Experimental and Simulative Approaches for the Determination of Discharge Coefficients for Inlet and Exhaust Valves and Ports in Internal Combustion Engines

摘要

In order to fulfill future exhaust emission regulations, the variety of subsystems of internal combustion engines is progressively investigated and optimized in detail. The present article mainly focuses on studies of the flow field and the resulting discharge coefficients of the intake and exhaust valves and ports. In particular, the valves and ports influence the required work for the gas exchange process, as well as the cylinder charge and consequently highly impact the engine’s performance. For the evaluation of discharge coefficients of a modern combustion engine, a stationary flow test bench has been set up at the Chair of Internal Combustion Engines (LVK) of the Technical University of Munich (TUM). The setup is connected to the test bench’s charge air system, allowing the adjustment and control of the system pressure, as well as the pressure difference across the particular gas exchange valve. Extensive investigations regarding the pressure level, as well as the pressure difference across the valve gap indicate a significant influence of the particular flow conditions on the calculation of these static discharge coefficients. Moreover, the article presents a more detailed evaluation of the flow field within the valve gap by means of 3D-CFD simulations. One of the most important factors for meaningful simulation results is the meshing strategy. Especially the structure of the computational grid around the valves shows a crucial impact on the numerical stability, as well as the macroscopic simulation results. Therefore, the present article describes the chosen meshing strategy in detail, as well as the critical influences on the convergence of the calculation. Furthermore, since the discharge coefficients are conventionally determined from stationary flow conditions, the article describes an approach for the evaluation of crank angle dependent discharge coefficients, based on a 3D-CFD gas exchange simulation. The results are explicitly discussed regarding the differences between stationary and transient evaluation of the flow field.