Shock-Tube Laser Absorption Measurements of CO and H₂O during Iso-Octane Combustion

The oxidation of iso-octane was studied in two different shock tubes by recording mole fraction time histories of CO and H₂O at various equivalence ratios (0.5, 1.0, and 2.0) at around 1.5 atm, between 1320 and 1815 K. Mixtures were diluted in 99% inert gases. Results show that the induction delay time for both CO and H₂O are particularly sensitive to the temperature and the equivalence ratio. The CO profiles for the fuel-lean and stoichiometric mixtures present a peak in CO formation, due to the oxidation of CO to CO₂. This peak was not observed for the fuel rich mixture, where the CO profile reaches a plateau within the time frame investigated. For the water profiles, they all present a plateau after the main water formation process, although this plateau is still ascending for the fuel-lean and stoichiometric mixtures during the test time. Experimental results were compared with detailed kinetics mechanisms from the literature, the most recent one (Atef et al. Comb. Flame 2017, 178, 111–134) being in overall good agreement with the data except for the maximum CO mole fraction at the lowest temperatures investigated. A numerical analysis was conducted with this model to explain the results and to identify ways to improve the model.