Conditioned Analysis of Effervescent Atomization

Effervescent atomizers have a number of significant advantages over conventional injectors. They can operate at much lower injection pressures, their atomization performance is largely insensitive to fuel physical properties, and very fine atomization can be achieved at lower air flow-rates when compared to air-blast atomizers. Despite these advantages, there is a lack of quantitative data describing the near-field atomization zone, which is difficult to probe due to the unstable nature of effervescent fragmentation. This lack of data has prevented a fundamental understanding of this atomization mode and delayed the development of advanced numerical models. Here, the near-field characteristics of a series of effervescent sprays are examined using advanced image processing. The study provides new quantitative insights into the nature of the regime transitions that occur as a function of the gas-to-liquid ratio (GLR). The distinct regime transitions, noted through quantitative measurements of the liquid jet outer diameter, closely coincide with previously quoted bubble type and transitional tree-regime transitions. The distribution of the outer diameter of the ejected air-laden liquid jet progresses from bimodal at low GLR values ($<0.5\%$) to monomodal distribution at a higher GLR. Measurements of ligament thickness in the near field have allowed for direct evaluation of a previously developed analytical model that predicts droplet Sauter mean diameter (SMD) as a function of the GLR. This model has been confirmed here over a wider GLR range by using number-based conditioning and further extended into a simple analytical model that can estimate the total number of objects generated per unit time.