الفهرس 
Cover EnglishOnly 14 pages are availabe for public view
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Abstract
The design of practical combustion system must ensure a flexible range of operating condition and comply with the increasingly tighter pollution restrictions. Partially premixed flames, defined as flames where the mixture is inhomogeneous and varies from fuel-rich to stoichiometry and fuel-lean, are found in many engineering applications. In modern internal combustion engines, using multiple injections of fuel to control emissions, partially premixed environment is typically formed before ignition. The aim of this work is to present a comprehensive study for the effect of coflow on the flame stability of partially premixed Propane flames in a concentric flow conical nozzle (CFCN) burner. Also, structure and flow field of some selected cases are presented using high-speed Stereoscopic Particle Image Velocimetry, SPIV, plus OH Planar Laser-Induced Fluorescence, OH-PLIF, followed by Simultaneous PIV/OH-PLIF. In addition, the effects of the mixing fields on the structure and stability of partially premixed NG flames. The flame stability is first mapped then the mixing field in a concentric flow conical nozzle (CFCN) burner with wellcontrolled mechanism of the mixing is investigated using Rayleigh scattering technique. The experimental data of the mixing field cover wide ranges of Reynolds numbers, equivalence ratios and mixing lengths. The results show that higher stability of partially premixed flames as compared to non-premixed flames has been observed and the flame is stable between two extinction limits of mixture inhomogeneity, and the optimum stability is obtained at certain degree of mixture inhomogeneity. Increasing the coflow velocity leads to a stronger recirculation zone and improves the flame stability with co flow. The time averaged SPIV results show that the coflow induces a large annular recirculation zone surrounding the jet flames. The size and location of this zone is seen to be sensitive to coflow velocity. However, the instantaneous images show the existence of a small vortical structure close to the shear layer, where the flame resides there in the case of no-coflow. These small vertical structures are seen to play a vital role in the flame structure, and increasing the flame corrugation close to the nozzle exit. Additionally, the mixing field is significantly affected by the mixing length and the air-to-fuel velocity ratios. The Reynolds number has a minimum effect on the mixing field in high turbulent regime and the stability is significantly affected by the turbulence level. The temporal fluctuations in the range of mixture fraction within the mixing field correlate with the flame stability. The highest point of stability occurs at recess distances where fluid mixtures near the jet exit plane are mostly within the flammability limits.