Quantification of Fuel Concentrations and Estimation of Liquid/Vapor Ratios in Direct Injection Gasoline Sprays by Laser-Induced Fluorescence

Gasoline direct-injection sprays are studied in a pressurized vessel with the help of optical diagnostic techniques. Exciplex laser-induced fluorescence images show that the liquid phase is located on the edges of the spray induced recirculation zone, while the vapor is contained within this zone. These trends are particularly pronounced with a low ambient pressure (0.12 MPa), and a short injection duration. A new method is proposed to calculate the global evaporated fuel fraction of the spray. In typical iso-octane sprays, the evaporated fuel is less than 50 % at 6 ms after start of injection, for an ambient temperature of 75°C.

A low boiling point fuel - n-pentane - is used to model the behavior at high temperatures, which enhances evaporation. Quantified fuel/air ratio images are obtained using laser-induced fluorescence of acetone. The accuracy is poor if high liquid concentrations exist. The fuel/air ratio often exceeds 5 in large zones. Fuel spreading depends strongly on mixing, via air entrainment. The most influencial parameters are ambient pressure and injection duration, and not ambient temperature under our conditions.