Studies of high pressure 1,3-butadiene flame speeds and high temperature kinetics using hydrogen and oxygen sensitization

The high pressure flame speeds and high temperature kinetics of 1,3-butadiene mixtures are studied by using spherical flames at fuel rich and lean conditions at 1–18 atm with H₂ and O₂ additions. H₂ and O₂ are added in the mixture to perturb concentrations of H/O radicals and the flame speed sensitivity to 1,3-butadiene + O/H reactions. The presently measured 1,3-butadiene/air flame speeds agree with previous studies at ambient pressure, but are lower at 5 atm. Comparison between the new experimental data and the prediction by the recently developed 1,3-butadiene model (Zhou et al., 2018) shows over-prediction of the flame speeds, especially at high pressure and fuel lean conditions. With H₂ and O₂ sensitization, the discrepancy between the model prediction and experiments becomes even larger. Sensitivity analysis shows that the flame speed is very sensitive to 1,3-butadiene + O/H reactions, especially to the branching and termination reaction ratio of 1,3-C₄H₆ + O = C₂H₃+ CH₂CHO (R₁) and 1,3-C₄H₆+ O = CH₂O + C₃H₄-a (R₂). The sensitivity of the flame speed to the branching ratio of these two reactions increases with the increase of H₂ and O₂ enrichment. Due to the lack of accurate theoretical calculations of these two reaction rates, the new flame speed data and previously measured ignition delay time were used to assess the uncertainty of the branching ratio and reaction rates of R₁ and R₂. It shows that the optimized branching ratio significantly improves the flame speed and ignition delay time predictions, especially at high pressure and fuel lean conditions. The present study reveals that H₂ and O₂ sensitization in flames provides an important way to identify the uncertainties of fuel + O/H reactions and to improve the model predictability for flames.