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 C 3 H 8 /O 2 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 O 3 (+M) = O 2 + 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 O 3 + HO 2 = OH + O 2 + O 2 has a significant effect on the explosion limit in the high-pressure and low-temperature region, as the concentration of HO 2 increases through the rapid third-body reaction H + O 2 + M = HO 2 + M.