Atomization instabilities in bubble induced break-up

Effervescent atomization, or bubble induced atomization is one of the more uncommon methods of primary jet break-up. As a technique, it offers a substantial degree of atomization at very low mass gas-to-liquid ratios (GLR). This advantage however comes with a significant deficiency being the near-field spray instability which can arise due to bubbles traversing down the liquid jet in discrete packets. These injected bubbles create dominant frequencies in the primary atomization region which are driven by a complex two-phase flow that initiates upstream of the nozzle ejection orifice. There is a severe lack of understanding of bubble dynamics in effervescent sprays. In this paper, using high speed microscopic imaging techniques, and laser Doppler anemometry (LDA), an initial study of the near-field jet break-up is conducted. The LDA system is used in order to measure the physical locations in the spray where dominant frequencies are no longer measurable. These locations represent the portions of the spray where significant entrainment and turbulent mixing has occurred such that dominant bubble frequencies are 'destroyed'. The results presented here allow for an understanding of spray instability in effervescent atomization, which would ultimately facilitate the design of more stable fuel injection systems leading to reduced combustion instabilities in a wide range of applications.4 page(s