Measurements of the three-dimensional structure of flames at low turbulence

The development of spark-ignited flame kernels in a turbulent field is strongly dependent upon the nature of the three-dimensional (3-D) turbulence adjacent to the ignition source. The turbulence scales vary in 3-D from shot to shot, resulting in successive flame kernels developing differently and thereby causing cyclic variations in, for example, spark ignition engines. It is necessary to quantify the scales affecting the flame at any instant for the accurate measurement of burn rate of such flame kernels, which requires visualization of the flame surface in 3-D. The experiments reported here employ a multiple sheet mie-scattered light technique to successfully characterize a nonstabilized expanding turbulent flame kernel in 3-D. A novel algorithm was developed to construct the flame surface in 3-D, which enabled accurate calculation of parameters such as flame surface density, reaction progress variables, and turbulent flame thickness.