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Technical Paper

PRF and Toluene/n-heptane Mixture Comparison in HCCI Mode Ignition Using Transient Species Measurements and Simplified Model Analysis, Supported by 0-D and 3-D Simulations

Exhaust gas analysis has been conducted for a test engine operated in HCCI mode at hot ignition suppressed condition, to detect intermediate species formed in low temperature oxidation (LTO). PRF (isooctane/ n-heptane) and NTF (toluene/ n-heptane) were used as fuel mixtures. The LTO fuel consumption decreases with increasing iso-octane content in PRF and toluene content in NTF, but only NTF showed a nonlinear effect. These tendencies were reproduced by O-D and 3-D simulations with detailed chemistry; however, quantitative differences were found between chemical models. The essential mechanism of high octane number fuel affecting the ignition property of n-heptane is discussed by developing a simplified model summarizing chain reaction of LTO, in which OH reproduction and fuel + OH reaction rate play important roles.
Journal Article

Chemical Kinetic Mechanism of Compression Ignition Derived from Intermediate Species for PRF and Toluene/n-Heptane Fuel Systems

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 opposite trend was found in NTF. These tendencies correspond to the difference in the detail reaction mechanism for PRF and NTF oxidation.
Journal Article

Comparison of PRF and toluene/n-heptane mixture fuel in the mechanism of compression ignition using CA resolved sampling

Chemical kinetic mechanism of compression ignition with PRF (iso-octane/ n-heptane) and NTF (toluene/ n-heptane) is investigated according to crank angle resolved in-cylinder sampling experiments. Profiles of two-stage consumption of fuel components in accordance with the timings of heat releases have been obtained. As well, production and consumption of intermediate species were observed. It was found that toluene consumption at the first stage is considerably less than that of n-heptane, whereas iso-octane consumption is comparable to that of n-heptane, which is accounted for by the smaller rate constant of toluene with OH. N-heptane and iso-octane are considered to produce formaldehyde; however, toluene has no or little contribution.
Technical Paper

Mechanism Controlling Autoignition Derived from Transient Chemical Composition Analysis in HCCI

The chemical mechanism responsible for controlling ignition timing by using additives in HCCI has been investigated. Dimethyl ether (DME) and methanol were used as the main fuel and the additive, respectively. Fuel consumption and intermediate formation in the first stage (cool ignition) were measured with crank angle resolved pulse-valve sampling and exhaust gas analysis, where HCHO, HCOOH, CO, H2O2 and other species were detected as the intermediate. The effect of methanol addition retarding ignition is represented by an analytical model in which the growth rate of the chain reaction is reduced by the methanol addition.