Intermediate species formed in the cool ignition stage of autoignition were evaluated by exhaust gas analysis with FT-IR in a test engine at hot ignition suppressed conditions. PRF (iso-octane/n-heptane) and NTF (toluene/n-heptane) were used as the fuels. The fuel consumption rate decreases with increasing iso-octane content in PRF and toluene content in NTF. HCHO generation rate increases with increasing iso-octane content in PRF but the opposide trend was found in NTF. These tendencies correspond to the difference in the detail reaction mechanism for PRF and NTF oxidation. Finally the essential mechanism affecting the ignition property of n-heptane is discussed by developing a simplified model reproducing the experimental results.
