Combustion – Flame holder having protective flame enclosing or flame... – Including means feeding air axially spaced points of the flame
Patent
1979-07-27
1982-07-06
Dority, Jr., Carroll B.
Combustion
Flame holder having protective flame enclosing or flame...
Including means feeding air axially spaced points of the flame
431265, 431278, 239406, F23Q 300
Patent
active
043380760
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an oil burner for low heating capacities, particularly for heating capacities ranging from approximately 12 to 30 Mcal/h, and comprising an oil conveying device, an air blower and a burner head which comprises a substantially cylindrical burner tube with a section tapering towards its outlet orifice and a burner nozzle arranged in the burner tube as well as a baffle plate which is provided with a central opening and which is arranged in the burner tube so that its outer edge is situated in the area of the tapering section and so that an annular clearance exists between the baffle plate and the inner surface of the burner tube.
Such burners for low heating capacities present considerable problems with respect to attaining an adequate combustion quality and, bound up therewith, a good utilisation of the fuel fed to the oil burner and a correspondingly high efficiency.
Until a solution was found by CH patent specification No. 575 573, it had to be accepted in oil heating engineering that the combustion efficiency of low heating capacity oil burners is substantially lower than that of burners having a relatively high heating capacity. The carbon dioxide proportion of the waste gases serves as a measure for the combustion efficiency. The conditions of oil burners for higher or even normal heating capacities, namely heating capacities above 50 Mcal/h, cannot be transferred to oil burners for low heating capacities. In fact, it has turned out that on prior art burner heads for oil burners of a heating capacity below 50 Mcal/h the diameter at the mouth end is much too large in relation to the amount of air required for combustion and that the opening in the baffle plate is also proportionally much larger than it is on oil burners having a high heating capacity. The low combustion efficiency is primarily caused by the fact that the pressure in the burner tube, and accordingly also the flow rate of the air in the mixing zone, is substantially less in smaller oil burners than in relatively large oil burners. A dimensioning of the air blower in a small oil burner to the effect that the air flows through the opening in the baffle plate at the same flow rate as in a large oil burner would cause an amount of air to be supplied exceeding by far the air required for combustion. This would result in the flame temperature dropping severely and the carbon dioxide proportion in the exhaust gas becoming very small and a high proportion of the generated heat being carried away with the excessive air in an undesired manner.
On the other hand, throttling the air supply to the value for an approximately stoichiometric oxygen/fuel mixture would give an air flow having only a low flow rate. However, since the mixing effect of the burner head depends to a very large extent on the flow rate of the air, this would result in the air and the fuel being mixed incompletely. This in turn would cause the fuel to be only partly burnt, which would result in a poor efficiency, on the one hand, and a considerable soot formation, on the other hand. Another disadvantage of a large baffle plate opening and a low flow rate is that the pressure difference between the interior of the burner tube and the combustion chamber becomes very small. The relatively large opening in the baffle plate and the low positive pressure in the burner tube results in the air flow, and thus the combustion efficiency, being very largely influenced by changes in the pressure in the combustion chamber, such as are usually caused, for example, by a change in the chimney draught or by blasts of wind.
In order to provide an effective remedy for this situation and to obtain a combustion efficiency which is as good as that of conventional oil burners for high and medium heating capacities, the central opening of the baffle plate of a generic oil burner has been given a diameter of 11 to 14 mm, according to CH patent specification No. 575 573, and the air blower has been dimensioned so that it produces a positive pressure giving a water column of 32 to 36
REFERENCES:
patent: 1953483 (1934-04-01), Higinbotham
patent: 3309027 (1967-03-01), Chadwick et al.
patent: 3694135 (1972-09-01), Dancy et al.
Straumann Fritz
Sutter Franz
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