Pre-nozzle Mixing Cap Assembly for Gas Turbine Combustors
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Solution Overview
Problem
Gas turbine engine combustors face challenges in reducing NOx emissions while maintaining operational efficiency, as existing designs like Dry Low NOx combustors are prone to flame holding, flashback, and auto-ignition, especially with highly reactive fuels, due to irregular fuel and air flow mixing and recirculation zones.
Innovation Solution
A pre-nozzle mixing cap assembly is introduced, featuring a fuel plenum and air tubes with fuel holes for mixing air and fuel upstream of the fuel nozzles, providing faster mixing and reduced flame holding risks, along with a cooling flow to enhance durability and reduce air requirements for cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If fuel and air are premixed upstream of fuel nozzles to reduce NOx emissions, then NOx emissions are reduced, but flame holding and flashback risks increase due to irregular flow mixing and recirculation zones
Solution Approach 1:
The mixing cap is segmented into multiple tubes, each containing multiple fuel holes. This segmentation creates numerous small mixing zones rather than a single large mixing zone, improving flow distribution and reducing recirculation areas where flame holding could occur. The fuel is injected through multiple discrete holes in each tube, creating distributed fuel-air mixing throughout the cap structure.
Solution Approach 2:
Different regions of the mixing cap provide different functions: some tubes are positioned to optimize fuel-air mixing in specific zones, while the overall cap structure provides cooling airflow paths. The fuel holes are strategically positioned on tubes at different locations to create locally optimized mixing patterns that prevent flame holding while maintaining low NOx emissions.
2Stability of the object's composition
If fuel injection is performed upstream of head-end to improve mixing, then mixing is enhanced, but flow disturbances create recirculation zones that lead to stable pockets of ignitable fuel-air mixtures
Solution Approach 1:
Fuel is injected and mixed with air upstream of the head-end through the mixing cap structure. This preliminary mixing action occurs before the flow reaches the combustion zone, ensuring thorough fuel-air distribution. The mixing cap with its multiple tubes and fuel holes creates controlled mixing patterns that prevent later recirculation and flame holding issues.
3Reliability
If more air is used for cooling the combustor, then cooling effectiveness is improved, but air consumption increases
Solution Approach 1:
The mixing cap structure serves multiple functions simultaneously: it provides fuel-air mixing through the tubes and fuel holes, and it provides cooling airflow paths through its structure. The same cap that performs fuel injection also channels cooling air to the liner, eliminating the need for separate cooling components and optimizing air utilization.
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 solution achieves improved fuel-air mixing, lower flame holding risks, and increased combustor durability by reducing residence time and accommodating higher reactivity fuels, while meeting emission targets and minimizing combustion dynamics impacts.
Implementation Method 1
Each of the tubes may include a number of fuel holes therein such that the flow of fuel in the fuel plenum passes through the fuel holes and mixes with the flow of air
Implementation Method 2
having a cooling flow of air extending therethrough
Data Source
AI summary
The present application and the resulting patent provide a pre-nozzle mixing cap assembly positioned about a cap member of a combustor for mixing a flow of air and a flow of fuel. The pre-nozzle mixing cap assembly may include a fuel plenum in communication with the flow of fuel and a number of tubes in communication with the flow of air and extending through the fuel plenum. Each of the tubes may include a number of fuel holes therein such that the flow of fuel in the fuel plenum passes through the fuel holes and mixes with the flow of air.