Two-phase Fuel Distribution in an Air Assisted DI Gasoline Engine(S.I. Engines, Combustion Diagnostics)

Abstract

During the injection and mixture formation processes of a DI gasoline engine fuel may exist in either the liquid or vapour phase and it is therefore advantageous to be able to observe both phases simultaneously. However, traditional LIF techniques are not suitable for this purpose since the large differences in fluorescence intensity from the two phases make the selection of a suitable light collection level virtually impossible. In an attempt to overcome this problem the Laser Induced Exiplex Fluorescence (LIEF) technique was applied to a single cylinder DI gasoline engine. The engine was equipped with an air assisted fuel injection system and it had full optical access through a quatz liner and transparent piston crown. Isooctane was used as the test fuel with dopants Naphthalene (7%) and N,N-dimethlylaniline (DMA) (7%). The expanded laser beam from a XeCl Excimer laser was used to illuminate the whole combustion chamber and act as the excitation source for the LIEF system. In order to collect simultaneously fluorescence signals from both liquid and vapour phases emissions an image doubling and filtering system was designed and constructed. The fluorescence images were recorded from the front of the cylinder, perpendicular to the axis of the crankshaft. In order to investigate the effect of absorption on the fluorescence signal the beam was introduced to the cylinder from 3 directions. Initially the beam entered from the left of the image. The experiment was then repeated with the beam entering from the right and finally entering from below through the transparent piston crown. The crank angle resolved results, from the start of injection to the end of the compression stroke are presented with an image for each illumination direction.