Combustion Staging System Fuel Flow Scheduling
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Solution Overview
Problem
The existing combustion staging systems for gas turbine engines face challenges in managing failed open mains flow scheduling valves (FSVs), leading to potential hot streaks and turbine damage, and are limited by phase lag in closed-loop control and sensitivity to valve friction, which affects flow distribution and emissions.
Innovation Solution
A combustion staging system that includes a splitting unit to control the fuel flow into pilot and mains manifolds, with mains flow scheduling valves operated by a pressure differential between a servo line and the mains fuel manifold, enhancing the closing force margin and reducing the risk of FSV failure, and utilizing a metering and spill architecture for precise fuel control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a separate recirculation manifold is provided to keep fuel cool in the mains manifold during pilot-only operation, then fuel temperature is controlled to prevent coking, but the risk of hot streaks increases when mains FSV fails open
Solution Approach 1:
The invention extracts the cooling function from the main fuel manifold by providing a separate recirculation manifold that is thermally isolated from the mains manifold. This allows the mains manifold to be cooled without creating a direct flow path that could lead to hot streaks if FSV fails open. The cooling function is separated from the fuel distribution function.
Solution Approach 2:
The invention introduces an intermediary cooling manifold that acts as a buffer between the hot engine environment and the mains fuel manifold. This intermediary structure provides thermal protection while preventing direct communication between the cooling flow and the combustor, thus eliminating the hot streak risk associated with FSV failure.
2Ease of operation
If closed-loop control is used to control fuel split between manifolds, then fuel distribution is controlled, but phase lag reduces control precision
Solution Approach 1:
The invention replaces the electronic closed-loop control system with a hydro-mechanical open-loop control system. The fuel split is controlled by pressure differential and flow dynamics rather than electronic feedback, eliminating phase lag and improving control precision. The system uses the natural physics of fluid flow to achieve accurate fuel distribution.
Solution Approach 2:
The invention enables the fuel control system to self-regulate fuel split between manifolds using inherent pressure and flow relationships. The system automatically balances fuel distribution through its hydro-mechanical design without requiring external electronic control or feedback, achieving precise control through self-correcting fluid dynamics.
3Reliability
If FSV cracking pressure is set high to prevent gas ingress, then seal degradation is reduced, but flow distribution becomes sensitive to valve friction
Solution Approach 1:
The invention changes the operating parameters of the FSV by reducing the cracking pressure and instead relying on the hydro-mechanical control system to maintain proper fuel distribution. This allows the valves to operate in a more stable pressure range that is less sensitive to friction variations, while the overall system maintains reliability through the open-loop control architecture.
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 system reduces the probability of FSV failure, improves flow distribution, and enhances the robustness against contamination and friction, leading to reduced emissions and extended turbine lifespan by ensuring accurate and dynamic control of fuel flow.
Implementation Method 1
the piston being movable to the closed position under an increase in pressure in the servo line relative to the mains fuel manifold
Implementation Method 2
a splitting unit which receives a metered total fuel flow and controllably splits the metered total fuel flow into out-going pilot and mains fuel flows
Data Source
AI summary
A combustion staging system is provided for fuel injectors of a multi-stage combustor of a gas turbine engine. The system has a splitting unit which receives a metered total fuel flow and controllably splits the metered total fuel flow into out-going pilot and mains fuel flows to perform pilot-only and pilot-and-mains staging control of the combustor. The system further has pilot and mains fuel manifolds which respectively receive the pilot and mains fuel flows. The system further has a plurality of mains flow scheduling valves which distribute the mains fuel flow from the mains fuel manifold to mains discharge orifices of respective injectors of the combustor. The system further has servo line which extends to the mains flow scheduling valves, the servo line being controllably fillable with pressurised fuel to change the pressure in the servo line relative to the pressure in the mains fuel manifold. Each mains flow scheduling valve has a chamber containing a movable piston, the chamber to a mains side of the piston being fed by the mains fuel manifold, and the chamber to a servo side of the piston being fed by the servo line. The piston has an open pilot-and-mains position which allows flow out of the mains side of the chamber to the mains discharge orifice of the respective injector. The piston is biased towards a closed pilot-only position which prevents flow out of the mains side of the chamber to the mains discharge orifice of the respective injector. The piston is movable to the closed position under an increase in pressure in the servo line relative to the mains fuel manifold.