Combustion – Timer – programmer – retarder or condition responsive control – By combustion or combustion zone sensor
Patent
1997-12-03
1999-11-16
Price, Carl D.
Combustion
Timer, programmer, retarder or condition responsive control
By combustion or combustion zone sensor
431 12, 431 18, F23N 1500, F23N 100, F23N 500
Patent
active
059846640
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to apparatus for providing an air/fuel mixture particularly an air/fuel gas mixture to a fully premixed burner.
In such a burner fuel gas is mixed, before combustion in the burner, with air in a plenum chamber.
The fuel gas is usually supplied from a main while the air is supplied by a fan.
To prevent incomplete combustion of the fuel gas and the production of poisonous carbon monoxide gas, the volume flow rate of air is usually intended to be maintained in excess of the rate theoretically necessary for full combustion of the gas. Typically this excess amounts to 30%, and the burner is then said to be operating with 130% of the stoichiometric air requirement or, for brevity, "at 130% aeration".
SUMMARY OF THE INVENTION
According to the present invention, apparatus provides an air/fuel mixture to a fully premixed burner, the apparatus comprising means for providing fuel to the burner, means for supplying air at a variable flow rate to the fuel to form the mixture, means for sensing aeration of fuel combustion products and control means for controlling the air flow rate in dependence upon the aeration sensed such that the air flow rate is sufficient to maintain the aeration at or close to a predetermined value, the controller, in use, maintaining the air flow rate at one of a number of differing predetermined values which are in the form of a geometric series characterised by a constant value of the ratio between successive values.
Suitably the geometric series contains a predetermined number N.sub.max of terms, each term being in accordance with the following relationship: steps, constitutes the lowest of the permitted rates of flow, value of R being chosen according to the resolution desired between successive steps in flow rate, and lowermost value of unity and an uppermost value of N.sub.max, the latter being determined jointly by the chosen value of the constant R and the ratio of magnitude between the highest and lowest air flow rates to be provided.
Conveniently the constant R is allocated a value of 1.025.
The advantage of making a change on the basis of a geometric series of flowrate values is that in making an adjustment to a physio-chemical process such as combustion, one can institute such an alteration as a percentage change in the existing value of the flowrate.
Preferably the means for supplying air at a variable rate comprises a variable speed fan, but may alternatively comprise a variable throttle valve.
Suitably the means for sensing aeration comprises a sensor for sensing the oxygen content of the fuel combustion products and for providing a signal representative of the oxygen content.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 which is a schematic view of a domestic combustion system in a gas-fired domestic heating appliance, together with control apparatus therefor.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, there is illustrated a domestic combustion system which comprises a gas boiler 1 located within a room-sealed casing 2 mounted on the inner surface of an outside wall 3 of a dwelling. The boiler 1 includes a fully-premixed gas burner 4 mounted on and sealed to an enclosure 5, the gas burner being designed to fire downwardly into an uppermost part of the enclosure 5 which forms a combustion chamber.
The enclosure 5 terminates in a lowermost flue 6 which has a vertical part 7 immediately beneath the enclosure and a horizontal part 8 connected to the vertical part 7 and extending with a clearance 9 through a hole in the wall 3. The clearance 9 is formed by the horizontal part of a flanged outlet 10. The horizontal part 8 of the flue has a circumferential flange 11 spaced from the outer surface 12 of the wall 3. The flange 11 forms with a flanged guard 13 in the wall surrounding the clearance 9 and the outer surface 14 of the horizontal flue part 8 an air intake of the so-called "balanc
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patent: 4330260 (1982-05-01), Jorgensen et al.
patent: 4396369 (1983-08-01), Kaessemann
patent: 4545009 (1985-10-01), Muraki et al.
patent: 4586893 (1986-05-01), Somerville et al.
patent: 4994959 (1991-02-01), Ovenden et al.
EP A 0 339 135, Dec. 1988.
Abstract, Japan vol. 017, No. 520 (M-1482) and JP A 05 138332, Sep. 1993.
BG plc
Holt William H.
Price Carl D.
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