NEAR-FIELD SPRAY TIP CHARACTERISTICS OF ISO-OCTANE/DIETHYL ETHER BLENDS AS PROMISING GCI FUELS

Effects of bio-fuel diethyl ether (DEE) addition on the near-field spray tip characteristics of iso-octane have been investigated at different ambient temperatures experimentally by using high-speed imaging with a long-distance microscope. The near-field spray screening is focused on the early stage of ~0.2 ms after starting the injection and the measuring length scale is less than 3.0 mm below the nozzle exit. Results show that, first, the DEE blending ratio and ambient temperature significantly affect the state of the previous injection residual fuel, which leads to four typical near-field spray tip patterns: mushroom, umbrella, helmet, and vapor hemisphere, as the liquid phase residual fuel is vaporized. Second, quantitative description of the near-field spray tip has been conducted. High ambient temperature and DEE blending ratio favor faster tip penetration because of the enhanced residual fuel vaporization and reduced axial obstruction. Finally, different near-field spray tip patterns resulting from the residual fuel state are shown as function of the ambient temperature and DEE blending ratio, followed by a conceptual scheme regarding the state of the residual fuel and its evolution after the start of injection, at different ambient temperatures and DEE blending ratios.