A lean partially premixed swirling combustor operated with synthesis gases is studied using large-eddy simulation (LES). The linear-eddy model (LEM) is employed to close the unresolved scalar fluxes with the nonunity Lewis number assumption. Several terms resulting from the LES filtering operation are not modeled but directly resolved considering their unique length and time scales, such as molecular diffusion, scalar mixing, and chemical reactions. First, the validation results on a well-established jet flame indicate a good level of correlation with the experimental data and allow a further analysis of syngas combustion on a practical combustor. Second, the effects of preferential diffusion on the characteristics of flow and combustion dynamics on a lean partially premixed swirling combustor are investigated. The obtained results are expected to provide useful information for the design and operation of gas turbine combustion systems using syngas fuels.