Gas Turbine Combustor Modal Coupling Reduction
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Solution Overview
Problem
Combustion instabilities in gas turbines due to modal coupling of combustion dynamics lead to undesirable vibrations and reduced efficiency, which conventional combustor tuning attempts to mitigate but at the cost of limiting the operating range.
Innovation Solution
The system and method involve varying the convective time between combustors by adjusting the flow rate of compressed working fluid through fuel injectors and flow openings, creating a frequency difference between combustors to reduce modal coupling, thereby minimizing coherence and vibratory responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional combustor tuning is used to limit combustion dynamics amplitude, then combustion instabilities are reduced, but the operating range of the combustor is unnecessarily limited
Solution Approach 1:
The patent applies parameter changes by varying the convective time between combustors through adjustments to flow opening areas and fuel injector cross-sectional areas. This changes the acoustic frequency characteristics of individual combustors, allowing them to operate stably across a broader range of conditions without requiring restrictive tuning that limits the operating range.
2Productivity
If combustors are tuned to the same frequency, then combustion efficiency is optimized, but modal coupling occurs causing sympathetic vibrations in downstream components
Solution Approach 1:
The patent applies asymmetry by deliberately creating asymmetric frequency characteristics between combustors through different convective times. This asymmetric tuning causes combustors to operate at different acoustic frequencies, preventing the coherent coupling that leads to sympathetic vibrations in downstream components while maintaining individual combustor efficiency.
Solution Approach 2:
By changing the convective time parameter for each combustor through different flow opening and injector area configurations, the patent achieves different acoustic frequencies for each combustor. This parameter differentiation eliminates the harmful modal coupling effect while preserving combustion efficiency in each combustor.
3Reliability
If the convective time is increased to reduce combustion instability frequency, then the magnitude of combustion dynamics is reduced, but the frequency becomes closer to resonant frequencies of downstream components
Solution Approach 1:
The patent applies local quality by giving each combustor unique local characteristics through different convective times and acoustic frequencies. This localized differentiation ensures that while each combustor operates stably, their frequencies are spread out to avoid collectively exciting resonant modes in downstream components.
Solution Approach 2:
The patent uses parameter changes to adjust convective times to achieve stable combustion dynamics with frequencies that are deliberately spread apart. This prevents both individual combustors from operating at problematic frequencies and prevents coherent coupling that would amplify vibrations in downstream 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 approach enhances thermodynamic efficiency, promotes flame stability, and reduces emissions over a wide range of operating conditions while protecting against accelerated wear in downstream components.
Implementation Method 1
the delay between the time that the fuel is injected through the fuel ports and the time when the fuel reaches the combustion chamber and ignites, defined as 'convective time' (tau)
Data Source
AI summary
A system and method for reducing modal coupling of combustion dynamics among multiple combustors are provided. Each combustor may include one or more fuel nozzles axially aligned with a combustion chamber; one or more fuel injectors downstream from the fuel nozzles; and a set of flow openings integrated with the combustor. The fuel injectors provide fluid communication through a liner that circumferentially surrounds each combustion chamber. The flow rate of compressed working fluid diverted through the fuel injectors may be different and/or variable between the combustors to produce different combustion instability frequencies.