Low temperature combustion in homogeneous charge compression ignition (HCCI) engines is an alternative combustion technique to existing automotive spark ignition and diesel engines. The present study is aimed at fundamental understanding of phenomena affecting combustion and emissions of gasoline fuelled HCCI engines with internal gas re-circulation. The experiments that yielded the results were performed using dedicated engine test stand with single cylinder research engine. Different control parameter sweeps were accomplished to provide comprehensive data on engine operating parameters, combustion evolutions and emissions under variable conditions. Experimental analysis was also supported by engine cycle simulation to provide more comprehensive data on in-cylinder processes.