Remote Flame Sensing System Using Insulated Rod
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Solution Overview
Problem
Current flame sensing devices for long burners, such as pipe, line, and ribbon burners, are unreliable due to flimsy materials like stainless steel rods that can ground out when ceramic insulators move or crack, and the added steel can expand and touch the burner surface, causing misfire and requiring complex maintenance.
Innovation Solution
A robust flame sensing system using an insulated electric element with a nichrome wire and magnesium oxide insulation, housed in a stainless steel sheath, which extends along the burner without grounding issues, reducing reliance on ceramic insulators and using high-temperature alloys like Kanthal for improved durability and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flame rod with ceramic insulators is used to sense flame at the farthest point of a long burner, then flame detection capability is improved, but the reliability deteriorates due to ceramic insulators moving or cracking causing grounding
Solution Approach 1:
The patent removes the ceramic insulators from the flame rod assembly entirely. The flame rod is mounted directly to the burner body through alternative means that eliminate the need for ceramic insulators, thereby eliminating the source of the reliability problem while preserving flame detection capability.
Solution Approach 2:
Instead of using ceramic insulators to electrically isolate the flame rod from the burner body, the patent inverts the approach by using the burner body itself as part of the electrical circuit. The flame rod is electrically connected to the burner body through a reliable mechanical connection, and the flame sensing function is achieved through the ionized flame path between the rod and a separate ground reference.
2Measurement precision
If extra steel is added over the flame area to increase sensing surface area, then flame sensing capability is improved, but the reliability deteriorates due to thermal expansion causing contact with burner surface
Solution Approach 1:
The patent changes the material parameters by using a flame rod with a smaller cross-sectional area and different thermal expansion characteristics compared to the extra steel approach. The rod is designed with precise dimensions that account for thermal expansion, ensuring it maintains its position and electrical isolation throughout the operating temperature range.
Solution Approach 2:
The patent segments the flame sensing function from the burner body structure. Instead of adding steel over the flame area that is structurally integrated with the burner, the flame rod is a separate, independent component that can be precisely positioned and dimensioned to prevent thermal expansion contact issues.
3Measurement precision
If a flame rod runs the length of the burner with multiple ceramic insulators and brackets, then flame detection at farthest point is improved, but the device complexity increases
Solution Approach 1:
The patent removes the complex assembly of multiple ceramic insulators and brackets from the flame rod mounting system. The flame rod is simplified to a single component that mounts directly to the burner body with minimal supporting structure, eliminating the complexity of the multi-component assembly while maintaining the ability to detect flame at the farthest point.
Solution Approach 2:
The patent merges the flame rod mounting function with the burner body structure itself. Instead of using separate brackets and insulators as independent components, the burner body is designed to directly support and electrically connect to the flame rod, integrating multiple functions into a single structural element.
4Reliability
If ceramic insulators are used to protect the flame rod from grounding, then electrical isolation is improved, but the ease of operation deteriorates due to maintenance requirements when insulators fail
Solution Approach 1:
The patent removes the ceramic insulators that require maintenance when they fail. The flame rod is designed to mount directly to the burner body without insulators, eliminating the need for maintenance related to insulator degradation, cracking, or displacement.
Solution Approach 2:
The flame rod assembly is designed to be self-maintaining by eliminating the ceramic insulators that are prone to failure. The direct mounting design ensures long-term reliability without requiring periodic inspection or replacement of insulator components.
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
The solution provides reliable flame detection at the farthest point from ignition, reducing maintenance needs and ensuring consistent operation by preventing electrical contact with the ground and withstanding high temperatures, thus maintaining stable flame sensing over time.
Implementation Method 1
As a flame burns, it produces an ionized region in its vicinity, thereby providing an electrically conductive medium. This property can be utilized in conjunction with a probe placed into the flame, and a grounded metal burner to produce a usable electrical signal. If such apparatus is constructed with an effective grounded burner area greater than the effective probe area, typically in at least a 4 to 1 ratio, the flame will exhibit electrical characteristics somewhat similar to those of a diode in series with a 10 Mega-ohm resistor. If an alternating current signal is injected into the flame by the probe, the signal will be rectified by the flame.
Data Source
AI summary
The present invention is a burner flame detector to detect a flame at a farthest end of a burner using a flame rectification rod. It comprises of a rod-element comprising of an inner electric-wire, an electrically insulating material surrounding the inner electric-wire, a metallic tubular outer rod protecting the insulating material and the inner electric-wire. The metallic tubular outer rod is electrically insulated from the inner electric-wire, and a flame rectification sensor is attached to the rod-element at the farthest end of the burner, which goes through the flame. The flame rectification sensor becomes exposed to a flame and sends a flame rectified signal to a controller, through the inner electric-wire.