Spray characterizations from outward-opening DISI engine injector under various fuel superheat degree conditions

Fuel sprays from outward-opening DISI engine injector were characterized under various fuel superheat degree (SD) conditions using laser sheet Mie-scattering and Phase Doppler Interferometer (PDI). N-hexane was used for a gasoline surrogate as it has a fixed boiling point and saturated vapor pressure. The macroscopic characteristics of the spray structure including the spray penetration and the spray angle, and the microscopic characteristics including Sauter Mean Diameter (SMD) and size distributions of droplets, were investigated. The ratio of ambient pressure to saturation pressure (Pa/Ps) is used as an indicator of the SD. The results show that the spray structure deforms from an “umbrella” shape to a “bell” shape when SD increases from non-flash-boiling to full-flash-boiling area. And as Pa/Ps decreases (SD increases), the spray penetration decreases at first and turns to increase at about Pa/Ps = 0.3. The spray angle keeps relatively steady until Pa/Ps decreases to about 0.3, but significantly decreases when Pa/Ps <; 0.3, which corresponding to the flare flash boiling conditions. SMD and droplet size distributions also interpret a fact that increasing SD results in a better atomization of fuel spray.