Planar Laser-Induced Fluorescence and Chemiluminescence Analyses of CO2-Argon-Steam Oxyfuel (CARSOXY) Combustion

Strict regulations and acts have been imposed to limit NOx and carbon emissions. The power generation industry has resorted to innovative techniques to overcome such a low level of tolerance. Amongst those in the literature, CO2-argon-steam oxyfuel (CARSOXY) gas turbines have theoretically been proven to offer an economically sustainable solution while retaining high efficiency. Although theoretical studies have characterized CARSOXY, no experimental evidence has been provided in the literature. Therefore, this paper attempts to experimentally assess CARSOXY in comparison to a CH4/air flame. OH* chemiluminescence integrated with OH Planar Laser-Induced Fluorescence (PLIF) imaging has been utilized to study flame stability and flame geometry (i.e., the area of highest heat intensity (AOH¯Max center of highest heat intensity (COH¯Max)) over a range of working fluid Reynolds’ numbers and oxidizing equivalence ratios. In addition, the standard deviation of heat release fluctuations (σOH*/OH¯) has been utilized as the base-criteria to compare the stability performance of CARSOXY to CH4/air combustion. Moreover, turbulence-chemistry interactions have been described using Damköhler numbers and by plotting Borghi regime diagrams. This paper suggests a modified numerical approach to estimate Damköhler numbers and plot regime diagrams for non-premixed combustion by utilizing the Buckingham π theorem based on experimental observations and results. CARSOXY flames showed lower flame intensity than that of the CH4/air flame throughout the entire Re interval by approximately 16%, indicating higher heat release. The Damköhler numbers of the CARSOXY flame were also greater than those of the CH4/air flame in all conditions, indicating more uniform CARSOXY flames. It was found that the tendency of the CARSOXY flame of approaching the concentrated reaction zone is greater than that of the CH4/air flame.

Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement—laser-induced fluorescence photobleaching anemometer (LIFPA)—has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the photobleaching process of LIFPA, an approximation of uniform laser distribution was applied. This is different from the actual condition where the laser power density distribution is normally Gaussian. In this investigation, we numerically studied the photobleaching process of fluorescent dye in the laser focus region, according to the convection–diffusion reaction equation. The profiles of effective dye concentration and fluorescence were elucidated. The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient is revealed. With the established model, we further discuss the effective spatial resolution of LIFPA and study the influence of the detection region of fluorescence on the performance of the LIFPA system. It is found that at sufficiently high excitation laser power density, LIFPA can even achieve a super-resolution that breaks the limit of optical diffraction. We hope the current investigation can reveal the photobleaching process of fluorescent dye under high laser power density illumination, to enhance our understanding of fluorescent dynamics and photochemistry and develop more powerful photobleaching-related flow diagnostic techniques.

Laser-induced fluorescence experimental spectroscopy and theoretical calculations of uranium monoxide

As a model molecule of actinide chemistry, UO molecule plays an important role in understanding the electronic structure and chemical bonding of actinide-containing species. We report a study of the laser-induced fluorescence spectra of the U16O and U18O using two-dimensional spectroscopy. Several rotationally resolved excitation spectra were investigated. Accurate molecular rotational constants and equilibrium internuclear distances were reported. Low-lying electronic states information was extracted from high resolution dispersed fluorescence spectra and analyzed by the ligand field theory model. The configuration of the ground state was determined as U2+(5f37s)O2-. The branching ratios, and the vibrational harmonic and anharmonic parameters were also obtained. Radiative lifetimes were determined by recording the time-resolved fluorescence spectroscopy. Transition dipole moments were calculated using the branching ratios and the radiative lifetimes. These findings were elucidated by using quantum-chemical calculations, and the chemical bonding was also analyzed. The findings presented in this work will enrich our understanding of actinide-containing molecules.

Design of a High Uniformity Laser Sheet Optical System for Particle Image Velocimetry

Particle image velocimetry (PIV) is a non-contact, instantaneous and full-flow velocity measurement method based on cross-correlation analysis of particle image. It is widely used in fluid mechanics and aerodynamics. Laser sheet optical system is one of the key equipment of PIV, and it is an important guarantee to obtain high definition particle image. In the PIV measurement task of large low speed wind tunnel, in order to solve the problem of sheet light illumination uniformity of large size model and take into account the requirements of PIV technology on the thickness of the sheet light, a hybrid algorithm is used to design a high uniformity laser sheet optical system based on the theory of physical optics. The simulation results show that the size of the sheet light is 400 mm ×1 mm, the diffraction efficiency reaches 97.77%, and the non-uniformity is only 0.03%. It is helpful to acquire high-resolution images of particles in the full field of view. It also can be applied to a series of non-contact flow field measurement techniques such as plane laser induced fluorescence, filtered Rayleigh scattering and two-color plane laser induced fluorescence temperature measurement.