Ionization Electrode Flame Detection Using Low Impedance AC Waveforms
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flame sensing methods in fuel burners face challenges such as distinguishing combustion current levels at high flame power, signal instability due to oxide formation, and parasitic impedances, leading to unreliable combustion control and potential boiler shutdowns.
Innovation Solution
A method using an ionization electrode powered by alternating voltage with low internal impedance, where the voltage waveform has a significantly shorter positive duration than negative, allowing for separation of flame current from parasitic current, reducing the impact of oxide layers and parasitic impedances, and enabling continuous, accurate combustion control across a wide power range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional flame sensing methods are used with high impedance electrode powering circuits, then the system can operate with simple circuit design, but the flame current levels become very difficult to distinguish and the correlation curve between flame and combustion parameters becomes flat
Solution Approach 1:
The patent changes the electrical parameters of the electrode powering circuit by using a low impedance circuit instead of a high impedance circuit. This parameter change enables the detection of flame currents in the range of 15-200 microamperes with a flat correlation curve, significantly improving measurement precision while maintaining circuit simplicity
Solution Approach 2:
The patent employs periodic alternating voltage to power the electrode, with a duty cycle that can be varied between 0.1% and 99.9%. This periodic action allows for time-separated measurement of flame current and parasitic current, enabling precise differentiation between combustion-related signals and parasitic signals while keeping the circuit design straightforward
2Reliability
If conventional flame sensing is used, then the system can operate initially, but oxide formation on the electrode rod causes signal reduction and instability over time
Solution Approach 1:
The patent uses periodic alternating voltage with adjustable duty cycle to periodically reverse the polarity of the electrode. This periodic action prevents continuous oxide accumulation on the electrode surface by alternately removing electrons during negative half-cycles, thereby maintaining stable flame signals and reliable combustion control over extended periods
Solution Approach 2:
The low impedance powering circuit automatically compensates for oxide formation effects without requiring external intervention. The circuit maintains stable flame current measurements despite oxide layer development on the electrode, providing self-correcting operation that ensures long-term reliability
3Ease of manufacture
If conventional high impedance reading circuits are used in low-cost systems, then the system cost is reduced, but parasitic impedances from moisture and impurities falsify the flame signal reading
Solution Approach 1:
The patent employs periodic alternating voltage with time-separated measurement phases. During the negative half-cycle, the system measures parasitic current flowing through moisture and impurities. During the positive half-cycle, it measures the combined flame and parasitic current. By subtracting the parasitic component, the system achieves accurate flame signal reading even with simple low-cost circuitry
Solution Approach 2:
The patent extracts and separates the parasitic current component from the total measured current. By measuring parasitic current during the negative half-cycle when flame current is absent, the system isolates and removes the erroneous signal component, leaving only the true flame signal for combustion control
4Measurement precision
If conventional flame sensing methods are used, then the system can detect flame presence, but it cannot reliably distinguish combustion current from parasitic current at high flame power
Solution Approach 1:
The patent uses periodic alternating voltage to create time-separated measurement opportunities. During the negative half-cycle, only parasitic current flows through the electrode. During the positive half-cycle, both flame current and parasitic current flow. This temporal separation makes it trivial to differentiate and subtract the parasitic component, enabling precise combustion parameter measurement even at high flame powers where conventional methods fail
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 provides reliable and consistent combustion control, minimizing the need for automatic resetting and ensuring operation within optimal parameters, reducing emissions and preventing boiler shutdowns.
Implementation Method 1
By utilizing the aforesaid ionisation phenomenon, a direct current passage is sensed (normally by a signal integration circuit) in the electrode corresponding to the presence of the flame
Implementation Method 2
a known method uses the known flame rectification effect as produced by the combustion of a solid, liquid or gaseous fuel in a burner. By virtue of this effect, flame formation can be sensed by integrating and measuring a direct current flowing through an electrode positioned in the burner
Data Source
Figure 1
Figure 2~9
Figure 10
AI summary
An improved method- for flame sensing in a solid, liquid or gaseous fuel burner, said flame being generated at an ionization electrode (1), the flame presence resulting in an ionising effect on said electrode (1), said electrode being powered by an alternating voltage signal, the ionization phenomenon generating in the electrode a direct current, said current being sensed by a suitable sensing circuit (3) comprising a control unit (7), this signal generator being of relatively low internal impedance to enable the measured generated current to have a high value compared with that normally used and of waveform such as to tend to limit the value of the direct current flowing through the electrode (1), said sensing and control circuit being such as to enable the presence of a parasitic current (10) on the flame sensing electrode to be measured. A device for implementing said method is also claimed.