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Analysis of Scramjet Combustion Chamber
S.Sridhar1, T.Dinesh 2, V.Bharath 3 ,K.Jayakumar4
1. Assistant Professor, Department of Mechanical Engineering, NSIT, Salem, India 2, 3, 4 Students, Department of Mechanical Engineering, NSIT, Salem, India
1,[email protected] 2,[email protected] 3,[email protected], 4,[email protected]
ABSTRACT- Numerical simulations of the scramjet combustor by using the commercial CFD code Fluent
with the coupled implicit method with second-order accurate discretization have been obtained for the reacting
flows with the parallel fuel injection (ramp injection). The k-ε model has been used to examine supersonic flow
in a model scramjet combustor. Scramjet combustor model and it is consists of a one-sided divergent channel
with a Ramp type flame holder at the base of which hydrogen is injected. Ramp injector is re-designed to
increase the combustion efficiency. The cavity is introduced and extended to the nozzle exit. The cavity is
mainly introduced to increase the fuel and air mixture. The presence of cavity after the injector increases the re-
circulation flow inside the cavity. Due to the shape, the rate of mixing and combustion increased, it also results
in increase of pressure. The total pressure losses are minimized. The scramjet combustor model is designed and
analyzed by using GAMBIT and FLUENT software. In the analyzed result is compared with theoretical
calculations. The k-ε computations are capable of predicting mixing and combustion simulations well and good.
Index Terms—supersonic combustion ramjet (SCRAMJET), computational fluid dynamics (CFD)
I.INTRODUCTION
An airframe integrated scramjet propelled vehicle has advantages for application to several missions. In its
simplest form, such a vehicle will combine the features of quick reaction, low vulnerability to counter attack and
better propulsion efficiency. The Supersonic Combustion Ramjet (SCRAMJET) engine has been recognized as
the most promising air breathing propulsion system for the hypersonic flight (Mach number above 5).In recent
years, the research and development of scramjet engine has promoted the study of combustion in supersonic
flows. Extensive research is being carried out over the world for realizing the scramjet technology with hydrogen
fuel with significant attention focused on new generations of space launchers and global fast-reaction
reconnaissance missions. However, application for the scramjet concept using high heat sink and hydrogen fuels
offers significantly enhanced mission potential for future military tactical missiles. Scramjet being an air-
breathing engine, the performance of the missile system based on the scramjet propulsion is envisaged enhance
the payload weight and missile range. Supersonic combustion ramjet engine for an air-breathing propulsion
system has been realized and demonstrated by USA on ground and in flight. X- 43 vehicle used hydrogen fuel.
Hydrocarbon fuel scramjet engine is still under study and research. Mixing, ignition and flame holding in
combustor, ground test facilities and numerical simulation of Scramjet engine are the critical challenges in the
development of scramjet engine. In our project to plan combine Ramp and wall injectors for further increasing
mixing. Analysis process is carried for with cavity and without cavity type combustion chamber. Cavity is mainly
introduced for creating circulation. Circulation helps further mixing of air and fuel.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:425
II.LITERATURE SURVEY
Among the three critical components of the scramjet engine, the combustor presents the most
formidable problems. The complex phenomenon of supersonic combustion involves turbulent mixing, shock
interaction and heat release in supersonic flow. The flow field within the combustor of scramjet engine is very
complex and poses a considerable challenge in design and development of a supersonic combustor with an
optimized geometry. Such combustor shall promote sufficient mixing of the fuel and air so that the desired
chemical reaction and thus heat release can occur within the residence time of the fuel-air mixture. In order to
accomplish this task, it requires a clear understanding of fuel injection processes and thorough knowledge of the
processes governing supersonic mixing and combustion as well as the factors, which affects the losses within the
combustor. The designer shall keep in mind the following goals namely,
i) Good and rapid fuel air mixing.
ii) Minimization of total pressure loss.
iii) High combustion efficiency.
One of the strategies to solve the aforesaid problems of mixing is generation of axial vortices. Axial vortices
possess a better far field mixing characteristics. Also they are being propagated to a considerable distance, even
with the suppressing characteristics of the supersonic core flow. Ramp injectors are considered to be a key
feature to generate axial vortices. Figure 4 & 4A depicts some of the characteristics of Ramp injectors flow field.
The following are the characteristics of the ramp injectors. The spillage vortices (contra rotating vortices)
generated by Ramp compression.
1. Pre-compression by the Ramp face produces favorable region for injection.
2. Stagnation region near the leading edge of the Ramp injector improves ignition.
Generation of acoustic oscillations is also considered to be a better candidate to achieve better mixing.
Unsteady shear layers generate acoustic oscillations. Wall mounted cavities generates these oscillations to aid the
mixing enhancement. The Cavity parameters in figure 1, Cavities are characterized by their L/D ratio. There are
three regimes of cavity behavior, categorized by the shear layer separation and its reattachment. For cavities of
L/d less than 1, the shear layer reattaches way past the trailing edge of the cavity it generates transverse
oscillations. These cavities are called as „Open Cavities‟. This type of oscillations aid in penetration of fuel For
L/D more than 2, the separated shear layer attaches to the bottom wall of the cavity, it generates longitudinal
oscillations, which aid in flame holding characteristics.
Figure: 1 Combination of ramp and wall injector.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:426
III. COMBUSTION CHAMBER DESIGN
We have referred more than ten journals and gathered information is about the injectors, combustion
chamber design and cavity creating. We compared all these journals and we made a model of combustion
chamber with the combination of ramp and wall injectors. Which is placed before the cavity? We design the
model in CATIA software Mesh generation is performed in a Fluent pre-processing program called Gambit.
The current model is combining of Ramp and wall injector combustion chamber type as shown in figure. The
boundary conditions are such that, the air inlet and fuel inlet surfaces are defined as pressure inlets and the
outlet is defined as pressure outlet. In this particular model the walls of the combustor duct do not have
thicknesses. The domain is completely contained by the combustor itself; therefore there is actually no heat
transfer through the walls of the combustor.
1) Air inlet-30mm.
2) Outlet-50mm.
3) Combustion chamber length-667mm.
4) Cavity length and depth-80,20mm.
Figure: 2. with and without cavity combustion chamber design
Case-1
Figure: 3.Meshed 3D Combustion chamber with cavity model.
Case-2
Figure: 4.Meshed 3D Combustion chamber without cavity model.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:427
Boundary Conditions: During analysis we have taken same pressure for both fuel and air for all the models.
Pressure inlet and pressure outlet conditions were taken on the left and right boundaries respectively. Pressure
inlet condition was taken for fuel injector. The top and bottom boundaries, which signify the sidewalls of the
isolator, had symmetry conditions on them. The walls, obstacles and other materials were set to standard wall
conditions. The computations were initially carried out with various levels of refinement of mesh. The input
parameters that were for the model is shown in tabulated form,
Table: 1. Boundary conditions
Modeling details: The .msh file obtained from the GAMBIT was exported to FLUENT for subsequent
analysis. The .msh file was read using FLUENT and subsequently its grid checking was done, the grid was
checked with no error and the formation of one default interior. The following models were selected:
1. The pressure based solver,
2. Energy equation
3. Standard k-ε model,
4. RNG k-ε model,
5. Eddy-dissipation criterion in the
species transport section.
IV. ANALYSIS RESULT
Circulation in Cavity: Below figure shows circulation creation in their cavity. Color shows pressure variation
near to the cavity and inside the cavity. Pressure is less inside cavity.
Case-1
Figure: 5. Path lines colored by static pressure
Input parameters Air Fuel
Mach No 3.12 1.5
Temperature 1000k 300k
Pressure 80325Pa 80325Pa
Mass fraction of
O2
0.213 0
Mass fraction of
N2
0.767 0
Mass fraction of
H2
0 1
Mass fraction of
H2O
0.02 0
Inlet length 0.04m 0.002m
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:428
Case-2
Figure: 6. Path lines colored by static pressure
Cavity type combustion chamber:
1) Static Temperature: The static temperature was taken as an indication of combustion efficiency of the fuel
(hydrogen). Higher combustion efficiency means a greater percentage of the injected fuel undergoes combustion
resulting in a higher static temperature at the combustor exit. The maximum temperature is 3443K.
Figure: 7 Static temperature
Figure: 8 X, Y plot of Static temperature
2).Static pressure: Static pressure is the pressure that is exerted by a fluid. Specifically, it is the pressure
measured when the fluid is still, or at rest. The value of static pressure at the outlet is nearly 1.03e+04 Pa. but
the entrance given static pressure is 80325 pa, the pressure is decreased due to circulation creation in cavity area
Figure: 9 Static pressure.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:429
Figure: 10 .X, Y plot of Static pressure.
3) Total pressure: Figure 11 is giving the details about total pressure variation; it is clear that total pressure is
getting decreased gradually up to sudden level after that the variation is high due to shock wave creation. Figure
4.2.3 shows the variation of total pressure in the top and bottom side of the wall in the top wall total pressure
loss is more compare to bottom wall it is because of the change in area at top side.
Figure: 11 Total pressure
Figure: 12.X, Y plot of total pressure
4)Density: Plot of density distribution at air in, out shows that density increases with H2 injection and then, it
decreases gradually with mixing and combustion of air and hydrogen fuel mixture and the subsequent expansion
of the combustion products.
Figure13.Density
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:430
Figure14.X, Y plot of Density
5).Mass Fraction of H2: The below graph shows the distribution of H2 In the air in, out of the combustor. As
can be seen, the mass fraction of hydrogen is maximum at the fuel injection port and continues to decrease
along the length of the combustor due to combustion. Thus, the graph provides evidence of combustion.
Figure: 15 Mass Fraction of H2
Figure: 16.X, Y plot of Mass Fraction of H2
6) Mass Fraction of H2O: The contour and XY Plot of water Mass fraction for the flow field downstream of
the air in, out is shown in the figure. Typically, when dealing the chemical reaction, it is important to remember
that mass is conserved, so the mass of product is same as the mass of reactance. Even though the element exists
in different the total mass of each chemical element must be same on the both side of equation
Figure: 17 Mass Fraction of H2O
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:431
Figure: 18 X, Y plot of Mass Fraction of H2O
7) Mass Fraction of O2: The contour and XY Plot of O2 Mass fraction for the flow field downstream of the
air in, out is shown in the figure. Oxygen is decreased in every combustion reaction. Decreasing of oxygen it
shows burning rate is increased inside the combustion chamber
Figure: 19 Mass Fraction of O2
Figure: 20 X, Y plot of Mass Fraction of O2
V. RESULT COMPARISION
The table 2 shows Comparison between with and without cavity combustion chamber. Pressure is high in with
cavity type combustion chamber compare to without cavity type combustion chamber. Temperature is high in
without cavity type combustion chamber compare to with cavity type combustion chamber. Mass friction of H2,
H2Oand O2 is slightly varying in the both combustion process.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:432
Table: 2. Result comparison
V.CONCLUSION
In the scramjet engine the air fuel mixture is less in the combustion chamber due to the supersonic flow
which takes limited time to escape from the combustion chamber. To increase the time of air to stay in
combustion chamber we have modified the injector design with the cavity in the combustion chamber.
The reason is why the cavity is introduced to create circulation of air. So that the air fuel mixing can be
obtained maximum. The circulation reduces the pressure inside the combustion chamber. The total pressure loss
will simultaneously maximum due to the circulation. The efficiency will be maximum only when the total
pressure loss is maintained minimum. The total pressure loss is maintained by providing cavity place at a specific
angle 300.
The combustion chamber design is analyzed by using fluent software. The standard fluent conditions are
used for analysis. The K epsilon turbulence model is selected. We referred journals for the Boundary conditions.
In this we are analyzed two cases. One is with cavity type combustion chamber and another one is without
cavity type combustion chamber.
In with cavity type combustion chamber pressure is obtained 75012.32pa. The pressure is high in the
upper wall compared to bottom wall. Pressure is decreased in the cavity, so the pressure loss is more at bottom
wall compared to top wall. Temperature is obtained 3443k.Increasing of temperature it shows increasing of
burning rate.
Temperature is high at the bottom wall compared to top wall. Along the combustion chamber
temperature is increased. Mass fraction of H2is 0.9995785, Mass fraction of H2O is 0.2513, Mass fraction of
O2is 0.23.In without cavity type combustion chamber we got maximum pressure level is 73476.26pa. Pressure
loses is less in both the walls due to the no circulation inside the combustion chamber. Temperature is obtained
4357k. In bottom wall temperature is high compared to top wall. The maximum temperature shows the
increased burning rate.
Parameters
Inlet Conditions Combustion Chamber
With Cavity Without
Cavity
Pressure 80325pa 75012.32pa 73476.26pa
Total Pressure 80325pa 80857.75pa 80408.41pa
Temperature 1000k 3443k 4357k
Density( kg/m3) 1.225
0.35146 0.351
Mass Fraction of
H2
1
0.9995785
0.9999699
Mass Fraction of
H2O
0.02
0.2513 0.25155
Mass Fraction of
O2
0.213
0.23
0.23
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:433
Compare to both the cases, pressure is high in cavity type combustion chamber. Pressure range is
75012.32Pa. Temperature range is high in cavity type combustion chamber compare to without cavity type
combustion chamber. Maximum Temperature is 4357k. The mass fraction of H2, H2O and O2 is slightly
varying.
REFERENCES
1. Arnaut Stalin, A. S. and Robinson, Y. (2012) “Numerical Simulation of Mixing Enhancement of Cavity Based
Transverse Injection in a Scramjet Combustor”, - European Journal of Scientific Research”, Vol.81 No.4.
2. Andreas Mack* and Johan Steel ant, (2006) “Mixing enhancement by shock impingement in a generic scramjet
combustion chamber”, - European conference on computational fluid dynamic.
3. Markus Kindler, Thomas Bacha, Markus Lempel, Peter Erlanger, and Manfred Aligner, “Numerical Investigations of
Model Scramjet Combustors”,
4. Pandey, K.M. and Singh, A.P. (April 2011) “Numerical Analysis of Supersonic Combustion by Strut Flat Duct
Length with S-A Turbulence Model”, - IACSIT International Journal of Engineering and Technology, Vol.3, No.2.
5. Schumacher, J. (2000.) "Numerical Simulation of Cantilevered Ramp Injector Flow Fields for Hypervelocity Fuel-Air
Mixing Enhancement".
6. Shigeru As, Rainer Hakim, Shingo Miyamoto, Kei Inoue and Yasuhiro Tami, (2005), “Fundamental study of
supersonic combustion in pure air flow with use of shock tunnel”, Department of Aeronautics and Astronautics, Kyushu University,
Japan , Act Astronautic, vole 57,
7. Suk anta Rogan, Pandey,K.M. and Singh,A.P,( May 2012) “Computational Analysis of Supersonic Combustion Using
Wedge-Shaped Strut Injector with Turbulent Non-Premixed Combustion Model”, - International Journal of Soft Computing and
Engineering (IJSCE) ISSN: 2231-2307, Volume-2, Issue-2
8. Pandey,K.M. and Singh,A.P and Sukanta Roga, (April 2012) “CFD Analysis of Supersonic combustion using
Diamond shaped Strut Injector with standard K-Є Non-premixed Turbulence model”, International Journal of Advanced Trends
in Computer Science and Engineering Volume 1, No.1.
9. Pandey, K.M. and T.Sivasakthivel, (October 2011) “CFD Analysis of Mixing and Combustion of a Hydrogen Fueled
Scramjet Combustor with a Strut Injector by Using Fluent Software”, -IACSIT International Journal of Engineering and
Technology, Vol. 3, No. 5.
10. Pandey, K.M. and T.Sivasakthivel, (April 2011) “CFD Analysis of Mixing and Combustion of a Scramjet Combustor
with a Planer Strut Injector” - International Journal of Enviromental Science and Development, Vol. 2, No. 2.
12. Pandey, K.M, Anup Baishya and Vishwa Bhushan Singh, (October 2011) “A Comparative Study of Cantilevered Ramp
Injector with Standard k-ε and RNG k-ε Turbulence Models”, International Journal of Chemical Engineering and Applications,
Vol. 2, No. 5.
13. Strykowski, P.J., Krothapali, A., and Wishart, D., “The Enhancement of Mixing in High-Speed Heated Jets Using a
Counterflowing Nozzle,” AIAA Paper 92-3262, July 1996.
14. Strykowski, P.J., and Niccum, D.L., “The Stability of Countercurrent Mixing Layers in Circular Jets,” Journal of Fluid
Mechanics, Vol. 227, 1991,
15. Seiner J. M., Dash S. M., and Kenzakowski D.C., “Historical survey on enhanced mixing in scramjet engines,” AIAA
Journal of Propulsion and Power, Vol. 17, pp 1273-1286, 2001.
16. Morris, P.J., Giridharan, G., and Lilley, G.M., “On the Turbulent Mixing ofCompressible Free Shear Layers,”
Proceedings Royal Society London, Series A: Mathematical and Physical Sciences, Vol 431, 1990, pp. 219-243.
17. Lu, G., and Lele, S.K., “Spatial Growth of Disturbances in a Skewed Compressible Mixing Layer,” AIAA Paper 93-
0214, Jan. 1993.
18. Lele, S. K., “Direct Numerical Simulation of Compressible Free Shear Layer Flows,” AIAA Paper 89-0374, Jan.
1989.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September /2018
ISSN NO: 1076-5131
Page No:434
19. Childs, R., Nixion, D., Keefe, L. R., and Rodman, L. C., “A Study of Compressible Turbulence,” AIAA Paper 93-
0659, Jan. 1993
20. Birch, S. F., and Eggers, J.M., “A Critical Review of the Experimental Data for Developed Turbulent free Shear
Layers,” Free Turbulent Shear Flows, SP321, NASA, Vol. 1, 1972, pp. 11-37.
21. Brown, G. L., and Roshko, A., “On Density Effects and Large Structure in Turbulent Mixing Layers,” Journal of
Fluid Mechanics, Vol. 64, Pt. 4, 1974, pp. 775-816.
22. Papamouschou, D., and Roshko, A., “The Compressible Turbulent Shear Layer: An Experimental Study,” Journal of
Fluid Mechanics, Vol. 197, 1988, pp. 453-47
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ISSN NO: 1076-5131
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