Fourier-Based Flame Ionization Probe for In Situ FAR Measurement
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Solution Overview
Problem
Accurately measuring the fuel-to-air ratio (FAR) in combustion chambers is challenging due to harsh conditions and the need for new sensor hardware, which is costly and complex, especially in industrial applications where existing systems cannot be easily modified.
Innovation Solution
A Fourier-based flame ionization probe system using existing electrodes with a step-up isolation transformer to inject excitation waveforms, processing the resulting signal in the frequency domain to produce a monotonic and linear signal proportional to the FAR, independent of combustion gas composition and flame velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If new sensor hardware is added to measure FAR accurately, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The existing flame ionization probe electrode is made to serve dual functions: its original flame detection function and the new FAR measurement function. By injecting excitation waveforms through the existing electrode and processing the resulting signal in the frequency domain, the system extracts FAR information without requiring additional sensor hardware, thus achieving multi-functionality from a single component.
Solution Approach 2:
The system changes the electrical parameters of the existing flame ionization probe by injecting excitation waveforms at specific frequencies and analyzing the frequency-domain characteristics of the resulting current signal. This parameter transformation allows the same hardware to provide FAR measurement capability, converting a simple flame presence detector into a quantitative FAR sensor through signal processing rather than hardware modification.
2Ease of manufacture
If existing flame ionization probe is used for FAR measurement, then ease of manufacture is improved, but measurement precision deteriorates due to harsh combustion conditions
Solution Approach 1:
The system replaces mechanical/sensor hardware modifications with an electrical signal processing approach. Instead of modifying the physical structure of the flame ionization probe or adding new sensors, the invention uses electrical excitation waveforms and frequency-domain signal processing to extract FAR information, substituting complex hardware solutions with a more elegant electrical measurement methodology that is insensitive to combustion chamber harsh conditions.
Solution Approach 2:
The excitation waveforms act as an intermediary that couples the external measurement system with the flame plasma. By introducing known frequency signals through the flame ionization probe and analyzing the modulated current response, the system indirectly measures FAR without direct physical intrusion into the combustion zone, allowing existing hardware to function as a precise sensor through signal mediation.
3Measurement precision
If multiple excitation frequencies are used, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The system uses periodic excitation waveforms at specific frequencies to probe the flame ionization probe. By applying sinusoidal excitation signals and analyzing the frequency-domain response, the method extracts FAR information through periodic measurement cycles rather than continuous high-energy input, reducing overall energy consumption while maintaining measurement precision through time-multiplexed frequency analysis.
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
Enables real-time, cost-effective, and robust measurement of FAR for closed-loop feedback control, providing a high signal-to-noise ratio and minimizing combustion instability across various fuels and operating conditions.
Implementation Method 1
a flame ionization probe which operates in the acoustic frequency domain
Data Source
AI summary
A means of detecting the in-situ fuel-to-air-ratio (FAR) in a combustor or flame zone using a Fourier-based flame ionization probe is presented. The use of multiple excitation frequencies and its detection at certain frequencies or combinations of harmonics of those excitation frequencies, namely, the inter-modulation distortion, provides a novel means of extracting a high signal-to-noise ratio (SNR) FAR measurement in a combustor.