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Technical Paper

Predictions of In-Cylinder Swirl Velocity and Turbulence Intensity for an Open Chamber Cup in Piston Engine

A flow model is presented that predicts the swirl and turbulent velocities in an open chamber, cup-in-piston I.C. engine. The swirl model is based on an integral formulation of the angular momentum equation solved with an assumed tangential velocity profile form, Vθ(r). This enables the swirl model to predict a non-solid body rotation which is a function of the inlet flow, wall shear and squish motion during the engine cycle. The mean flow model is coupled with a global K-ε model which together predict shear stresses, mixing rates and heat transfer coefficients. An integrated form of the K-ε turbulence model is used which includes the compressibility, shear and boundary layer effects. Turbulence generated by the inlet flow is included and assumed to be proportional to the velocity past the intake valve. Also, the production of turbulence due to the boundary layer effects are included.
Technical Paper

The Effect of In-Cylinder Flow Processes (Swirl, Squish and Turbulence Intensity) on Engine Efficiency — Model Predictions

A computer simulation for the performance of a four-stroke spark-ignition engine is used to assess the effects of in-cylinder flow processes on engine efficiency. The engine simulation model is a thermodynamic model coupled to submodels for the various physical processes of in-cylinder swirl, squish and turbulent velocities, heat transfer and flame propagation. The swirl and turbulence models are based on an integral formulation of the angular momentum equation and a K-ε turbulence model, These models account for the effects of changes in geometry of the intake system and the chamber design on in-cylinder flow processes. The combustion model is an entrainment burn-up model applicable to the mixing controlled region of turbulent flame propagation. The flame is assumed to propagate spherically from one or two spark plug locations. A heat transfer model that is dependent upon the turbulence level is used to compute the heat loss from the unburned and burned gases.