Lean Direct Injection Atomizer Combustion Stability
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Solution Overview
Problem
Existing lean direct injection systems for gas turbines face challenges with combustion instability, poor atomization, and mixing quality, leading to higher NOx emissions and reduced lean blowout margin due to difficulties in controlling the interaction between pilot and main combustion zones.
Innovation Solution
A fuel nozzle design with a radially outer main fuel delivery system and an on-axis pilot fuel delivery system, featuring pre-filming air-blast type atomization, swirl vanes, and an intermediate air swirler for cooling, which mechanically and aerodynamically separates the combustion zones to enhance mixing and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If lean direct injection is used to reduce NOx emissions, then pollutant formation is reduced, but combustion instability increases and lean blowout margin decreases
Solution Approach 1:
The combustion process is divided into two distinct stages: a pilot combustion stage that provides stable ignition and a main combustion stage that operates at lean conditions. This segmentation allows each stage to be optimized independently - the pilot stage ensures combustion stability while the main stage achieves low NOx emissions through lean burning.
Solution Approach 2:
A recirculation zone is introduced as an intermediary region between the pilot and main combustion zones. This recirculation zone acts as a buffer that stabilizes the lean combustion by recirculating hot gases back into the combustion region, thereby maintaining combustion stability while enabling lean operation and reducing NOx emissions.
2Object-generated harmful factors
If staged combustion is implemented to control fuel-to-air ratios, then emissions are reduced, but device complexity increases
Solution Approach 1:
Multiple combustion stages and flow paths are merged into a single integrated combustor design. The pilot fuel injector, main fuel injector, air splitters, and recirculation zones are combined in one compact structure, achieving staged combustion functionality without requiring separate combustion chambers or complex external control systems.
Solution Approach 2:
The air splitter serves multiple functions simultaneously: it separates the pilot and main air streams, creates the recirculation zone, and acts as a flow director. This multi-functionality reduces the need for additional separate components, thereby controlling device complexity while achieving effective staged combustion for emissions reduction.
3Productivity
If rapid fuel-air mixing is achieved through direct injection, then combustion efficiency improves, but atomization quality deteriorates
Solution Approach 1:
High-velocity air streams are used to atomize the liquid fuel injected into the combustor. The pneumatic action of the air streams breaks up the liquid fuel into fine droplets, achieving rapid evaporation and mixing. This pneumatic atomization method enables fast fuel-air mixing for high combustion efficiency while maintaining adequate atomization quality through proper air flow management.
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 achieves improved atomization, increased fuel-air mixing rates, reduced pollutant formation, lower NOx emissions, and enhanced lean blowout margin by effectively separating and stabilizing the combustion zones, thereby improving the operational efficiency and emissions control of gas turbine engines.
Implementation Method 1
an intermediate air swirler located radially inward of the main inner air swirler for providing a cooling air flow along the downstream surface of the radially inner wall of the main inner air passage
Implementation Method 2
The liquid film is then stripped off into droplets by the action of compressor discharge air
Implementation Method 3
main inner air swirler defined in part by a main inner air passage having a radially inner wall with a diverging downstream surface
Data Source
AI summary
A lean direct injection fuel nozzle for a gas turbine is disclosed which includes a radially outer main fuel delivery system including a main inner air swirler defined in part by a main inner air passage having a radially inner wall with a diverging downstream surface, an intermediate air swirler radially inward of the main inner air swirler for providing a cooling air flow along the downstream surface of the radially inner wall of the main inner air passage, and a radially inner pilot fuel delivery system radially inward of the intermediate air swirler.