Combustion Humming Instabilities Overview Tim Lieuwen Assistant Professor
Combustion Humming (Instabilities) Overview Tim Lieuwen Assistant Professor Georgia Institute of Technology tim. lieuwen@aerospace. gatech. edu , 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) , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
Basic Feedback Cycle Heat release Pressure Data showing growth in amplitude of pressure oscillations due to feedback loop • Oscillations due to resonant coupling between flames and acoustic waves , 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 , 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 , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
How Well Can We Predict Dynamic Characteristics of Combustor? Increasing difficulty • Three basic issues: – What is frequency of oscillations? – Under what conditions will oscillations occur? – What is the amplitude of oscillations? , 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 OEM’s have developed models of varying sophistication with good success , 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 , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
Predicting Dynamics Amplitude of Oscillations • Neither predictive nor “postdictive” capabilities exist • Don’t even know key parameters with which to correlate data • Subject of intensive investigation , 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 , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
Monitoring Dynamics Standoff Tubes • High temperature environments often necessitate physical separation between combustor and transducer Sound dissipation in 1/4” tube • Need to understand acoustics of coil arrangement – Bends in pipe, very slight area changes, valves can have MAJOR affects!!! , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
Historical Overview Humming is not unique to gas turbines! From Liquid Propellant Rocket Combustion Instability, Ed. Harrje and Reardon, NASA Publication SP-194 , 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 Purdue’s Thermoacoustic Refrigerator Los Alamos NL’s Thermoacoustic Engine , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
Industrial Systems (see Putnam’s 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 , 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 , 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 , 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 From Blomshield, AIAA Paper #2001 -3875 Adverse effects –thrust oscillations, mean pressure changes, changes in burning rates , 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: • – Minimal combustor cooling air (to minimize CO) as in aero combustors: • – acoustic damping substantially reduced High velocity premixer for flashback: • – system already right on stability line, small perturbations give very large effects 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 , Copyright T. Lieuwen, 2003, Unauthorized reproduction prohibited
- Slides: 18