Laminar flame structures in meso-scale experiments
Laminar flame structures have been investigated through the whole history of combustion studies. Various flame structures have been introduced such as a premixed flame, a diffusion flame, an edge flame and a flame ball. However, we do not have a generalized theory that can connect all these flame structures. One additional notable fact is that each flame structure has respective characteristic scales in length and time. For instance, a premixed flame has a flame thickness and a reaction time, which determines the burning velocity. Similarly, a diffusion flame has a flame thickness and the diffusion time scale, which determines the scalar dissipation rate. Therefore, understanding the relationship between the characteristic length scales and the time scale is the starting line in the combustion studies, and so many studies have been conducted related to these issues. However, difference of the diffusivities in mass, momentum, and energy equations made this problem difficult. How can we escape from this endless tread mill? We may need to understand the scale effects of mass transfer, momentum transfer, and heat transfer on the real flame structures having multi-dimensional inherent characteristics. It will be the most important thing as well in designing of a new combustion system at a new combustion environment in the future. In this talk, various meso-scale test burners will be introduced such as a meso-scale opposed-flow-burner, an annular-stepwise-diverging-tube, and a narrow-gap-disk-burner. In addition, various flame structures and structural transition in such meso-scale burners will be introduced. Conclusively, I suggest that a meso-scale test burner can be a tool for a closer look at the real flame characteristics in specific length scales, and that the transition between different flame structures will extend our understanding on the flame structures and related theories.