Investigation on Mixture Formation and Combustion Process in a CNG-Engine by Using a Fast Response 3D-CFD-Simulation 2004-01-3004

The research institute FKFS in cooperation with the IVK Universität Stuttgart has recently presented QuickSim, a 3D-CFD-tool, that works integrated into the commercial 3D-CFD-code Star-CD. QuickSim has been developed to cover a vacancy in the market of simulation programs for engine development. The code introduces a new concept in the 3D-CFD-simulation of internal combustion engines (SI-Manifold-Injection and SI-GDI), that drastically reduces the CPU-time in comparison to a conventional 3D-CFD-simulation. QuickSim, as a 3D-CFD-tool, combines the advantages of local resolution of the fluid-dynamical field of internal combustion engines exactly like that provided by traditional 3D-CFD-simulations and the versatility and clearness of the real working-process analysis (WP) and of the full 1D-flow calculations. The CPU-time always remains in an acceptable range (few hours over a full operating cycle for a single-processor computing simulation). Numerous validation tests on different engine meshes during the last years show, that QuickSim is able to predict the engine behavior with a very high accuracy over widespread applications.

The present paper introduces the aforementioned 3D-CFD-tool QuickSim and it reports a particular application of this tool, in which the mixture formation and combustion process of a turbocharged CNG-engine (Compressed Natural Gas) have been investigated. The results of this work are mainly intended to set a focus both on the injection system modeling and on the problem related to the influence of the initial conditions on the results. In comparison to a traditional 3D-CFD-simulation, whose calculation starts before inlet valve opening (IVO) and ends before exhaust valve opening (EVO) of the same operating cycle, QuickSim allows the simulation of several successive operating cycles. Thanks to this capability, the influence of the initial conditions, which is in many cases a critical factor for the accuracy of the results, can be completely removed. As will be shown in this paper, the 3D-CFD-simulation of several successive operating cycles is especially required in case of inlet manifold fuel-injection.