Abstract: It is widely accepted that the Homogeneous Charge Combustion Ignition (HCCI) can enhance engines’ efficiency. However, finding optimal operating conditions to yield optimal engines’ ignition timing is still an on-going issue and difficult to achieve. This is because combustion in HCCI engines is automatically occurred from chemical kinetics of the fuel-air mixtures and therefore altering one parameter (out of many parameters) could change the engines’ ignition timing, leading to highly nonlinear behavior of the HCCI engines.