3D-CFD analysis on scavenging and mixture formation for CNG direct injection with an outward-opening nozzle

On the basis of comprehensive experimental measurements, 3D-CFD analyses of CNG direct injection, using an outward-opening nozzle, were performed. Main objective of the presented work was the examination of influencing factors on the hollowcone jet propagation, fuel distribution and therewith directly associated back flow into the intake manifolds.For charged operation with scavenging, experimental investigations identified the injector needle tip protrusion, or mounting depth, as one of the dominating factors. By means of the conducted 3D-CFD simulations, assumed affect on the fuel-wallinteraction could be confirmed. It causes an expansion or collapse of the hollow-cone jet and determines the amount of fuel that is stored in the intake manifold and scavenged into the exhaust system in the subsequent operating cycle.During the numerical studies, a thorough definition of the spray angles to describe the hollow-cone jet shape turned out to be of utmost importance in order to ensure high quality and validity of the spray simulation. Schlieren images, taken in a constant volume spray chamber as well as measurements in a two-cylinder SI-engine, provided by Robert Bosch GmbH, served as a reference for injector and engine calibration and results validation.