Development of a fuel stratification spark ignition engine

Abstract

A fuel stratification concept is being researched and developed in a three-valve twin-spark ignition engine. This concept requires that two different fuels or fuel components 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. Similar to the traditional air/fuel stratification engine, this fuel stratification engine can operate in very lean mixture or high exhaust gas dilution at part loads to reduce fuel consumption and NOx emissions. While at high-load operation, a higher compression ratio may be allowed owing to a potential increase in antiknock features if the lower research octane number (RON) fuel or component is ignited first, leaving the higher RON fuel in the end gas region. As a result, the fuel economy can be improved not only at part loads but possibly at full loads as well. This paper reports the development of such a fuel stratification engine. Firstly, the intake system of the engine was modified to produce a strong tumble 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 visualize the fuel stratification in the cylinder. The engine combustion at part and full loads was also tested and analysed from cylinder pressure history. These research results show that the present strong tumble flow was characterized 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 flowfield created good fuel stratification laterally. The lean burn limit was considerably extended at part loads, and the knock limit at high loads also had a noticeable difference when higher and lower RON fuels respectively were ignited first.