Asymmetric Combustor Cap Axial Lengths for Dynamics Reduction
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Solution Overview
Problem
Combustion dynamics in gas turbines lead to instability, accelerated wear, and undesirable emissions due to interactions between combustion processes and acoustic resonant frequencies, which affect the life of combustor components and emissions.
Innovation Solution
The system includes multiple combustors with differently configured fuel nozzles and tubes, where the axial distances between fuel ports, vanes, and combustion chambers are varied to produce distinct combustion instability frequencies, reducing constructive interference and enhancing thermodynamic efficiency and flame stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the axial length of cap assemblies in multiple combustors is made different, then combustion instability frequencies are decoupled and destructive interference is promoted, but device complexity increases
Solution Approach 1:
The patent applies asymmetry by deliberately making the cap assemblies of different combustors have different axial lengths. This asymmetric configuration causes each combustor to operate at different combustion instability frequencies, preventing coherent coupling and promoting destructive interference. The asymmetric design directly addresses the combustion stability problem while accepting increased device complexity as a necessary trade-off.
2Use of energy by moving object
If combustion gas temperature is increased, then thermodynamic efficiency is improved, but flame holding conditions worsen causing accelerated wear
Solution Approach 1:
The patent changes the geometric parameters of the cap assemblies (specifically axial length) to modify combustion dynamics. By adjusting these parameters, the system can maintain stable combustion at higher temperatures without excessive flame holding, thereby improving thermodynamic efficiency while protecting against accelerated fuel nozzle wear.
3Use of energy by moving object
If combustion gas temperature is increased, then thermodynamic efficiency is improved, but nitrogen oxide emissions increase
Solution Approach 1:
The patent modifies combustion parameters through different cap assembly configurations to achieve more complete and stable combustion. This allows the system to operate at optimized temperatures that improve efficiency while reducing the formation of nitrogen oxides by preventing excessive temperature conditions that promote NOX generation.
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 extends the operating life and maintenance intervals of combustor components, improves design margins, and reduces undesirable emissions by decoupling combustion instability frequencies and promoting destructive interference, thereby enhancing overall system stability and efficiency.
Implementation Method 1
produce a combustion instability frequency in a first combustor that is different from the combustion instability frequency in a second combustor
Implementation Method 2
reducing constructive interference and enhancing thermodynamic efficiency and flame stability
Data Source
AI summary
A system and method for reducing combustion dynamics includes first and second combustors arranged about an axis, and each combustor includes a cap assembly that extends radially across at least a portion of the combustor and a combustion chamber downstream from the cap assembly. Each cap assembly includes a plurality of tubes that extend axially through the cap assembly to provide fluid communication through the cap assembly to the combustion chamber and a fuel injector that extends through each tube to provide fluid communication into each tube. Each cap assembly has an axial length, and the axial length of the cap assembly in the first combustor is different than the axial length of the cap assembly in the second combustor.