2006 HOTWC Chapter Title:
Instrumentation for Bench- and Large-scale Test Fixtures
Kevin L. McNesby U. S. Army Research Laboratory Aberdeen Proving Ground, MD. Erik Johnsson NIST Gaithersburg, MD
Army Research Laboratory (APG, MD) 2006 HOTWC Project working title:
3.C - Laser-Based Instrumentation for Real-Time, In-Situ Measurements of Combustible Gases, Combustion By-Products, & Suppression Concentrations
Kevin McNesby, Erik Johnsson, George Mulholland, Reed Skaggs, Andrzej Miziolek, Edwin Lancaster, Robert Daniel, Bill Bolt, Craig Herud, Brian Kennedy
Army Research Laboratory (APG, MD) 2006 HOTWC Working Description:
OPTICAL SPECTROSCOPIC TECHNIQUES FOR ARMY APPLICATIONS
Kevin McNesby, Reed Skaggs, Andrzej Miziolek, Erik Johnsson, George Mulholland, Edwin Lancaster, Robert Daniel, Bill Bolt, Craig Herud, Brian Kennedy, Bill Jackson, Ian McLaren, Don Horton, Steve Modiano
Army Research Laboratory (APG, MD) 2006 HOTWC
• joint, effort at ARL (Army Research Laboratory), ATC (Aberdeen Test Center), NIST Using Optical Spectroscopy
•(FY97-02)
• work focussed on needs pertaining to armored vehicles
• field-scale to laboratory scale environment
Army Research Laboratory (APG, MD) 2006 HOTWC
Talk Outline
¾ Introduction – Tanks ¾ Species (Suppressants; Toxic By-products; Fuels; Oxidizers) ¾ Fast Vibrational/Visible Spectroscopy ¾ Differential Infrared Rapid Agent Concentration Sensor (DIRRACS) ¾ Laser Induced Breakdown Spectroscopy for Fire and Explosive Suppressant Measurement ¾ Diode Laser Spectroscopy for Toxic and Combustible Gas Measurement
Army Research Laboratory (APG, MD) Differential Infrared Rapid Agent Concentration Sensor (DIRRACS)
¾Measurement of suppressant concentration ¾Previous instrument response time ~ 200 ms (viscosity sensor) ¾1 ms response time ¾Infrared absorption ¾Insensitivity to vibration Instrument Filter
HFC 125 DIRRACS II Schematic DIRRACS II Instrument DIRRACS II Test Rig
Transient Application Recirculating Pool Fire (TARPF) Facility at NIST. DIRRACS Testing Time Response < 10 ms Sensitivity < .005 volume fraction
HFC 125 agent volume fraction versus time for two releases of HFC-125 in the TARPF facility. 2006 HOTWC Suppressant Gas Measurement: Laser Induced Breakdown Spectroscopy (LIBS)
• Plasma Formation – Multiphoton Absorption --> Ionization – Absorption of Laser Radiation by Free Electrons, i.e. Inverse Brehmstrahlung – Electron Collisions --> Ionization --> Heating --> Breakdown – Typical Gas Temperatures, ca. 20,000 K • Spectrochemical Analysis based on Collection of Emission of Atomic and Molecular Constituents Usually after Plasma Continuum Radiation Decays (2-100 usec).
Army Research Laboratory (APG, MD) 2006 HOTWC
LIBS Instrumentation
Collimator / Fiber Plasma Coupler Spectrograph
Gated Intensified Analyte Gas Camera Flow
Focusing Lens
1064 nm Pulsed Laser Radiation
Army Research Laboratory (APG, MD) 2006 HOTWC LIBS of DMMP
P 25000 C
20000 P
15000
10000 Signal Intensity
0.5 5000 ) us ( y la e 25 D 0 e 210 220 230 240 250 260 270 m Ti Wavelength (nm)
Army Research Laboratory (APG, MD) 2006 HOTWC LIBS of Fire Suppressants
Halon-14
FM-200
Halon-1301
HFC- 134a Signal Intensity (arbitrary units) Signal Intensity
0 0 2000 4000 6000 8000 10000 12000 14000 16000 Concentration (ppm) Army Research Laboratory (APG, MD) 2006 HOTWC Toxic and Combustible Gas Measurement: Near Infrared Tunable Diode Laser (TDL) Spectroscopy
HF, O2 , CO, CH4, HCl, other small molecules
16 0.06 Transmission - no modulation 15 0.05 14 Transmission - with modulation (note RAM) 13 0.04
12 0.03 11 Wavelength Modulation Spectroscopy 10 0.02 Signal Intensity (a.u.) Signal at Detector (V)
9 0.01 8 Demodulated signal (2f) 7 0 7665.5 7665.51 7665.52 7665.53 7665.54 7665.55 7665.56 Wavelength (nm) 2006 HOTWC HF Gas Measurement During Suppressant Testing
1400 FE-36 FE-36 + 7 % APP 1200 FE-36 + 15 % APP 100 1000 %
800 T r a 600 n s 50 400 m i t 200
Average HF Concentration, ppm t a 0 n c 0 P2 ν=0-2 -200 e 0 50 100 150 200 5000 6000 7000 8000 Time, seconds wavenumbers Figure 2
Army Research Laboratory (APG, MD) 2006 HOTWC Oxygen Measurement Using TDL Spectroscopy
Oxygen Concentration Oxygen Absorption Near 760 nm (b ↔X , 1 + 3 - Σg ↔ Σg ) 24
22 7.00E-05
20 6.00E-05
18 5.00E-05
% Oxygen 16 4.00E-05
3.00E-05 14 Intensity
2.00E-05 12
1.00E-05 10 0 100 200 300 400 500 600 700 800 900 0.00E+00 Time (seconds) X .001 13147 13163.8 13123.6 13131.4 13139.2 13148.1 13154.7 13162.5 13170.3 JP-8 - air fire, inhibition by C3F8 , crew compartment Wavenumbers (cm-1) test fixture, fire extinguished 150 ms after detection.
Army Research Laboratory (APG, MD) Multiple Species Gas Sensing Using Tunable Diode Lasers (TDL)
λ1
M o Laser d 1
Fiber to Free space λ2 Mod 2 Demod λ Fiber free space to fiber 1 (lock-in, mixer, λ WDM, etc.) 2 Laser Mixer λ3
Absorption as function 3
d of time for each wavelength λ3 o M (I.e., for each gas)
Laser Time Division Multiplexing
Fiber optic cable A/D D/A Diode Detector laser
lens Transmits best at: 780 nm
Fiber optic cable 1310 nm 1550 nm Semi-conductor diode laser Detection and Measurement of Middle Distillate Fuel Vapors Using Tunable Diode Lasers 160 140 120 100 DF2 n 80
o
i JP-8
s
s i 60
m
s n 40 a Unleaded
r
T Gasoline
20 (regular)
% 0 1.2 1.7 2.2 2.7 3.2 3.7
Wavelength (micrometers) Spectrum of dry air saturated at 294K with vapor from unleaded gasoline, JP-8, DF2. Spectra offset for clarity. Limitations of TDL Spectroscopy For Measurement of High Molecular Weight Vapors
Absorption features are unstructured.
Can’t use traditional wavelength or frequency modulation techniques to measure big molecules (e.g., middle distillate fuels - JP-8, DF-2, etc.). Unable to scan on and off resonance with single DFB laser.
Develop a near-infrared diode laser-based sensor capable of measuring hydrocarbon fuel vapor concentrations with a time resolution of 10 msec per measurement point; maintain S/N advantages of WMS. 2006 HOTWC Measurement Technique
uses laser diode absorption spectroscopy in the near-infrared spectrum (1.3 microns and 1.71 microns)
Emission intensity from two lasers is varied sinusoidally, with emission from first laser 180 degrees out of phase with emission from second laser.
Measurement is made in situ.
Phase sensitive detection is used to measure differential absorption at the two laser emission wavelengths.
10 msec response time Laser Mixing Apparatus
Function Laser Laser 1 Generator 1 Driver 1 1.31 microns Fiber optic Function Laser Laser 2 coupler Generator 2 Driver 2 1.71 microns
GRIN Lens 1
4 m optical cell
Lock-in Laptop InGaAs Detector Oscilloscope Amplifier Computer
Figure 3: The experimental apparatus used to measure vapors from middle distillate fuels. Overlap of Fuel Absorbance Spectra and Mixed Laser Probe Beam
Laser 1 Laser 2
0.4 DF-2 vapor 1.25 0.3
0.2 0.75 JP-8 vapor 0.1 0.25
Absorbance 0 Gasoline vapor -0.1 -0.25 Laser Emission (arb. units) 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Wavelength (micrometers)
Figure 4: shows the vapor phase absorption spectrum of air saturated by vapor at 294K from JP-8, DF-2, and gasoline between wavelength values of 1.3 and 1.75 micrometers superimposed upon the emission from the optical fiber which carries the mixed wavelength probe beam. Results: Approach to Lower Explosion Limit (LEL) in a Gasoline Fuel Tank at Room Temperature
) 12000 0.3
10000 0.25 ppm O2 8000 0.2
6000 0.15 LEL 4000 gasoline 0.1
2000 0.05
0 0 Fraction Oxygen
Gasoline Vapor ( 0 100 200 300 400 500 Time (sec) Simultaneous measurement of fuel/oxygen concentration (by volume) during displacement of contents (dry air) of a 14 liter vessel by air saturated by gasoline vapor at 294K and 1 atmosphere total pressure. Oxygen sensor courtesy of Oxigraf, Inc. Results: “Aging” of JP-8 Detected Using Mixed Laser Sensor
3000 Fresh sample 2500
2000 Sample after 5 runs 1500
1000
ppm JP-8 Vapor 500
0 0 1000 2000 3000 4000 Time (s) FT Diode Laser Spectroscopy
For a monochromatic source: fixed mirror I(σ) = I(ν)cos2πνσ
direction of to detector motion For a polychromatic source: ∞ I(σ) = ∫ I(ν)cos2πνσd ν beam splitter moving 0 mirror
σ= mirror position ν = light frequency (cm-1) I(σ) = intensity at detector from light source I(ν) = source intensity FT Diode Laser Spectroscopy
3.22 μ
3.24 μ
3.26 μ
3.28 μ Analyte region detector
IC, QC laser
lens FT Diode Laser Spectroscopy 4.50E-02
4.30E-02
4.10E-02
3.90E-02
3.70E-02 Signal at detector Laser 1 (100 KHz) at 1.31μ 3.50E-02 Laser 2 (110 KHz) at 1.71 μ 3.30E-02
3.10E-02 Intensity (a.u) Intensity 2.90E-02
2.70E-020.00E+00 4.00E-04 8.00E-04
2.50E-02
-3.00E+01 Time (sec)
-4.00E+01
-5.00E+01
-6.00E+01 Fourier transform of
signal at detector -7.00E+01 (res.= 100 Hz) -8.00E+01 Intensity (a.u) Intensity
-9.00E+01 2.00E+04 4.00E+04 6.00E+04 8.00E+04 1.00E+05 1.20E+05
-1.00E+02
Frequency (sec-1) FT Diode Laser Spectroscopy
1.10E+00
1.05E+00
1.00E+00 Absorption of laser 9.50E-01 radiation at 1.71μ as air in 2m cell is displaced 9.00E-01 by air saturated with gasoline vapor. 8.50E-01 Fraction Transmitted 9.50E+04 9.90E+04 1.03E+05 1.07E+05 1.11E+05 1.15E+05
8.00E-01
Frequency (sec-1) 0.09
0.08
0.07
0.06 LEL
0.05
0.04
0.03 Absorbance 0.02
0.01 0 500 1000 1500 2000 2500 0
Time (sec) Conclusions/Successes/Failures ¾Project greatly enhanced knowledge of fire suppression on board combat vehicles.
¾Laser diode systems fielded at ATC/ARL for HF and O2 .
¾DIRRACS II testing at WPAFB.
¾FTLS work continues.
¾JP-8 sensor vibration problems
¾COF2 formation documented Conclusions/Successes/Failures (cont.)
¾Lasers outside communication bands still very expensive ¾Mid-IR RT CW lasers still unreliable ¾Narrow BW, broadly tunable, fast light sources still unavailable
Publications 9 open literature, 1 book chapter, 11 Gov’t Tech Reports Acknowledgements
Dick Gann, NIST
Gamboa International
Lawrence Ash, NAWC
Oxigraph, Inc.