| A quantitative investigation has been carried out on the behavior of laminar spray diffusion flames in an attempt to bridge the gap between the study of isolated droplet or droplet array combustion and turbulent spray combustion.;First, attention was focused on counterflow flames. It was observed that the structure of counterflow diffusion spray flames can be dramatically changed by interactions between the spray and the flame. Flames without this interaction appeared as a thin blue sheet, whereas flames with the interaction exhibited an additional thick orange soot region on the oxidizer side of the flame. The change of structure can also affect the flame peak temperature. An interaction criterion was established based on an evaporation Damkohler number, Da;Next, coflow spray combustion was investigated under conditions in which internal group combustion was experienced, with the bulk of the droplets evaporating in the spray core with a few droplets burning outside of the cloud-enveloping flame. Group behavior was found to be present even under very diluted spray conditions, with relative interdroplet spacing, l/D, as large as 160. Droplet life-histories showed that the droplets in the bulk of the spray core followed the d;Lastly, the coulombic fission of evaporating charged fuel droplets in flames was studied. For the first time, evidence of the secondary atomization in the combustion of electrically charged sprays was collected in spray flames if no direct spray-flame interaction existed. It is concluded that the coulombic fission is an abrupt ejection process resulting in offspring droplets much smaller than parent droplets and with high speed. This phenomenon suggests a possible approach to induce secondary atomization based on droplet charge. |
