Increasing oil prices and emission legislation have forced car manufacturers and suppliers to investigate new methods and technologies to improve the efficiency of current spark ignition engines.
In order to follow these trends and to yield a contribution in the development of modern combustion concepts, spark plugs with improved ignition performance are required. Reliable ignition and inflammation in operating points employing stratified and lean air/fuel charge is thereby a challenging task.
In this study we are using a full 3D model of the engine which is offering a possibility to conduct a virtual replacement of the spark plug. With this modeling concept we are able to investigate the influence of different spark plug designs on the ignitability of the air/fuel mixture at the ignition time. For evaluation of results, two quantities that are of particular importance for a successful ignition and subsequent inflammation have been analyzed: flow velocity and concentration of the evaporated fuel in the discharge volume of the spark plug. The presented modeling approach allows solely a qualitative comparison of different spark plug designs. Thus, recommendation regarding appropriate spark plug geometry for a given engine can be deduced from such a study.
Prior to engine simulation an adjustment and optimization of the spray layout for the given engine has been performed. In order to obtain reliable parameters for accurate simulation of fuel injection and evaporation, a rather complex investigation of spray characteristics was necessary. All calculations that are published in this paper have been accomplished using the CFD software package AVL FIRE™ v8 [1].
The results obtained with two different spark plug designs obtained in one operating point running with stratified fuel charge will be presented.