Hurst Exponent Analysis for Combustion Instability Prediction
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Solution Overview
Problem
Existing methods for controlling oscillatory instabilities in devices like combustors and turbomachinery are ineffective in predicting the onset of instabilities, often requiring external actuators, sensors, and modifications, and can only control instabilities after they occur, leading to performance losses and increased NOx emissions.
Innovation Solution
A system and method that includes a measuring device, instability detection unit, amplitude estimation unit, and control unit to predict the onset of oscillatory instabilities using techniques like the 0-1 test, burst counting, and Hurst exponent analysis, allowing for proactive control of device parameters to prevent instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques (delay feedback controller, bandwidth analysis, autocorrelation) are used to control oscillatory instabilities, then the instabilities can be controlled after they occur, but the methods require external actuators, sensors, and modifications, and cannot predict instability onset proactively
Solution Approach 1:
The patent applies preliminary action by using the Hurst exponent to detect instability precursors before full oscillatory instabilities occur. The system monitors the Hurst exponent of pressure signals and identifies impending instabilities through early warning signals, enabling proactive control adjustments rather than reactive control after instability has fully developed.
Solution Approach 2:
The patent replaces complex mechanical control systems (external actuators, sensors, feedback controllers) with a simpler signal processing approach based on the Hurst exponent calculation. This substitution eliminates the need for additional hardware while achieving more effective and proactive instability control through mathematical analysis of existing sensor data.
2Reliability
If conservative stability margins are incorporated in combustor design, then instabilities are prevented from occurring, but NOx emissions increase
Solution Approach 1:
The patent changes the parameter used for stability assessment from conservative design margins to real-time dynamic monitoring of the Hurst exponent. This allows the system to operate closer to stability limits without triggering instabilities, as the Hurst exponent provides continuous early warning of approaching critical conditions, thereby reducing unnecessary conservative margins and associated NOx emissions.
3Measurement precision
If frequency domain analysis is used to determine combustor stability, then stability can be assessed, but noise in the combustion chamber makes the technique inefficient
Solution Approach 1:
The patent substitutes frequency domain analysis with time-domain Hurst exponent calculation. The Hurst exponent is calculated from the temporal structure of pressure signals, making it inherently resistant to noise interference. This time-domain approach directly analyzes the scaling properties of fluctuations without requiring spectral decomposition, thereby maintaining measurement precision despite the presence of noise in the combustion chamber.
Data Source
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AI summary
A system for predetermining the onset of oscillatory instabilities in combustion devices is described. The system consists of a measuring device (102), an instability detection unit (104) and a control unit (106). The measuring device (102) is configured to generate signals corresponding to the dynamics happening inside the practical device. The instability detection unit (104) along with an amplitude estimation unit (130) is configured to diagnose the stability of the practical device from the signals that are generated by the measuring device (102). Further, the control unit (106) is configured to control various operating parameters in the practical device based on the information obtained from the instability detection unit (104).