内壁をそのまま交差させた角部を形成しているため、これらの箇所でミキシング室１３内の排気流通方向への断面形状が急激に変化し、ミキシング室１３内の外周部で内壁に沿って移送される排ガスが断面形状の変化に倣って移送方向を変化できず、これが排ガスの剥離域が形成される要因となる。 That is, in the prior art of Patent Document 1 shown in FIG. 7, the cross-sectional shape of the portion corresponding to the first to third boundary portions 41 to 43 forms a corner portion that intersects the inner walls of the upstream side and the downstream side as they are. Therefore, the cross-sectional shape in the exhaust gas flow direction in the mixing chamber 13 changes abruptly at these locations, and the exhaust gas transferred along the inner wall at the outer peripheral portion in the mixing chamber 13 follows the change in the cross-sectional shape. The transfer direction cannot be changed, and this is a factor for forming a flue gas separation zone.

これに対して本実施形態では、第１境界部４１については、縮径部１３ａと絞り部１３ｂとの内壁を交差させた角部をベースとして所定の曲率半径ｒ1の断面Ｒ状に形成され、第２境界部４２については、絞り部１３ｂと拡径部１３ｃとの内壁を交差させた角部をベースとして所定の曲率半径ｒ2の断面Ｒ状に形成され、第３境界部４３については、拡径部１３ｃと下流側ケーシング１２との内壁を交差させた角部をベースとして所定の曲率半径ｒ3の断面Ｒ状に形成されている。 On the other hand, in the present embodiment, the first boundary portion 41 is formed in a cross-section R shape having a predetermined radius of curvature r1 based on a corner portion where the inner walls of the reduced diameter portion 13a and the narrowed portion 13b intersect. The second boundary portion 42 is formed in a cross-section R shape with a predetermined radius of curvature r2 based on the corner portion where the inner walls of the narrowed portion 13b and the enlarged diameter portion 13c intersect, and the third boundary portion 43 is expanded. It is formed in a cross-section R shape having a predetermined radius of curvature r3, with a corner portion where the inner wall of the diameter portion 13c and the downstream casing 12 intersected as a base.

本発明者は、各境界部４１〜４３の最適な曲率半径ｒ1〜ｒ3を決定すべく、シミュレーション試験を実施した。このシミュレーション試験では、各境界部の曲率半径ｒ1〜ｒ3を段階的に変更した解析モデルを設定し、各解析モデルにおける排ガスの剥離状況を求め、その排ガスの剥離状況から各境界部４１〜４３の最適な曲率半径ｒ1〜ｒ3を決定する手順で行われる。 The inventor conducted a simulation test in order to determine the optimum radii of curvature r1 to r3 of the respective boundary portions 41 to 43. In this simulation test, an analysis model in which the radii of curvature r1 to r3 of each boundary portion are changed in stages is set, the flue gas separation state in each analysis model is obtained, and each boundary portion 41 to 43 is determined from the flue gas separation state. The procedure is performed to determine the optimum radius of curvature r1 to r3.

最適な曲率半径ｒ1〜ｒ3はミキシング室１３の大きさに応じて変動することから、ＮＯx触媒１６の入口に相当する下流側ケーシング１２の半径Ｒを基準とした比ｒ1／Ｒ，ｒ2／Ｒ，ｒ3／Ｒを指標として各曲率半径ｒ1〜ｒ3を求めるものとしている。
また、排ガスの剥離状況は数値表現できないことから、剥離状況と相関する指標として排気流速Ｖに着目した。即ち、通路内を流れる流体特性の一つとして、通路内で流体が渦や淀みを生じて局所的に圧力低下すると、自ずと圧力低下を抑制するように排気流速が増加する現象が知られている。この現象は、上記境界部４１〜４３で形成される剥離域でも同様に発生し、剥離域での排ガスの渦や淀みによる圧力低下を抑制するように排気流速Ｖが増加する。従って、ミキシング室１３内の外周部で各剥離域を流通する排ガスの流速Ｖは各剥離域で発生する排ガスの剥離状況と相関し、ある排気流速Ｖ以下では各剥離域で排ガスの剥離が発生していないと見なすことができる。 Since the optimal curvature radii r1 to r3 vary depending on the size of the mixing chamber 13, the ratios r1 / R, r2 / R, based on the radius R of the downstream casing 12 corresponding to the inlet of the NOx catalyst 16 are used. The curvature radii r1 to r3 are obtained using r3 / R as an index.
Further, since the state of exhaust gas separation cannot be expressed numerically, the exhaust gas flow velocity V was focused as an index correlated with the state of separation. That is, as one of the characteristics of the fluid flowing in the passage, there is known a phenomenon in which the exhaust flow velocity increases so as to suppress the pressure drop when the pressure is locally reduced due to vortex or stagnation in the passage. . This phenomenon also occurs in the separation region formed by the boundary portions 41 to 43, and the exhaust flow velocity V increases so as to suppress the pressure drop due to the vortex or stagnation of the exhaust gas in the separation region. Therefore, the flow velocity V of the exhaust gas flowing through each separation region at the outer peripheral portion in the mixing chamber 13 correlates with the separation state of the exhaust gas generated in each separation region, and the exhaust gas separation occurs in each separation region below a certain exhaust flow velocity V. Can be considered not.

ミキシング室１３内の外周部を流通する排ガスの流速Ｖは縮径部１３ａ、絞り部１３ｂ、拡径部１３ｃの通路断面積に応じて変化するが、何れの箇所であっても排ガスの剥離状況とは所定の相関関係が成立する。そこで、本実施形態では、絞り部１３ｂの入口外周の排気流速Ｖを指標として定め、この排気流速Ｖが排ガスの剥離が生じる虞がない値として設定された上限値Ｖ0未満に抑制できる範囲内で、各境界部４１〜４３の比ｒ1／Ｒ，ｒ2／Ｒ，ｒ3／Ｒ（即ち、曲率半径ｒ1〜ｒ3）を定めている。なお、排気流速Ｖは絞り部１３ｂの入口外周に限る必要はなく、例えば下流側ケーシングの入口外周の排気流速Ｖを指標としてもよい。 The flow velocity V of the exhaust gas flowing through the outer peripheral portion in the mixing chamber 13 changes according to the cross-sectional areas of the reduced diameter portion 13a, the narrowed portion 13b, and the enlarged diameter portion 13c. And a predetermined correlation is established. Therefore, in the present embodiment, the exhaust flow velocity V at the outer periphery of the inlet of the throttle portion 13b is determined as an index, and the exhaust flow velocity V is within a range that can be suppressed to less than the upper limit value V0 that is set as a value that does not cause separation of the exhaust gas. The ratios r1 / R, r2 / R, r3 / R (that is, the radii of curvature r1 to r3) of the boundary portions 41 to 43 are determined. The exhaust flow velocity V need not be limited to the outer periphery of the inlet of the throttle portion 13b. For example, the exhaust flow velocity V of the outer periphery of the inlet of the downstream casing may be used as an index.

実際のシミュレーション試験では、何れか２つの境界部４１〜４３の曲率半径ｒ1〜ｒ3を適当な値に固定した上で、残りの一つの境界部４１〜４３の曲率半径ｒ1〜ｒ3を変化させて、曲率半径ｒ1〜ｒ3毎に絞り部１３ｂの入口の排気流速Ｖを求め、この作業を各境界部４１〜４３について実施する。
図３はシミュレーション試験から得られた各境界部４１〜４３での排ガスの剥離特性を示す図である。第１及び第２境界部４１，４２での排ガスの剥離特性は共通し、これに対して第３境界部４３の剥離特性は全体的には第１及び第２境界部４１，４２と近似するものの、より絞り部１３ｂの入口の排気流速Ｖが低い（剥離が発生し難い）傾向となっている。この相違は、第１及び第２境界部４１，４２がミキシング室１３内の最小径に相当する絞り部１３ｂに位置して排気流速Ｖが速いのに対し、第３境界部４３は最大径の下流側ケーシング１２の入口に位置して排気流速Ｖが遅いことから、排ガスの剥離が発生し難いためである。 In an actual simulation test, the curvature radii r1 to r3 of any two boundary portions 41 to 43 are fixed to appropriate values, and the curvature radii r1 to r3 of the remaining one boundary portions 41 to 43 are changed. The exhaust flow velocity V at the inlet of the throttle portion 13b is determined for each of the curvature radii r1 to r3, and this operation is performed for each of the boundary portions 41 to 43.
FIG. 3 is a diagram showing the flue gas separation characteristics at the respective boundaries 41 to 43 obtained from the simulation test. Exhaust gas separation characteristics at the first and second boundary portions 41 and 42 are common, whereas the separation characteristics of the third boundary portion 43 are generally similar to the first and second boundary portions 41 and 42. However, the exhaust gas flow velocity V at the inlet of the throttle portion 13b tends to be lower (peeling hardly occurs). This difference is that the first boundary portion 41 and the second boundary portion 42 are located in the throttle portion 13b corresponding to the minimum diameter in the mixing chamber 13 and the exhaust flow velocity V is fast, whereas the third boundary portion 43 has the maximum diameter. This is because the exhaust gas flow rate V is slow and is located at the inlet of the downstream casing 12 so that the flue gas does not easily peel off.

なお、このように排ガスの剥離状況は排気流速Ｖの影響を受け、排気流速Ｖが高いほど排ガスの剥離域が生じ易いことから、シミュレーション試験はエンジン１の運転領域から求めた排気流速Ｖの上限付近を前提として実施されている。勿論、前提となる排気流速Ｖはこれに限ることはなく任意に変更可能である。
また、第１及び第２境界部４１，４２と第３境界部４３との何れにおいても、全体的な特性として、曲率半径ｒ1〜ｒ3（比ｒ1／Ｒ，ｒ2／Ｒ，ｒ3／Ｒ）の増加に伴って絞り部１３ｂの入口の排気流速Ｖが次第に低下し、それぞれの境界部４１〜４３での排ガスの剥離が次第に抑制されることが判る。この傾向は、各境界部４１〜４３の曲率半径ｒ1〜ｒ3が増加するほどミキシング室１３の内壁の排気流通方向への断面形状の変化が緩やかとなり、断面変化に倣って剥離を生じることなく排ガスが移送方向を変化し易くなるためと考えられる。 The exhaust gas separation state is affected by the exhaust flow velocity V, and the exhaust gas separation region is more likely to occur as the exhaust gas flow velocity V is higher. Therefore, the simulation test is performed with the upper limit of the exhaust flow velocity V obtained from the operation region of the engine 1. It is implemented on the assumption of the vicinity. Of course, the exhaust flow velocity V as a premise is not limited to this and can be arbitrarily changed.
In addition, in any of the first and second boundary portions 41 and 42 and the third boundary portion 43, the curvature radius r1 to r3 (ratio r1 / R, r2 / R, r3 / R) is an overall characteristic. It can be seen that the exhaust gas flow velocity V at the inlet of the throttle portion 13b gradually decreases with the increase, and the separation of the exhaust gas at the respective boundary portions 41 to 43 is gradually suppressed. In this tendency, as the radii of curvature r1 to r3 of the boundary portions 41 to 43 increase, the change in the cross-sectional shape in the exhaust flow direction of the inner wall of the mixing chamber 13 becomes gradual, and the exhaust gas does not cause separation according to the cross-sectional change. This is considered to be because the transfer direction is easily changed.

そして、この試験結果では、予め排ガスの剥離の虞がない排気流速Ｖの上限値としてＶ0が設定され、第１及び第２境界部４１，４２に関しては、絞り部１３ｂの入口の排気流速Ｖが上限値Ｖ0未満となる0.07が比ｒ1／Ｒ，ｒ2／Ｒの下限として導き出されている。また、第３境界部４３に関しては、上限値Ｖ0に基づきより小さな0.05が比ｒ3／Ｒの下限として導き出されている。 In this test result, V0 is set in advance as the upper limit value of the exhaust gas flow velocity V at which there is no risk of flue gas separation. With respect to the first and second boundary portions 41 and 42, the exhaust gas flow velocity V at the inlet of the throttle portion 13b is 0.07 which is less than the upper limit value V0 is derived as the lower limit of the ratios r1 / R and r2 / R. For the third boundary 43, a smaller 0.05 is derived as the lower limit of the ratio r3 / R based on the upper limit value V0.

一方、図３の特性から明らかなように、排ガスの剥離の観点からは曲率半径ｒ1〜ｒ3の上限を制限する必要はなく、曲率半径ｒ1〜ｒ3の上限はミキシング室１３の形状に関する幾何学的な観点から定められる。この試験結果では、ミキシング室１３の全長（排気流通方向の長さ）がある程度長い解析モデルを設定していることから、下流側ケーシング１２の半径Ｒと同等の曲率半径ｒ1〜ｒ3で境界部４１〜４３を形成することも可能であり、このため第１及び第２境界部４１，４２と第３境界部４３との何れにおいても、比ｒ1／Ｒ，ｒ2／Ｒ，ｒ3／Ｒの上限として1.0が導き出されている。 On the other hand, as is clear from the characteristics of FIG. 3, it is not necessary to limit the upper limit of the curvature radii r1 to r3 from the viewpoint of exfoliation of the exhaust gas, and the upper limit of the curvature radii r1 to r3 is geometrical with respect to the shape of the mixing chamber 13. Is determined from various viewpoints. In this test result, an analysis model is set in which the overall length of the mixing chamber 13 (length in the exhaust gas flow direction) is somewhat long, so that the boundary portion 41 has a radius of curvature r1 to r3 equivalent to the radius R of the downstream casing 12. ˜43 can be formed, and therefore, as the upper limit of the ratios r1 / R, r2 / R, r3 / R in any of the first and second boundary portions 41, 42 and the third boundary portion 43, 1.0 has been derived.

なお、ミキシング室１３の全長が短い場合には、比ｒ1／Ｒ，ｒ2／Ｒ，ｒ3／Ｒの上限を1.0より適宜減少すればよい。
従って、第１及び第２境界部４１，４２に関しては、比ｒ1／Ｒ，ｒ2／Ｒが0.07〜1.0の範囲内となるように曲率半径ｒ1，ｒ2を設定すればよく、第３境界部４３に関しては、比ｒ3／Ｒが0.05〜1.0の範囲内となるように曲率半径ｒ3を設定すればよい。図２に示す本実施形態のミキシング室１３では、図３中にＡで示す比ｒ1／Ｒ〜ｒ3／Ｒを達成するように曲率半径ｒ1〜ｒ3を設定している。 If the total length of the mixing chamber 13 is short, the upper limit of the ratios r1 / R, r2 / R, r3 / R may be appropriately reduced from 1.0.
Accordingly, with respect to the first and second boundary portions 41 and 42, the curvature radii r1 and r2 may be set so that the ratios r1 / R and r2 / R are in the range of 0.07 to 1.0. With respect to, the radius of curvature r3 may be set so that the ratio r3 / R is in the range of 0.05 to 1.0. In the mixing chamber 13 of the present embodiment shown in FIG. 2, the radii of curvature r1 to r3 are set so as to achieve the ratios r1 / R to r3 / R indicated by A in FIG.

従って、図２に破線で示すように、ミキシング室１３内の外周部において、縮径部１３ａの内壁に沿って第１境界部４１に到達した排ガスは、第１境界部４１の内壁から剥離することなくその断面形状に倣って移送方向を変更されて絞り部１３ｂに移送され、その後に絞り部１３ｂの内壁に沿って第２境界部４２に到達した排ガスは、第２境界部４２の内壁から剥離することなくその断面形状に倣って移送方向を変更されて拡径部１３ｃに移送される。さらに拡径部１３ｃの内壁に沿って第３境界部４３に到達した排ガスは、渦や淀みを生じることなく第３境界部４３の断面形状に倣って移送方向を変更されてＮＯx触媒１６に流入する。 Therefore, as shown by a broken line in FIG. 2, the exhaust gas that has reached the first boundary portion 41 along the inner wall of the reduced diameter portion 13 a at the outer peripheral portion in the mixing chamber 13 is separated from the inner wall of the first boundary portion 41. Without changing the transfer direction according to the cross-sectional shape, the exhaust gas that has been transferred to the throttle portion 13b and then reached the second boundary portion 42 along the inner wall of the throttle portion 13b is removed from the inner wall of the second boundary portion 42. The transfer direction is changed according to the cross-sectional shape without peeling, and the transfer is transferred to the enlarged diameter portion 13c. Further, the exhaust gas that has reached the third boundary portion 43 along the inner wall of the expanded diameter portion 13c flows into the NOx catalyst 16 without changing vortex or stagnation, changing the transfer direction according to the cross-sectional shape of the third boundary portion 43. To do.

結果として、何れの境界部４１〜４３でも排ガスの剥離域は形成されず、排ガスに含まれる尿素水溶液の内壁への付着が最小限に抑制される。よって、結晶化した尿素水溶液がミキシング室１３の内壁に堆積したときの通路断面積の縮小を抑制でき、もって排圧増大に要因するエンジン性能の低下を未然に防止することができる。
また、堆積による無駄な尿素水溶液の消費を抑制できるため、常に必要量の尿素水溶液ひいてはアンモニアをＮＯx触媒に供給でき、もってＮＯx触媒１６に最大限の浄化性能を発揮させることができる。 As a result, no separation region of the exhaust gas is formed at any of the boundary portions 41 to 43, and adhesion of the urea aqueous solution contained in the exhaust gas to the inner wall is minimized. Therefore, it is possible to suppress a reduction in the cross-sectional area of the passage when the crystallized urea aqueous solution is deposited on the inner wall of the mixing chamber 13, and thus it is possible to prevent a decrease in engine performance that causes an increase in exhaust pressure.
Further, since wasteful consumption of the urea aqueous solution due to deposition can be suppressed, the necessary amount of urea aqueous solution, and thus ammonia, can always be supplied to the NOx catalyst, so that the NOx catalyst 16 can exhibit the maximum purification performance.

以上の作用効果は、シミュレーション試験で導き出した比ｒ1／Ｒ〜ｒ3／Ｒの範囲内となるように各境界部４１〜４３の曲率半径ｒ1〜ｒ3を設定すれば当然得られるものであり、図４，５に曲率半径ｒ1〜ｒ3の別の設定例を示す。
図４は、図３中にＢで示す比ｒ1／Ｒ〜ｒ3／Ｒを達成するように曲率半径ｒ1〜ｒ3を設定しており、図２に比較して各曲率半径ｒ1〜ｒ3は大幅に小さく形成されている。また、図５は、図３中にＣで示す比ｒ1／Ｒ〜ｒ3／Ｒを達成するように曲率半径ｒ1〜ｒ3を設定しており、図２に比較して各曲率半径ｒ1〜ｒ3は大幅に大きく形成されている。しかし、何れの場合も比ｒ1／Ｒ〜ｒ3／Ｒは下限として決定されている0.07及び0.05以上であるため、上記作用効果を十分に得ることができ、且つ、上限として決定されている1.0以下であるため、幾何学的な矛盾を生じることなくミキシング室１３を形成できる。 The above effects can be obtained naturally by setting the radii of curvature r1 to r3 of the boundary portions 41 to 43 so as to be within the range of the ratio r1 / R to r3 / R derived in the simulation test. 4 and 5 show other setting examples of the curvature radii r1 to r3.
4 sets the radii of curvature r1 to r3 so as to achieve the ratios r1 / R to r3 / R indicated by B in FIG. 3, and each of the radii of curvature r1 to r3 is significantly larger than that of FIG. It is formed small. Further, in FIG. 5, the curvature radii r1 to r3 are set so as to achieve the ratios r1 / R to r3 / R indicated by C in FIG. 3, and each of the curvature radii r1 to r3 is compared with FIG. It is significantly larger. However, since the ratios r1 / R to r3 / R are 0.07 and 0.05 or more which are determined as the lower limit in any case, the above-mentioned effects can be sufficiently obtained, and 1.0 or less which is determined as the upper limit. Therefore, the mixing chamber 13 can be formed without causing a geometric contradiction.

また、図６は図４の変形例であるが、拡径部１３ｃの内壁を曲率半径ｒ4でミキシング室１３の中心側に向けて湾曲させている。排気流速Ｖが高いときには第２境界部４２を通過後の排ガスが自己の慣性力で拡径部１３ｃの内壁から剥離する可能性があるが、拡径部１３ｃの湾曲により排ガスの剥離が抑制される。よって、図４のミキシング室１３に比較して排ガスの剥離を一層確実に防止することができる。 FIG. 6 is a modification of FIG. 4, but the inner wall of the enlarged diameter portion 13c is curved toward the center of the mixing chamber 13 with a radius of curvature r4. When the exhaust gas flow velocity V is high, the exhaust gas after passing through the second boundary portion 42 may be peeled off from the inner wall of the enlarged diameter portion 13c by its own inertial force, but the flue gas is prevented from being separated by the curvature of the enlarged diameter portion 13c. The Therefore, it is possible to more reliably prevent the flue gas from being separated as compared with the mixing chamber 13 of FIG.

以上で実施形態の説明を終えるが、本発明の態様はこの実施形態に限定されるものではない。例えば上記実施形態では、選択還元型ＮＯX触媒１６を備えたディーゼルエンジン１の排気浄化装置に具体化したが、還元剤の供給を要する後処理装置を備えたエンジンであればこれに限ることはない。例えば排ガス中のＮＯxを吸蔵する吸蔵型ＮＯx触媒を排気通路に備え、吸蔵したＮＯxをＮＯx触媒から放出還元するために、膨張行程や排気行程でのポスト噴射により還元剤として未燃燃料をＮＯx触媒上に供給するＮＯxパージを定期的に実行する必要があるエンジンに適用してもよい。この場合には図１においてＮＯx触媒１６を吸蔵型ＮＯx触媒に置換した構成となるが、ミキシング室１３の形状を上記実施形態と同様に設定することにより同様の作用効果を得ることができる。 This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the exhaust purification device of the diesel engine 1 provided with the selective reduction type NOx catalyst 16 is embodied. However, the present invention is not limited to this as long as the engine is provided with an aftertreatment device that requires supply of a reducing agent. . For example, a storage type NOx catalyst that stores NOx in exhaust gas is provided in the exhaust passage, and in order to release and reduce the stored NOx from the NOx catalyst, unburned fuel is used as a reducing agent by post-injection in the expansion stroke or exhaust stroke. You may apply to the engine which needs to perform NOx purge supplied above regularly. In this case, the NOx catalyst 16 in FIG. 1 is replaced with an occlusion-type NOx catalyst, but the same effect can be obtained by setting the shape of the mixing chamber 13 in the same manner as in the above embodiment.

また、上記実施形態では、ミキシング室１３の第１から第３境界部４１〜４３を全て断面Ｒ状に形成したが、何れか１つまたは２つの境界部のみを断面Ｒ状に形成してもよい。上記したように第３境界部４３に比較して排気流速Ｖが高い第１及び第２境界部４１，４２を断面Ｒ状に形成することが、排ガスの剥離抑制のために効果的なため、何れか２つの境界部４１〜４３を断面Ｒ状に形成するときには第１及び第２境界部４１，４２を選択するのが効果的である。また、第１及び第２境界部４１，４２を比較した場合、排ガスが縮流し終えた縮流地点に位置する第１境界部４１より、排ガスが拡流し始める拡流地点に位置する第２境界部４２の方が排ガスの剥離は発生し易い。従って、何れか１つの境界部４１，４２を断面Ｒ状に形成するときには第２境界部４２を選択するのが効果的である。 Moreover, in the said embodiment, although the 1st-3rd boundary parts 41-43 of the mixing chamber 13 were all formed in the cross-section R shape, even if only one or two boundary parts are formed in the cross-section R shape. Good. As described above, forming the first and second boundary portions 41 and 42 having a high exhaust flow velocity V in comparison with the third boundary portion 43 in a cross-sectional R shape is effective for suppressing flue gas separation, It is effective to select the first and second boundary portions 41 and 42 when any two of the boundary portions 41 to 43 are formed in a R-shaped cross section. In addition, when the first and second boundary portions 41 and 42 are compared, the second boundary located at the expansion point where the exhaust gas begins to expand from the first boundary portion 41 positioned at the contraction point where the exhaust gas has been contracted. The part 42 is more likely to be stripped of exhaust gas. Therefore, it is effective to select the second boundary portion 42 when any one of the boundary portions 41 and 42 is formed in a cross-section R shape.

また、上記実施形態では、ミキシング室１３内の縮径部１３ａに噴射ノズル１９を配設し、その噴射ノズル１９の上流側にフィン装置１８を配設したが、これらの配置に限ることはなく、例えばフィン装置１８を廃したり、或いは噴射ノズル１９を絞り部１３ｂ内に設けたりしてもよい。 Moreover, in the said embodiment, although the injection nozzle 19 was arrange | positioned in the diameter reduction part 13a in the mixing chamber 13, and the fin apparatus 18 was arrange | positioned in the upstream of the injection nozzle 19, it does not restrict to these arrangement | positioning. For example, the fin device 18 may be eliminated, or the injection nozzle 19 may be provided in the throttle portion 13b.

実施形態のディーゼルエンジンの排気浄化装置を示す全体構成図である。1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to an embodiment. 実施形態のミキシング室の詳細を示す部分拡大断面図である。It is a partial expanded sectional view which shows the detail of the mixing chamber of embodiment. シミュレーション試験から得られた各境界部での排ガスの剥離特性を示す図である。It is a figure which shows the peeling characteristic of the waste gas in each boundary part obtained from the simulation test. 曲率半径を小さく設定したミキシング室の別例を示す部分拡大断面図である。It is a partial expanded sectional view which shows another example of the mixing chamber which set the curvature radius small. 曲率半径を大きく設定したミキシング室の別例を示す部分拡大断面図である。It is a partial expanded sectional view which shows another example of the mixing chamber which set the curvature radius large. 拡径部の内壁を湾曲させたミキシング室の別例を示す部分拡大断面図である。It is a partial expanded sectional view which shows another example of the mixing chamber which curved the inner wall of the enlarged diameter part. 特許文献１に記載された排気浄化装置のミキシング室の詳細を示す部分拡大断面図である。It is a partial expanded sectional view which shows the detail of the mixing chamber of the exhaust gas purification apparatus described in patent document 1.

Explanation of symbols

１エンジン
１０排気通路
１２下流側ケーシング
１３ミキシング室
１３ａ縮径部
１３ｂ絞り部
１３ｃ拡径部
１６ＮＯx触媒（後処理装置）
１９噴射ノズル（還元剤噴射手段）
Ｒケーシング半径
ｒ1〜ｒ3 曲率半径 DESCRIPTION OF SYMBOLS 1 Engine 10 Exhaust passage 12 Downstream casing 13 Mixing chamber 13a Diameter reduction part 13b Restriction part 13c Diameter expansion part 16 NOx catalyst (post-processing apparatus)
19 Injection nozzle (reducing agent injection means)
R Casing radius r1-r3 Curvature radius

Claims

A post-processing device that is disposed in a casing that is disposed in the exhaust passage of the engine and has substantially the same diameter in the exhaust circulation direction, and purifies the exhaust gas of the engine by supplying a reducing agent;
Provided on the upstream side of the aftertreatment device in the exhaust passage, and has a venturi shape that continues from a reduced diameter portion that reduces the diameter downstream to a diameter enlarged portion that expands downstream via a minimum diameter restrictor, A mixing chamber connected to the upstream end of the casing with the enlarged diameter portion;
In an engine exhaust purification device comprising a reducing agent injection means for injecting a reducing agent into the mixing chamber,
The boundary between the enlarged diameter portion and the casing, formed in a predetermined radius of curvature of the cross-sectional shape along the exhaust flow direction,
When the radius of the casing is R, and the radius of curvature of the boundary between the expanded portion and the casing is r3,
0.05 ≦ r3 / R ≦ 1.0
An exhaust purification device for an engine characterized by satisfying

In addition to the boundary between the enlarged diameter portion and the casing, a boundary between the throttle portion and the enlarged diameter portion is formed on the cross-sectional shape of a predetermined curvature radius, the curvature radius of the boundary between the throttle portion and the enlarged diameter portion an exhaust purification device of an engine according to claim 1, characterized in that larger than the radius of curvature of the boundary between the enlarged diameter portion and the casing.

In addition to the boundary between the enlarged diameter portion and the casing, a boundary between the throttle portion and the enlarged diameter portion is formed on the cross-sectional shape of a predetermined curvature radius,
The radius of the casing R, the radius of curvature of the boundary between the throttle portion and the enlarged diameter portion r2, the radius of curvature of the boundary between the enlarged diameter portion and the casing when the r3,
0.07 ≦ r2 / R ≦ 1.0
0.05 ≦ r3 / R ≦ 1.0
The exhaust emission control device for an engine according to claim 1, wherein: