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 and impinging fuel, showing the strict relationship between cooling effect after impingement and enhancing of wallfilm formation. The study focuses on a fundamental task in terms of pollutant emissions in internal combustion engines, aiming at giving a major contribution to the optimization of energy conversion systems in terms of environmental impact. The paper is based on experimental campaigns relevant at taking measurements of an impinging spray over a heated wall in a confined vessel. The results, in both qualitative and quantitative terms (measurements of liquid and vapour radial penetration and thickness), are numerically reproduced by a computational model based on a RANS approach, properly validated through customized sub-models. The paper provides quantitative results about the agreement between radial penetration and vapour thickness between measurements and simulation, achieved by taking into account the cooling effect determined by the fuel impingement. This validation of the numerical model allows the author to give more considerations about the link between wall temperature and wallfilm formation. The paper develops and examines in depth the dependency of the wallfilm formation from the local value of wall temperature, enhancing the predictability of future numerical researches in terms of soot formation. This paper presents an original approach for the simulation of wall heat transfer, by imposing a boundary condition at the wall that may consider the heat conduction and temperature cooling given 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 on calculating the unsteady process that couples the heat fluxes between the fluid and the solid material and within the solid itself