Cryogenic Fuel Recirculating Cycle for Exhaust Heat Recovery
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Solution Overview
Problem
Existing gas turbine engines waste significant thermal energy due to limited capability of the working fluid to accept heat, limiting the amount of work generated in a bottoming cycle.
Innovation Solution
Aircraft propulsion systems utilize a cryogenic fuel system with a series of heat exchangers and a turboexpander to recover thermal energy from exhaust gas, converting it into shaft power and vaporizing the fuel for the core engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional working fluid is used in the bottoming cycle, then the system structure is simple, but the capability to accept heat is limited, reducing energy recovery efficiency
Solution Approach 1:
The patent changes the physical state parameters of the working fluid by using cryogenic fuel (extremely cold liquid or gas) instead of conventional working fluids. This parameter change enables the working fluid to accept significantly more heat from the exhaust gas, directly resolving the contradiction between heat acceptance capability and energy recovery efficiency
Solution Approach 2:
The patent introduces a heat exchanger as an intermediary device between the exhaust gas and the cryogenic fuel. This intermediary enables efficient thermal energy transfer from the hot exhaust gas to the cold cryogenic fuel, facilitating the heat acceptance process while managing the complexity through a standardized component
2Loss of energy
If thermal energy from exhaust gas is recovered, then energy efficiency improves, but additional equipment is required increasing system complexity
Solution Approach 1:
The cryogenic fuel serves multiple functions: it acts as the working fluid for heat absorption in the bottoming cycle, provides the cold source for cooling, and ultimately serves as fuel for the combustor. This multi-functionality reduces the need for separate dedicated cooling systems, thereby recovering thermal energy while limiting the increase in equipment quantity
Solution Approach 2:
The patent recovers thermal energy that would otherwise be discarded in the exhaust gas by using it to heat the cryogenic fuel. This transforms waste thermal energy into useful cooling capacity and potential work output, directly addressing the energy loss issue
3Productivity
If cryogenic fuel is used as working fluid, then thermal energy recovery is enhanced, but fuel system complexity increases
Solution Approach 1:
The patent merges the bottoming cycle working fluid system with the aircraft fuel system by using cryogenic fuel for both purposes. This consolidation enhances thermal energy recovery capability while avoiding the need for a completely separate working fluid system, thus limiting the increase in fuel system structure 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 utilizing thermal energy to generate additional shaft power and vaporize fuel, improving overall system performance.
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 from the core engine 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
Implementation Method 4
converting it into shaft power and vaporizing the fuel for the core engine
Data Source
AI summary
An aircraft propulsion system includes a cryogenic fuel system and a fuel flow path where a fuel flow is circulated from upstream in a direction downstream to a combustor of the core engine. A first heat exchanger inputs heat into the fuel flow downstream of the first heat exchanger is used to heat the fuel flow from the fuel storage tank and a second heat exchanger inputs thermal energy from a heat source into the fuel flow from the core engine downstream of the first heat exchanger. A turboexpander 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.