Comparison of Experimental and Numerical Modeling of Reforming HCCI Combustion

Homogeneous charge compression ignition (HCCI) engines have high potential to provide better fuel economy with low emissions than conventional spark ignition (SI) engines. In an HCCI engine, combustion phasing strongly depends on the initial temperature and composition. Negative valve overlap (NVO) with reforming has been investigated as combustion phasing control strategy. However, the reforming process is not yet fully understood and further research is necessary to fully utilize the NVO reforming strategy. In this research, optically measured reforming process was modeled by 3D CFD simulation and the results were compared to understand the reforming process better. The optical measurement was carried out with sodium additive to enhance the combustion luminosity. Numerical simulation was carried out with state-of-art spray model with chemical kinetics for ignition and combustion. The chemical reaction mechanism was optimized for modeling the reforming process. It was found that the luminosity from the optical measurement correlates well with the chemical reaction source terms from the simulation.Copyright © 2013 by General Motors