Schech, J., Siedentop, A., Herbst, F., Wiebe, A. et al., "Conceptual Design of Small Direct-Injection Spark-Ignition Engine Concepts with Various Injector Positions by Use of CAE-Tools," SAE Technical Paper 2012-32-0066, 2012, doi:10.4271/2012-32-0066.
Within a project of a research association (Forschungsver-einigung Verbrennungskraftmaschinen e.V.) a DI spark-ignition engine with small engine displacement was designed at the Institute of Internal Combustion Engines of the Technische Universitat Braunschweig. The objective of the project is to investigate the minimum bore diameter which allows the reasonable use of the advantages of gasoline direct injection.This article outlines the preliminary studies to identify suitable geometry variants for lateral and central injector position concerning effective engine operating data.Under consideration of current production possibilities and geometries of available injector and spark plug CAD studies were carried out. All suitable valve concepts, beginning with a two-valve (2V) concept and up to a four-valve (4V) concept, were examined in the CAD studies. The bore diameter was varied in a range from 56 to 62 mm combined with a variation of the stroke/bore ratio from 0.9 to 1.2. Further the valve angles, spark plug and injector position were changed in wide ranges. The selection of the most suitable variant was based on the criteria of intake valve seat ring diameter and the spark plug eccentricity.The effective operating data was calculated by 1D simulations. Due to the unknown net heat release of the engine the combustion process was determined by the "turbulent-flame" model implemented in the simulation software GT-Power. The influence of the stroke/bore ratio on combustion process was adapted in respect to published results. The supercharging system also has a significant influence on effective operating data. The efficiency of the exhaust turbocharger was modeled by the scavenging pressure difference of a VTG turbocharger and variable compressor inlet guide vanes presented in . The engine friction was considered by an approach developed in . The influence of the stroke/bore ratio, as can be expected from literature, was added to this approach. The final assessment of the variants determined by the CAD studies was carried out by the criteria of charging pressure, gas exchange losses, residual gas rate and BSFC at design point and nominal output point.As a result of the preliminary studies an engine displacement of 200 cm₃ with a bore diameter of 60 mm and a stroke of 71 mm is the most suitable concept with respect to the boundary conditions. Whereas the 3V concept is most appropriate for the vertical and the 4V concept for the horizontal mounted injector position. Both concepts were designed at the institute and will be tested on engine test bench.