Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion

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1 Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion Yiguang Ju AFOSR MURI Review Meeting Ohio State University Nov 9-1, 211 Princeton Team members: Wenting Sun, Joe Lefkowitz, Mruthunjaya Uddi, Sang Hee Won Collaborators AFRL: Campbell Carter, Timothy Ombrello International: Fei Qi, Huijun Guo (USTC) 1

2 Report Documentation Page Form Approved OMB No Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 124, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE NOV REPORT TYPE 3. DATES COVERED to TITLE AND SUBTITLE Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Princeton University,Princeton,NJ, PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 1. SPONSOR/MONITOR S ACRONYM(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES U.S. Government or Federal Rights License 14. ABSTRACT 11. SPONSOR/MONITOR S REPORT NUMBER(S) 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Same as Report (SAR) 18. NUMBER OF PAGES 44 19a. NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

3 Motivation Hypersonic propulsion Hypersonic system propulsion system F135 engine: (F35, 211) X-51A Mach 6-8 Ignition instability Ignition time (~1ms) Da= >>1 Flow residence time (~1ms) Challenges: Ignition time, Ignition energy Flame stabilization Combustion completion 2

4 Plasma assisted combustion Plasma Temperature increase Thermal enhancement Ions/electrons Excited species Radicals O, NO O 2 (a g ) Kinetic enhancement Fuel fragments H 2, CO CH 4 Transport enhancement Understanding: Good poor marginal 3

5 Temperature Change of ignition and extinction diagram: the S-curve transition Plasma generated species: O, H, O 2 (a g ) Scramjet Residence time 4

6 Research goals Understand the fundamental enhancement mechanism of plasma-flame chemistry Develop new experimental tools to validate plasma flame kinetic mechanism Develop numerical methods to achieve efficient modeling of detailed plasma flame chemistry 5

7 Outline 1. Background 2. Experimental investigations Effects of plasma assisted fuel oxidation on flame extinction Effects of in situ plasma discharge on ignition enhancement Molecular beam mass spectrometry study of low temperature chemistry 3. Conclusion and future work 6

8 Number Denisty of OH Strain Rate, 1/s Background and previous study: flame extinction N H 2 & N N 2 N 2 6 Fuel Fuel 1.8E E Watts, a=83.3 1/s 48 Watts, a=183 1/s 78 Watts, a= /s Computation Percent Methane Diluted in Nitrogen Bundy et al. Puri & Seshadri No Plasma 33 Watts 44 Watts 6 Watts 78 Watts Air 2 Air 6.E Silicon Controlled Rectifier, 2. Silicon carbide heater, 3. R-type thermocouple, 4. Fuel injection spacer 5. MGA plasma power supply, 5. MGA device, 6. MGA power supply, 7. Cathode, 8. Anode, 9. Magnets, 1. Gliding arc initiation wire, 11. MGA, 12. Insulator, 13. Nozzle with N 2 co-flow, 14. K-type thermocouple & FT-IR probe, 15. Diffusion flame, 16. Water-cooled nozzle with N 2 co-flow..e Distance Between Nozzles, cm Ombrello, et al, AIAA J, 26 Only thermal effect! 7

9 Previous work - Ignition study CH 4 /air counterflow diffusion flame H 2 /air counterflow diffusion flame CH CH 3O2 NO CH3O NO2 3 NO2 CH3O NO HO H NO OH 2 NO 2 NO2 OH NO NO x catalytic effect 1. non in situ discharge 2. Short life times of radicals and excites species Ombrello, et al, IEEE Plasma Sci, 28 8

10 S lifted [m/s] Enhancement [%] Previous researches O 3.5 ppm O3 592 ppm O3 111 ppm O ppm O ppm O ppm O ppm O Ombrello, et al, CNF, Mixture fraction gradient dy F /dr S L S lifted (~ 1/axial distance) b u Flame speed extraction 9

11 Concentration [ppm] Previous researches O 2 (a 1 g ) [O 2 (a 1 Δ g )], ppm ΔH L, mm O 2 (a 1 Δ g ) + H = OH+O fast O 2 + H = OH +O slow 5 ppm O 2 (a 1 Δ g ) 2-3 % Lifted Flame Speed Enhancement 6 5 SDO (w/ NO) SDO (w/o NO) O3 (w/o NO) 4 3 Energy Coupling Into Flow 1 ev to produce O 2 (a 1 Δ g ) 2 1 Nozzle Tip Change of Flame Liftoff Height, ΔH L [cm] Ombrello, et al, CNF, 21 1

12 Previous researches Atomic oxygen effect O 2 /Ar discharge O concentration (1 15 cm -3 ) ppm 12 ppm Pulse repetition frequency (KHz) CH 4 /Ar Crossover T: 9 K O quenched even at 6 Torr: How to utilize radicals efficiently? Sun, et al, PCI, 21 11

13 Research focus in the second year Thrust 1. Kinetic effects of non-equilibrium plasma-assisted fuel oxidation on diffusion flame extinction limits Thrust 2. Direct ignition and the S-curve transition by in situ nanosecond pulsed discharge Thrust 3. Plasma flame chemistry study in a flow reactor with Molecular Beam sampling Mass Spectrum (MBMS) Thrust 4. Development of a plasma assisted jet stirred reactor with molecular beam sampling and a high pressure ignition chamber 12

14 Thrust 1. Kinetic effects of non-equilibrium plasma-assisted fuel oxidation on diffusion flame extinction limits 13

15 Voltage (V) Experimental setup O 2 /Ar/He/CH 4 15 mm 22 mm 1 mm 1 mm away from exit FWHM= 12 ns f = ~5 khz Time (ns) FTIR/GC sampling (heated) E/N~1-15 Vcm 2 Power~1.3 mj/pulse P= 6 Torr 2 & 28 mm ID U 1 U The thermocouple was coated with MgO and covered with grounded Nickel-Chrome sheath to remove EMI a O 2U L O f O 14 f O

16 Laser diagnostics schematic Nd:Yag SHG Tunable Dye Laser BBO Doubling BBO Mixing Pulser 164nm PMT Flow direction UV Separator Boxcar Filters 84nm Collection lens 225.7nm UV focusing lens SRS272 Photodiode 225nm mirrors 225nm mirrors 15

17 Ar/He/O 2 /CH 4 (.32/.4/.26/.2) discharge Numerical model electrode 22 mm 1 mm Counterflow nozzle exit Species concentrations from simulation Kinetic model: OSU air plasma model [1,2] with USC mech II in addition of Ar/He/CH 4 related reactions. Physical model: quasi-one dimensional flow equation + steady two-term expansion Boltzmann equation [1] Reactions [1-8] Rate Const (cm 3 s -1 ) e+ O 2 e+2o f(e/n) e+ O 2 e + O + O(D) f(e/n) e + CH 4 CH 3 + H + e e + Ar Ar* + e e + Ar Ar(+) + 2e e + He He* +e e + He He(+) + 2e f(e/n) f(e/n) f(e/n) f(e/n) f(e/n) Ar* + CH 4 Ar +CH 2 +2H Ar* + CH 4 Ar +CH +H 2 + H Reactions Rate Const (cm 3 s -1 ) Ar(+) + CH 4 Ar +CH 3 (+) + H Ar(+) + CH 4 Ar +CH 2 (+) + H Ar* + CH 4 Ar +CH 3 + H Ar* + CH 4 Ar +CH 2 +H He(+) +O 2 O(+) + O + He T.5 Ar* + O 2 Ar+2O He(+) +O 2 (a) O(+) + O + He T.5 He+2O He* + O He* + CH 4 CH + H 2 + H+ He Reference: [1]. A. Bao, Ph.D thesis (28) OSU [2]. M. Uddi et al, PCI 32(29) 929 [3]. I.N. Kosarov et al, C&F 156(29) 221 [4]. A. Hicks et al, JPD, 38(25) 3812 [5]. D. 16S. Stafford et al, JAP, 96(24) 2451 [6]. M. Tsuji et al, JCP, 94(1991) 277 [7]. A.M. Starik et al, C&F, 157(21) 313 [8]. I.N. Kosarev et al, C&F 154(28) 569

18 f=3 khz Emissions: He*, OH*, HCO*, and CH* 17 Strongest emission: Ar*, O* ~ ~ < ~ -~ ~... = 9 =-= '-" w ~ U"l Intensity (a.u) ~ N w ~ U"l L- C H ( nm) and (431.2 nm) I?" H e (51.6 nm) and (52 nm) \ ';==-----He (587.5 nm) ~---.;...--~ H e (667.8 nm) \ -...) ~ Ar (696.5 nm) Ar (77 nm) and He (76.5 nm) Ar (727 nm) and He (728.1 om) QO L i~~i~~~~~~~~a~r~(7~3~8~.4~n~n~l):a:o:d::o (738.7 om) QO Ar (75 nm) Ar (772.4 nm) Ar (763.5 nm).r ( 7 ~ 5 ~ (777.4 nm) Ar (8 r.~ nm) and (81.7 nm) :.\r (811.4 nm) Ar (826 nm) (844.7 om) (853.4 nm) O2(.26)/Ar(.32)/He(.4)/CH 4 (.2) Experimental observations of discharges

19 Absorbance Discharge repetition effect on species concentrations FTIR spectrum with different pulse frequency.5 f=1 khz CH 4 CH 4 H 2 O f=4 khz.25 H 2 O CO 2 CO CH2 O..5 f=4 khz f=3 khz % CH4 no plasma f=2 khz Wavenumber (cm -1 ) Wavenumber (cm -1 ) 18

20 CH 4 concentration (ppm) CH 4 oxidization ratio (%) Concentration (ppm) Discharge repetition effect on species concentrations K 613 K Concentration Oxidization rate 743 K 933 K 843 K Pulse repetition frequency (khz) Under prediction: CO 2 Over prediction: CO, H 2, H 2 O CO (exp) CO 2 (exp) CH 2 O (exp) H 2 O (exp) H 2 (exp) CO (sim) CO 2 (sim) H 2 O (sim) H 2 (sim) CH 2 O (sim) Pulse repetition frequency (khz) Carbon deficiency: 5% Relative uncertainties: <1% for CH 4, CO, CO 2 5% for H 2 O and H 2 The uncertainty of CH 2 O measurement is 8 ppm 19

21 Reaction path analysis-ch 4 &H 2 f = 4 khz P = 6 Torr T = 3 to 933 K CH 3 O 5.3% OH, O, H, e, Ar(+), Ar* 66% 1% 1% CH 4 CH 3 CH 2 O HCO CO 98.5% 1.3% 27.3% 1.3% e, Ar* 23.4% 68.6%.2% CH 2 1.4% 1% CH 77.4% H 2 O 98.8% H + M H 2 M=CH 4, CH 2 O, HO 2, HCO, CH 2, CH 3 1.2% 21.6% OH + H Ar* + CH 4 CO 2 1% 5.3% 2

22 Reaction path analysis-h&o OH + H % CO + OH 4.1% CH 3 + O 51% H 5.6% 1.5% 11.7% CH 2 * + H 2 3.2% HCO + H 2 O/O CH 4 +Ar*/e/Ar(+) O + H 2 f = 4 khz P = 6 Torr T = 3 to 933 K H + O 2 Ar* + O 2 2.4% 33.6% 33.5% O 2 + e O 2 ( a1 Δ g )/O 2 ( b1 Σ) + H 9.7% O 2.8% 54.3% + CH 4, HO 2, 47.6% + CH.6% 3, H 2, CH 2 O, H 2, HCO, CH 2, HCO He(+) + O 2 OH H O 2 Mechanism was not validated below 7 K Large uncertainty at low temperature the reaction rate at 3 K for O( 1 D) + H 2 = H + OH ( /cm 3 s) is much larger than O + H 2 = H + OH ( /cm 3 s). 21

23 Extinction strain rate (1/s) Extinction strain rate (1/s) Extinction limit measurement & calculation Faster fuel oxidization, larger extinction extension no plasma with plasma (f=4 khz) with plasma (f=1 khz) simulation (To= 336 K) simulation (To= 423 K) simulation (To= 613 K) Fuel mole fraction Simulations were performed with experimentally measured boundary conditions. OH, H concentrations were estimated from simulation by matching O concentrations Reference (2% CH 4 ) Fuel oxidization Fuel reforming 4% CH 4 was oxidized to CO 2 and H 2 O 4% CH 4 was reformed to CO and H Oxidization or reforming ratio Case 1: fuel was oxidized to CO 2 & H 2 O Case 2: fuel was reformed to CO & H 2 Fuel reforming enhancement: fast H 2 chemistry Fuel oxidization enhancement: extracting chemical enthalpy rapidly 22

24 Extinction strain rate (1/s) Extinction limit measurement & calculation CH 4 oxidization ratio (or f) increased, extinction limits increased significantly 1 9 Experiments Simulation X f =.2 5.3% enhancement from H The dominant enhancement mechanism is plasma introduced rapid fuel oxidization Pulse repetition frequency (f) Deviation is due to additional reaction paths, but not significant (1%). Simulations were performed with experimentally measured boundary conditions. OH, H concentrations were estimated from simulation by matching O concentrations. 23

25 Thrust 2. Direct ignition and the S-curve transition by in situ nanosecond pulsed discharge 24

26 Experimental setup P = 72 Torr f = 24 khz Laser beam 25.4 mm Power ~ 17 W 25

27 ICCD images OH* emission ~31 nm 3 ms gate Single shot Single shot (a) ICCD image, He/O 2 (.6:.4) and He/CH 4 (.75:.25), 5 ns gate (b) ICCD image, He/O 2 (.6:.4) and He/CH 4 (.86:.14), 5 ns gate (c) direct photo of (a), 5 ms exposure time (d) direct photo of (b), 5 ms exposure time P = 72 Torr, f = 24 khz, a = 175 1/s 26

28 Classical S-curve hysteresis between ignition and extinction: S curve Rayleigh Scattering [1,2] method for T measurement at 532 nm from Nd:YAG laser Relationship between OH* emission intensity, local maximum temperature and fuel mole fraction, T o =65 K, T f =6 K He/O 2 =.66:.34, P = 72 Torr, f = 24 khz, a = 4 1/s [1] R.B. Miles, W.R. Lempert, J.N. Forkey, Meas. Sci. Technol. 21 [2]J.A. Sutton, J.F. Driscoll, Exp Fluids 26 27

29 S curve transition Relationship between OH* emission intensity, local maximum temperature and fuel mole fraction, P = 72 Torr, f = 24 khz, a = 4 1/s He/O 2 =.45:.55 He/O 2 =.38:.62 Can the hysteresis be removed? ignition and extinction points were pushed to lower fuel concentrations monotonic ignition and extinction curve (monotonics curve) 28

30 Numerical modeling OPPDIF + electron impact Kinetic mechanism: USC mech II + OSU air plasma model [1] e + O 2 reactions Rate (cm 3 s -1 ) He related reactions Rate (cm 3 s -1 ) e + O 2 2O + e e + O 2 O + O(D) + e e + O 2 O 2 (+) + 2e e + O 2 O 2 (a) + e f(e/n) f(e/n) f(e/n) f(e/n) He + e He* +e f(e/n) He + e He(+) + 2e f(e/n) He* + O 2 O 2 (+) + He + e T.5 He(+) +O 2 O(+) + O + He T.5 e + CH 4 reactions Rate (cm 3 s -1 ) e + CH 4 CH 3 + H + e f(e/n) e + CH 4 CH 2 + H 2 + e f(e/n) e + CH 4 CH 4 (+) + 2e f(e/n) He* + CH 4 CH + H 2 + H+ He Recombination reactions Rate (cm 3 s -1 ) e + O 2 (+) 2O T -.5 He(+) + e + M He + M e + O 2 + M O 2 (-) + M T -1 E: electric field, N: particle density e + CH 4 (+) CH 3 + H Rate constants: Boltzmann equation solver [1, 2] [1]. A. Bao, Ph.D thesis (28) OSU [2]. M. Uddi et al, PCI 32(29)

31 Simulation results X O2 =.34, X CH4 =.16, P = 72 Torr, f = 24 khz, a = 4 1/s fuel oxidizer e + CH 4 CH 3 + H + e e + O 2 O+O(D) + e In situ discharge, increased T, increased E/N, increased rate const no flame, but reaction zone was built up by radicals generated from plasma 3

32 Path flux analysis (a) OH: 39.9% e: 25.2% O: 12.7% H: 9.6% CH 3 O 6.3% 11.5% CH 2 * 65.4% 23.1% 7.3% 17.9% 82.1% CH 4 CH 3 CH 2 O HCO 11.5% 1% 14.8% 24.5% 1.1% 45.9% CH 4 (+) C 2 H 6 CH 3 OH (b) O 2 ( a1 Δ g )/O 2 ( b1 Σ) + He OH 27.5% H 59.4% 53.6% 37.9% 21.7% O 2 (+) + e 5.4% O O e He(+) + O % 47.7% O O 2 + e CO other paths 1.9% 43.7% 56.1%.2% CO 2 OH H O 2 31

33 Change of branching ratio Change of the branching ratio at the reaction zone! Reactions H + O 2 = O + OH 1 e + O 2 = O + O(D) + e.48 e + O 2 = O + O(+) + e.42 e + CH 4 = CH 3 + H + e.22 He(+) + O 2 = O + O(+) + He.52 e + O 2 = 2O + e.6 H + O 2 + M = HO 2 + M.2 Normalized branching ratio 1.7 S curve transition Increased productivities of radicals 76% of O production by e and ions from plasma Radical generation initiated the reaction zone and controlled the transition!! 32

34 Thrust 3. Plasma flame chemistry study in a flow reactor with Molecular Beam sampling Mass Spectrum (MBMS) 33

35 Temperature (K) Characteristic of low T chemistry Ignition delay, Low T ignition H 2 O 2 was stable Transition from low T to high T ignition H 2 O 2 2OH 15 K H 2 O 2 : low T chemistry indicator Difficulties: Absorption - overlap with H 2 O GC decomposition/low reactivity K Time (sec) ignition j=1, n-heptane/air, 1 atm 34

36 Molecular Beam Mass Spectrum Sampling system Time of fly pump S S D He D He He He S : signal intensity D : mass discrimination factor : cross sections : mole fractions 35

37 Reaction products Reactor exit Schematic of experiments with MBMS Laser beam High pressure, high temperature chamber 1 st Turbo pump 2 nd Turbo pump Preheated air Skimmer Mass analyzer Fuel Mixing DBD discharge Jet stirred reactor MBMS analysis Quartz nozzle Molecular beam Charged ion separation.1-5 atm 1-4 Torr 1-6 Torr Jacket heater oven MBMS 2 inch 14 inch 36

38 H 2 O 2 Concentration (ppm) Flow tube experiments DME: rich low temperature chemistry Pressure: 1 atm H 2 O 2 measurement experiments simulation DME: 1% O 2 : 5% He: 94% residence time:.2 S Temperature (K) DME model: Zhao et al., Int. J. Chem. Kinet., (4) 28 37

39 x2 Relative Signal Flow tube experiments (HCHO) 32(O 2 ) DME: rich low temperature chemistry Pressure: 1 atm (CH 3 OCH 2 ) 46(DME) (H 2 O 2, 34 O 2 ) 6 (CH 3 OCHO) (CO 2 ) m/z 38

40 Conclusions 1. Plasma can significantly accelerate the fuel oxidization at low temperature to extend the extinction limit dramatically. 2. Major kinetic pathways in plasma assisted combustion were identified. 3. A new counterflow burner with in situ discharge was developed. This burner provides a new platform to study kinetic effect of plasma assisted combustion. 4. The In situ discharge can maximize E/N at high T flame region, therefore, maximize the electron energy and effect on reaction zone, and enhance ignition and extinction. 5. The In situ discharge can dramatically enhance the ignition and modify the classical S-curve to be a monotonic curve. 6. MBMS was developed and H 2 O 2 was successfully measured directly for the first time in reacting system, enabling diagnostics of intermediate species in plasma assisted combustion at low T. 39

41 Future work Plasma part: 1. OH PLIF for counter flow diffusion flame with in situ discharge and compare with simulations 2. Low temperature plasma assisted combustion for large alkanes 3. Flow reactor experiments on liquid fuel with QCL diagnostics on H 2 O, H 2 O 2 and HO 2 4. Develop validated plasma flame models MBMS part: 1. Develop a JSR to study the low temperature and high pressure chemistry 2. Integrate JSR with plasma discharge to investigate plasma chemistry 3. Develop advanced light source to ionize the molecular beam 4

42 Thanks the support from AFOSR! Questions? 41

43 T/K Flow tube experiments Jacket heater oven MBMS inch 14 inch upstream downstream Distance/inch 42

44 H 2 O 2 calibration Dissociation: do it quickly changing H 2 O 2 concentrations monitor O 2 peak 45 K H2O2 solution Syringe pump Vaporizer MBMS Dilution gas 43

45 Temperature (K) w. discharge w.o discharge w. discharge w.o discharge Position (mm) O2 = 53.5%, CH4 = 2%, a = 4 1/s 44