Infrared laser-absorption sensing for combustion gases

Abstract

Infrared laser-absorption spectroscopy (IR-LAS) sensors play an important role in diagnosing and characterizing a wide range of combustion systems. Of all the laser-diagnostic techniques, LAS is arguably the most versatile and quantitative, as it has been used extensively to provide quantitative, species-specific measurements of gas temperature, pressure, composition and velocity in both laboratory-and industrial-scale systems. Historically, most IR-LAS work has been conducted using tunable diode lasers, however, today's researchers have access to a wide range of light sources that provide unique sensing capabilities and convenient access to nearly the entire IR spectrum (≈1 to 20 μm). In particular, the advent of room-temperature wavelength-tunable mid-infrared semiconductor lasers (e.g., interband-and quantum-cascade lasers) and hyperspectral light sources (e.g., Fourierdomain mode-locked lasers, dispersed supercontinuum lasers, and frequency combs) has provided a number of unique capabilities that combustion researchers have exploited. The primary goal of this review paper is to document the recent development, application, and current capabilities of IR-LAS sensors for laboratory-and industrial-scale combustors and propulsion systems. A thorough review and description of the fundamental spectroscopy governing the accuracy of such sensors, and recent findings and databases that enable improved modeling of molecular absorption spectra will be provided. Modern light sources and the most commonly used diagnostic techniques are also discussed.

Ultrafast laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH4 in flames

“…Laser-absorption spectroscopy (LAS) is a powerful technique for non-invasive, quantitative measurements of temperature and species concentrations in combustion environments (1). LAS diagnostics often employ narrowband, wavelengthtunable lasers (e.g., tunable diode lasers, quantum-cascade lasers) which are capable of measuring gas conditions via spectra measured over several cm −1 at rates up to 1 MHz (1,2).…”

“…Laser-absorption spectroscopy (LAS) is a powerful technique for non-invasive, quantitative measurements of temperature and species concentrations in combustion environments (1). LAS diagnostics often employ narrowband, wavelengthtunable lasers (e.g., tunable diode lasers, quantum-cascade lasers) which are capable of measuring gas conditions via spectra measured over several cm −1 at rates up to 1 MHz (1,2). While highly useful, the narrowband nature of this approach can: 1) limit the dynamic range of such diagnostics (3), 2) complicate measurements of molecules with broad spectra (e.g., at high pressures), and 3) often prevents multispecies measurements using a single light source.…”

Laser absorption spectroscopy for combustion diagnosis in reactive flows: A review

“…Some representative techniques mainly include laser absorption spectroscopy (LAS) (11)(12)(13)(14), laser induced fluorescence (LIF) (15,16), laser induced breakdown spectroscopy (LIBS) (17,18), photoacoustic spectroscopy (PAS) (19,20) and coherent anti-Stokes Raman scattering (CARS) (21)(22)(23). With respect to the target physical parameters and measurable dimensions illustrated in Table 1, each of these laser spectroscopic techniques has its superiority and feasibility to specific applications in the field of combustion research.…”

“…To be specific, LAS is implemented by monitoring the absorbance while the laser wavelength is scanned over a certain spectral range for an absorbing species. Line-of-sight LAS has been validated to quantitatively measure the path-averaged temperature, species concentrations, pressure and velocity in the combustion fields (11). Spatially resolved 1D and 2D distributions of the parameters in the reacting flows are enabled by the combination of LAS and hard-field tomography (24).…”

Optics and Spectroscopy for Fluid Characterization

“…The large number of review articles that are frequently published in these areas is evidence of this. Recent examples have focused on applications of optical diagnostics to gas phase environments [1][2][3][4][5], liquids [1,4,6,7], and multiphase systems [7][8][9][10]. A key feature of such light-based methods is that they are usually non-intrusive, and hence they do not notably affect the system under investigation.…”