The combustion mechanism of n-heptane have been investigated using a zero-dimensional thermodynamic model coupled with a detailed kinetic model. At low temperature reaction, the main initial reactions are NC7H16 + O-2 = C7H15-2 + HO2 and NC7H16 + O-2 = C71H15-3 + HO2. H-atom abstraction from n-heptane occurs primarily by OH and HO2. The first O-2 addition and the second O-2 addition are the most important paths for the low temperature branching. High temperature reaction includes two stages: blue-flame reaction and hot-flame reaction. Blue-flame reaction which is controlled by H2O2 decomposition is mainly the process of the conversion of CH2O to CO by reactions CH2O + OH = HCO + H2O and HCO + O-2 = CO + HO2. Hot-flame reaction which is dominated by reaction H + O-2 = O + OH is mainly the process of the oxidization of CO to CO2 by reaction CO + OH = CO2 + H. There are four regions for HCCI combustion including: I complete combustion region; 11 high CO emissions region where low-temperature reaction and blue-flame reaction occur; III high CH2O emissions region where only low-temperature reaction occurs and IV misfire region. (c) 2006 Elsevier Ltd. All rights reserved.