Air Entrainment in Diesel-Like Gas Jet by Simultaneous Flow Velocity and Fuel Concentration Measurements, Comparison of Free and Wall Impinging Jet Configurations

The air entrainment process of Diesel like gas jet was studied by simultaneous measurements of concentration and velocity fields. A high pressure gas jet was used to simulate Diesel injection conditions. The injection mass flow rate was similar to that of typical Diesel injection. The experiments were performed in a high pressure vessel at typical ambient gas density of Diesel engine during spray injection. The ambient gas density was varied from 25 to 30 kg/m(3) and three nozzle diameters, 0.2, 0.35 and 0.5 mm were used. Both free and wall impinging jet configurations were investigated by combining Laser Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV) to obtain simultaneous planar measurements of concentration and velocity. Fuel concentration fields were used to define the edges of the jet and allow an accurate determination of the air entrainment rate both in free and wall impinging configurations. The effects of ambient gas density, nozzle hole diameter and wall impingement on the air entrainment process were investigated. It was found that the presence of wall impingement results in a local increase of air entrainment, while the overall mass of air entrained in the jet is reduced. Also the effect of aerodynamic structures on the mixing process was investigated in details by local and statistical analysis to highlight the role of coherent structures on the air entrainment process.