Stability of rich premixed polydisperse spray flames

A new numerical study of rich laminar polydisperse spray flame propagation in a two-dimensional channel is presented. Two different polydisperse sprays having the same Sauter mean diameter were considered. A constant density model was adopted thereby eliminating the Darrieus-Landau instability. Attention is focused on the development of spray induced instabilities and the way they are sensitive to the initial droplet size distribution. Previous work in this field was based on a linear stability analysis. The current work allows nonlinear stability aspects to be captured. It was found that both cellular and oscillating instabilities can develop, depending on the evaporation coefficient of the liquid fuel. However, the transitions from planar propagation to cellular propagation and from the latter to oscillating propagation occur at different critical values of the evaporation coefficient depending on what the initial droplet size distribution actually is. Therefore, use of the Sauter mean diameter to represent a polydisperse spray can be misleading in the current context and the real size distribution must be considered.