Quantification of Rotating Detonations Using OH* Chemiluminescence at Varied Widths

Abstract

Rotating detonation combustors (RDCs) are studied with significant interest in recent years, due to their promulgated benefits over other pressure gain combustion systems. Although notable strides have been made, the fundamental understanding of rotating detonation wave dynamics is still nascent. Toward this end, high-speed ${\mathrm{OH}}^{*}$ chemiluminescence imaging is used to spatiotemporally track the detonation wave as it propagates through annular RDCs of three different channel widths at varied flow rates and equivalence ratios. Several algorithms are used to attain quantitative metrics on the observed rotating detonations, namely, speed, strength, height, and stability. It is shown that higher flow rates of 0.4 and $0.5\mathrm{kg}/\mathrm{s}$ (and hence higher fresh mixture fill height due to increased mass flux) produce small wave speed deficits, more consistency in wave propagation denoted by less variance in structure from lap to lap, as well as higher luminosity (proportional to combustion strength). It is also shown that at these high flow rates before wave bifurcation, rotating detonation waves exhibit the canonical diamond-shaped cellular pattern composed of the triple point interactions seen in planar detonations, but with cell widths bigger by an order of magnitude due to the streamtube effect. The experimentally gathered visualization data are used to formulate empirical guidelines that can help predict rotating detonation waves’ velocity deficit, height, and combustion strength for a given mass flux through the combustor. It is shown that velocity deficits in rotating detonations are a linear function of the effective perimeter inscribed by the wave, where the lowest deficits of 10% are seen at the highest perimeters, which in turn only manifests at the highest tested flow rates. This finding is linked to similar observations seen in planar detonations in tubes, where two distinct, perimeter-predicated loss mechanisms (one due to heat and momentum losses and the other due to streamtube effect) cause velocity deficits at near-limits conditions.