Ozonolysis activated autoignition in non-premixed coflow

While the majority of fuel oxidation reactions require high-temperature conditions, those involving ozone (O-3) and unsaturated hydrocarbons, e,g, ethylene (C2H4), occur very rapidly at low temperatures, even at room temperature. The subsequent radical production and heat release could induce further fuel oxidation and even autoignition in a fuel/oxidizer mixture. The autoignition events activated by ozonolysis reactions were investigated in a non-premixed coflow burner using C2H4 as the fuel, Both gas chromatography samples and chemiluminescence images indicated ongoing low-temperature reactions before autoignition occurred, which confirmed that ozonolysis reactions initiated autoignition. As expected, the autoignition time decreased with the increase of O-3 concentration in the mixture, Moreover, the autoignition time decreased as the fuel jet Reynolds number (Re) increased. At lower Re, this trend was explained by the inverse relation between the mixing timescale and flow velocity. At higher Re, this trend was attributed to the mixing promoted by turbulence. Owing to the ozonolysis reactions, fuel can be 'preprocessed' and therefore the reactivity of the fuel-oxidizer mixture increased, As a result, the flame propagation speed increased significantly after autoignition in a stratified environment owing to the existence of ozonolysis reactions. This enhancement, owing to 'in situ fuel preprocessing', plays an important role in flame stabilization and propagation mechanisms.