Lobed Injector Vortex Generators for Gas Turbine Combustion
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Solution Overview
Problem
Current lobed injectors in gas turbines face issues with flow separation and poor mixing, leading to increased NOx emissions and flashback risks due to auto ignition of the fuel-air mixture, which are exacerbated by the separation of the gas and fuel mixture at the nozzle outlets.
Innovation Solution
The use of grouped or alternating lobed fingers with vortex generators at the trailing edge, configured as streamlined bodies with specific lobe orientations and micro vortex generators to enhance mixing and prevent flow separation, creating large-scale vortices that improve fuel and oxidizer interaction and reduce pressure losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If flow separation is avoided by reducing penetration angle, then flow stability is improved, but mixing quality deteriorates
Solution Approach 1:
The injector is divided into multiple lobed fingers (typically 3-5) arranged around the central axis. Each finger contains nozzles that inject fuel and carrier air separately, allowing independent control of injection parameters while collectively achieving both stable flow and enhanced mixing through the segmented lobe structures
Solution Approach 2:
The lobed fingers feature curved lobe surfaces with specific radii of curvature. These curved surfaces guide the flow smoothly, preventing separation while the three-dimensional lobe geometry creates strong vortices that enhance mixing. The curvature radius is specifically designed to balance flow attachment and vortex generation
2Loss of energy
If penetration angle is reduced to prevent separation, then pressure loss is reduced, but mixing quality deteriorates
Solution Approach 1:
The lobe surfaces are designed with optimized curvature radii that allow the flow to follow the contour without separating, minimizing pressure loss. Simultaneously, the curved geometry generates strong vortices at the lobe tips and trailing edges that dramatically enhance mixing quality, resolving the trade-off between pressure loss and mixing
3Reliability
If residence time in mixing region is reduced to prevent auto ignition, then flashback risk is reduced, but mixing quality may be compromised
Solution Approach 1:
The lobed finger geometry generates strong periodic vortices and flow oscillations that rapidly enhance mixing. These dynamic flow structures accelerate the mixing process, reducing the residence time required to achieve adequate mixing quality, thereby preventing auto-ignition and flashback while maintaining low NOx emissions
Solution Approach 2:
The curved lobe surfaces create strong vortices that intensify turbulent mixing, rapidly homogenizing the fuel-air mixture before it reaches the combustion zone. This accelerated mixing reduces the time the mixture spends in the high-temperature region, preventing spontaneous ignition
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 enhances mixing quality, reduces NOx emissions, and minimizes the risk of flashback by promoting efficient fuel-air mixing and controlling flow separation, thereby improving the overall combustion efficiency and temperature distribution in gas turbines.
Implementation Method 1
vortex generators at the trailing edge, configured as streamlined bodies with specific lobe orientations and micro vortex generators to enhance mixing and prevent flow separation, creating large-scale vortices that improve fuel and oxidizer interaction
Implementation Method 2
Disadvantages related to flow separation are: a weak pressure gradient; a mixing vortex generates at a larger distance from the nozzle than where there is no separation; separation generates a bubble creating a pressure loss along the flow
Implementation Method 3
Since the second combustor 17 is fed by expanded exhaust gas of the first combustor 15, the operating conditions allow self ignition (spontaneous ignition) of the fuel air mixture without additional energy being supplied to the mixture. To prevent ignition of the fuel air mixture in the mixing region, the residence time therein must not exceed the auto ignition delay time.
Data Source
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AI summary
A lobed injector finger for a burner or a mixer of a gas turbine comprises a leading edge (23), a lobed trailing edge (24), a first and a second corrugated surfaces (40a, 40b) defining an airfoil cross section and converging in the trailing edge (24), a plurality of nozzles (27) located at the trailing edge (24) for injection of oil or fuel or carrier air in the burner or mixer, and a plurality of vortex generators (42) projecting from a suction side of lobes (28) defined by the first and second corrugated surfaces (40a, 40b) and positioned from the nozzles (27) to reduce flow separation and/or influence the location of a separation bubble.