便車窗玻璃升降器外殼沖壓模具設計（桂電子）,便車,窗玻璃,升降,外殼,沖壓,模具設計,電子 Analysis of pulsation inside pipe and study on exhaust sound Characterstics of V type 8 cylinder engine-study on Optimized front pipe junction structure ABSTRACT The research of pulsation wave propagation inside exhaust pipe in V8 engine shows that pulsation from engine was changed by joining two front pipes in entire exhaust pipe. In short ,frequency of pulsation inside the pipe is not always equal to engine explosion fitst order frequency or its harmonics.Accordingly,structure of junction has been studied,which indicated that having volume at junction add edgine revolution first order component pressure fluctuation to blow-down wave component and makes exhaust sound worse.This phenomena is caused by irregular explosion interval on each bank of V8 engine and phase delay of propagation at junction. INTRODUCTION Recently,V type engines meeting the LEV and ULEV emission regulations are equippen with a large capacity catalytic converter for each of the left and right banks,and the front pipes ten to be long and join in the middle of overall length of the exhaust sustem(Fig.1)and substantial changes have been made in the exhaust pipe structure.An optimum exhaust system superior in quietness and engine performance should be considered. Irregular exploslon intervals among cylinders on each bank of the V8 engine produce pulsation with complex characteristics inside the left and right front pipes,which is different from pulsation inside front pipes in the other type of engines,for instance ,in-line 4 cylinder engine and so on.There has been no studies of the mutual effect between pulsation inside right front pipe and that inside left front pipe and no studies of propagation of pulsation at junction of the front pipes.While analysis of junction has been studied regarding flow,there has been no irregular explosion intervals among cylinders on each bank of the V8 engine. While attenuation technique with muffler has been widely studied,there has been few studies with junction.Moreover,it is necessary to optimize the junction for exhaust sound quality recently focused on. In this paper,propagation of pulsation at junction was investigated to optimize the front pipe junction of V8 engine with experiments and numerical calculation. Linear frequency response calculation of exhaust noise using finite element method or the likeis not suitable for boundary condition and variety of frequency inside entire pipe of V8 engine.On the other hand,acoustic calculation using fluid dynamics model has studied to predict sound pressure and recently improved to apply to full size model with good results in modified one dimensional calculation,In hybrid linear/three-dimensional calculationand in hybrid one-dimensional/three-dimensional calculation.On the other hand there has been no application to analyzing mechanism of phenomena. In this paper,the mechanism of engine revolution first order component pressure fluctuation caused at the front pipe junction of V8 engine exhaust pipes was analyzed by measuring pressure inside pipe and calculation with fluid dynamics model from intake to exhaust with comparison between measured and calculated results. PULSATION WAVE PROPAGATION INSIDE EXHUAT PIPE WITH LONG FRONT PIPE INSTALLED IN V TYPE 8 CYLINDER ENGINE To meet requirements of the emission regulations,the exhaust pipe tends to be of a shape shown in Fig.1. The pipes of exhaust manifold join near the exhaust port at each of the left and right banks and then forms left and right front pipes,each of which is equipped with a large capacity catalytic converter,and resultant long front pipes join in the middle of the entire exhaust pipe. Fig.2 shows the pulsation inside the pipe at each part of the exhaust pipe during steady operation at a constant engine speed.Seven major peaks were observed at the outlet of exhaust port during engine’s second rotation,while there were eight peaks at the junction having a uniform interval between peaks and an equal peak level.That is,the frequency of the pulsation wave propagated inside the pipe was changed by joining two front pipes.In the case of the most genersl in-line 4 cylinder engine,the frequency of the pulsation wave inside the pipe is almost equal to engine explosion first order frequency or its harmonic frequencies at each of the exhaust pipe. There is an essential difference in the pulsation propagating process inside the pipe between the V type 8 cylinder engine and in-line 4 cylinder engine.Fig.3 shows the order of explosion in each cylinder of the V type 8 cylinder engine,where explosion does not occur alternately but at irregular intervals of crank angles of 180,90,180 and 270 degrees on each bank. Next,results of measurement of the pulsation wave at each part inside the front pipe are shown in Fig.4.Considering exhaust requirements,the pulsation wave at the exhaust port outlet was detemined by the length from exhaust port toexhaust maniflod junction and the volume of the junction,and pressure peaks existed according ti the interval of explosions on the bank,which were transmitted to the downstream of the front pipe.The pressure decreased in the middle of the front pipek while the frequency of the pulsation wave remained unchanged.However,the frequency changed near the juntion of the front pipeslm.That is,the frequency changed under the effect of the pulsation wave from the front pipe of the other bank.The wave froms immediately before and after the junction(l,m)were almost equal,at almost the same magnitude under the effect of the opposite bank,and the perssure levels were equal.This can be explained by combining peaks of the blow-dowm pressure from each cylinder according to the order of explosion.In addition,the junction structure of two front pipes and the pulsation wave propagation were analtzed.The purpose of the junction on the exhaust sound characteristics. STRUCTURE OF JUNCTION Two exhaust pipes shown in Fig.5 were compared to analyze the junction structure of two front pipe.The length from engine to muffler was equal for both,but the difference between them is whether two front pipes joined before the muffler or inside the muddler. Fig.6 shows the measured results of the exhaust sound overall from the two exhaust systems,where exhaust pipe 1 shows a smaller level. To resesrch the difference of sound pressure between exhaust pipe 1 and exhaust pipe 2,sound pressure at engine speed 2500rpm in relation to the casnk angle was mensured. The wave form of the pressure wave in relation to the crank angle is shown in Fig.7. There are eight peaks during crank gngle 720 degrees in case of exhaust pipe 1,while in the case of exhaust pipe 2,engine revolution first order component pressure fluctuation shown as Fig.8(b) is added to exhaust blow-down component shown as Fig.8(a) and make exhaust noise worse.Next,the mechanism for why engine revolution first order componment pressure fluctuation occurs in the case of the two front pipes joining inside the muffler was analyzed. ANALYSIS OF ENGINE REVOLUTION FIRST ORDER PRESSURE FLUCTUATION The pulsation wave inside two exhaust pipes were measured to research the location of engine revolution first order pressure fluctuation occurrence. The compared results are shown in Fig.9. The pressure at the outlet of exhaust port was almost equal between two exhaust pipes. This seemed to be because the effect of reflected wave from exhaust manifold junction on the pressure at the outlet of exhaust port was larger than that from front pipe junction. While exhaust pipe 1 showed peaks at an equal interval and almost the same level immediately before the muffler and similar pulsation. After the muffler, exhaust pulsation before and after the muffler of exhaust pipe 2 was considerably different, indicating that engine revolution first order pressure fluctuation occurred at the junction.. Fig.10 shows comparison of the inside pipe pulsation immediately before the junction between left and right front pipe in the case of exhaust pipe 1 and 2, repectively.While the pulsation wave from of both front pipe immediately before the junction were different in exhanst pipe 2.That is,while the mutual effect between both front pipes was large with exhaust pipeq 1 and pulsation of one front pipe progagated into the other front pipe occurred with delay. Further, to study the mutual effect between both front pipes,the exhaust gas was input from single bank (left bank)in the cindition engine firing and right bank routed to other exit and comparison of pulsation was made with case the exhaust gas input from two banks,and the measured front pipe pulsation wave form immediately before the junction is shown in Fig.11. In the case of an input from single bank,irregular interval between explosions in the bank poduce pressure peaks existing according to the interval of explosion with either exhuast pipe 1 or exhuast pipe 2.While,in the case of an input from both banks,peaks of front pipe pulsation wave from existed at equal interval with exhuast pipe 1,indicateing that pulsation from the other front pipe propagated without phase delay.On the other hand,even in the case of an input from both banks,peaks of pulsation did not exist at equal interval with exhuast pipe 2, indicateing that pulsation from the other front pipe propagated with phase delay, Compariton of exhaust sound pressure between an input from a single bank and that from both banks is shown in Fig.12,An input from both banks presented smaller exhaust sound,This was because a cycle of explosions at interval of 180,90,180 and 270 degrees was repeated in the eft and right banks at a phase difference of 360 degrees of tbe crank angle to make pulsation in the recerse phase ,to be canceked at the junction. This indicated that the phenomenon was largely effected by the blow-down pressure from the engine. At this, one dimensional fluid dynamics calculation using finite volume approach(5) was conducted as to a model of exhaust pipe 2 including not only the wxhaust pipe but the intake system and main body of the engine. The munerical result of pressuerd rusults,where engine revolution first order pressure fluctuatone occurring in wxhaust pipe 2 is sumulated,indicating that fluid dynamics calculation can simulate the measuerd phenomena. To study flow at junction of two front pipes,the result of one-dimensional calculation was input as a boundary condition to the three-dimensional model concerning the junction to the upstream and downstream of the muffler,and the transient flow was calculated.The velocity vector calculated by coupling one dimensional model and three dimensional model is show in Fig. 14. While the flow at the junction of exhaust pipe 1 entered the other front pipe and downstream without delay,exhaust gases were accumulated at the muffler of exhaust pipe 2,delaying propagation to the other front pipe and the downstream.That is,a capacity at the junction caused a delay in propagation to the other front pipe and downstream.Pulsation of exhaust pipe 1 differed from that of exhaust pipe 2 immediately before the muffler.In the case of exhaust pipe 1,the two front pipes had been joined before the muffler and peaks of pulsation before the muffler were observed at equal intervals,while in the case of exhaust pipe 2,two front pipes were not joined before the muffler and peaks of pulsation before the muffler were observed at irregular intervals.As pulsation propagates at volume with delay,some peaks which exist at short interval effected the next peak to generate one group of peaks and peaks gathered at each of the two front pipes.A cycle of explosions at intervals of 180,90,180 and 270 degrees was repeated in the left and right banks at a phase difference of 360 degrees of the crank angle,resulting in two groups of peak in two revolutions of the engine,which generated engine revolution first order component pressure fluctuation. As a conclusion ,engine revolution first order component pressure fluctuation appearing after muffler is caused by irregular explosion intervals among cylinders on each bank of V 8 engine and propagation of pulsation at muffler with delay. To verify this,previously mentioned one-dimensional fluid dynamics calculation was conducted as to a model of exhaust pipe 2 including intake and main body of the engine to have explosions at a uniform interval on the left and right bank respectively. The calculated result of pressure wave form after muffler at same place as Fig. 13 is shown in Fig.15,where engine revolution first order component did not exist. Fig.16shows the calculated result of pressure wave form inside the front pipe immediately before the muffler where pressure peaks exist at equal interval. These results indicate that engine revolution first order component pressure fluctuation appearing after muffler does not exist with the pressure peak immediately before the muffler with equal explosion interval and the mechanism above mentioned was verified to be true. RELATIONSHIP BETWEEN CAPACITY OF JUNCTION AND ENGINE REVOLUTION FIRST ORDER COMPONENT PRESSURE FLUCTUATION The measured result of sound level pressure with various capacities of two front pipes junction is shown in figs 18. The connection between two front pipes and muffler are unchanged among the specimens, and the muffler length was changed to change the capacity of the junction. Muffler of 1/4V volume was installed in Exhaust pipe 3 shown as fig 17(b), Muffler of 1/2V volume was installed in Exhaust pipe 4 shown asfig 17(c). Eight peaks exist during crank angle 270 degrees in exhaust pipe 1. While increasing total capacity of muffler in entire exhaust pipe makes sound pressure a amplitude of exhaust pipe smaller, two group of peaks (engine revolution first order component peak) were generated in proportion to capacity of junction. That is, the smaller capacity of junction, the smaller the amplitude of a engine revolution first order component produced after junction. This indicates that a smaller capacity at junction caused less engine revolution first order component fluctuation due to less delay in pulsation propagation at junction. Effect of shape and angle of junction Comparison was made between in the shape of the junction of two front pipe among figs 19 (a) and (b). Fig 19(a) is the case two front pipes join with same angle, (b) is the case front pipes join in parallel. Fig 20 shows the measured result of exhaust sound pressure. Almost no difference was observed in exhaust sound. That is , the angle of junction and the separation of junction did not have much effect on the exhaust sound Conclusion Analysis of pressure waves inside the exhaust pipe using experiments and simulations revealed the following 1. the pulsation wave frequency inside the pipe is different in the entire exhaust pipe with long front pipes of 8V engine. The characteristics of the pulsation wave inside the pipe are changed due to joining, and the two front pipes dissipate each other 2 .the V type 8 sylinder engine has irregular explosion intervals among sylinders on each bank and pulsation with irrigation interval peaks propagate into left and right front pipe. In the exhaust pipe where the two pipes join upstream of the muffler, pulsation inside front pipes propagate into junction without phase delay and pulsation peaks immediately before the muffler exist at equal interval. While, in exhaust pipe in which the two front pipes join at muffler. Pipe in which the two front pipes join at muffler, pulsation peaks immediately before the muffler exist at irregular intervals. As pulsation propagates at volume with delay, some peaks which exist at short interval effected the next peak to generate one group of peaks and peaks gathered at each of the two front pipes, which generated an engine revolution first order component pressure fluctuation. This new engine revolution first order component pressure fluctuation generated at muffler makes exhaust sound worse. 3. In the case an exhaust pipe has long front pipes and explosion intervals among cylinders on each bank of engine are irregular, such as the one described in this paper, the calculated results of pulsation and flow using fluid dynamic model representing the entire intake system, engine and exhaust system can simulate actual phenomena and suitable to predict pulsation and exhaust noise. ACKNOWLEDGMENTS The acthors thank Mr. Toshiyuki Hashimoto, Kazunori Okubo and Sumio Ogawa gor their helpful discussion and useful indication, and also thank Mr. Toyoharu Yoshitake and Norihiko Konishi for their work in the Lab and valuable contribution towards understanding the mechanism. REFERENCES Flamang, P. et al. “Experimental theoretical analysis of the floe in exhaust pipe junction”, IMeche 1989 Katayama, T., et al., “An estimation of method for acoustic characteristics of muffler”, Toyota Tech., vol. 41,1991 Hosomi, M., et al., “Optimization of Exhaust Pipe Muffling Performance by Sound Pressure Modal Analysis”, FISIYTA 96,1996 Tanaka, T., et al., “Analysis of a Three Dimensional Sound Field by Using The Boundary Element Method”, Transaction of The Japan Society of Mechanical Engineers(c),vol.53,No.491,1987 Morel, T., Morel, J. and Blaser, D. A., “Flhid Dynamic and Acoustic Modeling of Concentric-Tude Resonators/Silencers”, SAE paper 910072, 1991 Desantes,. J. 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