Two-phase fuel distribution measurements in a gasoline direct injection engine with an air-assisted injector using advanced optical diagnostics

Abstract

The fuel distribution and mixture formation processes within an internal combustion (IC) engine can greatly affect its ignition, combustion, pollutant formation, and fuel consumption. For more than two decades the laser-induced fluorescence (LIF) technique has been successfully applied to the study of mixture formation and distribution. However, in a gasoline direct injection (GDI) engine the fuel may exist in either the liquid or vapour phase, and it is therefore advantageous to be able to observe both phases simultaneously. One means of achieving this is the laser-induced exciplex fluorescence (LIEF) technique. This paper details its application to a single-cylinder GDI engine equipped with an air-assisted fuel injection system and full optical access. Naphthalene and N, N-dimethlylaniline (DMA) tracers were used to track the fuel and were excited using the expanded beam from an XeCl excimer laser at 308 nm. An image doubler and optical filtering system was used to collect the images that were recorded from the front of the cylinder. Early and late injection timings were investigated, and the spray characteristics and mixture formation from the two strategies were found to differ considerably. In order to investigate the effect of absorption on the fluorescence signal, the beam was introduced into the cylinder from three directions. 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 and injection timing.