Premixed Pilot Nozzle Flame Stabilization
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Solution Overview
Problem
Gas turbine engines face challenges in reducing nitrogen oxides (NOx) emissions while maintaining stable combustion, as lean fuel-air mixtures can lead to flame instability and increased NOx production, necessitating improved premixed pilot assemblies that stabilize flames while minimizing NOx emissions.
Innovation Solution
The premixed pilot nozzle design features axially elongated tubes within a plenum, with a fuel injection port and an air supply, and an optional non-combustible fluid plenum, such as air or water, to stabilize the flame and reduce NOx production by enhancing fuel-air mixing and temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If lean fuel-air mixtures are used to reduce NOx emissions, then emissions are reduced, but flame stability deteriorates and combustion becomes unstable
Solution Approach 1:
The combustion system is segmented into multiple zones with different fuel-air mixing ratios. The pilot zone uses a richer mixture (higher fuel concentration) to ensure stable combustion, while the main combustion zone uses leaner mixtures to reduce NOx emissions. This spatial segmentation allows each zone to optimize for its specific function without compromising overall system performance.
Solution Approach 2:
Different regions of the combustor are assigned different local qualities in terms of fuel-air mixture composition. The pilot region maintains a locally richer mixture to provide stable ignition and flame anchoring, while the surrounding and downstream regions use leaner mixtures for low-emission combustion. This local differentiation resolves the contradiction by allowing richness where stability is needed and leanness where emissions are the concern.
2Object-generated harmful factors
If fuel and air are mixed within the fuel nozzle (premixed) to reduce NOx, then emissions are reduced, but flame stability worsens compared to diffusion flames
Solution Approach 1:
The premixing process is segmented into a controlled pilot region and a main combustion region. In the pilot region, fuel and air are premixed to a specific ratio that ensures stable flame establishment. This segmented approach allows premixing benefits (low NOx) in the main zone while maintaining stability through the rich pilot zone.
Solution Approach 2:
The pilot flame acts as an intermediary between the premixed fuel-air mixture and the main combustion zone. It provides a stable ignition source that bridges the gap between the lean premixed flow and the combustion process, ensuring reliable flame establishment and anchoring without requiring the main flow to be rich.
3Reliability
If diffusion flames are used to maintain stable combustion, then flame stability is maintained, but NOx emissions increase
Solution Approach 1:
The system merges diffusion flame characteristics in the pilot region with premixed flame characteristics in the main combustion zone. The pilot diffusion flame provides stable ignition and anchoring, while the main zone operates as a premixed low-emission combustor. This hybrid merging allows the system to capture the stability benefits of diffusion flames and the emissions benefits of premixed flames simultaneously.
Solution Approach 2:
Different combustion modes are applied to different local regions: diffusion combustion in the pilot zone for stability, and premixed combustion in the main zone for low emissions. This local quality differentiation allows each combustion mode to be used where it is most effective without the drawbacks of using it system-wide.
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 premixed pilot nozzle effectively stabilizes the flame and reduces NOx emissions by ensuring a well-mixed fuel-air mixture and controlled combustion temperatures, improving the operational stability and emissions performance of gas turbine engines.
Implementation Method 1
An exemplary pre-mixing fuel nozzle may be internally supported by a center body disposed along a longitudinal axis of the fuel nozzle
Implementation Method 2
A second shroud is disposed radially inward of the first shroud, such that a fuel plenum is defined between the first shroud and the second shroud, and the fuel plenum is in communication with a gaseous fuel supply
Implementation Method 3
each of the tubes extending between a tube inlet defined through a forward face of the premixed pilot nozzle and a tube outlet defined through an aft face of the premixed pilot nozzle
Implementation Method 4
Gas turbine engines are widely used to generate power for numerous applications. A convention gas turbine engine includes a compressor, a combustor, and a turbine
Data Source
AI summary
The premixed pilot nozzle includes axially elongated tubes defined within a plenum between an outer shroud and a first shroud disposed radially inward of the outer shroud. The tubes extend between tube inlets defined through a forward face and tube outlets defined through an aft face. A second shroud is disposed radially inward of the first shroud, thereby defining a fuel plenum between the first shroud and the second shroud, and the fuel plenum is in communication with a gaseous fuel supply. A fuel injection port, which is positioned between the tube inlet and the tube outlet of each tube, is in fluid communication with the fuel plenum. An air supply configured to fluidly communicate with the tube inlet of each tube. The second shroud defines a second plenum therein, the second plenum being coupled to a source of a non-combustible fluid.