Cryogenic Bottoming Cycle Control for Variable Engine Operation
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Solution Overview
Problem
Bottoming cycles in gas turbine engines are constrained by operating conditions and do not operate optimally at all operating points, limiting the recovery of heat for additional useful work.
Innovation Solution
Aircraft propulsion systems incorporate a cryogenic fuel system, a bottoming cycle with a closed circuit, and a control system that adjusts parameters based on core engine operation, using sensors and actuators to optimize heat exchange and power generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a bottoming cycle is used to recover heat from exhaust gas flow, then additional useful work is generated, but the bottoming cycle cannot operate optimally at all operating points due to constraints from the gas turbine engine operating conditions
Solution Approach 1:
The bottoming cycle system employs dynamic control mechanisms that allow operating parameters (such as heat exchanger effectiveness, turbine inlet temperature, and pressure ratios) to be adjusted in real-time based on the gas turbine engine's operating conditions. This enables the bottoming cycle to adapt its performance characteristics across different operating points, maintaining optimal heat recovery efficiency whether the engine is operating at high power, idle, or transient conditions.
Solution Approach 2:
The system utilizes parameter changes by modifying key thermodynamic parameters of the bottoming cycle (temperature, pressure, flow rates) in response to varying engine operating conditions. Control systems adjust these parameters dynamically to optimize the heat exchange process and power generation efficiency across the entire operating range of the gas turbine engine, resolving the contradiction between energy recovery and adaptability.
2Productivity
If the bottoming cycle operates with fixed parameters, then the system structure is simplified, but it cannot maximize power recovery across varying core engine operating conditions
Solution Approach 1:
The bottoming cycle system incorporates feedback control mechanisms where sensors monitor operating parameters (temperature, pressure, flow rates) and feed this information to control systems. The control systems then adjust actuators and operating parameters to optimize power recovery. This closed-loop feedback approach enables maximum power recovery across varying engine conditions while keeping the control system architecture manageable through systematic control strategies.
Solution Approach 2:
The control system is designed with multi-functionality to handle various operating modes (idle, cruise, maximum power, transient) using a unified control framework. This universal control approach maximizes power recovery across all conditions without requiring separate complex control systems for each operating mode, thereby balancing productivity improvement with acceptable device 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
The system optimizes the operation of the bottoming cycle to align with core engine conditions, maximizing power recovery and efficiency by dynamically adjusting heat input and fluid volumes, thereby enhancing overall propulsion system performance.
Implementation Method 1
a first heat exchanger where heat is input into the working fluid
Implementation Method 2
a second heat exchanger where the working fluid is cooled by the cryogenic fuel flow
Implementation Method 3
the working fluid within a closed circuit is heated and expanded through a bottom turbine to generate shaft power
Data Source
AI summary
An aircraft propulsion system includes a core engine driving a propulsive fan, a cryogenic fuel system and a bottoming cycle where a working fluid within a closed circuit is heated and expanded through a bottom turbine to generate shaft power. An actuator control is configured to vary a parameter of the bottoming cycle system, and a controller is programmed to operate the control system to adjust operation of the bottoming cycle to correspond to operation of the core engine.