Hydrogen direct-injection engines allow a wide variety of operation strategies. In order to optimise engine design, advanced development methods such as Computational Fluid Dynamics (CFD) are required. The present work outlines numerical analysis of the mixture formation and combustion process employing a modified version of the commercial CFD-code ANSYS CFX. Special emphasis is given to the influence of laminar flame speed on combustion. As computational model for combustion analysis a turbulent flame speed closure (TFC) is selected where a mixture fraction approach is applied and chemical reaction is described in terms of a non-adiabatic laminar flamelet library based on probability density functions. Regarding turbulence modelling, a two-equation Shear Stress Transport (SST) turbulence model has been chosen where a turbulence/frequency kappa-omega approach is solved at the wall and a standard kappa-epsilon model is used in the outer part of the flow. Computations are conducted on an unstructured tetrahedral grid with prismatic layers, which is incrementally refined at the injection zone. Initial and boundary conditions are taken from experiments and onedimensional calculations. Regarding turbulent combustion the hydrogen laminar flame speed is recognised to be the crucial input parameter for the employed modelling approach. The difficulty of obtaining established values of laminar flame speed at engine-like conditions is taken into consideration. Laminar flame speed data published by different authors are compared, where, remarkably, a contrary influence of increasing pressure on the flame velocity is predicted. Finally, own data for laminar flame speed to be used at engine relevant regimes of pressure, temperature and equivalence ratio are derived on the basis of calculations using a reaction mechanism with 10 species and 19 reactions. Computational results are validated with experimental data available in literature. Results of CFD combustion calculations are presented in terms of in-cylinder pressure and burn rate and are validated with experimental data of thermodynamic research engine measurements.
Numerical analysis of the mixture formation and combustion process in a direct injected hydrogen internal combustion engine
Numerische Analysis der Gemischbildung und des Verbrennungsprozesses in einem Wasserstoff-Direkteinspritz-Verbrennungsmotor
2006
13 Seiten, 9 Bilder, 17 Quellen
Aufsatz (Konferenz)
Englisch
Verbrennungsmotor , Wasserstoff , Direkteinspritzung , numerische Analyse , Gemischbildung , Verbrennung (Oxidation) , numerische Strömungssimulation , Flamme , Laminarströmung , turbulente Strömung , Computer-Modell , Wahrscheinlichkeitsdichte , Turbulenzmodell , Scherspannung , Druck (Mechanik) , Temperatur
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