Turbomachine Fuel Metering Setpoint Signal Compensation
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Solution Overview
Problem
Existing fuel metering systems in turbomachines face inaccuracies due to assumptions of constant fuel density and temperature variations, leading to imprecise setpoint signals for fuel injection.
Innovation Solution
A method that combines a signal from the slide valve position with a precise flow measurement from a flowmeter, using a digital model to generate a compensation signal, which improves the accuracy of the setpoint signal by accounting for fuel flow dynamics and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the volumetric density of fuel is assumed to be constant and predetermined, then the calculation is simplified, but inaccuracies are introduced in the evaluation of the metering device position due to fuel temperature variations and nature changes
Solution Approach 1:
The patent implements a feedback mechanism where the actual fuel flow measurement from the flow meter is continuously compared with the flow rate evaluated from the metering device position. The difference (error signal) is fed back to adjust and optimize the setpoint signal, thereby compensating for inaccuracies caused by variable fuel density without requiring complex real-time density calculations
Solution Approach 2:
The patent replaces the conventional approach of directly using metering device position to determine fuel flow with an optimized signal generation method. Instead of relying solely on mechanical position measurements, the system substitutes in a calculated setpoint signal that incorporates feedback from actual flow measurements, replacing the simple mechanical measurement system with a hybrid measurement-calculation system
2Measurement precision
If a flow meter measurement is used to generate the setpoint signal, then measurement accuracy is improved, but signal crenellations appear that require filtering
Solution Approach 1:
The patent applies preliminary action by filtering the setpoint signal through a low-pass digital filter before it is used to control the metering device. This anticipatory filtering removes signal crenellations and high-frequency noise in advance, ensuring smooth operation of the fuel injection system without causing instability or oscillations
Solution Approach 2:
The patent changes the temporal parameters of the signal by applying a low-pass filter with a specifically chosen time constant. This parameter transformation smooths the signal while maintaining the essential dynamic characteristics, converting a noisy measurement signal into a usable control signal
3Speed
If the setpoint signal is updated frequently to track fuel flow dynamics, then responsiveness is improved, but noise and instability are introduced
Solution Approach 1:
The patent implements dynamics by using a low-pass digital filter with an optimized time constant that adapts to the system's operational requirements. The filter allows the setpoint signal to track fuel flow dynamics at an appropriate rate while automatically attenuating high-frequency noise, achieving a dynamic balance between responsiveness and stability
Data Source
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AI summary
The setpoint signal (C1) represents a delivery of fuel to be supplied by a slide-valve type (in-line) metering device (2) to a fuel injection system (4) for injecting fuel into a combustion chamber of a turbomachine, the position of the slide valve (2A) being dependent on the setpoint signal. The method involves: obtaining a first signal (S1) representative of a measurement delivered by a flow meter (6) of a delivery of fuel injected into the chamber; evaluating a second signal (S2) representing the delivery of fuel injected into the chamber on the basis of a measurement (M) of the position of the slide valve; estimating a third signal representing the measurement delivered by the flow meter by applying a numerical model of the flow meter to the second signal; formulating the setpoint signal by adding to the first signal a compensation signal that is obtained by subtracting the third signal from the second signal.