Structure of a Laminar Premixed Flame with Spatially Non-uniform Stretch Rate

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To gain further understanding of turbulent combustion, I investigated experimentally the structures of a laminar premixed flame with spatially non-uniform stretch effect. A flame surface with stretch rate variation was formed by creating a wrinkled laminar premixed flame in a spatially periodic flow field of a lean propane/air mixture, and the relation between flame stretch and flame temperature was discussed from the velocity and temperature distributions. The velocity or temperature was measured using PIV or thermocouple, respectively.The measured flame temperature was lower/higher than the adiabatic flame temperature at flame segments with positive/negative stretch rates. This was a result of flame stretch and Lewis number effect for Lewis number greater than unity. The flame temperature estimated using the conventional theory of flame stretch and Lewis number effect, which is based on a uniform stretch rate along the flame surface, did not agree quantitatively with the measured temperature. Therefore, I revised the theory, taking into account heat transfers along the flame surface and toward the burned gas, and then produced estimates that agreed quantitatively with the measured temperature. I found that flame stretch and Lewis number effect is changed along the flame surface which has spatially stretch rate variation, causing a temperature gradients along the surface and toward the burned gas, which in turn transfer heat and change the flame temperature. Thus, such heat transfers are important factors in estimating flame temperature. In addition, it is clarified that the heat transfer along the flame surface affects more than that toward the burned gas.