GB2270750A

GB2270750A - Mixing chamber for gaseous fuel burner

Info

Publication number: GB2270750A
Application number: GB9317632A
Authority: GB
Inventors: Benjamin Frank Gostelow; Geoffrey John Edmund Brown
Original assignee: Stoves PLC
Current assignee: Stoves PLC
Priority date: 1992-09-11
Filing date: 1993-08-25
Publication date: 1994-03-23
Anticipated expiration: 2013-08-25
Also published as: GB9317632D0; GB2270750B

Abstract

A gaseous fuel mixture burner has a mixing chambers from which the fuel mixture is fed to the burner 1, the mixing chamber being otherwise closed to the atmosphere and having an inlet pipe 9 for the admission of gaseous fuel to the chamber end an inlet pipe 10 for the admission to the chamber of primary air under pressure from a fan 10b. The burner may be part of a gas-fired cooking appliance and may be a grill burner of the appliance. The fan is started when fuel control tap 9a is turned to a first position after which movement of the top to the "on" position allows gaseous fuel to enter the mixing chamber. A pressure detector 10c ensures that there is air pressure, if not it prevents operation of the fuel control tap. Details of a mixing chamber in a cooker are disclosed with air from a plenum chamber at the rear of the cooker also being used to cool the oven door. <IMAGE>

Description

Improvements in and relating to Gaseous Fuel Burners, to methods of operating such Burners and to Appliances incorporating such Burners.

This invention relates to gaseous fuel burners, that is to say burners that burn a gaseous mixture of gaseous fuel and air, to methods of operating such burners and to appliances, particularly domestic appliances which may be cooking appliances, incorporating those burners.

Conventionally, gaseous fuel mixture burners for domestic appliances are supplied with a gaseous mixture comprising a gaseous fuel, for example natural gas, and air commonly called primary air. The gaseous fuel is fed via an injector into the open mouth of the burner, which may be of venturi shape, where the primary air direct from the atmosphere is entrained by and mixed with the gaseous fuel for supply to the burner.

Such an arrangement is not entirely satisfactory because the volume of entrained primary air varies, and that affects combustion of the gaseous fuel and because there is sometimes inadequate mixing of the gaseous fuel and the primary air.

It is an object of the present invention to provide a gaseous fuel mixture burner and a method of operating the burner that overcome the problems just referred to.

According to the present invention a gaseous fuel mixture burner has a mixing chamber, an inlet for the admission of gaseous fuel to the chamber, and an inlet for the supply of primary air under pressure to the chamber, and an outlet joinable, in use, to the combustion zone of the burner.

Except for the outlet and the inlets, the mixing chamber is closed thereby preventing admission thereto of non-pressurised air directly from the atmosphere or from some other source.

A method of operating a gaseous fuel mixture burner according to the present invention comprises the steps of feeding gaseous fuel via a first inlet to the mixing chamber of the burner and of supplying primary air under pressure via a second inlet to the mixing chamber and of feeding the mixture to the combustion zone of the burner.

A gas-fired appliance according to the present invention comprises a gaseous fuel mixture burner having a mixing chamber, a first inlet for supplying gaseous fuel to the mixing chamber, a source of air under pressure and a conduit for conveying air from the source via a second inlet to the mixing chamber.

The appliance may be a cooking appliance having at least one gaseous fuel mixture burner, which may be a grill burner, or a combined grill and oven burner, a plenum chamber into which air is pumped by a fan which draws air into the plenum chamber from around the cooker, the or each burner having a mixing chamber to which gaseous fuel is supplied via an inlet and a conduit leading from the plenum chamber to the mixing chamber for supplying air under pressure via an inlet to the mixing chamber.

The appliance may have an oven cavity with an oven door of a composite construction comprising front and back door panel separated by a passageway open at both ends and to which air from the plenum chamber is supplied for the purpose of maintaining the temperature of the outer surface of the door at a temperature that does not present a hazard.

Preferably, the first inlet comprises a flow restrictor, which may be an injector, to enable the rate of flow of gaseous fuel to the mixing chamber to be accurately controlled.

It is also preferable that the second inlet also comprises a flow restrictor, for example an injector, to enable the rate of flow of pressurised air to the mixing chamber to be accurately controlled.

By way of example only embodiments of the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is a schematic representation of part of a first embodiment, Fig. 2 is a schematic representation of other parts of the first embodiment, and, Fig. 3 is a schematic representation of a second embodiment.

Fig. 1 shows, in schematic form only, a gaseous fuel mixture burner 1 which is a grill burner of the surface combustor type having a ceramic plaque 2 that is the combustion surface of the burner. The plaque 2 is located in the mouth of an elongate housing 3 into which extends a tube 4 from a mixing chamber 5 in an injector block 6. The tube 4 extends about halfway along the length of the housing 3 and terminates above a baffle 7 that also extends along the housing 3 for about one half of the length of the latter. As can be seen from Fig.l, the baffle 7 extends from that end of the housing 3 that is remote from the end through which the tube 4 enters the housing. The baffle 7 helps to improve the distribution of gaseous fuel mixture over the ceramic plaque 2.

Gaseous fuel is supplied to the mixing chamber via an injector indicated diagrammatically at 8 from a gaseous fuel supply pipe 9. Also supplied to the chamber 5 via a pipe 10 is air under pressure. Air is pumped into the chamber 5 from atmosphere by a fan indicated diagrammatically at lob in Fig. 1.

The pipe 10 contains a restrictor shown schematically at lOa and whose size taken in conjunction with the pressure of the air supply is such that the rate of supply of air to the mixing chamber is sufficient to provide the correct amount of primary air for gaseous fuel entering the mixing chamber via the injector 8. The pressure of the gaseous fuel in the supply pipe 9 taken in conjunction with the size of the injector 8 determines the rate of flow of gaseous fuel and thus the air/gas ratio can be accurately controlled.

The flow of gas to the chamber 5 is controlled by a tap or other suitable form of flow control valve shown diagrammatically at 9a in Fig. 1. The mixing chamber 5 is closed to the admission of air directly from the atmosphere, primary air being supplied under pressure only from pipe 10. The use of primary air under pressure also assist the mixing of such air with gaseous fuel entering chamber 5 from the fuel supply pipe 9.

The fan lOb supplying the pressurised air will be energised automatically when the control tap or valve 9a controlling the supply of gaseous fuel along pipe 9 is operated to an first control position after which movement of the tap to an "on" position will allow gaseous fuel to enter the mixing chamber 5. Similarly, the fan 6a will be de-energised when the fuel control tap 9a is operated to an "off" position.

The pressurised air supply will be fitted with means for detecting the presence in the air supply of pressurised air, such means acting to prevent the supply of gaseous fuel to the burner in the absence of an air supply. The means shown diagrammatically at lOc may comprise a pressure sensitive device that is coupled, as indicated by the dotted line lOd, to the fuel control tap 9a to prevent operation of the latter in the event that the device lOc fails to detect air pressure and also to close the tap in the event that the detected air pressure falls below an acceptable value.

It is normally the case with grill burners that they are either fully "on" or "off" so that no alteration in the rate of supply of gaseous fuel or the flow rate of air is required after the burner is in use.

The grill burner may be part of a domestic cooker of the construction described in UK Patent Application No. GB 2257503 A, the air supply to the mixing chamber being supplied from the plenum chamber behind the oven cavity.

Such an arrangement is shown in part and in schematic form only in Fig. 2. The grill burner is in two parts 11 and 12 as is the case of the grill burner described in UK Patent Application No. GB 2257503 A referred to above. Each part has its own supply of gaseous fuel mixture which is fed to the parts 11 and 12 via supply pipes 13 and 14 respectively. The pipes 13 and 14 terminate in an injector block 15 inside which are respective mixing chambers for the two pipes. The separate fuel supply lines to the mixing chambers are not shown in Fig. 2. The mixing chambers are similar to the mixing chamber 5 described above.The block 15 is positioned above a plenum chamber 16 that is located behind the oven cavity cooker in the manner described in UK Application No. GB 2257503 A which also describes the construction of the oven.

A fan 16a draws air into the plenum chamber 16 through an opening 17 in the rear wallof chamber 16 and such air may be drawn from around the oven cavity as described in UK Patent Application No. GB 2255632 A. The plenum chamber may also supply air for cooling the oven door as is also described in the Application just referred to.

When embodied in a cooker of the form described in UK Application No. GB 2257503 A with reference to Fig. 4 thereof in which the grill burner is the sole heat source for the cooker oven, the air supply to the burners 11 and 12 is present as long as the plenum chamber is under pressure. The fan 16a that draws air into the plenum chamber 16 is brought into use when the tap or control valve for the grill burner or that one of the burners that is to be brought into use is operated to a first control position which may be labelled "fan". Further movement of the tap to an "on" position allows gas to flow to the burner or burners. Movement of the tap to an "off" position at the end of a grilling or cooking operation may deenergise fan 16a immediately or de-energisation may occur after the expiry of a predetermined time delay.During that delay the fan 16a continues to run allowing air to be drawn into the plenum chamber from around the oven cavity thereby cooling the latter and the oven door. The control taps are not shown in Fig. 2.

Again, a pressure sensitive device is fitted to ensure that gas tap or control is operable to an "on" only when the supply of pressurised air has been detected and to terminate the supply of gaseous fuel, in the event that the detected air pressure falls below an acceptable level. Such a device may be located in the plenum chamber 16 but is not shown on Fig. 2.

The grill burners 11 and 12 shown in Fig. 2 are mounted externally of the oven cavity as is described in UK Patent Application No.GB 2257503A and are directly above and close to a heat conductive part 18 of the roof 19 of the oven cavity. Those grill burners form the sole heat source for the oven and are used both in grilling operations and in cooking operations in the oven as is described in the Application just referred to.

However, the invention may also be embodied in cooking apparatus in which the oven has its own independent heating means.

Fig.3 is a schematic representation of a domestic cooker in which the oven has a separate heater in the form of a gas burner that is controllable independently of the grill burner.

An oven 20 is accommodated in an enclosure 21 so arranged as to provide a plenum chamber 22 behind the rear wall 23 of the oven 20. The roof 24 of the oven 20 is also separated from the roof 25 of the enclosure 21 by a space 26 in which a grill heater 27 consisting of gas burners similar to burners 11 and 12 described above is located.

The burners are positioned directly above and spaced slightly from a heat conductive part (not shown) of the roof 24. The heat conductive part may be an integral part of the roof or it may an insert as is described above.

The plenum chamber 22 accommodates, at its lower end, an electrically-driven centrifugal fan 28 that draws air into the chamber 22 via an air inlet 29 in the rear wall of the enclosure 21, the inlet 29 being adjacent the eye of the fan 28. Air is drawn around the enclosure 21 as indicated by the arrow 30 and also, as indicated by the arrow 31, from a passageway 32 above the floor 33 of the enclosure 21. Air enters the passageway 32 via a series of inlets spaced across the lower part of the front of the cooker. One such aperture is shown at 34.

Positioned above passageway 32 is a second passageway 35, the two passageways being separated by a partition 36.

Passageway 35 communicates, at one end, with the plenum chamber 22 and, at its other end, with atmosphere via a series of apertures 37 spaced across the cooker front just above the inlets 34.

The cooker has an oven door 38 of a composite construction comprising inner and outer door panels 39, 40 separated by a passageway 41 open at both ends as shown in Fig. 3. In the closed position of the door 38 (shown in Fig. 3), the lower open end of the door passageway 41 registers with the apertures 37 thereby allowing air from the passageway 35 to flow through the passageway 41 in the door 38 so cooling the panels and keeping the temperature of the outer panel 40 at a comparatively safe level. The air flow through the passageway 41 is in an upward direction and the air exits from the passageway at the upper end thereof as indicated by the arrow.

Oven 20 has its own gas burner for heating the oven during a cooking operation and is shown diagrammatically at 42. The burner 42 is located in a recess 43 in the floor 44 of the oven. The recess 43 is closed except for an aperture 45 directly above the burner 42 through which the hot products of combustion from the burner pass into the oven as indicated by the arrow 46.

The grill burner 27 is supplied with a gaseous fuel mixture via a supply pipe 47 that terminates, at one end, in an injector block 48 similar in construction to block 6 described above. The block 48 contains a mixing chamber in which gaseous fuel from a gas supply conduit part only of which is shown at 49 is mixed with air under pressure from the plenum chamber 22 via a connecting pipe 50. The supply of gaseous fuel to burner 27 is controlled by a control valve (not shown) having a control knob (also not shown) that is mounted in a control panel 51 lying across the front of the cooker above the oven door 39 as shown in Fig.

3. Beneath the control panel 51 the cooker front is recessed as shown at 52, the rear wall of the recess having a series of spaced apertures one of which is shown at 53.

The control valve is linked to an air pressure sensing device positioned in the plenum chamber but not shown in Fig. 3 and which operates to prevent the supply of gaseous fuel to block 48 in the event that the sensing device fails to detect pressure in the plenum chamber 23.

The oven burner 42 is supplied with gaseous fuel mixture from an injector block 54 similar to block 6 described above and which has gaseous fuel supply conduit (not shown) and a pipe 55 for supplying air under pressure from the passageway 35 or direct from the plenum chamber 22.

As in the case of the grill burner 23, the supply of gaseous fuel to the injector block 54 is controlled by a main flow control valve (not shown) having a control knob also mounted in the control panel 51. The valve is also operatively linked to an air pressure sensing device which may be the device described above that is linked to the grill burner control valve or it may be a separate device.

The oven burner control valve is thermostaticallycontrolled, the control being linked to the air supply in a manner such that the supply of air under pressure is adjusted to suit the gas supply which is also controlled by the thermostat.

The space 26 between the roof 25 of the enclosure 21 and the roof 24 of the oven is also supplied with air from the plenum chamber 22 by a route not shown, such air exiting from the apertures 53 as indicated by the arrow 56.

Air entering the space 26 serves to cool the roof 25 of the enclosure 21 and the control panel 51 as well as helping to carry away the products of combustion of the grill burner 27.

To bring the grill burner 27 into use, a user simply operates the grill tap to a first position which may be labelled "fan" so energising fan 28 and allowing primary air under pressure to flow to the mixing chamber in block 48. Subsequent movement of the grill tap to an "on" position which opens the gas flow control valve fully allows gaseous fuel to flow into the mixing chamber in block 48 where it mixes with the pressurised flow of primary air, the resultant gaseous fuel mixture passing to the grill burner 27 via pipe 47. At the end of the grilling operation, the tap is turned to an "off" position which terminates the supply of gaseous fuel to the mixing chamber and may also de-energise fan 28. Alternatively, the fan may be allowed to run for a predetermined time as described above.

When it is desired to carry out a cooking operation, the oven burner 42 is brought into operation by turning the oven gas flow control valve to a first position which may be labelled- "fan" in which the fan 28 is energised and primary air under pressure flows to the mixing chamber in block 54. The control valve is then set to the desired oven temperature and this action allows gaseous fuel to flow to the mixing chamber in block 54 where it mixes with the primary air that reaches the chamber from pipe 55 before passing to the oven burner 42. Hot products of combustion from the burner 42 enter the oven through the aperture 45 and heat the interior of the oven and the foodstuffs therein. Combustion products and cooking fumes leave the oven through a gap between the top of the oven door 38 and the adjacent lower edge of the recess 52 as indicated by the arrow 57.Such emerging products are prevented from flowing over the surface of the control panel by the flow indicated by arrow 56 emerging from apertures 53. At the end of the cooking operation the control is operated to an "off" position which terminates the supply of gaseous fuel to the mixing chamber and may also de-energise fan 28 although, preferably, the latter is allowed to continue to run for the predetermined time referred to above.

It will be understood that the grill burner may be brought into use when the oven burner is in use and vice versa. In those cases, the fan will already be energised when the other burner is brought into use. Also, the fan will continue to be energised until both burners have been taken out of use and the predetermined period (if incorporated) has elapsed.

It will be understood that the invention may be embodied in burners other than grill and oven burners. For example, the invention may be incorporated in top burners for cookers and in this case, provision will be made to allow control over the flow rates of both gaseous fuel and air so that a user is able to adjust the heat output of the burner to a desired level. Control valves in the supply lines that supply gaseous fuel and air under pressure may be linked in a manner such that a change in the rate of supply of gaseous fuel results in an appropriate change in the rate of supply of air that maintains the gas/air ratio at the correct value.

Similarly, where the invention is embodied in a top burner subject to thermostatic control,-linked flow valves may be used to allow the maintenance of the gas/air ratio.

If the thermostatic control is of the "on/off" type the linked valves are not needed. The supply of pressurised air will be left on ready for the time that the supply of gas is resumed. It will be understood that air pressure detectors will be fitted to all such embodiments.

Claims

Claims.

1. A gaseous fuel mixture burner with a mixing chamber from which the fuel mixture is fed to the burner, the mixing chamber and having a first inlet for the admission of gaseous fuel to the chamber and a second inlet for the admission of primary air under pressure to the chamber, the chamber being otherwise closed to the admission of air at atmospheric pressure.

2. A method of operating a gaseous fuel mixture burner comprises the steps of feeding gaseous fuel to the mixing chamber of the burner and of supplying primary air under pressure to the mixing chamber via a second inlet thereof and of feeding the mixture to the burner.

3. A gas-fired appliance having at least one gaseous fuel mixture burner having a mixing chamber from which the fuel mixture passes to the burner, the chamber being otherwise closed to the admission of air at atmospheric pressure and having a first inlet for the admission of gaseous fuel to the chamber and a second inlet for the admission of primary air under pressure to the chamber.

4. A gas-fired cooking appliance having at least one gaseous fuel mixture burner having a mixing chamber from which the fuel mixture passes to the burner, the chamber being otherwise closed to the admission of air at atmospheric pressure and having a first inlet for the admission of gaseous fuel to the chamber and a second inlet for the admission of primary air under pressure to the chamber.

5. An appliance as claimed in claim 4 or 5 and further comprising a flow control means controlling the flow of gaseous fuel to the mixing chamber, a source of pressurised air, a connection from the source to the second inlet and means responsive to the air pressure supplied to the second inlet and operable to prevent the flow of gaseous fuel to the chamber in the event that the pressure of the supplied air falls below a predetermined level.

6. An appliance as claimed in claim 5 in which the responsive means is operatively connected to the flow control means in a manner such that the flow control means terminates the flow of gaseous fuel to the mixing chamber in the event that the air pressure falls below a predetermined level.

7. An appliance as claimed in claim 4, 5 or 6 in which the source comprises a plenum chamber with an air inlet aperture for the admission to the chamber of air, a fan for drawing air through the inlet aperture into the chamber and in which the second inlet is in communication with the interior of the chamber.

8. An appliance as claimed in claim 7 in which the responsive means is located in the plenum chamber.

9. An appliance as claimed in claim 8 having a cooking oven and in which the plenum chamber is located to the rear of the oven.

10. An appliance as claimed in claim 9 in which the fan draws air into through the inlet aperture from around the exterior of the oven.

11. An appliance as claimed in claim 9 or 10 in which the oven has an oven door of a composite construction comprising inner and outer panels separated by an openended passageway in communication with the plenum chamber when the door is closed, air from the chamber then circulating through the passageway.

12. A gaseous fuel mixture burner as claimed in claim 1 or a gas-fired appliance as claimed in any one of claims 3 to 11 in which flow restrictors are provided for determining the rates of flow of gaseous fuel and of primary air into the mixing chamber.

13. An appliance as claimed in any one of claims 4 to 12 in which the burner is a grill burner.

14. A gaseous fuel mixture burner substantially as herein described with reference to and as illustrated by Fig. 1 of the accompanying drawings.

15. A gas-fired cooking appliance substantially as herein described with reference to and as illustrated by Fig. 2 or Fig. 3 of the accompanying drawing