Two-dimensional imaging of fuel-vapour concentration byuse of LIEF technique during mixture formation process in a DIdiesel engine

Abstract

The laser-induced exciplex fluorescence (LIEF)technique, which is based on spectrally resolved two-colour fluorescentemissions, has been applied to anevaporating diesel spray for the simultaneous separation ofliquid and vapour phases on the two-dimensional images. Theexciplex system is based on the TMPD/naphthalene systemproposed by Melton. The temporal and spatial distribution ofliquid and vapour phases during the mixture formation process was detected by this technique. In the LIEF technique, the vapourphase is detected by the monomer fluorescence while the liquidphase is tracked by the exciplex fluorescence. It is able toprovide quantitative information on the diffusion state forapplying the statistical entropy concept. This concept was putinto practice in the image sets obtained through LIEFmeasurement in order to investigate the diffusion process of vapour phase in the evaporating diesel spray. The lasershadowgraph was taken to deduce the effect of turbulent mixingon the ignition. The experiments were conducted in a directinjection diesel engine with optical access required forthe two-dimensional laser imaging.From the results, it is found that ignition occurs in the regionwhere turbulent mixing has advanced a nearly homogeneousmixture of fuel vapour and air. Multi-sectional images obtainedby LIEF indicate that there is a spatial dependence ofignition on the vapour-phase fuel in the combustion chamber.