Fixed Nozzle Thrust Augmentation via Secondary Combustion
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Solution Overview
Problem
Current mixed flow turbofan engines face challenges in generating additional thrust without increasing cost and complexity, particularly when using variable exhaust nozzles for augmentation, and there is a need for a fixed nozzle area augmentation system that balances thrust and fuel efficiency.
Innovation Solution
A thrust augmentation system comprising a fixed area exhaust nozzle and an augmentation duct that receives primary and secondary air, allowing for secondary combustion to increase thrust without variable nozzle throat areas, thereby simplifying design and maintaining compression system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a variable exhaust nozzle with augmentation is used, then additional thrust can be generated, but the cost and complexity of the turbine engine increase
Solution Approach 1:
The exhaust system is segmented into two independent components: a fixed exhaust nozzle and a separate augmentation system. The fixed nozzle maintains constant geometry while the augmentation system (with its own combustion chamber and fuel injection) provides variable thrust. This segmentation allows each component to be optimized independently, reducing overall system complexity while maintaining thrust augmentation capability.
Solution Approach 2:
The invention merges the augmentation combustion system with the exhaust nozzle assembly, positioning the augmentor upstream of the fixed nozzle. The hot gases from the augmentor mix with the exhaust flow through the fixed nozzle, combining two thrust-generating processes into a unified system that achieves thrust augmentation without requiring a variable geometry nozzle.
2Reliability
If the nozzle throat area is increased for augmented operating conditions, then fan or low compressor surge is prevented, but the fuel efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts the effective exhaust area through fuel injection control rather than physical nozzle geometry changes. By controlling the timing and amount of fuel injected into the augmentor, the system can modulate the exhaust flow characteristics and pressure pulses, maintaining compression system stability while avoiding the permanent area increase that would hurt fuel efficiency during non-augmented operation.
Solution Approach 2:
The augmentation system uses periodic or pulsed fuel injection to generate thrust augmentation only when needed. This periodic activation of the augmentor allows the fixed nozzle to maintain its optimal geometry for fuel-efficient cruise operation, while providing temporary thrust increases during takeoff or combat maneuvers through controlled, intermittent combustion events.
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 achieves a 20-30% increase in thrust while maintaining fuel efficiency and avoiding destabilizing pressure increases, with a simplified design that optimizes nozzle throat area for both augmented and non-augmented operations.
Implementation Method 1
utilizing the remaining oxygen in the exhausted air and an injected fuel stream to perform a secondary combustion process
Data Source
AI summary
A thrust augmentation system for a mixed exhaust turbofan engine comprises an augmentation duct, a combustion system and a fixed area exhaust nozzle. The augmentation duct receives primary and secondary air of the turbofan engine and is positioned co-axially with an exhaust case of the turbofan engine. The combustion system increases the thrust produced by the mixed exhaust of the turbofan. The fixed area exhaust nozzle has a throat area larger than that which would maximize the non-augmented thrust.