George Kychakoff

Fiber‐optic evanescent field absorption sensor

Waveguide evanescent field absorption has been measured as a function of cladding refractive index and bulk absorption coefficient. A simple theory for interpreting these results has been developed. An all‐fiber species concentration sensor has been constructed and its performance characterized.

Instantaneous temperature field measurements using planar laser-induced fluorescence

A single-pulse, laser-induced-fluorescence diagnostic for the measurement of two-dimensional temperature fields in combustion flows is described. The method uses sheet illumination from a tunable laser to excite planar laserinduced fluorescence in a stable tracer molecule, seeded at constant mole fraction into the flow field. The temporal resolution of this technique is determined by the laser pulse length. Experimental results are presented for a rodstabilized, premixed methane-air flame, using the Q(1) (22) line of the nitric oxide A(2) Sigma(+) (v = 0) ? X(2)II((1/2))(v = 0) transition (lambda approximately 225.6 nm).

Quantitative flow visualization technique for measurements in combustion gases.

A quantitative flow visualization technique for combustion research is described. The method uses sheet illumination from a tunable laser to excite planar laser-induced fluorescence (PLIF) which is detected using 2-D detector. This technique has been used to make single-shot simultaneous multiple-point measurements of species concentration and has recently been extended to measurements of other properties such as temperature and velocity. The light sources, image intensifiers, detector arrays, computer hardware, and computer software needed to implement this scheme are described. The detectivity, dynamic range, spatial resolution, and temporal resolution of the technique are discussed and a recent application of the technique (to view the OH concentration in a rod-stabilized flame) is presented.

Visualization of Turbulent Flame Fronts with Planar Laser-Induced Fluorescence

This report concerns the quantitative time-resolved visualization of reaction zones in laminar, transitional, and turbulent nonpremixed flames. Two-dimensional OH molecular concentrations were measured with planar laser-induced fluorescence excited by a sheet of light (formed from a single tunable ultraviolet laser pulse) and detected with a two-dimensional, image-intensified photodiode array camera. From the resulting data details of instantaneous flame front structures (including positions, shapes, and widths) were obtained.

High resolution digital flowfield imaging of jets

High resolution digital imaging, using planar laser-induced light scattering is being developed for analysis of gaseous flowfields. High resolution image data, implying both high spatial resolution and wide signal dynamic range, can be readily processed to yield two-dimensional distributions of species concentrations and, in turn, accurate two-dimensional images of concentration gradients and turbulence scales. Critical aspects of the technique are discussed; details of the design and the performance of the imaging system are presented; and results for laminar, transitional, turbulent and birfurcating nitrogen jets, using planar-laser-induced fluorescence of biacetyl, are reported. Initial results from imaging processing and the potential implications for flowfield analysis are described

Flow visualization in low pressure chambers using laser‐induced biacetyl phosphorescence

Two optical probes, utilizing laser‐induced biacetyl phosphorescence recorded by an image‐intensified solid state camera, have been developed and used to characterize velocity fields in a low pressure chamber (similar to a plasma‐enhanced CVD reactor). The method has been demonstrated at pressures as low as 0.5 Torr; measurements at lower pressures should be possible. Reactor flow velocity fields influence gas residence times and deposition rates. The method discussed in this paper can be used to investigate these effects.

Simultaneous multiple-point measurements of OH in combustion gases using planar laser-induced fluorescence

The imaging of planar laser-induced fluorescence (PLIF) has been used for simultaneous, multiple-point measurements of OH concentration in a variety of combustion flows including a premixed laminar flat flame, a premixed turbulent flame, a sooting flame and a nonpremixed turbulent flame. Sheet illumination from a tunable laser was used to excite the fluorescence which was detected using an image-intensified, Reticon array camera. Experimental results are presented and the detectivity and resolution of the technique are discussed.

Fiberoptic Absorption/Fluorescence Combustion Diagnostics

Abstract A new application of fiberoptics to spectroscopic measurement of minor species in combustion products is discussed. Fiberoptics could be applied to other optical combustion diagnostics as well. They provide optical access to enclosed combustion systems and allow sensitive equipment to be located remotely. Optical fibers and their use are dicussed in detail, as is probe design. The two most promising spectroscopic techniques for use with fiberoptics are absorption and fluorescence. Examples of both techniques are discussed in detail. We were able to detect 30 ppm of OH (at 310 nm) in a flow reactor using our fluorescence probe. Suggestions for improvement of the technique are given.

A miniature fiberoptic probe for optical particle sizing

A miniature fiberoptic probe has been developed for in-situ particle size measurements. The probe is based on a near-forward scattering technique and makes use of a two color scheme in which one wavelength is used for the size measurement while the second wavelength is used to monitor the presence of a particle in the center of the scattering volume. Tests of the probe have shown particle size range and sensitivity similar to that observed using fixed lens train systems but with the advantages of portability, ease of remote access and inherent alignment stability.A miniature fiberoptic probe has been developed for in-situ particle size measurements. The probe is based on a near-forward scattering technique and makes use of a two color scheme in which one wavelength is used for the size measurement while the second wavelength is used to monitor the presence of a particle in the center of the scattering volume. Tests of the probe have shown particle size range and sensitivity similar to that observed using fixed lens train systems but with the advantages of portability, ease of remote access and inherent alignment stability.

Optical Fiber Probe Using Tunable Laser Absorption Spectroscopy For Combustion Measurements

A tunable laser absorption probe for remote, spatially-defined measurements of species concentration has been developed for application in combustion research. In order to demonstrate the performance of a first generation absorption probe, the non-uniform distribution of Na atoms in a laboratory flat flame has been measured.