AbstractThis paper presents a numerical study of swirl flow effects on the combustion and emissions in single-cylinder spark ignition engine. First, a three-dimensional (3D) computational fluid dynamics (CFD) simulation was performed at two engine operating points to obtain the reference results of in-cylinder flow quantities required for the verification of a new K-k-ε turbulence model integrated with a cycle simulation. Then a zero-dimensional (0D) (quasi-dimensional) combustion model was used to analyze the swirl flow variations on the combustion and emissions where experimental results of 6 operating points were used to calibrate combustion and emission submodels in a cycle simulation. The coupling of the new turbulence and combustion model enabled the reconstruction of ordered in-cylinder swirl flow and the application of velocity operators on flame particles. The double swirl ratio increased the peak cylinder pressure by approximately 20%, and nitrogen oxide emissions were approximately 44% higher, while hydrocarbon (HC) emissions decreased by 44%. The twice lower swirl ratio decreased peak pressure by approximately 6%, and nitrogen oxide emissions were around 15% lower, while HC emissions were increased by 28%. If knock-limited spark advance is found for a double swirl ratio, the engine indicated that efficiency can be increased by 8.7% while HC emissions can be reduced by 20%.