Schlieren and Mie scattering techniques for the ECN "spray G" characterization and 3D CFD model validation

The paper focuses on the heat transfer phenomenon occurring between heated walls andimpinging fuel, showing the strict relationship between cooling effect after impingement and enhancing ofwallfilm formation. The study focuses on a fundamental task in terms of pollutant emissions in internalcombustion engines, aiming at giving a major contribution to the optimization of energy conversion systemsin terms of environmental impact. The paper is based on experimental campaigns relevant at takingmeasurements of an impinging spray over a heated wall in a confined vessel. The results, in both qualitativeand quantitative terms (measurements of liquid and vapour radial penetration and thickness), are numericallyreproduced by a computational model based on a RANS approach, properly validated through customizedsub-models. The paper provides quantitative results about the agreement between radial penetration andvapour thickness between measurements and simulation, achieved by taking into account the cooling effectdetermined by the fuel impingement. This validation of the numerical model allows the author to give moreconsiderations about the link between wall temperature and wallfilm formation. The paper develops and examines in depth the dependency of the wallfilmformation from the local value of wall temperature, enhancing the predictability of future numericalresearches in terms of soot formation. This paper presents an original approach for the simulation of wall heat transfer, byimposing a boundary condition at the wall that may consider the heat conduction and temperature coolinggiven by fuel impingement in both lateral and normal directions. The classical Dirichlet boundary condition,characterised by imposing a fixed temperature value, is instead, replaced by an approach based oncalculating the unsteady process that couples the heat fluxes between the fluid and the solid material andwithin the solid itself