Analysis of In-cylinder Flow in a Small-Bore Spark-Ignition Engine Using Computational Fluid Dynamics Simulations and Zero-Dimensional-Based Modeling

The evolution of in-cylinder flow involves small and large-scale structures during the intake and compression strokes, significantly influencing the fuel-air mixing and combustion processes. Extensive research has been conducted to investigate the flow evolution in medium to large-sized engines using laser-based diagnostic methods, computational fluid dynamics (CFD) simulations, and zero-dimensional (0-D) based modeling. However, in the present study, we provide a detailed analysis of the evolution of flow fields in a small-bore spark ignition engine with a displacement volume of 110 cm3. This analysis employs a unique methodology where CFD simulation is performed and validated using measured particle image velocimetry (PIV) data. Subsequently, the validated CFD results are utilized to develop and validate a 0-D-based model as it is computationally more efficient. The validated CFD simulation and 0-D-based model are used to evaluate the quantified strength of the flow fields by calculating the tumble ratio and turbulent kinetic energy (TKE). The streamlines and velocity vectors of the flow fields obtained from CFD simulations are utilized to explain the evolution of these parameters during intake and compression strokes. The study is further extended to analyze the effect of engine speed on the evolution of flow fields. With an increase in engine speed, relatively higher values of tumble ratio and TKE at the end of the compression stroke are observed, which is expected to improve the fuel-air mixing and combustion efficiency.