Ignition delay times of ethanol-containing multi-component gasoline surrogates: Shock-tube experiments and detailed modeling

Ignition delay times for binary (ethanol/iso-octane, 25%/75% by liquid volume) and quinary (iso-octane/toluene/n-heptane/diisobutylene/ethanol, 30%/25%/22%/13%/10%) gasoline surrogate fuels in air were measured under stoichiometric conditions behind reflected shock waves. The investigated post-shock temperature ranges from 720 to 1220 K at pressures of 10 bar for the binary mixture and 10 bar and 30 bar for the quinary mixture. Ignition delay times were evaluated using side-wall detection of CH* chemiluminescence (λ = 431.5 nm). Multiple regression analysis of the data indicates global activation energy of ∼124 kJ/mol for the binary mixture and ∼101 kJ/mol for the quinary mixture and a pressure dependence exponent of −1.0 was obtained for the quinary mixture. The measurements were compared to predictions using a proposed detailed kinetics model for multicomponent mixtures that is based on the reference fuels (PRF) model as a kernel and incorporates sub-mechanisms to account for the chemistry of ethanol, toluene and diisobutylene. The model was tested using the measured ignition delay times for the surrogate fuels. Additional comparisons are based on literature data for other fuel combinations of the single constituents forming the quinary surrogate to insure that the modified mechanism still correctly predicts the behavior of simple fuels. The proposed model reproduces the trend of the experimental data for all pure fuels and blends investigated in this work, including the pressure dependence.