ECN Spray D visualization of the spray interaction with a transparent wall under engine-like conditions. Part I: Non-reactive impinging spray

Abstract

The possibility for a jet of fuel to collide against the surfaces of the combustion chamber or the piston bowl into a thermal engine, has a direct effect on the droplets breakup and the spray atomization. In order to study the spray/wall interaction phenomenon and its influence on the macroscopic spray behavior, a diesel spray was visualized when impinging on a flat wall made of quartz at various ambient, injection and wall position conditions. Two high-speed cameras were employed simultaneously to perform Schlieren imaging and diffuse back illumination diagnostics, in order to observe both spray vapor and liquid phases during their contact with the wall. The experiments were performed in a constant pressure-flow test rig, able to reproduce diesel-like thermodynamic conditions. Two different fuels (n-dodecane and diesel #2) were injected within the chamber by employing a single-hole injector referred to as Spray D into the framework of ECN research group. To place the wall in the spray path, a wall positioning structure capable of being fitted into the chamber and of support the wall at various inclination angles and distances from the injector tip, was designed. The test rig was filled with N2 to keep an inert atmosphere and isolate the spray development from possible alterations produced by combustion. Results provide the influence of the injected fuel, operating and wall conditions on the macroscopic features of the transient spray in terms of spreading onto the wall and spray thickness characterized both temporally and spatially. Spray spreading was evaluated by a novel penetration-based parameter. It showed to be proportional to the square root of time similarly as free-penetration and is largely affected by the wall inclination respect to the spray axis. Spray angle showed to be influenced by the morphology of the spray that affects its air entrainment capacity and that changes with a wall respect to a free-jet configuration. This variation in the morphology also has a remarkable effect on spray evaporation, characterized in terms of liquid length and liquid spreading onto the wall. Finally, the large amount of data was used to obtain correlations for all the studied parameters.