This presentation consists of a definition, different instabilities occur due to supersonic flame, Ignition and flame stabilization techniques, Fuel-air mixing enhancement, and problem.

1. Seminar-I ROSHAN SAH
Roll no:- 17AE60R01
M.Tech (1st Year)
Dept. of Aerospace Engg.
Indian Institute of Technology
Kharagpur (IIT KGP)
SUPERSONIC COMBUSTIONINSTABILITY

2. Contents :-
 Definitionof Combustion Instability.
 Supersonic Combustion Instabilities.
 Ignition and Flame stabilizationand its techniques.
 Fuel-air mixing problem.
 Fuel- air mixing enhancement.
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3.  Definition:-
Combustion Instability:-
• Combustion instabilities are typically violent pressure oscillations in a
combustion chamber.
• Unsteadiness or abnormality in the combustion of fuel, as may occur in a
rocket engine and scramjet.
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4. Supersonic Combustion Instabilities :-
They are:-
o Fuel droplets size and its distribution.
o Ignition and Flame Stabilization .
o Fuel-air mixing problem (Turbulent mixing problem)
o Stabilization of Flame holder .
o Aerodynamics effects of heat release.
o Testing difficulties.
o Thermo-acoustic instability.
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5. Ignition and Flame stabilization:-
Flame stabilization techniques are :
1. Transverse injection of fuel from a wall orifice.
2. Step followed by transverse injection.
3. Fuel injection at angle.
4. Cavity flame holder
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6. Under expanded fuel injection normal to
the cross•-flow
Injection behind a sudden expansion
produced by a step
Fuel injection at angle Cavity flame holder
[1]
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7. Fuel-air mixing problem (Turbulent mixingproblem)
It occur due to
• Fluid residence time is only of order of milliseconds.
• Weak shock wave formation.
• Non-uniformity in flow.
• Complex flow.
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8. Fuel- air mixing enhancement:-
It can be done by following methods:-
 Ramp-injection configurations
1.Swept and straight ramps.
2.Recessed swept ramp.
3.Multiple ramps with a partially recessed wall.
 Aerodynamic ramp.
 Upstream fuel injections.
 Aerated Injectors.
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9. Ramp-injection configurations :-
• Its main fundamental principle is that the airflow spills over ramp, forming
vortical structures that lift the fuel from the wall and enhancing mixing.
Swept and straight ramps
(Northam et al 1992)
• Swept ramps is more effective
than un-swept ramps.
• It forms axial counter- rotating
vortices.
• Ramp vortex sheddinghelps lift the
fuel from a low injection angle and
promotes penetration into the core
airstream.
Swept ramps
[2]
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10. Recessed swept ramp :-
( Owens et al 1997)
• It consists multiple injection port
occupying entire duct.
• It forms small recirculation region
between the ramp downstream face
and combustion chamber wall and
help promoting flame holding.
• Enhance mixing without incurring
unacceptable level of pressure loss
Recessed swept ramp
[3]
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11. Multiple ramps with a partially recessed wall :-
(Goldfeld et al 2004)
• It has complex configuration.
• It consists partially protruding ramps and
partially recessed wall to maintain the
duct constant area and staggered layout
on opposite chamber walls.
• Forms large no. of recirculationregion
for mixingand also help in flame holding.
Multiple ramps with a partially
recessed wall
[4]
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12. Computationalresults of mixing:-
Injectant mole fraction at selected cross flow locations
(Hartfield et al, 1994)
[7]
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13. Aerodynamicsramps:-
(Fuller et al, 1998)
• It consists of an array of wall jets with various injections angles in
both axial and lateral direction.
• Simulate the physical ramp vortex generationby no. of fuel sources.
• Mixing is enhancedby multiple vortex- injectant interactions.
• It eliminates the cooling requirements of physical ramps (especially
in localized hot spots such as recirculation regions).
• It is expected to reduce the drag while maintainingfar-fieldmixing
characteristics.
Aerodynamics ramps
[5]
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14. Upstream fuel injection:-
• It increases the fuel residence time, thus achieving a higher degree of mixing in
CC.
• It may be useful to inject part of the fuel upstream of the CC in the isolator or
in inlet or further upstream on the vehicle fore body.
• In case of pre-injection of liquid fuel in the inlet duct, several practical issues
arises. They are:-
1.balancing mixing efficiency
2. flow deceleration
3. inlet performance
4. ability to avoid flashback by eliminating the
residence of the fuel on the inlet-isolatorwalls
• This method induces additionalinteractions betweenthe fuel injection and the
hypersonic layer formed on the vehicle fore-body.
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15. Liquid injectionbehind a thin pylon
Cross-flow light scattering with pylons
shows the fuel concentrated in the
airflow core.
(Livingston et al., 2000)
Absence of the pylon, the jet
reaches the inlet duct walls.
• The pylon creates a low-pressure region that enables the jet to be lifted above
the wall and to penetrate the flow to the pylon height.
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16. Aerated Injectors:-
(Sabel’nikov and Prezin, 2000)
• It helps the liquidfuel to undergoes the physical processes before molecular-
level mixing.
• It accelerates the physical processes by injection of a gas concentric with the
liquid jet to generatean effervescent liquid at injection station.
• Gas can be either air or gaseous fuel. Ex, hydrogen(H2).
Aerated liquid-fuelinjector with a concentric gas .
[6]
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17. • It participates in heat generationin CC.
• At certain conditions air injection may prove beneficial
1. Reduce the local equivalenceratio.
2. Promoting combustion and flame holding.
• This method accelerates the jet breakupand along with it, turbulent
mixing, leading shorter combustion length.
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18. References:-
[1] Adela Ben-Yakar and Ronald K. Hanson. “Cavity Flame-Holders for
Ignition and Flame Stabilization in Scramjets,” Journal Of Propulsion And
Power Vol. 17, No. 4, July–August 2001.
[2]Northam, G. B., Greenberg, I., Byington, C. S., and Capriotti, D. P.
(1992). “Evaluation of parallel injector configurations for Mach 2
combustion,” J. Propul. Power 8, 491–499.
[3]Owens, M. G., Segal, C., and Auslander, A. H. (1997). “Effects of mixing
schemeson kerosene combustion in a supersonic airstream,” J. Propul.
Power 13, 525–531.
[4] Goldfeld, M. A., Mishunin, A. A., Starov, A. V., and Mathur, A. B. (2004).
“Investigationof hydrocarbon fuels combustion in supersonic combustor,”
AIAA Paper 2004–3487.
[5] Fuller, R. P., Wu, P.-K., Nejad, A. S., and Schetz, J. A. (1998).
“Comparison of physicaland aerodynamic ramps as fuel injectors in
supersonic flow,” J. Propul. Power 14,35–145.
[6] Sabel’nikov, V. A. and Prezin, V. I. (2000). “Scramjet research and
development in Russia,” in Scramjet Propulsion (E. T. Curran and S. N. B.
Murthy, eds.), Vol. 189 of Progress in Astronautics and Aeronautics, AIAA,
pp. 223–367.
[7] Corin Segal, The Scramjet Engine :Processes And Characteristics, book
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