The PI has recently demonstrated that stretch and preferential diffusion can have a significant effect on laminar burning velocities and consequently on turbulent flame speeds in practical applications. This proposal is an extension of this work and will include some measurements of laminar burning velocities under low-gravity conditions in order to minimize the effects of buoyancy. The PI proposes to use an outwardly-propagating spherical laminar flame technique and a short drop tower (test time ~ 500 ms) to carry out these measurements. Specific objectives will include: (1) New measurements of unstretched laminar burning velocities and preferential-diffusion/stretch interactions (or Markstein numbers), using various fuels, oxidant/diluent mixtures and pressures. (2) Numerical simulation of both unstretched and stretched premixed flames including detailed models of chemical kinetics and multicomponent diffusion. (3) Use of these results to evaluate theoretical predictions, and to help diagnose the mechanism of preferential-diffusion/stretch interactions and estimate flame behavior under negative stretch conditions.
