Impinging jets of fuel on a heated surface: effects of wall temperature and injection conditions

In spark ignition engines, the nozzle design, fuel pressure,injection timing, and interaction with the cylinder/piston wallsgovern the evolution of the fuel spray inside the cylinder beforethe start of combustion. The fuel droplets, hitting the surface, mayrebound or stick forming a film on the wall, or evaporate under theheat exchange effect. The face wetting results in a strong impacton the mixture formation and emission, in particular, onparticulate and unburned hydrocarbons. This paper aims to reportthe effects of the injection pressure and wall temperature on themacroscopic behavior, atomization, and vaporization of impingingsprays on the metal surface.A mono-component fuel, iso-octane, was adopted in the spraywallstudies inside an optically-accessible quiescent vessel byimaging procedures using a Z-shaped schlieren-Mie scatteringset-up in combination with a high-speed C-Mos camera. Thearrangement was capable to acquire alternatively schlieren andMie-scattering images in a quasi-simultaneous fashion using thesame optical path. This methodology allowed complementing theliquid phases of the impact, obtained by the Mie scattering, withthe liquid/vapor ones collected by the schlieren technique fordetermining both the phases inside a single cycle. A Delphisolenoid-activated eight-hole electro-injector was used, 0.165 mmin diameter, L/d=2 having a static flow of 15 cc/s @10.0 MPa.This injector is part of a set of six items, chosen by the EngineCombustion Network (ECN) for the gasoline characterization(Spray G), at defined injection conditions. The wall and ambienttemperature ranged within 296 to 573 K, under atmospheric gasdensities at the injection pressure of 20.0 MPa. The contours ofthe liquid phase and the vapor/atomized zone, indicative of impactevolution, were extracted by a customized algorithm operating onthe data set. Repetition cycles at fixed conditions were carried outfor a spread analysis on the events. Spatial and temporalevolutions were measured for the liquid and vapor/atomizedphases in terms of fuel slipping (width) and reboundingpenetration on the wall (thickness).