Aircraft APU Bleed Air Temperature Control via Flow Regulation
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Solution Overview
Problem
Traditional auxiliary power units (APUs) in aircraft struggle to precisely control bleed air temperature due to the increasing uncoupling of exhaust gas temperature and bleed air temperature, especially in extensively operated aircraft under extreme conditions, making it difficult to maintain optimal system operation.
Innovation Solution
An auxiliary power system with a BAT sensor and APU controller that measures and regulates the bleed air temperature by adjusting the flow rate through a flow regulator assembly, independent of the rotational speed of the powerhead turbine, using a BAT signal to generate a flow regulator command and control the flow rate of the load compressor airflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If exhaust gas temperature is used to indirectly regulate bleed air temperature, then the system complexity is reduced, but the temperature control precision deteriorates
Solution Approach 1:
The patent implements a feedback control system where a bleed air temperature sensor directly measures the bleed air temperature and feeds this information back to the controller. The controller then adjusts the load compressor flow rate based on this direct feedback, creating a closed-loop control system that maintains precise temperature control despite variations in exhaust gas temperature or aircraft operational conditions.
Solution Approach 2:
The patent replaces the indirect mechanical/thermal coupling method (using exhaust gas temperature as a proxy) with a direct electronic sensing and control system. The bleed air temperature sensor provides direct electronic measurement of the actual parameter, substituting the indirect thermal relationship with a precise electronic measurement and control loop.
2Temperature
If flow rate to load compressor is reduced to lower bleed air temperature, then bleed air temperature decreases, but the ability to meet system demand deteriorates
Solution Approach 1:
The patent implements dynamic control of the load compressor flow rate based on real-time bleed air temperature measurements and system demand conditions. Rather than using a fixed flow rate or simple reduction, the controller dynamically adjusts the flow regulator assembly to optimize both temperature control and system demand fulfillment, allowing the system to adapt to changing operational requirements.
Solution Approach 2:
The patent changes the control parameter from exhaust gas temperature (which is uncoupled from bleed air temperature) to direct bleed air temperature measurement. This parameter change enables precise control of the actual parameter of interest while maintaining the ability to meet system demand through the flow regulator assembly's ability to modulate flow rate independently of compressor rotational speed.
3Device complexity
If indirect temperature regulation is used, then the device complexity is lower, but the reliability of temperature control deteriorates
Solution Approach 1:
The patent implements a feedback control system where a bleed air temperature sensor directly measures the bleed air temperature and feeds this information back to the controller. The controller then adjusts the load compressor flow rate based on this direct feedback, creating a closed-loop control system that maintains reliable temperature control despite variations in exhaust gas temperature or aircraft operational conditions.
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 allows for precise control of bleed air temperature, ensuring optimal operation of aircraft systems by maintaining the temperature below a threshold, even when the exhaust gas and bleed air temperatures are uncorrelated, thereby protecting components and improving system reliability.
Implementation Method 1
The load compressor is configured to compress the load compressor airflow to generate a bleed air flow
Implementation Method 2
The BAT sensor is configured to measure the BAT of the bleed air flow and to generate a BAT signal based, at least in part, on the BAT
Data Source
AI summary
Auxiliary power systems, aircraft including the same, and related methods. An auxiliary power system comprises an auxiliary power unit (APU) controller and an APU with an air intake, a powerhead, and a load compressor stage. The load compressor stage includes a flow regulator assembly, a load compressor, and a bleed air temperature (BAT) sensor for generating a BAT signal. The APU controller regulates a flow rate of a load compressor airflow through the load compressor based on the BAT signal. A method of utilizing an auxiliary power system includes compressing a load compressor airflow to generate a bleed air flow, measuring the BAT with a BAT sensor, generating a BAT signal based on the BAT, transmitting the BAT signal to an APU controller, generating a flow regulator command with the APU controller, transmitting the flow regulator command to a flow regulator assembly, and controlling a flow regulator assembly.