Effects of ozone on n-heptane low temperature chemistry and premixed cool flames

Ozone (O3) has been shown to accelerate low and high temperature chemistry and is a promising strategy to effectively enhance and control combustion and ignition processes, such as for engines. There has, however, been a lack of experimental investigation of O3 enhancement effects on low temperature chemistry and premixed cool flames. This study undertook a detailed experimental and numerical assessment of O3 enhancement effects on ignition behavior, propagation speeds, flame temperatures, and CH2O production of n-heptane cool flames as functions of O3 addition. Zero-dimensional simulations were used to gain insights into the effects of O3 on two-stage ignition behavior and gradual suppression of NTC phenomena. Propagation speeds of O3-enhanced cool flames were experimentally determined using a flame lift-off technique, and one-dimensional simulations utilizing several full and reduced mechanisms were performed for comparison. Enhancement by O3 versus enhancement by preheating were experimentally compared and analyzed to evaluate relative effectiveness of these enhancement strategies. Finally, downstream temperature measurements and formaldehyde planar laser-induced fluorescence imaging (CH2O PLIF) were performed at different O3 enhancement levels to further elucidate O3 impacts, and numerical simulations were performed to support experimental insights. Results of this study reveal O3 impacts on low temperature kinetics and resulting impacts on low temperature ignition and cool flames.