Study of Near Nozzle Spray Characteristics of Ethanol under Different Saturation Ratios

Atomization of fuel sprays is a key factor in controlling the combustion quality in the direct-injection engines. In this present work, the effect of saturation ratio (Rs) on the near nozzle spray patterns of ethanol was investigated using an ultra-high speed imaging technique. The Rs range covered both flash-boiling and non-flash boiling regions. Ethanol was injected from a single-hole injector into an optically accessible constant volume chamber at a fixed injection pressure of 40 MPa with different fuel temperatures and back pressures. High-speed imaging was performed using an ultrahigh speed camera (1 million fps) coupled with a long-distance microscope. Under non-flash boiling conditions, the effect of Rs on fuel development was small but observable. Clear fuel collision can be observed at Rs=1.5 and 1.0. Under the flash boiling conditions, near-nozzle spray patterns were significant different from the non-flash boiling ones. Reducing Rs from 1.0 to 0.2 would lead to clear radial expansion in both the initial and quasi-steady stages due to the bubble formation and explosion. However, the micro cone angle was smaller when further reducing Rs to 0.1 as the nozzle flow developed into the hydraulic flipping regime.