2009 muri topic #11: chemical energy enhancement by ... · dod muri fourth year review meeting...

Nonequilibrium Thermodynamics Laboratories The Ohio State University

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

Program Overview and 4th Year Progress

W. Lempert Departments of Mechanical&Aerospace Engineering and Chemistry

The Ohio State University

Columbus, OH

DoD MURI Fourth Year Review Meeting October 22 - 24, 2013

2009 MURI Topic #11: Chemical Energy Enhancement by Nonequilibrium Plasma Species

PRINCETON University


MURI Principal Investigators

• Walter R. Lempert, Igor V. Adamovich, J. William Rich, Jeffrey Sutton.

Ohio State University – Program Lead Institution. • Yiguang Ju, Richard B. Miles, and Mikhail Shneider , and Andrey

Starikovskiy Princeton University. • Richard Yetter Pennsylvania State University • Vigor Yang Georgia Institute of Technology


Primary Scientific Issues

Plasma sources have shown promise in enhancing several fundamental combustion phenomena such as:

I. Reduction of ignition delay which impacts high speed (supersonic/hypersonic) propulsion.

II. Increase flammability limits, particularly fuel-lean combustion (potential for decreased temperature and reduced NOx.

III. Increased extinction strain rate (lower temperature turbulent combustion). Despite the progress in development of plasma-based “devices”

(torches, filamentary discharges), there has been very little effort in developing a comprehensive understanding of the

underlying non-equilibrium plasma-chemical oxidation (and pyrolysis) kinetics and mechanisms.

This MURI focuses on developing such a fundamental understanding, particularly plasma-chemical fuel oxidation at

low (300 – 1000 K) temperatures.


Multidisciplinary Approach

This MURI effort is inherently multidisciplinary, blending the following disciplines:

• Low Temperature Plasma Physics and Chemistry (Adamovich, Starikovskii, Schneider).

• Atomic and Molecular Energy Transfer (Rich, Adamovich, Miles, Lempert).

• Combustion Kinetics (Yetter, Ju, Sutton). • Optical Diagnostics (Lempert, Miles, Sutton, Ju). • Gas Dynamics (Rich, Yang) • High Fidelity Simulation (Yang).


Program Principal Objective, Primary Deliverables, and Potential Breakthroughs.

PRINCIPAL OBJECTIVE “Develop experimentally validated kinetic mechanisms and modeling codes capable of predicting the impact of nonequilibrium plasmas on reactive processes, particularly on ignition, chemical energy release, and flameholding in combustors of flight vehicle engines.“

PRIMARY DELIVERABLES • Extensive new experimental data sets of non-equilibrium plasma chemical energy

conversion kinetics over a wide range of initial temperatures (300 – 1800 K) and pressures (0.1 – 70 bar), in a variety of complementary new test facilities, specifically designed and fabricated for this program.

• Detailed non-equilibrium plasma chemical energy conversion kinetic mechanisms, validated over a wide range of conditions, using data from multiple facilities.

• Extensive experimental data sets on ignition delay, flameholding and laminar flame speed augmentation by nonequilibrium discharges, including nsec pulsed, DC/RF, and microwave.

• High fidelity multi-dimensional plasma combustion modeling codes, validated in a series of model flows, with emphasis on the high subsonic to supersonic flow regimes.

POTENTIAL BREAKTHROUGH Development of Predictive Capability for use in Future Air Force

Plasma-Based Propulsion Systems!


Principal Thrust Areas

Thrust 1. Experimental studies of nonequilibrium air-fuel plasma kinetics using advanced non-intrusive diagnostics.

Thrust 2. Kinetic model development and validation. Thrust 3. Experimental and modeling studies of fundamental

nonequilibrium discharge processes. Thrust 4. Studies of diffusion and transport of active species in

representative two-dimensional reacting flow geometries.


MURI Thrusts: Inter-Relationships

Experimentally validated kinetic mechanisms and modeling codes capable of predicting the impact of

nonequilibrium plasmas on reactive processes, particularly on ignition, chemical energy release, and flameholding in combustors of flight vehicle engines

Mechanisms

Studies of diffusion and transport of active species

in representative two dimensional

reacting flow geometries

Experimental and modeling studies of fundamental non-

equilibrium discharge processes

MURI : Chemical Energy Enhancement by Non-equilibrium Plasma Species

Experimental studies of non-equilibrium air-fuel

plasma kinetics usingadvanced non-intrusive

diagnostics

Kinetic model development and

validation

Scientific approach structure for 2009 Plasma Assisted Combustion MURI program.

(1) Advanced methodologies and facilities for acquisition of new experimental plasma kinetic data sets.

(2) Development of advanced plasma chemical oxidation mechanisms.

(3) Development of validated numerical modeling codes.


Facility Summary* (Designed to Span Wide T, P Range)

(*All facilities designed and fabricated specifically for this program.)

3000K

1000K

300K 0.01atm 1atm 100atm

Flames (Ju, Sutton)

Flow Reactors ( Yetter,

Adamovich)

Shock Tube (Starikovskiy)

RCM (Starikovskiy)

MW+laser (Miles)

JSR/Flow Reactor (Ju)


MURI Team Major Interconnections

Technical Activities • OSU/Princeton/GT/Penn State: Plasma Kinetic Model. • Princeton/Georgia Tech: Plasma Diffusion Flame

Expt./Simulation. • OSU/Georgia Tech: Nsec Plane-to-Plane DBD Discharge Model

and H2/Air Ignition Expt. • OSU/Penn State: OSU Supplied Pulsed Discharge for PSU

Reactor, Collaborative OH LIF Measurements.

Team Coordination and Communication

• ~Monthly Telecoms. • AIAA Aerospace Sciences (and other) Meetings. • Yearly Program Reviews.


A Few Year 4 Highlights


OSU Temporal Evolution of Electron Density and Temperature in Diffuse Single Filament Discharge

Helium, 200 torr, Coupled energy ~18 mJ/pulse.

Thomson scattering spectra obtained 10 and 90 ns after application of single ~100 ns discharge pulse in pin-to-pin plasma.

Afterglow begins

Weak Secondary Pulse.

Predicted ne rise faster than 10 ns measurement resolution.


[NO] reproduced only when complete set of N2 excited states is incorporated in N2

* + O → NO + N reaction [NO] reduction ~ equals initial [N], ~1015 cm-3: NO+ N → N2(v) + O reaction.

OSU: Air chemistry, ~150 nsec pulse, P=100 torr: “Full set” of data (T, [N2(v)], [N], [O], [NO], NO PLIF)

N, O, and NO data with baseline (upper) and enhanced (lower) kinetic models.

N2(a" 1Σg+)

Ground

N2(a' 1Σu- )

N2(w 1Δu) N2(a 1Πg)

N2(E 3Σg+)

N2(C 3Πu)

N2(B' 3Σu-)

N2(W 3Δu) N2(B 3Πg) N2(A 3Σu

+)

N2* electronic states in baseline (blue) and enhanced (blue + red) NO NEQ kinetics model

NO PLIF image 10 µs after discharge pulse.


OSU: 2-D Kinetic model development and validation

• Model validation: plane-to-plane and “diffuse filament”, point-to-point nsec pulse discharges • Electric field in N2 and H2 (nsec and psec CARS-like four-wave mixing) • Electron density, electron temperature in He and H2-He (Thomson scattering) • N2 populations in N2 and air (vibrational CARS) • Air plasma chemistry (simultaneous O TALIF, N TALIF, NO LIF and PLIF) • Fuel-air chemistry: radial distributions of T (Rayleigh scattering), [OH] (LIF), [H] (TALIF)

• Nonequilibrium plasma model / code used as a starting point: non-PDPSIM (developed by M. Kushner, U. Michigan), widely used in low-temperature plasma community, well-documented

• Quasi-1-D and 2-D (plane, axisymmetric) geometries • Poisson equation for the electric field: predict electric field in plasma, cathode voltage fall • Boltzmann equation for EEDF (experimental cross sections): predict rates of electron impact

excitation, dissociation, and ionization processes • Charged species equations (ionization, recombination, attachment, detachment processes, ion-

molecule reactions): predict electron density in plasma • Excited neutral species equations (electron impact excitation, non-reactive and reactive

quenching): predict contribution to radical species formation • Master equation for N2 (X,v) populations; V-T, V-V processes, V-Chemistry coupling • Neutral species reactions: fuel-air air chemistry, enhanced by radical production in plasma • Coupling between chemistry, transport processes (diffusion, conduction), and flow


101

102

103

104-20-10

010

200

100

200

300

400

time, usaxial location, mmIn

tens

ity c

ount

s

OSU: Relative [H], [OH] distributions after 50-pulse burst (2% H2 in 20% O2-Ar, P=40 torr, electrode gap 12 mm)

100

101

102

103

104-20-10

010

200

1

2

3

4x 105

time, usaxial location, mm

Inte

nsity

cou

nts

“Pin-to-Pin” Discharge

H →

OH →


ϕ = 1.07 ϕ = 0.81 ϕ = 0.62

OSU: Effects of Non-Equilibrium Plasmas on Premixed Combustion Chemistry (CH4/Air)

FACILITY BURNER

CONFIGURATION

DIRECTLY-COUPLED PLASMA/FLAME

• McKenna burner; Low-pressure 1D flame (20-30 Torr).

• Temperature and species vary with distance above burner.

• Porous HV electrode (40 mm above burner) – no flow field disturbance (burner is ground).

0.000

0.005

0.010

0.015

OH

Mol

e Fr

actio

n

NO PLASMA

Belhke (70 kHz; 400 pulses)

FID (40 kHz; 200 pulses)

Simulation - No Plasma

0 5 10 15 20

Height Above Burner (mm)0 5 10 15 20

Height Above Burner (mm)0 5 10 15 20

Height Above Burner (mm)


OSU: Experimental (4-wave mixing) and predicted E-field in N2 plane-to-plane nsec pulse discharge.

• Experiment (Ruhr Universität Bochum, Germany, nsec pulse 4-wave mixing): N2, P=0.25 bar, 1.2 mm gap, pulse repetition rate 2 kHz

• Field in plasma before breakdown follows applied voltage, E=U/d • Field in plasma after breakdown is significantly lower, significant cathode voltage fall • Model predictions for time-resolved electric field, pulse current: good agreement with experiment • Cathode fall increases significantly with current density (e.g. in a point-to-point geometry)

0.35 bar 0.35 bar


Penn State: Plasma Flow Reactor Studies (P = 1 atm, Q = 1 LPM, 1600ppm CH4 / 3000ppm O2 / Ar, Vplasma = 10kV, v = 1 kHz)

Strategy: Dilute Mixtures Enables Low T Kinetics to be Studied Under Isothermal Conditions. Data Obtained With/Without Plasma.

Major Species Minor Species

Inlet

Outlet

Heating Zone = 2 ft

0

10

20

30

40

50

60

400 600 800 1000 1200

NA.1 - 15.406 minNA.2 - 19.748 minNA.3 - 20.011 min

Sign

al A

rea

[pA*

s]

Temperature [K]

CH3CH2CHO, propanal

CH2O

CH3COCH3, acetone

0

500

1000

1500

400 600 800 1000 1200

C3H

8CO

CO2

C2H

4

Spec

ies

Con

cent

ratio

n [p

pm]

Temperature [K]0

20

40

60

80

100

400 600 800 1000 1200

CH4

C2H

6C

3H

6C

4H

10C

4H

8

Spec

ies

Con

cent

ratio

n [p

pm]

Temperature [K]Minor Species

0

0.2

0.4

0.6

0.8

1

600 650 700 750 800 850

Nor

mal

ized

Fue

l Con

cent

ratio

n [C

3H8]

/[C3H

8]i

Temperature (K)

• Plasma oxidation of C3H8 exhibits cool flame chemistry (negative temperature coefficient regime, 700 – 750 K) at 1 atm not typically seen in thermal systems until elevated pressures

• Increase in aldehyde (R’CHO) intermediates suggests reaction routes shift to a chain-branched process

@ 10 atm - D. N. Koert, et. al. Combust. Flame (96) 1994

PSU 3 Zone Plasma Flow Reactor


Penn St/OSU: Flow Reactor Initial OH LIF in Dilute H2/O2/ Ar System

P = 1 atm, Q = 1 LPM, 2000 ppm H2/3000 ppm O2 / Ar by balance

Plasma 10 kV v = 1 kHz, T = 814 K

• in-situ OH LIF implemented into existing flow reactor experiment in collaboration with OSU group (Zhiyao Yin and Kraig Frederickson)

• Qualitative observations indicate the presence of OH not seen under thermal conditions (T < 860K). Influence of the plasma also suggests OH formation formed through linear chain opposed to branched chain in thermal systems

5

10

15

20

25

30

35

0 10 20 30 40 50

Inte

nsity

[a.u

.]

Position [mm]

Laser Excitation: Q1(4) in OH A-X (1,0), ~1mJ/pulse

0D Plasma Chemical Kinetics Code

00.5

11.5

22.5

3

0 5 10 15 20 25 30 35 40

OH

(ppm

)

Time (ms)

Experimental OH Profile

Linear growth of OH indication of linear chain propagation.


Princeton – Ju Plasma: Activated Cool Flames: A New Way to Burn

(a) Hot diffusion flame

(b) Cool diffusion flame

Heated N2 @ 550 K

N2 @ 300 K

Stagnation plane

Oxidizer @ 300 K with plasma discharge

Fuel/N2 @ 550 K

Hot and cool n-heptane diffusion flames at the same condition


Multipath (24) mini-Herriott cell.

Image of DBD plasma discharge at 1 kHz.

Princeton - Ju: Mid-infrared in-situ multi-species and temperature measurements by TDLAS

Detector

QCL Laser

Diluents

Diluents

Oxidizer

Fuel

To Vacuum

Electrode

VacuumChamber

Nanosecond-Pulsed

Power Supply

Pulsed Signal Generator

Digital Delay Generator

Function Generator

Oscilloscope

7.03-7.72 μm

DBD – Multi-Pass TDLAS ns Discharge Facility.

→ 0

100

200

300

400

500

600

0 0.005 0.01 0.015

Mol

e Fr

actio

n (p

pm)

Time from first pulse (s)

Pyrolysis C2H2Pyrolysis CH4C2H2 ModelCH4 Model

C2H4 Pyrolysis (Oxidation data also obtained)

With updated C1 model


Radar REMPI Measurement of Atomic Oxygen (O) Using Xenon (Xe)

Calibration.

Absolute [O] in 1 atm CH4/air flame inferred by seeding with trace amounts of Xe.

Princeton Miles: Diagnostic Development

Hyperspectral Temperature Profile Imaging by FLEET: (Femtosecond

Multiphoton Excitation of Molecular Nitrogen)

• Excite C state by multiphoton absorption, which rapidly thermalizes rotation.

• Spectrally analyze 2nd positive band emission.

• Provides temperature sensitivity of UV emission spectroscopy with laser enabled spatial resolution (~30 microns)!

FLEET T Line Image


Princeton Miles: Sodium Enhanced Microwave Coupling to Flames

• Microwaves couples directly into flame front. • Conductivity from chemi-ionization.

CH+OHCO+ + e-

• Metal vapor addition improves coupling. • Increased conductivity NaNa++e-. • Reduced microwave power requirement.

High Q Microwave resonator cavity with flat plate stabilized flame

Principal Chemi-ionization Processes

Enhanced Microwave Energy Deposition.


Princeton Starikovskiy: Plasma Shock Tube and Rapid Compression Machine (for High

Pressure Measurements.)

Discharge Section

Temporal Traces E/n and Electron

Density

Coupled Energy


Princeton Starikovskiy: Plasma Shock Tube Measurements of Ignition Delay Reduction

С2Н2:О2:Ar(90%), φ = 0.5 Combustion model: Wang et al. (2007)

0.5 0.6 0.7 0.8 0.9 1.010

100

1000

PAIauto

Tim

e, µ

s

1000/T, K-1

Ignition Delay Time Decrease at 0.1 eV/molecule for several fuels

0.6 0.7 0.8 0.9 1.0 1.1 1.2100

101

102

103

104

105

106

107

108

Plasma assisted ignition efficiencyQ = 0.1 eV/mol

H2:AIR CH4:O2:N2:Ar CH4:O2:Ar C2H2:O2:Ar C2H5OH:O2:Ar C2H6:O2:Ar C3H8:O2:Ar C4H10:O2:Ar C5H12:O2:Ar

τ aut

o/τpl

asm

a

1000/T, K-1


Georgia Tech: High Fidelity Simulation

Ignition studies

C2H4-air plasma enhanced flame H2-air, CH4-air, C2H4-air

• NS plasma “volumetric” ignition. • Effect of pressure, initial temperature, eq. ratio,

dielectric properties on ignition characteristics. • importance of NOX catalytic reactions on ignition

chemistry. nHeptane-air

• Effect of nanosecond plasma on the 2-stage ignition process.

• Validation of the steady-state flame solution with CHEMKIN.

• Effect of temperature/species gradients (presence of flame) on plasma E/N and species production.

OSU Plasma Enhanced Premixed Flat Flame

OSU nsec Pulsed Plane-to-Plane Discharge


Georgia Tech: Effect of Nanosecond Plasma on nHeptane-Air Ignition

• 160 torr, 600 K, ϕ = 1.0 • 10 kV Gaussian pulse • Input energy ~ 0.5 mJ/pulse • discharge gap = 0.25 cm

Operating conditions • 1st ignition limit is extremely sensitive

to radical addition (5 pulses causes “instantaneous” ignition).

• 2nd ignition limit is less sensitive to plasma radical addition.

• Staggered application of nsec pulses is most optimal (1-5 pulses at t = 0 and 10-50 pulses after 1st stage ignition).

Temperature evolution at the center of the discharge gap


Plasma Kinetics Working Group

Members: Igor Adamovich, Yiguang Ju, Andrey Starikovskiy, Richard Yetter, Chiping Li.

Mission: Delineate the current status of plasma combustion kinetic

mechanisms, identify most needed experimental parameter data and most significant gaps, and develop a “Road Map” for future progress.

In 2013, in response to comments by Air Force personnel at 3rd review meeting, a plasma kinetics working group was established.


Working Group: Plasma Assisted Combustion Chemistry Model Development

1-D Gas Phase Model Simulation

and Analysis transport, heat release,

and chemistry

0-D Gas Phase Model Simulation

and Analysis complex chemistry only

Theory electronic structure

reaction rate transport

electron cross section

Semi-Empirical Theory

rate constant estimates critical data analysis

thermochemistry

Isolated Species and Reaction Experiments

rate constant measurements, product

detection, transport

Chemistry Experiments

shock tube, flow reactor, static reactor, rapid

compression

Coupled Chemistry, Transport, & Heat

Release Exp. diffusion and premixed

flames

Sensitivity Analysis at all

Levels

Model/Theory Experiments

Multiple and Complementary Diagnostics at

all Levels

Scal

e Iteration

Para

llel M

odel

/The

ory

and

Expe

rim

ent

for

Com

pari

son

at e

ach

Leve

l


Summary – What Has Been Accomplished in 4+ Years

• Wide variety of facilities have been constructed and are operational. Facilities cover wide temperature range from 300 to 3000 K, pressures from 1 Torr to 100 atm, pulsed voltage amplitude up to 120 kV, plasma power 0.2 GW in nanosecond scale, 0.5 MW in millisecond scale.

• Multiple new experimental plasma kinetic data sets have been obtained, both for high-temperature and low-temperature regimes. Above self-ignition threshold measurements performed of plasma assisted ignition for H2, C2H6, C2H5OH, C2H2. In the range 300-800 K plasma-assisted oxidation and pyrolysis has been investigated in H2, saturated hydrocarbons C1-C4, C2H4, and dimethyl ether. Plasma assisted cool flame observed.

• Plasma kinetic models for wide range of fuels and conditions were developed and disseminated. The role of translational nonequilibrium, vibrational and electronic excitation, ionization and energy transfer processes for fast heating, radical production and chain propagation mechanisms were investigated. These plasma-chemical models are still under development – specifically, for low-temperature regimes, high-pressure conditions and heavy/unsaturated hydrocarbons.

• New diagnostics (FLEET, Radar REMPI, Multi-pass Mid IR TDLAS, MB-MS) have been developed.


Where Do We Go From Here?

• Expanded Validated Kinetic Mechanisms. • Elucidation of role of vibrational excited states for chain propagation

mechanisms. • Elucidation of role of electronic states with more quantitative description of

energy transfer (Ex: quenching of electronic states – rates, energy partitioning, and products).

• Elucidation of role of ion chemistry in fast heating and radicals production. • Higher pressure, temperature and velocity regimes. • Higher C hydrocarbons and oxygen containing fuels. • Database of “reference” experiments for plasmachemical models validation.

• Improved Diagnostic Capability. • 1 and 2-dimensional quantitative temperature, and species field measurements. • 1 and 2-dimensional quantitative fundamental discharge parameter

measurements (Electric field, electron density and temperature). • Expand list of measurable species (beyond OH, atomics, NO, CH, etc.).


WE THANK AFOSR AND AFRL FOR ITS SUPPORT OF THIS

MURI PROGRAM!

2009 muri topic #11: chemical energy enhancement by ... · dod muri fourth year review meeting...

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