Analysis of hydrogen direct-injection internal combustion engines with methods of computational fluid dynamics

You are here: Homepage > Search

Analysis of hydrogen direct-injection internal combustion engines with methods of computational fluid dynamics

Gerke, Udo / Boulouchos, Konstantinos / Wimmer, Andreas / Kirchweger, Wolfram

Hydrogen direct-injection (DI) engines offer a wide range of possibilities for combustion design, such as fuel stratification and multiple injections. Combustion may involve premixed, partially premixed and non-premixed modes. Key issue of a non-homogeneous engine operation is an accurate preparation of the fuel/air mixture. Optical investigations and three-dimensional numerical analysis are applied with regard to an improvement of the injection parameters and combustion process. The present work outlines results of Computational Fluid Dynamics (CFD) with respect to mixture formation and combustion in comparison to experimental data. Special emphasis is given to the influence of turbulence models on mixture formation calculations. As to CFD simulation of stratified operation, the hydrogen mixture formation is of crucial importance for the subsequent fuel conversion. Consequently, numerical analysis of the combustion process can only be as accurate as the computation of the mixture distribution it is based upon. Main influence on mixture formation calculations of hydrogen-jet propagation was recognised to be the numerical grid as well as the turbulence modelling approach. The influence of molecular diffusion on the hydrogen mixture formation process was found to be negligible. The performed CFD analysis discusses different two-equation turbulence models as well as a Reynolds Stress Model approach. The influence of the models on results of mixture formation and turbulent kinetic energy (velocity fluctuations) is demonstrated. CFD results are validated against optical experimental data from a research engine, using planar laser induced fluorescence (PLIF) measurements. Results of combustion analysis are depicted in terms of pressure traces and burn rates. CFD-results of both port fuel injection and direct injection operation are compared to experimental data for stoichiometric mixtures at 2000 rpm. A turbulent flame speed closure approach is applied as combustion model, where the mean reaction progress is depicted in terms of a transport equation of a reaction progress variable. Regarding description of the turbulent flame speed, a model based on laminar flame speed data as proposed by Zimont (1999) is applied.