Flow optimization and fuel stratification for the stratified fuel spark ignition engine

Abstract

In order to take advantage of the 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 fuel stratification is realized by means of strong tumble flows in the cylinder. The detailed in-cylinder flow measurement and flow optimization in a three-valve twin-spark spark ignition (SI) engine were carried out using a digital particle image velocimetry (PIV) system. A two-tracer laser-induced fluorescence (LIF) system was developed and applied to visualize the in-cylinder fuel stratification. During the LIF measurements, two dopants, 3-pentanone and N, N-dimethylaniline (DMA), were used as fluorescence tracers when mixed into hexane and isooctane respectively. The two tracer fluorescence images were recorded simultaneously on to an intensified charge coupled device (ICCD) camera using a specially designed image doubling and filtering system. The results show that the presence of strong tumble was necessary to obtain good fuel stratification. Because of symmetrically distributed mean velocity and a small cycle-to-cycle variation of strong tumble flows, clear fuels stratification was obtained along the direction of the tumble rotational axis. It was also found that better fuel stratification was obtained when the closed valve fuel injection (injection during the exhaust stroke) was used.