GB2151767A - Gas burner - Google Patents

Abstract

A gas burner comprises an outer burner tube (17) having a supply jet (15) at one end, an air inlet (20) downstream of the jet and, an insert member (18) which defines a flow passage (22, 23, 24) of decreasing cross section in the direction of gas flow. The downstream end of the member defines a central gas outlet, and outwardly extending flow passages (25) direct a portion of the gas to an outer annular secondary gas outlet (27). <IMAGE>

Description

SPECIFICATION Burner This invention relates to a gas burner for use as part of a blowtorch or similar appliance. The burner is particularly suitable for use with liquifiable petroleum gas (L.P.G.) such as propane, butane and mixtures thereof.

An object of the present invention is to provide a burner which has good flame retention characteristics and low tendency to self-extinguish over a range of gas 10. flows.

Accordingly the present invention provides a gas burner comprising a burner tube, a gas supply jet at one end of the tube, an air inlet in the tube downstream of the jet and, downstream of the air inlet and within the tube, a member which defines within itself a flow passage of decreasing crosssection whose downstream end constitutes a central gas outlet, and which has one or more outwardly extending flow passages which direct a portion of the gas flow to a secondary outlet which at least partially surrounds the central gas outlet.

Preferably the secondary outlet is an annular passage defined between the outer periphery of the member and the surrounding burner tube.

The member can be an insert pressed into the burner tube. The member can have a plurality of radially outwardly extending flow passages which direct gas to the annular passage. These passages can be six in number spaced at equal angles around the insert.

The total area of these passages can be related to the area of the central gas flow passage in the ratio from 2.3 to 2.8 :1, preferably 2.6 to 1.

A portion of the burner tube can extend downstream of the insert and this portion can be enlarged.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein the single figure is a longitudinal view, partly in cross-section of a preferred burner of the invention.

A preferred burner 10 of the invention is of brass and comprises a support 11 which is of increasing diameter from its input end 12 which connects with a gas supply conduit 13 to its output end 14 which centrally mounts a jet 15 and which has a surrounding annular flange 16. Flange 16 is surrounded by and has attached thereto, as by a threaded connection or a press fit, one end of a generally cylindrical burner tube 17, into which, near to its other end is pressed a member in the form of an insert 18. The free end portion 19 of the burner tube 17 beyond insert 18 is belled out to have an increased diameter. Between the jet 15 and insert 18 the tube 17 is formed with six equiangularly spaced slots 20 which constitute an air inlet to the tube 17.

The insert 18 is circular in cross-section and has a central through-passage which has a first conically-tapered portion 21, a second cylindrical portion 22, a third, also conically-tapered portion 23 and a final short cylindrical portion 24. The reduction in the cross sectional area of the through passage causes an increase in the pressure and velocity of the combustible gas mixture which enters the insert 18. At the junction of portions 22 and 23 six, equi-angularly spaced radially outwardly extending bores 25 are provided which lead to an annular space 26 defined between the insert 18 and the tube 17. This annular space 26 communicates with a narrow annular outlet 27 defined between the tube 17 and an outwardly extending rim 28 on the insert 18. Outlet 27 surrounds a central outlet constituted by the downstream end of portion 24.

The two outlets 27, 24 from the insert coincide with an abrupt widening of the effective flow passage through the burner and at the outlets there occurs an abrupt drop in gas flow velocity which forms a flame-retaining step or shoulder, ie,to the right of the outlet the velocity of the gas mixture is lower than the velocity of flame propagation through the gas and to the left of the outlet the velocity of gas flow is higher than the velocity of flame propagation. Along the two lines indicated at 29, the two velocities coincide.

Because of the flow construction provided by apparatus 25, space 26 and outlet passage 27, the flow through the outlet passage 27 is much less sensitive to variations in the velocity of gas arriving at the insert, due for example to sudden and rapid turning up of the supply, or due to wind or draughts. This greatly enhances flame retention.

The annular body of cool, unburnt gas issuing from passage 27 and whose downstream limit is indicated by one of lines 29, tends to adhere to the wall of the burner tube 17 to an extent somewhat greater than that indicated by the one line 19, and this reduces heat transfer to the tube 17 and thus back to the insert 18 and jet 15. An annular groove 30 in the insert 18 serves to reduce the weight of the insert 18.

The total area of the apertures 25 is related to the area of outlet 24 in a ratio of from 2.3 to 2.8 1, preferably 2.6 1. The distance from the outlet of jet 15 to outlet 24 should not vary by more than 5% from that shown.

The number of the apertures 25 can vary from two to a preferred six or more. More than six apertures, however, leads to smaller apertures which apply excessive resistance to flow and cause greater manufacturing expense.

The burner 10 of the invention is particularly suitable for burning propane or a propane-containing mixture, and can provide a flame hot enough and of sufficient heat capacity to enable the user to effect brazing operations. Flame retention and stability are good and combination of this burner with the regulating assembly of our co-pending application No. 83 filed herewith gives very good adjustability.

The outer outlet 27 can be intermittent if desired consisting of a ring of individual outlet parts formed by or with the insert 18. However, a continuous annular outlet is preferred.

Claims (2)

1. A gas burner comprising a burner tube, a gas supply jet at one end of the tube, an air inlet in the tube downstream of the jet, which air inlet is constituted by one or more apertures in the tube connecting the interior of the tube to atmosphere and enabling flow of gas from the jet in use, to cause an inward supply of air through the aperture(s), and, downstream of the air inlet and within the tube, a member which defines within itself a flow passage of decreasing cross-section whose downstream end constitutes a central gas outlet, and which has one or more outwardly extending flow passages which direct a portion of the gas flow to a secondary outlet which at least partially surrounds the central gas outlet.

1. A gas burner comprising a burner tube, a gas supply jet at one end of the tube, an air inlet in the tube downstream of the jet and, downstream of the air inlet and within the tube, a member which defines within itself a flow passage of decreasing cross-section whose downstream end constitutes a central gas outlet, and which has one or more outwardly extending flow passages which direct a portion of the gas flow to a secondary outlet which at least partially surrounds the central gas outlet.

2. A burner as claimed in claim 1 wherein the secondary outlet is an annular passage defined between the outer periphery of the member and the surrounding burner tube.

3. A burner as claimed in claim 1 or 2 wherein the member is an insert pressed into the burner tube.

4. A burner as claimed in claim 1, 2 or 3 wherein the member has a plurality of radially outwardly extending flow passages which direct gas to the annular passage.

5. A burner as claimed in claim 4 wherein these passages are six in number spaced at equal angles around the insert.

6. A burner as claimed in claim 5 wherein the total area of these passages is related to the area of the central gas flow passage in.the ratio from

2.3 to 2.8:1.

7. A burner as claimed in claim 6 wherein the ratio is 2.6 to 1.

8. A burner as claimed in any preceding claim wherein a portion of the burner tube extends downstream of the insert.

9. A burner as claimed in claim 8 wherein this portion is enlarged.

10. A gas burner substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed, and have the following effect: (a) Claim 1 above have been deleted or textually amended.

(b) New or textually amended claims have been filed as follows: