Water cooled exhaust duct

An aircraft propulsion system comprising:

• a core engine section defining a core flow path where an inlet airflow is compressed, mixed with fuel, and ignited to generate an exhaust gas flow that is communicated through the core flow path;
• a condenser where water is extracted from the exhaust gas flow;
• an evaporator system where thermal energy from the exhaust gas flow is utilized to generate a steam flow for injection into the core flow path;
• a duct system including a duct defining a pathway for the exhaust gas flow between the core engine section and the evaporator system and a cooling passage for a flow of water that accepts heat from the exhaust gas flow to cool the duct, wherein the cooling passage includes an inlet that receives the flow of water from a water source and an outlet;
• a control valve configured to control the flow of water into the cooling passage;
• and
• a controller programmed to operate the control valve to maintain the duct within a predefined temperature range.

A method of operating a gas turbine engine, the method comprising:

• generating an exhaust gas flow that is communicated through a core flow path;
• expanding the gas flow through a turbine section to generate a mechanical power output;
• routing the exhaust gas flow through a duct defining a pathway for the exhaust gas flow between the turbine section and an evaporator system;
• extracting water from the exhaust gas flow in a condenser;
• controlling a temperature of the duct between the turbine section and the evaporator by transferring heat from the exhaust gas flow into a flow of water in thermal communication with the duct to generate a heated flow of water by directing the flow of water through the cooling passage in the same direction as the exhaust gas flow;
• and
• generating a steam flow by vaporizing the heating flow of water with heat from the exhaust gas flow in the evaporator system.