Experimental and kinetic analysis of laminar burning velocity and radical chemistry in ozone-enriched ethylene/air flames

Lean premixed combustion of ethylene-containing fuels is proving progressively important for decarbonizing gas-fueled power and high-temperature industrial processes. Ozone (O 3 ) serves as a highly reactive radical carrier for advanced gas-fired systems, but its impact on the structure and dynamics of unsaturated-fuel flames is inadequately characterized. Previous flame studies have focused mainly on alkanes, in which O 3 acts through thermal decomposition to O atoms in the preheat zone. For ethylene, the competition between direct ozonolysis (O 3 + C 2 H 4 ) and radical-driven O 3 consumption (O 3 + H, O 3 + M) inside a propagating flame has not been quantified. This study investigates the influence of ozone (O 3 ) enrichment on laminar burning velocity and flame structure chemistry in premixed ethylene–air flames. In this study, laminar burning velocity of C 2 H 4 /air flames doped with 0–3000 ppm O 3 was measured in a constant-volume spherical vessel at ϕ = 0.8 and 1.0, T 0 = 300 K and P 0 = 1 bar. Experiments at ϕ = 0.8 and ϕ = 1.0 show that laminar burning velocity increases approximately linearly with ozone concentration. Kinetic analysis was performed using the HP-Mech., which incorporates the Konnov mechanism and is coupled with an O 3 sub-mechanism. A comprehensive investigation of one-dimensional simulations in a normalized flame coordinate (ξ) shows that the peaks of CH 3 CHO, H 2 O 2 , HO 2 , and CH 2 O grow monotonically with ozone enrichment while remaining anchored close to the flame front, suggesting accelerated front-centered oxidation instead of a displaced reaction zone. A Radical Amplification Index (RAI) is introduced to quantify the impact of ozone, and radical profiles (H, O, and OH) exhibit a marked shift toward OH-driven chemistry. Despite ethylene’s distinctive ozonolysis chemistry, in-flame ozone consumption is dominated by H-abstraction (O 3 + H <=> O 2 + OH), exceeding the ozonolysis channel by roughly an order of magnitude; ozonolysis instead acts as a localized upstream primer for CH 2 O/HCO formation. Ozone increases the absolute rate of the primary branching step (H + O 2 <=> O + OH) while reducing its relative sensitivity, redistributing rate control toward the HO 2 -buffered network instead of following classical branching route. A parallel reorganization is observed for C 2 H 4 + H reactions: ozone addition suppresses the low-temperature association channel C 2 H 4 + H(+M) <=> C 2 H 5 (+M) in favor of the abstraction channel C 2 H 4 + H <=> C 2 H 3 + H 2 , redirecting flux away from the radical-consuming, chain-terminating association pathway and toward the chain-propagating abstraction route.