Ignition and Flame Propagation in Dilute Polydisperse Sprays ; Importance of d 32 and <

Suitability of the Sauter mean diameter and the surface-area mean diameter for representing the ignition and combustor behavior of polydisperse sprays is examined. Initial size distributions considered are the Nukiyama-Tanasawa distribution and a bidisperse spray. Two physical situations are analyzed. In the first, the ignition characteristics of a polydisperse spray in the viscinity of a hot wall are studied. In the second, the flame propagation through a mixture of air and polydisperse spray in a constant-volume combustor is investigated. For both situations, the relevant two-phase equations are solved by a hybrid Eulerian-Lagrangian numerical method. The results indicate that the ignition behavior of polydisperse sprays is best represented by the surfacearea mean diameter, whereas the flame propagation characteristics are best correlated by the Sauter mean diameter. These correlations are observed over a wide range of initial droplet size, size distribution, fuel volatility, and overall equivalence ratio, which is typical in practical combustion systems.