Experimental and numerical analysis of high pressure diesel spray-wall interaction

The interaction between impacting and splashed droplets and air motion plays a fundamental role on the mixture formation process, which is a crucial aspect for the correct operation of modern DI Diesel engines as it greatly influences the combustion process and the exhaust emissions. A complete understanding of spray impingement is quite complex. A mixed numerical-experimental approach is proposed in this paper. The experimental tests are carried out with a high pressure (up to 120 MPa) diesel spray emerging from an axial disposed single-hole nozzle in an optically accessible vessel, pressurized up to 5.0 MPa at ambient temperature. The jet impacts on a .at stainless steel wall heated up to 500°C by a 200 W temperature regulated electrical resistance wire. The experimental analysis is performed using a Bosh tube as the injection mass flow meter, a pulsed laser sheet generated on the second harmonic of a Nd-YAG laser and a synchronized CCD camera. Digital image post-processing allows extraction of the radial penetration and thickness growth of the impacted fuel versus injection pressure, vessel back-pressure and wall temperature. Moreover, a procedure to relate light intensity to average fuel density is proposed. The numerical analysis is carried out by means of a multi-dimensional numerical tool, based on the KIVA-3V code. The spray-wall interaction is simulated through a phenomenological splash model available in literature and validated for low injection pressures (up to 300 bar) and ambient back-pressure. The comparison between experimental and numerical results demonstrates the inability of the model in predicting high pressure spray-wall interaction, especially under increasing back-pressures. Based on the experimental evidences, a modified version of the model is proposed and the new model is proven to be an adequate representation for different injection pressures and back-pressures.