Cryogenic Fuel Cooled ECS Precooler Design
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Solution Overview
Problem
Conventional aircraft environmental control systems (ECS) rely on engine bleed air for cooling, which leads to drag and inefficiencies due to the use of fan duct air for precooling, and conventional fuels have temperature limitations, restricting their use as cooling mediums.
Innovation Solution
The implementation of a precooler system using cryogenic fuels like liquid hydrogen or ammonia, which act as a heat sink to cool engine bleed air, reducing the size of precooler heat exchangers and eliminating the need for fan air cooling, by employing a two-pass heat exchanger configuration with distinct temperature and density states of the fuel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional fan duct air is used to cool bleed air in the precooler, then the bleed air can be cooled from about 450°C to below 250°C, but this uses space in the fan duct leading to drag on the engine
Solution Approach 1:
The invention extracts the precooler from the fan duct environment and replaces fan duct air with cryogenic fuel as the cooling medium. This removes the harmful interaction between the precooler and fan duct airflow, eliminating the drag penalty while maintaining the cooling function.
Solution Approach 2:
The invention changes the thermal parameter of the cooling medium from ambient temperature fan air to cryogenic temperature fuel (approximately -250°C). This parameter change enables more effective cooling and eliminates the need for fan duct space, resolving the drag issue.
2Quantity of substance
If conventional fuels are used for cooling, then they can be supplied to the engine, but their temperature limitations restrict their use as cooling mediums
Solution Approach 1:
The invention changes the temperature parameter of the fuel from conventional storage temperatures to cryogenic temperatures (approximately -250°C). This parameter change enables the fuel to serve dual purposes: as a cooling medium for the precooler and as combustible fuel for the engine, resolving the temperature limitation issue.
Solution Approach 2:
The invention makes the cryogenic fuel serve multiple functions: it acts as the cooling medium in the precooler, is supplied to the engine for combustion, and preheating occurs during the heat exchange process. This multi-functionality resolves the limitation of conventional fuels that cannot serve as effective cooling mediums.
3Volume of moving object
If a two-pass heat exchanger configuration is used with cryogenic fuel, then the precooler size is reduced by up to three times, but the system complexity increases
Solution Approach 1:
The invention segments the heat exchange process into two distinct passes: the first pass cools the bleed air from approximately 450°C to below 250°C, and the second pass further cools it to the required ECS temperature. This segmentation allows for more efficient heat extraction and compact design, reducing overall precooler volume despite the increased process 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
This solution reduces precooler size by up to three times, enhances packing flexibility, ensures safe use of cryogenic fuels, and eliminates the need for additional heat exchangers, improving engine efficiency and providing suitable air temperatures for ECS while preheating the fuel for combustors.
Implementation Method 1
a precooler configured to receive the cryogenic fuel and engine bleed air. The precooler includes a first heat exchanger configured to receive the cryogenic fuel and a second heat exchanger configured to receive the engine bleed air
Implementation Method 2
The first state of the fuel has a first density, the second state of the fuel has a second density, and the third state of the fuel has a third density, wherein the first density is greater than the second density, and the second density is greater than the third density
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
Aircraft systems including a fuel tank (302) containing a cryogenic fuel, an engine (304) configured to consume the fuel, and an ECS having a precooler (308) arranged to receive the fuel and air from the engine (304). The precooler (308) includes a first heat exchanger (320) configured to receive a first state of the fuel and output a second state of the fuel and a second heat exchanger (322) configured to receive the second state fuel and output a third state fuel. The first state has a first density, the second state has a second density, and the third state has a third density, wherein the first density is greater than the second density, and the second density is greater than the third density. The engine air is directed through the second heat exchanger (322) first and then through the first heat exchanger (320).