Turbomachine Combustion Chamber Corner Recirculation Fuel Injection
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Solution Overview
Problem
In aircraft turbomachines, the current fuel injection technology faces challenges in initiating and sustaining combustion during in-flight restarts due to cold air input and insufficient fuel concentration, leading to flameout issues, especially at low speeds, as the energy core is not effectively captured by central recirculation zones and corner recirculation zones suffer from poor carburation.
Innovation Solution
The introduction of additional fuel injection devices with secondary fuel injection nozzles that directly inject fuel into corner recirculation zones, which are activated at idle speeds or below to reignite the combustion chamber and stabilize the flame, and are deactivated at higher speeds to optimize fuel distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fuel injection technology is used with central recirculation zones, then fuel is injected towards the center, but the energy core is not effectively captured and corner recirculation zones suffer from poor carburation
Solution Approach 1:
The fuel injection system is segmented into multiple injection devices: conventional central injectors and additional corner injectors. This segmentation allows fuel to be delivered to both central and corner recirculation zones simultaneously, ensuring proper carburation in all regions and effective capture of the energy core.
Solution Approach 2:
Different regions of the combustion chamber receive tailored fuel injection: the central region receives fuel from main injectors while corner regions receive fuel from additional corner injectors. This local quality approach ensures each recirculation zone receives appropriate fuel concentration for stable combustion.
2Reliability
If additional fuel injection devices are added to target corner recirculation zones, then combustion stability is enhanced, but device complexity increases
Solution Approach 1:
The additional corner injection devices are integrated into the existing injection system architecture, sharing common components such as fuel supply lines and control systems. This multi-functionality approach allows the system to address both central and corner recirculation zones without proportionally increasing overall system complexity.
3Reliability
If fuel concentration is increased to ensure proper carburation, then combustion initiation is improved, but NOx emissions may increase due to higher fuel concentrations
Solution Approach 1:
Fuel concentration is optimized locally in different regions: corner injectors provide targeted fuel delivery to previously under-carbured zones, achieving proper fuel-air mixture ratios where needed without globally increasing fuel concentration. This reduces the formation of excessive NOx while ensuring reliable combustion initiation.
Solution Approach 2:
The additional corner injectors operate continuously during combustion to maintain proper fuel distribution and carburation throughout the combustion chamber, ensuring stable combustion that prevents flameout without requiring periodic high-fuel-concentration bursts that would increase NOx emissions.
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 solution enhances combustion stability and reduces flameout risks by targeting corner recirculation zones for ignition, improving combustion homogeneity and reducing NOx emissions by ensuring proper fuel distribution and temperature profiles.
Implementation Method 1
The air inlet swirlers 56, 58 can create a rotational flow 61, sometimes called a 'swirled flow' that creates two types of recirculation zone
Implementation Method 2
create a rotational flow 61... that creates a central recirculation zone 62 and a corner recirculation zone 64
Implementation Method 3
each injection system 42 usually comprises a bushing 52... in which a fuel injection nozzle 54 is installed
Implementation Method 4
stabilise the combustion flame
Data Source
AI summary
A combustion chamber for an aircraft turbomachine includes an annular chamber end wall and an annular row of injection systems mounted in the annular chamber end wall. Each injection system includes at least one air inlet swirler and a main fuel injection nozzle to output a fuel stream centered on an injection axis and including a central recirculation zone and a corner recirculation zone extending as an annulus around the central recirculation zone chamber. The combustion chamber also includes a plurality of additional fuel injection devices mounted in the chamber end wall to inject fuel directly into the corresponding corner recirculation zones produced by the corresponding injection systems at an operating speed less than or equal to the idling speed.