Cryogenic Fuel Recirculation Bottoming Cycle for Exhaust Heat Recovery
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Solution Overview
Problem
Existing gas turbine engines waste significant thermal energy due to limitations in the capability of working fluids to absorb heat, limiting the amount of work generated in bottoming cycles.
Innovation Solution
Aircraft propulsion systems utilize a cryogenic fuel system with multiple heat exchangers and a turboexpander to recover thermal energy from exhaust gases, vaporize liquid fuel, and generate additional shaft power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional working fluid is used in a bottoming cycle, then the system structure is simple, but the thermal energy recovery capability is limited
Solution Approach 1:
The patent changes the physical and chemical parameters of the working fluid by using cryogenic fuel (such as liquid hydrogen or liquid methane) instead of conventional working fluids. This parameter change enables the working fluid to absorb significantly more thermal energy while maintaining system functionality, directly resolving the contradiction between energy recovery and device complexity
Solution Approach 2:
The cryogenic fuel serves multiple functions: it acts as both the fuel for the combustor and the working fluid for the bottoming cycle. This multi-functionality allows the system to recover thermal energy effectively without adding separate complex subsystems, thus improving energy recovery while limiting the increase in device complexity
2Power
If more thermal energy is recovered in a bottoming cycle, then power generation increases, but the working fluid's heat absorption capability becomes the limiting factor
Solution Approach 1:
The patent fundamentally changes the thermal properties of the working fluid by selecting cryogenic fuels with superior heat absorption characteristics. These fuels can absorb significantly more thermal energy per unit mass compared to conventional working fluids, thereby removing the heat absorption capability limit and enabling increased power generation in the bottoming cycle
Solution Approach 2:
The patent utilizes phase transitions of cryogenic fuels (from liquid to gas) in the bottoming cycle to enhance heat absorption. The phase change process absorbs large amounts of latent heat, significantly increasing the working fluid's heat absorption capability and enabling higher power generation without proportionally increasing system complexity
3Loss of energy
If cryogenic fuel is used as working fluid, then thermal energy recovery is enhanced, but fuel vaporization requirements increase system complexity
Solution Approach 1:
The patent makes the fuel vaporization system multi-functional by designing it to serve both as the vaporization pathway for combustion fuel delivery and as the heat absorption pathway for bottoming cycle power generation. This integration allows thermal energy recovery enhancement without proportionally increasing system complexity, as the same infrastructure serves dual purposes
Solution Approach 2:
The patent merges the fuel vaporization function with the bottoming cycle working fluid heating function into a single integrated process. By combining these two functions, the system recovers thermal energy more effectively while avoiding the need for separate, complex vaporization equipment, thus enhancing energy recovery without excessive increase in device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances engine efficiency by effectively recovering thermal energy and converting liquid cryogenic fuel into vapor for combustion, thereby increasing overall power generation.
Implementation Method 1
a first heat exchanger where heat input into the fuel flow downstream of the first heat exchanger is used to heat the fuel flow from the fuel storage tank
Implementation Method 2
a second heat exchanger where thermal energy from a heat source is input into the fuel flow downstream of the first heat exchanger
Implementation Method 3
a turboexpander that is configured to generate shaft power from expansion of the fuel flow exhausted downstream from at least one of the first heat exchanger and the second heat exchanger
Data Source
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AI summary
An aircraft propulsion system (20) includes a cryogenic fuel system (62) and a fuel flow path (88) where a fuel flow (70, 72, 78, 84, 86) is circulated from a fuel storage tank in a downstream direction to a combustor (26) of a core engine (25). A first heat exchanger (78) inputs heat into the fuel flow (70) from the fuel storage tank using heat from the fuel flow (86) downstream of the first heat exchanger (78). A second heat exchanger (80) inputs thermal energy from a heat source into the fuel flow (84) downstream of the first heat exchanger (78). A turboexpander (92) is configured to generate shaft power from expansion of the fuel flow (84, 86) exhausted downstream from at least one of the first heat exchanger (78) and the second heat exchanger (80).