  Compound drop impacting on a solid surface is of considerable importance in
industrial applications, such as combustion, food industry, and drug
encapsulation. An intriguing phenomenon associated with this process is the
occurrence of singular jets that are up to dozens of times faster than the
impact velocity. These jets break into micro-droplets, which can produce
aerosols and affect the quality of printing technologies. Here, we investigate
experimentally and numerically the jetting process after a coaxial water-in-oil
compound drop impacts on a glass substrate with different releasing heights and
volumetric ratios. After impact, the water core spreads and retracts, giving
rise to a vertical jet initially made of oil. For certain values of the
impacting velocity, high speed and very thin jets are observed, the so-called
singular jets. Depending on the volumetric ratio, one or two velocity peaks can
be observed when varying the impact velocity, triggered by the contraction
dynamics of a deep and cylindrical cavity. The self-similar time-evolution of
the collapse for the first singularity regime follows a 1/2 power law in time,
which can be derived from bubble pinch-off. In contrast, the collapse at the
second peak follows a 2/3 power law, which can be accounted for by a balance
between inertial and capillary forces.
