Studies on the Air flow Behaviour in an Intake Manifold of Multi

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          M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




       Studies on the Air flow Behaviour in an Intake
            Manifold of a Multi Cylinder S I Engine
                                M.Sc. (Engg.) Dissertation in
                                   Automotive Engineering




   Submitted by                         : Rakesh D.

   Academic Supervisor                  : Dr. S. N. Sridhara
                                          Dean PEPs, MSRSAS

   Academic Supervisor                  : Farhath Alam
                                          Project Engineer, MSRSAS

        M.S. RAMAIAH SCHOOL OF ADVANCED STUDIES
                          Postgraduate Engineering Programme
                                   Coventry University (UK)
              Gnanagangothri Campus, New BEL Road, MSR Nagar, Bangalore-560 054
      Tel/Fax: 2360 5539 / 1983 / 4759 e-mail: msrsas@vsnl.com website: http://www.msrsas.org

                                        April-2007
     M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




  M.S.RAMAIAH SCHOOL OF ADVANCED STUDIES
                  Postgraduate Engineering Degree Programme
                               Coventry University (UK)
                                        Bangalore


                                   Certificate
This is to certify that the M.Sc. (Engg) Project Dissertation titled “Studies on
Airflow Behaviour in an Intake Manifold of a Multi Cylinder SI engine” is a
bonafide record of the project work carried out by Mr. Rakesh D in partial
fulfilment of requirements for the award of M.Sc. (Engg) Degree of Coventry
University in Automotive Engineering.
                                    September-2007

Dr. S. N. Sridhara                                            Farhath Alam
Academic Supervisor                                           Academic Supervisor
MSRSAS - Bangalore                                            MSRSAS - Bangalore


Prof. Ashok C. Meti                                           Dr. S. N. Sridhara
Programme Manager – (Automotive Engg.)                        Dean-PEPs
MSRSAS – Bangalore                                            MSRSAS – Bangalore


                                 Dr. S. R. Shankapal
                                       Director
                                  MSRSAS – Bangalore
        M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




                                                                                 Declaration


“Studies on the Airflow Behaviour in an Intake Manifold of a Multi Cylinder S I
                                           Engine”


  The Project Dissertation is submitted in partial fulfilment of academic requirements for
M.Sc (Engg) Degree of Coventry University in Automotive Engineering. This dissertation is
a result of my own investigation. All sections of the text and results, which obtained from
other sources, are fully referenced. I understand that cheating and plagiarism constitute a
breach of University regulations and will be dealt with accordingly.




Signature:

Name of the Student:          Rakesh D

Date:                         10 Feb 2007
           M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




                                                                          Acknowledgement
   I would like to express my thanks and gratitude to Dr. S. N. Sridhara, Dean PEPs for his
continuous support, helpful advice and valuable guidance throughout this project work. In
spite of his busy schedule, he was kind enough to guide and help me to complete this project.
I also thank Mr. Farhath Alam, Project Engineer - SAS Techno Solutions for his support
and guidance extended during my project work.


   My sincere gratitude to Dr. S. R. Shankapal, Director MSRSAS whose emphasis for
excellence kept me focused on to my project and helped me complete it on time. I thank him
for providing the necessary resources and facilities to carry out this project in time. My
sincere thanks to Prof. Ashok C. Meti, Program Manager, Centre for Automotive
Engineering for his valuable and timely advice and suggestions. I would also like to show my
sincere appreciation to Mr. Abdul Nassar, Lecturer, Centre for Automotive Engineering,
MSRSAS for giving me valuable inputs and suggestions at times during the course of my
project.
   I would like to thank all faculty members of MSRSAS especially                 Mr. Ratheesh R.
Nath, Mr. D. Vamshidhar, Mr. Rajesh Kadam, Mr. V. Sapthagiri and Mr. J. Krishna,
who helped me learn the software tools and clarified my doubts, which helped to complete
this project successfully. I would like to extent my thanks to all teaching and non-teaching
staff of MSRSAS for their support during my project work.
   I would like to express my special thanks to my friends at the Centre for Automotive
Engineering for their priceless suggestions. Finally I would like to thank my friends at the
Centre for Rotating Machinery Design for their co-operation and to my family for their great
support and continuous encouragement throughout this project.
         M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




                                                                                       Abstract
       Air motion within the intake manifold is one of the important factors, which governs
the performance of an engine. Hence the flow phenomenon inside the intake manifold should
be understood in order to consider the current requirement of higher engine efficiency and
lower emission. A well-designed intake manifold will reduce the flow resistance and hence
offer better breathing of the engine. Thus intake manifold geometry has strong influence on
the volumetric efficiency in I C engines.


   In the current project work an existing intake manifold of a 4-cylinder, 1.6L S I engine
was modelled and analysed numerically for evaluating the fluid flow. In this process, to
obtain the geometric model, laser scanning was done on the intake manifold by reverse
engineering. The flow domain was extracted from the geometric model for computational
analysis. The CFD analysis was done using commercially available code FLUENT and
Ricardo VECTIS. The analyses were carried out for steady state and unsteady state cases
with values of pressure assigned at the inlet and outlets of the manifold. 1-D Wave code was
used for unsteady state boundary condition calculations.


   The pressure drops observed in individual runners were determined using steady state
simulation. Results showed a higher-pressure drop in the runner 1 which is due the large flow
separation region near runner 1. From the unsteady analysis, flow field velocity variation and
the mass flow rates were analysed and the airflow behaviour inside the manifold was
observed. Based on the analysis it was concluded that the velocity and mass flow rates at
runner 2 and 3 were significantly higher as compared to runners 1 and 4. Based on the results
obtained, a few recommendations have been made towards improving the performance of the
intake manifold.
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                                                                                                         Table of Contents
Title Page………………………..…………………………………….…………………..i
Certificate……………………………………………………………………………..….ii
Declaration.......................................................................................................................... 3
Acknowledgement .............................................................................................................. 3
Acknowledgement .............................................................................................................. 4
Abstract ............................................................................................................................... 5
Table of Contents ............................................................................................................... 6
List of Tables ...................................................................................................................... 8
List of Figures ..................................................................................................................... 9
List of Figures ..................................................................................................................... 9
Nomenclature .................................................................... Error! Bookmark not defined.xi
1–Introduction .................................................................................................................. 11
       1.1   Introduction to the air intake system .......................................................... 11
           1.2 Intake manifold - an overview ....................................................................... 12

2 – Literature Review ...................................................................................................... 14
        2.1 Summary of the literature review .................................................................. 17

3 – Problem Definition ..................................................................................................... 18
       3.1 Problem definition ......................................................................................... 18
           3.3 Problem statement .......................................................................................... 18
           3.3 Project objective............................................................................................. 18
           3.4 Methodology adopted to meet the objective .................................................. 18

4 – Model Construction and Solution............................................................................. 20
      4.1 Manifold dimensions ..................................................................................... 20
           4.5 Solution .......................................................................................................... 21
                  4.5.1 Steady state analysis ............................................................................ 21
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                 4.5.2 Unsteady state analysis ........................................................................ 21

5 – Validation and Discussion of Results ....................................................................... 23
       5.1 Steady state analysis ...................................................................................... 23
                 5.1.1 Flow in plenum chamber ..................................................................... 23
                 5.2.4 Velocity vector along plenum chamber ............................................... 24

6 – Conclusions and Recommendations for future work ............................................. 25
       6.1 Conclusion ..................................................................................................... 25
           6.2 Recommendations for further work ............................................................... 26

References ......................................................................................................................... 27
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                                                                                          List of Tables

Table 4. 1 Dimensions required for surface modelling...................................................... 21
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                                                                                                  List of Figures
Figure 1. 1 Air induction system [2] .................................................................................. 11
Figure 1. 2. Typical intake manifold. [3] ........................................................................... 12
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                                                                              Nomenclature

Symbol                         Unit                     Description
A                              mm2                      Inlet area
D                              mm                       Bore diameter
DH                             mm                       Hydraulic diameter
I                              _                        Intensity ratio
L                              mm                       Stroke length
Re                             _                        Reynolds number
d                              m                        Hydraulic diameter
u                              m/s                      Mean flow velocity
v                              m/s                      Velocity
                              m2/s3                    Dissipation rate
k                              m2/s2                    Turbulence kinetic energy
                              kg/m-s                   Viscosity of air
ρ                              kg/m3                    Density


Abbreviations
CAD            -       Computer Aided Design
CFD            -       Computational Fluid Dynamics
EGR            -       Exhaust Gas Recirculation
MPI            -       Multi-Point Injection
PIV            -       Particle Image Velocimetry
PISO           -       Pressure-Implicit with Splitting of Operators
SIMPLE         -       Semi-Implicit Method for Pressure-Linked Equations
VVT            -       Variable Valve Timing
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                                                                                   1–Introduction


       A properly designed intake manifold is essential for optimal functioning of an internal
combustion engine. Traditional intake manifold optimisation has been based on the direct
testing of prototypes. This trial and error method can be effective, but expensive and time
consuming. Moreover this method cannot provide any information about the actual flow
structure inside the intake manifold. Without this information, the design engineer can never
really understand whether a particular intake manifold performs correctly or not. One of the
possible ways to obtain this information within a reasonable amount of time and cost is to
conduct computational analysis.[1]
1.1   Introduction to the air intake system




                                                Pic




                             Figure 1. 1 Air induction system [2]

       The main function of air intake system is to filter; meter and measure the air flow into
the engine cylinders. The air intake system consists of air filter and throttle body assembly,
which includes throttle valve, intake manifold and either fuel injectors or a carburettor to
inject fuel. The manifold consists of plenum chamber and manifold runners. Cylinder head
         M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




intake path and intake valves also form part of air intake system. Figure 1.1 shows different
parts of a general air intake system.
1.2 Intake manifold - an overview
       An intake manifold is one of the primary components regarding the performance of
an internal combustion engine. An intake manifold is usually made up of a plenum, throttle
body connected to the plenum and runners depending on the number of cylinders, which
leads to the engine cylinder. A typical intake manifold is shown in Fig.1.2.




                                                Pic




                           Figure 1. 2. Typical intake manifold. [3]

The main aims of a good intake manifold design are as follows:
      To provide as direct a flow as possible to each cylinder.
      To provide equal quantities of charge to each cylinder.
      To assist fuel atomisation and vaporization.
      To provide equal aspiration intervals between the branch pipes.
      To provide the smallest possible induction tract diameter that will maintain adequate
       air velocity at low speed without impeding volumetric efficiency in the upper speed
       range.
      To create as little internal surface fractional resistance in each branch pipe as
       possible.
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   To pre-heat the fuel charge for cold starting and warm up periods.
   To provide a means to prevent charge flow interface between cylinders as far as
    possible.
   To provide a measure of ram pressure charging.
   To provide a means for drainage of heavier liquid fraction.[4] [5]
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                                                                           2 – Literature Review


        Many persons have studied flow through intake manifold in the past. This chapter
reviews the previous published literatures, which lays the foundation and basis for further
work in this project. This helps to give a better understanding about the topic and also acts as
a guideline for this thesis.
        Safari et al [7] carried out 3D simulation of a 1.6L MPFI engine intake manifold by
using FLUENT code. Both steady and unsteady state simulations were performed for this
case. The pressure drop across runners was obtained from steady state simulation results,
which were compared with flow bench rig data for validation. Boundary condition for
unsteady state simulation was obtained from 1-D WAVE code. Based on the results of steady
and unsteady simulations the authors suggested some design modifications to improve the
performance of intake manifold. The computational domains consisting of 150,000-cells
were used for both steady and unsteady simulations.
        The manifold selected was symmetric in nature; hence the result of runner1 and 2
were used for runner 3 and 4. CFD code FLUENT was used for steady state simulation and
1D wave code was used to obtain the boundary conditions for unsteady state simulation. The
boundary condition selected for the analysis was total pressure at the manifold inlet and static
pressure at outlet of runners.
        Bensler [9] conducted a 3D simulation similar to Safari et al [7] to analyse the flow
within the intake manifold of a 4-cylinder engine in VW Company. In this work both steady
and unsteady state conditions were simulated and the results were analysed to improve the
intake manifold performance. This paper highlighted the importance of 3D CFD analysis of
intake manifold based on auto-mesh generation using VECTIS auto mesh generator. For this
study 150,000 cells generated in 4.5 hours on a 150 MHz single processor Silicon graphics
workstation was used. A constant normalized mass flow rate of 0.80 (80% of the maximum
         M.S Ramaiah School of Advanced Studies –Postgraduate Engineering Programmes (PEPs)




unsteady intake manifold mass flow rate) was used as the inlet for runner 4-outlet boundary
condition. Steady and unsteady analysis was carried out and the recirculation zones were
highlighted along the plenum chamber. An unsteady 3-D CFD analysis was performed for
two 720-degree engine cycles. Ricardo VECTIS software along with 1-D gas dynamic code
was used for unsteady analysis. Mass flow rate boundary condition was specified. Figure2.1
shows the transient boundary condition obtained from 1-D gas dynamic code studied by
Bensler [9]. A comparative study was carried out between the results of steady and unsteady
analysis and some similarities were found in the flow structure inside the plenum at the same
plane. A brief review of intake manifold functions and some corresponding design criteria,
which can improve engine performance were discussed. Suggestions to improve flow under
the throttle body was made so that the recirculation in the regions of plenum can be reduced
thus increasing the effective inlet cross-section allowing better filling of cylinders.




                                                    Pic




   Figure 2. 1 Transient boundary condition obtained from 1-D gas dynamic code. [9]

       Kale and Ganesan [10]investigated steady flow through intake manifold, port, valve
and valve seat of a S.I engine for various valve lifts using CFD code STAR-CD. From the
studies, the flow field details in different regions of the manifold for various valve lift were
predicted. The analysis was carried out for runner1 and 3 at three different valve lifts for
various speeds at wide-open throttle condition. Multi-block, trimmed cell were used for
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meshing the geometry. Grid independence studies were conducted to obtain a grid
independent solution. The mesh size selected was between 450,000 and 600,000 cells,
varying slightly between the low, medium and high valve lift. Since the velocity variation
between 450,000 and 600,000 grids were less than 1%, grid distribution of 450,000 was
selected. Standard k- model was used as turbulence model. The input for boundary
conditions was given as manifold pressure for the inlet of the plenum chamber and cylinder
pressures (corresponding to the valve lift) for the exit of the valve.
        Due to the absence of measured data, a turbulence intensity of 5% and a length
scale of 10 per cent of port diameter at the inlet plane were specified. The authors
concluded that the valve lift has a predominant effect on flow structure of intake manifold.
The results were validated with experimental data.
       A steady state 3D simulation was performed to obtain the discharge and pressure loss
coefficient representing the flow losses within the plenum. A comparative study was carried
out with the steady flow bench experimental results. The 1D model of the whole engine was
built and was validated against experimental data at full load condition. Then, 3D CFD
simulation of the transient flow through the plenum was performed by imposing time
dependent boundary conditions obtained from 1D gas dynamic simulation. An integrated 1D
and 3D-CFD simulations was carried out for 3 engine cycles to determine real flow
conditions under actual engine operations. At the beginning of the combined simulation,
the 1D code runs alone for 30 cycles in order to reach a stabilized condition. In case of
transient simulation, 10 monitoring points spread throughout the CFD model was considered
to assess cycle-by-cycle solution stability. On comparing the steady and transient results, the
author concluded that the actual flow is more dissipating than the steady one. Mainly,
transient pressure loss coefficients in the intake pipe bend were more than the steady state
analysis.
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2.1 Summary of the literature review
   For steady state simulations CFD codes FLUENT and STAR-CD have been widely used
    in the literature. Ricardo WAVE and GT Power have been used as 1D gas dynamic code
    to obtain the boundary conditions for unsteady state simulation. For most of simulations
    comparative studies have been carried out with the steady flow bench experimental
    results.
   The manifold used in most of the studies were symmetrical in design.
   Grid independent study was conducted to obtain grid independent solution. Unstructured
    mesh was used for most of simulations, but for certain studies hexahedral elements were
    used.
   Standard k- model was considered as the turbulence model for most of the studies.
   In most of the studies, pressure boundary conditions were used to define the fluid
    pressure at inlet and outlet of intake manifold. But the study conducted by Bensler [9],
    used mass flow rate at outlet as the boundary condition.
   For most of the integrated 1D and 3D-CFD simulations, 3 to 4 engine cycles were used
    to determine real flow conditions of the engine operations.
    Thus the experimental studies and CFD simulations reported in the literatures act as base
guidelines for understanding the flow behaviour in an intake manifold. The developments
reported in the literature have been taken into consideration in the current project.
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                                                                          3 – Problem Definition


3.1 Problem definition
    Air motion inside the intake manifold is one of the important factors, which governs the
engine performance of multi cylinder SI engines. Hence the flow phenomenon inside the
intake manifold should be fully understood in order to consider the current requirement of
higher engine efficiency and lower emission. The role for computational tools for internal
combustion engine design is rapidly changing. CFD can perform the base of virtual
simulation of the experimental tests. By significantly lowering the need for costly and time-
consuming tests, CFD has the potential in reducing the overall engine design cycle time.
Based on this approach, the flow behaviour in an intake manifold was carried out.
3.3 Problem statement
    To study the airflow behaviour in an intake manifold of a multi-cylinder SI engine and to
suggest necessary design modifications for improving the flow behaviour.
3.3 Project objective
   To study the pressure drop through different runners of intake manifold in steady
    conditions.
   To study flow velocity and mass flow rate distribution through different runners at
    unsteady conditions.
   To suggest for performance improvement for the intake manifold based on the analyses
    results.
3.4 Methodology adopted to meet the objective
   Collection of the geometric data of Intake Manifold of FORD IKON 1.6 through reverse
    engineering and creation of 3-D model of the Intake Manifold using CATIA V5 R11
   Calculation of boundary conditions for unsteady state simulation using 1- D Wave code.
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   CFD modelling (generation of grid and assigning boundary conditions) using Hypermesh
    and Gambit software.
   Obtaining flow field results using the CFD solvers (FLUENT 6.1.22 and Ricardo
    VECTIS).
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                                                         4 – Model Construction and Solution



       In the current work both steady state and unsteady state analysis has been carried out.
Steady state analysis was carried out in Fluent 6.2 and unsteady analysis using Ricardo
VECTIS. The geometry of the model is the primary input for any CFD analysis. A geometric
model describes the shape of a physical object by means of geometric concepts. The output
of the analysis was based upon the accuracy of the model. The 3-D model required for
analysis was created using CATIA V5R11.
4.1 Manifold dimensions
   For the current study, a Ford Ikon 1.6L engine’s manifold was considered, which is
asymmetric in nature. The dimension required for modelling the intake manifold was
obtained from reverse engineering. The details of the dimensions are shown in Table 4.1 and
Fig. 4.1 shows the physical model.




                                               Pic




                  Figure 4. 1 Dimension required for surface modelling
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Table 4. 1 Dimensions required for surface modelling

                        Inlet duct diameter            (mm)             60
                        Length of plenum chamber       (mm)            185
                       Diameter of runner outlets        (mm)           40
                       Length of inner runners           (mm)          190
                        Length of outer runners        (mm)            240
4.5 Solution
4.5.1 Steady state analysis
   The main aim of steady state analysis was to find the pressure drop across individual
runners. The pressure drop across individual runners helps in identifying the flow structure
within the intake manifold. The velocity and pressure distribution within the intake manifold
is studied in depth and discussed in the next chapter.
4.5.2 Unsteady state analysis
   Flow through an intake manifold is dependent on the time since crack angle positions
vary with respect to time. To understand the flow behaviour with respect to the crank angle
positions unsteady state simulations are necessary. So, unsteady state simulation was carried
out to predict how an intake manifold work under real conditions. In this case the boundary
conditions time dependent. The boundary conditions that were obtained from the 1D gas
dynamics analysis using WAVE code were the inputs for the unsteady analysis in Ricardo
VECTIS. The unsteady analysis was carried out using WAVE – VECTIS Coupling.
   The pressure variation along runners is shown in Fig. 4.9. During the induction stroke,
the suction created by the cylinder produces an expansion wave. This wave travels towards
the open end of intake pipe, where it will reflect as the compression wave. Thus just before
inlet valve closes, the pressure surge caused by this compression wave helps to ram fresh
charge into the cylinder. At Intake valve open condition, the cylinder pressure is almost
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higher than the inlet pressure. However at the time of induction, due to down ward motion of
the piston a rapid reduction in intake pressure occurs along runners. It is observed that at the
end of induction stroke if the pressure is above atmospheric then maximum filling takes
place. The results obtained from unsteady analysis follows the same characteristics as
reported in literature. After intake valve closes the residual wave within the intake pipe
oscillate between the open end and the closed valves, causing reverse flow within the
runners. This results in pressure losses occurring along the corresponding runners. The
results of unsteady simulation are discussed in depth in the next chapter.




                                                Pic




                        Figure 4. 2 Pressure variation along runners
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                                                      5 – Validation and Discussion of Results

   Both steady and unsteady flow analysis has been carried out. The first section of this
chapter covers on the steady state analysis carried out using Fluent and the second section
covers on the unsteady simulations carried out using Ricardo WAVE-VECTIS coupling.
5.1 Steady state analysis
The steady state analysis has been carried out for three different conditions.
      All runners open
      1st & 3rd runners open
      2nd & 4th runners open
In order to understand the flow field within the intake manifold planes were created along the
plenum chamber and runners as shown in Fig.5.1. The velocity and pressure contours on
these planes are discussed in the subsequent sections.




                                                Pic




                            Figure 5. 1 Layout of intake manifold

5.1.1 Flow in plenum chamber
   The function of plenum chamber is to distribute the airflow to various manifold runners
and also to dampen the pressure pulses, which are created because of valve events. For
discussing the flow within the plenum, plane 1 is considered (Fig.5.1). Figure 5.2(a) shows
the velocity contour along plenum chamber with all runners in open condition. It is observed
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that velocity drops as the flow proceeds through the plenum chamber. This is due to sudden
increase of the area within the plenum. There is a drop in velocity at the inlet of the runner 1
compared to other runners when all runners are in open condition. This is due to a sharp bend
at the region of runner 1 inlet and the plenum wherein the flow does not smoothly enter
runner 1. At runner 2 and 4 local regions with increased velocity is observed.
5.2.4 Velocity vector along plenum chamber
       At 370 crank angles after spark ignition the normalised pressure value at runner
   outlet 4 is 0.9 bar. Figure 5.21 shows the flow structure inside the plenum chamber at the
   same section cut as for steady flow as shown in Fig 5.2.




                                                Pic




         Figure 5. 2 Velocity vector along plenum chamber at 370 crank angle

   Figure 5.21 show some similarities in the flow structure with the steady state condition.
As expected, a similar recirculation occurs near to the runner entry 1 (R1). However the flow
in the plenum near to the runner 4 is different. A new recirculation zone (R3) appeared just to
the left of runner entry 4. One more recirculation is found at the lower part of plenum
chamber (R2).
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                                     6 – Conclusions and Recommendations for future work

    The numerical evaluation of the airflow through an intake manifold was carried out using
commercial software Fluent and Ricardo VECTIS. The following conclusions are drawn
from the current work.
6.1 Conclusion
   From the steady state analysis the pressure drop for individual runners were determined.
    It was observed that the pressure drop across runners was non-uniform due to the
    asymmetrical geometric model.
   Higher-pressure drop in the runner 1 was observed which is due the large flow separation
    region near runner 1.
   From the unsteady analysis, flow field velocity variation and the mass flow rates were
    analysed and the airflow behaviour inside the manifold was evaluated. Based on the
    analysis it was concluded that the velocity and mass flow rates at runner 2 and 3 were
    significantly higher as compared to runners 1 and 4.
   The performance of intake manifold can be improved by making modifications at runner
    entry 1 and plenum chamber. These changes can remove the recirculation R2 and R3 (Fig
    5.21) along the plenum chamber and thus increase the effective cross-section of inlet so
    as to allow better filling of the cylinders.
   The flow field shows that the location of the throttle body is not at its optimum position.
    Because of the asymmetric design of the intake manifold, the axial airflow from throttle
    into the plenum results in a non-uniform air distribution to the cylinders. Hence
    symmetrical intake manifold design is suggested.
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6.2 Recommendations for further work
   To carry out the flow analysis through intake manifold at part throttle condition.
   To conduct a computational study of steady flow through intake manifold for various
    valve lifts.
   To analyse the unsteady intake manifold flow with EGR.
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                                           References


[1]   Heywood, J .B., (1988), “Internal Combustion Engine Fundamentals,” McGraw-Hill
      International Editions, pp. 309-321, ISBN 0-07-100499-8.
[2]   www.autoshop101.com/forms/h21.pdf
[3]   www.autoshop101.com/forms/h51.pdf
[4]   Hoag, Kevin L., (2006), “Vehicle Engine Design Powertrain,” Springer Wien New
      York, pp 105-106., ISBN 1613-6349.
[5]   Heisler, H., (2003), “Advanced Engine Technology”, SAE international., ISBN 1-
      56091-734-2.
[6]   Crouse and Anglin, (1993), “Automotive Mechanics”, Mc Graw-Hill international
      Editions, pp.130-133., ISBN 0-07-113884-6.
[7]   Safari, M., Ghamari, M. and Nasiritosi, A., (2003) “Intake manifold optimization by
      using 3-D CFD analysis”, SAE 2003-32-0073.
[8]   Makgata, K.W, (2005) “Computational analysis and optimization of the inlet system of
      a high-performance rally engine”, University of Pretoria.
[9]   Bensler, H., (2002) Intake manifold optimization by using CFD analysis, Volkswagen
      AG, Powertrain Calculations Dept.
[10] Kale, S.C., and Ganesan, V., (2004) “ Investigation of the flow field in the various
      regions of intake manifold of a S.I. engine,” Indian journals of Engineering and
      Material Sciences. pp 134-148.

				
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