Study of the evaporation and combustion of droplets by a new optical sizing method

In the experiments of the present paper the evaporation and the combustion of well defined monodisperse droplet streams is studied. A new droplet sizing method with an accuracy of 2% is presented, which allows to study the temporal evolution of evaporating or burning droplets. The droplets are produced with a vibrating-orifice droplet generator. In order to measure the burning rate or the evaporation rate, the droplet velocity as well as the droplet diameter have been measured simultaneously at different locations along the axis of the droplet stream. The velocity of the droplets is measured with a laser Doppler technique. The droplet size has been determined from the fringe spacing of the interference pattern produced by the droplets. A CCD-array was used to register the angular intensity distribution. This method has the advantage of being independant of the absolute intensity of the laser light. Evaporation rates have been measured in a large Knudsen number range. In the experiments with burning droplet streams the droplets have been ignited by a heated coil of filament. The droplet stream is then surrounded by a laminar flame. The specific character of the droplet stream, the uniformity and regularity, is not changed by the combustion process.