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Microwave Enhanced Combustionand New Methods for Combustion
Diagnostics
Richard Miles, Michael Shneider, Sohail Zaidi ,Arthur Dogariu
James Michael, Tat Loon Chng, Chris LimbachMathew Edwards
2011 Plasma Enhanced Combustion MURI Review
Ohio State University
Nov 9-10, 2011
Highlights
1. Microwave enhanced combustion (+ 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 Flames
4. Radar REMPI Measurement of Species in Flames(poster)
5. Double pulsed laser designated and sustained ionization
(follow on presentation by Mikhail Shneider)
Microwave Flame coupling
Laminar flame speed enhancement
Stockman, et al., Combustion and Flame, 156 (2009).
Microwave Coupling to Outwardly propagating flame
kernels
1 atm
CH 4/ air mixtures
laminar flowtube
Initiation by ns laser spark (532 nm; 20 mJ; 15 ns)
Pulsed laser shadowgraph for observation at t0+5 ms
Outwardly propagating flames
Effective flame speed increase
1 kHz pulse train; 25 mJ per pulse
MW power ~ 5% of combustion power
Increase determined by increase of kernel size over time 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 tunable, narrow linewidth
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 forinstantaneous temperature measurement
Eliminates background scattering from windows, walls and particles (soot)
Assumes constant pressure (atmospheric for this work)
Modeled Rayleigh-Brillouin (Pan S7)
Narrow-linewidth molecular iod ine filter to block background laser light
(particle/ surface scattering not exhibiting thermal broadening)
Injection seeded Spectra Physics GCR-170 Nd:YAG
PI-MAX 512 Intensified CCD
FRS signal to temperature
FRS sensitivity
Single pulse temperature jump
Deposition localized near
flame 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
Efficient absorption; especially after initial breakdown
1 μs 2 μs
ηabs upper 0.57 0.53
ηabs lower 0.31 0.34
Etr/ EMW 15 mJ (~60%) 25 mJ (50%)
Transition to High Power
Test Chamber construction complete
12 feet long , 4feet by four feet
Shielded
High extinction pyramid waffle structure at ends for reflection suppression
Simulates 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
FLEETFeatures
• 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
Delayed 8.3 μsec lifetime
“Pink afterglow”
First positive band in air
Prompt – 1.1 μsec lifetime
Second positive band in air
Persistent emission from first positive system of nitrogen
FLEET Experimental setup
D = 1mm
Top View Side View
Laser: ~150 fs, 800 nm, 1.2 mJ
Fast-gated ICCD Camera
Princeton Instruments PI-MAX 512
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
10 shot
average
Hencken Burner
FLEETfor 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 Temperature485K – higher than ambient due to laser heating
Research Challenges
Microwave enhanced combustion
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
Measurements of species
Radar REMPI
Quantitative measurement of species in flames
Transitions
• NAVAIR (STTR with Princeton Scientific
Instruments)
• For F35 noise generation measurements in hot exhaust
• For model validation
• NASA Langley (planned)
• For SCRAM engine stud ies
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