Turbofan Afterburner Core Plug Flow Diversion
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Solution Overview
Problem
Conventional afterburner systems for turbofan engines impose significant performance penalties during non-afterburning operations due to their impact on the entire exhaust flow, leading to increased noise and material requirements for high-temperature components.
Innovation Solution
An afterburner system with a core plug and second core flow duct that allows diversion and rejoining of the core exhaust flow, featuring doors that can be closed during reheat operations to restrict reheat flow to the second core flow duct, reducing pressure losses and limiting reheating to the core flow, while using fuel injectors and igniters to provide a thrust boost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional afterburner system is used to increase thrust during supersonic flight, then the temperature of the exhaust flow increases and thrust is improved, but significant performance penalties occur during non-afterburning operations due to impact on the entire exhaust flow
Solution Approach 1:
The exhaust flow path is segmented into a first core flow duct for undiverted flow and a second core flow duct for diverted flow. The second core flow duct is located within the core plug and provides a separate pathway that can be selectively activated. During normal operation, flow passes through the first duct without restriction. During afterburning, doors close to divert flow through the second duct where fuel injection and ignition occur, isolating the afterburner effects to only the diverted portion.
Solution Approach 2:
The afterburner function is extracted from the main exhaust flow path by creating a separate second core flow duct within the core plug. This allows the afterburner to operate on a diverted portion of the exhaust flow rather than the entire flow, so that during normal operation the main exhaust flow through the first duct remains unaffected and maintains optimal performance.
2Power
If conventional afterburner systems are used, then thrust is increased during reheat operation, but noise output increases significantly
Solution Approach 1:
The exhaust flow is segmented into treated and untreated portions. Only the diverted portion through the second core flow duct undergoes afterburning with fuel injection and ignition, while the majority of exhaust flow through the first core flow duct remains untreated. This segmented approach localizes the noise-generating combustion process to a smaller portion of the total exhaust, reducing overall noise output while still providing thrust enhancement.
3Power
If conventional afterburner systems are used to provide thrust boost, then engine performance is improved, but high-temperature materials are required for components exposed to reheated bypass air flow
Solution Approach 1:
The exhaust flow path is segmented to separate the afterburner treatment from the bypass flow. The second core flow duct where fuel injection and ignition occur handles only a diverted portion of the core exhaust. The bypass duct and its associated components remain exposed only to cold bypass air from the fan, not to the high-temperature afterburner gases, eliminating the requirement for high-temperature materials in bypass system components.
Solution Approach 2:
The afterburner function is extracted and isolated to the second core flow duct within the core plug. This extraction ensures that the high-temperature reheating process is confined to core exhaust gases only, while the bypass air flow system remains separate and exposed only to ambient-temperature bypass air, avoiding the need for expensive high-temperature materials in the bypass duct and nozzle 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
This configuration reduces pressure losses during non-afterburning operations, provides an additional thrust boost by area change, and avoids the need for high-temperature materials in other components by limiting bypass air flow reheating, thus reducing noise and material costs.
Implementation Method 1
one or more fuel injectors and one or more respective igniters operable, during the reheat operation, to respectively inject and ignite fuel within the second core flow duct
Data Source
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AI summary
A turbofan engine, an afterburner system, and a method of operating a turbofan engine are provided. The turbofan engine has: an engine core comprising a compressor, a combustor, a turbine, and a core shaft connecting the turbine to the compressor, and producing a core exhaust flow; a fan upstream of the engine core; a bypass duct surrounding the engine core and carrying a bypass air flow produced by the fan; an exhaust assembly comprising a first exhaust nozzle defining a downstream end of a first core flow duct which receives the core exhaust flow produced by the engine core. The turbofan engine further has an afterburner system comprising: a core plug defining a radially inner surface of the first core flow duct; a second core flow duct located in the core plug, and having one or more entrances from the first core flow duct for diversion into the second core flow duct of a portion of the core exhaust flow, and further having an exit therefrom for re-joining the diverted portion of the core exhaust flow to the undiverted portion of the core exhaust flow; one or more respective doors for the entrances to the second core flow duct, the doors being open during normal operation of the engine but being closable, during a reheat operation, to at least partially block the entrances to the second core flow duct; and one or more fuel injectors and one or more respective igniters operable, during the reheat operation, to respectively inject and ignite fuel within the second core flow duct, thereby providing a reheat flow into the core exhaust flow from the exit of the second core flow duct.