Comparison of PRF and toluene/n-heptane mixture in the mechanism of compression ignition using transient species measurements and simplified model analysis

Intermediate species formed in the low temperature heat release (LTR) of autoignition were evaluated in test engines by crank angle resolved in-cylinder sampling and exhaust gas analysis with FT-IR at hot ignition suppressed conditions. PRF (iso-octane/n-heptane) and NTF (toluene/n-heptane) were used as the fuels. The LTR fuel consumption decreases with increasing iso-octane content in PRF, whereas the effect of toluene in NTF is weaker. Formaldehyde generation yield increases with increasing iso-octane content in PRF but the opposite trend was found in NTF. The chain reaction mechanism of LTR accounts for the observations; i.e., the chain carrier OH reproduced by n-heptane is consumed by iso-octane, toluene and intermediates such as formaldehyde. Reaction pathways for product species characteristic to each fuel component are also discussed.