Stacked Cryogenic Bottoming Cycles for Aircraft Waste Heat Recovery
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Solution Overview
Problem
Existing gas turbine engines waste a significant amount of energy in the form of heat, and existing bottoming cycles are limited by the heat absorption capability of their working fluids, which restricts the recovery of thermal energy.
Innovation Solution
Implementing two bottoming cycles with different working fluids having distinct heat absorption capacities, utilizing a cryogenic fuel as a heat sink, and incorporating a main heat exchanger system to transfer thermal energy into each cycle, along with fuel/working fluid heat exchangers to optimize heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single bottoming cycle with one working fluid is used, then the system is simple, but the heat absorption capability is limited
Solution Approach 1:
The single bottoming cycle is segmented into two separate bottoming cycles, each with its own working fluid (first working fluid and second working fluid) and heat exchanger system. This segmentation allows each cycle to be optimized for specific temperature ranges and heat absorption characteristics, thereby improving overall waste heat recovery capability while managing system complexity through modular design
Solution Approach 2:
Different working fluids are selected for different bottoming cycles based on their local heat absorption requirements. The first working fluid is optimized for absorbing heat at certain temperature levels, while the second working fluid is optimized for other temperature levels. This local optimization of fluid properties enables more complete utilization of the available waste heat spectrum
2Loss of energy
If the heat absorption capability of the working fluid is increased, then more thermal energy can be recovered, but the complexity of the heat exchanger system increases
Solution Approach 1:
The heat exchanger system is segmented into a first heat exchanger for the first bottoming cycle and a second heat exchanger for the second bottoming cycle. Each heat exchanger is designed and optimized for its specific working fluid and temperature range, which simplifies the design process compared to a single complex heat exchanger handling multiple fluids and temperature ranges simultaneously
Solution Approach 2:
The system transitions from a single-dimension heat recovery approach (one working fluid, one temperature range) to a multi-dimensional approach by stacking two bottoming cycles with different working fluids operating at different temperature levels. This dimensional expansion in the temperature-working fluid space enables more comprehensive thermal energy recovery
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 recovery of thermal energy by leveraging the full heat absorption capability of cryogenic fuels, increasing the overall efficiency of the propulsion system by capturing more waste heat.
Implementation Method 1
a first fuel/working fluid heat exchanger where the first working fluid is in thermal communication with the cryogenic fuel, and a second fuel/working fluid heat exchanger where the second working fluid is in thermal communication with the cryogenic fuel
Implementation Method 2
a main heat exchanger system for communicating thermal energy into the working fluid of each of the first bottoming cycle and the second bottoming cycle
Data Source
AI summary
An aircraft propulsion system includes a core engine, a first bottoming cycle and a second bottoming cycle that utilize different working fluids having different critical temperatures such that each of the bottoming cycles have different heat absorption capabilities.