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, Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Combustion Humming (Instabilities) Overview Tim Lieuwen Assistant Professor Georgia Institute.

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Presentation on theme: ", Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Combustion Humming (Instabilities) Overview Tim Lieuwen Assistant Professor Georgia Institute."— Presentation transcript:

1 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Combustion Humming (Instabilities) Overview Tim Lieuwen Assistant Professor Georgia Institute of Technology tim.lieuwen@aerospace.gatech.edu

2 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited What is Humming? Combustion humming referred to by a variety of terms: –Combustion instabilities –Combustion dynamics –Rumble, screech, growl, buzz, howl, … All of them refer to essentially the same phenomenon: –Large amplitude pressure oscillations in combustion chamber, driven by heat release oscillations –Oscillations are destructive to engine hardware (damage is measured in billions of dollars)

3 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Basic Feedback Cycle Heat release Pressure Oscillations due to resonant coupling between flames and acoustic waves Data showing growth in amplitude of pressure oscillations due to feedback loop

4 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Fourier Transform of Combustor Pressure During an instability, combustion process generally excites one or more of the natural acoustic modes of the combustor

5 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Key Problem: Flame is sensitive to acoustic perturbations From Ducruix et al., Proc. Comb. Inst., Vol. 28, 2000, pp.765-773, used with permission of S. Ducruix

6 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited How Well Can We Predict Dynamic Characteristics of Combustor? Three basic issues: –What is frequency of oscillations? –Under what conditions will oscillations occur? –What is the amplitude of oscillations? Increasing difficulty

7 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Predicting Dynamics Frequency Predictions Reasonable predictive capabilities occur Typical frequency predictions accurate to within 5-20% with no calibration Most OEMs have developed models of varying sophistication with good success

8 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Predicting Dynamics Conditions of Occurrence Mechanisms reasonably well understood Complexity of flame region renders predictive capabilities difficult –existing codes have difficulty with steady flame characteristics –Can post-dict characteristics –We know the key parameters, how to correlate the data

9 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Predicting Dynamics Amplitude of Oscillations Neither predictive nor post- dictive capabilities exist Dont even know key parameters with which to correlate data Subject of intensive investigation

10 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited How Well can We Monitor these Oscillations? Availability of high temp pressure instrumentation has increased dramatically in last 5 years Most are piezo-electric based –Be careful about depolarization –Be careful about claims about high temperature capabilities, they may degrade substantially with time –If your dynamics amplitude is gradually decreasing with time, you should check your transducer! From Kistler product literature

11 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Monitoring Dynamics Standoff Tubes High temperature environments often necessitate physical separation between combustor and transducer Need to understand acoustics of coil arrangement –Bends in pipe, very slight area changes, valves can have MAJOR affects!!! Sound dissipation in 1/4 tube

12 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Historical Overview From Liquid Propellant Rocket Combustion Instability, Ed. Harrje and Reardon, NASA Publication SP-194 Humming is not unique to gas turbines!

13 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Thermo-acoustics Related phenomenon see in non-combusting systems with temperature gradients: –Rijke Tube (heated gauze in tube) –Self-excited oscillations in cryogenic tubes –Thermo-acoustic refrigerators/heat pumps Purdues Thermoacoustic Refrigerator Los Alamos NLs Thermoacoustic Engine

14 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Industrial Systems (see Putnams book) Oil fired heating units Scrap melting burners Boilers Pulse combustion From Thring et al., ed., Pulsating Combustion: The Collected Works of F.H. Reynst, Pergamon Press, 1961

15 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Liquid Rockets BIG OSCILLATIONS (>1000 psi)!!! e.g., F-1 Engine –used on Saturn V – largest thrust engine developed by U.S –Problem overcome with over 2000 (out of 3200) full scale tests From Liquid Propellant Rocket Combustion Instability, Ed. Harrje and Reardon, NASA Publication SP-194

16 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Ramjets and Afterburners Vortex-flame interactions generated large oscillations Ramjets: Caused un-starting of inlet shock Afterburners: Lightweight construction causes damage, loss of flameholders From D. Smith, Ph.D. thesis

17 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Solid Rockets Examples: –SERGEANT Theater ballistic missile – tangential instabilities generated roll torques so strong that outside of motor case was scored due to rotation in restraints –Minuteman missile –USAF experienced 5 flight failures in 1968 during test due to loss of flight control because of severe vibrations –Sidewinder missile –Space shuttle booster- 1-3 psi oscillations (1 psi = 33,000 pounds of thrust) –Mars pathfinder descent motor Adverse effects –thrust oscillations, mean pressure changes, changes in burning rates From Blomshield, AIAA Paper #2001-3875

18 , Copyright T.Lieuwen, 2003, Unauthorized reproduction prohibited Gas Turbines Dry low NOx systems have huge dynamics problems! –Introduced by low emissions designs Some reasons: –Operate near lean blowout: system already right on stability line, small perturbations give very large effects – Minimal combustor cooling air (to minimize CO) as in aero combustors: acoustic damping substantially reduced –High velocity premixer for flashback: Pressure maximum at flame –Compact reaction zone for CO Heat release concentrated at pressure maximum From Flamebeat: Predicting Combustion Problems from Pressure Signals, by Adriaan Verhage, in Turbomachinery, Vol. 43(2), 2002


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