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Experiments on Low-Temperature Combustion Combustion Development of a Stabilized Cool Flame Platform & Faraday Rotation Spectroscopy Diagnostic for In-Situ Measurement of HOx Radicals 2nd Flame Chemistry Workshop San Francisco San

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Experiments on Low-Temperature Combustion Combustion

Development of a Stabilized Cool Flame Platform & Faraday Rotation Spectroscopy Diagnostic for In-Situ Measurement of HOx Radicals

2nd Flame Chemistry Workshop San Francisco San Francisco 2 ‐ 3 August 2014

Sang Hee Won and Brian Brumfield (Joseph Lefkowitz)

Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA

PRINCETON

Mechanical and Aerospace Engineering

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Introduction

  • Take‐home messages from the 1st Flame Chemistry Workshop

– What is the definition of flame chemistry?

  • Chemical kinetics constrained by transport
  • Chemical kinetics constrained by transport

– Development of well‐defined experimental platforms

  • Extend ability to access low temperature chemistry (LTC)
  • Advanced laser diagnostic technique

R t d d i

  • Recent advanced engines

– Operate at low to intermediate temperature at higher pressure conditions – Near‐limit combustion behaviors tend to be correlated with LTC

50000 1300 1200 1100 1000 900 800 700

Temperature / K

LBO test by Med Colket (UTRC)3

10000 50000

Detailed Model + Surrogate Fuels Jet-A, POSF 4658 IPK, Iso Paraffinic Kerosene S-8, Coal-to-Liquid SPK, Gas-to-Liquid e, τ / μs

Temperature window for DCN (CN) measurements

1000

Ignition delay time

2

1)

  • H. Wang, M. A. Oehlschlaeger, Fuel 98 (2012) 249-258.

2)

  • S. H. Won, et al., “Comparative Evaluation of Global Combustion Properties of Alternative Jet Fuels,” 51th AIAA Aerospace Sciences Meeting, Grapevine, Texas (2013).

3) Med Colket, 2013 MACCCR meeting

(CN) measurements

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 50 100

1000K / T 20 atm, stoichiometric fuel in air

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Motivations

1. Experimental platform for cool flame

–To stabilize LTC‐driven flame

2. Development of FRS technique

–Quantifying the LTC related species

3

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Development of a Stabilized Cool Flame Development of a Stabilized Cool Flame Platform

2nd Flame Chemistry Workshop San Francisco San Francisco 2 ‐ 3 August 2014

Sang Hee Won1, Bo Jiang1, Pascal Diévart1, Chae Hoon Sohn2, Yiguang Ju1

1Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA 2Department of Mechanical Engineering, Sejong University, Seoul 143‐747, Republic of Korea

PRINCETON

Mechanical and Aerospace Engineering

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Challenges to Stabilize LTC‐Driven Flames

  • Induction chemistry at low temperature is very slow

– Inability to initiate the radical pool (RH + X = R + HX) – Very sensitive to molecular structure

  • Then, how to shorten the induction chemistry?

l fl l b f

  • Cool flames; mostly observed in premixed configuration

– Flow reactor, jet‐stirred reactor, etc..

  • Is it possible to observe cool flames in diffusive configuration ?

10000 100 1000 10000

imes [ms]

experiment, 13.5 atm, 2nd ig. model, 13.5 atm, 2nd ig. model, 13.5 atm, 1st ig. model, 1.0 atm, 2nd ig. model, 1.0 atm, 1st ig. 3 τ @ 2nd stage ignition at 700 K

Adiabatic Constant Volume Ignition

0 1 1 10

nition delay t

1 2 20 40 60 80 100 120

time [ms]

pressure τ @ 1st stage ignition

1 atm 13 5 5

0.01 0.1 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Ign 1000/T [1/K]

time [ms] 13.5 atm

770 K 850 K

1) H. J. Curran, P. Gaffuri, W. J. Pitz, C. K. Westbrook, Combust. Flame 114 (1998) 149-177.

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Hints from Recent Studies

Zero‐Gravity Experiment1,2

  • Observed cool diffusion flame
  • Observed cool diffusion flame

in a droplet combustion

  • Cool flame exists in diffusive

configuration!

6 1) V. Nayagam et al., Combust. Flame 159 (2012) 2) T. I. Farouk, F. L. Dryer, Combust. Flame 161 (2014) 3) W. Sun, S. H. Won, et al, Proc. Combust. Inst. 34 (2013) 4) T. Ombrello, S. H. Won, et al., Combust. Flame 157 (2010) 5) T. M. Vu, S. H. Won, et al., Combust. Flame 161 (2014)

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PRINCETON

Mechanical and Aerospace Engineering

Hints from Recent Studies

Zero‐Gravity Experiment1,2

  • Observed cool diffusion flame

Plasma‐Assisted Combustion3‐5

  • Initiation of radical pool can be
  • Observed cool diffusion flame

in a droplet combustion

  • Cool flame exists in diffusive

Initiation of radical pool can be accelerated by Plasma

  • Enhancing flame ignition,

propagation speed, and stabilization

CH

configuration!

  • Electronically excited species and
  • zone, etc.

Increasing fuel loading

4x10

15

5x10

15

6x10

15

7x10

15

Smooth Transition Extinction

χO2=34% χO2=62%

r density (cm

  • 3)

CH4

perature Plasma generated species: O, H, O2(a∆g) …

Extinction

flame initiation flame stabilization

Increasing fuel loading

0.05 0.10 0.15 0.20 0.25 0.30 0.35 1x10

15

2x10

15

3x10

15

Extinction Ignition F l l f ti OH number

Residence time Temp O, H, O2(a∆g) … the classical S‐curve

Ignition

Low pressure counterflow diffusive configuration with nano-second pulsed discharge3

Fuel mole fraction

7

New combustion regime

1) V. Nayagam et al., Combust. Flame 159 (2012) 2) T. I. Farouk, F. L. Dryer, Combust. Flame 161 (2014) 3) W. Sun, S. H. Won, et al, Proc. Combust. Inst. 34 (2013) 4) T. Ombrello, S. H. Won, et al., Combust. Flame 157 (2010) 5) T. M. Vu, S. H. Won, et al., Combust. Flame 161 (2014)

discharge

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Mechanical and Aerospace Engineering

Experiments

  • A heated counterflow burner integrated with vaporization system1

– n‐heptane/nitrogen vs. oxygen/ozone

  • Ozone generator (micro‐DBD) produces 2‐ 5 % of ozone in oxygen

stream, depending on oxygen flow rate

  • Speciation profiles by using a micro‐probe sampling with a micro‐

GC 2 GC.2

Heated N2 @ 550 K Fuel/N2 @ 550 K Positioning stage N2 @ 300 K Stagnation plane Pressure chamber Micro-GC O2 + O3 @ 300 K Ozone generator O2 @ 300 K Thermal gradient in mixing layer initiates reaction of O3 + (M) = O + O2 + (M)

8 1) S. H. Won, et al., Combust. Flame 157 (2010) 2) J. K. Lefkowitz, S. H. Won, et al., Proc. Combust. Inst. 34 (2013)

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PRINCETON

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Initiation of Cool Diffusion Flames

  • Procedure to initiate a cool diffusion flame

1) Setting nitrogen (fuel side) and oxygen (oxidizer side) 1) Setting nitrogen (fuel side) and oxygen (oxidizer side) flow rates 2) Turning on the ozone generator 3) Flowing fuel (n‐heptane) to fuel side 3) Flowing fuel (n heptane) to fuel side

Lower fuel mole fraction: Cool diffusion flame Higher fuel mole fraction: Hot diffusion flame

9

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Initiation of Cool Diffusion Flames

  • Existence of cool diffusion flames in counterflow

configuration with n‐heptane

2400 ]

– cool flame regime exists regardless of addition of ozone – .

2000 e Tmax [K]

nC7H16/N2 vs O2 or O2/O3 in counterflow burner Xf = 0.05,Tf = 550 K, and To = 300 K Extinction limit of conventional hot diffusion flame HF branch

1200 1600 emperature

conventional hot diffusion flame (HFE) Extinction limit of cool diffusion flame without O3

(a) Cool diffusion flame 800 Maximum te

cool diffusion flame (CFE) CF branch HTI LTI

(b) Hot diffusion flame 400 0.1 1 10 100 1000 10000 M Strain rate a [1/s]

LTI 10

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PRINCETON

Mechanical and Aerospace Engineering

Initiation of Cool Diffusion Flames

  • Existence of cool diffusion flames in counterflow

configuration with n‐heptane

2400 ]

– cool flame regime exists regardless of addition of ozone – Addition of ozone extends cool flame regime.

2000 e Tmax [K]

nC7H16/N2 vs O2 or O2/O3 in counterflow burner Xf = 0.05,Tf = 550 K, and To = 300 K Extinction limit of conventional hot diffusion flame HF branch

1200 1600 emperature

conventional hot diffusion flame (HFE) Extinction limit of cool diffusion flame without O3 ith O

(a) Cool diffusion flame 800 Maximum te

cool diffusion flame (CFE) with O3 CF branch HTI LTI

(b) Hot diffusion flame 400 0.1 1 10 100 1000 10000 M Strain rate a [1/s]

LTI 11

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Mechanical and Aerospace Engineering

Speciation Profiles

  • Temperature measurements

700 900

e [K]

T [K] exp

Temperature measurements

– Over‐estimation of heat release in model prediction

300 500 700 4 8 12 16 20 24

Temperature

T [K], exp. T [K], model

(a)

  • Failure to predict the flame

position

Distance from fuel side nozzle [mm]

40000 60000 80000 100000 120000

ecies mole ction [ppm]

nc7h16, exp. nc7h16, model

  • 2/10, exp

position.

– Boundary conditions were tested previously.1

20000 4 8 12 16 20 24

Spe frac Distance from fuel side nozzle [mm]

  • 2/10, model

30000 40000

  • le

pm]

h2o, exp. h2o, model co exp

(b)

– Consistent even without putting sampling probe or thermocouple.

10000 20000

Species mo fraction [pp

co, exp. co, model co2, exp. co2, model

(c)

12

6 10 14 18

Distance from fuel side nozzle [mm]

1) J. K. Lefkowitz, S. H. Won, et al., Proc. Combust. Inst. 34 (2013)

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Mechanical and Aerospace Engineering

Speciation Profiles

  • Reasonable prediction of acetaldehyde and CH2O
  • Significant over estimation of C H and CH formation
  • Significant over‐estimation of C2H4 and CH4 formation

– Factor of 10.

4000 6000 8000

cies mole ion [ppm]

acetaldehyde, exp acetaldehyde, model ch2o, exp ch2o, model

R + O2 RO2 Olefin + HO2

Propagation 2000 6 10 14 18

Spec fracti Distance from fuel side nozzle [mm]

1000

]

(a)

QOOH Olefin + Carbonyl Olefin + HO2 QO + OH + O2

  • O2

Propagation

+ HO2

400 600 800

pecies mole action [ppm]

c2h4, exp. c2h4/10, model ch4, exp ch4/10, model

O2QOOH Ketohydroperoxide + OH + HO2

13

200 6 10 14 18

Sp fra Distance from fuel side nozzle [mm]

(b)

CH2O + R + CO + OH

Branching

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PRINCETON

Mechanical and Aerospace Engineering

Quick Summary

  • Well‐defined experimental platform of cool flames for LTC study
  • Speciation profiles revealed deficiency of kinetic model at cool

fl flame regime

– Over‐prediction of small hydrocarbon species (CH4, C2H4, etc.)

  • Sophisticated diagnostic techniques might be able to point out

O i i f d l di i l h i b hi – Origin of model over‐prediction: low temperature chain branching vs. propagation reaction pathways

R + O2

P i

600 5

RO2 QOOH Olefin + HO2

Propagation

Olefin + Carbonyl Olefin + HO2 QO + OH

Propagation

400 500 3 4

HO2 mole fr ction [ppm]

Olefin + Carbonyl O2QOOH K t h d id OH + O2

  • O2

+ HO2

100 200 300 1 2

raction [ppm H mole frac

14

Ketohydroperoxide + OH CH2O + R + CO + OH

Branching

100 9 10 11 12 13 14 15

m] OH Distance from fuel side nozzle [mm]

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Faraday Rotation Spectroscopy Di ti f I Sit M t f Diagnostic for In-Situ Measurement of HOx Radicals

Brian Brumfield1 Brian Brumfield1

Joseph Lefkowitz2

, Xueliang Yang2, Yiguang Ju2,

Gerard Wysocki1

1Department of Electrical Engineering, Princeton University, Princeton, NJ, USA 2 Mechanical and Aerospace Engineering Department, Princeton University, Princeton NJ

PRINCETON

Mechanical and Aerospace Engineering

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Mechanical and Aerospace Engineering

Challenges w/ LTC HOx Measurements

  • General challenges with radical quantification

– Wall quenching q g – Spectral Interference

  • Species specific complications
  • Species specific complications

– OH

  • Present at low concentrations (<1 ppmv)
  • Difficult to quantify via LIF in situ
  • Difficult to quantify via LIF in situ

– HO2 N t d t t bl i LIF ( h t f t ti LIF* i ibl )

  • Not detectable via LIF (photo-fragmentation LIF* is possible)
  • Fluorescence Assay by Gas Expansion (FAGE) †

16 *Johansson, O.; Bood, J.; Li, B.; Ehn, A.; Li, Z. S.; Sun, Z. W.; Jonsson, M.; Konnov, A. A.; Aldén, M.:

  • Combust. Flame 2011, 158, 1908-1919

† Blocquet, M.; Schoemaecker, C.; Amedro, D.; Herbinet, O.; Battin-Leclerc, F.; Fittschen, C.:

  • Proc. Natl. Acad. Sci. U.S.A 2013, 110, 20014-20017
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Faraday Rotation Spectroscopy (FRS)

  • Apply Magnetic Field → Zeeman Splitting → Faraday Effect
  • Polarization rotation → Linear Polarizer → Intensity Variation

Polarization rotation Linear Polarizer Intensity Variation

Radical transition Radical transition

  • Sample modulation by varying magnetic field (AC-FRS)*
  • Strong suppression of absorption signals from non-radicals

17

g pp p g

  • Zero background technique

* Litfin, G.; Pollock, C. R.; Curl, J. R. F.; Tittel, F. K.: J. Chem. Phys. 1980, 72, 6602-6605. Brumfield, B.; Sun, W.; Ju, Y.; Wysocki, G.: J. Phys. Chem. Lett. 2013, 4, 872-876

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Faraday Rotation Spectroscopy (FRS)

  • Apply Magnetic Field → Zeeman Splitting → Faraday Effect
  • Polarization rotation → Linear Polarizer → Intensity Variation

Polarization rotation Linear Polarizer Intensity Variation

Radical transition Radical transition

  • Marginal increase in experimental complexity from TDLAS

18

(polarizers, 1‐2 lock‐in amplifiers, magnetic coil)

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Experimental Demonstration of FRS

Laser er Fl

  • Target OH (2.8 µm) and HO2 (7.1 µm)
  • 1.7 cm optical path from reactor opening

Main Heate

  • w Reacto
  • Measure 2 mm from exit
  • Laser wavelength + magnetic field modulation→ DM-FRS*

M r

  • Laser wavelength + magnetic field modulation→ DM-FRS

– Detect HO2 at 1fL±fM (1f DM-FRS) – Detect OH at 2fL±fM (2f DM-FRS)

* Brumfield, B.; Sun, W.; Wang, Y.; Ju, Y.; Wysocki, G.: Opt. Lett. 2014, 39, 1783-1786

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Example DM‐FRS Spectra

OH HO

20

HO2

* Brumfield, B.; Sun, W.; Wang, Y.; Ju, Y.; Wysocki, G.: Opt. Lett. 2014, 39, 1783-1786

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PRINCETON

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Observed Species Profiles

OH

  • Conditions:

– Composition: 0.96/0.0375/0.00225 He/O2/CH3OCH3 He/O2/CH3OCH3 – Plug-flow residence time: 0.45 to 0.2 seconds

  • DME,CH2O, and CO measured with gas

chromatography

  • OH/HO2 concentrations consistent with

model †

  • Observed low‐reactivity ~600 K similar to

i t * prior measurements*

21

† Zhao, Z.; Chaos, M.; Kazakov, A.; Dryer, F. L.: Int. J. Chem. Kinet. 2008, 40, 1-18

* Brumfield, B.; Sun, W.; Ju, Y.; Wysocki, G.: J. Phys. Chem. Lett. 2013, 4, 872-876 Kurimoto, N.; Brumfield, B.; Yang, X.; Wada, T.; Diévart, P.; Wysocki, G.; Ju, Y.: Proc. Combust. Inst., in Press DOI: 10.1016/j.proci.2014.05.120

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Proposed Future Work

Fuel/N2 @ 550 K CH2O laser

Electromagnetic coils

OH/HO2 laser O2 + O3 @ 300 K

  • Merge FRS diagnostic with cool flame platform

Ozone generator O2 @ 300 K

  • Employ mid‐IR absorption diagnostic for CH2O quantification
  • Potential to spatially profile cool flame
  • Use LIF imaging to extract absolute concentration profile

22

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Extension of FRS technique

  • Applicable to many other small radical species
  • Relevant to combustion and atmospheric

p chemistry studies

  • Many potential targets;

CH CH CH NO* NO † HCO HCN t – CH, CH2, CH3, NO*, NO2

†, HCO, HCN etc…

23 *Wang, Y.; Nikodem, M.; Wysocki, G.: Opt. Express 2013, 21, 740-755

† Zaugg, C. A.; Lewicki, R.; Day, T.; Curl, R. F.; Tittel, F. K.: 2011, 79450O-79450O-7

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Mechanical and Aerospace Engineering

Conclusion

  • Develop

a experimental platform to study cool flame chemistry

  • Significant

disagreement from

  • bserved

vs. predicted speciation profiles using existing n-heptane mechanism

  • Quantification of HOx would aid in constraining kinetic model

FRS h b d t t d t id iti d

  • FRS

has been demonstrated to provide sensitive and selective measurements of HOx Combination of platform with diagnostic will provide insight

  • Combination of platform with diagnostic will provide insight

into LTC chemistry

24

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Acknowledgements

Funding

Princeton Environmental Institute Andlinger Center for Energy and the Environment Air Force Office of Scientific Research Air Force Office of Scientific Research

MURI research grant grant # FA9550‐07‐1‐0136 grant # FA9550‐13‐1‐0119 grant # FA9550 13 1 0119.

US Department of Energy, Office of Basic Energy Sciences

Energy Frontier Research Center on Combustion Grant # DE

25

Energy Frontier Research Center on Combustion, Grant # DE‐ SC0001198