Pressure-coupled vaporization response of n-pentane fuel droplet at subcritical and supercritical conditions

The dynamic response of a liquid fuel droplet to externally impressed pressure oscillations is studied comprehensively over a wide range of mean pressures. Both subcritical and supercritical conditions are considered. The formulation treats a complete set of conservation equations and incorporates real fluid thermodynamics and transport theories. As a specific example, the situation with isolated n-pentane droplets in nitrogen is studied at various forcing frequencies. Results are correlated with the liquid thermal inertial time, instantaneous droplet radius, and oscillation frequency. The magnitude of the vaporization response increases with increasing pressure, mainly due to the decreased enthalpy of vaporization at high pressures. The increased sensitivity of droplet thermophysical properties to ambient flow variations at high pressures also plays a role. The phase angle of the vaporization response function, however, appears to be independent of the ambient pressure. An abrupt increase in the response function takes place when the droplet surface reaches its critical mixing state. A major factor contributing to this phenomenon is the abnormal variations of fluid thermophysical properties near the critical mixing point.