Present technologies of diesel engine combustion involve various operating conditions that can lead to a broad spectrum of combustion regimes. Existing combustion models for diesel engines usually lack universality across combustion regimes. In this study, a mixed-mode combustion model was developed to cover the major regimes pertaining to diesel engine combustion. The model uses kinetically controlled, quasi-steady homogeneous, quasi-steady flamelet, and partially premixed combustion modes. The combustion regime is identified locally by two combustion indices based on the local chemical and mixing conditions. The combustion model takes advantage of mixing details provided by large-eddy simulation. The model was tested over a wide range of engine conditions including conventional diesel-type and low-temperature combustion operating conditions. The model results compared well with experimental data and exhibited strength in both universality and computational efficiency.