Microwave Enhanced Combustion and New Methods for Combustion Diagnostics Richard Miles, Michael Shneider, Sohail Zaidi,Arthur D ogariu James Michael, Tat Loon Chng, Chris Limbach Mathew Edw ards 2011 Plasm a Enhanced Com bu stion MURI Review Ohio State University N ov 9-10, 2011
Highlights 1. Microw ave enhanced com bu stion (+ poster) 2. Filtered Rayleigh Scattering Measurement of Temperature in Flames 3. Femtosecond Laser Electronic Excitation Tagging for Measurement of Velocity, Temperature, Density and Species Profiles in Flam es 4. Rad ar REMPI Measu rem ent of Species in Flam es(poster) 5. Double pulsed laser designated and sustained ionization (follow on presentation by Mikhail Shneid er)
Microwave Flame coupling Laminar flame speed enhancement Stockm an, et al., Combustion and Flame, 156 (2009).
Microwave Coupling to Outwardly propagating flame kernels
Outwardly propagating flames 1 atm CH4/ air mixtures laminar flowtube Initiation by ns laser spark (532 nm; 20 mj; 15 ns) Pulsed laser shadowgraph for observation at t0+5 ms
Effective flame speed increase 1 khz pulse train; 25 mj per pulse MW power ~ 5% of combustion power Increase d eterm ined by increase of kernel size over tim e interval
Lean limit extension CH4/ air; 1 khz; 25-75 mj per pulse Lean flammability limit
Microwave Coupling to Stagnation Flames (1 atm, CH4/air, φ=0.3-1.0)
CH4/air stagnation flames Uexit ~ 60 cm/ s Dexit = 0.6 cm φ = 0.6-0.9 532 nm, injection seeded Nd:YAG for tu nable, narrow linew id th
MW-driven plasma luminosity φ = 0.77 Good localization near reaction zone Short MW pulse -> no drift in deposition location at low rep rate
Filtered Rayleigh scattering for instantaneous temperature measurement Eliminates background scattering from windows, walls and particles (soot) Assumes constant pressure (atmospheric for this work) Mod eled Rayleigh-Brillou in (Pan S7) Narrow-linewidth molecular iodine filter to block background laser light (p article/ su rface scattering not exhibiting therm al broad ening) Injection seed ed Spectra Physics GCR-170 N d:yag PI-MAX 512 Intensified CCD
FRS signal to temperature
FRS sensitivity
Single pulse temperature jump Deposition localized near flam e front/ reaction zone 25 mj, 1 us pulse gives ~200 K rise 50 mj, 2 us pulse gives ~350 K rise Low Tad results from drift in FRS laser frequency
Energy deposition 1 μs 2 μs ηabs u pper 0.57 0.53 ηabs low er 0.31 0.34 Etr/ EMW 15 mj (~60%) 25 mj (50%) Efficient absorption; especially after initial breakdown
Transition to High Power Test Cham ber constru ction com plete 12 feet long, 4feet by four feet Shield ed High extinction pyramid waffle structure at ends for reflection suppression Sim u lates propagation in free space High power (500 kw) KHz pulsed microwave installed.
FLEET Femtosecond Laser Electronic Excitation Tagging for air, nitrogen and for combusting environments
FLEET Features One laser no tuning required Time delayed camera Can follow the flow evolution with multiple images of the same tagged region Cross and grid patterns can be written easily Operational in humid air Works in combusting environments Strong signal even at low pressure Spectrum also indicates the temperature and species present Simultaneous Rayleigh scattering gives the density profile
HOW FLEET WORKS: Multi photon Dissociation of Nitrogen followed by Long Lived Recombination Fluorescence
Nitrogen Atom Recombination 800 nm = 1.55 ev
Fluorescence Lifetime Double exponential 1.1 μsec (second positive band) 8.3 μsec (first positive band)
Spectra Prompt 1.1 μsec lifetime Second positive band in air Delayed 8.3 μsec lifetime Pink afterglow First positive band in air
Persistent emission from first positive system of nitrogen
FLEET Experimental setup Top View Side View Fast-gated ICCD Cam era Princeton Instru m ents PI-MAX 512 Laser: ~150 fs, 800 nm, 1.2 mj D = 1mm U ~ 400 m/ s p 0 = 30 psig
Applications of emission: FLEET
Single shot and 10shot averaged FLEET images in a low speed methane air flame (~1900K) Single shot Hencken Burner 10 shot average
FLEET for Temperature Profiles
Prompt UV Emission Line shapes reflect the rotational temperature
Modeling of the Second Positive Emission
Fit with optimized slit function and frequency offset Minimum is Measured Instantaneous Temperature 485K higher than ambient due to laser heating
Research Challenges Microw ave enhanced com bu stion Operation in turbulent flames using high power source Reduction of NO emissions at lower equivalence ratios High Power for operation outside of microwave cavity FLEET Measurement of temperature and density profiles Tagging in high temperature and combusting environments Measurements of turbulence Measu rem ents of species Radar REMPI Quantitative measurement of species in flames
Transitions NAVAIR (STTR with Princeton Scientific Instru m ents) For F35 noise generation measurements in hot exhaust For model validation NASA Langley (planned) For SCRAM engine studies