Mixing and combustion characteristics of ethylene-air continuous rotating detonation in the cavity-based annular combustor with different injection schemes

In the present study, four fuel injection schemes including outer injection (Scheme1), inner injection (Scheme2), bilateral injection (Scheme3) and bilateral injection-bilateral cavity (Scheme4) are designed in conjunction with the cavity-based annular combustor. Mixing and combustion characteristics of ethylene-air continuous rotating detonation (CRD) in the cavity-based annular combustor with the four injection schemes are comprehensively investigated by high-fidelity simulations. Results show that the ethylene-air CRD wave propagates in a single-wave mode in Schemes1 to 3, whereas it transitions to a co-rotating two-wave mode in Scheme4. Both the average pressure peak and propagation velocity of the CRD wave increase progressively from Scheme1 to Scheme3, followed by a decrease from Scheme3 to Scheme4. Higher reactant mixing efficiency over a shorter blending distance is achieved by the bilateral injection scheme and the bilateral injection-bilateral cavity scheme compared to the inner or outer injection configurations due to a deeper penetration distance. Moreover, the detonation combustion is intensified with mixing efficiency improves as the injection scheme transitions from Scheme1 to 3, reaching the maximum detonation-dominant combustion fraction (f_dt) at 61.78% in Scheme3. Whereas, the detonation combustion attenuates sharply to a low f_dt of 25.97% in Scheme4 due to the severe premature deflagration combustion. The pre-heating effect of high-temperature cavity may elevate the mixture temperature and thus intensify the detonation combustion under insufficient mixing. Nevertheless, the same pre-heating effect may induce premature deflagration combustion under the sufficient mixing circumstance, resulting in partial consumption of the mixture and attenuation of the detonation wave.