抄録
A new charge stratification concept - fuel stratification is being researched and developed in a three-valve twin-spark SI engine. This concept requires that two different fuels or fuel components in a specially formulated composite be introduced into the cylinder separately through two independent inlet ports. The fuels will be stratified laterally by means of strong tumble in the cylinder. Different fuel properties may be employed in this way to increase fuel economy and reduce toxic emissions. This paper reports the development of the fuel stratification technique. The intake system of the engine was firstly modified to obtain a strong in-cylinder tumbling flow, which was measured by a digital Particle Image Velocimetry (PIV) system. Then a two-tracer Planar Laser Induced Fluorescence (PLIF) system was developed to visualise the in-cylinder fuel stratification. The charge stratification was further verified by examining the lean-burn limit at part load of engine operation. These research results show that the present strong tumble field was characterised by a symmetrically-distributed mean velocity in the intake stroke and a very small velocity component along the direction of the tumble rotational axis in the compression stroke. This bulk flow characteristic resulted in a clear fuel stratification laterally and therefore the lean-burn limit was considerably extended. The cyclic variation of the bulk flow affected the charge stratification.
