Annular Mixing Duct Flashback Prevention in Gas Turbines
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Solution Overview
Problem
Lean premix combustion systems in gas turbine engines face challenges with flashback of flames into the premixing section, which poses a risk to the engine's operation and efficiency.
Innovation Solution
An annular mixing duct is introduced to impart swirl to the air and fuel mixture, with a decreasing pressure gradient and curvilinear passage that expels any hot spots formed by ignition into the combustion chamber, preventing flashback and ensuring reliable ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a lean premix combustion system is used to reduce NOx emissions, then pollutant emissions are reduced, but the risk of flashback into the premixing section increases
Solution Approach 1:
The combustor is divided into distinct functional zones: a premixing zone where fuel and air are mixed, a transition zone with the annular duct that prevents flashback, and a combustion zone where burning occurs. This segmentation isolates the flashback-prone premixing section from the combustion region, allowing lean premix operation without compromising reliability.
Solution Approach 2:
The annular duct acts as an intermediary element between the premixing section and combustion chamber. It receives the swirled premixed flow, provides a controlled transition path, and expels hot spots into the combustion chamber rather than allowing them to propagate back into the premixing zone, thus mediating the flashback risk.
2Productivity
If swirl is imparted to the fuel and air mixture to enhance mixing, then combustion efficiency is improved, but the complexity of the duct design increases
Solution Approach 1:
The annular duct incorporates curvilinear passages with specific curvature radii that naturally generate and control swirl in the fuel-air mixture. The curved geometry of the duct itself imparts the necessary rotational flow without requiring additional mechanical swirl generators, thereby improving combustion efficiency while maintaining relatively simple duct construction.
Solution Approach 2:
The annular duct performs multiple functions simultaneously: it transports the fuel-air mixture, imparts swirl for enhanced mixing, provides a pressure gradient for flow control, and acts as a flashback prevention barrier. This multi-functionality achieves improved combustion efficiency without proportionally increasing device complexity.
3Reliability
If a pressure gradient is applied to expel hot spots from the annular duct, then flashback is prevented, but the energy loss increases
Solution Approach 1:
The pressure gradient in the annular duct is carefully optimized to be sufficient for expelling hot spots and preventing flashback, but not excessively high to cause significant energy loss. The gradual pressure decrease along the curvilinear passage provides just enough driving force for flashback prevention while minimizing unnecessary energy dissipation.
Solution Approach 2:
The hot spots that would otherwise represent harmful energy losses are deliberately channeled and expelled into the combustion chamber where they serve a beneficial function as ignition sources. This converts what would be energy waste into useful combustion initiation, simultaneously preventing flashback and reducing net energy loss.
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 solution effectively prevents flashback and stabilizes the flame, ensuring safe and efficient combustion by expelling hot spots into the combustion chamber, where they can ignite the fuel and air mixture, thus enhancing engine operation and reducing pollutant emissions.
Implementation Method 1
imparting swirl to a fluid including air
Implementation Method 2
subjecting the hot spot to a pressure gradient within the annular duct
Implementation Method 3
igniting a portion of the fuel and air mixture within the annular duct to form a hot spot
Implementation Method 4
subjecting the hot spot to a pressure gradient within the annular duct to expel the hot spot from the annular duct and into the combustion chamber
Data Source
Figure 1~2
Figure 3~4
AI summary
A combustion chamber device having a field static pressure gradient adapted to expel a flame kernel or hot spot from a fuel-air mixing duct. The swirling flow passing through an annular mixing duct is turned from a radial direction to an axial direction before entering the combustion chamber. An ignition source located within the fuel-air mixing duct can then be used to start the combustion process in the gas turbine.