CHAPTER 1 INTRODUCTION

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22 févr. 2014 (il y a 3 années et 3 mois)

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CFD SIMULATION OF HYDROGEN COMBUSTION


Sree Narayana Gurukulam College Of Engineering Department Of Mechanical Engineering



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CHAPTER 1


INTRODUCTION


Over the past three decades there has been considerable effort in the world to develop and
introduce alternative transportation fuels to replace conventional fuels such as gasoline
and diesel, environmental issues, most notably ai
r pollution and limited availability of
conventional fuels are among the principle driving forces behind this movement.



If one tries to find for the definition of perfect fuel, hydrogen probably satisfies
most of
the desirable characteristics of such a fuel. Plentiful and clean burning, hydrogen has very
high energy content.



Due to difficulties in conducting spatially resolved measurements of combustion
charact
eristics in devices, the numerical simulation can be cost effective approach to
study the combustion mechanism.



In this work, Computational Fluid Dynamics (CFD) based numerical simulations have
been performed to study the combustion of

non
-
premixed hydrogen
-
air mixture in
cylindrical chamber.


The performance of the combustor is evaluated by using CFD package FLUENT 6.0
under adiabatic wall condition at various equivalence ratios and mass flow rates of
hydrogen & air.


1.1

Objectives and
Scope


The objective of this work is to study the fundamentals of Computational Fluid Dynamics
(CFD), Numerical modeling, combustion phenomenon and various aspects in order to use
them for solving the realistic problems. The objectives of this research eff
ort are:



The understanding of the basics of Hydrogen
-
oxygen reaction mechanism, its
combustion and the geometry of the cylindrical chamber used in this study is very
important for simulating hydrogen
-
air combustion system.



To develop a two dimensional num
erical mesh and flow model which adequately
and accurately represent the physical model of combustion chamber and is simple
enough to limit the amount of computational time for obtaining a solution.



To prepare a mathematical model for hydrogen
-
air combusti
on system.



The objective of this study is to find and apply appropriate model that improve the
simulation of combustion with the commercial CFD
-
package FLUENT.



Generate numerical data/solutions which correlate as much as possible with the
experimental data

for various conditions including equivalence ratios, mass flow
rates of hydrogen
-
air mixture.




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The main objective of the research presented in this seminar, is the development of a
numerical infrastructure for the multidimensional numerical simulation of
combustion
processes with the maximum level of accuracy.
































CHAPTER 2


HYDROGEN AS A FUEL



CFD SIMULATION OF HYDROGEN COMBUSTION



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Figure 1: Periodic Table


Hydrogen is a colorless, odorless, tasteless, and nonpoisonous gas under n
ormal
conditions on Earth. It typically exists as a diatomic molecule. Hydrogen is the most
abundant element in the universe, accounting for 90 percent of the universe by weight.
However, it is not commonly found in its pure form.



2.1 Properties of Hydrogen as a fuel



Hydrogen has several important chemical properties that affect its use as a fuel:



It readily combines with oxygen to form water, which is absolutely necessary for
life on this planet.



It has a high
-
energy conte
nt per weight (nearly 3 times as much as gasoline), but
the energy density per volume is quite low at standard temperature and pressure.
Volumetric energy density can be increased by storing the hydrogen under
increased pressure or storing it at extremely
low temperatures as a liquid.
Hydrogen can also be adsorbed into metal hydrides.




Hydrogen is highly flammable; it only takes a small amount of energy to ignite it
and make it burn. It also has a wide flammability range, meaning it can burn when
it makes u
p 4 to 74 percent of the air by volume.




Hydrogen burns with a pale
-
blue, almost
-
invisible flame, making hydrogen fires
difficult to see.



The combustion of hydrogen does not produce carbon dioxide (CO
2
), particulate,
or sulfur emissions. It can produce nit
rous oxide (NO
X
) emissions under some
conditions.




Hydrogen can be produced from renewable resources, such as by reforming
ethanol (this process emits some carbon dioxide) and by the electrolysis of water
(electrolysis is very expensive).



CFD SIMULATION OF HYDROGEN COMBUSTION



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Energy Content f
or 1 kg (2.2 lb) of Hydrogen = 424 Standard Cubic Feet
(Reacting with oxygen to form water).




Higher Heating Value


Lower Heating Value

141,600 KJ


119,600 KJ

Table 1: Heating Values

of H
2



Properties of Hydrogen as a fuel


The properties of hydrogen are listed in table 2. along with conventional fuels
i.e.Gasoline & Diesel and other alternative fuels such as CNG, LPG, and Biogas.




Properties



CNG



Hydrogen



Gasoline



LPG



Bio
gas



Lower Heating Value
(KJ/Kg)



50000



12000


42000


46000


5000


Density (Kg/m
3
)



0.69


0.09


720
-
750



2.24


1.1


Flame Speed (cm/sec)



34.0


265
-
325




38.25


25.0


Stoichiometric A/F
(Kg/Kg)



17.3


34.3


14.6


15.5


6


Flammability limit (
%
vol of air)


5.3
-
15


4
-
75


1.4
-
7.6


2.15
-
9.6


7.5
-
14


Octane No.



130


130+


86
-
94


103
-
105


120


Auto Ignition
Temp.(
0
C)



730


585


222


428


700

Latent Heat of
Vaporizations
(KJ/m
3
)


509




375


428


493
-
549



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Molecular Weight



18.88
-
17.05





1
00


55
-
60




Specific Gravity



0.424


0.07



0.72
-
0.78







Boiling Temp. (F)



-
259


-
423



80
-
437







Table 2: Properties of fuels


2.1.1 Limits of Flammability


The limits of flammability are one of the most impo
rtant properties of a fuel. These
parameters are a measure of the range of the fuel/air ratios over which an engine can
operate. Hydrogen has wide range of flammability in comparison with other fuels. One of
the significant advantages is that hydrogen engi
ne can run on a lean mixture.When engine
is run on slightly lean mixtures fuel economy is greater and the combustion reaction is
more complete. Additionally, the final combustion temperature can be lowered by using
ultra
-
lean mixtures, reducing the amount
of NO
x
emissions.


2.1.2 Minimum Ignition Energy


The minimum energy required for ignition for hydrogen is about an order of magnitude
less than that required for gasoline. This enables hydrogen engines to run well on lean
mixtures and ensures prompt igni
tion. Unfortunately, since very little energy is necessary
to ignite a hydrogen combustion reaction, and almost any hydrogen/air mixture can be
ignited due to wide limits of flammability of hydrogen, hot gases and hot spots on the
cylinder can serve as sou
rces of ignition, creating problems of premature ignition and
flashback.




2.1.3 Quenching Gap or Distance


In the combustion chamber, the combustion flame is typically extinguished at certain
distance from the cylinder wall due to heat losses called as q
uenching distance. For
hydrogen, the quenching distance is less than that of gasoline, so that flame comes closer
to the wall before it is extinguished. Thus it is more difficult to quench a hydrogen flame
than a gasoline flame.


2.1.4 Self Ignition Tempe
rature



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The self ignition temperature is the temperature that a combustible mixture must reach
before it will be ignited without an external source of energy. For hydrogen, the self
ignition temperature is relatively high. The high self
-
ignition temperatur
e of hydrogen
allows larger compression ratios to be used in hydrogen engine without increasing the
final combustion temperature beyond the self ignition temperature and causing premature
ignition. The hydrogen is difficult to ignite in a compression ignit
ion or diesel
configuration, because the temperatures needed for this type of ignition relatively high.


2.1.5 Flame Speed


The flame speed of hydrogen is nearly an order of magnitude higher than that of gasoline.
For stoichiometric mixtures, hydrogen engi
nes can more closely approach the
thermodynamically ideal engine cycle. At leaner mixtures, the flame velocity decreases
significantly.


2.1.6 Diffusivity


Hydrogen diffusivity, or its ability to disperse in air, is considerably greater than that of
gasoli
ne.The high diffusivity is advantageous for two main reasons. First, it facilitates the
formation of uniform mixture of fuel and air. Secondly, if a hydrogen leak does develop,
the hydrogen will disperse rapidly. Thus unsafe conditions can either be avoide
d or
minimized.


2.1.7 Density


Hydrogen has extremely low density. This creates two problems: (1) a very large volume
is necessary to store enough hydrogen to give a vehicle an adequate driving range, (2) the
energy density of hydrogen air charge and henc
e the power output is reduced.




2.1.8 Flame characteristics


Hydrogen flames are very pale blue and are almost invisible in daylight due to the
absence of soot. Visibility is enhanced by the presence of moisture or impurities (such as
sulfur) in the air.

Hydrogen flames are readily visible in the dark or subdued light.





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Figure 2: Invisible Hydrogen Flame Igniting Broom


Hydrogen flames are almost invisible in daylight.Hydrogen fires can only exist in the
re
gion of a leak where pure hydrogen mixes with air at sufficient concentrations. For
turbulent leaks, air reaches the centerline of the leakage jet within about five diameters of
a leakage hole, and the hydrogen is diluted to nearly the composition of air w
ithin
roughly 500 to 1000 diameters. This rapid dilution implies that if the turbulent leak were
into open air, the flammability zone would exist relatively close to the leak. Therefore,
when the jet is ignited, the flame length is less than 500 diameters
from the hole (for
example, for a 0.039 in/1 mm diameter leak, the flame length will be less than 19.7 in/0.5
m).



In many respects, hydrogen fires are safer than gasoline fires. Hydrogen gas rises quickly
due to its high buoyancy and diffusivity. Conseq
uently hydrogen fires are vertical and
highly localized. When a car hydrogen cylinder ruptures and is ignited, the fire burns
away from the car and the interior typically does not get very hot. Gasoline forms a pool,
spreads laterally, and the vapors form
a lingering cloud, so that gasoline fires are broad
and en
-
compass a wide area.




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Figure 3: Hydrogen Flame from Ruptured Fuel Cylinder


2.2 Benefits of Hydrogen Economy


Widespread use of hydrogen as an energy source in this co
untry could help address
concerns about energy security, global climate change, and air quality. Fuel cells are an
important enabling technology for the Hydrogen Future and have the potential to
revolutionize the way we power our nation, offering cleaner,
more
-
efficient alternatives
to the combustion of gasoline and other fossil fuels. These benefits are:
-




Strengthen National Energy Security




Reduce Greenhouse Gas Emissions




Reduce Air Pollution




Improve Energy Efficiency


2.3 Hydrogen Storage and Delivery


In engine applications the storage and portability of adequate mass of hydrogen for
practical applications remain one of the most difficult problems yet to be overcome.
Hydrogen can be stored as a compressed gas in suitably designed high
-
pressure vessels
.
However, the very low density of hydrogen in comparison to other gaseous fuels, dictates
that extremely high
-
pressure cylinders that are sufficiently light in weight and compact in
volume need to be devised and used. The compression of the gas to such hi
gh pressures
requires the expenditure of much expensive compression work and the provision of the
necessary infra structure. Also, these hydrogen gas cylinders would add significantly to
the total weight, cost and bulkiness of the fuel installation.






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Hydrogen also can be carried on board vehicles and engine installations in the form of
various metallic hydrides that would permit the controlled release of hydrogen through
the supply of heat, often from the engine exhaust gas or i
ts cooling water. These methods
are of limited usefulness as they add much cost and weight while reducing the flexibility
of the fuel system and contributing to an increase in undesirable emissions. The carrying
of hydrogen as a cryogenic liquid has its se
rious limitations also. The work and
infrastructure required to liquefy hydrogen are much too expensive and energy intensive
to become widely usable. The energy consumed in the liquefaction process can be up to
around 30% of the heating value of the hydrog
en. Also, the cryogenic tanks needed to
carry the liquid hydrogen, despite the very substantial progress made in recent years in
their design, safety and manufacture, remain relatively expensive and bulky.



2.3.1 Hydrogen Deli
very Methods


The hydrogen currently in the marketplace for industrial use is transported as a gas at low
(100
-
300 psig) or high (3000
-
5000 psig) pressure or as a cryogenic liquid via gas
pipelines, gas or cryogenic liquid trucks, tube trailers, barge, or
rail cars. At high
volumes, hydrogen delivery by pipeline is currently the lowest cost option. Liquefaction
is often cost
-
effective in situations where lower volumes are needed.




Compressed Gas and Cryogenic Liquid Storage

Hydrogen can be physically stored

as either a gas or a liquid. Storage as a gas typically
requires high
-
pressure tanks (5000
-
10,000 psi tank pressure). Storage of hydrogen as a
liquid requires cryogenic temperatures, since the boiling point of hydrogen at one
atmosphere pressure is
-
252.8
0
C.




Materials
-
based Hydrogen Storage

Hydrogen can also be stored on the surfaces of solids (by adsorption) or within solids (by
absorption). In adsorption, hydrogen is attached to the surface of a material either as
hydrogen molecules or as hydrogen atoms
. In absorption, hydrogen is dissociated into H
-
atoms and then the hydrogen atoms are incorporated into the solid lattice frame work.
Hydrogen storage in solids may make it possible to store larger quantities of hydrogen in
smaller volumes at low pressure
and at temperatures close to room temperature. It is also
possible to achieve volumetric storage densities greater than liquid hydrogen because the
hydrogen molecule is dissociated into atomic hydrogen within the metal hydride lattice
structure.






Curren
t Technology

Current on
-
board hydrogen storage approaches involve compressed hydrogen gas tanks,
liquid hydrogen tanks, metal hydrides, carbon
-
based materials/high surface area sorbents,
and chemical hydrogen storage. Storage as a gas or liquid or storage
in metal hydrides or
high surface area sorbents constitute reversible on
-
board hydrogen storage systems, since
hydrogen regeneration or refill can take place on
-
board the vehicle. For chemical
hydrogen storage approaches (such as a chemical reaction on boa
rd the vehicle to


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produce hydrogen), hydrogen regeneration is not possible on
-
board the vehicle and thus
these spent materials must be removed from the vehicle and regenerated off board.






























CHAPTER 3


COMBUSTION


3.1 Combustion Ph
enomena

Combustion is a key element of many of modern society's critical technologies.
Combustion accounts for approximately 85 percent of the world's energy usage and is
vital to our current way of life. Spacecraft and aircraft propulsion, electric power


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production, home heating, ground transportation, and materials processing all use
combustion to convert chemical energy to thermal energy or propulsive force.

Examples of combustion applications:



Gas turbines and jet engines




Rocket propulsion




Piston eng
ines




Guns and explosives




Furnaces and boilers




Flame synthesis of materials (fullerenes, nano
-
materials)




Chemical processing (e.g. carbon black production)




Forming of materials




Fire hazards and safety

Combustion is a complex interaction of physical (f
luid dynamics, heat and mass transfer),
and chemical processes (thermodynamics, and chemical kinetics). Practical applications
of the combustion phenomena also involve applied sciences such as aerodynamics, fuel
technology, and mechanical engineering.The t
ransport of energy, mass, and momentum
are the physical processes involved in combustion. The conduction of thermal energy, the
diffusion of chemical species, and the flow of gases all follow from the release of
chemical energy in the exothermic reaction.
The subject areas most relevant to
combustion in the fields of thermodynamics, transport phenomena, and chemical kinetics
can be summarized as follows:





Thermodynamics:




Stoichiometry




Properties of gases and gas mixtures




Heat of formation




Heat of react
ion




Equilibrium




Adiabatic flame temperature




Heat and Mass Transfer:




Heat transfer by conduction




Heat transfer by convection




Heat transfer by radiation




Mass transfer




Fluid Dynamics:




Laminar flows




Turbulence




Effects of inertia and viscosity




Combu
stion aerodynamics



Chemical Kinetics:

Application of thermodynamics to a reacting system gives us the equilibrium
composition of the combustion products and maximum temperature corresponding to this
composition, i.e. the adiabatic flame temperature. Howeve
r, thermodynamics alone is not


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capable of telling us whether a reactive system will reach equilibrium. If the time scales
of chemical reactions involved in a combustion process are comparable to the time scales
of physical processes (e.g. diffusion, fluid
flow) taking place simultaneously; the system
may never reach equilibrium. Then, we need the rate of chemical reactions involved in
combustion. Combustion processes can be sub
-
divided based on mixing as premixed,
non
-

premixed and partially premixed. Combu
stion in homogeneous
-
charge spark
-
ignition engines and lean burn turbines is under premixed conditions. Contrastingly,
combustion in Diesel engines or industrial furnaces is under non
-
premixed conditions. In
the nonpremixed cases, fuel is injected into the

combustion chamber along with air,
where it is ignited due to pre
-
existing hot gases or auto
-
ignites due to high temperatures
second criterion for subdividing the turbulent combustion relates to the ratio of
turbulence to chemical reaction time scales. Ab
ove a certain cross
-
over temperature,
hydrocarbon oxidation occurs by chain
-
branching. Chain
-
branching ceases when the
temperature falls below this limit, thus causing extinction of flame. This crossover
temperature increases with pressure. While the fast
chemical processes can be simulated
using equilibrium approach, slow chemical reactions require being modeled using kinetic
expressions. Presence of slow and very fast reactions in the same reaction mechanism can
pose problems in numerical solutions due to

stiffness of the equations. Most industrial
combustion processes involve turbulent flows. Laminar flows are encountered in few
industrial cases and a large number of academic cases. Flow simulations require the
solutions of balance equations (of mass, ene
rgy and momentum). These equations are
mostly of partial differential form. Laminar flow cases are much simpler and
straightforward and can often be approximated with one dimensional treatment. Presence
of turbulence in the flow requires special treatment
to account for the complex nature of
turbulence. Combustion requires that fuel and oxidizer be mixed at the molecular level
and in turbulent flows; this mixing is done not only by molecular (thermal) processes, but
also by the turbulent fluctuations. Molec
ular mixing takes place at the interface of the
smallest eddies.



3.2 Hydrogen Combustion


One the reasons for which we are interested in hydrogen is because its chemistry is
considered a starting point for the more complex hydrocarbon chemistry. It is im
portant
to stress that in the auto ignition stages of any flame, the fuel air mixture may follow a
low temperature reaction mechanism and in the latter stages, an explosive reaction due to
the increase in temperature and/or pressure causing the operating p
oint to shift between
the regions of the graph of figure 4. This point is especially significant in hydrocarbon
chemistry, because it is in the low
-
temperature regime that particular pollutant
compounds are formed. Figure 4 depicts the explosion limits of
a stoichiometric mixture,
but equivalent plots can be obtained for many different mixture compositions.








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Figure 4: Explosion Limits of Stoichiometric Hydrogen
-
Oxygen Mixture





The general characteristics are:




The
first and second limits are ones that correspond to conditions of very low
pressures (up to an absolute pressure of about 0.3 bar) and will not be considered.
Our lowest working pressure is atmospheric pressure, 1 bar.





The third limit follows the trend t
hat one would expect from simple density
considerations. As the pressure increases, the initial densities of the reactants
increase and a lower temperature is necessary for the reactions to become fast
enough for explosion. Furthermore, noting the logarith
mic axis, we can see that
the effect of temperature is much stronger than that of pressure, a trend one would
expect and correctly captured by the considerations of simplified one
-
step
Arrhenius chemistry.







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CHAPTER 4


GRID GENER
ATION AND MATHEMATICAL MODELING


4.1 Model geometry and mesh


The geometry of the cylindrical chamber used in this study is shown in figure 5.The non
premixed hydrogen and air are injected into the cylindrical chamber from inlets located at
one axial end a
s shown in figure 5. A small nozzle in the center of the combustor
introduces hydrogen at 90m/s and air enters the combustor coaxially. Because of the axial
symmetry of the combustion chamber, the geometry is modeled as a two
-
dimensional
axi
-
symmetric mode
l.




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Figure 5: Schematic Diagram of the Combustion Chamber for Hydrogen Combustion
Modeling


4.1.1 Grid Generation


Mesh or grid generation consists of creating a set of grid points along the boundaries and
throughout the domain of interest. The numerical

simulation of Navier
-
Stokes equation
requires the gen
-
eration of grids in the flow domain. As the hydrogen injected centrally
and air enters co
-
axially in the combustion chamber more variation in the properties will
be seen along the central axis as well
as at the inlet. So clustering is done from
combustion wall surface towards central axis and from inlet towards exit.


For the scenarios analyzed in this study, the number of nodes and number of quadrilateral
cells are 1705 and 1615 respectively used to me
sh the model for the CFD simulations.
This fine mesh size will be able to provide good spatial resolution for the distribution of
most variables within the combustion chamber.




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Figure 6: Combustion Chamber Grid


4.2 Mathematical Model
ing


Modeling is the representation of a physical system by a set of mathematical relationships
that allow the response of the system to various alternative inputs to be predicted. In
Computational Fluid Dynamics, we model the physical system involving flu
id flow
within the definite boundaries by the set of mathematical equations usually in differential
form and obtain the numerical solution of these governing equations describing the fluid
flow by the use of computational methods. The governing equations m
ay include: the set
of the Navier
-
Stokes equations, continuity equation, and any additional conservation
equations, such as energy or species concentrations. The fluid flow is modeled by the
governing equations, which show the effect of the governing pheno
mena on the fluid
flow. These governing phenomena may include: conduction, convection, diffusion,
turbulence, radiation and combustion. The following is brief description of the governing
equations.





4.3 Governing Equations

4.3.1 Continuity Equation

Con
sidering the law of conservation of mass the continuity equation,




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+ u.div (

) +


.div (u) = 0

In the given equation the first term is the rate of change of density. In the second and the
third terms the divergence div is the flux density or
flux/volume. The first two terms
show the two ways the density of the fluid element changes. If we assume the
incompressibility condition i.e. density of the fluid is constant, the above equation
reduces to, div (u) =0.


4.3.2 Momentum Equations

Also known

as Navier and Stokes equations, these are derived for a viscous flow and give
the relationships between the normal/shear stresses and the rate of deformation (velocity
field variation).We can obtain these equations by making a simple assumption that the
s
tresses are linearly related to the rate of deformation (Newtonian fluid), the constant of
proportionality for the relation being the dynamic viscosity of the fluid. Following is
stated the Navier and Stokes equation for i
-
th coordinate direction,



+

=
-


+

+ Fi

Where

is the viscous force tensor and F
𝑖

represents a body force in the
𝑖
-
th coordinate
direction. In practical situations of combustion, all fluids are assumed to be Newtonian
and the viscous stress tensor is:


= µ {

+

}
-


µ

{

}

Where µ is the molecular viscosity which depends on the fluid. The Kronecker delta is

=1,if i = j, 0 otherwise.


4.3.3 Species




+

=
-


+

(α=1,
2, 3… n)

Where n is the number of species,


is the molecular diffusivity flux of the species α in
the

j
-
th coordinate direction,

is the mass reaction rate of this species per unit volume,
and
is

the mass fracti
on of species α.

The diffusive flux,
,can be approximated by:

=
-



=
-




where


is the Schmidt number of the species α, defined as:






=




Where D

is the molecular diffusivity of the species α relative to the other species.


4.3.4 Standard k
-
ε turbulence model



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In this simple model, two additional transport equation are solved for the two turbulence

quantities viz. the turbulent kinetic energy k and the energy dissipation rate ε. These two
quantities are related to the primary variables and can give a length scale and time scale
to form a quantity with dimension of

, thus making the mod
el complete (no more
flow
-
dependent specifications are required). This is a widely used model in CFD
simulations.





=




The balance equation for k is:



+


) =
-
(2/3)

+
σ :

+

{


}
-


+




4.4 Boundary conditions


The inlet temperature of hydrogen and air is considered to be uniform at 300 K. A fixed,
uniform velocity 9
0 m/s is specified at the hydrogen inlet.Axis
-
symmetric boundary
conditions are applied along the central axis of the combustion chamber. At the exit, a
pressure outlet boundary condition is specified with a fixed pressure of 1.01325 * 105 Pa.
At the chamb
er wall, no
-
slip boundary condition and no species flux normal to the wall
surface are applied. The thermal boundary condition on the chamber wall is taken as
adiabatic wall condition.












CHAPTER 5


CFD SIMULATION


A number of numerical simulations

have been performed to study the combustion
phenomena under adiabatic wall conditions when hydrogen air mixture changes from


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lean to rich and also at different mass flow rate of mixture. Figure. 7 shows the contours
of temperature (K) on the cross section

along central axis of combustion chamber at
stoichiometric air fuel ratio i.e. at
Ф=1. And Figure 8 shows the gas temperature
distribution along the central axis. It can be seen from Figures 7 and 8 that the highest
temperature is obtained at the exit of combustion chamber. The flame temperature can be
as high as 2365 K which is almost
the same as the adiabatic flame temperature of the
Combustion of non premixed stoichiometric hydrogen
-
air mixture. Figures 9 to show the
contours of molecular species on the cross
-
section along the central axis at Φ=1 under
adiabatic wall condition.




Figure 7: Temperature Contours at Ф=1




















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Figure 8: Contours of Mole fraction of























Figure 9: Contours of

Mole fraction of N
2
















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Figure 10: Contours of Mole fraction of O
2
















Figure 11: Contours of Mole fraction of H
2






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Figure 12: Contours of Mole fraction of OH




















Figure 13: Contours of Mole fraction of O



CHAPTER 6



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CONCLUSION


In this work, the CFD based combustion simulations have been applied to analyze the
combustion characteristics of non
-
premixed hydrogen
-
air in a 2D combustor. The CF
D
simulations, taking in to account the coupling of fluid dynamics, heat transfer and
detailed chemical kinetics, are used to investigate the effects of various operating
conditions. The combustor performance is evaluated by predicting the temperatures of
exit gas of the combustor and outer wall of the combustor. To make the combustor
operable, the heat output should meet the design criteria, the wall temperature should be
lower than the material allowable temperature and the exit gas temperature should be
high enough.




























CHAPTER 7



CFD SIMULATION OF HYDROGEN COMBUSTION



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CFD SIMULATION OF HYDROGEN COMBUSTION



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CFD SIMULATION OF HYDROGEN COMBUSTION



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CFD SIMULATION OF HYDROGEN COMBUSTION



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CFD SIMULATION OF HYDROGEN COMBUSTION



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