Thermometry of an oxy-acetylene flame using multiplex degenerate four-wave mixing of C2

Progress in Energy and Combustion Science

2011

131

112

Laser-based methods have transformed combustion diagnostics in the past few decades. The high intensity, coherence, high spectral resolution and frequency tunability available from laser radiation has provided powerful tools for studying microscopic processes and macroscopic phenomena in combustion by linear and nonlinear optical processes. This review focuses on nonlinear optical techniques based on resonant four-wave mixing for non-intrusive measurements of minor species in combustion. The importance of minor species such as reaction intermediates is outlined together with the challenges they present for detection and measurement in the hostile environments of flames, technical combustors, and engines. The limitations of conventional optical methods for such measurements are described and the particular advantages of coherent methods using nonlinear optical techniques are discussed.The basic physics underlying four-wave wave mixing processes and theoretical models for signal calculation are then presented together with a discussion of how combustion parameters may be derived from analysis of signals generated in various four-wave mixing processes. The most important four-wave mixing processes, in this context, are then reviewed:Degenerate Four-Wave Mixing (DFWM), Coherent Anti-Stokes Raman Scattering (CARS), Laser Induced Grating Spectroscopy (LIGS) and Polarization Spectroscopy (PS). In each case the fundamental physics is outlined to explain the particular properties and diagnostic advantages of each technique. The application of the methods mentioned to molecular physics studies of combustion species is then reviewed along with their application in measurement of concentration, temperature and other combustion parameters. Related nonlinear techniques and recent extensions to the ultra-fast regime are briefly reviewed. Finally practical considerations relevant to multi-dimensional and multi-species measurements, as well as applications in technical combustion systems are discussed.Keywords: nonlinear optical spectroscopy, four-wave mixing, combustion diagnostics, minor species detection, laser-induced gratings, polarization spectroscopy IntroductionEnergy from renewable sources such as solar and wind power is the goal of much current research and technological development. Combustion, however, is and is likely to remain for the foreseeable future, the most important energy source for heat, electrical power and especially for transportation. In technical combustion systems the chemical energy of fossil fuels such as coal, crude oil and natural gas is converted into heat through oxidation with oxygen from air. However, fossil fuel resources are limited and alternatives like biofuels [1] or novel technologies such as fuel cells [2] are not yet able to meet the demand. Consequently, for a sustainable use of fossil fuels it is desirable to further improve the efficiency, maintainability and reliability of existing combustion devices. Achieving such improvements depends upon an improved understanding of t...

Section: The Potential Of Resonant Dfwm For Thermometry Was Demonstramentioning

confidence: 99%

Section: Multi-species and Multiplex Measurementsmentioning

confidence: 99%

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Kiefer

Progress in Energy and Combustion Science

2011

131

112

“…The use of multiplex DFWM spectroscopy of C 2 , again yielding Doppler broadened spectra, has been demonstrated for single-shot temperature measurements in the oxy-acetylene flame. 11 In the work reported here DFWM in the phase conjugate geometry, which uses counterpropagating pump beams, was applied for the first time in the oxy-acetylene flame for the spectroscopy of C 2 . The use of counterpropagating pump beams leads to a signal beam which counterpropagates with the probe and, consequently, the effective elimination of Doppler broadening provided the laser linewidth is significantly less than the Doppler width.…”

Section: Introductionmentioning

confidence: 99%

Degenerate four-wave mixing spectroscopy and spectral simulation of C2 in an atmospheric pressure oxy-acetylene flame

Kaminski

Hughes

The Journal of Chemical Physics

1997

Self Cite

Rotational level dependence of ground state recovery rates for OH X 2 Π(v ″ =0) in atmospheric pressure flames using the picosecond saturating-pump degenerate four-wave mixing probe technique Highly predissociative levels of the D 2 Π state of CH studied with the two-color resonant four-wave mixing technique Absolute HCO concentration measurements in methane/air flame using intracavity laser spectroscopyThe d 3 ⌸ g ↔a 3 ⌸ u Swan bands of C 2 have been recorded with high resolution using DFWM in the nearly Doppler free, phase conjugate geometry. C 2 was probed in a standard oxy-acetylene welding flame with excellent signal-to-noise ratio and spectral resolution. Theoretical spectra were simulated and fitted directly to the complex overlapping spectra. The good agreement obtained shows that DFWM holds promise to become a robust and reliable tool for flame thermometry. Current theories of DFWM are reviewed in context of the present work and advantages and disadvantages of the technique are discussed.

“…The principles and practice of multiplex FWM for thermometry have been described in detail elsewhere, 7 and we outline here only the basics and relevant experimental details. In this work we focus on broadband FWM spectra of C 2 recorded using the d 3 ⌸ g -a 3 ⌸ u (0,0) Swan band system.…”

Section: Multiplex Fwm Thermometrymentioning

confidence: 99%

“…Broadband DFWM has been demonstrated and applied to thermometry in OH and C 2 . [5][6][7][8] In principle a temperature can be derived from the relative intensity of only two spectral lines, and this principle has been exploited for two-dimensional ͑2D͒ imaging of temperature fields in flames. 9,10 For point measurements the accuracy and precision of temperature measurements is improved by recording spectra over many transitions and hence monitoring the relative populations of a large number of thermally populated energy levels.…”

Section: Introductionmentioning

confidence: 99%

Optical dephasing effects in broadband four-wave mixing in C2: Implications for broadband FWM thermometry

Lloyd

The Journal of Chemical Physics

2002

Self Cite

The effects have been studied of increasing laser bandwidth and intensity on temperatures derived from broadband four-wave mixing (FWM) spectra. A simple model of optical dephasing arising from pumping of coupled transitions is presented and validated by experimental measurements. The model is found to predict qualitatively the effect on relative spectral intensity in broadband FWM of increasing bandwidth and input intensity. The implications for thermometry are discussed to indicate the circumstances in which accurate and precise temperatures may be derived from broadband FWM spectra.