Hydrogen steam injected turbine engine with turboexpander heat recovery

A propulsion system for an aircraft comprising:

• a core engine including a core flow path where air is compressed in a compressor section, communicated to a combustor section, mixed with a fuel and ignited to generate an exhaust gas flow that is expanded through a turbine section;
• a fuel system for storing and pressurizing fuel as a liquid, boiling the fuel, and supplying a gaseous fuel to the combustor through a fuel flow path;
• a first heat exchanger thermally communicating a first heat load into a flow of the gaseous fuel;
• a turboexpander where heated fuel flow from the first heat exchanger is expanded to generate shaft power and cooled to provide a cooled gaseous fuel flow;
• a second heat exchanger providing a second source of heat that is input into a first portion of the cooled gaseous fuel from the turboexpander, wherein the reheated fuel flow is communicated to the combustor;
• and
• a third heat exchanger receiving a second portion of the cooled gaseous fuel flow from the turboexpander and transferring an additional heat load into the cooled gaseous fuel flow before communication to the combustor section.

A method of recovering thermal energy from a cryogenic fuel flow of an aircraft propulsion system, the method comprising:

• configuring a core engine to generate an exhaust gas flow from a cryogenic fuel;
• configuring a condenser to extract water from the exhaust gas flow with a cooling cryogenic fuel flow;
• configuring an evaporator generate a steam flow by heating extracted water from the condenser with a portion of the exhaust gas flow;
• configuring a first heat exchanger to thermal communicate a first heat load into a flow of the cryogenic fuel;
• configuring a turboexpander to expand and cool a heated cryogenic fuel flow communicated from the first heat exchanger to generate shaft power and generate a cooled fuel flow;
• and
• configuring a condenser cooling flow path from the turboexpander to the condenser to thermally communicate a first portion of the cooled fuel flow with the exhaust gas flow for cooling the exhaust gas flow to liquify water in the exhaust gas flow;
• providing a fuel flow path for a fuel flow from the condenser to a combustor;
• and
• configuring an additional heat exchanger to input an additional amount of heat into a second portion of the cooled fuel flow from the turboexpander before communication into the combustor.