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Over the past few decades, Homogeneous Charge Compression Ignition (HCCI) or Controlled Auto-Ignition (CAI) if it is fuelled with gasoline type of fuels has shown its potential to overcome the limitations and environmental issue concerns of the Spark Ignition (SI) and Compression Ignition (CI) engines. However, controlling the ignition timing of a CAI engine over a wide range of speeds and loads is challenging. Combustion in CAI is affected by a number of factors; the local temperature, the local composition of the air/fuel mixture, time and to a lesser degree the pressure. The in-cylinder engine charge flow fields have significant influences on these factors, especially the local gas properties, which leads to the influences towards the CAI combustion. In this study, such influences were investigated using a Computational Fluid Dynamics (CFD) engine simulation package fitted with a real optical research engine geometry.

This paper deals with the numerical investigation of the in-cylinder flow structures under steady-state conditions utilizing the finite-volume CFD package, STAR CCM+. Two turbulence models were used to simulate the turbulent flow structure namely, Realizable k-ε and Reynolds Stress Turbulence Model, RSTM. Three mesh densities of polyhedral type are examined. The three-dimensional numerical investigation has been conducted on an engine head of a pent-roof type (Lotus) for a number of fixed valve lifts (2mm, 5mm, 8mm) at two pressure drops 2451.662 Pa and 6227.222 Pa that is equivalent to engine speeds of 2500 and 4000 RPM respectively. This correlation between pressure drop and engine speed is provided by Lotus engineering according to real engine studies. Based on the comparison between two turbulence models, the turbulent flow structure was simulated using RSTM model for a number of tumble and swirl planes.

This paper presents the findings from a numerical study of a gasoline direct injection engine flow using the Large Eddy Simulation (LES) modelling technique. The study is carried out over 30 successive engine cycles. The study illustrates how the more simple but robust Smagorinsky LES sub-grid scale turbulence model can be applied to a complex engine geometry with realistic engineering mesh size and computational expense whilst still meeting the filter width requirements to resolve the majority of large scale turbulent structures. Detailed description is provided here for the computational setup, including the initialisation strategy. The mesh is evaluated using a turbulence resolution parameter and shows the solution to generally resolve upwards of 80% of the turbulence kinetic energy.