Laboratory crestCombustion andLaser Sensing Laboratory
中文EN

CLS · RESEARCH AREAS

Optical Diagnostics and Multidimensional Imaging

Developing advanced optical diagnostics and multidimensional imaging for combustion and multiphase reacting flows to reveal the spatial and temporal evolution of flow, heat transfer and chemical reactions.

Swirler-stabilized ammonia flame, laser optics and ICCD camera: an optical-diagnostics concept illustration

Overview

Flow structures and chemical reactions interact during combustion, together determining flame stability and pollutant formation. Detailed measurements of temperature, species and velocity distributions are essential for understanding reacting flows and flame dynamics. We use light–matter interactions to develop optical diagnostics that resolve spatial structures and transient changes in flow fields, with a particular focus on laser absorption spectroscopy (LAS) and tomographic reconstruction, complemented by imaging of multiphase reacting flows. Reliable quantitative measurements provide experimental evidence for understanding combustion processes, evaluating numerical models and improving device design.

Research themes

Laser absorption spectroscopy and tomographic reconstruction

Using tunable laser absorption spectroscopy, we investigate spectral-line selection, signal analysis and quantitative temperature and species-concentration measurements for combustion environments. By arranging optical paths at different positions and viewing angles, we use tomography to reconstruct spatial distributions from line-integrated absorption signals. Particular attention is given to the effects of high-temperature spectroscopic models, flow-field nonuniformity, limited observations and measurement noise on reconstruction, improving spatial resolution and reliability in complex reacting flows.

Diagnostics of multiphase reacting flows and flame dynamics

We use particle image velocimetry (PIV) to measure velocity fields and characterize recirculation, shear and turbulence structures. Phase Doppler particle analysis (PDPA) provides spray-droplet size and velocity measurements for studies of atomization, transport and gas–liquid interactions. Combined with reaction-zone imaging, these measurements reveal how fuel mixing, droplet evaporation and combustion influence one another, and clarify the relationships among flow fluctuations, vortical structures and flame response. Soot formation and transport are also included in our optical characterization of multiphase reacting flows.

Imaging temperature and species-concentration fields

We combine laser absorption, laser-induced fluorescence (LIF), emission spectroscopy and infrared imaging to investigate multidimensional, time-resolved measurements of temperature and key species-concentration fields. For different species and measurement conditions, we establish quantitative relationships between optical signals and the quantities of interest by accounting for molecular excitation, collisional quenching and radiative transfer. Our focus is on the spatial distributions and transient evolution of reaction zones, localized high-temperature regions and combustion pollutants, providing experimental evidence for interactions among mixing, reactions and heat transfer.

Advanced spectroscopy for reacting flows

We explore dispersion spectroscopy for combustion reacting flows, using gas-induced changes in optical phase to obtain information on species and thermodynamic states. This work examines the complementary roles of absorption and dispersion measurements and methods for extracting signals in complex environments. We also seek to explore broadband, high-resolution techniques such as optical frequency-comb and dual-comb spectroscopy for simultaneous multispecies measurements, analysis of overlapping spectra and diagnostics of transient reactions, extending the information available from conventional measurements using a small number of spectral lines.

Future directions

Future research will address complex combustion flows in power systems such as hydrogen engines and gas turbines, developing diagnostics for high temperatures and pressures and rapid transients to investigate flame propagation, combustion instabilities and pollutant formation. By combining spectroscopic models with machine-learning algorithms, we aim to improve reconstruction and imaging from limited observations, providing reliable data for reacting-flow model validation and power-system optimization.

Related publications

  1. Characterization of the non-uniform thermochemical structure of laminar premixed stagnation flame using mid-infrared laser absorption tomography

    T. Wan, Y. Liu*, W. Shao, S. Zhang, Y. Huang, L. Ma*

    Case Studies in Thermal Engineering · 2026; 78: 107707

    Combines mid-infrared laser absorption with tomographic reconstruction to quantify temperature and water-vapor concentration distributions in premixed stagnation flames, revealing nonuniform thermochemical structures.

  2. Spatially and temporally resolved temperature measurements in counterflow flames using a single interband cascade laser

    D. Wen, Y. Wang*

    Optics Express · 2020; 28(25): 37879–37902

    Uses mid-infrared laser absorption spectroscopy for spatially and temporally resolved temperature measurements in counterflow flames, demonstrating its application to nonuniform, unsteady reacting flows.

  3. Infrared imaging for two-dimensional soot and temperature measurements in laminar premixed and non-premixed flames

    J. Zhou, L. Xu*, J. Du, L. Ma, Y. Wang*

    Journal of the Energy Institute · 2025; 120: 102111

    Uses infrared imaging for two-dimensional measurements of flame temperature and soot, contributing to radiative measurement methods and reacting-flow imaging.

  4. Establishment of highly controllable unsteady counterflow diffusion flames and their time-varying flow-field characteristics (in Chinese)

    余超, 李国柱, 周梦祥, 王宇*

    Journal of Xi’an Jiaotong University · 2023; 57(2): 49–56

    Investigates controlled unsteady counterflow flames and their time-varying flow fields, providing an experimental basis for analyzing flow disturbances and flame dynamics.

  5. Calibration-free heterodyne phase-sensitive dispersion spectroscopy: Quantitative gas sensing and recovery of absorption spectra

    L. Ma, C. Zhou, Z. Wang, W. Ren, Y. Wang*

    Optics Express · 2024; 32(21): 37492–37515

    Investigates quantitative measurements and absorption-spectrum recovery using heterodyne phase-sensitive dispersion spectroscopy, providing a methodological basis for advanced spectroscopy in reacting-flow diagnostics.

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