Intake Manifold Design using Computational Fluid ...

Intake Manifold Design using Computational Fluid Dynamics

M.Tech Dissertation- II

By

Awanish Pratap singh (10904512)

DEPARTMENT OF MECHANICAL ENGINEERING LOVELY PROFESSIONAL UNIVERSITY PHAGWARA, PUNJAB (INDIA) -144402 2013-2014

Intake Manifold Design using Computational Fluid Dynamics DISSERTATION Submitted in Partial Fulfillment of the Requirement for Award of the Degree Of

MASTER OF TECHNOLOGY In MECHANICAL ENGINEERING By

Awanish Pratap Singh (Reg. No 10904512) Under the Guidance of Mr. Manish Gupta

DEPARTMENT OF MECHANICAL ENGINEERING LOVELY PROFESSIONAL UNIVERSITY PHAGWARA, PUNJAB (INDIA) -144402 2013-2014

I Would like to dedicate my dissertation to my Father, Sidheshwar Singh ; Mother, Kusum Singh ; Brother, Alok Kumar Singh ; and Late Grandparents.

Lovely Professional University Jalandhar, Punjab

CERTIFICATE I hereby certify that the work which is being presented in the dissertation entitled “Intake Manifold Design using Computational Fluid Dynamics” in partial fulfillment of the requirement for the award of degree of Master of Technology and submitted in Department of Mechanical Engineering, Lovely Professional University, Punjab is an authentic record of my own work carried out during period of Dissertation under the supervision of Mr. Manish Gupta, Assistant Professor, Department of Mechanical Engineering, Lovely Professional University, Punjab. The matter presented in this dissertation has not been submitted by me anywhere for the award of any other degree or to any other institute.

Date:

.

(Awanish Pratap Singh)

This is to certify that the above statement made by the candidate is correct to best of my knowledge. Date:

(Manish Gupta) Supervisor

The M- Tech Dissertation examination of Awanish Pratap Singh, has been held on .

Signature of Examiner

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ACKNOWLEDGMENTS

I would like to express my very great appreciation to Mr. Manish Gupta for his patient guidance, enthusiastic encouragement and useful critiques of this research work.

His

willingness to give his time so generously has been very much appreciated. I would also like to thank Dr. Rajeev Sharma, for his advice and assistance in keeping my progress on schedule. I would also like to extend my thanks to Mr. Gurpreet Singh Phull, for his valuable and constructive suggestions during the planning and development of this research work. I would also like to extend my thanks to the technicians of the laboratory of the Mechanical Engineering department for their help in offering me the resources in running the program. Finally, I wish to thank my parents for their support and encouragement throughout my study.

Awanish Pratap Singh Reg. No. 10904512

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ABSTRACT

In automotive technology, an intake manifold is the component of an engine that transports the air-fuel mixture to the engine cylinders. The main purpose of the intake manifold is to evenly distribute the combustion mixture to each intake port of the engine cylinder. Even distribution is important to optimize the volumetric efficiency and performance of the engine, but the major problem in the thesis identify that; to achieve the even distribution of flow at each cylinders, to select the best turbulence model for the analysis of manifold using computational fluid dynamics, to achieve the maximum mass flow rate through the restricted size C-D nozzle, to maintain the equal pressure throughout the plenum, to propagate back the higher pressure column of air to intake port within the duration of the intake valve‘s closure. To achieve the even flow of distribution and improve the volumetric efficiency, author divided his analysis in to three different part restrictor, plenum and cylinder runner

and then analyzed the final intake manifold. Dividing the work into three different

part and then combine them as single manifold part provide the greater refinement in result and act as meshing of manifold. To select the best turbulence model for this study, author took the design data of existing experimental model and find that Spalart-Allmaras model was approximately same as the experimental model. For designing the nozzle, author selected the four design variables; nozzle inlet diameter, inlet curvature radius, diffuser half angle and diffuser length with five level of each variable. With these four variable and five level of each variable, author had need to perform 625 experiments, but he design the matrix by the help of Taguchi method using statistical tool ―Minitab‖ and perform only 25 experiment in CFD package ―Ansys Fluent‖, to find the best result for restrictor, author again use the statistical tool to analyze the design matrix, and then predict the best result for restrictor. To propagate back the higher pressure column of air to intake port within the duration of the intake valve‘s closure, author use the Ram Theory and Helmholtz theory to calculate the runner length and diameter as well as total distance traveled by the pressure column during the intake valve closure. To find out the pressure variation in cylinder runner due to intake valve opening and closing, author design virtual engine of the same specification of Kawasaki Ninja ZX-6R by using leading engine designing software ―Ricardo Wave‖, and then use these pressure data to develop the transient boundary condition in ―Ansys Fluent‖. To achieve the static pressure Page | vi

inside the plenum and distribute the combustible air evenly to each intake runner, author select two design variables; plenum shape (rectangular, circular, elliptical and curved) and plenum size (2.0litre, 2.25litre, 2.5litre, 2.75litre and 3.0litre). To find the best result for plenum, author perform the experiment in Ansys Fluent for all possible experiment and find the curved and elliptical shape plenum were providing higher volumetric efficiency, static plenum pressure and even flow of distribution to each cylinder. For designing final intake manifold author select best design from all three part; restrictor, cylinder runner, plenum; and perform the experiment using computational fluid dynamics software Ansys Fluent, and in result he find that plenum with 2.5litre size curved shape with restrictor of 48mm nozzle inlet diameter, 41mm inlet curvature radius, 152mm diffuser length and 30and 70 diffuser half angle. Keywords: Intake Manifold, Plenum, Restrictor, Cylinder Runner, Volumetric Efficiency, Computational Fluid Dynamics

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Table of Contents ACKNOWLEDGMENTS ......................................................................................................... v ABSTRACT ............................................................................................................................. vi CHAPTER 1. INTRODUCTION .............................................................................................. 1 1.1 BACKGROUND ............................................................................................................. 1 1.2 FUNDAMENTAL KNOWLEDGE ................................................................................ 2 1.2.1 Introduction ............................................................................................................... 2 1.2.2 Fluid Flow through Duct and Pipe ............................................................................ 3 1.2.2.1 Pressure Losses in Pipes......................................................................................... 3 1.2.2.2 Velocity profiles ..................................................................................................... 3 1.2.3 Nomenclature of Intake ............................................................................................. 3 1.2.4 Wave Theory ............................................................................................................. 5 1.2.5 Computational Fluid Dynamics (CFD) ..................................................................... 6 CHAPTER 2. - LITERATURE REVIEW ................................................................................ 7 CHAPTER 3. PROBLEM IDENTIFICATION AND HYPOTHESIS ................................... 17 3.1 PROBLEM IDENTIFICATION.................................................................................... 17 3.2 HYPOTHESIS ............................................................................................................... 18 CHAPTER 4. METHODOLOGY ........................................................................................... 19 4.1 INTRODUCTION ......................................................................................................... 19 4.2 STAGE-1 SELECTION OF BEST TURBULENCE MODEL ..................................... 19 4.3 STAGE-2 SELECTION OF BEST RESTRICTOR MODEL ....................................... 21 4.4 STAGE-3 SELECTION OF BEST CYLINDER RUNNER SIZE AND BOUNDARY CONDITION ....................................................................................................................... 23 4.5 STAGE-4 SELECTION OF BEST PLENUM SHAPE AND SIZE ............................. 25 4.6 STAGE-5 FINAL INTAKE MANIFOLD SELECTION .............................................. 27 4.7 SIMULATION SETUP METHOD ............................................................................... 29 CHAPTER 5. RESULTS AND DISCUSSIONS .................................................................... 30 5.1 SIMULATIONS AND RESULT OF TURBULENCE MODEL .................................. 30 5.1.1 Simulation of Each Turbulence Model ................................................................... 30 5.1.2 Summary of Result for Turbulence Model ............................................................. 34 5.1.3 Pictorial View of Model Used For Turbulence Modeling ...................................... 34 5.2 SIMULATIONS AND RESULT OF RESTRICTOR ................................................... 35

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5.2.1 Effect of Variation in Nozzle Inlet Diameter .......................................................... 35 5.2.2 Effect of Variation in Diffuser Half Angle ............................................................. 36 5.2.3 Effect of Variation in Diffuser Length .................................................................... 38 5.2.4 Effect Variation in Inlet Curvature Radius ............................................................. 39 5.2.5 Overall Mean Result ............................................................................................... 41 5.2.6 Pictorial Representation of Simulation Model ........................................................ 42 5.2.7 Result Validation ..................................................................................................... 45 5.3 CALCULATION AND RESULT OF CYLINDER RUNNER..................................... 46 5.3.1 Calculation for Cylinder Runner Length ................................................................. 46 5.3.2 Calculation for Cylinder Runner Diameter ............................................................. 49 5.3.3 Boundary Condition at Cylinder Runner Outlet or Engine Intake .......................... 51 5.4 SIMULATIONS AND RESULT OF PLENUM ........................................................... 52 5.4.1 Effect of Different Plenum Shape and Size ............................................................ 53 5.4.2 Effect of Rectangular Shape Plenum ...................................................................... 54 5.4.3 Effect of Circular Shape Plenum ............................................................................. 54 5.4.4 Effect of Elliptical Shape Plenum ........................................................................... 55 5.4.4 Effect of Curved Shape Plenum .............................................................................. 56 5.4.5 Pictorial Representation of Results ......................................................................... 57 5.5 SIMULATIONS AND RESULTS OF INTAKE MANIFOLD .................................... 59 5.5.1 Simulation Result of All Intake Manifold ............................................................... 59 5.5.2 Effect of Curved Plenum Shape .............................................................................. 60 5.5.2 Effect of Elliptical Plenum Shape ........................................................................... 61 5.5.3 Effect of Plenum Size.............................................................................................. 62 5.5.4 Effect of Restrictor .................................................................................................. 63 5.5.5 Pictorial Representation of Intake Manifold Analysis ............................................ 64 CHAPTER 6. CONCLUSION AND FUTURE RECOMMENDATIONS ............................ 68 6.1 CONCLUSION .............................................................................................................. 68 6.2 FUTURE RECOMMENDATIONS .............................................................................. 69 APPENDIX A: Related To Restrictor Designing ................................................................... 70 A.1 Design table of ―Restrictor‖ with result ........................................................................ 70 A.2 Analytical Modelling .................................................................................................... 70 A.3 Taguchi Analysis By Statistical Tool ―MINITAB‖ For Nozzles ................................. 72 APPENDIX B: Data Related to Boundary Condition ............................................................. 75 Page | ix

B.1 Variation of Pressure with time for all four cylinders at 6000RPM ............................. 75 B.2 Profile Format: Fluent Transient Boundary Condition for All Four Cylinders ............ 78 APPENDIX C: Data Related To Plenum Modeling................................................................ 84 APPENDIX D: Data Related To Final Intake Manifold Modeling......................................... 85 APPENDIX E: Specification of Engine .................................................................................. 86 REFERENCES ........................................................................................................................ 87

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List of Figures

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CHAPTER 1. INTRODUCTION

1.1 BACKGROUND In automotive technology, an intake manifold (in American English) is the component of an engine that transports the air-fuel mixture to the engine cylinders. The term manifold originated from the traditional English word manigfeald (from the Anglo-Saxon manig [many] and feald [fold]) and relates to the folding together of multiple inputs and outputs. The main purpose of the intake manifold is to evenly distribute the combustion mixture to each intake port of the engine cylinder, and to create the air-fuel mixture, unless the engine has direct injection [1, 3]. Even distribution is important to optimize the volumetric efficiency and performance of the engine, the two most desirable techniques was found to increase the volumetric efficiency, and they are intake manifold design and variable valve timing technology for intake and exhaust valves. The design of the variable valve timing technology is quite complex and expensive to produce, and it offers quite less scope of research, thus almost every researchers and automotive industry is focused on improvement of intake manifold. However, there is always room for enhancement on intake system. The air intake system has seen many reiterations and improvements and substantially increased during the past years by controlling the dimension and shape, and permitting the engine to produce increasing amounts of power by improving their volumetric efficiency, best possible fuel consumption, reduced fuel emissions, and most of the research performed, by automotive researchers and engine manufacturers (i.e. Mazda, BMW, Audi, Ford, Renault etc.)[3]. Porsche in the 1980s developed an intake system to use on their vehicles that adjusted the length of the intake system by switching amongst the longer and shorter pair of tube utilizing a butterfly valve, developing some positive pressure, which usually enhances overall performance of the engine. Audi began to use a similar system in some cars in the 1990s and Ford Motor in 1997 [7, 14]. IC engines produce air pollution emissions as a consequence of uneven distribution of combustible air to the engine and incomplete combustion of air-fuel mixture. The principal products of the process are carbon dioxide, water, sulphur, black carbon and some unburnt Page | 1

hydrocarbons, which is produce due to lesser amount of air-fuel ratio supplied to the engine, and the additional products of the combustion process include nitrogen oxides, which is produced due to excess amount of air-fuel ratio supplied to the engine [14]. The amount of air is only one parameter which produces emission. Thus it is needed to design a manifold which deliver appropriate amount of air to combustion chamber. There is great contribution of Motorsport Company in the field of intake system designing. FIA conduct every year Formula 1 competition to allow automotive industry to contest against each other and compare their technology in a motor racing environment. A similar competition is conducted by Society of Automotive Engineers for students are Formula SAE since 1979, The "Formula", specified within the name, refers to a set of rules with which all participants' cars must follow. The key intention of designing this competition to permit University students to contest against each other in a motor racing environment, this competition is not just designed for engineering disciplines while applying many of the skills essential for the automotive industry. There are some restrictions in the competition related to intakes that, circular restrictor is positioned in the intake system between the throttle and the engine In order to limit the power capability from the engine, and all engine airflow must pass through the restrictor and maximum allowable diameter is 20mm. The engine used to power the car must be a piston engine using a four-stroke primary heat cycle with a displacement not exceeding 610 cc per cycle.

1.2 FUNDAMENTAL KNOWLEDGE 1.2.1 Introduction An engine intake manifold is the part of the engine, between the throttle body and the engine cylinders. In a multi-cylinder engine, the primary function of the intake manifold is to transport combustion air to the engine cylinder, and to create the fuel air mixture, unless the engine has direct injection. The intake manifold controls how much air can be drawn through, including the effects both in steady state and transients, how fast that air is moving, and how well it can be mixed with fuel, and restriction of the 20mm set how much mass of air can flow inside engine cylinder. Because the throat area of restrictor determines exactly the mass air flow, it has a large influence on engine volumetric efficiency [4-5].

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1.2.2 Fluid Flow through Duct and Pipe An intake manifold is ostensibly a network of pipes and ducts which feed air into the engine to feed the combustion process. As such it is open to analysis and optimization as any network of pipes and ducts may be. One well documented and theorised section of pipe flows involves a head loss, or pressure loss due to certain geometries within the flow, specifically for bends, valves, entrance and re-entrance flows. Another well researched characteristic of pipe flow is velocity profiles for both turbulent and laminar flows. 1.2.2.1 Pressure Losses in Pipes Pressure losses in pipes are split into two categories, major and minor. Major losses occur due to the physical length of the pipe and the viscous losses associated with the friction between the wall and the fluid. Minor losses occur due to variations in geometry through the piping such as bends, elbows, valves, entrances and re-entrances [26]. The terms major and minor do not refer to the relative sizes of the losses necessarily, but in typical piping systems involving many long straight sections with few bends and valves the major losses are more substantial than the minor. In the case of an intake manifold however, the ‗minor‘ losses are far more significant, and typically dominate the pressure losses experienced. Several text books quote pressure loss coefficients for various geometries whether they be entrances, reentrances, bends or valves. While these particular values are important in an analysis of a pipe system their values are not important specifically for the design of a new intake, but their relative size is. 1.2.2.2 Velocity profiles Figure 5.1.2 presents the velocity profile of flow through pipe, velocity profiles are of importance to the work being carried out as they are one of the tools utilized in validating the results of various simulations. The velocity profile within a pipe is a well-studied phenomenon and has been noted to depend on a number of factors. The predominant effect on the final shape is the non-dimensional quantity Reynolds number, more specifically whether it is above or below the transition from laminar to turbulent flow. This factor ultimately determines whether the profile is parabolic (laminar flow) or much flatter (turbulent flow). 1.2.3 Nomenclature of Intake Intake system consists typically of throttle body, restrictor, inlet pipe, plenum, cylinder runnPage | 3

-er, fuel injectors, air temperature sensor and manifold pressure sensor. It composed of two main parts, in combination with the throttle body, which include the plenum and the cylinder runners. Air enters in to plenum through restrictor due to vacuum created by engine, plenum stores the combustion air as reservoir and then transport the combustion air to engine through the cylinder runner.

(a)

(b )

(c)

(d )

Figure 1.1 Intake manifold model with highlight (a) Restrictor (b) Plenum (c) Cylinder Runner (d) Mesh

The information of the work which has been done formerly on intake manifolds allow a more systematic discussion of intake system. On the basis of those information and facts, the basic of acoustic wave theory and general terminology of intakes will be the major field of study, the general terminologies of intake system, which can be used for improvement are: i.

Plenum: It is storage device which placed between throttle valve and cylinder runner. The function of the plenum is to equalize pressure for more even distribution air-fuel mixture in side combustion chamber, because of irregular supply or demand of the engine cylinder, sometime plenum chamber also work as an acoustic silencer device. There are

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two types of intake manifold on the basis of manifold dimension, fixed length intake manifold and variable length intake manifold. ii.

Restrictor (C-D nozzle): Restrictor is part of the intake manifold is similar to what is usually known as a ―critical nozzle‖, ―critical flow venturi‖, or ―sonic choke‖. Such components are often used in practice of industries as simple control devices to control the mass flow rate. All such type of devices will be discussed to as ―restrictors‖ throughout the rest of this report. Excessive pressure losses caused by the high flow velocities [20-23].

iii.

Cylinder Runner: The cylinder runners are the parts of the air intake system which delivers air from plenum to the combustion chamber. In each runner, the principal phenomenon that governs its performance is actually, the effect of acoustic waves [18, 24]. As the purpose of the cylinder runner is distribution of air, performance to transport the maximum amount of air, and in the case of the engine, the successive enhancement in volumetric efficiency.

1.2.4 Wave Theory In order to understand the pressure waves which occur in an intake manifold it is easiest to consider the application in pipe organs. The overarching principle in a pipe organ is the way the pressure waves inside the pipes reflect back along the pipe based upon whether they encounter an open or closed end of the pipe. To briefly explain what occurs and for future reference, two main types of waves form inside the pipe. These waves are known as rarefaction and compression waves. A rarefaction wave is a wave of less than atmospheric pressure and a compression wave is one greater than atmospheric pressure. When a wave reaches an open end of a pipe a wave of opposite form is reflected back down the pipe, if the wave reaches a closed end, a wave of the same form is reflected back along the pipe [30]. In an intake manifold there are two significant events in the intake stroke of the engine, these are the opening and closing of the intake valve. When the intake valve closes, a compression wave forms, whereas when the intake valve opens a rarefaction wave is formed. These waves reflect up and down the intake runner, in the same fashion as in a pipe organ. As these waves are created and propagate they interact with each other in a similar fashion to any other sounds waves, they sum together to form either a wave of higher amplitude, or even possibly diminish to a wave of zero amplitude. In the instance where a rarefaction wave is created upon valve opening it travels along the intake runner to the plenum where a Page | 5

compression wave is reflected back to the valve, when this compression wave hits the intake valve it propagates into the cylinder and increases the pressure in the cylinder. These are parameter which can be tuned to optimize the engine efficiency on the basis of acoustic wave theory. The phenomena related to the acoustic wave are not only limited to the acoustics and musical instruments but also appear in automotive industry. Since the 1937s, the tuning of intake manifolds to harness, these acoustic waves [2]. While these acoustic waves are not a field of investigation in this study, the information of them and the capacity to harness them in the design are of great importance. 1.2.5 Computational Fluid Dynamics (CFD) There are many professional CFD software used in engineering, such as PHOENICS (it is the first commercialized CFD software), STAR-CD, ANSYS FLUENT/CFX and so on. All CFD software‘s have three main structures which are Pre-Processer, Solver and Post-Processor. It doesn't matter exactly what kind of CFD software is, the main procedures of simulation are similar. Establishing up governing equations is the prerequisite of CFD modelling; mass, momentum and energy conservation equation are the three foundation governing equations. After that, Boundary conditions are decided as different flow conditions and a mesh is created. The purpose of meshing model is discretized equations and boundary conditions into a single grid. A cell is the basic element in structured and unstructured grid. The basic elements of two-dimensional unstructured grid are triangular and quadrilateral cell. Meanwhile, the rectangular cell is commonly used in structured grid. In three-dimensional simulation, tetrahedral and pentahedra cells are commonly used unstructured grid and hexahedra cell is used in structured grids. The mesh quality is a prerequisite for obtaining the reasonably physical solutions and it is a function of the skill of the simulation engineer. The more nodes resident in the mesh, the greater the computational time to solve the aerodynamic problem concerned, therefore creating an efficient mesh is indispensable. Three numerical methods can be used to discretize equations which are Finite Different Method (FDM), Finite Element Method (FEM) and Finite Volume Method (FVM). FVM is widely used in CFD software such as Fluent, CFX, PHOENICS and STAR-CD, to name just a few. Compared with FDM, the advantages of the FVM and FEM are that they are easily formulated to allow for unstructured meshes and have a great flexibility so that can apply to a variety of geometries. Page | 6

CHAPTER 2. - LITERATURE REVIEW E.R.Burtnett in 1927 designed first gaseous-fuel manifold for two stroke cycle internal combustion engines of the type in which no inlet valves are used to controlling for the entrance of gaseous fuel to the pre-compression chamber. The determination of this invention was to improve the volumetric efficiency of the engine. As result of this invention, the quick demand developed by suction stroke from one of the pistons within the engine, the gaseous fuel volume within the manifold does not cause an unexpected or unusual of velocity and pressure on the carburetor [1]. W.A.Whatmough in 1937 recognized that pulsating flow inside the intake manifold had certain disadvantages due to pulsation. He also observed that there were both static and dynamic effects in the channel in which there was a fluid flow. The static effects were difference due to pressure and dynamic effects in the channel was difference due to velocity. So that, he designed a mechanism of control tube to automatic modify such pulsating flow to improve the operation of the engine; the general effect of return flow in the control tube is to reduce pulsation and facilitate unidirectional flow in manifold and improve volumetric efficiency [2]. D.A Sullivan in 1939 designed an improved intake manifold for and method of supplying fuel mixture to combustion chamber to improve the volumetric efficiency of the engine. One of the goal of the research was to offer comparatively short passages splitting without any obstructions passage for flow of the fuel mixture on all cylinders of an engine of this nature and that therefore, affords free breathing action, another goal of the research was to provide a manifold of such kind in which the air-fuel ratio produced by carburation means remains same throughout the intake manifold. Further object of this study provide communication among the branches of each unit of the manifold which, although limited enough to cause each branch to draw fuel mixture mainly from their respective means of carburizing, it is large enough to induce the further increase of the fuel mixture occurs in one branch, the other branch of the same section to restrict backflow of the mixture through the carburetor [3]. Jim C. Taylor in 1953 designed an inimitable type of intake manifold for internal combustion engines. The primary goal of the research was to design an intake manifold to produce maximum operating efficiency in internal combustion engines. Another object of the research was to provide an intake manifold of the character indicated above enabling an Page | 7

internal combustion engine equipped therewith, to completely fill its cylinders with fuel mixture during the intake stroke, and further object of the research was to provide an intake manifold of the character indicated above adapted to prevent pumping losses of the engine equipped with the manifold by reducing atmospheric pressure restrictions as far as possible. As result of the research, in internal combustion engine complete evaporation of the fuel was not necessary until the end of the compression stroke so that the mixture needed only to be partly evaporated when leaving the manifold. By arranging two air inlets, the efficiency of the engine was improved by lowering pumping losses due to atmospheric restriction. Such a mixture improve engine performance by maintaining a low temperature of the mixture leaving the manifold, and depending on the engine temperature from intake stroke to the end of compression stroke to aid in completing the evaporation of the fuel [4]. Futakuchi in 1984 designed an improved intake manifold, which enhance both charging and volumetric efficiency of the engine throughout the large range of engine speed and load. He found that the efficiency of the engine intake and combustion, especially at low and medium speeds can be improved by providing an auxiliary intake that communicates with the combustion chamber and that had a relatively small effective area. He found that such auxiliary intakes to result in a high velocity and turbulence in the combustion chamber at ignition time and that improve flame propagation and engine running. These devices also improve the efficiency of load to minimize pulsations in the intake system. Auxiliary intake passage located such that a high degree of swirl can be generated, the amount of the swirls were generated as the auxiliary intake passage increased, when the main inlet passage was in an offset relationship with respect to the associated axis of the cylinder. In combination with the use of auxiliary inlet had encountered advantageous to provide a volume of the air distribution, which deliver the auxiliary intake passage. By using such a volume or plenum chamber, it was found that the flow of the intake charge into the intake passage can be stabilized even at slow speeds and eliminate the pulsation or substantially reduced [5]. He again in 1986 repeat the same research and find out the much improved intake manifold than his previous research in 1984, and as result of repeated research, the volumetric efficiency of the new manifold was comparatively higher than the previous research [6]. C.L.Lee in 1997 found the two possible ways, which can used to increase the volumetric efficiency. The two solutions were variable intake manifold geometry and variable valve timing technology for intake and exhaust valves. By watching the scenario of that time, he

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designed a different type of variable intake manifold length for internal combustion engine, which may vary the geometry of inlet through which air was flowing. Since the primary function of an air inlet manifold for internal combustion engine was to feed desired amount of air to the engine combustion chamber [1-8]. To maximize the performance of the engine (torque and power), an inlet manifold should be capable of deliver air as much as possible for a given size. By using conventional approach, he tuned manifold based on their acoustic properties. The tuning enabled the amount of air moving as quick as possible at a particular engine speed, which achieved acoustic resonance in the excitation frequency caused by the work of pumping pistons. This result in a volumetric efficiency of intake air is more than 100% for given engine speed, while at other speed range efficiency falls below 100%. It was one in which the runner size were interchanged between long and short. Runners with longer length decrease the resonant frequency of the intake manifold and increasing the speed of intake air flow, and subsequently, high volumetric efficiency of the air intake occurs at a lower engine speed. Those deliver good engine torque at low engine speed for better stopand-running conditions [7]. Sattler et al. in 1999 found that, the previous research broken conventional intake manifold into three separate parts, plenum, runner cylinder and a supplement portion. Since a fixed runner length can be tuned optimally for a particular engine speed. In order to overcome this, a continuously adjustable runner length was needed to design. So that, they designed continuously adjustable runner length manifold for an internal combustion engine. Incorporating the purpose of a plenum, supplement flange, and continuously adjustable length runner into a plastic box designed from distinct shaped sections. The alternating or pulsating nature flow of the air through the manifold into each cylinder may create resonances (analogous to the vibrations in structure pipes) in the flow of air at specific speeds, This may increase volumetric efficiency and hence the power at certain engine speed but may reduce the efficiency at other speeds, depending on the dimensions and shape of the manifold [8, 10, 17]. As result of this research, With a continuously adjustable runner length system, depending upon the engine speed the intake manifold was capable set up automatically at the optimal runner length, fuel economy, vehicle speed, engine load, etc. and that increase engine performance at all functioning circumstances [8]. Davis et al. in 2001 designed multiple stage ram intake manifold for a four-cycle internal combustion engine to minimize imbalances air/fuel ratio and volumetric efficiency. Intake

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manifold consisting of a plenum chamber contained at least two stages of ram; the first Stage contained ram tubes, which transport the air/fuel mixture to the plenum chamber from the throttle body. The second stage consist of at least two ram tubes that transport the air/fuel mixture to a plurality of intake valves from the plenum chamber and through cylinder head intake ports., plenum chamber acts as a buffer between the carburetor or throttle body and each intake valves. The air/fuel mixture entered into the plenum chamber through first stage ram tube. These gaseous mixtures then flow into either one of the second stage ram tubes, depending on which cylinder was at the intake stroke; As result of the research, by drawing the air/fuel mixtures from the plenum instead of directly from the first stage ram tube, variations in the air/fuel ratio and volumetric efficiency were minimized. This was because the transient variations in the conditions that occur within the first stage ram were concentrated inside the plenum chamber [9]. M.F. Harrison et al. in 2002 describe the acoustic wave dynamics for intake manifold of an internal combustion engine shows the better understanding of a linear acoustic model. They performed on a Ricardo E6 single cylinder research engine and described model developed together with a set of measurements. The simplified linear acoustic model described by them create an estimate of the pressure time history at the port of IC engine, that agrees quite well with the measured data from the engine equipped with a simple intake system. Since the intake method were governed by the immediate values of the piston velocity and the area open under the valve, Subsequently, resonant wave action dominates the process; The model was shown to be useful in identifying the role of the resonance tube and the intake process had led to the development of a simple hypothesis to explain the structure of the time history of inlet pressure: The depth of the depression caused by early piston moving governed intensity wave action, that was a pressure ratio across the valve, which was favorable for continued inflow and was maximized when the opening period valve was such to permit at least, but not more than one complete oscillation of the pressure at its resonant frequency occur while the valve was open [10]. A. Dunkley et al. in 2003 study the effect of acoustics of inlet manifold for motor racing. They design the tuned inlet manifold for naturally aspirated racing engine and shows that volumetric efficiency and engine speed can be achieve in excess of 125% and 18,000 rev/min. since Formula SAE intake manifold divided into three separate parts, plenum, runner cylinder, and restrictor. As result of their study in intake process in a motor racing

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engine exposed the inertial ram effect, and make a strong influence to the inlet process at higher engine RPM, whereas at low engine speed, the nature of acoustic resonance effect were more weak wave action. The resonant wave action of an acoustic model presented the useful in differentiate among these two effects. The attributes of the acoustic model were compared by the researcher to those of more conventional time-marching gas-dynamics calculation approaches [10, 11]. M.F. Harrison et al. in 2003 further proceed the research of M.F. Harrison et al. [2002] and A. Dunkley et al. [2003] and study a linear acoustic model for multi-cylinder internal combustion engine intake manifolds including the effects of the intake throttle, that can be used as part of a hybrid frequency/time domain technique to calculate the intake wave dynamics of applied naturally aspirated engine. These technique permits the researcher to virtually create a model of manifold of complex geometry. These models created by the researcher were with an assemblage of sub-models; a straight pipe through fluid was flowing with open both ends, second sub-model was an intake throttle, third sub-model was an enlargement compartment involving the three lengths of pipe placed at end-to-end, fourth sub model was side-branch, which was including a model for a straight pipe with one end closed and fifth sub model was an expansion with two or more side-branches. They found good arrangement with measurement for respectively sub-model, when bench was tested in isolation and promising arrangement, and when various sub-models were organized to model a complex inlet manifold on a running engine [10-12]. Philip E.A. Stuart in 2005 further proceed the research of Sattler et al. [1999] and Davis et al. [2001] and, He designed a continuously variable intake manifold with an flexible plenum, which communicates with intake manifold of the internal combustion engine, and mainly to an intake manifold having an flexible plenum to offer adjustable runner length during engine operation. The intake manifold assembly was including a plenum volume at that time and mounted for movement within housing [8]. There was movement of the plenum within the housing in order to response to a drive system to define an effective runner length. A multiple of deformable runner passage was including a flexible section such that the plenum can retract and extend within the housing, the flexible section provide the variation in length while structural support provided by the housing. Intake channels equally consist of a flexible section to provide movement of the plenum volume. As result of this research, plenum length must be extended for low engine speeds and shortened as the engine speed increases. . As the

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operational size of the plenum itself is maintained constant and is comparatively small, a constant idle speed is delivered as compared to systems which vary plenum volume [13, 17]. M.A. Ceviz in 2006 studied on Intake plenum volume and its influence on the engine performance, cyclic variability and emissions, Inlet manifold system connected to the engine intake valve, through which the mixture of air or air-fuel is introduced into the engine cylinder. They found that the flow in intake manifolds was very difficult to examine. Since most of engine companies are concentrated on variable intake manifold technology due to their improvement on engine performance [7-9, 13]. He examines the effects of intake plenum volume variation on engine performance and emissions to constitute a base study for variable intake plenum [14, 17]. He also determine the indicated and brake engine performance characteristics, pressure of pulsating flow in the intake manifold runner, coefficient of change in indicated mean effective pressure as an indicator for cyclic variability, and CO, CO2 and HC emissions were taken into concern to estimate the effects of altered plenum volumes. As results of this study variation in the plenum volume causes an enhancement on the engine performance and the pollutant emissions. The brake and indicated torque and other associated performance characteristics enhanced pronouncedly about between 1700 and 2600 rpm by increasing plenum volume. Furthermore, while the increase in the intake runner pressure made leaner mixture due to increase in the plenum volume and lean mixtures inclined to increase the cyclic variability, a decrease was interestingly observed in the coefficient of variation in indicated mean effective pressure [14]. Mark Claywell et al. in 2006 study on design of intake restrictor required by the Formula SAE event to limit the performance, keep costs low, and maintain a safe racing experience. As the engine performance was limited by the intake restrictor. Thus researchers approach the method of ramifications of the restrictor on the engine, which lead to enhancement in engine performance and allow an edge over the competition. They use Ricardo‘s software WAVE (1D) and VECTIS (3D) to study the engine performance [15, 16]. There primary area of improvement was determined by the use of comparatively small diffuser angles. Acoustic filtering using Helmholtz resonators was studied using WAVE to determine enhanced restrictor performance by making flow at the throat more uniform over the cycle [16]. They also investigate Inline Helmholtz resonators in an attempt to increase upstream pressure of the throat. An extra coupled simulation considered the effect of turbulence vanes placed upstream of the restrictor throat. Turbulence vanes had little to no effect on the performance

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of the intake [16]. They also studied on various type of plenum and found that, ConicalSpline Intake Concept offer the best performance and give higher order of magnitude improvement in the deviation of cylinder-to-cylinder volumetric efficiency [15]. M.A. Ceviz et al. in 2010 further proceed the research of Sattler et al. [1999], Philip E.A. Stuart [2005] and M.A. Ceviz [2006] and, he studied the effects of variable intake plenum length on the engine performance characteristics of a SI engine with MPFI system using electronically controlled fuel injectors. He describes that, the intake manifold only transport the air from plenum to engine cylinder whereas, the fuel was injected onto the intake valve, the and also found that supercharging effects of the variable length intake plenum will be different from carbureted engine [4-10, 14, 17]. He carried out the engine test with the purpose of establishing a base study to design a new variable length intake manifold plenum. He takes consideration of Engine performance characteristics such as brake torque; brake power, thermal efficiency and specific fuel consumption into to estimate the effects of the different length of intake plenum. According to the test results, as the engine speed increases, the plenum is driven to shorten the deformable runner for maximum speed operation and also shows that the improvement on the engine performance characteristics caused by the variation in the intake plenum length, especially on the fuel consumption at low engine speed and high load which are put forward the system using for urban roads. [17] David Chalet et al. in 2011 studied on inlet manifold of internal combustion engine by frequency modeling of the pressure waves, they perform the simulation of pressure waves on inlet and exhaust manifolds of internal combustion engine, which remains challenging. In their study they design new model which is presented in order to investigate these pressures waves without the use of a one-dimensional explanation of the system. They study on the system which using a frequency approach. In order to originate this model, they used a dynamic flow bench. Latter they modified flow in order to generate waves in fluid which may be in moving condition or stationary condition. They characterized inlet system by its geometrical characteristics as well as the fluid characteristics. Certainly, the gas temperature and the gas velocity were major influence on the fluid behavior. They used new model in order to simulate the behavior of pressure waves into a 1-m pipe which is associated with driven engine, which act as a pulse generator. They proved that experimental and the numerical results keep good agreement. [18]

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Fluent-14.0 (2011) provide very good approach to solve the physical problem of computational fluid dynamics, for solving any physical problem on fluent turbulence model should be appropriate and there are some turbulence model presented in Fluent. The viscous turbulence modeling feature within FLUENT provides the user the ability to model turbulence making use of 4 different turbulence models, these are: 

Spalart–Allmaras



K-epsilon



K-omega



Reynolds Stress Model These models, all in simplistic effect, produce a time averaged equation to simplify

the governing equations of turbulence, which if considered in full are of such high frequency and small scale that it would be too computationally intensive to run even the simplest of simulations [27]. In order to determine which model was most appropriate for this particular case of internal ducted flow it was necessary to consider the backgrounds and merits of each model Spalart-Allmaras Model The Spalart-Allmaras model is a 1-equation turbulence model which solves a transport equation for kinematic turbulent viscosity. This is a relatively new turbulence model and has applications to the aerospace industry, specifically those involving wall-bounded flows [27]. A validation study on the model conducted by Paciorri et al. from the Von Karman Institute in Belgium concluded that the Spalart-Allmaras model provided excellent agreement with experimental data for most models tested. For those models where agreement was not as good it still produced excellent correlation for pressure distribution and heat transfer but under estimated the size of separation regions [28]. A critical survey on numerical methods by Knight et al. investigating the prediction capabilities of various turbulence models relating to shock wave/boundary layer interactions concluded that the Spalart-Allmaras model produced very accurate results when compared with experimental data [29]. K-Epsilon Model The k-ε turbulence model is a 2-equation turbulence model which independently calculates turbulent viscosity and a length scale. The two equations relate to kinetic energy of the Page | 14

turbulence k, and the rate of dissipation ε. The model has been widely used by industry and has become almost a standard by virtue of its economy of computational efficiency, accuracy and robustness for a wide range of turbulent flow applications [27]. A validation study for a k-ε model was conducted by Poroseva et al.in which they concluded that the k-ε model produced good agreement with experimental data, but that the k-ε model would often produce higher peaks in velocity than were obtained experimentally. The velocity profile by all three turbulence models produced a higher peak than was obtained experimentally and these peaks were generally sharper than what was obtained experimentally [32]. The study mentioned in the section on the Spalart-Allmaras model on shock wave/boundary layer interaction indicated that while the k-ε model produced agreement with the trends of experimental data, the results were less accurate [29]. K-omega Model The k-ω model is another 2-equation model similar to the k-ε model, it models the kinetic energy of the turbulence, k and the specific dissipation rate ω. The specific dissipation rate can be considered a ratio of ε to k [27]. Several journal articles have eluded to the sensitivity of the k-ω model on the upstream and or free stream values of turbulence variables, particularly ω. (Kok, 2000) and (Bredberg et al. 2002) While work has been conducted to reduce this dependence the update model has yet to be implemented into the version of FLUENT being utilised. In the case being simulated we only have an approximation of the turbulence of the flow entering the restrictor and this may indicate a potential weakness of this model. It will however still be included for comparison. Reynolds Stress Model (RSM) The Reynolds Stress Model is a 5-equation model in 2 dimensions and 7-equation in 3 dimensions. It calculates the individual Reynolds stresses utilizing differential transport equations. The equations are derived directly from the momentum equation; the equations are used to close the unknowns of the full momentum equation. The added complexity of this model and the 5 or 7 equations that need to be solved significantly increase the processing power required to conduct simulations. Improvements to the algorithm have significantly Page | 15

improved the performance of this model and computational time is approximately 50% higher per iteration than the 2-equation models [27]. A study into Reynolds Stress modelling involving shockwave boundary layer interactions by Vallet of the Pierre and Marie Curie University compared the performance of several Reynolds-stress models and also considers a k-ε model. The study concludes that the RSMs could reproduce, quite accurately, the experimentally determined values for the flow, while the k-ε model failed [33].

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CHAPTER 3. PROBLEM IDENTIFICATION AND HYPOTHESIS

3.1 PROBLEM IDENTIFICATION The primary function of the intake manifold system was to transport combustion air to the cylinder. Specifically, the primary design goal was to distribute the air evenly to each intake port, as doing so improve the engine ability to efficiently produce torque and power. The geometric design of the intake system affects the volumetric efficiency of the engine, and thus directly affects the performance of the vehicle [3]. The construction of the intake system has a major influence on how the engine performs at various RPM‘s [14]. The challenge, therefore, was to optimize the design of the intake system and remap the fuel injection system. To achieve primary design goal of distributing equivalent amounts of air to each cylinder, there are several objectives to consider when designing an intake system: i.

Minimize pressure loss, as pressure loss results in a decrease in output power.

ii.

Maintain equal static pressure distribution in the plenum, as this will cause the cylinders to pull the same vacuum, thus leading to even flow in each cylinder.

iii.

Minimize bends and sudden changes in geometry, as these geometric affects can cause pressure loss.

iv.

Maximize air velocity into the cylinder, as this provides a better mixture of fuel and air, which results in better combustion and performance.

v.

To select optimum plenum size according to the engine to maximum mass flow rate in order to improve the volumetric efficiency

vi.

To achieve the Mach number (M=1) at throat of restrictor nozzle, to increase the volume flow rate of air through restrictor but it depends upon boundary condition.

vii.

Minimize the mass of the system, a common goal of every subsystem of the vehicle.

viii.

Design a technique to fluctuate the intake plenum length, cylinder runner length and optimal profile for restrictor to operate the engine efficiently over a wide speed range.

ix.

To order to achieve minimum turbulence, it is necessary to design a profile with no flat edges with central inlet curved plenum which transferred the air at right angles to four tapered runners.

x.

The main objective for designing the cylinder runner is to propagate back the higherpressure column of air to intake port within the duration of the intake valve‘s closure. Page | 17

xi.

To keep minimum runner diameter area as much as possible, because increase in diameter provides additional surface area that creates more flow resistance and also reduce the air velocity.

3.2 HYPOTHESIS In some previous study and fundamental knowledge of flow through ducts and pipes, the base plate, sudden bends or valves were causing turbulence so that in this thesis assumption was made to design a profile without flat edges, sudden bends and re-entrances. In this study intake system was assumed to be central inlet with curved plenum, which transferred the air at right angles to all four tapered runners. The concept here was that the air will enter in the plenum and travels to the back wall in which the profile of the wall will distribute the air to all four runners. With this concept an even distribution of air among all four runners can achieved with minimum turbulence and for achieving minimum turbulence different type of turbulence model were also assume to be used for validation study, that provide excellent agreement with experimental data for most models tested. For achieving maximum volumetric efficiency, nozzle of ISO: 9300 category was assumed to be best design and most beneficial for the use, because it consists of an inlet radius, and exit angle and also certified by ISO: 9300. For designing any restrictor five variables were used to define the optimum profile of the restrictor, inlet diameter Di, choke diameter D, exit diameter De, radius R and exit angle ; and these five variable can be obtain by using standard profile of ISO:9300. In order to achieve this, the higher-pressure column of air, which starts forming upon the closing of the intake valve, will have to propagate to the open end of the runner, be reflected, and propagate back to the valve opening within the duration of the intake valve‘s closure. Knowing the time required for the distance travelled, as well as taking the assumption that this acoustic compression and expansion wave propagates at the speed of sound, by using Ram Theory and Helmholtz Theory a simple calculation can be done to obtain the runner length to accommodate such a distance. Having an intake runner sized at the appropriate length to increase the pressure of the air behind the intake valves when they open, is known as runner length tuning. A properly tuned intake runner system will be able to ―ram‖ more air into the cylinder and thus improve the overall volumetric efficiency. Page | 18

CHAPTER 4. METHODOLOGY

4.1 INTRODUCTION CFD allows the simulation of fluid flows through or over models of any size and or shape, furthermore it allows an in depth look at the occurring inside a model with great ease. In the case of an intake manifold it makes a clear choice for examining the flow occurring inside the manifold itself. Another significant advantage of CFD is it allows the comparison of different models without actually having to spend any resources constructing the models themselves. This will allow the author to compare several variations in intake geometry in both restrictor parameters and plenum parameters with great ease. 4.2 STAGE-1 SELECTION OF BEST TURBULENCE MODEL The findings of various literature reviews all have indicated that the previously mentioned turbulence models are, given the right set-up and capable of simulating the flow we wish to examine. Each model had identified strengths and shortcomings for various simulations and it was clear that no one model was able to be utilised reliably given any case. As a consequence there would have to be further investigations into each model in order to pick one as more suited than others and method is explained in flow chart. It was decided to conduct simulations applying each of the potential turbulence models and comparing the results obtained to each other, and to expected characteristics for pipe flow. Table 4.1 Design table for selecting turbulence model for simulation Turbulence Models

Range Value

Procedure

Spalart-Allmaras

N/A

Perform the experiment in Ansys Fluent of given model

k-ε Model

N/A

Perform the experiment in Ansys Fluent of given model

k-ω model Reynolds Stress Model

N/A

Perform the experiment in Ansys Fluent of given model

N/A

Perform the experiment in Ansys Fluent of given model

Other Model in Fluent

N/A

Perform the experiment in Ansys Fluent of given model

Response Variables

Target Value

Objective

Volume Flow Rate

Experimental Model

Nominal the Best

Velocity

Experimental Model

Nominal the Best

Pressure Drop

Experimental Model

Nominal the Best

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A schematic layout of the method used for selection of “Turbulence Model” indicated in flow chart:

Figure 4.1 Flow chart: Method used for “Turbulence Model ” selection

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4.3 STAGE-2 SELECTION OF BEST RESTRICTOR MODEL The restrictor is a very significant part of the intake system being modeled. The restrictor is the ultimate restriction on the amount of air which can flow into the intake system, and thus, the amount of power produced by the engine. Consequently this segment of the intake manifold is the logical place to commence simulations. A thorough understanding of the flow through this section will allow the author and to improve the design as much as possible, giving the best possible air flow into the plenum.. For achieving maximum volumetric efficiency, standard profile of ISO:9300 was best design and most beneficial for the use. For designing any restrictor five variables were used to define the optimum profile of the restrictor, inlet diameter Di, choke diameter d, , radius of curvature at inlet R, diffuser half angle

and diffuser length, these five variable can be

obtain by using standard profile of ISO:9300. As per this thesis motivation there is some restriction to keep choke diameter as constant, so that only four variables was used to optimize the restrictor profile.

Figure 4.2 Circular profile for restrictor nozzle design [ISO: 9300] [20]

When designing the engine components, then first step to choose the design variables which affect the target response, in this study, there were four factors with and each factor consists of five levels. Author feel that experiment was difficult to perform according to full factorial method because it was creating 625 possible experiments and taking much time, so that author design experiment by the help of Taguchi method with the help of statistical tool ―MINITAB‖, Taguchi method created 25 best possible experiment by combination of all four factors and five levels. Author then simulate all the 25 experiment by using best turbulence model chosen in stage-1 and compare each simulation with set target response value, if any of the simulated response value was approximately equal to the set target value then that model was chosen for designing final intake manifold else author analyse experiment in statistical Page | 21

tool ―MINITAB‖ to see the effect of all design variable on target response value and redesign new experiment. Author was repeating the experiment until he did not get best five result of restrictor for final intake manifold design. A schematic layout of the method used for “Restrictor” design indicated in flow chart:

Figure 4.3 Flow chart: Method used for “Restrictor” design and simulation

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Table 4.2 Design table for simulation of restrictor model Design Variables

Range Value

Level 1

Level 2

Level 3

Level 4

Level 5

Choke Diameter (mm) d

Constant (d=20)

20

20

20

20

20

Nozzle Inlet Diameter (mm) Di

2.4d< Di