In this work, turbulent premixed combustion was analyzed through CH (methylidyne) planar laser induced fluorescence (PLIF). Flame topography measurements in terms of flame surface density and curvature were calculated based on the flame front detected by the CH PLIF signal. The goal of this work was to investigate turbulent flames with extremely high turbulence intensity using a recently developed HiPilot burner (a Bunsen-type burner). The studies were first conducted on a series of piloted jet flames to validate the methodology, and then conducted on the highly turbulent flames generated by the HiPilot burner. All flames were controlled by combusting methane and air under a fuel to air equivalence ratio of Φ=1.05, and the Reynolds number varied from 7,385 to 28,360. Flame surface density fields and profiles for the HiPilot burner are presented. These flame surface density measurements showed an overall decrease with height above the burner. In addition, curvature statistics for the HiPilot flames were calculated and probability density functions of the curvature samples were determined. The probability density functions of curvature for the flames showed Gaussian-shaped distributions centered near zero curvature. To conclude, flame topography measurements were verified on jet flames and were demonstrated on the new HiPilot flames. / Master of Science / Optical diagnostics are powerful techniques that enable the study of turbulent flames without physical interruption. The optical diagnostic technique in this thesis implemented planar laser induced fluorescence. In planar laser induced fluorescence, a laser is used to excite a specific molecular species present within a two-dimensional plane in the flame. The excited species releases the extra energy by emission of light which is the signal captured on a camera. One useful purpose of using optical diagnostics, such as planar laser induced fluorescence, is the ability to image the flame structure of turbulent flames. The flame structure is significant for two reasons. First, the flame structure details how the chemistry of the flame interacts with the turbulent flow field. Second, the flame structure is directly related to the burning rate of the reactants. The primary contribution of this thesis investigated the two-dimensional flame structure of a newly designed burner named the HiPilot burner. However, in order to strengthen the fidelity of the methods for determining certain flame structure quantities a precursive analysis on the classical jet flame was completed. The results acquired show structural measurements of the HiPilot flames which contribute to the repository of data for the combustion community

Turbulent premixed propane/air and methane/air flames were studied using planar Rayleigh scattering and particle image velocimetry on a stabilized Bunsen type burner. The fuel-air equivalence ratio was varied from Φ=0.7 to 1.0 for propane flames, and from Φ=0.6 to 1.0 for methane flames. The non-dimensional turbulence intensity, u'/SL (ratio of fluctuation velocity to laminar burning velocity), covered the range from 3 to 24, equivalent to conditions of corrugated flamelets and thin reaction zones regimes. Temperature gradients decreased with the increasing u'/SL and levelled off beyond u'/SL > 10 for both propane and methane flames. Flame front thickness increased slightly as u'/SL increased for both mixtures, although the thickness increase was more noticeable for propane flames, which meant the thermal flame front structure was being thickened. A zone of higher temperature was observed on the average temperature profile in the preheat zone of the flame front as well as some instantaneous temperature profiles at the highest u'/SL. Curvature probability density functions were similar to the Gaussian distribution at all u'/SL for both mixtures and for all the flame sections. The mean curvature values decreased as a function of u'/SL and approached zero. Flame front thickness was smaller when evaluated at flame front locations with zero curvature than that with curvature. Temperature gradients and FSD were larger when the flame curvature was zero. The combined thickness and FSD data suggest that the curvature effect is more dominant than that of the stretch by turbulent eddies during flame propagation. Integrated flame surface density for both propane and methane flames exhibited no dependance on u'/SL regardless of the FSD method used for evaluation. This observation implies that flame surface area may not be the dominant factor in increasing the turbulent burning velocity and the flamelet assumption may not be valid under the conditions studied. Dκ term, the product of diffusivity evaluated at conditions studied and the flame front curvature, was a magnitude smaller than or the same magnitude as the laminar burning velocity.

Turbulent premixed propane/air and methane/air flames were studied using planar Rayleigh scattering and particle image velocimetry on a stabilized Bunsen type burner. The fuel-air equivalence ratio was varied from Φ=0.7 to 1.0 for propane flames, and from Φ=0.6 to 1.0 for methane flames. The non-dimensional turbulence intensity, u'/SL (ratio of fluctuation velocity to laminar burning velocity), covered the range from 3 to 24, equivalent to conditions of corrugated flamelets and thin reaction zones regimes. Temperature gradients decreased with the increasing u'/SL and levelled off beyond u'/SL > 10 for both propane and methane flames. Flame front thickness increased slightly as u'/SL increased for both mixtures, although the thickness increase was more noticeable for propane flames, which meant the thermal flame front structure was being thickened. A zone of higher temperature was observed on the average temperature profile in the preheat zone of the flame front as well as some instantaneous temperature profiles at the highest u'/SL. Curvature probability density functions were similar to the Gaussian distribution at all u'/SL for both mixtures and for all the flame sections. The mean curvature values decreased as a function of u'/SL and approached zero. Flame front thickness was smaller when evaluated at flame front locations with zero curvature than that with curvature. Temperature gradients and FSD were larger when the flame curvature was zero. The combined thickness and FSD data suggest that the curvature effect is more dominant than that of the stretch by turbulent eddies during flame propagation. Integrated flame surface density for both propane and methane flames exhibited no dependance on u'/SL regardless of the FSD method used for evaluation. This observation implies that flame surface area may not be the dominant factor in increasing the turbulent burning velocity and the flamelet assumption may not be valid under the conditions studied. Dκ term, the product of diffusivity evaluated at conditions studied and the flame front curvature, was a magnitude smaller than or the same magnitude as the laminar burning velocity.