Flame Current Frequency Analysis for Combustion Stability
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Solution Overview
Problem
Existing ionization-based flame monitoring systems in gas-fired heating appliances are unreliable for long-term feedback on flame quality due to aging and contamination, and they often result in incomplete combustion when trying to maintain peak flame rod current, especially when the air-fuel ratio is near-stoichiometric.
Innovation Solution
A control apparatus and method that uses a sensor to generate a flame current signal, which is Fourier transformed into a frequency spectrum to detect flame instability caused by an inadequate air-to-fuel ratio, and adjusts the combustion air blower speed to maintain optimal combustion by increasing air flow relative to fuel flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ionization current monitoring is used to maintain peak flame rod current, then flame presence detection is improved, but combustion quality deteriorates due to incomplete combustion from air shortage
Solution Approach 1:
The patent changes the monitoring parameter from flame rod current magnitude to flame rod current frequency characteristics. By analyzing the frequency spectrum of the ionization current signal rather than its absolute value, the system can detect combustion quality issues without interfering with the air-fuel ratio, thus resolving the contradiction between accurate flame detection and maintained combustion quality
Solution Approach 2:
The system implements feedback by continuously monitoring flame rod current frequency characteristics and using this information to detect combustion quality degradation. This feedback mechanism allows the control system to identify when combustion is becoming incomplete and take corrective action, maintaining reliable combustion while preserving accurate flame presence detection
2Measurement precision
If ionization sensor is used for flame monitoring, then flame detection capability is improved, but sensor reliability deteriorates over time due to dirt deposition and chemical decomposition
Solution Approach 1:
The patent transitions from monitoring the magnitude of ionization current (which is affected by sensor aging) to monitoring the frequency spectrum characteristics of the ionization current signal. Frequency-based characteristics remain stable even when sensor sensitivity changes due to dirt or chemical decomposition, thereby maintaining both flame detection capability and sensor reliability over time
Solution Approach 2:
The frequency spectrum analysis acts as an intermediary that decouples the measurement from the sensor's absolute output characteristics. By transforming the time-domain ionization current signal into the frequency domain, the system creates a measurement that is independent of sensor aging effects, preserving both detection capability and reliability
3Device complexity
If flame rod current magnitude is monitored, then simple flame presence indication is achieved, but combustion quality feedback capability is lost
Solution Approach 1:
The patent adds a new dimension to the measurement by transforming the ionization current signal from the time domain to the frequency domain using Fourier transform. This dimensional transformation enables extraction of combustion quality information from frequency spectrum characteristics while maintaining the simplicity of the original ionization current measurement approach
Solution Approach 2:
The system segments the ionization current signal into frequency components through spectral analysis. By dividing the signal into different frequency bands and analyzing their characteristics, the system can extract combustion quality information without complicating the overall monitoring approach, maintaining simplicity while gaining diagnostic capability
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 effectively detects and corrects flame instability, ensuring reliable and efficient combustion by analyzing changes in the flame current signal's frequency spectrum, thereby overcoming the limitations of aging sensors and contamination, and maintaining optimal air-fuel ratios.
Implementation Method 1
Gas fired heating appliances use a source of gas and a source of air that are mixed and transmitted to a burner where an igniter initiates combustion... a sensor for sensing a flame and providing an output of a flame current signal
Data Source
AI summary
A control apparatus for a gas-fired heating appliance having a burner is provided for sensing burner flame instability. The apparatus includes a sensor for sensing a flame and providing an output of a flame current signal, and a controller in communication with the sensor for sensing flame current. The controller is configured to receive the flame current signal and to detect the occurrence of a flame instability condition. The controller detects flame instability from flame current signal data that is measured and Fourier transformed into a frequency spectrum which changes from a stable to instable spectrum when flame instability is caused by an inadequate air-to-fuel ratio. The controller is configured to respond to flame instability by generating an output signal to increase the speed of a combustion air blower that supplies air to the burner, to thereby increase the air flow relative to fuel flow until normal combustion is attained.