APU Fire Enclosure Drain Seal for Thermal Expansion
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Solution Overview
Problem
Conventional fire enclosures in auxiliary power units (APUs) face challenges with thermal expansions and misalignments, leading to strain and limited ability to absorb loading, and existing drain systems fail to prevent fuel pooling and fire hazards due to faulty check valves and precise alignment requirements.
Innovation Solution
A drain assembly with a fire enclosure, a drain fitting, a discharge port, and a piston seal that forms an expansion joint to accommodate radial and axial displacement, preventing air leakage and allowing fuel drainage while maintaining structural integrity and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If rigid bolting of fire enclosure to fixed positions is used, then structural stability is improved, but thermal expansion strain increases
Solution Approach 1:
The fire enclosure transitions from a rigid fixed-position structure to a dynamic system with adjustable positioning. The drain assembly incorporates a bellows mechanism that allows the fire enclosure to move and adapt its position in response to thermal expansion, converting static rigidity into dynamic flexibility.
Solution Approach 2:
The system changes the positional parameters of the fire enclosure relative to the APU components. By allowing the fire enclosure to move along the longitudinal axis through the bellows mechanism, the system accommodates dimensional changes caused by thermal expansion without generating excessive strain.
2Ease of operation
If check valves are used for draining fuel, then fuel drainage function is improved, but reliability deteriorates due to valve failure
Solution Approach 1:
The check valve component is completely removed from the system. Instead of using a valve mechanism to control fuel drainage, the invention employs passive gravity-driven flow through the bellows and drain assembly, eliminating the unreliable moving parts while maintaining the drainage function.
Solution Approach 2:
The drain assembly utilizes the natural force of gravity to drive fuel drainage without requiring active valve control. The bellows structure passively accommodates the drainage flow and thermal movements, creating a self-regulating system that does not rely on mechanically controlled valves.
3Reliability
If bulb seals with precise alignment are used, then sealing effectiveness is improved, but device complexity increases
Solution Approach 1:
The bellows structure acts as a flexible sealing element that can deform and adapt to misalignments between the fire enclosure and APU components. This flexible membrane approach replaces rigid bulb seals that require precise alignment, maintaining sealing effectiveness while accommodating positional variations.
Solution Approach 2:
The sealing system transitions from a static rigid connection requiring precise alignment to a dynamic flexible connection. The bellows can expand, contract, and deform to maintain sealing contact despite relative movements and misalignments between components.
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
The solution effectively manages thermal growth and misalignments, prevents fuel pooling and fire hazards, and maintains the structural stability of the fire enclosure, enabling the use of lighter materials and ensuring efficient operation of the APU.
Implementation Method 1
Temperature variations that arise during different operating cycles of the APU produce thermal expansions of various APU components that alter the distances between the fixed positions
Implementation Method 2
Thermal growth of the APU thus induces strain into the fire enclosure
Data Source
AI summary
A drain assembly for an auxiliary power unit having a hot zone formed by a combustor case comprises a fire enclosure, a drain fitting, a discharge port and a piston seal. The fire enclosure encapsulates the hot zone of the combustor case. The drain fitting connects to the fire enclosure. The discharge port extends from the combustor case into the drain fitting. The piston seal is positioned between the drain fitting and the discharge port.