Solvent effects on two-line atomic fluorescence of indium.

We aim to investigate the potential of four different organic solvents, namely, acetone, ethanol, methanol, and isopropanol, and the organic-solvent-water mixtures as a seeding medium for the two-line atomic fluorescence technique. Water is used as the reference case. Indium, which has been previously shown to have suitable spectroscopic attributes, is chosen as the thermometry species in the present study. Acetone and methanol are shown to enhance the fluorescence signal intensity the most (approximately threefold to fivefold at stoichiometric conditions) when used. Acetone and methanol are shown to improve the fluorescence emission over the entire stoichiometric envelope of flame, most significantly in the rich combustion region, as well as a twofold enhancement in the signal-to-noise ratio.

Instantaneous temperature imaging of diffusion flames using two-line atomic fluorescence.

This work investigates the first demonstration of nonlinear regime two-line atomic fluorescence (NTLAF) thermometry in laminar non-premixed flames. The results show the expediency of the technique in the study of the reaction zone and reveals interesting findings about the indium atomization process. Indium fluorescence is observed to be strongest at the flame-front, where the temperature exceeds 1000 K. The uncertainty in the deduced temperature measurement is approximately 6%. The temperature profile across the reaction zone shows good agreement with laminar flame calculations. The advantages and inherent limitations of the technique are discussed.

Development of temperature imaging using two-line atomic fluorescence.

This work aims to advance understanding of the coupling between temperature and soot. The ability to image temperature using the two-line atomic fluorescence (TLAF) technique is demonstrated. Previous TLAF theory is extended from linear excitation into the nonlinear fluence regime. Nonlinear regime two-line atomic fluorescence (NTLAF) provides superior signal and reduces single-shot uncertainty from 250 K for conventional TLAF down to 100 K. NTLAF is shown to resolve the temperature profile across the stoichiometric envelope for hydrogen, ethylene, and natural gas flames, with deviation from thermocouple measurements not exceeding 100 K, and typically ≲30 K. Measurements in flames containing soot demonstrate good capacity of NTLAF to exclude interferences that hamper most two-dimensional thermometry techniques.

Corrections to facilitate planar imaging of particle concentration in particle-laden flows using Mie scattering. Part 2: diverging laser sheets.

Part 1 describes a model to account for the effect of particles on laser sheet attenuation in flows where particles are heterogeneously distributed and where particles are small compared with the imaged volume. Here we extend the model to account for the effect of a strongly diverging light sheet, which is desirable when investigating many turbulent flows, e.g., in two-phase combustion problems. A calibration constant, C(kappa), is derived to account for the attenuation of the incident laser sheet due to extinction of the laser beam through a seeded medium. This is shown to be effective in correcting both the effect of in-plane laser sheet attenuation and out-of-plane signal trapping due to particles in a jet flow heavily seeded with 5 g/s of 25-40 microm spherical particles. In the uncorrected case, attenuation causes up to 15% error in the mean concentration and 35% error on the rms fluctuations. Selecting an appropriate C(kappa) was found to remove the error in the mean concentration and reduce error on the rms fluctuation by half. Methods to estimate or measure an appropriate value of C(kappa) are also presented.

Corrections to facilitate planar imaging of particle concentration in particle-laden flows using Mie scattering, part 1: collimated laser sheets.

Planar nephelometry is a laser-based technique of imaging the light scattered from particles to provide information about the local number density of these particles. In many seeded flows of practical interest, such as pulverized coal flames, particle loadings are sufficiently high for the incident laser beam to be severely attenuated. Measurements in these flows are therefore difficult, and limited data are available under these conditions. Laser attenuation experiments were conducted in suspensions of spherical particles in water at various concentrations. This is used to formulate a calibration for the effects of diffuse scattering and laser sheet extinction. A model for the distribution of light through a heavily seeded, light-scattering medium is also developed and is compared with experimental results. It is demonstrated that the scattered signal may be considered proportional to the local particle concentration multiplied by the incident laser power. The incident laser power varies as a function of the attenuation by obscurement. This correction for planar nephelometry images thus extends the technique to provide pseudoquantitative data for instantaneous particle concentration measurements.