In the search for cleaner and greener power generation systems, researchers are relentlessly searching for a new engine technology that can perform at a higher efficiency with lower environmentally unsafe gas and particulate matter emissions. A Homogeneous Charge Compression Ignition (HCCI) is one such class of engines, which uses high compression ratio to ignite pre-mixed homogeneous air-fuel mixture without the need for any spark plugs. One of the major challenges associated with the HCCI engine is the very rapid combustion rate that results in very high rate of pressure rise and high heat release rate. One way to address this issue is to reduce the combustion temperature by inducting exhaust gas recirculation (EGR) inside the combustion chamber to dilute the reactant mixture and subsequently lower the reaction rate and harmful emission. The objective in this study is to observe the effects of EGR fraction on HCCI engine combustion process, and its effect on the engine efficiency and emission compositions. This study includes analysis of an HCCI engine using a simulation analysis model based on a three-dimensional turbulent CFD model along with detailed chemical-kinetics and non-isothermal wall heat loss. A sensitivity analysis of the effects of the EGR flow rate fraction and the engine RPM on the combustion, pressure-rise rates (PRR) and heat-release rates (HRR), engine efficiency, and emission concentration is carried out.