THE EFFECT OF FUEL VELOCITY MODULATION ON ATOMIZATION AND SPRAY COMBUSTION. Charles A. Cook, S. Rao Charagundla, Cary Presser, John L. Dressler, National Institute of Standards and Technology, Gaithersburg, MD, USA.

Control of the atomization process of liquid fuels is important in many combustion systems because of its effect on fuel vaporization rates, the mixing process between fuel and oxidizer, combustion efficiency, and emission of pollutants. One device that has been used to control liquid atomization is a velocity-modulated atomizer. In this device, an electro-mechanical piston is used to impart disturbances to the fuel stream, which affect the subsequent atomization process. The purpose of this study is to characterize sprays produced by velocity-modulated atomization and to relate the spray features to the combustion process.

In this study, a piezoelectric driver was used to modulate the velocity of kerosene fuel through a commercially available pressure-jet nozzle. Droplet characteristics and gas-phase chemical composition of the resulting spray flames were studied. Phase Doppler interferometry was used to measure droplet size and velocity in the spray flames. Gas samples were extracted from the spray flames, and concentrations of chemical species were determined using FTIR spectroscopy and a chemiluminescent NO/NOx analyzer. Global flame characteristics were recorded photographically. Experiments were performed at two different piezoelectric driving frequencies and compared to a base case without velocity modulation. The results show that velocity modulation decreases overall droplet size and increases mean droplet velocity and number density near the spray centerline. These characteristics increase the flame standoff distance and flame length. However, velocity modulation decreases the number of droplets escaping the spray flame unburned.