Effect of ozone addition on curved detonations

Abstract

The influence of ozone on quasi-steady curved detonations was numerically studied in stoichiometric H2-air and DME-O2(-CO2) mixtures with 0%, 0.1% and 1% O3 addition. Detonation speed - curvature (D-κ) relations were determined for both fuels. The H2-air mixture has one critical point related to high-temperature chemistry whereas the DME-O2(-CO2) mixture has two critical points, one sustained by high-temperature chemistry, and the other supported by low-temperature chemistry. O3 addition significantly increases the curvature at all the critical points by speeding up both high- and low-temperature chemistry. Two mechanisms were found to be responsible for the results. First, O3 addition increases the rate of reaction initiation by fast decomposition to provide O radical via O3 (+M) = O2 + O (+M). The dominant reaction with fuel therefore changes from a fuel + OH/CH3 radical chain propagation reaction to a fuel + O radical chain branching reaction during the initial stage, which establishes the radical pool more rapidly. Second, O3 influences the reaction pathways. For H2-air with 1% O3, H + O3 = O2 + OH becomes the most important reaction for OH radical and heat generation during the initial stage. For DME-O2-CO2, O3 changes the respective contributions of competing low-temperature chemistry reactions, i.e. CH3OCH2 = CH2O + CH3 vs. CH3OCH2 + O2 = CH3OCH2O2 and CH2OCH2O2H = 2CH2O + OH vs. CH2OCH2O2H + O2 = O2CH2OCH2O2H. The change of dominant reactions either enhances (0.1% of O3) or eliminates (1% O3) the negative temperature coefficient behavior. Our study contributes to the detailed understanding of the thermo-chemical impact of ozone on detonation limits.