A CFD model with optical validation on in-cylinder charge performances of CAI engines

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. Applying a Laser Doppler Anemometry (LDA) to the same engine, the cycle averaged time history mean and Root Mean Square (RMS) velocity profiles for the axial and radial velocity components in three axial planes were measured throughout the inlet and compression stroke. The calculated results were compared with the experimental results in terms of the vectors flow fields, averaged integrated tumble ratio as a function of crankangle and the local velocities in this paper. The results from both studies showed good correlations.