From dilute to dense turbulent sprays: Combustion, auto-ignition and atomization

In line with the general theme of the International Workshop series on Turbulent Combustion of Sprays (TCS), this Chapter addresses relevant issues of turbulent flame structure, auto-ignition and atomization with reference to wellcharacterized burners that could be implemented by modelers with relative ease. The discussion of turbulent combustion is limited to dilute sprays stabilized on a simple piloted burner. Attention is shifted to the structure of the reaction zones and the challenges of computing chemical composition of flames of different fuels. Another section is dedicated to studying auto-ignition of turbulent dilute spray flames as observed in a hot vitiated co-flow. A common feature to all liquid fuels studied here is the presence of ignition kernels which grow (and sometimes extinguish) to induce flaming combustion further downstream. It is noted that this downstream region is responsible for the bulk of heat release and its local compositional structure depends on the parent fuel. The last section focuses on non-reacting dense sprays with a view to shed some light on the effects of turbulence on secondary atomization. Two configurations are discussed: one for droplets flowing in a pipe and the other uses dense sprays generated with an air assisted atomizer. The carrier velocity is changed in both configurations to induce turbulence which affects atomization as clearly demonstrated by the reported measurements. While this chapter is not necessarily a roadmap for the efforts of future TCS workshops, the topics addressed here form a logical progression that is somewhat commensurate with the increasing order of complexity generally sought for computations.