Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion Walter R. Lempert, Igor V. Adamovich, J. William Rich, Jeffrey A. Sutton Department of Mechanical and Aerospace Engineering Ohio State University MURI Annual Review Meeting November 9-1, 211
Research Focus Research Thrust 1: Experimental studies of non-equilibrium air-fuel plasma kinetics using advanced non-intrusive diagnostics Task 1: Low-to-Moderate (T=3-8 K) temperature, spatial and time-dependent radical species concentration and temperature measurements in nanosecond pulse plasmas in a variety of fuel-air mixtures, pressures, and equivalence ratios. Task 2: Laminar Flow Reactor and Nanoparticle Studies at Low to Intermediate Temperatures Task 3: Additional Species Measurements at Low-to-Moderate (3-8 K) Temperatures Using a Plasma Assisted Jet Stirred Reactor with Molecular Beam Sampling. Task 4: Moderate-to-high (T=8 18 K) temperature PAC oxidation kinetics in Discharge Shock Tube Facility at pressures up to 1 bar. Tasks 1-4 will result in generating extensive experimental New Task: Temperature and Radical Species Concentration data sets for PAC oxidation kinetics and ignition over a wide Measurements in plasma-enhanced flame system: Exploring the range of temperatures at low to moderate pressures. effects of non-equilibrium plasmas on combustion chemistry with an emphasis on moderate-to high temperature reaction chemistry.
Research Task Examining the Effects Non-Equilibrium Plasma Discharges on Combustion Chemistry Using Advanced Optical Diagnostics Ting Li, Igor V. Adamovich, Jeffrey A. Sutton
Experimental Facility Goal: Examine the effects of plasma discharges on combustion kinetics in a 1D low-pressure flame/plasma chamber FACILITY BURNER CONFIGURATIONS CONCEPT HVE Flame Burner (Ground) Flame Burner (Ground) HVE McKenna flat flame burner HVE HVE
McKenna Flat Flame Burner Has been used as a standard calibration source and experimental platform for combustion research for more than 25 years Commonly applied calibration burner for laser diagnostic applications It produces a quasi-1d flat flame, where temperature and species concentrations vary only with height-above-the-burner (chemical residence time); straightforward to model and is a valuable testbed to assess chemical kinetic mechanisms. HVE
Voltage (kv) Plasma Discharge FID DISCHARGE CCD 4 2-2 -4-6 5 ns N 2-8 -1 1 2 3 4 5 Time (ns) ICCD Images (2 ms gate) 2 Torr, 3 K; 1 pulses at 1 khz 1 st pulse 2 nd pulse 3 rd pulse 4 th pulse 1 th pulse HVE
Experimental Facility Goal: Examine the effects of plasma discharges on combustion kinetics in a 1D low-pressure flame/plasma chamber Upstream Plasma Generation 2 Torr, C 2 H 4 /O 2 /N 2 (f = 1. ) Plasma off Plasma ON Plasma Directly Coupled to Flame 2 Torr, HVE C 2 H 4 /O 2 /N 2 (f = 1. ) Plasma off HVE Plasma ON
Intensity Intensity Plasma Temperature Electrode Temperature = 75 8K Burner Temperature = 38-42 K 12 9 Plasma ON Using N 2 2nd Positive emission 1 st pulse 2 nd pulse 4 th pulse 6 Fit at T=52K Experimental Data T = 52 K n = 1 Hz f = 1 25 2 15 1 Fit at T=56K Experimental Data T = 56 K n = 1 khz Small DT due to Joule Heating 3 HVE 5 333 335 337 339 Wavelength (nm) 333 335 337 339 Wavelength (nm) Similar for plasma only: 3K/35 K (.1/1 khz)
Intensity (arb. units) Intensity (arb. units) Intensity Intensity (arb. units) Intensity (arb. units) Results Emission Spectroscopy 8 6 4 2 1 8 6 4 2 Upstream Plasma Generation (C 2 H 4 /O 2 /N 2 ; 2 Torr) f =.8 OH (A-X) N2 (C-B) CH (B-X) 3 36 42 48 54 Wavelength (nm) Turbulence and Combustion Wavelength (nm) Research Laboratory 1 Hz f = 1 1 KHz reasonably 5 KHz 1 KHz 8separated CH (A-X) C 2 C 2 6 4 2 OH (A-X) N2 (C-B) CH (A-X) Plasma off CH (B-X) Hz 1 KHz 5 KHz 1 KHz 3 36 42 48 54 Wavelength (nm) N 2 Directly-Coupled 8 Plasma/Flame(C 2 H 4 /O 2 /N 2 ; 2 Torr) OH (A-X) N2 (C-B) 2 16 12 f =.8 4 CH (B-X) CH (A-X) Hz 1 KHz 5 KHz 1 KHz 3 36 42 48 54 Plasma and flame spectra are OH* 25 2 15 1 5 OH (A-X) N2 (C-B) f = 1. CH (B-X) CH (A-X) 3 36 42 48 54 Wavelength (nm) C 2 C 2 Hz 1 KHz 5 KHz 1 KHz C 2 3 35 4 45 C 2 H b Plasma C 2 Hz Flame, No OnPlasma 1KHz Plasma, Flame No Flame Off Wavelength (nm) CH* Plasma ON C off 2 H b Plasma ON measurement measurement
Signal (arb. units) Signal (arb. units) Signal (arb. units) Results Emission Spectroscopy Directly-Coupled Plasma/Flame(C 2 H 4 /O 2 /N 2 ; 2 Torr, f =.8) 3 25 2 15 CH* O Hz (No Plasma) 1 KHz 5 KHz 1 KHz 1 8 6 OH* Hz (No Plasma) 1 KHz 5 KHz 1 KHz May be real? C 2 H + O CH*+ CO CH + O 2 OH* + CO H + O + M OH* + M 1 5 3 6 9 12 15 Height Above Burner (mm) 4 2 1 8 6 4 3 6 9 12 15 Height Above Burner (mm) C 2 * Hz (No Plasma) 1 KHz 5 KHz 1 KHz C + CH 2 C 2 * + H 2 C 3 + O C 2 * + CO CH + CH C 2 * + H 2 Introduction of plasma increases OH*, CH*, and C 2 * (as expected) due to possible increase in O, H, and C X H Y radicals from discharge? Plasma ON 2 3 6 9 12 15 Height Above Burner (mm) What will be the trends of the species in the ground state?
Relative Intensity Relative Intensity Relative Intensity Relative Intensity Results Emission Spectroscopy Upstream Plasma Generation (C 2 H 4 /O 2 /N 2 ; 2 Torr) 3. 2.5 2. 1.5 1. OH* CH* C2* f =.8 2. 3. 2.5 1.5 2. 1.5 1. 1. OH* CH* C2* f = 1..8 For lean case: O, H, and C production from discharge may penetrate moderateand higher-temperature regions (or produce more chain-branching reactions).5.5 2 4 6 8 1 2 4 6 8 1 Discharge Repetition Rate (khz) Discharge Repetition Rate (khz) Directly-Coupled Plasma/Flame(C 2 H 4 /O 2 /N 2 ; 2 Torr) 4. 3. 2. 1.. OH* f =.8 CH* C2* Hb* 2 4 6 8 1 Discharge Repetition Rate (khz) 4. OH* CH* 3. C2* Hb* f =.8 1. 2. 1.. 2 4 6 8 1 Discharge Repetition Rate (khz) Introduction of plasma into high-temperature regions increases OH* production compared to upstream injection case for all cases. CH* and C 2 * are increased for f =1 and similar for f =.8 (compared to upstream injection). H b also is observed.
Relative LIF Signal ln(i/b(2j+1)) Laser-Induced Fluorescence Measurements Laser Induced Fluorescence (LIF) The LIF system has been set up recently. We have generated UV laser light and all data acquisition software is completed. Current work is focusing on OH LIF for temperature and species concentration data (starting this week). Following OH, O and H will be measured via TALIF 1 5.5.8 R1 2.5 12.5 8.5 R2 5.5 1.5.6.4 Q21 5.5 8.5.2 281. 281.2 281.4 281.6 281.8 282. 282.2 282.4 Excitation Wavelength (nm) -21 T = 24K -22-23 -1/k B T -24-25 1 2 3 4 Rotational Energy (cm -1 ) Examples from previous work
Research Task Investigation of Low-Temperature Reaction Pathways Under Plasma-Assisted Combustion Conditions: Role of HO 2 Suzanne M. Lanier, Walter R. Lempert, Jeffrey A. Sutton
Motivation for HO 2 Measurements HO 2 is an important radical in hydrogen and hydrocarbon (low-temperature) combustion chemistry Borrowing from Glassman [1], we examine typical kinetics in H 2 -O 2 systems Initiation H M H H M 2 H2 O2 HO2 H Branching H O O OH 2 O H2 H OH H2 OH H2O H O H2O OH OH High Temperatures Low Temperatures Termination H H M H 2 M O O M O2 M H O M OH M H OH M H2O M H O M HO M 2 2 What happens as O 2 (a 1 Δ) or O 2 (X,v) is loaded? Does this shift the ratio of the reactions so that there is an effective lowtemperature OH formation pathway? classic boundary between high and low temperature chemistry Consider that non-equilibrium plasmas create large radical pools, metastable electronic states, and vibrationally-excited molecules H O a D O OH ( 1 ) 2 g H O ( X,v) O OH 2 1 Glassman, Combustion, 2 nd Ed., 1987 (R1) (R2) (R3) (R4)
Motivation for HO 2 Measurements HO 2 is an important radical in hydrogen and hydrocarbon (low-temperature) combustion chemistry In addition, OSU H 2 -air plasma model indicates that HO2 O O2 OH Low Temperatures HO2 H H2O O HO2 H OH OH Intermediate Temperatures become important at low and intermediate temperatures, increasing fuel oxidation by opening additional chain-branching pathways Due to an increase in H and O created by plasma discharge?
HO 2 Diagnostic Cavity Ringdown Absorption Spectroscopy Thiebaud et al. (27) HO 2 has been detected by UV absorption in the range 22-23 nm. Structureless due to the predissociative B-X transition. Other species such as H 2 O 2, H 2 O, C x H y have absorption features in this region. Quantitative measurements are difficult! The 1.5 mm region corresponds to absorption due to the H-OO stretching overtone, 2ν 1, more specifically the (2,,)-(,,) lines, in the ground electronic state (X 2 A ) somewhat isolated from OH, H 2 O, C x H y We will develop cavity ringdown absorption spectroscopy for HO 2 at 1.5 mm
Near-IR CRDS Line We will spacing use an < injectionseeded OPO to 1 GHz Doppler generate broadening narrowband is 215 624 MHz nm light at 3K A Difference narrowband Frequency source at 1.5 Mixing mm (DFM) is preferred of 624 for nm quantitative and 164 nm output will measurements generate narrowband Dye 15 laser nm output output > 823 nm 1GHz 624 nm 164 nm 624 nm
Near-IR CRDS Optical Parametric Oscillator 355 nm pump source (injectionseeded Nd:YAG); n L ~ 15 MHz w idler + w signal = w pump 823 nm + 624 nm = 355 nm ECDL 823 nm 78 88 nm 624 nm 164 nm Type I BBO R ~.2 UV, 22 39 nm 624 nm 355 nm ~1 mj/pulse at 624 nm Wavemeter
Signal (arb. untis) Signal (arb. untis) Near-IR CRDS Difference Frequency Generation 624 nm beam (< 2 MHz) is combined with 164 nm (< 1 MHz) to generate near-ir via DFG (or DFM) w DFG = w 1 w 2 ; w 1 > w 2 156 nm = 624 nm 164 nm 624 nm 164 nm.4 1 156 nm.3 164nm OPO signal (624 nm).8 ~ 5 mj/pulse.6.2.1.4.2 FWHM determined by detector FWHM determined by "fall time" of detector 1 2 3 4 5 Time (ns) 4 8 12 16 2 Annual Time (ns) PAC MURI Review
Near-IR CRDS 624 nm 164 nm CRDS CRDS cell is constructed and set up. We are currently in the process of alignment and then assessment of accuracy, sensitivity, etc.
Research Tasks Development of a new, low-pressure, plasma-enhanced flame facility for directly monitoring the effects of non-equilibrium, volumetric plasmas on combustion chemistry Investigation of plasma enhancement in moderate- and high-temperature regimes by monitoring H, O, OH, (and C x H y ) distributions Assessment of current kinetic (w/plasma) modeling capabilities under moderate- and high-temperature conditions in a well-defined geometry Development of a diagnostic for quantitative HO 2 measurements under lowand moderate-temperature plasma-enhanced oxidation conditions Examination of the effects of plasma-generated radical pools and metastable electronic states (e.g., O 2 (a 1 D g ) or O 2 (X,v)) on opening new reaction pathways at low temperatures and pressures. Examination of HO 2 reactions as chain-branching reactions under PAC conditions