Three-dimensional spray-flow interaction in a spark-ignition direct-injection engine

Large efforts are currently being made toward improving internal combustion engine efficiency without degrading overall performance. To this end, advanced combustion strategies that require in-cylinder fuel/air mixtures to be prepared with unprecedented care and exactness are being implemented. Spray-guided stratified-charge operation is an example of one such strategy that offers high efficiency under light-load operation but requires precise fuel injector and combustion chamber design to ensure robust engine performance. Understanding the mixture formation processes aids in the success of such strategies and is therefore an important goal for internal combustion engine research. Direct visualization via optical diagnostics remains one of the most powerful tools for gaining insight into in-cylinder mixing processes, such as liquid fuel spray atomization. Although substantial efforts have been made over the last few decades to develop and implement liquid fuel spray diagnostics in the challenging in-cylinder environment, such techniques have been almost exclusively two-dimensional or too complex to be used regularly in design practices. Only now are practical, commercially available three-dimensional visualization technologies beginning to mature to a level for which they can be adapted to perform in-cylinder diagnostics. In this study, the three-dimensional fuel spray structure and its variations are visualized by a single plenoptic camera in an optically accessible spark-ignition direct-injection engine. The engine is operated under a variety of conditions relevant to conventional homogeneous-charge and spray-guided stratified-charge engine strategies. The spray and flow field interaction under different bulk flow conditions as well as engine speeds are clearly discernable in the instantaneous three-dimensional spray images, establishing the imaging technique as a viable and unique new tool for complex three-dimensional engine in-cylinder processes research.