US-12617537-B1 - Hybrid turbofan and solid oxide fuel cell propulsion system and related methods

US12617537B1US 12617537 B1US12617537 B1US 12617537B1US-12617537-B1

Abstract

Hybrid propulsion systems that utilize liquid natural gas solid oxide fuel cells in a manner practical for use in aircraft that avoid the use of heavy batteries, provide transient response times suitable for use in aircraft, and/or simplify reactant pre-conditioning systems using a compressor and turbine pair operatively coupled to the solid oxide fuel cell. Such hybrid propulsion systems for an aircraft may include a liquid natural gas solid oxide fuel cell, a motor driven by electric power from the solid oxide fuel cell, a gearbox operatively coupled to the motor, and a turbofan engine configured to generate thrust for the aircraft. The turbofan engine may be configured to provide electric power and shaft power and may include a duct fan that is operatively coupled to the motor via the gearbox, with the duct fan being driven by mechanical power from the gearbox and by the motor.

Inventors

Mingxuan Shi

Assignees

THE BOEING COMPANY

Dates

Publication Date: 20260505
Application Date: 20241223

Claims (19)

1 . A hybrid propulsion system for an aircraft, the hybrid propulsion system comprising: a liquid natural gas solid oxide fuel cell; a motor driven by electric power from the solid oxide fuel cell; a gearbox operatively coupled to the motor; and a turbofan engine configured to generate thrust for the aircraft, wherein the turbofan engine is configured to provide electric power by way of engine exhaust from the turbofan engine being used in electricity generation via the solid oxide fuel cell, wherein the turbofan engine is further configured to provide shaft power, wherein the turbofan engine comprises a duct fan that is operatively coupled to the motor via the gearbox, wherein the duct fan of the turbofan engine is driven by mechanical power from the gearbox and by the motor, wherein liquid natural gas is used as fuel for the turbofan engine and for the solid oxide fuel cell, and wherein the solid oxide fuel cell and the turbofan engine are operatively coupled together to decrease a transient response time of the turbofan engine.
2 . The hybrid propulsion system according to claim 1 , wherein fan bleed air extracted from the duct fan of the turbofan engine is used as source air for the solid oxide fuel cell.
3 . The hybrid propulsion system according to claim 1 , further comprising a compressor and turbine pair configured to primarily compress and pressurize fan bleed air from the duct fan of the turbofan engine to pre-condition the fan bleed air for the solid oxide fuel cell, wherein the fan bleed air is extracted from the turbofan engine upstream of a low-pressure compressor of the turbofan engine.
4 . The hybrid propulsion system according to claim 3 , wherein the compressor and turbine pair are configured to extract power from fuel cell exhaust of the solid oxide fuel cell.
5 . The hybrid propulsion system according to claim 3 , further comprising a splitter and a mixer configured to control pre-conditioning working conditions of fan bleed air for the solid oxide fuel cell, wherein the splitter and the mixer are downstream of a cathode of the solid oxide fuel cell, and wherein the splitter and the mixer are installed around a turbine of the compressor and turbine pair, the turbine being operatively coupled to the solid oxide fuel cell.
6 . The hybrid propulsion system according to claim 1 , wherein steam is generated by extracting water condensed out of engine exhaust from the turbofan engine.
7 . A hybrid propulsion system for an aircraft, the hybrid propulsion system comprising: a liquid natural gas solid oxide fuel cell; a motor driven by electric power from the solid oxide fuel cell; a gearbox operatively coupled to the motor; a turbofan engine configured to generate thrust for the aircraft, wherein the turbofan engine comprises a duct fan that is operatively coupled to the motor via the gearbox, and wherein the duct fan of the turbofan engine is driven by mechanical power from the gearbox and by the motor; and a turbo generator operatively coupled to the duct fan and a turbine downstream of the turbofan engine, the turbo generator being parallel with the solid oxide fuel cell.
8 . The hybrid propulsion system according to claim 7 , wherein the motor is driven by electric power from the solid oxide fuel cell and from the turbo generator simultaneously.
9 . The hybrid propulsion system according to claim 8 , wherein the hybrid propulsion system comprises an electronic engine controller configured to distribute a ratio of electric power load to the solid oxide fuel cell, the motor, and the turbo generator, thereby determining a ratio of fuel consumption of the solid oxide fuel cell, the motor, and the turbo generator.
10 . The hybrid propulsion system according to claim 7 , wherein fan bleed air extracted from the duct fan of the turbofan engine is used as source air for the solid oxide fuel cell.
11 . The hybrid propulsion system according to claim 7 , wherein high-pressure fuel cell exhaust from the solid oxide fuel cell is mixed back into the turbofan engine via a turbofan mixer to increase power generation.
12 . The hybrid propulsion system according to claim 7 , further comprising: a condenser configured to cool engine exhaust from the turbofan engine and condense liquid water out of engine exhaust; and a water extractor configured to extract liquid water from the liquid water condensed out of the engine exhaust by the condenser.
13 . The hybrid propulsion system according to claim 12 , wherein liquid natural gas from a fuel system of the hybrid propulsion system is pre-heated by engine exhaust in the condenser before the liquid natural gas is provided to an anode of the solid oxide fuel cell, wherein the condenser is configured to convert the liquid natural gas to gaseous natural gas, wherein the gaseous natural gas is heated by fuel cell exhaust in a recuperator, wherein a portion of the gaseous natural gas is received by the water extractor and mixed with the liquid water condensed out of the engine exhaust to get humidified natural gas, and wherein the humidified natural gas is received by the anode of the solid oxide fuel cell.
14 . The hybrid propulsion system according to claim 7 , wherein the hybrid propulsion system is configured such that a transient response time of the duct fan of the turbofan engine is sufficiently fast so as to be suitable for propulsion for the aircraft.
15 . An aircraft, comprising: a fuselage; a wing supported by the fuselage; a turbofan engine; and the hybrid propulsion system according to claim 1 .
16 . An aircraft, comprising: a fuselage; a wing supported by the fuselage; a turbofan engine; and the hybrid propulsion system according to claim 7 .
17 . A method of providing thrust to an aircraft via a hybrid propulsion system, the method comprising: generating a first amount of electric power via a liquid natural gas solid oxide fuel cell and driving a motor therewith, wherein the motor is operatively coupled to a duct fan of a turbofan engine of the aircraft via a gearbox; driving the motor via a turbo generator simultaneously with driving the motor with the first amount of electric power from the solid oxide fuel cell; driving the duct fan of the turbofan engine by mechanical power from the gearbox and the motor, thereby providing the thrust to the aircraft; extracting fan bleed air from the duct fan of the turbofan engine; and using the fan bleed air as source air for the solid oxide fuel cell.
18 . The method according to claim 17 , further comprising: compressing the fan bleed air from the duct fan of the turbofan engine, thereby pre-conditioning one or more reactants for the solid oxide fuel cell, wherein the compressing is performed by a compressor and turbine pair of the hybrid propulsion system; and extracting power from fuel cell exhaust of the solid oxide fuel cell via the compressor and turbine pair of the hybrid propulsion system.
19 . The method according to claim 17 , further comprising mixing high-pressure fuel cell exhaust from the solid oxide fuel cell back into the turbofan engine, via a turbofan mixer.

Description

FIELD The present disclosure relates to propulsion systems, and more particularly to solid oxide fuel cell propulsion systems using liquid natural gas. BACKGROUND Turbofan engines are a form of jet engine that have long been used in the propulsion systems of aircraft and other vehicles or machinery. Attempts have been made to design turboshaft engines with reduced or zero carbon dioxide emissions and other greenhouse gases. One such solution, electrified propulsion, suffers from the excessive weight penalties which are too large to be feasible in the aviation industry. Attempts also have been made to incorporate fuel cells into such propulsion systems, though conventional fuel cell systems suffer from slower transient response times that are not suitable for aviation, and may disadvantageously require a complex system to pre-condition (heat and pressurize) the fuel cell reactants. SUMMARY Presently disclosed hybrid propulsion systems may be configured to reduce emissions and improve efficiency of overall airplane propulsion systems using alternative energy sources and configurations not contemplated in the prior art while at the same time avoiding the disadvantages of prior art systems such as excessive weight from electrified propulsion and slow transient response times. By addressing these disadvantages of prior art systems, presently disclosed hybrid propulsion systems may utilize liquid natural gas solid oxide fuel cells in a manner practical for use in aircraft. Presently disclosed hybrid propulsion systems also may be configured to simplify reactant pre-conditioning systems. In an example, a hybrid propulsion system for an aircraft may include a liquid natural gas turbofan engine, a liquid natural gas solid oxide fuel cell, a motor driven by electric power from the solid oxide fuel cell, a gearbox operatively coupled to the motor, and a turbofan engine configured to generate thrust for the aircraft, with the turbofan engine being configured to provide electric power and shaft power. The turbofan engine may include a duct fan that is operatively coupled to the motor via the gearbox, and the duct fan may be driven by mechanical power from the gearbox and by the motor. Liquid natural gas may be used as fuel for the turbofan engine and for the solid oxide fuel cell, and the solid oxide fuel cell and the turbofan engine may be operatively coupled together to decrease a transient response time of the turbofan engine. Aircraft including a fuselage, a wing supported by the fuselage, a turbofan engine, and presently disclosed hybrid propulsion systems also are within the scope of the present disclosure. In some examples, a hybrid propulsion system for an aircraft may include a liquid natural gas solid oxide fuel cell, a motor driven by electric power from the solid oxide fuel cell, a gearbox operatively coupled to the motor, a turbofan engine configured to generate thrust for the aircraft, and a turbo generator operatively coupled to the duct fan and a turbine downstream of the turbofan engine, the turbo generator being parallel with the solid oxide fuel cell. The turbofan engine may include a duct fan that is operatively coupled to the motor via the gearbox, and the duct fan of the turbofan engine may be driven by mechanical power from the gearbox and by the motor. Methods of providing thrust to an aircraft via a hybrid propulsion system also are disclosed. Such methods may include generating a first amount of electric power via a liquid natural gas solid oxide fuel cell and driving a motor therewith, driving the duct fan of the turbofan engine by mechanical power from the gearbox and motor, thereby providing the thrust to the aircraft, extracting fan bleed air from the duct fan of the turbofan engine, and using the fan bleed air as source air for the solid oxide fuel cell. In such methods, the motor may be operatively coupled to a duct fan of a turbofan engine of the aircraft via a gearbox. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of an example aircraft according to the present disclosure. FIG. 2 is a schematic diagram representing non-exclusive examples of hybrid propulsion systems according to the present disclosure. FIG. 3 is a schematic diagram representing non-exclusive examples of hybrid propulsion systems according to the present disclosure. FIG. 4 is a flowchart schematically representing methods according to the present disclosure. DESCRIPTION FIG. 1 illustrates a non-exclusive example of an aircraft 12 that may comprise one or more hybrid propulsion systems 10 and/or 11 according to the present disclosure. While illustrated as a fixed-wing airliner comprising a fuselage 60 having a cabin 18, two wings 62 supported by the fuselage 60, a tail 14, and a jet engine 16 supported by each wing 62, other configurations of aircraft 12 are within the scope of the present disclosure, including, for example, rotorcraft, military craft, autonomous aircraft, etc. FIG. 1 schematically illustrat