A D² law for supercritical droplet vaporization

To achieve higher efficiencies in rocket, jet, and diesel engines, the combustion pressures are increasing, meaning the fuels are often injected under supercritical conditions. Supercritical fluids are unique as they no longer have a liquid-gas phase equilibrium or surface tension. However, supercritical droplets have been observed in injection experiments. The common explanation is the droplets form due to a local subcritical pressure region caused by the fluid mixture, but the exact mechanism is still unknown. We provide an alternative physical mechanism for the formation of supercritical droplets. We demonstrate the formation of droplets in a pure supercritical fluid without surface tension, and it is driven by heat transfer and unique fluid properties. Also, like subcritical droplets, the supercritical droplets follow the $D^2$ law for vaporization. The interface temperature is at the pseudo boiling temperature, similar to subcritical droplets, as the interface temperature is at the saturation temperature. At supercritical conditions, pseudo boiling supersedes boiling, so the pseudo boiling temperature supersedes the saturation temperature. With these results, we provide a new physical mechanism that causes the formation of supercritical droplets without surface forces.