IGNITION OF A BINARY-FUEL (SOLVENT-SOLUTE) CLUSTER OF DROPS

Evaporation and ignition of a binary-fuel cluster of drops is describe d by models under the assumptions that the volatile compound has infin ite volatility with respect to the solvent and that the chemistries of the two compounds are independent. A Damkohler number criterion devel oped for use in sprays is utilized to determine the ignition time. Ano ther criterion is used to determine the ignition location which can be either around individual drops, or around groups of drops inside the cluster, or around the entire cluster. Results show that except for ve ry dilute situations where the initial liquid mass fraction of the vol atile is very small, ignition always occurs around the entire cluster. Otherwise, ignition occurs around groups of drops inside the cluster but never around individual drops even though the ratio of the distanc e between the centers of two adjacent drops by the drop diameter is gr eater than thirty five. Studies performed by varying the air/fuel mass ratio for a variety of parametric combinations show that: (1) At typi cal gas temperatures for combustion devices, the ignition of very dens e and very dilute clusters of drops is evaporation-controlled for iden tical chemistries; it is strongly-controlled by solvent ignition in th e very dense cluster regime, it is strongly-controlled by ignition of the volatile in the very dilute regime. In the intermediary regime, ig nition is controlled by the relative ignition chemistries of the compo unds. These conclusions are independent of the amount of volatile init ially present in the liquid. (2) The concept of volatile is more stron gly associated with the latent heat of evaporation in the dense regime , and more strongly associated with the saturation pressure curve in t he very dilute regime. (3) By increasing the surrounding gas temperatu re one gradually gains control of ignition in the dense and dilute reg imes through the evaporation of solvent and volatile respectively. (4) The initial slip velocity between phases affects ignition only in the very dilute regime. (5) Changes in the cluster size affect the igniti on time only in the very dense regime. Conclusions (3) and (4) are val id under the assumption of identical kinetics for the two compounds; w hen different kinetics are considered, it turns out that kinetic effec ts overwhelmingly dominate ignition.