GB2095817A

GB2095817A - Premixing pilot burner

Info

Publication number: GB2095817A
Application number: GB8207563A
Authority: GB
Original assignee: Joh Vaillant GmbH and Co
Current assignee: Vaillant GmbH
Priority date: 1981-03-27
Filing date: 1982-03-16
Publication date: 1982-10-06
Also published as: FR2502748A1; NL8200876A; NL178274C; FR2502748B1; GB2095817B; NL178274B

Abstract

The present invention relates to a premixing pilot burner 13 for a gas- fired heat source, such as a gas-fired flow heater, gas-fired closed-circuit heater or boiler or gas stove, the pilot burner has a gas nozzle 23, which blows gas into a mixing tube 16 in order to suck primary air as 26. Prior gas nozzles 23 have been arranged to blow vertically upwardly. But in addition to air, dust enters the region of the gas nozzle through the inlet opening for the air to be sucked and said dust will deposit in that region. Such deposits will change the blowing characteristics of the gas nozzle and will thus change also the gas-air mixture so that such contamination will have a decisive influence on the stability of the burning operation of the pilot burner. That object of the present invention is substantially accomplished in that the outlet end of the nozzle is directed downwardly. <IMAGE>

Description

SPECIFICATION Premixing pilot burner This invention relates to a premixing pilot burner for a gas-filled heat source, comprising a mixing tube which is supplied from a gas nozzle.

Such a pilot burner is known, e.g., from German Published Patent Application No.

2,000,813.

In accordance therewith, a pilot gas nozzle disposed on a relatively low level blows vertically upwards into the lower end of a mixing tube, from the top end of which the pilot flame enters the region of the main burner.

In the reduction of such proposals to practice it has been found that the top end face of the pilot gas nozzle is relatively sensitive to dust deposits, which will change the gas jet so that the pilot gas burner does not burn and ignite the gas with safety.

It is an aim of the present invention so to design a premixing pilot gas burner that it is reliable in operation even under influences tending to soil the burner.

This aim is accomplished, in accordance with the invention, by arranging for the outlet of the nozzle to be directed downwardly.

This affords the important advantage that the end face of the nozzle, from which the gas jet emerges, can no longer constitute a surface for the deposition of dust. In that design according to the main claim it makes no difference whether the mixing tube of the premixing pilot burner constitutes a substantially straight tube extending downwardly to the level of the main burner so that the pilot gas nozzle is disposed above the burner, or whether the pilot gas tube is curved in U-shape and its outlet opening at the top extends into the region of the pilot gas burner.

Further features and particularly desirable further developments of the invention will become apparent from the sub-claims and the following description, in which illustrative embodiments of the invention will be explained more fully with reference to Figures 1 to 3.

Figure 1 is a diagrammatic transverse sectional view showing a gas-fired water heater having main and pilot burners, Figure 2 is also a diagrammatic transverse sectional view showing a gas-fired water heater having a different pilot burner, Figure 3 shows another modification of the pilot burner, and Figures 4 to 8 show embodiments of the deflecting shield.

In all figures, like reference characters designate the same details.

The gas-fired water heater shown in Figure 1 comprises an outer shell 1, which encloses an interior chamber 2, in which a heating shaft 3 is disposed, which consists of copper and at its top end, not shown, carries a finned heat exchanger core of copper. A brazed water pipe 3 exceeds around the heating shaft 3.

The heating shaft 3 is open at its lower end 5.

A main burner 7 is spaced a distance 6 under the heating shaft 3 and comprises several combustion chambers 8, which are gratelike and fed by a gas-distributing chamber 9, which is connected to a series of injectors 10. Main gas nozzles, not shown, blow gas into the lower ends 11 of the injectors 10.

A flame-directing shield 2 of a pilot 13 is disposed between two burner chambers 8 so that a flame exiting there can wipe over the top face 14 of the burner chambers 8. The flame deflecting shield 1 2 is associated with an outlet 1 5 of a Ushaped mixing tube 16, which has two 900 bends 17 and 18 and between the two bends 17 and 18 has a horizontal portion 19, which is adjoined on both sides by vertical portions 20 and 21. The vertical portion 21 is disposed between the first bend 18 and the inlet end 22, with which a gas nozzle 23 is associated. The gas nozzle 23 is secured to a mounting plate 24, which has openings for mounting a thermocouple, not shown, and an igniting electrode.

The heating shaft 3, the main burner 7, the mounting plate 24 and the mixing tube 16 are secured to a carrying frame by means which are not shown. The enamelled shell 1 is secured to the carrying frame.

The arrangement shown in Figure 1 operates as follows. When it is desired to ignite the pilot burner 13, a gas switch, not shown, is operated so that the pilot gas flows out of the gas nozzle 23. That exiting pilot gas jet enters the inlet end 22 of the mixing tube 16 and entrains primary air through an air gap 26 between the gas nozzle and the end 22. A gas-air mixture is formed inside the mixing tube 1 6 and exits at the outlet 15 and is ignited by the igniting electrode, which is held in the mounting opening 25. The igniting flame begins to burn inside the deflecting shield 12 and extends beyond the shield and is directed toward the burner openings of the burner chamber 8 so that a main gas-air mixture exiting there will be ignited.The hot flue gas from the main and pilot burners enters the interior chamber of the heating shaft 3 so that the latter is heated and transfers heat to the water pipes 4. The main part of the heat of the flue gases is transferred in the finned heat exchanger core of the heating shaft 3 te the water pipe 4.

In the embodiment shown in Figure 2 the mixing tube 1 6 has been modified in that the two bends 17 and 18 have been combined to form a single bend, which has a relatively large radius, and the horizontal portion 1 9 of the mixing tube has been omitted. This mixing tube is U-shaped and has a single bend having a relatively large radius so that the resistance to flow is minimized.

In the embodiment shown in Figure 3, the mixing tube 1 6 consists of an elongated, substantially vertical tube, which is provided at its lower end with the deflecting shield 1 2. The gas nozzle 23 is the uppermost part of the entire pilot burner. There is no U-shaped tube having one or two bends. The mounting plate 24 is correspondingly designed and at its lower end has the mounting apertures 25 for the pilot burner and the igniting electrode and at its upper end carries the gas nozzle 23. To prevent an excessive radiation of heat from the hot heating shaft into the space 2, a heat-insulating plate 29 is mounted between the heating shaft 3 and the mixing tube 16.

As is apparent in detail from Figures 4 to 8, the deflecting shield 12 may be integral with the outlet end of the mixing tube 1 6. For instance, as is shown in Figure 4 and 5, the mixing tube 16 may be cut off at an oblique line 33 at the end of the last bend 27 or 17 so that the remaining top portion 34 of the mixing tube has the same effect as the deflecting shield 12.

As is apparent from Figures 6 and 7, the outlet end 15 may have a squeezed portion 35 which is approximately elliptic in cross-section at 36. That portion may be squeezed to a larger extent in the middle so that there is a constriction 37, as is apparent from Figure 8.

Claims

1. A premixing pilot burner for a gas-fired heat source, comprising a mixing tube which is supplied from a gas nozzle, in which the outlet of the nozzle is directed downwardly.

2. A premixing pilot burner according to claim 1, in which the outlet of the nozzle is directed vertically downwardly.

3. A premixing pilot burner according to claim 1 or claim 2, in which the mixing tube is U-shaped and the outlet of the mixing tube is directed upwardly.

4. A premixing pilot burner according to claim 3, in which the mixing tube comprises two bends and an intervening horizontal portion.

5. A premixing pilot burner according to any one of claims 1 to 4, in which the inlet end of the mixing tube is provided with a shield.

6. A premixing pilot burner according to any one of claims 1 to 5, in which the gas nozzle is disposed laterally of the main burner.

7. A premixing pilot burner according to any one of claims 1 to 6, in which the length of the horizontal portion of the mixing tube exceeds the lengths of the two adjoining vertical portions of the mixing tube.

8. A premixing pilot burner according to any one of claims 1 to 7, in which the mixing tube has a single bend of 1800.

9. A premixing pilot burner according to any one of claims 1 to 8, in which a mounting plate for mounting the mixing tube is provided and constitutes also a shield for keeping dust from the gas nozzle.

1 0. A premixing pilot burner according to any one of claims 1 to 9, in which the mixing tube of the pilot burner is provided with a deflecting shield which is integral with the mixing tube.

11. A premixing pilot burner according to claim 10, in which the deflecting shield is defined by an oblique cut of the mixing tube.

12. A premixing pilot burner according to claim 10, in which the deflecting shield is formed by a squeezed portion of the outlet end of the mixing tube.

1 3. A premixing pilot burner according to any one of claims 1 to 12, in which the ratio of the length of the mixing tube to its free end inside diameter is substantially 50:1.

14. A premixing pilot burner substantially as described herein with reference to the accompanying drawings.