The temperature of 225-ixm-dia I Introduction Vaporization in fuel sprays is a complex phenomenon involving heat and mass transfer in a dynamic mixture of droplets, fuel vapor, and ambient gas. Most workers in the field attempt to understand these processes in sprays by treating sprays as aggregates of individual drops, and therefore, understanding the processes that govern vaporization of individual fuel droplets becomes paramount. Many studies, both computational and empirical, of droplet vaporization have been performed, and reviews of the current understanding are available in the literature (Law, 1982; The vaporization of individual fuel droplets is generally studied photographically, a technique that yields only the droplet diameter Determination of the temperature of a droplet using thermocouples unavoidably perturbs both the droplet and the environment surrounding it and may alter the transfer of heat into or away from the droplet. In addition, suspended droplets are in physical contact with a support structure that may similarly make interpretation of the data uncertain. In this paper we describe the determination of the temperature of a decane droplet falling in a hot, relatively quiescent environment. The optical techniques described here can provide instantaneous, minimally perturbing measurement of even the surface temperatures of freely moving fuel droplets. The technique used to measure the droplet surface temperature is exciplex fluorescence thermometry (EFT), which exploits the temperature-dependent fluorescence resulting from the reaction of an excited dopant molecule to form a
