Compact, fiber-coupled, single-ended laser-absorption-spectroscopy sensors for high-temperature environments

Abstract

The design and demonstration of a compact single-ended laser-absorption-spectroscopy sensor for measuring temperature and HO in high-temperature combustion gases is presented. The primary novelty of this work lies in the design, demonstration, and evaluation of a sensor architecture that uses a single lens to provide single-ended, alignment-free (after initial assembly) measurements of gas properties in a combustor without windows. We demonstrate that the sensor is capable of sustaining operation at temperatures up to at least 625 K and is capable of withstanding direct exposure to high-temperature (≈1000 K) flame gases for long durations (at least 30 min) without compromising measurement quality. The sensor employs a fiber bundle and a 6 mm diameter antireflection-coated lens mounted in a 1/8 NPT-threaded stainless-steel body to collect laser light that is backscattered off native surfaces. Distributed-feedback tunable diode lasers (TDLs) with a wavelength near 1392 nm and 1343 nm were used to interrogate well-characterized HO absorption transitions using wavelength-modulation-spectroscopy techniques. The sensor was demonstrated with measurements of gas temperature and HO mole fraction in a propane-air burner with a measurement bandwidth up to 25 kHz. In addition, this work presents an improved wavelength-modulation spectroscopy spectral-fitting technique that reduces computational time by a factor of 100 compared to previously developed techniques.

Compact Open-Path Sensor for Fast Measurements of CO2 and H2O using Scanned-Wavelength Modulation Spectroscopy with 1f-Phase Method

“…here I t is the transmitted intensity; α(v) represents the spectral absorbance, P is the total gas pressure; χ i is the mole fraction of the absorbing species; L is path length; T is the temperature; S j (T) and φ j are the line-strength and the line-shape function of transition j. A similar model can be found in the literature, where Hanson et al employs an approximation formula 1 − α(v) ≈ exp (−α(v)) for weak absorption and expanded the expression in a Fourier cosine series [28,30,33]. The Fourier series of the spectral absorbance κ(v) are given by:…”

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

“…SE-LAS MIR sensors based on QCLs have also been developed for simultaneous in situ measurements of H 2 O, CO 2 , CO, and temperature in combustion flows [132]. Most recently, C. S. Goldenstein has designed and demonstrated a compact SE-LAS sensor for measuring temperature and H 2 O in high-temperature combustion gases by collecting laser light backscattered off native surfaces [133]. The SE-LAS sensor achieved an optical collection efficiency and provided a measurement accuracy and precision that is similar to or better than the conventional line-of-sight-based LAS sensor.…”

Study on spectral lines to improve the measurement accuracy of H2O molecular concentration based on TDLAS technology

“…H2O is an important molecule in the atmosphere, which is closely related to climate change and industrial applications (such as combustion process), and its concentration change has a great impact on the earth's ecology and industrial production [1][2][3][4][5] . For combustion, H2O is a wide range of combustion products, and its concentration can indirectly reflect the combustion situation to improve combustion efficiency; In flue gas treatment, the H2O content will affect the catalytic effect of the catalyst.…”