Bottoming Cycle Heat Source Sequencing for Cryogenic Fuel Recovery
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Solution Overview
Problem
Existing gas turbine engines waste a significant amount of thermal energy through exhaust, limiting the efficiency of bottoming cycles due to the limited capability of working fluids to accept heat.
Innovation Solution
Aircraft propulsion systems incorporating a bottoming cycle with a cryogenic fuel system and multiple heat exchangers that sequentially recover thermal energy from various sources, including core engine flows, bypass flows, lubrication systems, and aircraft loads, using a predefined hierarchy to maximize heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a bottoming cycle uses a working fluid to recover heat from exhaust, then additional useful work is generated, but the limited heat acceptance capability of the working fluid restricts energy recovery
Solution Approach 1:
The heat recovery system is divided into multiple heat exchangers arranged in series, each handling a specific temperature range. The first heat exchanger recovers heat at lower temperatures while the second heat exchanger recovers heat at higher temperatures, segmenting the overall heat recovery process to overcome the limited heat acceptance capability of a single working fluid stream
Solution Approach 2:
The patent introduces a hierarchical temperature dimension to the heat recovery system by arranging heat exchangers in series along the exhaust flow path. This creates multiple thermal zones where heat is recovered at different temperature levels, effectively adding a temperature dimension to the heat exchange process and enabling comprehensive energy recovery that a single heat exchanger cannot achieve
2Loss of energy
If multiple heat exchangers are added to recover heat from various sources, then thermal energy recovery is improved, but system complexity increases
Solution Approach 1:
The bottoming cycle system is designed to serve multiple functions: it recovers heat from exhaust gases, heats cryogenic fuel, and generates additional shaft power through the bottoming turbine. The working fluid circulates through a unified closed loop system that integrates these multiple functions, reducing overall system complexity despite the presence of multiple heat exchangers
Solution Approach 2:
The patent combines the heat recovery function with the fuel heating function by using the same working fluid stream to absorb heat from multiple sources and subsequently transfer that energy to cryogenic fuel. This merging of functions allows the system to recover waste thermal energy while simultaneously preparing fuel for combustion, achieving two objectives with a integrated approach
3Productivity
If the second heat exchanger operates at higher temperatures than the first, then heat recovery hierarchy is optimized, but thermal management complexity increases
Solution Approach 1:
The working fluid first absorbs heat from lower temperature sources in the first heat exchanger before proceeding to absorb heat from higher temperature sources in the second heat exchanger. This preliminary action of sequential heat absorption prepares the working fluid with a temperature gradient that optimizes heat recovery efficiency while simplifying thermal management through natural heat flow direction
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 the efficiency of the propulsion system by reclaiming additional thermal energy, improving compressor efficiency, and generating additional shaft power through a bottoming turbine.
Implementation Method 1
a first heat exchanger where thermal energy from a first heat source is communicated into the working fluid of the bottoming cycle
Implementation Method 2
a fuel/working fluid heat exchanger that provides thermal communication between a flow of the cryogenic fuel and the working fluid to cool the working fluid flow in the bottoming cycle
Implementation Method 3
the working fluid is compressed in the bottoming compressor section and expanded through the bottoming turbine section to generate shaft power
Implementation Method 4
the working fluid is compressed in the bottoming compressor section
Data Source
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AI summary
An aircraft propulsion system (20) includes a bottoming cycle (60) where a working fluid (66) is circulated within a closed circuit that includes a bottoming compressor section (62) and a bottoming turbine section (64). A first heat exchanger (70) provides for thermal energy from a first heat source to be input into the working fluid (66) of the bottoming cycle (60). A second heat exchanger (44) that is downstream from the first heat exchanger (70) communicates additional thermal energy from a second heat source into the working fluid (66) of the bottoming cycle (60) after the thermal energy from the first heat source is input into the working fluid (66).