A dynamic heat sink engine including a storage vessel having a working fluid outlet and a working fluid inlet. The lower portion of the storage vessel contains a cryogenic working fluid, such as liquid hydrogen, at a temperature at near its boiling point. The engine further includes a working fluid circuit extending between the working fluid outlet and the working fluid inlet of the storage vessel. The working fluid circuit includes the serial connection of the following components from the working fluid outlet to the working fluid inlet: a fluid pump; a vaporizer having a liquid line passing therethrough; a heater; an expansion engine having a rotary output shaft; an electrical generator connected to the rotary output shaft of the expansion engine; a vapor line passing through the vaporizer, the vaporizer including a heat exchanger providing thermal communication between the liquid line and the vapor line.