Multi-Level Modeling of Real Syngas Combustion in a Spark Ignition Engine and Experimental Validation
To be published on September 9, 2019 by SAE International in United States
Syngas produced from biomass gasification is being increasingly considered as a promising alternative to traditional fuels in Spark-Ignition (SI) Internal Combustion Engines (ICEs). This gaseous fuel, composed by a mixture of CO, CH4, H2, CO2, N2 (and other minor hydrocarbon compounds), is however characterized by an extreme variability of its composition and a low energy density. In order to assure good energy performance and stability of operation as the syngas composition slightly changes, numerical modeling can give an important contribution as a tool to investigate the main parameters affecting the combustion process development and the formation of main pollutants. The present work introduces a multi-level set of numerical approaches to a SI ICE fueled with syngas deriving from biomass gasification. Combustion characteristics are investigated at different levels of increasing detail, aiming at giving a complete outlook over the influence of this non-conventional fuel on the engine performances and on its environmental impact. At first, a specific characterization of the dependency of the syngas laminar flame speed upon its composition is achieved through an iterative approach pursued in the ANSYS ChemkinTM environment, where validated correlations of the flame speed tuning parameters are obtained in a zero-dimensional framework. Subsequently, the interaction between the combustion kinetics and the fluid dynamics is taken into account through the development of a mono-dimensional (1D) model of the whole engine system in the GT-Power environment. A predictive combustion model, this last tuned on the ground of the combustion parameters determined through the previous 0D approach, is implemented to guarantee the correct prediction of the engine efficiencies when varying the primary energy related to the gaseous fuel composition. At last, a 3D Computational Fluid Dynamics (CFD) model is developed within the AVL FIRETM software environment to reproduce the engine behavior over the whole engine cycle within a Reynolds Averaged Navier Stokes (RANS) approach. The combustion process is modelled employing the general gas phase reaction approach through the implementation of the detailed chemical reaction mechanism GRI-Mech 3.0, considered the best choice to reproduce the syngas combustion characteristics. All the numerical results are validated with respect to literature data as regards the laminar flame speed prediction, and with respect to experimental measurements as concerns the engine performances.