Effect of Ozone Addition on the Cool Flame and Negative Temperature Coefficient Regions of Propane-Oxygen Mixtures

In this study, the effects of ozone addition on the cool flame and NTC (negative temperature coefficient) regions of stoichiometric C₃H₈/O₂ mixtures are computationally studied through the explosion limit profiles. The results show that with minute quantities of ozone addition (the mole fraction of ozone is 0.1%), the cool flame area is enlarged to the low-temperature region. Further increases in the mole fraction of ozone gradually weaken the NTC behavior, and a monotonic explosion limit is eventually achieved. The sensitivity analysis of the main reactions involving ozone reveals that the explosion limit is mainly controlled by the ozone unimolecular decomposition reaction O₃ (+M) = O₂ + O (+M). However, as its reverse reaction is a third-body reaction, this reaction will lose its effect on the explosion limit in the high-pressure region. On the contrary, the reaction O₃ + HO₂ = OH + O₂ + O₂ has a significant effect on the explosion limit in the high-pressure and low-temperature region, as the concentration of HO₂ increases through the rapid third-body reaction H + O₂ + M = HO₂ + M.