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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