The influence, of turbulence, through Changes in swirl velocity and exhaust gas reeireulation (EGR), and the combustion process was investigated theoretically and experimentally in it homogeneous charge compression ignition (HCCI) engine fuelled with diesel fuel compatible with EN590. The results show that Combustion chamber geometry can play it relevant role in HCCI combustion. The combustion process in a high swirl bowl in piston combustion chamber has been compared to that in all almost flat piston (nearly disk shape.). Under the same operating conditions-engie speed, injected fuel per cycle, and FOR rate the peak of the heat release rate for the high swirl piston was lower compared to the disk-shaped combustion chamber. In addition, combustion duration was increased, which is thought to be due to the. reduction of gas temperature, larger heat. losses, and mixing improvement. Intensity swirl control offers a potentially effective approach to modulating the combustion process in HCCI engines-although a penalty in efficiency is expected-in addition to other methods based on. control of intake temperature extent of exhaust gas recirculation (EGR). Performance and engine emissions (NOx, HC, CO, and soot) with different EGR rites and changes in swirl velocity are analyzed in this paper. The results have allowed 4 deeper knowledge of the HCCI combustion process with diesel file[ when injected at compression stroke but far from top dead center,