Passive radiative emission measurements of H 2 O, CO 2 , CO and Temperature

1. Passive radiative emission measurements of H2O, CO2, CO and Temperature Terry Parker and Eric Huelson Engineering Division Colorado School of Mines Presented at: WPAFB Dayton, Ohio March 25, 2004

2. Acknowledgements • Phase I and II support as a subcontractor to Innovative Scientific Solutions, Inc. • Dr. Campbell Carter • Dr. Mark Hsu • Justin Spelman (CSM)

3. Measurements of all flow properties and species concentrations is the “holy grail’ of diagnostic efforts For research, measurements provide insight into physical processes and device performance For control, measurements provide metrics for performance Laser based measurements provide the opportunity to measure a host of molecular concentrations as well as temperature, velocity, and pressure Cost is complexity both in hardware and data reduction Line-of-sight measurements tend to be simpler to apply and interpret (typically one laser per metric) Line-of-sight emission measurements can monitor multiple species and temperature in a single instrument Potential for a robust and cost effective instrument Nonintrusive measurements of flow properties facilitate both research and system control

4. Molecular radiation is the cornerstone of passive radiative emission measurements • Hot gas or gas particle systems radiate in a predictable fashion • Observed emission depends on wavelength, temperature, concentration of species, and path length • The key to a radiative emission measurement is the ability to monitor radiation over a very a wavelength range that allows determination of the property of interest

5. Initial CSM efforts focused on single line measurements of NO • Radiative emission measurements of an isolated line near 5.2 mm • Hardware was a custom designed and manufactured Fabry-Perot Interferometer • System was applied to a Denver power plant • Results : • Spelman, J., S. Skrien, and T.E. Parker, Applied Optics 41(15), p. 2847-2857 (2002). • Spelman, J. and T.E. Parker, Combustion Science and Technology 172, p. 23-33 (2001). • Spelman, J., S. Skrien, and T.E. Parker, Review Of Scientific Instruments 72(9), p. 3699-3705 (2001).

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7. Infrared transmissive fibers and multiple line measurements simplified the system • Single line measurements difficult from a hardware and signal level perspective • Judicious choice of wavelength regions provides measurement of parameter of interest • ZrF2 fibers transmissive to 4.5 microns • Etendue similar to that for instrument, simplifies optical collection Spelman, J., T.E. Parker, and C.D. Carter, Journal of Quantitative Spectroscopy and Radiative Transfer 76(3-4), p. 309-330 (2003).

8. Multiple line system successful but error levels were a concern • Error levels would be helped by including larger spectral range and sampling to produce an over determined system • Acousto Optical Tunable Filter provides a robust and luminous method of acquiring emission spectra • Scan speed can be quite high so a full spectra can be acquired in less than 1 second

9. Success of the new measurement requires several critical areas to come together • Critical issues to successful measurement • Benchmark data production • Produced burners and supporting measurements • Predictive database • Identified appropriate data base and shortcomings (CO) • Optical hardware operation • Identified critical issues for the AOTF • Data analysis and reduction • Integrated predictive data base into a nonlinear fitting program • Result is a working system • Primary difficulties are CO measurement and AOTF issues

10. Custom built premixed slot burners produce a highly controlled and quantified radiation field • Slot burners used to provide relatively long pathlengths • 3.5 inch and 7 inch pathlength • Supporting measurements include high temperature thermocouples and FTIR extractive concentration measurements • Gradients at edge quantified with thermocouples and extractive measurements • Results are a well known radiating source • Collection optics feed into either monochromator or AOTF

11. A predictive capability for spectra as a function of flow properties is critical to overall success • Significant databases available are HITRAN and RADCAL • Hitran is a line-by-line database developed for atmospheric use • Extension to high temperature is HITEMP • Radcal is a narrow band model based primarily on data acquired by Ludwig • 25 wavenumber resolution

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13. Each of the two databases have critical flaws • Hitran continuously under predicts radiance at high temperatures • Line-by-line format is attractive because of ability to correct for atmospheric absorption • Radcal is more accurate than Hitran but cannot be corrected for absorption and is inadequate for CO determination

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15. CO measurement requires development of calibration data • RADCAL wavelength resolution is not sufficient to allow monitoring of CO • No region of dominant CO radiance • Identified wavelength region that is relatively narrow in wavelength which RADCAL cannot model • Results are very promising

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17. The optical collection system is relatively compact for the overall instrument • Collection from the burner is through a fiber into the AOTF • Critical issues are: • Scattered light subtraction for AOTF • Fiber stability and collection of all emission from fiber • Calibration over same pathlength to minimize atmospheric absorption effects

18. AOTF performance was hindered by the vendor • AOTF was a dual acoustic crystal model for greater than one octave in wavelength range • Combination of wavelength range and dual crystal was beyond vendor’s capability • Result was an AOTF that operated reliably for wavelength range 1.9 to 3.3 microns

19. Data Reduction relies on nonlinearleast squares fitting techniques • System produces spectra at 12 nm intervals from 1.9 to 4.5 microns • Over determined system requires some sort of fitting to produce “best” parameters • Marquadt iteratively minimizes c2 by incorporating radiative database into the calculations • Numerical derivatives are used to determine step size and direction in iteration • Result properly accounts for interactions of parameters • Result can be “tuned” by omitting regions of the spectrum from the fitting procedure • Absorption effects • Improving accuracy for a narrow operating range

20. Overall results show an ability to produce temperature and concentrations of CO2 and H2O • The nonlinear fitting is capable or producing reasonable values for temperature and concentrations • Approximate Accuracies: • Water, 5% • Carbon Dioxide, 10 to 15% • Temperature, 2% • Experiments with acetylene show decreased accuracies

22. The measurement concept relies on the AOTF to acquire spectral information • AOTF acquires spectral data for the combined water/carbon dioxide band • Radiation from the 4.4 mm range is acquired using a bandpass filter • Critical to temperature measurements • Radiation at 4.9 mms is acquired to determine CO concentrations • Data reduction is based on the Marquadt Method • Improvements in AOTF hardware would remove the requirement for a 4.4 mm measurement

23. Conclusions • Radcal is a more appropriate data base for high temperature prediction • Hitran/HITEMP should be used with care • CSM has produced a HITRAN radiance prediction code that we will offer as freeware • Nonlinear fitting methods work well in terms of determining the system parameters when an accurate database is used • Accuracies observed ranged from 2% (Temperature) to 10% (CO2) • CO measurement region has been identified • Overall system concept is very promising