Gas Turbine Combustor Modal Coupling Reduction
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Solution Overview
Problem
Combustion dynamics in gas turbines can lead to reduced component lifespan, increased emissions, and instability due to modal coupling and combustion instabilities, which are exacerbated by high combustion gas temperatures and acoustic resonances.
Innovation Solution
The system and method involve arranging combustors with varying axial distances between fuel ports and combustion chambers to produce distinct combustion instability frequencies, reducing coherence and modal coupling by adjusting the phase and coherence of combustion dynamics across the combustor array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If combustors are arranged with identical axial distances to simplify design and manufacturing, then manufacturing precision and ease of manufacture are improved, but combustion instabilities occur due to modal coupling and coherent combustion dynamics across all combustors
Solution Approach 1:
The patent applies asymmetry by deliberately introducing axial distance variations among combustors. Specifically, at least one combustor has a different axial distance between its fuel port and combustion chamber compared to other combustors. This asymmetric configuration creates different convective times and breaks the coherence of combustion dynamics, preventing modal coupling while maintaining manufacturability through controlled geometric variations.
Solution Approach 2:
The patent implements local quality by applying axial distance variations to specific combustors rather than uniformly changing all combustors. The variation can be applied to individual combustors or groups, allowing targeted modification of local combustion characteristics to achieve overall system stability while minimizing manufacturing complexity.
2Reliability
If axial distances between fuel ports and combustion chambers are varied to reduce modal coupling, then combustion stability is improved, but device complexity increases due to multiple different combustor configurations
Solution Approach 1:
The patent applies parameter changes by modifying the axial distance parameter of combustors to achieve different convective times. This single parameter variation is sufficient to break coherence and reduce modal coupling without requiring complex structural changes. The approach changes the geometric parameter within reasonable manufacturing tolerances rather than introducing entirely new combustor designs.
Solution Approach 2:
The patent reduces device complexity by applying local quality principles - only certain combustors need to have varied axial distances rather than all combustors. This selective application means that manufacturing processes can remain largely standardized, with only specific combustors requiring adjusted positioning or assembly, thereby limiting the increase in device complexity.
3Use of energy by moving object
If higher combustion gas temperatures are used to improve thermodynamic efficiency, then energy efficiency is improved, but combustion instabilities are exacerbated and component lifespan is reduced
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring combustors with varied axial distances before operation. This preventive design approach addresses potential combustion instabilities that could arise at high temperatures by breaking coherence across the combustor array. The varied convective times created by different axial distances prevent the synchronized combustion dynamics that would otherwise be exacerbated by high temperature operation, allowing efficient high-temperature operation without proportional increases in instability.
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 enhances thermodynamic efficiency, promotes flame stability, and reduces undesirable emissions by minimizing constructive interference and increasing destructive interference among combustors, thereby extending maintenance intervals and improving design margins.
Implementation Method 1
the compressed working fluid mixes with fuel before igniting to generate combustion gases having a high temperature and pressure
Implementation Method 2
combustion instabilities that result from an interaction or coupling of the combustion process or flame dynamics with one or more acoustic resonant frequencies of the combustor
Implementation Method 3
the delay time between the injection of the fuel and the time when it reaches the flame zone, known in the art as 'convective time' (Tau)
Implementation Method 4
the acoustic pressure pulsations cause a mass flow fluctuation at a fuel port which then results in a fuel-air ratio fluctuation in the flame
Data Source
AI summary
A system and method for reducing combustion dynamics includes first and second combustors, and each combustor includes a fuel nozzle and a combustion chamber downstream from the fuel nozzle. Each fuel nozzle includes an axially extending center body, a shroud that circumferentially surrounds at least a portion of the axially extending center body, a plurality of vanes that extend radially between the center body and the shroud, a first fuel port through at least one of the plurality of vanes at a first axial distance from the combustion chamber, the plurality of vanes being located at a second axial distance from the combustion chamber. A second fuel port is provided through the center body at a third axial distance from the combustion chamber. The system further includes structure for producing a combustion instability frequency in the first combustor that is different from the combustion instability frequency in the second combustor.