Dual Mixing Passage Combustion Apparatus for Low Fan Stability
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Solution Overview
Problem
Existing combustion apparatuses face limitations in achieving a large turndown ratio due to instability in primary air supply when the combustion fan's revolution falls below a certain threshold, leading to fluctuations in combustion amount and reduced turndown capability.
Innovation Solution
The apparatus incorporates a dual mixing passage system with separate air adjusting valves for each passage, allowing for high-performance and low-performance modes, where the primary air flows through both passages in high-performance mode and only the second passage in low-performance mode, enabling the adjustment of air inlet port openings to maintain stable primary air supply even at lower fan revolutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the combustion fan's number of revolution is reduced below the lower-limit value, then energy consumption is reduced, but the primary air supply becomes unstable and proportional characteristics are lost
Solution Approach 1:
The single mixing passage is divided into two separate mixing passages (first and second), each with its own air adjusting valve. This segmentation allows independent control of air flow paths, enabling stable operation at low fan speeds by switching to the second mixing passage when the first passage's proportional characteristics deteriorate.
2Adaptability or versatility
If an air adjusting valve is added to maintain primary air supply at low fan revolutions, then the turndown ratio is improved, but the device complexity increases
Solution Approach 1:
The system is segmented into two mixing passages with separate air adjusting valves, allowing the turndown ratio to be improved by switching between passages rather than relying on a single valve operating across its entire range.
Solution Approach 2:
The system dynamically switches between two mixing passages based on operating conditions. The controller selects which passage to use based on fan speed and combustion requirements, optimizing performance across the full operating range while maintaining simplicity in each individual passage design.
3Quantity of substance
If the opening degree of the air inlet port is throttled below a certain limit, then the primary air amount is reduced for lower combustion amounts, but the primary air supply becomes unstable due to minute valve displacements
Solution Approach 1:
By dividing the air supply into two separate passages, each can be optimized for different operating ranges. The second mixing passage is designed to handle low flow rates stably, allowing the system to achieve low primary air amounts without the instability that would occur in a single passage system operating at extreme throttling positions.
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 configuration allows for a significantly larger turndown ratio by maintaining stable primary air supply at lower fan revolutions, enabling smaller minimum combustion amounts and larger turndown ratios compared to single passage systems.
Implementation Method 1
The mixing passage has disposed therein a narrowed part in order to accelerate a flow speed of the primary air
Implementation Method 2
a combustion fan for supplying the burner with primary air
Data Source
AI summary
A combustion apparatus having: an upstream-side air supply chamber and a downstream-side mixing passage, both being respectively interposed between a fan and a burner; and a zero governor which is interposed in a gas supply passage and which adjusts a secondary gas pressure to a pressure equivalent to an internal pressure in the air supply chamber, thereby enabling to maximize a turndown ratio to the extent possible. The combustion apparatus has: first and second, totally two, mixing passages; a first gas outlet which is in communication with a narrowed part of the first mixing passage; a second gas outlet which is in communication with a narrowed part of the second mixing passage; a first air valve which varies an opening degree of an air inlet of the first mixing passage; a second air valve which varies an opening degree of an air inlet of the second mixing passage; and a gas valve.