A reaction mechanism for ozone dissociation and reaction with hydrogen at elevated temperature

Ozone is considered to be an effective combustion promotor and has the potential to be applied to a variety of fuels. In this work, the reaction mechanism for thermal conversion of ozone in the absence and presence of hydrogen was updated, based on theoretical work and novel flow reactor experiments. The H-2-O-3 reaction subset, which is the foundation for modeling ozone-assisted combustion of any hydrogen-containing fuel, was further validated against experiments from literature. Experiments for conversion of O-2-O-3 and H-2-O-2-O-3, highly diluted in N-2, were conducted in an atmospheric pressure flow reactor at temperatures of 400-575 K. In establishing the kinetic model, special attention was paid to the key ozone reactions: O-3 (+M) = O2 + O (+M) (R1), O-3 + O = 2O(2) (R2), and O-3 + OH = O-2 + HO2 (R4). For ozone dissociation (R1), relative third-body collision efficiencies compared to N-2 were calculated for Ar, O-2, and O-3, allowing a more accurate assessment of k(1)(N-2), k(1)(O-2) and k(1)(O-3). The flow reactor data for H-2-O-2-O-3 provided information on the competition be-tween hydrogen and ozone for radicals and served to constrain the rate constants for O-3 + O (R-2) and O-3 + OH (R4). Comparison between experiments and model predictions show that all current H-2-O-3 mechanisms predict well ozone dissociation, but only the present mechanism provides a good agreement for the hydrogen-ozone reaction rate. A sensitivity analysis showed that the competition for oxygen atoms and hydroxyl radicals be-tween ozone and hydrogen molecules has a profound influence on both the flow reactor reaction rate and flame speed.

Automated summary

This study updated the reaction mechanism of ozone in combustion and validated the simulation results. The experimental data provided insights into the competition between ozone and hydrogen, and constrained the rate constants of key reactions. Comparison between experiments and model predictions showed good agreement for ozone dissociation, but only the present mechanism accurately predicted the hydrogen-ozone reaction rate.