Impact of exhaust gas recirculation and nitric oxide on the autoignition of an oxygenated gasoline: Experiments and kinetic modelling

Exhaust gas recirculation (EGR) and NO_x affect the autoignition of gasoline in internal combustion engines. In this work, ignition delay times of an oxygenated gasoline (Euro 6 E10) are investigated with EGR and NO_x addition. The experimental data are of interest for gasoline surrogate modeling and for predicting fuel ignition behavior in various engine combustion modes. We studied Euro 6 E10 reactivity with EGR additions of 20 % and 40 % (by mass) doped, in select cases, with high levels of NO_x (874, 1501, 3174, and 5568 ppm, by mol%). Experiments were performed in two high-pressure shock tubes (HPSTs) and two rapid compression machines (RCMs) over a wide range of temperature (658–1610 K), equivalence ratio (0.5, 1.0) and at pressures of 20 and 30 bar. Results show that EGR addition inhibits Euro 6 E10 gasoline reactivity in the intermediate- and low-temperature regimes, while it is minimally affected at high-temperatures. In contrast, a strong reactivity-promoting effect of NO_x is observed at temperatures greater than 825 K for all equivalence ratios investigated, while an inhibiting effect is seen at lower temperatures with a high doping of NO_x (1501 ppm). For fuel-lean cases, where Euro 6/EGR mixtures are sensitized with 3174 – 5568 ppm NO_x, a significant reactivity-promoting effect is observed across the entire range of conditions investigated, except at temperatures below 830 K, where the NO_x-inhibiting effect dominates. A gasoline surrogate model is developed by combining a detailed gasoline surrogate mechanism with appropriate sub-models and making minor updates. The proposed model captures well the influence of EGR and EGR/NO_x on Euro 6 E10 autoignition over the wide range of conditions studied here. Finally, sensitivity analyses were conducted to identify key reactions contributing to the perturbative effects of EGR and EGR/NO_x on oxygenated gasoline ignition.