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A Study of Two Dimensional Tomography Reconstruction of Temperature and Gas Concentration in a Combustion Field Using TDLAS
摘要： Based on tunable diode laser absorption spectroscopy (TDLAS), two-dimensional (2D) distribution reconstructions of gas concentration and temperature are realized using an algebraic reconstruction technique (ART). The influence of the beam distribution and grid size on combustion field reconstruction is investigated to attain optimal reconstruction results with a limited number of beams. Under limited optical-path numbers, it shows that a better spatial resolution is attainable only when the laser beam paths are vertical and parallel to the symmetry axis of the combustion field. Furthermore, experiments with 16 beam paths using one and two flat flame combustion fields are carried out in different fuel-air equivalence ratios under room temperature. The results are in agreement with the simulation results, and the time resolution is less than 1 s.
关键词： tomographic imaging,diode lasers,temperature,spectroscopy,combustion diagnostics,absorption
更新于2025-09-23 15:23:52
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Diffuse-reflection-based single-ended laser absorption sensor for H2O temperature and concentration in kerosene-fuelled combustor
摘要： The design, optimization and demonstration of a compact, single-ended laser absorption sensor based on diffuse-wall-reflected signal is presented for temperature and H2O concentration measurements in a kerosene-fuelled aero-combustor. Challenges of laser measurements in such harsh, practical combustion environments involve strong beam-steering, low signal-to-noise ratio (SNR), and constrained optical access. We here present detailed characterization and optimization procedure of a single-ended optical configuration using a holed off-axis parabolic mirror as the pitch and catch optics, and the coked wall surface of the combustor as a diffuse reflector. A near-infrared distributed-feedback diode laser near 1.4 μm scanned at 1 kHz for direct absorption detection was used to access two H2O transitions for concentration and temperature measurement. Optical system design and adaptive Savitzky-Golay signal processing algorithm was used for noise suppression and SNR amelioration. The sensor was demonstrated under practical conditions in a kerosene-fuelled swirl combustor. High signal fidelity was achieved and allowed for single-scan H2O concentration detection limit of 122 ppm-m-Hz-1/2 despite a low reflected laser intensity level of ~50 μW. In situ, time-resolved measurements detected temperatures ranging from ~1100 K to 1300 K, and H2O concentration ranging from ~8% to 12% as global equivalence ratio varied between 0.2 and 0.45. The results revealed expected trend while demonstrating much faster response and less delay versus a comparing thermocouple. This successful field manifestation provides direct proof for the robustness and reliability of diffuse-reflection-based single-ended sensor system in engine combustion chamber environments.
关键词： single-ended,turbulent environment,combustion diagnostics,laser absorption sensing,kerosene-fuelled combustor
更新于2025-09-23 15:19:57
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Express: Time-Gated Single-Shot Picosecond Laser-Induced Breakdown Spectroscopy (ps-LIBS) for Equivalence-Ratio Measurements
摘要： Time-gated picosecond laser-induced breakdown spectroscopy (ps-LIBS) for the determination of local equivalence ratios in atmospheric-pressure adiabatic methane–air flames is demonstrated. Traditional LIBS for equivalence-ratio measurements employ nanosecond (ns)-laser pulses, which generate excessive amounts of continuum, reducing measurement accuracy and precision. Shorter pulse durations reduce the continuum emission by limiting avalanche ionization. Furthermore, by contrast the use of femtosecond lasers, plasma emission via picosecond-laser excitation has high signal-to-noise ratio (S/N), allowing single-shot measurements suitable for equivalence-ratio determination in turbulent reacting flows. We carried out an analysis of the dependence of the plasma emission ratio Hα (656 nm)/NII (568 nm) on laser energy and time-delay for optimization of S/N and minimization of measurement uncertainties in the equivalence ratios. Our finding shows that higher laser energy and shorter time delay reduces measurement uncertainty while maintaining high S/N. In addition to atmospheric-pressure flame studies, we also examine the stability of the ps-LIBS signal in a high-pressure nitrogen cell. The results indicate that the plasma emission and spatial position could be stable, shot-to-shot, at elevated pressure (up to 40 bar) using a lower excitation energy. Our work shows the potential of using ps-duration pulses to improve LIBS-based equivalence-ratio measurements, both in atmospheric and high-pressure combustion environments.
关键词： time-resolved spectroscopy,combustion diagnostics,Laser-induced breakdown spectroscopy,picosecond phenomena,LIBS
更新于2025-09-19 17:13:59