Premix Pilot Nozzle Curvilinear Tip Cooling Flame Stability
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Solution Overview
Problem
Existing premix pilot nozzles in gas turbine combustors face challenges in reducing flame instability while effectively cooling the downstream surface, which is exposed to high temperatures, often resulting in instability when cooling air intersects with the pilot flame.
Innovation Solution
The design incorporates a tip portion with a curvilinear downstream surface and axially extending premix tubes, where each tube's outlet is offset from the surface, allowing a cooling medium to attach securely and prevent interference with the pilot flame, maintaining stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling air is directed across the downstream surface of the tip portion, then the downstream surface is cooled and thermal stresses are reduced, but the cooling air strikes the pilot flame at or near the base causing flame instability
Solution Approach 1:
The harmful effect of cooling air striking the flame is eliminated by extracting the cooling function from the downstream surface area and relocating it to the upstream surface. The cooling air is directed to flow across the upstream surface of the tip portion, separating the cooling function from the flame interaction zone, thus cooling the downstream surface indirectly while preventing flame instability.
Solution Approach 2:
The tip portion itself acts as an intermediary medium that transfers cooling from the upstream surface to the downstream surface. By directing cooling air across the upstream surface, the tip portion conducts thermal energy away from the downstream surface through its structure, providing indirect cooling without requiring cooling air to contact the downstream surface directly.
2Duration of action of stationary object
If thermal barrier coatings are applied to the downstream surface, then component life is extended and thermal stresses are reduced, but the complexity of the nozzle assembly increases
Solution Approach 1:
The thermal protection function is extracted from the downstream surface coatings and relocated to the upstream surface cooling system. By applying thermal barrier coatings only to the upstream surface where cooling air contacts the tip, the design eliminates the need for downstream surface coatings while still achieving thermal protection through convective cooling, thus reducing overall complexity.
Solution Approach 2:
Thermal barrier coatings are applied selectively only to the upstream surface of the tip portion rather than the entire downstream surface. This localized application reduces material usage and manufacturing complexity while the cooling air flow pattern ensures thermal protection is achieved where most needed, maintaining component life without excessive complexity.
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
This configuration ensures minimal impact on pilot flame stability by keeping the cooling medium separate from the flame base, providing effective cooling without destabilizing the combustion process.
Implementation Method 1
directing air across an upstream or backside or surface of the tip
Implementation Method 2
At least a portion of the downstream surface is curvilinear... allowing a cooling medium to attach securely
Data Source
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AI summary
A premix pilot nozzle (200) includes a tip portion (220) having a downstream surface (236) that extends between a downstream end (240) of an inner wall (224) of the tip portion (220) and a downstream end (242) of an outer wall (242) of the tip portion (220). The downstream end (240) of the inner wall (224) terminates axially upstream from the downstream end (242) of the outer wall (226). At least a portion of the downstream surface (236) is curvilinear. The tip portion (220) further comprises a plurality of axially extending premix tubes (222) annularly arranged about the tip portion (220). Each premix tube (222) defines a premix flow passage (228) through the tip portion (200). Each premix tube (222) includes an outlet (234) that is axially offset from the downstream surface (236).