Natural gas spark ignition engines have been gaining market share in transportation over the last years. This study focuses on modeling lean combustion processes in natural gas engines using detailed computational fluid dynamics simulations. CONVERGE CFD (a commercial computational fluid dynamics software) is used for the modeling and simulations. This software was selected because it is the industry standard for CFD simulations in internal combustion engines. It also includes adaptive mesh refinement and grid embedding utilities, which are a new scientific approach to the computational solution of fluid dynamic problems.