الفهرس 
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Abstract
One of the most recently applied laser-based techniques in combustion environment is the Laser Induced Breakdown Spectroscopy (LIBS). The technique has been extensively and successfully applied to elemental concentration measurements in solids and liquids. The LIBS signal is much weaker in gases and hence more work is required for quantitative measurements in flames. The application of the Laser Induced Breakdown Spectroscopy (LIBS) technique for quantitative mixture fraction measurements in flames is addressed in this thesis. In the present work an orthogonal dual–pulse Nd:YAG lasers are used that operate at the fundamental wavelength with laser pulse energy of about 100 mJ/pulse. The measured spectra in different mixtures of natural gas and air are used to obtain the calibration parameters for local elemental mass fraction measurements and hence calculate the mixture fraction. The data are compared with the mixture fraction calculations based on the ratios of the spectral lines of H/N elements, H/O elements and C/(N+O) and show good agreement within the reaction zone of the flames. Some slight deviations are observed outside the reaction zone. This suggests that quantitative mixture fraction measurements using LIBS in turbulent flames are possible. The current developed technique is used to study the flame structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner. The data are presented as radial profiles of the average elemental mass fractions and their standard deviation. In addition the equivalence ratio and mixture fraction are also presented and discussed. The data describe the structure and show consistent profiles with both the degree of partial premixing and the level of Reynolds number for the flames near extinction. The mixing of the fuel and air above the cone is clear where the peaks of the fuel elements are detected at the outer layer where the fuel is injected at the early position. At downstream positions the fuel is diffused into the centerline where the concentrations of the fuel elements are increased. The stoichiometric mixture fraction is detected at the outer layer where the flame exists.Keywords: mixture fraction, LIBS, partial premixing flames.