Evaluation of Diesel Spray-Wall Interaction and Morphology around Impingement Location

The necessity to study spray-wall interaction in internal combustion engines is driven by the evidence that fuel sprays impinge on chamber and piston surfaces resulting in the formation of wall films. This, in turn, may influence the air-fuel mixing and increase the hydrocarbon and particulate matter emissions. This work reports an experimental and numerical study on spray-wall impingement and liquid film formation in a constant volume combustion vessel. Diesel and n-heptane were selected as test fuels and injected from a side-mounted single-hole diesel injector at injection pressures of 120, 150, and 180 MPa on a flat transparent window. Ambient and plate temperatures were set at 423 K, the fuel temperature at 363 K, and the ambient densities at 14.8, 22.8, and 30 kg/m³. Simultaneous Mie scattering and schlieren imaging were carried out in the experiment to perform a visual tracking of the spray-wall interaction process from different perspectives. The experiments provided the spatial distribution and time-resolved evolution of the spray impingement on the wall, as well as the post-impingement global spray characteristics under various operating conditions. A previously validated Lagrangian-Eulerian CFD model based on a Reynolds-Averaged Navier-Stokes (RANS) formulation was used to characterize the spray interaction with the surrounding gas and impinged wall, and the numerical results were compared against the available experimental measurements. Subsequently, local spray quantities were extracted at different locations in the vicinity of the impingement point where the spray was characterized in terms of Reynolds and Weber numbers. The cumulative distributions of these local quantities with respect to parcel mass were then compared for increasing number of injected parcels. It was shown that convergence of the global spray quantities does not necessarily imply convergence of local quantities in the impingement area unless a very large number of parcel is used to describe the spray.