Detonation and its limit in small tubes with ozone sensitization

Abstract Ozone as an ignition promoter was used to study the detonation limit behavior in small, round tubes. Experimentally, detonation cellular structures and velocity deficits of fuel-oxygen mixtures with and without 3000 PPM of ozone were measured in tubes of 32 and 6 mm in inner diameter. Both hydrogen-oxygen and methane-oxygen mixtures were tested. The addition of ozone reduces the detonation cell size and extends the transition to spinning detonation to lower initial pressures. Ozone addition, however, produces a negligible effect on velocity deficit far from the detonation limit while providing a measurable extension of the limit. The change in deficit caused by ozone does not correlate with the reduction in cell size, suggesting that the velocity deficit behavior is not solely a function of the detonation structure. By analyzing the velocity deficit data in the d/λ (the ratio of tube diameter to cell width) domain, two regimes of detonation limits are identified: a loss-governed regime where velocity deficiency results from various losses (mass, momentum, and heat) and is insensitive to detonation structure, and a geometry-limited regime determined by the geometric accommodation of the detonation structures. Two velocity deficit models were evaluated against the experimental results: a modified ZND model with heat and momentum losses (HML) and the flow divergence (FD) model. Velocity deficits in the loss-governed regime are well predicted by the HML model but not by the FD model. Velocity deficits in the geometry-limited regime can be correlated with the critical condition of d / λ = 1 / π and the transition point between the two regimes. Ozone addition extends the detonation limit by moving the reactive mixtures away from its geometric detonation limit, and promotes detonation propagation in miniaturized geometries.