Water Heater Burner Flashback Shutdown Using Thermal and Pressure Detection
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Solution Overview
Problem
Fuel-fired heating appliances, such as water heaters, face the issue of burner flashback conditions where the flame burns within the burner body instead of externally, leading to high carbon monoxide emissions and compromised ignition resistance, necessitating a protective system to detect and shut down combustion.
Innovation Solution
A protective system is integrated into the water heater to detect burner flashback conditions through temperature or pressure changes, using a meltable pilot fuel supply line or a pressure switch to extinguish the pilot burner flame, thereby shutting down the fuel supply and terminating operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If fuel/air premixing type burners are integrated into fuel-fired water heaters, then combustion efficiency is improved, but the risk of burner flashback conditions increases
Solution Approach 1:
A pilot flame is introduced as an intermediary element to ignite the main burner while providing a visual and thermal indicator of proper combustion. The pilot flame serves as a mediator between the fuel supply and main combustion process, allowing operators to verify combustion status and detect flashback conditions before they become hazardous.
Solution Approach 2:
The patent replaces complex mechanical flashback prevention mechanisms with a simpler thermal detection system. Instead of using mechanical devices to physically prevent flame propagation into the burner body, the system uses the pilot flame's thermal response and associated detection mechanisms to identify and respond to flashback conditions after they occur.
2Reliability
If a protective system is added to detect flashback conditions, then safety is improved, but device complexity increases
Solution Approach 1:
The pilot flame serves a dual function: it ignites the main burner and simultaneously acts as an indicator for combustion status. The system uses the pilot flame's own characteristics (presence, color, stability) to detect flashback conditions, eliminating the need for separate complex detection devices. The thermocouple leverages the pilot flame's thermal energy to generate the electrical signal needed for detection.
Solution Approach 2:
The pilot flame is designed to perform multiple functions simultaneously: ignition of the main burner, indication of proper combustion, and detection of flashback conditions. This multi-functionality reduces the need for additional components and simplifies the overall system architecture while maintaining comprehensive safety monitoring.
3Measurement precision
If the pilot fuel supply line is made meltable for detection purposes, then detection capability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The pilot fuel supply line is constructed from a material with a specific melting point parameter that is lower than the temperature of a flashback flame but higher than normal operating temperatures. This parameter change allows the line to serve as a thermal fuse, melting only under flashback conditions to interrupt fuel flow and stop the combustion process.
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
Effectively prevents extended burner flashback conditions by shutting down the water heater, reducing carbon monoxide emissions and ensuring safe operation by detecting temperature or pressure indicative of a flashback and terminating fuel flow.
Implementation Method 1
a thermocouple installed in a millivolt circuit thermoelectrically powered to hold the normally closed fuel supply valve in an open position
Implementation Method 2
a thermocouple installed in a millivolt circuit thermoelectrically powered
Implementation Method 3
a solenoid operable to overcome the spring bias and hold the valve in an open position
Implementation Method 4
a spring biased to hold the valve in a closed position
Data Source
AI summary
A fuel-fired water heater is provided with a premixing type main burner and an associated pilot burner for igniting it. A specially designed protective system is operative to detect a flame flashback burning condition in the main burner and responsively shut down the water heater. In one embodiment thereof, the protective system uses main burner body heat to melt a portion of a fuel supply line connected to the pilot burner during a flame flashback condition in the main burner. Such melting responsively causes an associated fuel supply valve to close and terminate water heater operation. In a second protective system embodiment a normally closed pressure switch is opened, thereby shutting down the water heater, when the switch detects a pressure indicative of a flame flashback condition in the main burner.