The thermal efficiency of spark-ignition engines can be enhanced by increasing the rate of exhaust gas recirculation (EGR) such that the low temperature combustion regime could be achieved. However, there is an upper limit on the amount of EGR rate, beyond which flame speed becomes slow and unstable, and local quenching starts to hurt the combustion stability, efficiency, and emission. To resolve this issue, the concept of dedicated EGR has been proposed previously to be an effective way to enhance flame propagation under lean burn condition with even higher levels of EGR with reformate hydrogen and carbon monoxide. In this study, the effects of thermochemical fuel reforming on the reformate composition under rich conditions (1.0 < ϕ < 2.0) have been studied using detailed chemistry for iso-octane, as the representative component for gasoline. The rich combustion products are then used to represent the composition of the dedicated EGR, whose influence on laminar flame speed and ignition delay time is further analyzed and reported. It is seen that the D-EGR could accelerate flame propagation, while retarding auto-ignition delay in the NTC regime. Moreover, the performance of the dedicated EGR in an SI engine system has been simulated using a one-dimensional model in the commercial software GT-Suite under both full and part load conditions. Parametric studies have been performed to provide guidance on the optimal operation conditions for SI engine with dedicated EGR.