Effect of Drop-Size Dependent Spray-Injection-Velocity on Multisize-Spray Diffusion Flames in a Unidirectional Shear-Layer Flow

Liquid fuel injectors produce sprays of a wide range of drop-sizes, where drops of each size-group travel at a different velocity. When the spray is injected into a quiescent environment or into a co-flowing air flow, a shear layer will develop at the edge of the spray between the two adjacent streams. The droplets and their vapors spread into the co-flowing stream in which the oxidizer is contained and feed a spray diffusion flame. Effects of drop-size dependent, spray-injection velocity on the lateral evolution in drop-size histograms, on fuel vapor profiles, on flame location, and on flame temperature are analyzed. The present results indicate that the larger the overall spray velocity (which is considered here to be lower than the host gas velocity), the higher the fuel vapor production rate and thus, the resulting spray diffusion flame sheet is pushed towards the oxidizer stream, resulting in a higher flame temperature. Since drops of each size-group travel at a different velocity, the intensity of the above described effect depends mainly on the change in velocity of the droplets of those size-groups which are most prevalent in the fuel spray. Thus, drop-size dependent droplet velocities must also be considered in future design of fuel injectors in order to achieve the desired performance of a combustion system.