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 H2-O3 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 O2-O3 and H2-O2-O3, highly diluted in N2, 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: O3 (+M) = O2 + O (+M) (R1), O3 + O = 2O2 (R2), and O3 + OH = O2 + HO2 (R4). For ozone dissociation (R1), relative third-body collision efficiencies compared to N2 were calculated for Ar, O2, and O3, allowing a more accurate assessment of k1(N2), k1(O2) and k1(O3).

The flow reactor data for H2-O2-O3 provided information on the competition between hydrogen and ozone for radicals and served to constrain the rate constants for O3 + O (R2) and O3 + OH (R4). Comparison between experiments and model predictions show that all current H2-O3 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 between ozone and hydrogen molecules has a profound influence on both the flow reactor reaction rate and flame speed.