Impact of exhaust gas recirculation on ignition delay times of gasoline fuel: An experimental and modeling study

Abstract

The ignition delay times of a research grade gasoline, RON95E10, are measured in a rapid compression machine and in a shock tube. The experiments are carried out for fuel/O2/Ar/N2 mixtures with two equivalence ratios of 0.77 and 1.18 at pressures between 20 and 40 bar over the temperature range of 700–1250 K. In particular, data are reported for two exhaust gas recirculation (EGR) loadings of 0 and 25% to demonstrate the impact of EGR on gasoline ignition delay times. The presented data are, to the authors’ knowledge, the first set of ignition delay times of real gasoline with EGR and at engine relevant high pressures covering the entire intermediate temperature range. A published gasoline mechanism (Cai and Pitsch, 2015) is modified as part of this study following the latest kinetic knowledge and is further used to compute the ignition delay times at the conditions experimentally investigated. The simulations employ a four-component surrogate consisting of n-heptane, iso-octane, toluene, and ethanol. It is shown that the proposed model predicts the total ignition delay times of gasoline accurately under various conditions and reflects correctly the influences of pressure, EGR, and equivalence ratio on ignition delay times, while it fails to predict the first stage ignition delay times with very high accuracy due to the neglect of the olefin and naphthene content in the surrogate formulation. Furthermore, the influence of exhaust gas addition on ignition delay times is analyzed and discussed in more detail using results from numerical simulations. The chemical impact of EGR is minor but not negligible and varies at different conditions depending on the EGR composition.