Multidimensional modeling of CNG direct injection and mixture preparation in a SI engine cylinder

In this study, a numerical model has been developed with AVL FIRE software to perform an investigation into a direct natural gas injection into the cylinder of spark ignition internal combustion engines. Two main parts have been taken into consideration, aiming to convert an MPFI gasoline engine to a direct injection NG engine. In the rst part, multi-dimensional numerical simulation of the transient injection process, the mixing and the ow eld have been performed using dierent validation cases in order to assure the numerical model validity of results. In all cases, the present results were found to have excellent agreement with experimental and numerical results from literature. In the second part, the validated model has been applied to methane injection into the cylinder of a direct injection engine. Five dierent piston head shapes have been taken into consideration and a centrally mounted inwardly-opening single-hole injector has been adapted to all cases. The eects of injection and combustion chamber geometry have been studied on the mixing of air-fuel inside the cylinder via quantitative and qualitative representation of results. Furthermore, the eect of real engine cylinder head shape on gas injection has been investigated. Based on the results, suitable geometrical conguration for a NG DI engine has been discussed.