Experimental characterization of early, quasi-steady and post-injection evolution of single-hole direct injection sprays for spark-ignited engines

Abstract

The atomization characteristics of the ethanol-gasoline (E85) blended fuel using a single-hole GDI atomizer were studied. The spray at early development, quasi-steady, and post-injection stages were studied in the near-nozzle region. A Galilean-type beam expander and an achromatic lens were used to achieve the desired magnification. In the early development stage, the jet velocity was measured to estimate the breakup regime based on the Ohnesorge (Oh) and Reynolds (Re) numbers. Spray during the initial stage at 2 MPa injection pressure shows second wind-induced breakup under 0.6 MPa chamber pressure (Pch). A transition between second-wind and atomization breakup for jets under 0.03 and 0.05 MPa Pch. The jet experiences atomization breakup under 0.1 MPa Pch. The effect of the injection pressure and chamber temperature were also studied. The post-injection liquid sheet formation near the nozzle exit was observed. Results show that the size of the liquid sheet depends on the liquid-to-gas density ratio (ρlg). The size of the sheet for E85 fuel at ρlg of 2363 was found to be 6 mm, which was reduced by 75 % with a reduction in ρlg by 95 %. The chamber temperature increased from 303 K to 363 K, ρlg increased from 702 to 842, and a reduction in the liquid sheet was observed from 2.5 mm to 1.8 mm, respectively. The necking phenomenon of the liquid sheet was observed at the nozzle tip before the sheet detached and disintegrated into droplets. The necking length for the E85 was compared with gasoline fuel.