Spray Characteristics of Gasoline-Ethanol Fuel Blends under Flash Boiling Conditions 2019-01-0297
The objective of this paper is to investigate the spray characteristics of gasoline-ethanol fuel blends injection under flash boiling conditions. The spray structure and vaporization processes of both non-flash boiling and flash boiling sprays in a constant volume chamber under a wide range of superheated conditions were experimentally investigated by a high-speed imaging technique. The Engine Combustion Network’s Spray G injector with an injection pressure of 200 bar was used. The ambient temperature was kept at 60 °C (±1 °C) and the ambient pressure ranged from 15 kPa to 290 kPa. For comparison, pure gasoline and ethanol were also investigated under the same conditions, and the fuel temperature varied from 20 °C to 90 °C. Spray penetration and spray-plume width were correlated to the degree of superheat, which is the ratio of the ambient pressure to saturated vapor pressure (pa/pv). It is found that the gasoline and ethanol sprays showed the similar patterns under non-flash boiling conditions. Ethanol evaporated slower than gasoline did at low temperature, but they reached similar evaporation rates when the temperature was close to 90 °C. Spray collapse was clearly observed when the value of pa/pv was around 0.8, and flash boiling occurred around 0.6 degree of superheat for pure gasoline, ethanol as well as their blends. For gasoline-ethanol fuel blends (E50), it behaves like pure ethanol at low temperature while like pure gasoline at high temperature. In summary, the fuel temperature affected not only fuel evaporation modes but also the breakup mechanisms.