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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.

A simplified reaction model of dymethyl ether (DME) oxidation has been developed by extracting essential elementary reactions from a previous detailed mechanism. It consists of 23 reactions for 23 species without modification of rate coefficients in low temperature oxidation of the original model. Spatially non-dimensional calculations were conducted along with HCCI compression profiles using SENKIN code in CHEMKIN package. Good agreement with the detailed model was obtained in terms of ignition timing and profiles of species such as DME, HCHO, O2, H2O2, and CO as functions of intake gas temperature, equivalence ratio, and intake pressure. Adding a few reactions to the mechanism, the effective range of the model was extended to rich side, where CO emission is significant. Effect of methanol addition as an ignition suppressor was also properly described.

Two different species measurements have been conducted for compression ignition of dimethyl ether in a motored engine. Crank angle resolved pulse-valve sampling with a resolution improvement scheme enabled to detect partial fuel consumption and formation of intermediate like H2O2 and HCHO at a cool ignition, as well as their total consumption at a hot ignition. FTIR analysis of exhaust gas in single cool ignition conditions confirmed formation of HCOOH and HCOOCH3 in cool ignitions. Results obtained in a range of equivalence ratio support the advantage of 2000 version of Curran et al. DME oxidation model.

Multi-stage heat releases in homogenous charge compression ignition (HCCI) near the ignition threshold are analyzed in this study. Motored engine experiments are conducted with exhaust gas analysis by Fourier transform infrared spectrometer under hot ignition suppressed condition, in order to provide a deeper insight into the ignition mechanism of n-heptane. By increasing intake temperature from room temperature, heat release of low temperature oxidation (LTO) can be observed. Moreover, second heat release was observed after primary heat release of LTO, which increases rapidly with increasing intake temperature within narrow range below the high temperature oxidation (HTO) threshold. The mechanism of HTO preparation reaction is discussed.

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.