Comparison Between Steady and Unsteady CFD Simulations of Two Different Port Designs in a Four Valve HSDI Diesel Engine: Swirl Intensity and Engine Permeability

Swirl control strategies are useful methods for controlling mixture formation in HSDI Diesel engines. Test rigs allows only steady state measurements of the Swirl number, and give only a rough estimation of the charge motion during the actual compression stroke within the engine. On the contrary, CFD simulations are powerful tools to characterize the air flow drawn into the cylinder, since they allow not only steady state operations, but also full dynamic modeling of the intake and compression strokes. This paper studies an application of computational fluid dynamics for predicting intake swirl intensity in an automotive 4 valve per cylinder C.I. Diesel engine. Two different intake ports are compared and the best trade off between engine permeability and swirl intensity is assessed. Both steady state and dynamic simulations of the induction process are carried out, and results demonstrate that steady state analysis is a reliable tool for predicting the port permeability, while the same capability is not proved in investigating the organized charge motion within the chamber.