Off-Center Fuel Injection for Gas Turbine Combustion Stability
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Solution Overview
Problem
Combustion instabilities in gas turbine engines, such as turboshaft and turbojet engines, pose a significant risk of structural damage and certification issues due to resonance between natural acoustic modes and combustion fluctuations, with existing solutions being costly and ineffective in completely eliminating these instabilities.
Innovation Solution
The method involves injecting fuel off-center relative to the central axis of the air/fuel mixer system, creating an asymmetric fuel flow that prevents resonance with the combustion flame, achieved through angularly offsetting the combustion chamber and using a fuel injector with an off-center axis of symmetry within the swirler.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fuel is injected along the central axis of the mixer system, then the fuel spray is symmetric and combustion is stable, but combustion instabilities occur due to resonance between the symmetric flame and natural acoustic modes
Solution Approach 1:
The patent applies asymmetry by deliberately offsetting the fuel injection axis from the central axis of the mixer system. This creates an asymmetric fuel spray pattern that breaks the symmetry of the combustion flame, thereby eliminating the resonance condition between the symmetric flame and the natural acoustic modes of the combustion chamber. The asymmetric injection prevents the flame from oscillating in phase with the acoustic standing waves, thus reducing combustion instabilities.
2Reliability
If the injection system is redesigned to eliminate combustion instabilities, then combustion stability improves, but development time and certification delays increase
Solution Approach 1:
The patent changes a key geometric parameter of the injection system - specifically, the position of the injection axis relative to the mixer center. By adjusting this parameter to create an offset injection configuration, the system achieves improved combustion stability without requiring a complete redesign of the combustion chamber or injection system architecture, thereby reducing development time and certification delays.
3Stability of the object's composition
If an annular valve with protruding head is used to control fuel flow, then fuel flow interruptions are reduced, but the complex architecture does not eliminate combustion instabilities
Solution Approach 1:
The patent extracts the essential function of stable fuel flow delivery from the complex annular valve mechanism and achieves it through a simpler offset injection geometry. By removing the need for complex flow control valves and their associated control mechanisms, the system maintains stable fuel flow while eliminating combustion instabilities through the asymmetric spray pattern, thereby reducing device complexity.
4Stability of the object's composition
If the air stream is divided into concentric currents, then a two-way recirculation zone is created, but combustion instabilities are not eliminated
Solution Approach 1:
The patent applies asymmetry to the fuel injection side of the system to achieve combustion stability, whereas the prior art attempted to achieve stability through symmetric air flow manipulation. The asymmetric fuel injection directly addresses the root cause of combustion instabilities by breaking the symmetry of the combustion source, which is more effective than creating symmetric recirculation zones in the air stream.
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 approach effectively reduces or eliminates combustion instabilities by breaking the symmetry of the fuel spray, preventing resonance and thereby minimizing vibrations and potential structural damage, allowing for more efficient engine operation and certification.
Implementation Method 1
These instabilities are produced when the fluctuations of combustion in the chamber resonate with physical phenomena located therein (natural mode of acoustic vibration, mechanical vibration, instability of fuel supply, etc.).
Data Source
AI summary
An air/fuel mixer system of a combustion chamber of a gas turbine includes at least one compressed air intake swirler, the swirler having a central axis of symmetry, and a fuel injector including an injection head having an axis of symmetry. Each injector is mounted in the corresponding swirler with aid of a guide mechanism, so that the axis of symmetry of the injection head is off-center with respect to the central axis of symmetry of the swirler. The system can reduce, or even eliminate, combustion instabilities, by injecting the fuel along a particular axis which is off-center relative to the axis of the air/fuel mixer system, inducing a flow of fuel which is no longer perfectly axially symmetrical.