Abstract: HCCI combustion incorporates the advantages of both Spark-Ignition (SI) engine and Compression Ignition (CI) engines. The homogeneous mixture is inducted into the cylinder without throttling losses and compressed until the mixture reaches the auto-ignition point then combustion occurs spontaneously without discernable flame propagation. This feature helps to improve engine performance while producing a relatively high thermal efficiency. In the present study, three-dimensional CFD calculation was used where mesh creation and specific zone name with different topologies of each zone has been meshed separately using ANSYS. Fluent was used to model combustion phenomenon in HCCI engine. The validation and simulation were conducted based an HCCI single-cylinder engine fuelled with gasoline in a 4-stroke engine at an engine speed of 1500 rpm with compression ratio of 11.7:1 evaluated using three split injection. Combustion parameters such as cylinder pressure, temperature and heat release rate were obtained from the validation work. The CFD Model yields good results for experiment and CFD simulation. The study focused on how different piston crown designs affect the performance of the HCCI engines. Three different designs have been created and evaluated through CFD analysis where all other engine-operating parameters were kept the same as the experimental work. The pistons names A, B and C for simplicity. Then, the study will analyze the in-cylinder pressure, in-cylinder temperature, heat release rate, turbulent kinetic energy, indicated mean effective pressure and power output of different piston designs and evaluate the most suitable piston to be used in HCCI engines in order to improve the engine performance. The results demonstrate the capability of improved piston crown design in HCCI engine to reduce the levels of gas emissions from engines. All pistons in the investigation reached a peak pressure and temperature above the experiment, pistons A had the highest peak pressure and temperature followed by pistons B and C, respectively. Compared to other piston crown designs, the piston A has the highest power output caused by high peak pressure towards the end of combustion that leads to passable diffusion combustion. Piston A’s design could be used in an HCCI engine configuration to improve engine performance.