Ozone Doping and Negative Temperature Response in the Explosion Limits of Ethylene–Oxygen Mixtures

In this work, effects of ozone (O₃) addition on ethylene-oxygen (C₂H₄-O₂) mixtures are computationally studied through the explosion limit profiles. The results show that the addition of minute quantities of ozone (with a mole fraction of 0.06% in the oxidizer) shifts the explosion limit of the C₂H₄-O₃-O₂ mixtures to the low-temperature regime. Further increases in the ozone concentration gradually strengthen the negative temperature coefficient (NTC) behavior at the second limit. That is because the explosion limit is primarily controlled by the ethylene ozonolysis reaction, and both the sensitivity analysis and chemical reaction rate perturbation method reveal specific kinetic reasons. Furthermore, it is shown that with the increasing equivalence ratio, the explosion limit curve with minute ozone addition rotates counterclockwise around a crossover point, while the explosion limit curve becomes complicated and the NTC behavior appears on the second limit with larger quantities of ozone addition. Furthermore, the effects of dilutions of nitrogen (N₂), argon (Ar), carbon dioxide (CO₂), and water (H₂O) on the explosion limits are also studied. To elucidate the different wall elimination effects of different explosion limit regimes, the impacts of surface reactions of six radicals (H, O, OH, HO₂, H₂O₂, and HCO) have been examined and the dominant radicals are found to be H and HO₂. The H radicals significantly influence the first explosion limit, while the HO₂ radicals impact the entire explosion limit.