A single-fuel RCCI concept has been proposed to avoid the need for a secondary fuel system required for conventional RCCI by generating the secondary fuel from the primary fuel through catalytic partial oxidation (CPOX) reformation. In conventional RCCI, gasoline or natural gas can be used as the low-reactivity fuel, and diesel can be used as the high-reactivity fuel. In this study, two reformate mixtures generated by reforming diesel fuel at different operating conditions were used as the low-reactivity fuel, with the parent diesel as the high reactivity fuel. The combustion characteristics of reformate-diesel RCCI were compared with the conventional RCCI. A CFD model was also developed and validated against the experimental results. The model was then used to validate a necessary approximation of the reformate mixture's species concentrations. Compared to conventional RCCI fuel pairs, reformate-diesel RCCI shows marginally better thermal efficiency, approximately 10% better THC emissions, approximately 50% lower NOx emissions, and good controllability. Because the reformate mixture has a high concentration of diluents it displaces a large fraction of intake air and acts similarly to EGR. The combustion behavior of reformate-diesel RCCI is in between that of gasoline-diesel and natural gas-diesel conventional RCCI. From the results, it can be concluded that reformate-diesel RCCI is not overly sensitive to the reformation process itself and the exact species concentrations in the reformate mixture. A small change in the start of injection of diesel, blend ratio, and EGR fraction can be used to compensate for reformate mixture concentration differences.