GB1588967A

GB1588967A - Hot gas generating burner

Info

Publication number: GB1588967A
Application number: GB4556376A
Authority: GB
Original assignee: THORMACK ENG Ltd
Current assignee: THORMACK ENG Ltd
Priority date: 1977-11-02
Filing date: 1977-11-02
Publication date: 1981-05-07

Description

(54) HOT GAS GENERATING BURNER (71) We, THORMACK ENGINEERING LIMITED, a British Company of Bellbrook Estate, Uckfield, Sussex, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed,-to be particularly described in and by the following statement: The present invention relates to a burner and more particularly to a burner having a combustion chamber in which, in use, a fuel/air mixture is burned in a flashback condition, i.e. in which combustion is complete in the chamber, the flame being always in the chamber, and also having an ignition device at the inlet of the chamber and an outlet nozzle, via which the hot gases produced by the combustion of the mixture issues and can be directed as a jet at a surface or article which is to be treated.

Burners of the above type are used in a variety of applications, usually where the surface to be treated is required to be both intensely heated and subJected to a high velocity stream of fluid. Thus one important area of application has been in the treatment of road surfaces where, for example, such burners have been used to remove unwanted road markings and to remove areas of tarmac and similar material during road repair.

An important practical difficulty which has been encountered with these burners is that of starting the burner up which often takes up to two minutes or even longer. In view of the very high temperatures encountered within the combustion chamber, typically 3,200 F, in order to prevent rapid failure, the ignition device, which is usually a spark plug, must be placed in as cool a location as possible within the chamber and is thus usually located in a recess of the wall of the combustion chamber adjacent the inlet end thereof. This means, however, that during start-up the fuel/air mixture which enters the chamber with a high velocity first tends to travel straight towards the outlet of the chamber and it is not until the mixture is deflected by the wall of the chamber around the outlet that mixture reaches the ignition device.When this mixture is ignited it tends to explode causing a sudden pressure pulse within the chamber and the detonated gases leave the combustion chamber with great rapidity and the chamber then starts to refill with fresh, unignited mixture. On being deflected back to the ignition device, this fresh mixture detonates and the process repeats until the outlet end of the combustion chamber heats up to a sufficient temperature to cause ignition of the mixture at that end. The start-up procedure thus causes the combustion chamber to produce a series of very loud explosions which can be of almost unbearable intensity for anyone in the near vicinity of the burner.The problem is often aggravated by the operator adjusting the mixture to attempt to reduce the noise since the mixture required to produce a stable flame within the combustion chamber is fairly critical and the operator's adjustments can tend to make the burner take longer to ignite.

The present invention seeks to reduce or eliminate the above described problem.

According to the present invention there is provided a burner comprising an enclosed combustion chamber in which, in use, a fuel/air mixture is burnt in a flashback condition, i.e. in which combustion is complete in the combustion chamber, an inlet for such fuel/air mixture, an outlet nozzle via which the hot gases produced, in use, by combustion of the mixture within the combustion chamber can-be directed onto a surface or article to be treated, an ignition device for igniting said mixture at the inlet end of the combustion chamber and a deflector within the chamber at the inlet end thereof for deflecting at least a proportion of the mixture entering the chamber via the inlet towards the ignition device.

The provision of the deflector within the enclosed combustion chamber enables the diverted proportion of the mixture to be ignited before it travels down the combustion chamber thereby eliminating, or at least substantially reducing, the occurrence of the periodic detonations which can occur during starting up with the prior burner described above. In the embodiment later described, the tube is closed at its inlet end by an annular plate having a central bore through which the mixture enters the combustion chamber. A spark plug for igniting the mixture is located in a recess in the end plate so that the material of the plate around the spark plug electrode can conduct heat away from the electrode to prevent overheating.

The deflector is provided by an annular member which extends part of the way towards the outlet end of the chamber and is welded onto that face of the end plate which faces into the combustion chamber. This annular member is dimensioned so that its periphery is spaced from the inner surface of the tube to form an annular space around itself and has a central bore part of the way therethrough which forms a continuation of the bore in the end plate.

In order to divert the mixture entering the chamber towards the spark plug, the wall of the annular member is pierced by a radial bore so as to divert part of the mixture radially of the tube whereby the diverted mixture tends to reach the spark plug before travelling down the tube. Suitably the radial bore is displaced angularly with respect to the axis of the tube from the spark plug as this enables the velocity of the diverted mixture to be reduced before it reaches the spark plug to increase the likelihood of successful ignition. The annular member may be provided with a cut-away surface portion which faces towards the spark plug so as to provide an enlargement to the annular space surrounding the annular member thereby to promote advantageous ignition conditions.

The cut-away portion also provides a reduced wall thickness for the annular member adjacent the spark plug and this helps the region around the spark plug electrodes to be cooled somewhat by the mixture entering the chamber via the central bore in the annular member.

In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which Figure 1 is a cross-section through one embodiment of burner according to the invention; and Figure 2 is a schematic view showing a burner apparatus using the burner of Figure 1.

As shown in Figure 1 the gas burner 1 comprises an elongate tube 3, the interior of which forms the combustion chamber for a mixture of air and propane which enters the combustion chamber at the upper, inlet end.

The tube 3 is made from a material, for example the nickel, chromium, iron and titanium alloy sold under the name INCONEL 600, suitable to withstand the temperature of the fuel air mixture which burns therein, this temperature normally being approximately 3,200 F and at its inlet end the tube 3 is closed by an annular plate 5 which has a central opening 7 therein through which the fuel/air mixture enters the combustion chamber. The plate 5 also has a stepped bore 9 in which a spark plug 10 is located which serves to ignite the mixture within the chamber. The bore 9 comprises a larger diameter portion to accommodate part of the body of the spark plug, while the smaller diameter portion is provided with screw-threads by means of which the spark plug is threadedly engaged with the end plate 5.It will be seen that the axis of the spark plug is inclined with respect to that of the tube so that the two axes intersect below the inlet end of the tube.

The outlet end of tube 3 is provided with a nozzle assembly 11 which is provided with a central bore through which the hot gases produced by the combustion of the fuel air mixture exit the chamber and an annular chamber surrounding this bore and through which fuel/air mixture on its way to the combustion chamber is passed both for the purposes of preheating this mixture and cooling the nozzle assembly. Thus nozzle assembly 11 comprises inner and outer annular members 13 and 15 respectively, the outer annular member 15 being provided with two diametrically opposed inwardly tapering radial bores 17 and 19 which communicate with a central opening 21 through member 15. The inner member 13 is provided with radially outwardly extending flanges at the opposite ends thereof and fits snugly in the opening 21 in member 15.The central bore 23 through member 13 serves as an outlet orifice for the hot gases from the interior of the tube 3.

Members 13 and 15 are secured together by means of a tungsten-inert gas (TIG) weld, the tube 3, end plate 5 and nozzle assembly 17 also being TIG-welded together.

The peripheral surface of the central portion 13a of member 13 is spaced from the inner peripheral surface of the outer member 15 so as to provide the above mentioned annular chamber to which the fuel air mixture passes via bores 17 and 19 before being delivered by means of tube 125 (Figure 2) to the inlet bore 7 of the combustion chamber.

The plate 5 is provided with a deflector which serves to divert the fuel/air mixture entering the chamber so as to reach the spark gap of the spark plug without having first to travel down towards the outlet end of the tube. This deflector is in the form of an annular metal member 25 welded to the downwardly facing surface of plate 5 and having a central bore which is coaxial with tube 3 and which is closed at its downstream end. Communicating with this bore is at least one radial bore 27 through which a proportion of the fuel air mixture enters the chamber. Mixture entering the combustion chamber through bore 27 impinges on the inner surface of tube 3 and thereby has a swirling motion imparted to it.Thus part of the mixture entering the chamber through bore 27 is caused to flow over the spark gap so that it can be ignited before passing towards the outlet end of the chamber so avoiding the difficulty encountered with prior apparatus where the mixture has first to be deflected from the outlet end of the chamber before reaching the spark plug during start-up.

It will be seen that bore 27 is angularly displaced, with respect to the axis of tube 3, from the spark plug and that the member 25 has a cut-away portion 29 provided with a flat surface facing radially of tube 3 and a concave surface which faces towards the spark plug. The cut-away portion of member 25 means that the annular space between member 25 and the inner surface of tube 3 is enlarged in the region of the spark plug and this, together with the fact that the bore 27 is angularly displaced from the spark plug serves to reduce the velocity of the mixture entering the chamber via bore 27 before it reaches the region of the spark plug, thereby to facilitate ignition of the mixture.The reduced wall thickness of member 25 provided by the cut-away portion 29 also by virtue of the relatively cool mixture flowing through the central bore in member 25 provides a "cool spot" in the region of the spark plug which can be expected to lengthen the useful working life thereof.

Figure 2 shows an apparatus incorporating the burner of Figure 1. Pressurized fuel, preferably propane gas at 25 psig from a tank 101 and air at 50 psig from a compressor 103 are delivered via respective pressure regulators 105 and 107 and metering valves 109 and 111 to a mixer 113 in which the fuel/air mixture is formed. Interconnected to the mixer by means of a flexible hose 115 is a burner assembly 121 which comprises the burner of Figure 1 and an inlet tube arrangement. A rigid tube 123 is connected to the flexible hose and is provided with a grip or other suitable hand, (not shown) to enable the assembly to be held by an operator so that he can direct the jet of hot gases issuing from the burner nozzle at a surface to be treated, such as a road surface having unwanted road markings thereon.

Tube 123 is connected to and communicates with the annular chamber in the outlet nozzle assembly whereby the mixture cools the nozzle and is itself preheated before entering the combustion chamber via tube 125. A bracket 127 serves to rigidify the assembly.

In use, the fuel/air mixture is completely burned in a flashback condition within the combustion chamber and the hot gases thus produced issue from the nozzle at a high temperature and high velocity. Typically the temperature of the hot gases will be approximately 3,200 F within the chamber and 3,000 F on exit therefrom and the gases will issue from the nozzle at a velocity of approximately 3,000 ft. per second. Since combustion is completed within the chamber, the flame is contained in the chamber and thus protected from adverse environmental conditions. During start-up the mixture within the burner is ignited by temporarily connecting the spark-plug to a suitable portable source of high voltage spark such as a battery operated vibrator.Once the combustion chamber has heated up and stable combustion has been achieved, the hot gases issuing from the nozzle can be directed at the surface which is to be treated.

It may be noted that, as compared with prior 'flashback' burners the volume of the annular chamber in the outlet nozzle assembly is enlarged, so removing the restriction to the flow of the incoming fuel air mixture which this chamber provides on the prior burner.

WHAT WE CLAIM IS:- 1. A burner comprising an enclosed combustion chamber in which, in use, a fuel/air mixture is burnt in a flashback condition, i.e. in which combustion is complete in the combustion chamber, an inlet for such fuel/air mixture, an outlet nozzle via which the hot gases produced, in use, by combustion of the mixture within the combustion chamber can be directed onto a surface or article to be treated, an ignition device for igniting said mixture at the inlet end of the combustion chamber and a deflector within the chamber at the inlet end thereof for deflecting at least a proportion of the mixture entering the chamber via the inlet towards the ignition device.

2. A burner according to claim 1, wherein the tube is closed at its inlet end by an annular plate having a central bore through which the mixture enters the combustion chamber.

3. A burner according to claim 2, wherein the ignition device is a spark plug, which is located in a recess in the end plate so that the material of the plate around the spark plug electrode can conduct heat away from the electrode to prevent overheating.

4. A burner according to claim 2 or 3, wherein the deflector is provided by an annular member which extends part of the way towards the outlet end of the chamber and is welded onto that face of the end plate which faces into the combustion chamber.

5. A burner according to claim 4, wherein said annular member is dimen

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. end. Communicating with this bore is at least one radial bore 27 through which a proportion of the fuel air mixture enters the chamber. Mixture entering the combustion chamber through bore 27 impinges on the inner surface of tube 3 and thereby has a swirling motion imparted to it. Thus part of the mixture entering the chamber through bore 27 is caused to flow over the spark gap so that it can be ignited before passing towards the outlet end of the chamber so avoiding the difficulty encountered with prior apparatus where the mixture has first to be deflected from the outlet end of the chamber before reaching the spark plug during start-up. It will be seen that bore 27 is angularly displaced, with respect to the axis of tube 3, from the spark plug and that the member 25 has a cut-away portion 29 provided with a flat surface facing radially of tube 3 and a concave surface which faces towards the spark plug. The cut-away portion of member 25 means that the annular space between member 25 and the inner surface of tube 3 is enlarged in the region of the spark plug and this, together with the fact that the bore 27 is angularly displaced from the spark plug serves to reduce the velocity of the mixture entering the chamber via bore 27 before it reaches the region of the spark plug, thereby to facilitate ignition of the mixture.The reduced wall thickness of member 25 provided by the cut-away portion 29 also by virtue of the relatively cool mixture flowing through the central bore in member 25 provides a "cool spot" in the region of the spark plug which can be expected to lengthen the useful working life thereof. Figure 2 shows an apparatus incorporating the burner of Figure 1. Pressurized fuel, preferably propane gas at 25 psig from a tank 101 and air at 50 psig from a compressor 103 are delivered via respective pressure regulators 105 and 107 and metering valves 109 and 111 to a mixer 113 in which the fuel/air mixture is formed. Interconnected to the mixer by means of a flexible hose 115 is a burner assembly 121 which comprises the burner of Figure 1 and an inlet tube arrangement. A rigid tube 123 is connected to the flexible hose and is provided with a grip or other suitable hand, (not shown) to enable the assembly to be held by an operator so that he can direct the jet of hot gases issuing from the burner nozzle at a surface to be treated, such as a road surface having unwanted road markings thereon. Tube 123 is connected to and communicates with the annular chamber in the outlet nozzle assembly whereby the mixture cools the nozzle and is itself preheated before entering the combustion chamber via tube 125. A bracket 127 serves to rigidify the assembly. In use, the fuel/air mixture is completely burned in a flashback condition within the combustion chamber and the hot gases thus produced issue from the nozzle at a high temperature and high velocity. Typically the temperature of the hot gases will be approximately 3,200 F within the chamber and 3,000 F on exit therefrom and the gases will issue from the nozzle at a velocity of approximately 3,000 ft. per second. Since combustion is completed within the chamber, the flame is contained in the chamber and thus protected from adverse environmental conditions. During start-up the mixture within the burner is ignited by temporarily connecting the spark-plug to a suitable portable source of high voltage spark such as a battery operated vibrator.Once the combustion chamber has heated up and stable combustion has been achieved, the hot gases issuing from the nozzle can be directed at the surface which is to be treated. It may be noted that, as compared with prior 'flashback' burners the volume of the annular chamber in the outlet nozzle assembly is enlarged, so removing the restriction to the flow of the incoming fuel air mixture which this chamber provides on the prior burner. WHAT WE CLAIM IS:-

1. A burner comprising an enclosed combustion chamber in which, in use, a fuel/air mixture is burnt in a flashback condition, i.e. in which combustion is complete in the combustion chamber, an inlet for such fuel/air mixture, an outlet nozzle via which the hot gases produced, in use, by combustion of the mixture within the combustion chamber can be directed onto a surface or article to be treated, an ignition device for igniting said mixture at the inlet end of the combustion chamber and a deflector within the chamber at the inlet end thereof for deflecting at least a proportion of the mixture entering the chamber via the inlet towards the ignition device.

5. A burner according to claim 4, wherein said annular member is dimen

sioned so that its periphery is spaced from the inner surface of the tube to form an annular space around itself and has a central bore part of the way therethrough which forms a continuation of the bore in the end plate.

6. A burner according to claim 5, wherein the wall of the annular member is pierced by a radial bore so as to divert part of the mixture radially of the tube towards the spark plug.

7. A burner according to claim 6, wherein the radial bore is displaced angularly with respect to the axis of the tube from the spark plug.

8. A burner according to claim 5, 6 or 7, wherein the annular member is provided with a cut-away surface portion which faces towards the spark plug so as to provide an enlargement to the annular space surrounding the annular member.

9. A burner substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.

10. A burner apparatus comprising a burner according to any preceding claim and sources of fuel and compressed air connected to supply fuel and air to said combustion chamber.

11. Burner apparatus constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.