Water effect on ignition delay times of ethanol/iso-octane mixtures at elevated pressures

The effect of water addition on the ignition delay times of ethanol/iso-octane mixtures was measured in a shock tube at pressures of 1.2 and 10 atm, temperatures from 943 to 1383 K, an equivalence ratio of 1.0, and water contents of 0 % to 40 % (mole fraction in total component). Results indicate that water addition non-monotonically affects ignition delay times at 1.2 atm, while at 10 atm, it has contrasting effects across different temperature ranges. Simulations from five representative literature models were compared with experimental data. Chemical kinetic analysis was conducted using both the Modified LLNL 2021 model and RWTH 2015 model at 10 atm and temperatures of 1300 K and 950 K. Reaction pathway analysis indicates that increased water content in the ambient enhances H-atom abstraction pathways by OH radicals during the ignition of both ethanol and iso-octane. Sensitivity analysis indicated that reactions involving hydrogen chemistry significantly influences ignition. Rate of production analysis identified consumption rates and pathways of H atom as key factors affecting temperature dependence after water addition. The fictitious diluent gas method was introduced to isolate thermal and chemical kinetics effects after water addition.