Airbreathing Jet Engine Thrust Control Using Chamber Pressure Ratios
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Solution Overview
Problem
Existing thrust control methods for airbreathing jet engines, particularly reheat systems, are inaccurate due to not accounting for differences between demanded and delivered fuel flow and combustion efficiency, leading to increased fuel consumption and potential operational issues.
Innovation Solution
A method that controls fuel flow rate based on the ratio of static pressures at different axial locations within the combustion chamber, using pressure measurements to accurately adjust fuel distribution and account for variables such as combustion efficiency and flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If thrust control is based on demanded fuel flow delivery, then the control system is simple to operate, but the thrust control accuracy deteriorates due to not accounting for differences between demanded and delivered fuel flow and combustion efficiency
Solution Approach 1:
The patent implements feedback control by measuring actual static pressure at multiple axial locations within the combustion chamber and using this information to adjust fuel flow rate. The system continuously monitors the pressure ratio and compares it against desired thrust settings, automatically correcting deviations by modulating fuel delivery. This closed-loop feedback mechanism resolves the contradiction by maintaining simple operation while significantly improving thrust control accuracy through real-time adjustments based on actual combustion chamber conditions.
Solution Approach 2:
The patent replaces direct mechanical fuel flow measurement and control with a pressure-based control system. Instead of relying on mechanical fuel flow meters and direct fuel delivery control, the system uses static pressure sensors to indirectly measure combustion chamber conditions and uses pressure ratio as the control variable. This substitution of mechanical measurement with pressure-based sensing improves accuracy while maintaining operational simplicity.
2Ease of manufacture
If thrust control is based on demanded fuel flow delivery, then the control system is easy to implement, but fuel consumption increases due to inaccurate thrust control
Solution Approach 1:
The feedback mechanism continuously monitors actual thrust production through static pressure measurements and adjusts fuel flow accordingly. By comparing actual pressure ratio against desired values, the system prevents both over-fueling (which wastes energy) and under-fueling (which fails to meet thrust requirements). This resolves the contradiction by maintaining easy implementation while reducing fuel consumption through precise, demand-matched fuel delivery.
Solution Approach 2:
The patent changes the control parameter from direct fuel flow rate to static pressure ratio across multiple axial locations. This parameter transformation allows the system to indirectly control thrust more accurately, ensuring fuel consumption matches actual thrust requirements. The pressure ratio serves as a more accurate proxy for thrust production, enabling the system to reduce energy loss while keeping the control system relatively simple to implement.
3Measurement precision
If pressure measurement at multiple axial locations is implemented, then thrust control accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the combustion chamber into multiple axial zones and places pressure sensors at specific locations (upstream and downstream of the fuel injection apparatus). This segmentation allows the system to capture pressure gradients that correlate with thrust production without requiring a complete pressure field measurement. The selective placement of sensors at key axial locations provides accurate thrust indication while limiting the number of sensors needed, thus resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The patent uses static pressure as an intermediary variable to indirectly measure thrust production. Instead of directly measuring thrust or fuel flow, the system measures static pressure at multiple axial locations and uses the pressure ratio as a proxy for thrust. This intermediary approach simplifies the measurement system compared to direct thrust measurement while maintaining high accuracy, as pressure changes correlate strongly with thrust production in the combustion chamber.
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 approach enhances thrust control accuracy, reduces fuel consumption, and optimizes fuel distribution, thereby improving the operational efficiency and reducing specific fuel consumption.
Implementation Method 1
obtaining a value of static pressure at a first axial location of the combustion chamber of the airbreathing jet engine and obtaining a value of static pressure at a second axial location of the combustion chamber
Implementation Method 2
a fuel injection apparatus configured to deliver fuel to a combustion chamber
Data Source
AI summary
A method of thrust control for an airbreathing jet engine includes obtaining a demanded thrust setting, a value of static pressure at a first axial location of a combustion chamber of the airbreathing jet engine and a value of static pressure at a second axial location of the combustion chamber of the airbreathing jet engine. The second axial location is downstream of the first axial location. The method also includes obtaining a ratio of the value of static pressure at the first axial location of the combustion chamber to the value of static pressure at the second axial location of the combustion chamber; and controlling a fuel flow rate of the airbreathing engine based at least in part on the demanded thrust setting and the ratio of the value of the static pressure at the first axial location to the value of the static pressure at the second axial location.