Abstract In this paper the work deals with the Experimental analysis of the early direct injected HCCI. The computational analysis of the engine was carried out using CHEMKIN-PRO Software. The computational analysis was carried out using the auto ignition chemistry by means of reduced chemical kinetics. For these investigations, the neat diesel and bio ethanol - diesel blend (E20) fuels were used as fuel and the pressure, combustion and emission characteristics were studied in the equivalence ratio of 0.6 (ɸ = 0.6). The injection timing was advanced to 18° rather than the normal 23° before top dead centre (BTDC) as specified engine conditions. Since pressure and temperature profiles plays a vital role in reaction path at certain operating conditions, an effort has been made here to present a comprehensive reaction path analysis on the formation/destruction of chemical species at peak temperature and pressure conditions.