A rankine cycle system includes: an internal combustion engine; a gas-liquid separator; a first pump; a steam generator; a superheater; an expander; a condenser; a first control valve; and a controller.

A pressure relief valve is opened from a first time to a second time for the purpose of reducing the pressure in the gas phase in a gas-liquid separator. A first water pump (WP) is driven at a third time and a fourth time. The third time and fourth time correspond to timings at which a difference between a boiling temperature and an actual temperature becomes equal to or greater than a predetermined temperature. Since liquid-phase coolant in a catch tank can be fed to another water pump by driving the first WP, the actual temperature of the liquid-phase coolant immediately upstream of the other water pump can be lowered. It is thus possible to prevent intense boiling of the liquid-phase coolant immediately upstream of the other water pump.

An ebullient cooling device includes: an internal combustion engine cooled by boiling a coolant flowing through a coolant passage formed within the internal combustion engine; a gas-liquid separator that separates a coolant discharged from the internal combustion engine into a liquid-phase coolant and a gas-phase coolant; a condenser that is disposed on a downstream side of the expander, and cools the gas-phase coolant having passed through the expander so as to be changed into a liquid-phase coolant; a first passage that supplies the liquid-phase coolant from the condenser to the coolant passage formed within the internal combustion engine; a second passage that is branched from the first passage, and is connected to the gas-liquid separator; and a control valve that controls a supply state of a liquid-phase coolant supplied to the gas-liquid separator from the condenser through the second passage.

A rankine cycle system includes: an internal combustion engine; a gas-liquid separator; a first pump; a steam generator; a superheater; an expander; a condenser; a first control valve; and a controller.

An ebullient cooling device includes: an internal combustion engine cooled by boiling a coolant flowing through a coolant passage formed within the internal combustion engine; a gas-liquid separator that separates a coolant discharged from the internal combustion engine into a liquid-phase coolant and a gas-phase coolant; a condenser that is disposed on a downstream side of the expander, and cools the gas-phase coolant having passed through the expander so as to be changed into a liquid-phase coolant; a first passage that supplies the liquid-phase coolant from the condenser to the coolant passage formed within the internal combustion engine; a second passage that is branched from the first passage, and is connected to the gas-liquid separator; and a control valve that controls a supply state of a liquid-phase coolant supplied to the gas-liquid separator from the condenser through the second passage.