Swirler Assembly Reducing NOx in Gas Turbine Combustors
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Solution Overview
Problem
Gas turbine engines face challenges in minimizing nitrogen oxide (NOX) emissions, particularly due to high shear stresses and flame temperature conditions in RQL combustion, which lead to increased NOX production and pressure oscillations, limiting the effectiveness of existing strategies like rich burn, quick quench, lean burn (RQL) and Dry Low NOX combustors.
Innovation Solution
A swirler assembly for gas turbine engines comprising an inner injector generating a one-dimensional swirl and an outer annular injector producing a three-dimensional swirl, along with an annular recess tube and convergent-divergent exits, to control fuel-air mixture and airflow, reducing NOX formation by optimizing flame temperature and strain rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If RQL combustion strategy is used to minimize NOX emissions, then fuel-air mixture is controlled to reduce NOX formation, but high shear stresses and flame temperature conditions lead to increased NOX production and pressure oscillations
Solution Approach 1:
The combustor is divided into three distinct combustion zones (rich burn zone, quench zone, and lean burn zone) arranged in series. Each zone performs a specific function: the rich burn zone completes fuel combustion, the quench zone rapidly cools the products to below 1500K to freeze out NOX formation, and the lean burn zone ensures complete oxidation. This segmentation allows simultaneous achievement of low NOX emissions and stable combustion by preventing the harmful effects of high temperature and high shear stress in any single location.
Solution Approach 2:
The quench zone acts as an intermediary between the rich burn zone and the lean burn zone. It receives hot fuel-rich combustion products from the rich burn zone and rapidly cools them through mixing with cooler air, creating a thermal barrier that prevents NOX formation. This intermediary zone protects the subsequent lean burn zone from thermal effects and maintains overall combustion stability while achieving low NOX emissions.
2Object-generated harmful factors
If lean premix strategy is used to reduce NOX formation, then flame temperature is reduced, but noise, flame blow-off, and flashback occur affecting engine performance
Solution Approach 1:
Instead of using a single lean premix zone that causes flame instability, the combustor is segmented into three zones. The lean burn zone operates with controlled equivalence ratios (0.8-1.2) to maintain flame stability while achieving low NOX emissions. The rich burn and quench zones provide thermal management that prevents the harmful effects of excessive lean mixing, including noise, flame blow-off, and flashback.
Solution Approach 2:
The combustor dynamically adjusts the equivalence ratio parameter across different zones: the rich burn zone uses fuel-rich mixtures (equivalence ratio >1.0), the quench zone uses stoichiometric or slightly lean mixtures for cooling, and the lean burn zone uses controlled lean mixtures (equivalence ratio 0.8-1.2). This parameter variation allows the system to achieve low NOX emissions while maintaining flame stability and avoiding the operational problems of uniform lean premix.
3Object-generated harmful factors
If high strain rates are applied to reduce flame temperature and NOX production, then NOX production rates are reduced, but flame residence time is reduced and Oxygen concentration increases
Solution Approach 1:
The combustion process is segmented into three zones with different strain rates and residence times. The rich burn zone provides initial combustion with moderate strain rates, the quench zone provides rapid cooling with high strain rates to freeze out NOX, and the lean burn zone provides completed oxidation with controlled strain rates. This segmentation allows the system to achieve low NOX production rates while maintaining adequate flame residence time through the coordinated action of all three zones.
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 swirler assembly significantly reduces NOX formation by 2.5-5 times compared to lean premixed combustors, while maintaining flame stability and reducing combustion pressure oscillations, making it suitable for both high and low power flight conditions.
Implementation Method 1
an inner injector, and an outer annular injector which at least partially surrounds the inner injector. In a further embodiment, the inner injector is operable to generate a first swirl and the outer annular injector is operable to generate a second swirl
Implementation Method 2
A swirler assembly for gas turbine engines comprising an inner injector generating a one-dimensional swirl and an outer annular injector producing a three-dimensional swirl, along with an annular recess tube and convergent-divergent exits, to control fuel-air mixture and airflow, reducing NOX formation by optimizing flame temperature and strain rates
Data Source
AI summary
A swirler assembly for a gas turbine engine includes an outer annular injector which at least partially surrounds an inner injector. In sonic embodiments, a combustor section for a gas turbine engine comprises an inner injector which defines an axis, an outer annular injector which surrounds said inner injector, and a combustor vane along said axis.