Annular Premixed Pilot Nozzle for Lean Combustion Stability
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Solution Overview
Problem
Gas turbine engines face challenges in reducing nitrogen oxides (NOx) emissions while maintaining engine performance, as lowering the fuel-to-air ratio for NOx reduction leads to unstable flame conditions and increased NOx production with diffusion flame pilots.
Innovation Solution
A fuel/air nozzle design with a premixed pilot nozzle that achieves a uniform equivalence ratio across the combustion chamber, using a premixed pilot to stabilize the flame at low fuel-to-air ratios, reducing NOx emissions without compromising engine stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the fuel-to-air ratio is lowered to reduce nitrogen oxides emissions, then nitrogen oxides emissions are reduced, but flame stability deteriorates and flame blowout occurs
Solution Approach 1:
The fuel nozzle is divided into two separate systems: a main fuel nozzle for bulk fuel delivery and a pilot fuel nozzle for flame stabilization. This segmentation allows the main nozzle to operate at low fuel-to-air ratios for reduced NOx emissions while the pilot nozzle provides a dedicated flame stabilization function, resolving the contradiction between emission reduction and flame stability.
Solution Approach 2:
The pilot fuel nozzle acts as an intermediary element that introduces a small amount of additional fuel specifically for flame stabilization. This intermediary fuel injection prevents flame blowout in the lean main fuel stream without significantly increasing overall NOx emissions, as the pilot fuel amount is controlled to be minimal.
2Reliability
If a diffusion flame pilot is used to stabilize the flame, then flame stability is improved, but nitrogen oxides emissions increase
Solution Approach 1:
The invention changes the operational parameters of the pilot fuel nozzle to operate at stoichiometric or slightly rich conditions specifically for flame stabilization, while keeping the main fuel nozzle at lean conditions for low NOx emissions. By controlling the pilot fuel flow rate to be a small percentage (0.5-5%) of total fuel flow, the overall NOx emissions remain low while flame stability is maintained.
3Object-generated harmful factors
If the fuel-to-air ratio is lowered for emissions reduction, then nitrogen oxides emissions are reduced, but engine performance deteriorates
Solution Approach 1:
The fuel delivery system is segmented into main and pilot nozzles, allowing the main nozzle to operate lean for emissions reduction while the pilot nozzle provides sufficient fuel for maintaining combustion stability and engine performance. This segmentation enables the engine to achieve both low NOx emissions and acceptable performance levels.
Solution Approach 2:
The pilot fuel nozzle provides a partial fuel contribution (0.5-5% of total fuel flow) that is excessive for emissions purposes but necessary for flame stabilization and performance maintenance. This partial fuel addition is sufficient to prevent flame blowout and maintain engine performance without significantly compromising emissions benefits.
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 design achieves stable combustion and reduced NOx emissions by maintaining a stoichiometric fuel-to-air ratio, preventing flame blowout and extending the lean-blowout operability window, thus meeting environmental regulations.
Implementation Method 1
Fuel-air mixing affects both the levels of nitrogen oxides generated in the hot gases of combustion of a gas turbine engine and the engine's performance
Implementation Method 2
The air entering the combustor is mixed with fuel and combusted. Hot gases of combustion are exhausted from the combustor
Implementation Method 3
The swozzle has curved vanes that extend radially from the center body across an annular flow passage and from which fuel is introduced into the annular flow passage to be entrained into a flow of air that is swirled by the vanes of the swozzle
Data Source
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AI summary
A combustor for a gas turbine engine has a head end portion that carries at least one fuel/air nozzle (12). Each fuel/air nozzle (12) includes a premixed pilot nozzle (40) having premix conduits (41) that are configured with concentric axes that direct the fuel/air mixture axially from the premixed pilot nozzle (40). The premixed pilot nozzle (40) can include an annular channel (70) disposed radially outwardly from the premix conduits (41) and including air jets (61) that direct air radially outwardly from the premix conduits (41).