Advances and challenges in droplet and spray combustion. I. Toward a unified theory of droplet aerothermochemistry

Major theoretical accomplishments in droplets and sprays in the twentieth century are reviewed in this two-part article, with emphasis focused upon the evolution of scientific concepts, paradigms and methodologies. A structural spray theory, which was developed from an early view of isolated droplets, has evolved in to a new view that the interacting droplet and meso-scale structures and clusters of many-droplet systems are also fundamental entities in practical sprays. The first part of this work addresses the major concepts in analytical developments, which serve as the framework of modern theories of an isolated and interacting droplet. Outstanding issues and critical bottlenecks that have prevented further advancement of the existing analytical theory of droplet physics are examined, and an emerging research trend in a unified theory of droplet phenomena discussed. Recent accomplishments and future prospects of a unified theory are presented to complement the status of this special branch of droplet science and its future application.