Developing a Fuel Stratification Concept on a Spark Ignition Engines 2007-01-0476
A fuel stratification concept has been developed in a three-valve twin-spark spark ignition engine. This concept requires that two fuels or fuel components of different octane numbers (ON) be introduced into the cylinder separately through two independent inlet ports. They are then stratified into two regions laterally by a strong tumbling flow and ignited by the spark plug located in each region. This engine can operate in the traditional stratified lean-burn mode at part loads to obtain a good part-load fuel economy as long as one fuel is supplied. At high loads, an improved fuel economy might also be obtained by igniting the low ON fuel first and leaving the high ON fuel in the end gas region to resist knock.
This paper gives a detailed description of developing the fuel stratification concept, including optimization of in-cylinder flow, mixture and combustion. To achieve fuel stratification, the intake valves were shrouded to produce a strong tumble flow which was measured by a particle image velocimetry (PIV) system. The PIV results showed that the flow was symmetrically distributed around the symmetric plane of the combustion chamber, benefit to keep two fuels apart to form a lateral stratification of fuel. The fuel stratification was verified by a two-tracer PLIF (planar laser induced fluorescence) technique which was developed for this purpose. As a result of flow and mixture optimization, the lean-burn limit at part loads was observed to extend considerably and the knock limit at high loads was also extended apparently when igniting the low ON fuel first comparing to igniting the high ON fuel first.