The naturally aspirated compressed natural gas (CNG) fueled homogeneous charge compression ignition (HCCI) engine operation region is narrow between heavy knock at rich air-fuel mixture side and misfire at the lean air-fuel mixture side. However, high activation energy is needed to attain autoignition temperature of CNG fueled HCCI engine. This paper seeks to provide guidance in overcoming challenges of CNG fueled HCCI engine by using CHEMKIN. It is used to investigate the fundamental characteristics of the homogeneous charge compression ignition combustion process for different air-fuel mixture inlet temperature, relative air-fuel ratio of 2.5, and with hemispherical bowl types of combustion chambers. The variation of various properties like the peak cylinder pressure, peak cylinder temperature, CO emission, NO emission, soot emission, and HC emission are studied. It is necessary to develop new combustion models to simulate and predict all parameters with high accuracy.