In-Cylinder Measurements of Fuel Stratification in a Twin-Spark Three-Valve SI Engine

In order to take advantage of different properties of fuel components or fractions, a new concept of fuel stratification has been proposed by the authors. This concept requires that two fractions of standard gasoline (e.g., light and heavy fractions) or two different fuels in a specially formulated composite be introduced into the cylinder separately through two separate intake ports. The two fuels will be stratified into two regions in the cylinder by means of strong tumble flows. In order to verify and optimize the fuel stratification, a two-tracer Laser Induced Fluorescence (LIF) technique was developed and applied to visualize fuel stratification in a three-valve twin-spark SI engine. This was realized by detecting simultaneously fluorescence emissions from 3-pentanone in one fuel (hexane) and from N,N-dimethylaniline (DMA) in the other fuel (iso-octane). Spectral analysis showed that when subject to irradiation by an Excimer laser at 308nm, 3-Pentanone and DMA emitted fluorescence at two different wavelength regions that could be effectively separated by means of two band-pass optical filters in a specially designed image doubling and filtering system. Measurements were carried out in a single cylinder Ricardo Hydra Engine with optical access, at a horizontal plane 5mm below the cylinder head and the vertical plane along the roof edge line. Measurement results in both planes showed that fuel stratification was present from the early intake stroke to the late stage of the compression stroke.