CRITICAL CONDITIONS OF DROPLET PUFFING AND MICROEXPLOSION MODES

Abstract

Microexplosion e¨ects in composite droplets make it possible to improve integral characteristics of secondary atomization processes in the combustion chamber, to increase completeness of fuel combustion, to reduce ignition time delay, and to diminish anthropogenic emissions [1]. The purpose of this work is experimental and theoretical research of critical conditions of pu©ng and microexplosion modes. The experimental research of microexplosion e¨ects in composite droplets was carried out by varying the temperature of the gaseous medium (473 1523 K) and atmospheric pressure [2]. The in§uence of the gaseous medium temperature and solid particles and gas bubbles concentrations on the time delay of droplets fragmentation were investigated. The droplet heating, evaporation, and breakup characteristics were recorded using a Phantom Miro high-speed slow-motion video camera with a frame rate of 2000 fps at 512 × 768-pixel resolution. The experimental video fragments were processed in the Phantom Camera Control software to analyze the initial droplet size before they enter the heating zone and to estimate the distance between them. The systematic errors in the measurement of these parameters did not exceed 0.025 and 0.05 mm, respectively. The problem of modeling pu©ng/microexplosion of composite water/fuel droplets was examined with using model for pu©ng/ microexplosions [3]. The most recent model [3] is based on the analytical solution to the one-dimensional heat transfer equation in a composite droplet assuming that a spherical water subdroplet is placed exactly in the center of a spherical fuel droplet. The analytical solution to this equation with the Robin boundary condition at the droplet surface was obtained, implemented into the numerical code, and used at each time step of the calculations. The e¨ects of thermal swelling and evaporation, using the Abramzon and Sirignano model, are considered. The developed mathematical apparatus can be helpful in developing high-temperature gas vapor drop technologies associated with ignition and combustion of liquid and slurry fuels.