US1738881A

US1738881A - Liquid fuel

Info

Publication number: US1738881A
Authority: US
Publication date: 1929-12-10
Anticipated expiration: 1946-12-10

Description

Dec. 10, 1929. B, EN E 1,738,881

METHOD AND MEANS FOR BURNING LIQUID FUEL IN FURNACES FOR HEATING BUILDINGS Filed Aug 6, 1925 4 Sheets-Sheet 1 Zia/@7710, Zia/6S8: A Q lB v7'11 vale fiqai 1929- A. B. FRENIER 1,738,881

METHOD AND MEANS FOR vBURNING LIQUID FUEL IN FURNACES FOR HEATING BUILDINGS I Filed Aug. 6, 1925 4 Sheets-Sheet 2 'I/Im (III fZ'izumafo/ Dec- 10, 192 A. B. FRENIER METHOD AND MEANS FOR BURNING LIQUID FUEL IN FURNACES FOR HEATING BUILDINGS Filed Aug.- 6, 4 Sheets-Sheet 3 A. B. FRENIER Dec. 10, 1929.

METHOD AND MEANS FOR BURNING LIQUID FUEL IN FURNACES FOR HEATING BUILDINGS 4 Sheets-Sheet 4 Filed Aug. 6, 1925 of the preferred modern Patented Dec. 10, 1929 ALBERT IB. FBENIER, OF CHICAGQ, ELLINOIS, ASSIG'EIQB, A PETROLEUM HEAT AND EOVJEP COMPANY, OF NEW YUR-Zfi, N.

OF DELAWARE l'fEF;

METHOD AND MEANS FOR BURNING LIQUID I FURNACES EOE, HEATING BUILDINGS Application filed August 6, 1925. flerial The invention relates to an improved method of burning liquid fuel in connection with furnaces generally, and more especially in connection with steam or hot water boilers or hot air furnaces used for heating homes, or other buildings and to an apparatus for practicing said process.

In the burning of liquid fuel, especially non-volatile or heavy hydrocarbons, the fuel is either atomized wholly or in part or vaporized, and is then mixed with air and with the air is forcibly discharged into open combustion chamber, wherein it is nited and burned. The combustion chamber construction is so formed with reference to the incoming mi ture of air and of atomized or partially atomized or vaporized liquid fuel, that the flame is caused to swirl about in the combustion chambe" in a substantially horizontal plane and to roll or wind upon itself within the combustion chamber so that the flame is practically confined therein until combustion is practically complete. Such method and combustion chamber are described in Lettors-Patent No. 1,2 4,182 to Doble, November 5, 1918, and in a patent granted to the present inventor, No. 1,379,008, May 2%, 1921.

It has been found in the operation of burners such as those described in the two patents referred to, that a very perceptible roaring noise is produced in the burning of the atomized liquid fuel, which in the case of lightly built or small houses has been more or less objectionable. Again, on account of the in tense heat produced in the metal combustion chamber, due to the fact that substantially complete combustion of all the fuel takes place in the combustion chamber, it has been desirable to make "he combustion chamber of special alloys which are expensive.

It has lo been known that when an inert Ab or neutral gas or a gas non-combustibl with to as.

oxygen is introduced with the air supplied.

to a furnace to support combustion of the fuel therein, the inert gas acts as a diluent of the air and delays combustion of the fuel. The flame, by reason of the dilution and delayed combustion, is expanded and lengthened beyond the combustion chamber of the furnace so as to render the heat of combustion effective in the region beyond the combustion chamber and the heat of the flame is not so intense in the vicinity of the combustion chamber itself as in the case where combustion is completed in the combustion chamber. Manifestly, however, the material surroundin and defining the passageways or flues in the regions beyond the combustion chamber must be raised to a temperature which will promote combustion in said regions.

la the temperature producing apparatus and controlling); means, therefor, described in my aforesaid Patent No. 1,379,008, the supply 0 air and. fuel to the combustion chamber is intermittent and its initial ignition at the begii ling of every interval during which the fuel i burned is thermostatically controlled. Anything that would in the begin ning delay combustion or reduce the heat of combustion in the combustion chamber would be highly objectionable in an apparatus of the kind. Again, any expansion of the flame and delay of combustion until the flame reaches the lines of the boiler is impracticable, since contact with the relatively cold lines would stop complete combustion and result in the formation of CO gas.

The object of the present invention is to provide a method and an apparatus whereby an inert diluent of the air may be introduced into the combustion chamber with the air and fuel during the process of combustion after initial i nition with air undiluted has taken place and after the fuel been brought to complete combustion, to thereafter somewhat retard combustion in the combustion cham her; and to do this without expanding or extending the flame to any considerable extent beyond the confines of the combustion chamber into the neighborhood of the furnace flues wherein complete combustion and the production of unconverted CO gas would result. When an inert is used in this way in burner of the kind hereinabove re have found that the noise of combusl materially reduced. In tead of tl white flame produced with air a burns with a lazy, purple or blue, s

tially noiseless flame which overflows the top of the burner. In addition the intense heating of the walls of the combustion chamber produced by burning the fuel with air alone, is appreciably reduced, so that cheaper metal may be used for the combustion chamber. And finally, as shown by tests, a maximum per cent of CO gas is produced by the flame burning in this manner.

A convenient diluent for the air and fuel and the one generally used is provided by the products of combustion which may be taken from the furnace beyond the burner, preferably from the stack. In carrying out my in vention, I lead by a conduit a small part of the products of combustion from the stack and introduce them in proportions capable of adjustment with the fresh air which is normally drawn in and discharged a fan into the combustion chamber, together with the atomized liquid fuel to be burnt. The supply of the products of combustion is automatically controlled, so that in the beginning and prior to the initial ignition of the fuel, air

I alone is introduced into the combustion cham her with the fuel and complete comb ustion in the combustion chamber as heretofore is allowed to continue for a predetermined time interval and until the fuel is burr "'ng at its maximum with complete or su s antially complete combustion in the combustion chamher.

The inert products of combustion are then introduced with the air to slow down or retard combustion in the confines of the combustion chamber and the supply of the inert diluent is continued during the remainder of the interval in which fuel is supplied to the burner and until by operation of the thermostat or otherwise in a well-known manner, the supply of fuel and of the mixture of air and diluent is shut off and combustion ceases. The supply of inert gas is then cut off and in the intermittent period when no combustion takes place, remains shut off until after liquid fuel and fresh air undiluted are again supplied to the burner, initially ignited, and brought to full combustion; whereupon the inert gas is again introduced with the air and the process takes place as first described.

Several different devices may be employed to control the supply of the products of combustion with the air and herein 1 have shown a thermostatic device, a pneumatic device and an electric motor device, any one of which may be efiiciently used for the purpose. Other devices may be used.

In illustrating the invention, l have shown it applied to an apparatus including a combustion chamber, a fan or him or for dis charging air together with liquid fuel atomized by the air into the combustion chamber and an automatic control for starting the fan and igniting the combustible mixture in the combustion chamber, substantially as illuswith air into said combustion chamber, such as described in my aforesaid patent, the same bemg provided with an apparatus for 1ntroducing the products of combustion with the air in accordance with my invention.

*igure 2 is a detail view on an enlarged scale, partly in side elevation and partly in section, illustrating a thermostatically operated device for controlling the introduction of the products of combustion with the air supply to the combustion chamber.

Figure 3 is a view representing a section through Figure 2, in a plane indicated by a line 3-3 of Figure 2.

Figure l is a top plan View of the air supply pipe, fan and combustion chamber with a pneumatically controlled member for the introduction of the products of combustion.

Figure 5 is a view representing a section through Figure 4 in-a plane indicated by a line 55 of Figure 4.

Figure 6 is a view representing a top plan View of the fan, of the air supply pipe leading to the combutsion chamber, and of the electric motor for closing and opening the switch in the fan motor circuit and for operating a valve controlling a pilot flame for initially igniting the combustible mixture in the combustion chamber.

Figure 7 is a View representing a side elevation of the parts shown in Figure Fig. 8 is a perspective view of part of the operating mechanism shown in Figs. 6 and 7.

Referring now to that embodiment of the invention illustrated in the drawings and particularly in Figures 1 to 3, inclusive :1(l

indicates a furnace of any usual construction provided with a fire-box 11 and with a stack 12 through which the products of combustion are discharged. 13 indicates a combustion chamber, which in this case, is a heavy metal box-like structure adapted to confine the flame. v14 indicates an electric motor driven fan or blower, by means of which fresh air is normally discharged through a pipe 15 into the combustion chamber, said air acting in the example illustrated to atomize the liquid hydrocarbon fuel supplied by a pipe 16 from any convenient, suitably controlled source of supply prior to or as it is introduced into the combustion chamber 13. 43 indicates an electric motor, controlled by a thermostat or other or auxiliary automatic control, not shown, which motor is adapted to close and open the switch in the circuit of the fan motor and to actuate the ignition device, as by opening and closing the valve supplying a pilot flame in the combustion chamber. Said parts of the apparatus are familiar and may be as described in the patent referred to and require no further illustration or description.

1? indicates a pipe or conduit of comparatively small crosssection which is adapted to introduce the inert gas, in this case a part of the products of combustion, along with the air into the fan casing, whence it is discharged with the fresh air through the pipe 15. The conduit 17, as illustrated, is connected in any suitable manner, as by a fitting 18 to the stack 12. The other end of said conduit is attached to a nipple 19 providing an inlet port to a valve casing 20 which opens by a passageway 21 into the casing of the fan or blower 14. Below the inlet nipple 19 on the diametrically opposite side of the valve casing 20 is an inlet port 22, for the admi sion of fresh air. An ordinary butterfly Valve 23 is mounted in the valve casing 20 on a spindle or shaft 24- which projects at one end beyond the valve casing 20.

The butterfly valve 23, when in the posit-ion shown in full lines in Figure 3, cuts off the inlet opening for the products of combustion from communication with the passage way 21 into the casing 14 of the fan, and leaves said passageway fully open to the inlet 22 for the entrance of air. Nith the valve in this position, the operation of the fan will draw into and discharge through the pipe 15, fresh air only. vVhen said valve 28 is shifted clockwise into the position shown in dotted lines at 23, the opening into the passageway 21, will proportion of the fluid discharged through the pipe will be products of combustion and the balance will be air; and the proportion of the products of combustion to the air of the mixture will depend upon how far the valve 23 has been shifted clock-wise. Thus, by this means a positive control of the proportions of the products of combustion or inert gas, as compared to the air, is provided.

The ro'tative movement of the valve 23 may be limited in any convenient way. As shown in Figure 3, a bolt 23 fixed in the cylindrical wall of the valve casing is placed in the path of an end of the valve 23 at a point so that the valve will strike the bolt when the intended limit of movement of the valve is reached. The bolt is engaged in a slot 23 in the valve casing wall with its head on the inside of the valve casing and a nut 23 engaged against the outside periphery of said casing. By this construction the position of .at in Figure 3.

the stop bolt may be varied to adjust the limit of opening movement of the valve and the resultant proportion of inert gas introduced with the air.

25 indicates a thermostatic element located in the fire-box 11 adjacent to the combustion Said thermostatic elei'nentis of familiar kind consis-ting a ribbon or band comprising two strips of metal of different co-efiicients of expansion arranged in a spiral coil about a rod or shaft 26. {inc end 25 of the ribbon coil 25 is attached'in any convenient manner to the rod 26. The rod 26 itself extends through a pipe 2? closed its ends by bearing

caps

28, 29, which are aperturcd to receive the rod 25. Said bearing caps are made integral with or attached to bracket arms 28 29 respective .,y,oue of which, 29 is attached to the shell of he combustion chamber and the other of which 28, is attacher to the air discharge pipe 15. thus mounting the parts, the 1 ribbon 25 is located in close rj to the combustion chamber and as- .senes the tem :erature thereof. The forward end 25 of the thermostatic ribbon 25 is fixed to the bearing cap and is thus made rigid auu. nou-rotative with respect to the pipe 2!. The rod on the other hand is capable of rotative movement in the bearing caps 28, 29. Eiaid rod extends into the neighborhood of the valve casing 20 where it has a cranlr arm 30 fixed to its end. A crank arm 81 is fixed to the butterfly Valve shaft 2% and a link connects the two crank

arms

30, 31.

l l hen in the operation of the apparatus the fan motor is started, fresh air is drawn in through the air port 22 and ti e passageway 21 now in full communication with said air port) and discharged with ti o fuel oil atomized thereby through the pipe 15 into the combustion chamber 13 where the combustible mixture is instantly ignited by a pilot light or otherwise in a familiar manner. Combustion takes place with a white, hot flame which is substantially confined within the limits of the combustion chamber 13 as heretofore. As the combustion chamber heats up, the heat of its metal body is imparted to the thermostatic ribbon 25 and said ribbon slowly uncoils. The uncoiling of the ribbon, by thus causing the connection of its rear end 25 to the rod 26 imparts a rotative movement to said rod in a clockwise direction, as looked This rotative movement of the rod is communicated through the crank arm 30, the link 32 and the crank arm 81 to the butterfly valve 23 so as to shift said butterfly valve clock-wise from the position shown in full lines to a position at or near that shown in dotted lines 25 in Figure 3.

Manifestly in this movement of the butterfly valve under the action of the thermostatic ribbon, there will be admitted first a small and then a gradually increasing proportion of the products of combustion with the fresh air into the pipe 15 to be discharged thereby into the combustion chamber to dilute the combustible mixture until a predetermined opening for the butterfly valve, determined by the position of the stop bolt 23, has been reached,-whereupon further movement of the butterfly valve is arrested.

It has been found that-upon the opening of the butterfly Valve 23 to the predetermined limit, the flame, which until the beginning of the dilution of the air by the introduction of the products of combustion has been a white hot flame practically confined to the combustion chamber, enlarges or expands somewhat above the combustion chamber and becomes lazy and of a bluish or deep purple color somewhat simulating the appearance in this respect of the flame of a Bunsen burner, but without the forcible discharge of the flame of such burner. In addition, the objectionable noise of burning, evident in burners of the kind as heretofore constructed and operated with air alone, is almost entirely, if not absolutely eliminated,the flame burning with a gentle purring which is hardly distinguishable when the furnace door is closed. And tests show a maximum percentage of C0 gas in the resultant products of combustion.

In addition, the heat of the flame in the combustion chamber, except at the beginning when the gas is first ignited and before the products of combustion are introduced, is considerably reduced and as the burning of the undiluted mixture is only required for the short time needed to ignite the flame and get it to its full capacity, it is possible to use cheapermetal in the construction of the combustion chamber.

In Figures 4: and 5, I have shown a modified form of the invention in which a pneu matic control tor the introduction of the products of combustion into the air supply to the combustion chamber is used instead of the thermostatic control member hereinbefore described In said views, lilre parts are indicated by the same numerals used hereteller-e.-

In case, a diaphragm chamber 33 is connecte with the air supply pipe 15 at some point intermc 'atethe fan 1a and the burner 13,

The diaphragm may be of n5 ml 0 familiar construction and is connected on one side by an apertured rod 34 ith the air pipe 15. The rod 34 has a small. bore 85 and has threaded laterally into it, a set screw 36, by means ot which the effective crosssectional area of said bore may be determined. 3? indicates the diaphragm in the casing. Said diaphragm is exposed on it nearest the pipe 15 to the air presin the the diaphragm with the pipe 15 through the bore ofthe pipe 34.

The diaphragm on its upper side has fixed to it a pin 38, which has suitable bearing for vertical movement in the upper side of the diaphragm casing, beyond which it projects to be pivoted at 39 to a lever 40. The lever 40 is tulcrumed to a stud 41 rising from the diaphragm casing on the side remote from the valve casing 20 and the other end of said lever 40 is connected by a link 42 to the crank arm 31.

The operation of the pneumatic control is as i ollows:vl hen air is discharged by the tan through the pipe 15 to begin combustion in the combustion chamber 13, pressure is built up in the pipe 15 and this pressure gradially builds up through the bore 35 of the rod 84 on the under side of the diaphragm 37.

ans a predetermined time limit, depending I r, on the eii ecizive cross-sectional area of the bore as determined by the set screw 36, this pressure will have been built up far enough lift the diaphragm 37 and through the pin to operate the lever lO, so as to swing the valve 93 from the position shown in full lines in liigr-Are 3 to the position shown in dotted l 3 2-3 therein, as heretofore described. 'i has, the products 01 combustion are again introduced with the air supply after the lapse of prcdetc mined time interval from the initial ignition of the combustible mixture in "3 V the combustion chamber In Figures 6 and 7, still another modification of the invention is shown,the'control member being in this case the electric motor 43 which closes and opens a switch in the fan motor circuit and simultaneously opens and closes the valve to the pilot flame in the combustion chamber or operates other mechanism to bring other ignition. means into play. De tailed description or illustration of the motor or of the parts operated thereby in the form of burner and ignition moans herein illustrated are not necessary, since that or another motor device adapted to operate at the time the combustible constituents are ignited and shut offbe used.

As before like parts are indicated by the same numerals used in the beginning. 4aindicates the shaft of the motor 43. At the end or the motor shaft is is tired a cam disc 45, having a cam projection 45. 46 indicates a rocking U-lrame pivotally mounted at 4'? on a fixed member 48 adjac nt the end of the shaft a l with said lJ-t'rame straddling the parts adjacent to its fulcrum l7 and has one leg 46 in the plane of the cam disc 45 with its end enp ged therewith. The other leg it? of said ll-irame is the short arm of a bell crank lever 29; Said bell-crank lever is normally depressed by a weight 49 so that the arm ll-6 of the lJ-frame d6 is always held in engagement with the cam disc 45. A. link 50 connects the lever 19 to the crank arm 31 of the butterfly valve shaft 24.

When the motor 43, by reason of the operation of the thermostat or other control is started into operation to close the switch in the fan motor circuit and to actuate the ignition device. the cam disc 45 will rotate w1th the motor sl t l rom the position shown in full lines in .i igure 7 until the cam project-ion lir is brought into operative engagement with the end of the arm This engagement with the arm 46 will rock the tlfram 46 on its fulcrum ll to swing the bell-crank lever upwardly so as to ill. the lever 49 and with it the linl: 50. T his upward movement of the link 50 rotates the butterfly valve shaft 2a to move the butterfly valve 23 from the position shown in full lines in Figure 3 to the position shown in dotted lines 23 therein, as before for admission of the products of combustion with the air. Thus the operation is again as heretofore described.

lt will be understood that no matter how the control member which actuates the valve 23 is operated nor what may be the character of the elements by which it is brought into play, said control member must be so correlated with and adjusted to the operation of the devices which bring about the initial ignition and combustion in the combustion chamber, that the predetermined time interval will elapse 1 before the valve is opened to admit the products of combustion with the air into the combustion chamber. This time interval is required in order that the temperature in the combustion chamber may be brought to that high degree which is neces sary in order that there may be complete combustion of the fuel before the oxygen supply has been diluted by the products of combustion. in the absence of this high temperature there will be a failure of complete combastion when the oxygen supply has been diluted with the inert gas with a resultant formation of the deadly CG gas in large quantities which would escape unconsumed and would be highly dangerous in a furnace for heating domestic and other buildings.

necessity for the elapse of this time interval during which the fuel is completely burnt with air alone until the required high tenmerature has been produced in parts of the struc ire in the neighborhood of which combustion is to take place, has been fully recognized where the products of combustion have been introduced with air to support combustion; but the problem in the present instance is to the benefits described without expanding or dilating the flame beyond the immediate vicinity of the combustion chamber since it would be practically impossible to maintain in the fines of a boiler or furnace a temperature of said flues sufficiently high to .romote complete combustion. ihe ratio of the amount of products of combustion to air in the diluted air injected with the fuel into the combustion chamber must be carefully determined for each kind of apparatus and size of combustion chamher. The said ratio may only be determined accurately by experiment and is then lined by adjustment of the stop, namely the stop-bolt 23 (Figure or equivalent device which arrests the movement of the mixing valve 23.

In making this determination (after first disconnecting the mixing valve from the control member used for actuating it and after initial ignition has taken place and the flame has been brought to its maximum temperature of combustion) the valve 23 is moved to admit gradually increasing proportions of products of combustion, the change in the color of the flame and its expansion being noted. The proportion of products of combustion is increased until the flame materially quiets down, the noise of combustion substantially diappears and the flame burns with purplish or blue color. Care must be used however not to expand the flame materially beyond the immediate vicinity of the combustion chamber or into contact with the boiler or furnace lines.

l have found that excellent results are obtained with a combustion apparatus of the kind herein illustrated and described includinn 2. burner of a capacity to burn approximately two gallons of fuel per hour where the products of combustion are from 15 to 2-0 per cent of the mixture of air and products of combustion injected into the combustion chamber.

While in illustrating and describing the invention l have shown an apparatus which contemplates preferably a complete atomization of the liquid fuel prior to or as it enters the combustion chamber, it will be understood that the invention is applicable, whether the fuel is completely atomized, atomized only in part or vaporized wholly or in part, either prior to its injection into the combustion chamber or at the instant it is injected into the combustion chamber or subsequent to its injection thereinto. The word fuel therefore as used in the claims is to be understood to cover and include liquid fuel when atomized, wholly or in part or vaporized, wholly or in part.

Again, the invention is not limited to use with a combustion chamber made of metal such as herein described, but contemplates a combustion chamber made of any material designed to produce substan ially complete combustion of the fuel within tl e combustion chamber; and it also contemplates a combustion chamber of any suitable form or shape which may function as a flaminn combustible confining means for the prompt production of hi gh temperature conditions. Such a combustion ch amber or confining;

- be an integral part of the oil burn.-

- saie inert gas through or proper or may be built into the fire box of the ordinary heating boiler or furnace.

I claim as my invention 1. The method of burning liquid fuel in a confining combustion chamber, which consists in introducing all the combustion-supporting air and the fuel into said combustion chamber, igniting the mixture of fuel and air and. swirling the burning mixture within the chamber with force to confine the burning mixture to the said chamber until combustion is practically complete; in thus burning the mixture with air alone for a period of time until combustion has developed to a maximum of temperature; and in then injccting with the air a neutral gas, non-combustible with air, said neutral gas and air being mixed in predetermined ratio adapted to somewhat delay combustion in said chamber and reduce the noise thereof, but without expanding the flame materially beyond the vicinity of said. combustion chamber.

2. In a liquid hydrocarbon fuel. burning apparatus, in combination with a flame confining combustion chamber, means for introducing a flame combustible including fresh air into said chamber, said combustion chamber being formed to produce a swirling movement of the burning combustible in the chamber, means for igniting said flame combustible, and an automatic control device for said introducing means, a valve casing, associated with said introducing means, said casing having an air inlet port and a second inlet port, a conduit adapted for leading an inert gas to said second inlet port, a mixing valve in said casing, said mixing valve normally closing off said second inlet port but being movable to a predetermined point for admitting that port in a predetermined ratio to the air admitted, and a valve control device adapted to move said valve to said predetermined point after combustion has been continued for a predetermined time interval.

3. In a liquid hydrocarbon fuel burning apparatus, in combination with a flame confining combustion chamber, means for introducing a flame combustible including fresh air into said chamber, said combustion chamber being formed to produce a swirling movement of the burning combustible in the chamber, means for igniting said flame combustible, and an automatic control device for said introducing means, a valve casing, associated with said introducing means, said casing having an air inlet port and a second inlet port, a conduit adapted for leading an inert gas to said second inlet port, a mixing valve in said casing, said mixing valve normally closing off said second inlet port but being movable to a predetermined point for admitting said inert gas through that port in a predetermined ratio to the air admitted, and an electrically operated valve control device adapted to move said valve to said predetermined point after combustion has been continued for a predetermined time interval.

4-. The method of burning liquid fuel in a furnace for heating buildings, which consists in introducing combustion supporting air and fuel into a combustion chamber located in said furnace, in i niting the mixture of fuel and air and bringing the same to substantially complete combustion in said coinbustion chamber; in thus burning the mixture with air alone until combustion has developed to a maximum of temperature; and in then injecting with the air a neutral gas, non-combustible with air, in a predetermined ratio to the air adapted somewhat to delay combustion in said chamber and reduce the noise thereof, but without expanding the flame materially beyond the vicinity of said combustion chamber. c

5. The method of burning liquid fuel which consists in automatically introducing combustion supporting air with the fuel into a combustion chamber, automatically igniting the mixture of fuel and air and burnthe same substantially within the cham her until the heat of combustion has develpod to a maximum of temperature; and in then automatically injecting with the air a neutral gas, non-combustible with air, in a predetermined ratio to the air adapted somewhat to delay combustion in said chamber and reduce the noise thereof, but without e2: ending the vicinity of said combustion chamber.

6. In a liquid hydrocarbon fuel burning apparatus, in combination with a combustion chamber, means for introducing a flame combustible, including fresh air, into said chamber, means for igniting said flame combustible, and an automatic control device for said introducing means, a valve casing associated with said introducing means, said casing having an air inlet port and a second inlet port, a conduit adapted for leading an inert gas to said second inlet port, a mixing valve in said casing normally closing off said second inlet port, but movable to a predetermined point for admitting said inert gas through that port in a predetermined ratio to the air admitted, and an electrically operated valve control device adapted to move said valve to said predetermined point after combustion has been continued for a predetermined time interval. 7

In testimony that I claim the foregoing as my invention, I atlix my signature this 31st day of July, 1925.

ALBERT B. FRENIER.

flame materially beyond the-