Rotating detonative combustion in partially pre-vaporized dilute n-heptane sprays: Droplet size and equivalence ratio effects

Eulerian-Lagrangian simulations are conducted for two-dimensional Rotating Detonative Combustion (RDC) fueled by partially prevaporized n-heptane dilute sprays by using coarse mesh resolution. The air is used as the oxidizer in the present simulations. The influences of droplet diameter and total equivalence ratio on detonation combustion and droplet dynamics are studied. It is found that small n-heptane droplets (e.g. 5 µm) are completely vaporized around the detonation wave, while intermediate n-heptane droplets (e.g. 20 µm) are consumed in or behind the detonation wave, with the escaped ones being continuously evaporated and deflagrated. The droplet distributions in the rotating detonation combustor are significantly affected by the droplet evaporation behaviors. Both premixed and non-premixed combustion modes are seen in two-phase RDC. The detonated fuel fraction is high when the droplet diameters are small or large, reaching its minimal value with diameter being 20 µm. The detonation propagation speed decreases with increased droplet diameter and is almost constant when the diameter is larger (>30 µm). The velocity deficits are 2-18% compared to the respective gaseous cases. Moreover, the propagation speed increases as the total equivalence ratio increases for the same droplet diameter. It is also found that the detonation propagation speed and detonated fuel fraction are considerably affected by the pre-vaporized gas equivalence ratio. The specific impulse first decreases for cases with initial diameter<5 μm, then increases with droplet diameter between 5 μm and 20 μm, and finally decreases with droplet diameter>20 μm.