Aircraft Fuel Injection System with Variable Air Duct
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Solution Overview
Problem
Existing injection systems for aircraft turbomachines face design constraints that optimize performance for certain operating points but reduce overall performance at other points, particularly due to conflicting requirements for air pressure and fuel atomization across different engine speeds.
Innovation Solution
The injection system allows for variable fuel film length and air through duct cross-section, enabling adaptable geometry to optimize flame stability and air-fuel mixture across all engine speeds, using motion-inducing means to adjust the central body position and cross-section of the air through duct.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a significant air pressure drop via the injection system is used, then fuel atomisation and mixing is improved for idling operation, but specific consumption increases in full throttle and cruising mode
Solution Approach 1:
The injection system incorporates a movable central body that can adjust its position along the axis of the aerodynamic bowl, dynamically changing the geometry of the air through duct and the length of the fuel film. This dynamic adjustment allows the system to optimize performance for different operating conditions: at idle, the central body position creates a smaller air through duct cross-section for higher pressure drop and better atomisation, while at full throttle, the central body moves to increase the duct cross-section and reduce pressure drop, thereby reducing specific consumption.
2Productivity
If the injection system geometry is optimized for full throttle operation, then cruising performance is improved, but low-speed operation performance is reduced
Solution Approach 1:
The system changes geometric parameters (air through duct cross-section and fuel film length) by moving the central body to different positions. For low-speed operation, the central body is positioned to create a smaller air through duct cross-section, increasing air pressure drop and improving fuel atomisation and mixing. For full throttle and cruising, the central body moves to increase the air through duct cross-section, reducing pressure drop and improving cruising efficiency.
3Device complexity
If the air through duct cross-section is fixed, then the injection system structure is simplified, but performance cannot be optimized for all operating points
Solution Approach 1:
The central body is made movable along the axis of the aerodynamic bowl, transforming the fixed geometry into a dynamic one. This movement allows the air through duct cross-section and fuel film length to be adjusted according to operating conditions, enabling the system to optimize performance across all operating points from idle to full throttle, despite the added complexity of the motion-inducing means.
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 adaptability enhances performance and stability across all engine speeds, optimizing ignition, relighting, pollutant emissions, and specific consumption by influencing the air-fuel mixture and fuel atomization.
Implementation Method 1
this ability to vary the cross-section of the air through duct makes it possible to influence fuel atomisation, which takes place at the outlet of the second widening end of the central body
Data Source
AI summary
An assembly includes an injection system and an injector for an aircraft turbomachine combustion chamber. The system includes an aerodynamic bowl including a first end widening toward the downstream end and centered on a central axis of the injection system, this also including a central body along which a film of fuel is intended to flow in the downstream direction. The central body includes a second end widening toward the downstream end, the first and second widening ends between them delimiting an air through duct and the system includes motion inducing a device allowing a relative movement between the first widening end which is stationary and the second widening end, along the central axis of the injection system, by moving the central body relative to the injector.