The Boundary Layer Structure of a Vaporizing Fuel Cloud

Abstract

The vaporization of a fuel cloud in an infinite, quiescent atmosphere is examined. A single global parameter which characterizes the vaporization process, and is related to the ratio of the thickness of a vaporization wave to the cloud radius, is identified. Typical fuel sprays correspond to very small ( e.g., 10⁴) values of this parameter. An asymptotic analysis of the cloud, predicated on this parameter being small, shows that the cloud and its environment are divided into four distinct regions: (1) the saturated, non-vaporizing cloud interior; (2) a quasi-steady vaporization wave located at the edge of the cloud and propagating radially inward; (3) a quasi-steady (”inner”) region located outside the cloud but in its vicinity and (4) an unsteady (”outer”) region located far from the cloud. A phenomenological model of the vaporization wave is also presented, along with sample calculations using typical cloud data.