Turbulent spray flames of intermediate density: stability and near-field structure

This paper presents an experimental study of turbulent spray jets and flames where the liquid loading is intermediate between the two extremes of dense and dilute; a region of significant importance in practical applications. A new piloted burner is introduced for this purpose featuring air-blast atomization, with liquid injection from a needle that can be translated within a co-flowing air stream. The stability characteristics are presented for three recess lengths using acetone as fuel. High-speed shadowgraph imaging is performed in the atomization region of jets and flames having different liquid loading and recess distances. Three types of fluid fragments are used to map the evolution of these sprays: droplets, ligaments and 'irregular' shapes. Statistics for each class of these fluid shapes are presented to map the boundary conditions at the jet exit plane and to track their evolution with downstream distance along the jet. These show clearly how ligaments and irregular shapes break down to supply more droplets further downstream. Measurements of liquid surface area show a peak in the mean area and its rms of fluctuations around two jet diameters from the point of injection marking the region of maximum atomization. It is also evident that the process of primary and secondary atomization is completed by about seven jet diameters from the liquid injection point. This burner provides a versatile platform for studying these flows and the resulting information is already proving to be extremely useful in the development and validation of related models for turbulent spray jets and flames.