Purged Flameholder Fuel Shield for Turbofan Afterburner
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Solution Overview
Problem
The thermal distress and limited useful life of pilot vanes in afterburner flameholders due to cold pilot fuel injection, which causes thermal cracking and premature failure, are significant challenges in turbofan engines.
Innovation Solution
A fuel shield is introduced in front of pilot vanes to protect the leading edge from direct fuel impingement, comprising obliquely joined wings and a hood that extends to the outer shell, creating a thermally insulating gap and aerodynamic configuration to reduce thermal gradients and prevent fuel quenching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pilot fuel is injected against the leading edges of pilot vanes to initiate afterburner combustion, then ignition and flame propagation are achieved, but thermal distress and thermal cracking occur in the pilot vanes reducing their useful life
Solution Approach 1:
A fuel shield is introduced as an intermediary component between the pilot fuel injection system and the pilot vanes. The shield protects the leading edges of the pilot vanes from direct fuel impingement while allowing the fuel to ignite and propagate flame in the exhaust flow, thus mediating between the ignition requirement and the thermal protection requirement
Solution Approach 2:
The flameholder assembly is segmented into distinct functional zones: a protected leading edge region with pilot fuel injection for ignition, a middle region with main fuel injection, and a trailing edge region for flame holding. The fuel shield creates a physical separation that allows different fuel injection strategies in different zones without mutual interference
2Object-generated harmful factors
If cold pilot fuel is injected directly at the leading edges of pilot vanes, then afterburner ignition is achieved, but thermal gradients and thermal stress increase causing thermal cracking
Solution Approach 1:
The fuel shield acts as a thermal mediator that blocks the direct path of cold fuel contact with the vane leading edges. It allows the fuel to perform its ignition function in the exhaust stream while preventing the harmful thermal shock and gradient formation that would occur with direct impingement on the vanes
Solution Approach 2:
The fuel shield provides beforehand protection by creating a physical barrier before the cold fuel can contact the pilot vane leading edges. This preemptive measure cushions the vanes against thermal shock and prevents thermal cracking before it can occur
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 fuel shield significantly increases the useful life of pilot vanes by reducing thermal distress and thermal gradients, preventing thermal cracking and extending the operational life of the flameholder assembly.
Implementation Method 1
creating a thermally insulating gap and aerodynamic configuration to reduce thermal gradients and prevent fuel quenching
Data Source
AI summary
A fuel shield is configured for use in the afterburner of a turbofan aircraft engine. The shield includes wings obliquely joined together at a nose to conform with the leading edge region of a flameholder vane. A hood is joined to the wings and extends obliquely therefrom to conform with a supporting outer shell of the flameholder.