Canted Mixing Tubes for Gas Turbine Combustor Flame Stability
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Solution Overview
Problem
Gas turbine engines face challenges in minimizing nitrogen oxides (NOx) emissions while maintaining engine performance, as reducing the fuel-to-air ratio for NOx reduction leads to unstable flame conditions and increased risk of flame blowout.
Innovation Solution
The design of a fuel nozzle with axially elongated centerbody and peripheral wall, featuring canted mixing tubes that induce swirling flow, which stabilizes the flame and reduces NOx emissions by optimizing the fuel-air mixture distribution and equivalence ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the fuel-to-air ratio is reduced to lower nitrogen oxides emissions, then NOx emissions are reduced, but flame stability deteriorates and flame blowout risk increases
Solution Approach 1:
The fuel nozzle is divided into multiple injection zones with different fuel-to-air ratios. The pilot zone maintains a higher fuel-to-air ratio for stable flame ignition, while the main combustion zone operates at lower fuel-to-air ratio for reduced NOx emissions. This segmentation allows simultaneous achievement of flame stability and emission reduction.
Solution Approach 2:
Different regions of the combustor are assigned different fuel-to-air ratios tailored to their specific functions. The pilot region uses rich mixtures for reliable ignition and flame holding, while the annular region uses lean mixtures for low emissions. This local optimization resolves the contradiction between overall emission reduction and local flame stability requirements.
2Reliability
If a diffusion flame pilot is used to stabilize the flame, then flame stability improves, but nitrogen oxides emissions increase
Solution Approach 1:
The pilot nozzle transitions from a conventional diffusion flame design to a premixed flame design. By changing the mixing mechanism from diffusion-controlled to premixed, the pilot operates at lower temperatures that reduce NOx formation while maintaining flame stability through the controlled premixed combustion process.
Solution Approach 2:
The combustor employs a composite combustion system combining a premixed pilot nozzle with a lean premixed main combustion zone. This composite approach integrates the flame stabilization capability of the pilot with the low emissions characteristic of lean premixed combustion, achieving both flame stability and reduced NOx emissions simultaneously.
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 canted mixing tube configuration enhances flame stability and reduces NOx emissions by creating a swirling pattern that effectively ignites the fuel-air mixture, even under lean-blow-out conditions, thereby improving overall engine performance and emission control.
Implementation Method 1
canted mixing tubes that are configured for inducing a swirling flow about the central axis in a collective discharge therefrom
Implementation Method 2
pilot nozzle that premix fuel and air to achieve lower nitrogen oxides
Data Source
AI summary
A fuel nozzle for a gas turbine engine that includes: an elongated centerbody; an elongated peripheral wall formed about the centerbody so to define a primary flow annulus therebetween; a primary fuel supply and a primary air supply in fluid communication with an upstream end of the primary flow annulus; and a pilot nozzle. The pilot nozzle may be formed in the centerbody and include: axially elongated mixing tubes defined within a centerbody wall; a fuel port positioned on the mixing tubes for connecting each to a secondary fuel supply; and a secondary air supply configured so to fluidly communicate with an inlet of each of the mixing tubes. A plurality of the mixing tubes may be formed as canted mixing tubes that are configured for inducing a swirling flow about the central axis in a collective discharge therefrom.