MODELING AND ANALYSIS OF INTAKE MANIFOLD
FOR A COMPRESSION IGNITION ENGINE USING STAR CCM+
A Thesis
Presented to the faculty of the Department of Mechanical Engineering
California State University, Sacramento
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE
in
Mechanical Engineering
by
Pradeep Garlapati
SUMMER
2012
MODELING AND ANALYSIS OF INTAKE MANIFOLD
FOR A COMPRESSION IGNITION ENGINE USING STAR CCM+
A Thesis
by
Pradeep Garlapati
Approved by:
______________________________________, Committee Chair.
Timothy Marbach, Ph.D.
______________________________________, Second Reader.
Dongmei Zhou, Ph.D.
_____________________
Date
ii
Student: Pradeep Garlapati
I certify that this thesis report has met the requirements for format contained in the
California State University, Sacramento format manual, and that this thesis is suitable for
shelving in the library and credit is to be awarded for the thesis.
__________________________, Department Chair
Susan L Holl, Ph.D.
Department of Mechanical Engineering.
iii
_________________________
Date
Abstract
of
MODELING AND ANALYSIS OF INTAKE MANIFOLD
FOR A COMPRESSION IGNITION ENGINE USING STAR CCM+
by
Pradeep Garlapati
Fuel combustion inside the cylinder of an engine is greatly affected
by the mixing of the air and the fuel. Better mixing leads to more efficient combustion.
There has been a lot of research in the past to improve the mixing of air fuel mixture in
the engine. Better mixing can be achieved by modifying the designs of inlet manifold or
piston head grove etc. In this Thesis the focus is on inlet manifold. This thesis compares
three designs of inlet manifold for combustion efficiency achieved by them. Those
designs are helical inlet manifold, spiral inlet manifold, helical-spiral inlet manifold.
Star CCM+ is used as a tool to model these three inlet manifold
designs, cylinder and a piston. Same tool is used to do the analysis for combustion
efficiency using some boundary conditions. Stoichiometric equation was given to the
program to do the calculations. CO, CO2, NO, H2, N2, H20, temperature and pressure
were chosen as the results that the program should give out once the calculation is done.
The comparison of these results for all the three designs would recommend the best
design among three designs of inlet manifolds.
iv
When compared, among three, Helical-Spiral inlet manifold design
stood the best. It had the fewer amounts of Carbon Monoxide, more Carbon Di-oxide and
more Nitrous Oxide. Having more Nitrous Oxide in the exhaust gases is contradicting the
thesis; however the reasons and remedies for that problem are addressed in the
conclusions section. Also Helical-Spiral design had higher pressure and temperatures
generated inside the cylinder than other two designs. So Helical-Spiral inlet manifold
design is suggested as the best design among the three.
__________________________________, Committee Chair
Timothy Marbach, Ph.D.
__________________________________
Date
v
ACKNOWLEDGEMENTS
I would like to thank Professor Timothy Marbach for his valuable guidance on
this Thesis. He helped me stream line all chapter of the thesis and made the course easier
for me. He was always there to answer my questions. His continuous support helped me
to develop immense interest on this Thesis.
Special thanks to Professor Dongmei Zhou for her support as second reader for
the thesis. Without being in her Computational Fluid Dynamics class this thesis could
have been a difficult one.
Thanks to my advisor Professor Akihiko Kumagai for helping me with the
requirements of the Thesis. Without his supervision I could not have finished the Thesis
in time.
Thanks to Professor SusanLHoll, Chair, Mechanical engineering department for
helping me throughout my courses at Sacramento State University. Everyone in the
department was very helpful when I needed.
Special thanks to Graduate studies office at Sacramento State University for
helping me with the format of the Thesis. Thanks for guiding me from the very beginning
till the date I submitted it.
Finally, thanks to each and every one who helped me in writing the thesis and
gave me suggestions towards this Thesis.
vi
TABLE OF CONTENTS
Page
Acknowledgements...……………………………………………………………...…….vi
List of Figures……………………………………………………………………….......xii
Software specifications………………………………………………………………….xv
Chapter
1. INTRODUCTION AND BACKGROUND …………………………...……………….1
1.1. Inlet Manifold (Definition)……………………………………………………...1
1.2. Diesel Engine Inlet Manifold…..……………………………………………….1
1.3. Issues in the Existing Designs………………………..…………………………2
1.4. Previous Researches ……………………………………………………………3
1.5. Objective of this Thesis………………………………………………………...4
2. COMPUTER PROGRAM SETUP.…………………………………………………5
2.1 Governing Equations……………………………………………………………5
2.1.1 The Eulerian Gas Phase……………………………………………….......5
2.1.2 The Continuity Equation………………………………………………….6
2.1.3 The Momentum Equation…………………………………………………6
2.1.4 The Energy Equation……………………………………………………...7
2.1.5 The Turbulence Model…………………………………………………….7
2.1.6 Basis of the k-e Model…………………………………………………….9
2.1.7 The Basic Chemical Equations…………………………………………..10
vii
2.2 Boundary Conditions……………………………………………………………11
2.3 Model Descriptions (Combustion Mechanism)………………………………...11
2.3.1 Modeling Space………………………………………………………….12
2.3.1.1 Two-Dimensional Model ……………………………………...13
2.3.1.2 Axisymmetric Model ………………………………………….13
2.3.1.3 Three-Dimensional Model ………………………………….....13
2.3.1.4 Selecting a Space Model ……………………………………...14
2.3.2 Modeling Time ………………………………………………………….15
2.3.2.1 Steady Model ………………………………………………….16
2.3.2.2 Implicit Unsteady Model ……………………………………...16
2.3.2.3 Explicit Unsteady Model ……………………………………...16
2.3.2.4 Selecting a Time Model ……………………………………….17
2.3.3 Modeling a Multi-Component Mixture..………………………………..18
2.3.3.1 Multi-Component Gas Model ………………………………...18
2.3.3.2 Gas Mixture …………………………………………………...18
2.3.4 Using Combustion Models ……………………………………………...20
2.3.4.1 Reacting Flow System ………………………………………...20
2.3.4.2 Combustions Flame Types ……………………………………20
2.3.4.3 Combustion Model ……………………………………………21
2.3.5 Modeling the Equation of State …………………………………………24
2.3.5.1 Ideal Gas (with Combustion) Model ………………………….25
viii
2.3.6 Modeling the Viscous Regime ………………………………………….25
2.3.6.1 Selecting the Viscous Regime..………………………………..26
2.3.7 Modeling Species ……………………………………………………….27
2.3.7.1 Segregated Species Model …………………………………….28
2.3.8 Modeling Flow …………………………………………………………..30
2.3.8.1 Segregated Flow Model ……………………………………….30
3. BASELINE DESIGN …………………………………………...…………………33
3.1 Geometry ……………………………………………………………………….33
3.1.1 Helical Geometry ………………………………………………………..33
3.1.2 Spiral Geometry …………………………………………………………34
3.1.3 Helical-Spiral Geometry ………………………………………………...34
3.2 Meshing ………………..……………………………………………………….35
3.2.1 Surface Mesh ……………………………………………………………35
3.2.2 Surface Remesher …………………………………………………….....36
3.2.3 Volume Mesh ……………………………………………………………37
3.3 Results…………………………………………………………………………..43
3.3.1 Flow Results………….………………………………………………….45
3.3.1.1 Plot Form of Results for Pressure……………………………..45
3.3.1.2 Scalar Plot Form of Results for Pressure………………….......46
3.3.2 Velocity Results…………….……….…………………………………...48
3.3.2.1 Plot Form of Results for Velocity...…………………………...48
ix
3.3.2.2 Vector Form of Results for Velocity…………………………..49
3.3.3 Temperature Results…………..…………………………………………51
3.3.3.1 Plot Form of Results for Temperature...………………………51
3.3.3.2 Scalar Plot Form of Results for Temperature...……………….52
3.3.4 Exhaust Gas Results………………………………….............................54
3.3.4.1 Plot Form of Results for CO…………………………………...54
3.3.4.2 Scalar Plot Form of Results for CO……………………………55
3.3.4.3 Plot Form of Results for CO2………………………………….57
3.3.4.4 Scalar Plot Form of Results for CO2…………………………..58
3.3.4.5 Plot Form of Results for NO…………………………………..60
3.3.4.6 Scalar Plot Form of Results for NO……………………………61
3.3.4.7 Plot Form of Results for O2……………………………………63
3.3.4.8 Scalar Plot Form of Results for O2…………………………….64
3.3.4.9 Plot Form of Results for C12H26……………………………….66
3.3.4.10 Scalar Plot Form of Results for C12H26………………………67
4. COMPARISON OF DESIGNS..……………………………………………….......69
4.1 Mass Fraction of CO Versus Position ………………………………………….70
4.2 Mass Fraction of CO2Versus Position …………………………………………72
4.3 Mass Fraction of NO Versus Position …………………………………………74
4.4 Pressure Versus Position ………………………………………………………76
4.5 Temperature Versus Position ………………………………………………….78
x
5. CONCLUSIONS ……………………………………………………………..........80
Bibliography..………………………………………………………………................82
xi
LIST OF FIGURES
Figures
Page
1. Stock inlet manifold and a custom inlet manifold used in competition made by
Volkswagen…………………………………………………………………………….2
2. Three dimensional model of a Helical inlet manifold………………………………..33
3. Three dimensional model of a Spiral inlet manifold…………………………………34
4. Three dimensional model of a Helical-Spiral inlet manifold………………………...35
5. Meshing for Helical inlet manifold…………………………………………………...41
6. Meshing for Spiral inlet manifold…………………………………………………….42
7. Meshing for Helical-Spiral inlet manifold…………………………………………....42
8. Plot form of results from the program………………………………………………..43
9. Scalar form of results from the program……………………………………………..44
10. Vector form of results from the program…………………………………………...44
11. Pressure Vs Position plot for Helical-Spiral model…………………………………45
12. Pressure Vs Position plot for Helical model………………………………………...45
13. Pressure Vs Position plot for Spiral model………………………………………….46
14. Scalar plot form of result for Pressure for Helical-Spiral model……………………46
15. Scalar plot form of results for Pressure for Helical model………………………….47
16. Scalar plot form of results for Pressure for Spiral model…………………………...47
17. Velocity Vs Position for Helical-Spiral model……………………………………...48
18. Velocity Vs Position for Helical model……………………………………………..48
xii
19. Velocity Vs Position for Spiral model………………………………………………49
20. Velocity Vector form of results for Helical-Spiral model…………………………..49
21. Velocity vector form of results for Helical model…………………………………..50
22. Velocity vector form of results for Spiral model……………………………………50
23. Temperature Vs Position results for Helical-Spiral model………………………….51
24. Temperature Vs Position results for Helical model…………………………………51
25. Temperature Vs Position results for Spiral model…………………………………..52
26. Temperature Vs Position results for Helical-Spiral model………………………….52
27. Temperature Vs Position results for Helical model…………………………………53
28. Temperature Vs Position results for Spiral model…………………………………..53
29. Mass fraction of CO vs Position for Helical-Spiral model…………………………………54
30. Mass fraction of CO Vs Position for Helical model…………………………………54
31. Mass fraction of CO Vs Position for Spiral model………………………………….55
32. Mass fraction of CO Vs Position for Helical-Spiral model…………………………55
33. Mass fraction of CO Vs Position for Helical model………………………………...56
34. Mass fraction of CO Vs Position for Spiral model………………………………….56
35. Mass fraction of CO2 Vs Position for Helical-Spiral model………………………...57
36. Mass fraction of CO2 Vs Position for Heical model………………………………...57
37. Mass fraction of CO2 Vs Position for Spiral model…………………………………58
38. Mass fraction of CO2 Vs Position for Helical-Spiral model………………………...58
39. Mass fraction of CO2 Vs Position for Helical model………………………………..59
xiii
40. Mass fraction of CO2 Vs Position of Spiral model…………………………………59
41. Mass fraction of NO Vs Position for Helical-Spiral model………………………………..60
42. Mass fraction of NO Vs Position for Helical model………………………………...60
43. Mass fraction of NO Vs Position for Spiral model…………………………………61
44. Mass fraction of NO Vs Position for Helical-Spiral model………………………...61
45. Mass fraction of NO Vs Position for Helical model………………………………..62
46. Mass fraction of NO Vs Position for Spiral model…………………………………62
47. Mass fraction of O2 Vs position for Helical-Spiral model………………………….63
48. Mass fraction of O2 Vs Position for Helical model…………………………………63
49. Mass fraction of O2 Vs Positin for Helical model………………………………….64
50. Mass fraction of O2 Vs Position for Helical-Spiral model………………………….64
51. Mass fraction of O2 Vs Position for Helical model…………………………………65
52. Mass fraction of O2 Vs Position for Spiral model…………………………………..65
53. Mass fraction of C12H26vs Position for Helical-Spiral model………………………66
54. Mass fraction of C12H26 Vs Position for Helical model…………………………….66
55. Mass fraction of C12H26 Vs Position for Spiral model……………………………...67
56. Mass fraction of C12H26 Vs Position for Helical-Spiral model……………………………..67
57. Mass fraction of C12H26 Vs Position for Helical model…………………………………….68
58. Mass fraction of C12H26 Vs Position for Spiral model……………………………………...68
xiv
SOFTWARE SPECIFICATIONS
1. Software programs needed
a. Star CCM+
b. Microsoft excel
c. Win zip
d. Windows paint
2. System requirements
a. Windows 7 or Windows Vista (preferred)
b. 4GB RAM
c. Core 2 Duo processor (minimum)
d. NVIDIA graphics card (required)
xv
1
CHAPTER 1
INTRODUCTION AND BACKGROUND
1.1 Inlet Manifold (Definition):
The inlet manifold is the part of the engine that supplies the fuel/air
mixture to the cylinders. In contrast, an exhaust manifold collects the exhaust gases from
multiple cylinders into one pipe called exhaust pipe. The primary function of the intake
manifold is to evenly distribute the combustion mixture in to each intake port in the
cylinder head(s) [1].
1.2 Diesel Engine Inlet Manifold:
In case of a Diesel engine,compression ignition engine or a direct
injection internal combustion engine inlet manifolds just distribute air, as the fuel will be
sprayed separately in to the cylinder just before the end of compression stroke. These
manifolds play major role in even distribution of air fuel mixture. Even distribution of air
fuel mixture is important to optimize the efficiency and performance of the engine. These
manifolds may also serve as a mount for the carburetor, throttle body, fuel injectors and
other components of the engine [1].
2
Figure 1. Stock inlet manifold and a Custom inlet manifold used in competition made by
Volkswagen
The figure 1 shows an example of two inlet manifolds. The upper
one is the stock intake manifold for a commercial Volkswagen engine. The bottom one is
the intake manifold for a custom built one for competitions. In the competition engine the
runners to the intake ports on the cylinder head are much wider and more gently tapered.
This difference improves the volumetric efficiency of the engine’s fuel/air mixture intake.
1.3 Issues in the Existing Designs:
As mentioned earlier the better the mixing of the fuel and air the
better the combustion would be and hence lesser the pollution. So the research to improve
the mixing of fuel and air is always going on. The existing designs for inlet manifolds
possess very simple shape to avoid the high cost manufacturing. But these simple shape
inlet manifolds will not result in high turbulence inside the combustion chamber hence air
3
and fuel will not mix enough for an efficient combustion. The focus of this thesis is to
improve the mixing by introducing new designs for inlet manifolds.
1.4 Previous Researches:
There was so much of research work done in the past to improve
the combustion efficiency by using different designs for inlet manifolds. So many of
those improved the combustion efficiencies for commercial engines where as some of
them gave more power to race (power or high speed) engines. The figure 1 above shows
the difference between intake manifolds of a commercial and a competition engine.
Among all these researches, the latest one is the research done by
two professors at Indian Institute of Technology, Chennai, India. In fact, this research
done by those two professors is the base for the currentthesis. The research done by
Professor Benny Paul and Professor V. Ganesan was published in International Journal of
Engineering, Science and technology in the year 2010 [2].
In their research they chose Helical, Spiral and Helical-Spiral as
inlet manifold geometries. They used Star CD as the tool. They concluded Helical-Spiral
as the better geometry among those three. The basis for their conclusion is the Swirl
Velocity inside the cylinder. The swirl velocity they got inside the cylinder for HelicalSpiral inlet manifold is higher than the other two. They did not use any other parameters
as basis for their conclusion.
4
1.5 Objective of this Thesis:
The objective of this thesis is to model Helical, Spiral and HelicalSpiral inlet manifold geometries using Star CCM+. With pre-determined boundary
conditions and Governing equations run the simulation for these individual geometries
using Star CCM+. After the simulation, get the mass fractions of exhaust gases,
temperatures and pressure values for each geometry from Star CCM+. Compare the mass
fractions of exhaust gases from each geometry, to determine the best geometry for the
inlet manifold among those three.
5
CHAPTER 2
COMPUTER PROGRAM SETUP
2.1 Governing Equations:
This chapter introduces theory of the models that have been
considered in the work. A general background of modeling is presented followed by
governing equations for gas and liquid phase respectively. Of particular interest in this
work is modeling of droplet- droplet interaction (collision) since an impinging nozzle
concept is investigated. Therefore, droplet-droplet interaction is described in two subsections. The first sub-section introduces collision physics and traditional modeling of
collision (the O’Rourke model), whereas the second describes the implementation and
evaluation of an enhanced collision model.
2.1.1The Eulerian Gas Phase:
The governing equations state the following dynamic and
thermodynamic properties :
• The mass of a fluid is conserved (The equation of continuity).
• The rate of change of momentum is equal to the sum of the forces acting on a fluid
particle (Newton’s second law).
• The rate of change of energy is equal to the sum of the rate of heat addition to the
particle and the rate of work done on the fluid particle.
As long as the fluid can be regarded as a continuum, the governing
equations are assumed to describe the motion of a fluid element. This fluid element
6
(control volume) is a particle, in accordance with the dynamic and thermodynamic
properties above and it is the smallest possible element of the fluid. Its macroscopic
properties are not influenced by individual molecules.
2.1.2 The Continuity Equation:
The equation for conservation of species mass fraction Yαis given
in the following equation.
    Ui    Y 


D
  r  s
t
xi
xj  xj 
The first term on the right hand side represents mass molecular
diffusion, where D is the mass diffusion coefficient. The second term is the chemical
mass source term and represents the net mass formation rate per unit volume through
reaction of species α. Finally, the third term represents mass source evaporated from the
liquid.
2.1.3 The Momentum Equation:
Newton’s second law states that the rate of change of momentum
is equal to the sum of the forces acting on a fluid particle. These forces are divided into
surface forces and body forces. The surface forces consist of pressure and viscous forces,
whereas the body forces contain gravity, centrifugal, coriolis and electromagnetic forces.
Conservation of momentum reads
Ui  UiUj 
p    Ui Uj 2 Uk  





ij   gi  Fs

t
xj
xi xj   xj xj 3 xk  
7
On the right hand side, the first term represents the pressure
gradient. The expression in the bracket in the second term is the molecular stress tensor,
where ij is the unit tensor (i.e. if i=j then δij=1, if i≠j then δij=0). The third term
indicates body force per volume unit. The last term represents rate of momentum gain or
loss per unit volume due to the spray.
2.1.4 The Energy Equation:
The energy equation can be formulated in many ways. In the
equation that follows, it is expressed as the specific total energy (E), which is the sum of
the specific internal energy and the specific kinetic energy.
 E   EUj  p 
ijUj      T   qg  Qs



t
xj
t xj
xj  xj 
The first term on the right hand side represents the temporal
change of pressure. It is of importance where large pressure changes occur, such as
internal combustion engines [8]. The second term is work due to external forces, where
σij is the stress tensor. The third term represents the heat influx through conduction. The
fourth term is work due to body forces. The last term is a source term due to spray
interaction.
2.1.5 The Turbulence Model:
The main classes of turbulence modeling approaches where it was
concluded that k-e model still provides the optimum solution for practical engineering
calculations. Some “arbitrariness” in disregarding particular terms in the k-e equations,
and different values of model coefficients, result in a number of versions of the model.
8
The model was first used in predictions of in-cylinder flows by Watkins ,and from then
on
by
a
number
of
researchers:
Syed
and
Bracco
,Moler
and
MansourElTahryAhmadi_Befrui and others.
The model adopted in this study is a Favre a the model is expanded
with additional source terms to allow for turbulence modulation, i.e. for so-called direct
effects the spray creates on turbulence properties of the gas. The turbulence modulation
excludes effects created by the spray modifying the mean gas velocity, often called an
‘indirect effect’ with consequences on the processes of generation and dissipation in
turbulence, comprising phenomena such as turbulence in a wake of drops and modified
local shear stresses in the gas by the interaction between drops and turbulent eddies
.Although current understanding of these phenomena is incomplete, they are included in
the turbulence model to investigate their effects onthe total gas-spray behavior.
This section is divided into four parts. The first part deals with the
basis of the k-e model. In the second part, a review of efforts to understand processes
involved in the turbulence modulation and to include them in turbulence models is
presented, it is concluded with a discussion of how these works relate to diesel sprays.
The last two parts comprise the transport equations for turbulence kinetic energy and its
dissipation, extended with additional spray-related terms which accounts for the
turbulence modulation.
9
2.1.6 Basis of the k-e Model:
A form of k-e model was first proposed by Harlow and Nakayama
, and later versions were proposed by Jones and Launder and Hanjali"c among others.
The present ‘standard’ form was given by Launder and Spalding and the particular
version employed here is that of El Tahry and Ahmadi_Befrui. The model is based on the
Boussinesq turbulent viscosity hypothesis, which assumes that the turbulent scalar fluxes
and turbulent stresses can be expressed by Equations where 
.t
is the turbulent
diffusivity and vt is the kinematic eddy viscosity. The latter is evaluated from:
vt  C
k2

where k stands for the turbulence kinetic energy and e represents
its dissipation rate, defined as:

1 '
T m : u ''
p
where Tm ' stands for the fluctuating component of molecular shear
stress tensor. The values of k and e are calculated from their own transport equations
which will be given at the end of this section.
A turbulent diffusivity  is expressed in terms of the turbulent
.t
Prandtl/SchmidtNumber,  , t and eddy viscosity as:
 , t 
vt

,t
The Prandtl/Schmidt numbers are determined from experiments
and assumed constant.
10
2.1.7 The Basic Chemical Equations:
The chemical equations are,
C12H26 + 6 O2 12 CO + 13 H2
CO + ½ O2 CO2
H2 + ½ O2 H2O
The following substances were chosen to be result of the simulation. They are
C12H26 - Diesel
O2 - Oxygen
CO- Carbon Monoxide
H2- Hydrogen
CO2- Carbon Dioxide
H20- water
N2- Nitrogen
NO- Nitrous oxide
TEMP- Temperature inside the cylinder
PRESSURE- Pressure inside the cylinder
Velocity – Swirl velocity inside the cylinder
11
2.2 Boundary Conditions:
Software program needs some boundary conditions for the
combustion mechanism. It needs those conditions for calculation purposes. There was
two boundary conditions given. One for the air and the other one are for fuel. The
boundary conditions given to the software program for simulation purpose are as below.
Boundary Conditions for Air:
Turbulent intensity = .0375
Turbulent length scale = .0028m
Velocity = 30 m/s
Temperature = 400 C
Boundary Conditions for Fuel:
Turbulent intensity = .0247
Turbulent length scale = .000049m
Velocity = 500 m/s
Temperature = 400 C
2.3 Model Descriptions (Combustion Mechanism):
There are some options that we should choose as combustion
mechanism as we go towards the simulation in the software program Star CCM+. The
options chosen were described below.
The space was chosen as a 3-Dimensional space, material was
chosen as “multi-component gas”. For reaction regime item “Reacting” option was
chosen, because there will be a chemical reaction happening inside the cylinder using the
12
governing equation. For combustion flow type “non-premixed combustion” was chosen
and in this option “Eddy Break up-ideal gas (combustion)” was chosen. For the time and
flow, “implicit unsteady” and “segregated flow” was chosen respectively.
For viscous regime, “turbulent” option was chosen and for species,
“segregated species” was chosen and as a sub option “segregated fluid enthalpy” was
chosen. For Reynolds averaged turbulence, “k-epsilon turbulence-realizable k-epsilontwo-layer all Y+ wall treatment “option was chosen on program’s recommendation.
The procedure of applying these choices to the software program is
explained below.
2.3.1 Modeling Space:
The primary function of the Space models in STAR-CCM+ is to
provide methods for computing and accessing mesh metrics such as cell volume and
centroid, face area and centroid, cell and face indexes, and Skewness angle.
This section describes the three Space models in STAR-CCM+ and how to select one:
• The Two-Dimensional Model
• The Axisymmetric Model
• The Three-Dimensional Model
13
2.3.1.1 Two-Dimensional Model:
The Two-Dimensional model is designed to work on twodimensional meshes, and should only be activated if the mesh is indeed two-dimensional.
In this model, the mesh is assumed to have a unit depth (in SI units) so that any
volumetric or area quantities reported for the two-dimensional model are assumed to be
“per meter”.
2.3.1.2 Axisymmetric Model:
The Axisymmetric model is designed to work on two-dimensional
axisymmetric meshes. The mesh must be oriented such that the axis of rotation will be at
y=0 in global coordinate space. No part of the mesh can be below y=0 and the boundary
edge that lies along the axis should be of type Axis.
For boundary conditions and reporting purposes, the mesh is
assumed to be swept through an angle of one radian. For applications that use a mass
flow inlet, the mass flow is therefore given in kg/rad/s. Any volumetric or area quantities
reported for the Axisymmetric model are assumed to be for a 1 radian sector.
2.3.1.3 Three-Dimensional Model:
The Three-Dimensional model is designed to work on threedimensional meshes, and should only be activated if the mesh is indeed threedimensional. The use of a one-cell-thick three-dimensional mesh is much less efficient
than using a true two-dimensional mesh for two-dimensional and axisymmetric
simulations. A better approach is to extract a two-dimensional mesh.
14
2.3.1.4 Selecting a Space Model
To select a Space model, open the Continua node of the simulation
tree, then right-click the Physics 1 node. Select the Select models... item from the pop-up
menu.
This opens the Model Selection dialog. Select the correct Space model for the simulation
by clicking on the relevant radio button.
15
The model selection dialog should now show the Space model enabled
2.3.2 Modeling Time:
The primary function of the Time models in STAR-CCM+ is to
provide solvers that control the iteration and/or unsteady time-stepping.
This section describes the three Time models in STAR-CCM+:
• Steady
• Implicit Unsteady
• Explicit Unsteady
16
2.3.2.1 Steady Model:
The Steady model is used for all steady-state calculations. When
this model is activated, the concept of a physical time-step is meaningless. Therefore, for
those objects that offer a choice between Iteration or Time-Step for a trigger (such as
Monitors or Scenes), the Time-Step option should not be activated since it will result in
no update occurring
2.3.2.2 Implicit Unsteady Model:
The Implicit Unsteady model is the only unsteady model available
with the Segregated Flow and Segregated Fluid Energy models. It uses the Implicit
Unsteady solver.
With the Coupled Flow and Coupled Energy models, the implicit
unsteady approach is the alternative to the Explicit Unsteady one. The choice between
these two approaches is based on the time scales of the phenomena of interest.
When this model is activated, objects that offer a choice between
Iteration and Time-Step for a trigger (such as Monitors or Scenes), can be set to update at
each time-step.
2.3.2.3 Explicit Unsteady Model:
The Explicit Unsteady model is available only with the Coupled
Energy model. It is only compatible with the Inviscid and Laminar viscous regime
models. It uses the Explicit Unsteady solver.
17
The explicit approach is the alternative to the Implicit Unsteady
model. The choice between these two approaches is based on the time scales of the
phenomena of interest.
When this model is activated, objects that offer a choice between
Iteration and Time-Step for a trigger (such as Monitors or Scenes), can be set to update at
each time-step.
2.3.2.4 Selecting a Time Model:
A model with unsteady terms such as the Coupled Flow model or
the Segregated Flow model must first be enabled to expose the Time model selections.
Before or after selecting the Equation of State model and the Viscous Regime, select the
relevant Time model radio button. The Explicit Unsteady model is only compatible with
the Inviscid and Laminar viscous regime models.
18
2.3.3 Modeling a Multi-Component Mixture:
To model a multi-component mixture, i.e. a miscible mixture of
two or more pure substances in the same phase, enable either the Multi-Component Gas
or Multi-Component Liquid model by selecting the appropriate radio button in the
Material section of the model selection dialog.
2.3.3.1 Multi-Component Gas Model:
The Multi-Component Gas model is used to simulate a miscible
mixture of two or more pure gases.When the Multi-Component Gas material model is
enabled it is represented by the Multi-Component Gas model node in the object tree as
shown below
2.3.3.2 Gas Mixture:
A Gas Mixture is a material representing a miscible mixture of two
or more pure gases. It is managed by the Multi-Component Gas model as outlined in the
section describing multi-component material models.
19
The following screenshot shows the Multi-Component Gas model
node, the Gas Mixture node it manages, and the mixture’s child nodes Gas Components
and Mixture Properties.
The Gas Components node is a manager node for the gases
composing the Gas Mixture. Initially, the Gas Components node is empty. It is here that
you add, remove and replace gases in the mixture as outlined in the section on managing
multi-component materials. The material properties of each individual gas component in
the mixture are then accessible and can be set as outlined in the section on setting
material properties. The Mixture Properties node is a manager node for the material
properties of the entire gas mixture as a whole, distinct from the properties of each
individual component. This node may be empty initially, but will be populated with
material property nodes once additional physical models are selected. The material
properties of the gas mixture can be set as outlined in the section on setting mixture
properties.
20
2.3.4 Using Combustion Models:
2.3.4.1 Reacting Flow System:
Reacting Flow system is a system containing a multi-component
fluid mixture whose constituents react chemically with each other. A node representing
such a system (Reacting in the following screenshot) appears in the simulation tree when
this type of flow problem is specified in the Physics Model Selection dialog.
2.3.4.2 Combustion Flame Types:
A combustion flame type is the object that represents how you
choose to model your combustion: premixed, non-premixed or partially premixed.
21
This choice becomes available after you specify a reacting flow
problem in the Physics Model Selection dialog. In turn, the combustion flame type that
you select affects the availability of specific combustion models.
2.3.4.3 Combustion Model:
The purpose of combustion models is to calculate the reaction state
space, i.e. the concentrations of the various species present in a chemical reaction, and the
quantities they influence, viz., density, viscosity, and temperature.
To this end, STAR-CCM+ provides several models based on
various physical and chemical approximations. The general principles underlying these
models are described below.
A large chemical reaction set, such as found in hydrocarbon
combustion, can span a wide range of time scales. In addition to these time scales, the
turbulent flow field imposes its own limits on length and time scales, ranging from the
Kolmogorov and Batchelor time scales at the low end to the large, energy-containing
22
eddy time scales at the high end. Resolving all the length and time scales affecting the
grid-mean properties in a reacting flow system demands computational resources beyond
those currently available. We therefore need combustion models to account for the
processes that occur at length and time scales below what we can resolve on a numerical
simulation grid.
The four basic types of combustion model currently available in STAR-CCM+ are:
• Eddy break-up (EBU) models
• The Homogeneous Reactor model
• The Coherent Flame model (CFM)
• Presumed Probability Distribution (PPDF) models
EBU Model:
EBU combustion models track individual mean species
concentrations on the grid through transport equations. The reaction rates used in these
equations are calculated as functions of the mean species concentrations, turbulence
characteristics and, depending on the specific model used, temperature. A mean enthalpy
equation is solved in addition to the species transport equations. The mean temperature,
density and viscosity are then calculated knowing the mean enthalpy and species
concentrations
23
Selecting the EBU Model:
This procedure is only for non-premixed and partially-premixed
combustion. When you select premixed combustion, you need to work with the Premixed
Eddy Break-Up model. To solve combustion problems using an EBU model:
• In the Physics Model Selection dialog, select a material model from the Material group.
Typically, this will be Multi-Component Gas but Multi-Component Liquid is also
acceptable.
• Specify that your problem involves simulation of chemical reactions by selecting
Reacting in the Reaction Regime group.
• Specify whether your combustion is premixed, non-premixed or partially premixed by
selecting the corresponding radio button in the Combustion group.
• Select the Eddy Break-up option from the particular combustion group, as shown
below.
24
The corresponding node (Eddy Break-up in the following
screenshot) is activated as soon as a combustion simulation using the EBU model is
selected.
2.3.5 Modeling the Equation of State:
The Equation of State model is used to compute the density and the
density derivatives with respect to temperature and pressure. This section describes the
various models available in STAR-CCM+:
• Constant Density
• IAPWS-IF97
• Polynomial Density
• Ideal Gas
25
• Ideal Gas (with Combustion)
• Real Gas
• User Defined Density
2.3.5.1 Ideal Gas (with Combustion) Model:
The Ideal Gas (with combustion) model only allows the
thermodynamic polynomial for calculation of specific heat of individual components of
the mixture. By contrast, the standard Ideal Gas model also allows the constant and
polynomial in T methods.
The thermodynamic polynomial is the recommended method for
getting specific heat (together with the heat of formation and enthalpy) of the mixture.
However, in some (very rare) instances, this method may not be available. In that case
you can select the standard Ideal Gas model and pick an alternate method for specific
heat calculations.
2.3.6 Modeling the Viscous Regime:
This section explains the following types of flows, termed viscous
regime in STAR-CCM+:
• Inviscid
• Viscous
• Laminar
• Transitional
• Turbulent
Turbulent Flow:
26
A flow that is in a state of continuous instability, exhibiting
irregular, small-scale, high-frequency fluctuations in both space and time is termed
turbulent.
Although it is strictly possible to simulate turbulent flow directly
by resolving all the scales of the flow (termed direct numerical simulation), the computer
resources required are too large for practical flow simulations. Therefore, a suitable
turbulence modeling approach must be selected.
2.3.6.1 Selecting the Viscous Regime:
To select a Viscous Regime, first select the Coupled Flow model
or select the Segregated Flow Model. This exposes the Viscous Regime selections. Select
the relevant one by clicking on a radio button.
27
The model selection dialog should now show the Viscous Regime model enabled.
2.3.7 Modeling Species:
A species model will be activated whenever a multi-component
liquid or multi-component gas is chosen from the Material model section of the Physics
Model Selection dialog. The specific models discussed are the Coupled Species model
and the Segregated Species model.
28
2.3.7.1 Segregated Species Model:
The Segregated Species model solves the species continuity
equations for a multi-component fluid mixture. For a mixture of N components the
Segregated Species model solves N-1 transport equations sequentially. Together with
global mass continuity, these equations provide a means for updating the field of N mass
fractions defining the mixture composition.
Turbulence Model
There are four major classes of turbulence models currently in
STAR-CCM+.
• Spalart-Allmaras models
• K-Epsilon models
• K-Omega models
• Reynolds stress transport models
K-Epsilon Turbulence Models:
A K-Epsilon turbulence model is a two-equation model in which
transport equations are solved for the turbulent kinetic energy and its dissipation rate.
Various forms of the K-Epsilon model have been in use for several decades, and it has
become the most widely used model for industrial applications. Since the inception of the
K-Epsilon model, there have been countless attempts to improve it. The most significant
of these improvements have been incorporated into STAR-CCM+.
STAR-CCM+ has a choice of seven different K-Epsilon turbulence models:
• Standard K-Epsilon
29
• Standard Two-Layer K-Epsilon
• Standard Low-Reynolds number
• Realizable K-Epsilon
• Realizable Two-Layer K-Epsilon
• Abe-Kondoh-Nagano low-Reynolds number
• V2F low-Reynolds number
Standard K-Epsilon Model:
The Standard K-Epsilon Model is a de facto standard version of
the two-equation model that involves transport equations for the turbulent kinetic energy
and its dissipation rate. The transport equations are of the form suggested by Jones and
Launder, with coefficients suggested by Launder and Sharma , Some additional terms
have been added to the model in STAR-CCM+ to account for effects such as buoyancy
and compressibility. An optional non-linear constitutive relation is also provided.
In its original form, the K-Epsilon turbulence model was applied
with wall functions, but was later modified to use the following approaches for resolving
the viscous sublayer:
• Low-Reynolds number
• Two-layer
Two-Layer Approach:
The two-layer approach, first suggested by Rodi, is an alternative
to the low-Reynolds number approach that allows the K-Epsilon model to be applied in
the viscous sublayer. In this approach, the computation is divided into two layers. In the
30
layer adjacent to the wall, the turbulent dissipation rate  and the turbulent viscosity t are
specified as functions of wall distance. The values of specified in the near-wall layer are
blended smoothly with the values computed from solving the transport equation far from
the wall. The equation for the turbulent kinetic energy is solved in the entire flow. This
explicit specification of 
t is arguably no less empirical than the damping
function approach, and the results are often as good or better. In STAR-CCM+, the twolayer formulations will work with either low-Reynolds number type meshes y+
-
function type meshes y+
2.3.8 Modeling Flow:
In this there are two fluid flow models.

Segregated Flow Model

Coupled Flow Model
2.3.8.1 Segregated Flow Model:
The Segregated Flow model solves the flow equations (one for
each component of velocity, and one for pressure) in a segregated, or uncoupled, manner.
The linkage between the momentum and continuity equations is achieved with a
predictor-corrector approach.
The complete formulation can be described as using a co-located variable arrangement
(as opposed to staggered) and a Rhie-and-Chow-type pressure-velocity coupling
combined with a SIMPLE-type algorithm.
31
This model has its roots in constant-density flows. Although it is
capable of handling mildly compressible flows and low Raleigh number natural
convection, it is not suitable for shock-capturing, high Mach number and high Raleighnumber applications.
Selecting the Segregated Flow Model:
To select the Segregated Flow model, first select a Gas or a Liquid
Material model. This exposes the Flow selections. Select the Segregated Flow radio
button.
The model selection dialog should now look something like this,
with the Segregated Flow model selected.
32
Segregated Fluid Energy Models:
There are three Segregated Fluid Energy models, which are
companion models to the Segregated Flow model:
• Segregated Fluid Enthalpy
• Segregated Fluid Temperature
• Segregated Fluid Isothermal
Segregated Fluid Enthalpy Model:
The Segregated Fluid Enthalpy model solves the total energy
equation with chemical thermal enthalpy as the independent variable. Temperature is then
computed from enthalpy according to the equation of state.
This model is recommended for any simulation involving combustion
33
CHAPTER 3
BASELINE DESIGN
3.1 Geometry:
Geometry is a 3-dimensional mathematical model. As mentioned
in the section 1.4 based on the previous work done, three geometries were chosen for
inlet manifolds. Those are Helical inlet manifold, Spiral inlet manifold, Helical-Spiral
inlet manifold. These three 3-dimensional curves vary in the shape as follows.
3.1.1 Helical Geometry:
Helical curve revolves around its own axis but it does not remain
on the same plane. It goes along its axis however the radius remains the same. Below is
the 3-dimensional model and mesh of a helical inlet manifold.
Figure 2 Three dimensional model of a Helical inlet manifold
34
3.1.2 Spiral Geometry:
Spiral curve revolves around its own axis but remains in the same
plane. The radius of the curve decreases as it revolves around its axis. Below is the 3dimensional model of a spiral inlet manifold.
Figure 3 Three dimensional model of a Spiral inlet manifold
3.1.3 Helical-Spiral Geometry:
Helical-Spiral geometry is the hybrid of above two geometries. It
revolves around its own axis and travels linearly along its own axis. Also the radius
reduces along the length of the axis. When looked from a side it looks like a cone. Below
picture shows a 3-dimensional model of a Helical-Spiral inlet manifold.
35
Figure 4 Three dimensional model of a Helical-Spiral inlet manifold
3.2 Meshing:
To be able to compute, the software needs to break the 3dimensional model in to very small pieces called cells. Converting the 3-dimensional
model in to these cells is called meshing. By using in-built tools called “Remeshing” and
“Trimmer” Star CCM+ can create meshes of three dimensional models. Depending on
the volume of the geometry the number of cells varies. Meshing feature in STAR CCM+
is explained below.
3.2.1 Surface Mesh:
The starting point for all the mesh models in STAR-CCM+ is a surface mesh that is
imported from a CAD package or some other third party pre-processing software. The
36
overall quality of the surface mesh can vary greatly from one package to the next. Typical
problems that can be encountered include:
• Holes and gaps
• mismatched edges
• Multiple edges
• Sharp angle folds
• Poor triangulation (needles cells)
• Self intersection and
• Non-manifold topology
In instances where there are only a small number of problems then
you can manually repair the surface mesh. If the problems are more extensive, then two
automatic tools are available to eliminate the above problems and improve the overall
quality of the starting surface mesh imported into STAR-CCM+. The two tools are:
• Surface remesher
• Surface wrapper
3.2.2 Surface Remesher:
The surface remesher is used to re-triangulate an existing surface
in order to improve the overall quality of the surface and optimize it for the volume mesh
models. The remeshing is primarily based on a target edge length that you supply and can
also include feature refinement based on curvature and surface proximity. Localized
refinement based on boundaries can also be included. Specific boundaries can also be
37
omitted from the process so that the original triangulation from the imported mesh can be
preserved.
The surface remesher is typically used for remeshing surfaces
produced by the surface wrapper and STL type data. As well as improving the surface for
the volume meshers it also aids the subsurface generator when the prism mesher option is
selected.
3.2.3 Volume Mesh:
In order to generate a volume mesh, the steps outlined below
should be followed:
1. Prepare the surface mesh according the requirements for STAR-CCM+.
2. Select the desired volume mesh model and the optional prism layer model, extruder
model and/or generalized cylinder model if applicable. Define additional continua with
the appropriate mesh models if different mesh types are to be used for each region or if a
inter-region conformal mesh interface is not essential.
3. Input the appropriate meshing values for the selected models.
4. Launch the volume mesh generator.
5. Visualize the volume mesh representation and check the mesh quality statistics.
6. Remove any invalid cells should they exist.
7. Export the mesh or continue with the simulation setup as normal.
38
Volume Mesh Models:
There are four different volume mesh models to select from:
• Tetrahedral mesher;
• Polyhedral mesher;
• Trimmer;
• Thin mesher
The volume mesh models can be selected for any mesh continuum you define. If you
want to have a different mesh type for each region then you will need to use additional
continua, which will result in a non-conformal mesh interface at inter-region boundaries.
39
Trimmer Meshing Model:
The trimmed cell mesher provides a robust and efficient method of
producing a high quality grid for both simple and complex mesh generation problems. It
combines a number of highly desirable meshing attributes in a single meshing scheme:
• Predominantly hexahedral mesh with minimal cell skewness;
• Automatic curvature and proximity refinement; and
• Surface quality independence
• Alignment with a user specified coordinate system
By default, the trimmer meshing model utilizes a template mesh
constructed from hexahedral cells from which it cuts or trims the core mesh based on the
starting input surface. The template mesh can contain refinement based on curvature and
proximity, as well as fixed cell sizes based on the boundary surface. Growth parameters
can be used to control the transitioning of the mesh cell sizes from small to big both at the
surface and far field. A maximum and/or minimum cell size can be supplied as well to
control the upper and lower cell size bounds. The template can be aligned in any direction
based on a user specified cartesian coordinate system.
An additional feature for users wishing to model external
aerodynamic flows is the ability to automatically refine cells in a wake region. This
region is generally the volume of fluid at the rear of a moving body.
40
The resulting mesh is composed predominantly of hexahedral cells
with trimmed cells next to the surface. Trimmed cells are polyhedral cells but can usually
be recognized as hexahedral cells with one or more corners and/or edges cut off.
The input values used for the trimmer model can be set on four different levels:
• Global;
• Region;
• Boundary; and
• feature curve
Volumetric controls can also be included to locally increase or
decrease the mesh density in the template based on a range of prescribed shapes.
The current implementation of the trimmer model is restricted to one region per continua.
In other words, a different mesh continuum must be used for each region you have, or
alternatively, the per-region meshing option can be activated to apply the same
continuum to all regions independently. A conformal mesh interface at inter-region
boundaries is therefore not achievable by the meshing process. Additionally, interfaces
can only be used with the trimmer meshing model when the boundaries in the interface
belong to the same region.
41
For these three geometries the number of cells is as follows.
Geometry
No of cells
Helical
360464
Spiral
498238
Helical-Spiral
749339
Below pictures show the meshing of three geometries.
Figure 5 Meshing for Helical inlet manifold
42
Figure 6 Meshing for Spiral inlet manifold
Figure 7 Meshing for Helical-Spiral inlet manifold
43
3.3 Results:
After all calculations are done, the software gives the results in
different formats. Among those Excel format, plot format, scalar plot and vectors formats
were chosen. Excel format means, the program gives the mass fraction of each chemical
component at each cell in excel sheet format. In the plot format the program actually
plots a 2-dimensional graph with piston diameter on X-axis and mass fraction on Y-axis.
Figure 8 explains this type of plots given by the program. In the scalar plot format the
program gives a chronological picture with the values of the mass fraction related to the
color as shown below in the figure 9. In vector format of results a 2-dimensional picture
is shown with velocity vectors in it for the geometry that is simulated. Figure 10 shows
the Vector form of result.
Figure 8 Plot form of results from the program
44
Figure 9 Scalar form of results from the program
Figure 10 Vector form of results from the program
45
3.3.1. Flow Results:
Results obtained for pressure inside the cylinders of three designs
are documented in this section. These results are in two different forms. They are Plot
form of results and Scalar plot form of results.
3.3.1.1 Plot Form of Results for Pressure:
Figure 11 Pressure Vs Position plot for Helical-Spiral model
Figure 12 Pressure Vs Position plot for Helical model
46
Figure 13 Pressure Vs Position plot for Spiral model
3.3.1.2 Scalar Plot Form of Results for Pressure:
Figure 14 Scalar plot form of result for Pressure for Helical-Spiral model
47
Figure 15 Scalar plot form of results for Pressure for Helical model
Figure 16 Scalar plot form of results for Pressure for Spiral model
48
3.3.2 Velocity Results:
Velocity results inside the cylinder were obtained for all the three
designs and are discussed in this section. Plot form of results and Vector form of results
and vector form of results are documented below.
3.3.2.1 Plot Form of Results for Velocity:
Figure 17 Velocity Vs Position for Helical-Spiral model
Figure 18 Velocity Vs Position for Helical model
49
Figure 19 Velocity Vs Position for Spiral model
3.3.2.2 Vector Form of Results for Velocity:
Figure 20 Velocity Vector form of results for Helical-Spiral model
50
Figure 21 Velocity vector form of results for Helical model
Figure 22 Velocity vector form of results for Spiral model
51
3.3.3 Temperature Results:
Temperature results inside the cylinder were obtained after the
simulation was done. These results are in two forms. They are Plot form of results and
Scalar plot form of results.
3.3.3.1 Plot Form of Results for Temperature:
Figure 23 Temperature Vs Position results for Helical-Spiral model
Figure 24 Temperature Vs Position results for Helical model
52
Figure 25 Temperature Vs Position results for Spiral model
3.3.3.2 Scalar Plot Form of Results for Temperature:
Figure 26 Temperature Vs Position results for Helical-Spiral model
53
Figure 27 Temperature Vs Position results for Helical model
Figure 28 Temperature Vs Position results for Spiral model
54
3.3.4 Exhaust Gases Results:
Exhaust gases results were obtained for all the three models of
inlet manifold and are document below. The exhaust gases chosen were Carbon
Monoxide, Carbon Di-Oxide, Nitrous Oxide, Oxygen and Diesel. These results are in two
forms. They are Plot form of results and Scalar Plot form of results.
3.3.4.1 Plot Form of Results for CO:
Figure 29 Mass fraction of CO vs Position for Helical-Spiral model
Figure 30 Mass fraction of CO Vs Position for Helical model
55
Figure 31 Mass fraction of CO Vs Position for Spiral model
3.3.4.2 Scalar Plot Form of Results for CO:
Figure 32 Mass fraction of CO Vs Position for Helical-Spiral model
56
Figure 33 Mass fraction of CO Vs Position for Helical model
Figure 34 Mass fraction of CO Vs Position for Spiral model
57
3.3.4.3 Plot Form of Results for CO2:
Figure 35 Mass fraction of CO2 Vs Position for Helical-Spiral model
Figure 36 Mass fraction of CO2 Vs Position for Heical model
58
Figure 37 Mass fraction of CO2 Vs Position for Spiral model
3.3.4.4 Scalar Plot Form of Results for CO2:
Figure 38 Mass fraction of CO2 Vs Position for Helical-Spiral model
59
Figure 39 Mass fraction of CO2 Vs Position for Helical model
Figure 40 Mass fraction of CO2 Vs Position of Spiral model
60
3.3.4.5 Plot Form of Results for NO:
Figure 41 Mass fraction of NO Vs Position for Helical-Spiral model
Figure 42 Mass fraction of NO Vs Position for Helical model
61
Figure 43 Mass fraction of NO Vs Position for Spiral model
3.3.4.6 Scalar Plot Form of Results for NO:
Figure 44 Mass fraction of NO Vs Position for Helical-Spiral model
62
Figure 45 Mass fractin of NO Vs Position for Helical model
Figure 46 Mass fraction of NO Vs Position for Spiral model
63
3.3.4.7 Plot Form of Results for O2:
Figure 47 Mass fraction of O2 Vs position for Helical-Spiral model
Figure 48 Mass fraction of O2 Vs Position for Helical model
64
Figure 49 Mass fraction of O2 Vs Position for Spiral model
3.3.4.8 Scalar Plot Form of Results for O2:
Figure 50 Mass fraction of O2 Vs Position for Helical-Spiral model
65
Figure 51 Mass fraction of O2 Vs Position for Helical model
Figure 52 Mass fraction of O2 Vs Position for Spiral model
66
3.3.4.9 Plot Form of Results for C12H26:
Figure 53 Mass fraction of C12H26vs Position for Helical-Spiral model
Figure 54 Mass fraction of C12H26 Vs Position for Helical model
67
Figure 55 Mass fraction of C12H26 Vs Position for Spiral model
3.3.4.10 Scalar Plot Form of Results for C12H26:
Figure 56 Mass fraction of C12H26 Vs Position for Helical-Spiral model
68
Figure 57 Mass fraction of C12H26 Vs Position for Helical model
Figure 58 Mass fraction of C12H26 Vs Position for Spiral model
69
CHAPTER 4
COMPARISON OF DESIGNS
To make the conclusions, the obtained results are to be compared
with each other. For comparing the results plots were drawn using the data from the excel
sheets that were obtained from the software program after the simulation was done.
In each table values for the Position are the distances of the nodes
from the axis of the cylinder. Values for the mass fractions of each exhaust gases were
taken from the excel sheet obtained from the software program after the simulation was
done. In each table below mass fractions of different exhaust gases were populated in
corresponding sections.
Plots were drawn populating position on X-axis and mass fraction
values on Y-axis for each table. Different curves were obtained for different geometries
and each curve is color coded. As mentioned in the plots green represents the HelicalSpiral curve, blue represents the Helical curve and red represents the Spiral curve.
Having these color coded curves for each geometry makes it easy for the comparison.
70
4.1 Mass Fraction of CO Versus Position:
Helical
Position Helical
Spiral
Spiral
-0.045
0.001
0.001
0.0005
-0.04
0.0025
0.0025
0.002
-0.03
0.011
0.0085
0.008
-0.02
0.031
0.0215
0.021
-0.01
0.045
0.037
0.035
0
0.052
0.0444
0.041
0.01
0.046
0.038
0.036
0.02
0.033
0.023
0.021
0.03
0.013
0.009
0.009
0.04
0.004
0.004
0.003
0.045
0.0015
0.0025
0.001
71
Mass Fraction of CO VS Position
0.06
Mass Fraction of CO
0.05
0.04
0.03
Helical
0.02
Spiral
Helical Spiral
0.01
0
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
Position(m)
Above graph shows the comparison between all the three
geometries based on mass fraction of Carbon Monoxide. Mass fractions of Carbon
Monoxide were taken from the excel sheet result across the cross section of the piston.
Taking distance of the piston from its axis on X-axis and mass fraction values on Y-axis
the above graph was drawn. As it is visible on the graph for Helical-Spiral geometry
which is represented by green curve has the least amount of mass fraction for Carbon
Monoxide among the rest of the two curves. Hence Helical-Spiral Geometry is the better
geometry among the three.
72
4.2 Mass Fraction of CO2Versus Position:
Helical
Position Helical
Spiral
Spiral
-0.045
0.01
0.007
0.001
-0.04
0.02
0.01
0.005
-0.03
0.045
0.02
0.032
-0.02
0.085
0.059
0.075
-0.01
0.125
0.118
0.131
0
0.138
0.133
0.147
0.01
0.128
0.12
0.13
0.02
0.089
0.063
0.074
0.03
0.048
0.03
0.028
0.04
0.023
0.02
0.009
0.045
0.012
0.015
0.001
73
Mass Fraction of CO2 VS Position
0.16
0.14
Mass Fraction of CO2
0.12
0.1
Helical
0.08
Spiral
0.06
Helical Spiral
0.04
0.02
0
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
Position(m)
Above graph shows the comparison between all the three
geometries based on mass fraction of Carbon Di-oxide. Mass fractions of Carbon Dioxide were taken from the excel sheet result across the cross section of the piston. Taking
distance of the piston from its axis on X-axis and mass fraction values on Y-axis the
above graph was drawn. As it is visible on the graph for Helical-Spiral geometry which is
represented by green curve has the more amount of mass fraction for Carbon Di-oxide
among the rest of the two curves. This means that more oxygen has formed into Carbon
Di-oxide instead of Carbon Monoxide, reducing the quantity of harmful gases. Hence
Helical-Spiral Geometry is the better geometry among the three.
74
4.3 Mass Fraction of NO Versus Position:
Helical
Position Helical
Spiral
Spiral
-0.045
0.0002 0.00009
0.0001
-0.04
0.0003 0.00013
0.00025
-0.03 0.00047 0.00022
0.0006
-0.02 0.00089 0.00049
0.0014
-0.01 0.00135 0.00081
0.0021
0 0.00158
0.0009
0.0025
0.01 0.00137 0.00078
0.0021
0.02 0.00092 0.00043
0.00135
0.03
0.0005 0.00015
0.00055
0.04 0.00035 0.00005
0.00015
0.045 0.00015 0.00001
0
75
Mass Fraction of NO VS Position
0.003
Mass Fraction of NO
0.0025
0.002
Helical
0.0015
Spiral
0.001
Helical Spiral
0.0005
0
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
Position(m)
Above graph shows the comparison between all the three
geometries based on mass fraction of Nitrous Oxide. Mass fractions of Nitrous oxide
were taken from the excel sheet result across the cross section of the piston. Taking
distance of the piston from its axis on X-axis and mass fraction values on Y-axis the
above graph was drawn. As it is visible on the graph for Helical-Spiral geometry which is
represented by green curve has the more amount of mass fraction for Nitrous Oxide
among the rest of the two curves. This contradicts the Thesis. The reason for this is the
higher temperatures generated inside the cylinder. By reducing the speed of the engine or
by increasing Air-Fuel ratio this issue can be solved.
76
4.4 Pressure Versus Position:
Helical
Position Helical
Spiral
Spiral
-0.045
370000
185000
410000
-0.04
385000
195000
430000
-0.03
420000
235000
490000
-0.02
560000
315000
600000
-0.01
720000
410000
740000
0
790000
440000
800000
0.01
722000
390000
690000
0.02
461000
260000
410000
0.03
221000
150000
190000
0.04
86000
80000
85000
0.045
4000
4000
4500
77
Pressure VS Position
900000
800000
700000
Pressure(pa)
600000
500000
Helical
400000
Spiral
300000
Helical Spiral
200000
100000
0
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
Position(m)
Above graph shows the comparison between all the three
geometries based on pressure generated inside the cylinder. Pressure values were taken
from the excel sheet result across the cross section of the piston. Taking distance of the
piston from its axis on X-axis and Pressure values on Y-axis the above graph was drawn.
As it is appearing on the graph for Helical-Spiral geometry which is represented by green
curve has the maximum pressure among the rest of the two curves. Hence Helical-Spiral
Geometry is the better geometry among the three.
78
4.5 Temperature Versus Position:
Helical
Position Helical
Spiral
Spiral
-0.045
620
500
560
-0.04
650
560
600
-0.03
850
700
750
-0.02
1300
1120
1250
-0.01
1820
1560
1830
0
1950
1720
2010
0.01
1800
1555
1825
0.02
1280
1120
1255
0.03
840
705
755
0.04
620
560
600
0.045
590
490
560
79
Temperature VS Position
2500
Temperature(k)
2000
1500
Helical
1000
Spiral
Helical Spiral
500
0
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
Position(m)
Above graph shows the comparison between all the three
geometries based on the temperature generated inside the cylinder. Temperature values
were taken from the excel sheet result across the cross section of the piston. Taking
distance of the piston from its axis on X-axis and Temperature values on Y-axis the
above graph was drawn. As it is appearing on the graph for Helical-Spiral geometry
which is represented by green curve has the maximum amount of temperature among the
rest of the two curves. Hence Helical-Spiral Geometry is the better geometry among the
three.
80
CHAPTER 5
CONCLUSIONS
The purpose of this thesis was to model three different geometries
for the inlet manifold of an internal combustion engine using Star CCM+. The Helical,
Spiral and Helical-Spiral geometries were modeled. Using the boundary conditions and
governing equations run the simulation with appropriate model options. The simulation
was done and the results were obtained. Obtained results were compared in between to
determine the best inlet manifold for the internal combustion among chosen three
geometries.
From the obtained results and the comparisons made in the
sections 4.1, 4.2, 4.3, 4.4 and 4.5 it is very apparent the Helical-Spiral geometry is the
best design for inlet manifold. Following are the reasons that proposes this geometry as
the best design,
1. From the graph in section 4.1 it is clear that the Helical-Spiral geometry has the
less amount of Carbon monoxide which is the most harmful gas among the
exhaust gases released by an internal combustion engine. The reason for this is
that the most of the oxygen became into Carbon Dioxide producing less Carbon
Monoxide.
2. The graph in section 4.2 states that the Helical-Spiral geometry has the maximum
Carbon Dioxide among all the designs. This suggests that most of the oxygen
81
became Carbon Dioxide rather than Carbon Monoxide resulting in less harmful
gases into the atmosphere.
3. The graph in section 4.3 states that the Nitrous Oxide produced in Helical-Spiral
design is more than other two designs. The reason for this result is the high
temperatures and pressures produced in the combustion chamber. These high
temperature and pressures produced are due to the more efficient mixing of air
and fuel in Helical-Spiral geometry. Either by increasing the air fuel ratio or by
reducing the engine speed the production of Nitrous Oxide can be reduced.
4. From the graph in section 4.4 it is clear that the pressure produced in the HelicalSpiral geometry design is higher than the other two designs. Because of this high
pressure, more torque will result on the crank shaft.
5. The graph in section 4.5 states that more temperature is produced in the HelicalSpiral geometry design among the other two designs. This result supports the
statement that this design is a better design among the rest of the two.
The above listed five points strongly support the fact that HelicalSpiral geometry design for an inlet manifold is very feasible among the Helical geometry
design and Spiral geometry design. So with the simulation done and the results obtained
it is concluded that Helical-Spiral geometry design is the best design for an internal
combustion diesel engine among the three designs.
82
BIBLIOGRAPHY
[1] Explanation for the inlet manifold
http://en.wikipedia.org/wiki/Inlet_manifold
[2] Previous research work done is available as a Journal online:
http://www.ajol.info/index.php/ijest/article/view/59089
[3] Tutorials used for working on Star CCM+ are available online:
http://www2.warwick.ac.uk/fac/sci/eng/pg/students/esrhaw/introduction_to_star.pdf
[4] Help for documentation was received from Microsoft office tutorials online:
http://office.microsoft.com/en-us/support/results.aspx?ctags=CL010256357
[5] Basic technical information was taken from Wikipedia:
http://www.wikipedia.org/