A Shock Tube Experimental and Modeling Study of Multicomponent Gasoline Surrogates Diluted with Exhaust Gas Recirculation

The ignition delay for pure cyclohexane and two quaternary gasoline surrogate fuels CTRF1 (isooctane/<i>n</i>-heptane/toluene/cyclohexane, 37.070/11/40.076/11.854 by mole fraction), CTRF2 (isooctane/<i>n</i>-heptane/toluene/cyclohexane, 30.538/11/43.077/15.385 by mole fraction) with the same research octane number of 95 (RON = 95) in air is measured under lean, stoichiometric, and rich conditions behind reflected shock waves, at temperatures of 1027 K–1400 K, and pressures of 10, 15, and 19 bar/20 bar. To analyze the effects of exhaust gas recirculation upon ignition, CTRF1/air mixtures are diluted with CO₂ to simulate different exhaust gas recirculation (EGR) loadings (0, 20%, 40%, and 60%). The experimental data are compared to the predictions calculated by a detailed chemical kinetic mechanism with 526 species and 2763 reactions generated in this work, which is also validated by the autoignition characteristics of pure cyclohexane, iso-octane, <i>n</i>-heptane, toluene, and their binary and ternary mixtures. The simulation results of the mechanism are in good agreement with the experimental measurements, and both the experimental and kinetic modeling data illustrate a negative correlation between the ignition delay of CTRF1/CTRF2 and the pressure, temperature, and equivalence ratio, and a clear rise of the ignition delay for CTRF1 with increased EGR loadings is also showed. Moreover, on the basis of the detailed kinetic model, the reaction pathway, rate of production analysis, and sensitivity analysis are also performed to clarify the influence of EGR on the ignition delay of CTRF1, which indicates the predominate role of thermal and dilution effects that CO₂ has on the ignition, while the chemical effects are proven negligible over the range of experimental conditions