Internal and near-nozzle flow of a pressure-swirl atomizer under varied fuel temperature

Abstract

Gasoline fuel spray from a swirl injector collapses at high fuel temperatures due to the flash boiling effect. In order to clarify the influence of fuel temperature on the spray structure, a variety of internal and near-nozzle flows were examined at different fuel temperatures. The initial development of fuel flows was analyzed by imaging the spray behavior with high-magnification optics and by static pressure measurements of the spray field with a piezoresistive transducer. The experimental results are discussed with a mathematical liquid film model. Fuel evaporation at high fuel temperatures causes static gas pressure to increase inside and near the nozzle. The reduced viscosity of fuel at high temperature causes enhanced swirl motion of the spray. These lead to reduced liquid film thickness inside the nozzle, in addition to increased flow divergence at the nozzle exit. At locations further downstream, the spray is driven toward the spray axis at high fuel temperatures as a result of the augmented pressure drop inside the spray and entrained air. The shorter breakup time at high fuel temperatures makes the spray lose its initial momentum and be easily affected by the pressure difference between the inner and outer parts of the spray and entrained air.