  Two-dimensional numerical simulations with Eulerian-Lagrangian method are
conducted to study propagation and extinction of stoichiometric hydrogen/air
detonations in fine water sprays. Parameterized by water mass loading and
initial droplet size, a detonation extinction map is developed. Detonation
extinction would occur with larger mass loading and/or smaller droplet size.
General features of gas phase and water droplets and local detonation frontal
structures are well captured. Numerical soot foils are used to characterize the
influence of mass loading and droplet size on the detonation wave. The results
also show that the detonation cell size increases with increased mass loading
or decreased droplet size. Analysis on unsteady detonation extinction process
is performed with the evolutions of detonation frontal structure, spatial
distribution of thermochemical variables and interphase transfer rates (mass,
energy, and momentum). Moreover, the chemical explosive mode analysis reveals
that for stable detonation, thermal runaway dominates behind the Mach stem,
while chemical propensities of auto-ignition and thermal runaway appear
alternately behind the incident wave. When the induction zone length increases
as the reaction front (RF) and shock front (SF) are decoupled, localized burned
pockets surrounded by the autoignition chemical explosive mode can be observed.
In addition, the interactions between detonation wave and water droplets
demonstrate that the energy and momentum transfer have more direct interaction
with SF and RF than the mass transfer. The interphase transfer rates increase
with the water mass loading. Under the same mass loading, the smaller the
droplet size, the larger the interphase transfer rates. However, the size of
fine water droplets has a limited influence on the interphase momentum
exchange.
