Droplet size distribution effects on liquid-fueled detonations

Detonations of liquid fuel droplets require complex multi-scale and multi-physics processes. Aerosolized fuel droplets must rapidly vaporize to contribute to the reactions and sustain the detonation. Droplet breakup processes are necessary to reduce the droplet size, increasing surface area and evaporation rates. The reaction, vaporization, and breakup processes are innately coupled and occur at overlapping timescales. The development of detonation propulsion devices utilizing liquid fuels requires an increased understanding of these coupled physics and how the individual shock-droplet interactions relate to bulk detonation behavior. In order to better characterize liquid-fueled detonations, this paper examines the effects of droplet size distributions on detonation and droplet breakup characteristics. The experiments are performed with sprays of dodecane fuel and oxygen at three different droplet size distributions and similar equivalence ratios, Φ . These droplets are generated with a modular array of piezoelectric atomizers that allow for control of droplet size and mass flow rate. The polydisperse size distributions are measured in-situ with commercial laser-optical droplet sizing equipment, measuring nominal Sauter Mean Diameters of 13.7, 15.0, and 24.0 μ m. Spatial measurements of droplet cloud position and Mie-scattering intensity, and CH ∗ chemiluminescence are reported. These measurements provide insight into the droplet breakup and evaporation processes relative to the detonation front. Observed correlations between droplet size, detonation velocity deficit, and time for complete breakup and evaporation are discussed and compared to previous studies and theory. • Three droplet size distributions are imaged in liquid-fueled detonations. • Droplet size distributions and equivalence ratios are measured in-situ. • Larger droplet size distributions show greater detonation velocity deficits. • Larger droplets persist for greater distances behind the detonation wave. • The data are consistent with a hydrodynamic droplet breakup model.