Turbojet Fuel-Air Mixing Guide Elements with Jagged Trailing Edges
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Solution Overview
Problem
In jet engines, fuel accumulates in 'wake regions' downstream of guide elements due to low flow velocity and the creation of a shear layer, impeding uniform mixing of air and fuel.
Innovation Solution
Guide elements with jagged trailing edges, featuring projections and/or recesses, are used to generate trailing edge vortices, enhancing mixing by preventing fuel accumulation and breaking the shear layer, thereby improving the air-fuel mixture and combustion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If guide elements with straight trailing edges are used, then the structure is simple and easy to manufacture, but fuel accumulates in wake regions downstream of the guide elements, preventing uniform air-fuel mixing
Solution Approach 1:
The guide elements are designed with asymmetric trailing edges featuring sharp edges and projections that create asymmetric flow patterns and vortices, which actively mix the fuel and air in the wake regions, transforming the symmetric but problematic straight trailing edge design into an asymmetric design that promotes uniform mixing
Solution Approach 2:
The trailing edges of the guide elements are designed with curved surfaces and rounded projections rather than sharp angular features, which helps generate smooth vortex flows that effectively mix the fuel and air while avoiding dead zones where fuel would accumulate
2Manufacturing precision
If guide elements with sharp trailing edges are used to generate vortices, then mixing between air and fuel is improved, but the device complexity increases
Solution Approach 1:
The trailing edge of each guide element is segmented into multiple projections and recesses rather than being a single continuous surface, which creates multiple small vortices that collectively achieve thorough mixing while keeping the overall device structure relatively simple
Solution Approach 2:
The complex vortex-generating features are localized only to the trailing edges of the guide elements, while the main body of the guide elements and the rest of the mixing device remains simple in structure, thus achieving improved mixing without proportionally increasing overall device 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
The design ensures a more homogeneous air-fuel mixture and efficient combustion by eliminating fuel accumulation in wake areas and enhancing mixing through the creation of trailing edge vortices, leading to improved operational performance.
Implementation Method 1
the guide elements are designed with at least one leading and/or trailing edge, at least partially with a sharp edge, in a rearward end region relative to the airflow direction. Thus, the guide elements each have a preferably serrated trailing edge, at least partially, to generate so-called trailing-edge vortices downstream of the guide elements
Implementation Method 2
Mixing between the airflow and the fuel is particularly hindered by the formation of a shear layer between the free flow and the wake regions, which prevents the two areas from mixing
Data Source
Figure 1
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AI summary
A device (9) for mixing fuel and air of a jet engine (1) is described, comprising at least one air-carrying channel (11, 12) and at least one further fuel-carrying channel (10, 13). Guide elements (14, 15) extending over the channel height and distributed around the circumference of the channel (11, 12) are provided, in the region of which a swirl can be imposed on the air flowing in the air-carrying channel (11, 12) downstream of the channels (10 to 13) to improve mixing between the air and the fuel. The guide elements (14, 15) are designed in a rear end region (16, 17) relative to the airflow direction with at least one projection and/or recess (16A, 16B, 17A) that is at least approximately, at least partially, sharply edged.