Tapered Outer Ring Combustor Flashback Suppression
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Solution Overview
Problem
Gas turbine combustors employing premixed combustion methods face the challenge of flashback occurrence due to low flow speed regions formed around the exit of main burners, which can be exacerbated by flow separation at the downstream end of the outer ring, leading to potential flame propagation and instability in combustion.
Innovation Solution
Incorporating a tapered surface on the outer ring, which gradually decreases in thickness from the upstream to the downstream side, prevents flow separation and stagnation regions, thereby reducing the likelihood of flashback by ensuring smooth gas flow and promoting efficient mixing of premixed gases and compressed air.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a straight outer ring is used, then the structure is simple, but flow separation occurs at the downstream end forming stagnation regions that cause flashback
Solution Approach 1:
The outer ring incorporates a tapered surface that curves gradually from the upstream to downstream direction, eliminating the abrupt step found in straight designs. This curved geometry guides the compressed air flow smoothly along the outer peripheral surface, preventing flow separation and stagnation region formation at the downstream end, thereby suppressing flashback while maintaining structural simplicity
2Ease of manufacture
If the outer ring thickness is uniform, then manufacturing is easy, but flow separation occurs at the downstream end
Solution Approach 1:
The outer ring features a tapered surface that varies the thickness locally from upstream to downstream, creating a gradual transition zone. This local variation in geometry optimizes the flow path for compressed air, maintaining higher flow velocities along the outer peripheral surface and preventing flow separation, while the overall structure remains manufacturable through standard machining processes
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 tapered surface design effectively suppresses flashback at the downstream end of the outer ring, stabilizes combustion, and reduces NOx emissions by enhancing gas flow continuity and mixing efficiency.
Implementation Method 1
the flow of the compressed air separates from the outer peripheral surface 115c of the outer ring 115 and forms a stagnation S1, while the flow of the premixed gas Fp separates from the inner peripheral surface 115b of the outer ring 115 and forms a stagnation
Implementation Method 2
a plurality of swirler tubes that are disposed inside a combustor basket and impart a swirl to a premixed gas
Implementation Method 3
By injecting compressed intake air through the gap 141, film-shaped air Af flows along the inner peripheral surface of a combustor transition piece (or exit outer ring) 112
Implementation Method 4
more and more gas turbine combustors employ the premixed combustion method for reduction of NOx
Implementation Method 5
a pilot burner that performs diffusion combustion in addition to main burners (premix burners) that perform premixed combustion
Data Source
AI summary
A gas turbine combustor provided with: a plurality of swirler tubes that are disposed inside a combustor basket and impart a swirl to a premixed gas, the premixed gas being obtained by premixing a fuel and air for combustion; and an outer ring that is disposed between the plurality of swirler tubes and the combustor basket with a gap provided between the outer ring and the combustor basket, and generates film-shaped air inside a combustor transition piece connected to the combustor basket via injection through the gap into the combustor transition piece, and at a downstream end of the outer ring, the outer ring includes a tapered surface formed such that the outer ring gradually decreases in thickness from an upstream side toward a downstream side.