ECN Spray D visualization of the spray interaction with a transparent wall under engine-like conditions, Part II: Impinging spray combustion

Abstract

In spite of the ever more comprehensive studies on diesel combustion, there is still an important gap on the fundamental knowledge about the interaction of fuel sprays with the piston and cylinder walls in internal combustion engines. The present research corresponds to the second part of an extensive investigation about the spray/wall impingement process at engine-like conditions and its sensitivity to several operating conditions. A constant pressure-flow test rig, which was filled with air extracted from the environment, was employed to perform the experiments at reactive conditions. A single-hole injector from the Engine Combustion Network, referred to as Spray D was employed and a quartz flat wall was set in front of the nozzle by using a supporting structure attached to the vessel. Parameters varied in this work are injected fuel, ambient density, gas temperature, injection pressure, and wall position in terms of distance from the injector hole and inclination angle. Three cameras were simultaneously used to observe the spray–wall interaction (SWI): Schlieren visualization to record the macroscopic evolution of the spray vapor phase and also to determine the ignition delay, a high-speed camera was placed in the front of the wall to directly observe the natural luminosity of the flame through the transparent wall and, finally an intensified camera was used to determine the lift-off length by observing the chemiluminescence of OH*. An extensive geometrical characterization of the spray geometry evolution was made and different metrics were introduced in this work as it is the case of wall lift-off radius to parametrize the observed formation of a lift-off area onto the wall. Similarly, ignition delay showed to be shortened by the presence of the quartz wall up to 15%due to its nearly isothermal configuration and its improvement on air–fuel mixing.