A New,Accurate Method for the Measurement of Rise Velocities in Laminar Flames

Abstract

A novel technique is introduced for the measurement of rise velocities of hot, laminar flames. The new technique is straightforward to implement, rapid to employ, and more accurate than previous methods based on the observation of moving heated particles. In the method, tiny individual droplets of a solution containing alkali or alkaline earth elements are repetitively introduced into the flame to be examined. The small cloud of atomic vapor which is produced upon atomization of a droplet is then monitored photometrically as it passes two well-defined points in the flame. Knowledge of the distance between the points and measurement of the time required for the atoms to traverse it thus enables the flame velocity to be calculated. Conveniently, velocity measurements with this technique are localized in the flame, thereby permitting spatial variations in flame velocity to be examined. Moreover, the negligible mass of the moving, measured atom cloud eliminates error otherwise caused by gravitational attraction and its decelerating effect. The utility of this new technique is demonstrated through the measurement of localized velocities in a laminar, air-acetylene flame.