A quasi-dimensional charge motion and turbulence model for engine process calculations

This paper describes the development of an in-cylinder turbulence model for use in an engine process calculation. The model calculates (zero-dimensional) turbulence quantities for a predictive burn rate model (homogeneous SI engine). The model is based κ-ε turbulence model. As a key feature, a quasi-dimensional tumble model is presented. Tumble generation and respectively turbulence production and decay of the tumble are modeled on a physical basis. Tumble generation is calculated as a function of stationary tumble numbers and boundary conditions obtained from a 1D-CFD calculation. A calculation of tumble spin-up is discussed. For the in-cylinder turbulence production, tumble, inflow, piston motion and compressibility are taken into account. Dissipation is calculated on the basis of turbulence length scales defined by cylinder geometry and intake valve lift. In addition, during intake an inhomogeneous distribution of turbulence in the cylinder is taken into account. A connection of the developed turbulence model to a predictive burn rate model is presented in the second part of this paper.