US2424154A - Subatmospheric gas burner - Google Patents

Description

jui? 5, w47. A. R. DUNHAM ET AL 2,424,154

SUB-ATMOSPHERIC GAS BRNER Filed sept. 12, 1940 2 sheets-sheet 1 I and, ura ,l/22500? fag@ WW/'amsm July 15, 1947,. A. R. DUNHAM ET AL.

SUB-ATMOSPHERIC GAS BURNER Filed Sept. 172, 1940 2 SheeLS-Sheet. 2

endl/g Patented '.luly 1.5, 1947 l SUBATMOSPHERIC GAS BURNER Aubra R. Dunham, Glencoe, and Hilding V. Williamson, Chicago, Ill., assignors to Experimental Laboratories Incorporated, Chicago, Ill.. a corporation of Illinois Application september 12, 1940, serial No. 356,4@

(el. s- 7) 12 Claims.

This invention relates to certain new and useful improvements in a gas burner, more particularly a burner especially adapted for use in a generator for producing heating medium consisting of a highly saturated mixture of steam and hot products of combustion for use in a heating system.

A heating system of this general type is shown in the patent to Dunham et al., 2,046,813, granted July 7, 1936. The uid fuel is burned in proximity to an enclosed body orbodies of water and the products of combustion are passed in intimate contact with the water so as to form steam and the heating medium consisting of the products of combustion yhighly saturated with steam is delivered into radiators wherein the steam is condensed and a large portion of the heat from the products of combustion is used for heating purposes. exhausted from the system thus producing a partial vacuum and causing the continuous circulation of heating medium and also maintaining a partial vacuum in the generator so as to draw in the fuel and combustion air. The condensate from the steam is returned to the generator to be reconverted into steam.

The present improved burner is adapted to be mounted transversely within the lower portion of the generator and separates an upper combustion chamber from a lower air-supply chamber.

The burner comprises a main lower metallic plate, and a. smaller circular upper plate spaced slightly above the lower plate, and fuel gas is introduced centrally through the lower plate into the space between the plates and iiows upwardly around the edges of the upper plate. Combustion air is drawn from the lower chamber through two concentric circular series of spaced holes in the main plate so directed that the air jets will meet and supply, together with the gas, a circular ame directed upwardly and inwardly into the combustion chamber. The air and gas are drawn in, in proper proportion, from separate sources each under substantially atmospheric pressure, by the vacuum existing in the combustion chamber.

The principal object of this invention is to provide an improved gas burner of the type briefly described hereinabove and disclosed more in detail in the specifications which follow.

Another object is to provide an improved burner which will not backfire, the air and gas being first mixed at the point of combustion so that the name can be turned down to a minimum.

Another object is to provide improved means for mixing the air and gas so as to more definitely determine and position the flame.

The cooled noncondensable gases are Another object is to provide an improved method and apparatus for properly proportioning and keeping substantially constant the rate of fuel and air supply to the burner.

Another object is to provide means for introduc-ing free air around the base of the flame, for the several reasons hereinafter speciiied.

Another object is to provide an improved pilotflame assembly.

Other objects and advantages of this invention will be more apparent from the following detailed description of one approved form of apparatus designed and operating according to the principles of this invention.

In the accompanying drawings:

Fig. 1 is an elevation, largely in central vertical section, of the generator with the improved burner installed therein, together with some portions of the heating assembly including the exhauster for maintaining the vacuum.

Fig. 2 is a vertical central section through the gas now-control valve.

Fig. 3 is a vertical central section through the burner, on a larger scale.

f Fig. 4 is a partial plan view of the burner assembly.

The general heating system will rst be briefly described. Referring lrst to Fig. 1, the generator indicated at A encloses the new burner B in its lower portion, this burner resting on a transverse partition i and separating the space Within the generator into a lower supply chamber 2 and an upper combustion chamber 3. The lower air chamber 2 is enclosed by the lower portion of the outer metallic shell t, and an opening l in this shell permits the free entrance of air. The gas supply pipe also passes in through this opening 5 and may be intermediately supported by any suitable bracket member 1. The upper portion of the combustion chamber 3 is enclosed by a cylindrical'shell 8 having a dome-shaped top 9 and an outwardly extending lower flange i0 extending to the shell or housing Il which holds the water supply. The lower portion of combustion chamber 3 is enclosed by an annular wall l2 of insulating material, within the outer shell t,

except for the opening enclosed by the metallic ,3 I hauster C is in operation and there is a partial vacuum within combustion chamber 3, the door id will be drawn into closed position so that the combustion chamber will be completely closed except for the air inlets through the burner B as hereinafter described. The space I8 within housing I l and surrounding the inner shell 8 up to the level :l: is filled with water, and the space I9 within housing II above this water level and below the dome-shaped top 20 serves as a mixing chamber for the products oi combustion and steam which flow out through outlet 2I into the supply pipe 22.

The mixing head D serves to conduct the products of combustion from combustion chamber 3 into the mixing chamber I3 so as to transfer a maximum of heat to the water, this portion of the apparatus being disclosed more in detail and claimed in the patent to Dunham et al. 2,169,683, filed August l5, 1939. This head comprises an outer cylindrical wall 23 which terminates above the water level x and which joins at its lower end with an intermediate horizontal partition 24 from which extends a central cylindrical member 25 enclosing a gas passage leading from combustion chamber 3. A skirt member 28 extends outwardlyuand downwardly from partition 24 and terminates somewhat above the top 3 of shell 8 so as to permit water to flow into 'the enclosed annular space 21 which becomes more highly heated than the larger body of water due to the fact that-it lis largely enclosed by the heated gases. VAn upper pan member 28 has its central bottom Z9 positioned somewhat below the water level :c and is supported by a plurality of vertical pipes or conduits 38 each having its lower and upper open ends ttedin the partition 24 and bottom `23 respectively so that water from the main body I8 will flow up through these pipes to maintain a normal liquid level at :I: within the pan 33. The upper portion of pan 28 is extended as shown at 3| so that a thin sheet of water 32 will overflow into the main body of water when the pan is filled as hereinafter described. Another series of vertical conduits 33, similar to the conduits 36 but longer, extend up through the pan 28 so as to discharge jets of water 33 from their upper ends into the domed mixing space i9.

ln operation, the highly heated gases from combustion space 3 will flow up through central passage 25 into the upper casing 23, flowing between and around the pipes 30 and 33, and thence out beneath the upper pan member 3l and into the mixing space I3. These gases will highly heat the water in the annular space 21 and in the pipes 38 and 33 and partially boil or vaporize this water so that its density will be reduced and the water will be forced up to fill the pan 28, and overflow at 32 into the main body of water. Also jets or fountains of water will be thrown up at 3d into the mixi g chamber I3 and against the domed top 26. I will be noted that the gases flowing out from beneath the pan 3l will ilow through the dispersed liquid 32 and also in con-- tact with the upper surface a; of the water pool la, while the liquid of jets 34 is beingdispersed through the heated gases in mixing chamber I3 and against the inner surface of dome 20. This tends to cool the dome .and also wets the inner surface so as to vaporize and mix with hot dry gases and increase the heating medium. Also the water surrounding inner shell 8 and the mixing head D will be highly pre-heated so that a comu paratively large volume of steam will be quickly formed and mixed with the combustion gases to form the heating medium that ilows upwardly the temperature of I ishing the water 4 through pipe 22 to the radiating system. The lower portion of the generator is insulated by the air space between outer shell 4 and inner shell II, although other insulating material could be used in this space.

The heating medium loses the greater portion of its heat in the radiating system. the steam being condensed and giving off its latent heat, and

the non-condensable combustion gases being considerably lowered. The condensate flows back from the radiating system through the pipes 38, 31, 38 and 33 into the main body of water I8. It will be noted that the pipe 33 is shown with a central portion broken away, and it is to be understood that at this point means (such as shown in the Dunham Patent 2,169,683 already referred to) may be provided for replensupply if necessary, draining ex cess water and sediment, and maintaining the proper water level a: in the generator. An exhauster or pump C, driven by motor 43, is connected through piping 4I, 42 and 31 with the return pipe 36 and through this piping non-condensible gases are withdrawn from the radiating system and then discharged from the pump through the vent pipe 43. The vacuum created in the radiators by the condensation of steam and by the withdrawal of gases through the venting system by pump C willcause a partial vacuum extending back into the combustion chamber 3, this vacuum serving to draw and fluid fuel, and also to maintain the circulation of 'heating medium through the Incidentally, this vacuum will hold the pilot-door I4 closed.

The improved burner B, which forms the particular subject matter of this invention, will now be described. This burner 'comprises a main plate 43 of generally circular form having an outer horizontal flange 44 which rests on and is secured to the horizontal partition I in the housing 4, this partition having a central opening corresponding to the general outline of plate 43 inside of the flange 44. The plate 43 has a central downwardly dished portion comprising the outer inwardly and downwardly sloping wall 45 leading to the horizontal bottom wall 43 having a. central downwardly extending inlet nipple 41 internally threaded at 48 to receive the gas-feed pipe 49. The upper edge of sloping wall 45 (which extends somewhat above the peripheral ange 44) is connected with ii'ange 44 by a short downwardly and outwardly extending flange 58.

A smaller upper circular plate 5I ts within the dished portion of the lower plate, this upper plate II having a. series of ribs 52 extending radially from a central hub 53, these ribs resting on the upper surface of wall 48 of the lower plate so as to space the two plates apart. The ribs 52 serve to divide the stream of gas ilowing in through pipe 43 and direct this gas equally through the radial passages between ribs 52 toward all edge portions of the plate El, around which edges the gas flows upwardly into the combustion chamber. A plurality of threaded stems or bolts 54 provided with wing-nuts 85 project down through the plates so as to hold them firmly in assembled relation. Metallic anchor members 86 held by the upper end of bolts 54 are imbedded in a cover member 51 of refractory material which is cast over the top of plate 5I, this refractory cover member having rounded edges 58 as shown.

A circular series of equally spaced upwardly directed air holes 58 are formed in the flat cenin the combustion air l radiators.

tamos tral portion 48 of plate l! adjacent the outer periphery of the top plate li. A second series of inwardly and `upwardly directed air holes 5B are formed in the sloping wall I5. The holes 60 in the second roware positioned radially outward from the holes 59 in the first row, pair by pair, so that the two jets of air of each pair willconverge and impinge against one another and, with the gas drawn from between the plates 5| andl 46 form a combustible mixture which will burn with a circular ilame directed upwardly and lnwardly above the central refractory member 5l. The iets will impinge at such an angle as to slow down the nal velocity of the air streams and mix with the gas so that the flame will remain substantially xed and will not wander or blow out.

A third row of openings 6l directed upwardly and outwardly are formed in the narrow inclined wall 56 of the lower plate I3. The air drawn in through this outer row oi holes 6l does not directly enter the name at all, but is quite important to the successful operation oi the burner, especially since no combustible mixture is formed until the gas and air are separately drawn into the chamber. This free air from the outer row of openings tends to stabilize the operating conditions around the base of the flame. When these outer holes are lacking, ignition takes place and the llame starts but soon a circulation oi d gases tends to sweep down and into the base of the name causing the llame to rise up and tend to blow away from the jets. The name will go out in spots and then reignite with explosive force tending to throw the pilot door it open and then pull it shut with a bang. This action may continue to a point where the entire llame is snuied out, including the pilot flame. By introducing sufflcient free air around the base of the llame the above action is prevented. If sui'licient of this free air is introduced, the main flame continues to burn down near the burner, the pilot is not ail'ected, and there is no tendency for the name to sputter or blow the door open. However, if too much air is brought in around the outside of the burner yellow flames will appear. The exact quantity of this free air desired will vary somewhat with the character of the gas and the velocity oi.' flame propagation with different gases. This can be determined by experience in any given locality and with any particular character of gas. 'I'he lower ends of air inlet holes 5t, to and 0i are all rounded s0 as to facilitate the iniiow of air.

'I'he gas will flow in under city-supply pressure through pipe 82, to the suction controlled valve B3, which operates as a zero pressure regulator to furnish gas at slightly lower than atmospheric pressure through pipe M, metering valve t5, and pipes 8 and 4t to and through the burner B. The metering valve o5 may be a suitable needle-valve and will be given a flxed manual adjustment which will depend upon the quality and character of the gas being used.

The valveft comprises an internal `web 66 having a valve opening tl that may be closed by ther valve 83 carried by stem' 89 secured at its lower end to a diaphragm 1i! separating the upper gas chamber il in diaphragm casing 'l2 from the lower chamber l@ open to the atmosphere at it. The valve t3 also includes a loose guide et' for the stem si?. A centering springlie enclosed in an upper housing extension lt exerts an upward pull on the upper end of stem et so as to carry the weight oi the iloating parts. The spring is iii) '.v adjusted so that the valve member et just barely ialls shut without the aid of gas pressure. The spring also tends to hold the valve centered so as to minimize friction between the valve parts and the valve-seat and guide. When a partial vacuum is developed in the combustion chamber t, this will partially evacuate the pipes te and t5 and reduce the pressure in upper chamber il so that the atmospheric pressure in lower chamber it will force the diaphragm l@ upwardly and open valve Se so as to yadmit gas from the supply pipe t2. Obviously. the more valve 68 is opened the greater will be the dow of gas into the combustion chamber.

This suction controlled valve 63 opens by a slight vacuum from the combustion chamber and tends to feed gas to the needle valve at a substantially constant pressure slightly below atmospheric.

The rst step to get proper gas and air ratio control is to reduce the gas pressure in pipe @d to substaantially atmospheric pressure, and the vacuum in the combustion chamber will then be able to draw air from the normal atmospheric pressure source through the air inlets tit, t@ and ti in the same proportion that it draws gas through the needle valve t5 and thence through the burner. Valve t3 is also a safety valve because the exhauster must be running and creating a vacuum in the combustion chamber before valve 6l will open and any gas can be drawn into the burner.

With the apparatus properly designed and ad@ justed the proportionate now of air and gas into the combustion chamber will remain substantially constant so as to provide o, proper mixture, although the size of the 'dame can be increased or decreased by changing the vacuum in charn-g ber t, and within reasonable limits the size of the flame will increase or decrease to corre spond with the demandsfor heating medium.

Within one side portion of the lower burner plate 43 (preferably the side adjacent the door it) is formed a depressed well ll for housing the pilot burner B. This pilot burner eorn= prises a small gas jet it so inclined that the naine it (Fig. l) will project inwardly suiiloient to ignite the main burner when the combustible mixture is owing. At the same time this jet 'itl is housed withinthe well il so that the jet will not blow out when che door it is opened. When the main burner is extinguished and the exhauster C is not operating, that is when the vacuum is broken in chamber t and the heat-s ing medium is no longer circulating, the door id will :all open (see Fig. l)4 and the gases from the pilot-burner can vent through this door opening. In this way the pilot-burner can continue in operation at all times. In the example here shown, a thermo-couple et is positioned adjacent the pilot-burner le, this thermo-couple acting, when heated. to hold open e supply valve in the :main fuel-pipe. ln case the pilot burner should be extinguished the thermo-couple t@ wiil cool off and permit this kvalve to close. The cable 8l leading from the thermo-couple to and the gas supply pipe t2 for the pilot-burner may conveniently enter 11e generator through the air inlet opening b.

This improved burner will not backfire since the gas and air enter the combustion chain separately and are not mixed until they reach substantially the point of combustion, conse silently the burner can be turned down to minimum. By using a number oi small inist air holes or orifices producing forceful air iets which inspirate the gas, a better gas and air mixture is obtained `which gives a shorter hotter flame and makes it possible to use a smaller combustion chamber. By arranging these small jets in a circle, ignition starts at one side and moves around rapidly but not with the explosiveness that wouldresult if all the gas and air were introduced at one point with a single jet. By arranging the combustion air jets in pairs which strike one another so as to create eddies, the flame is held in place and the increased turbulence tends to mix the air and gas and improve the mixture so that combustion takes place almost instantly. The gas and air are both pre-heated to some extent in passing through the burner orifices thus aiding in combustion. The burner plates 43 and 5I are preferably made of aluminum so that heat will -be drawn down to pre-heat the combustion materials, but the refractory covering l on the upper plate serves to protect this portion of the burner from too much heat. This refractory plate also creates a central hot zone Where combustion can take place with the best results.

This apparatus is adapted to operate under a rather small vacuum, but a greater vacuum than natural draft will as a rule produce. Such a system has the advantage that there is no outward leakage. It will also be noted that while the usual gas burner operates by inspirating the combustion air into the gas which enters under pressure, in the present burner the combustion air jets are drawn or sucked into the burner and the gas is inspirated into the mixture by the force of the air jets. There will never be an excess of fuel since the gas is drawn in by the air and is also controlled by a cut-off valve responsive to the degree of vacuum within the combustion chamber. It will also be noted that this improved burner can readily be used as a. conversion burner unit in existing boilers or heating plants by transversely sealing this burner within the combustion space and installing a suction or exhaust means acting on the stack or vent.

We claim:

l. A gas burner comprising a main metallic,

plate adapted to separate an air-supply chamber from a combustion chamber, said plate being centrally dished so that the plate comprises a central substantially circular horizontal portion surrounded by an upwardly and outwardly sloping rim extending to a main outer horizontal portion, an upper substantially circular metallic plate having downwardly projecting radial ribs which rest on the flat-central portion of the main plate within the dished recess and support the upper plate in spaced position above the main plate, the

main plate having an opening in its central portion for receiving gas from a supply-pipe said gas flowing outwardly between the radial ribs and upwardly around the circumferential edge of the upper plate and cover, a circular series of upwardly directed air-holes adjacent the edge of the upper plate, and a second concentric circular series of upwardly and inwardly directed airholes formed in the upwardly sloping rim of the dished portion of the main plate so that the air from these holes will implnge against the air from the inner holes and combine with the gas to supply a circular flame projecting upwardly and inwardly into the combustion chamber.

2. .A gas burner comprising a main metallic plate adapted to separate an air-supply chamber from a combustion chamber, said plate being plate, a covering of refractory material mounted on the upper surface of the upper circular plate; the main plate having an opening in its central portion for receiving gas from a supply-pipe said gas flowing outwardly between the radial ribs and upwardly around the circumferential edge of the upper plate and cover, a circular series of upwardly directed air-holes adjacent the edge of the upper plate, and a second concentric circular series of upwardly and inwardly directed airholes formed in the upwardly sloping rim of the dished portion of the main plate so that the air from these holes will implnge against the air from the inner holes and combine with the gas to supply a circular flame projecting upwardly and inwardly into the combustion chamber.

3. A gas burner comprising a main metallic plate adapted to separate an air-supply chamber from a combustion chamber, said plate being centrally dished so that the plate comprises a central substantially circular horizontal portion surrounded by an upwardly and outwardly sloping rim extending to a main outer horizontal portion. an upper substantially circular metallic plate having downwardly projecting radial ribs which' rest on the flat-central portion of the main plate within the dished recess and support the upper plate in spaced position above the main plate, the main plate having an opening in its central portion for receiving gas from a supply-pipe said gas flowing outwardly between the radial ribs and upwardly around the circumferential edge of the upper plate, a circular series of upwardly directed air-holes adjacent the edge of the upper plate, a second concentric circular series of upwardly and inwardly directed air-holes formed in the upwardly sloping rim of the dished portion of the main plate so that the air from these holes will implnge against the air from the inner holes and combine with the gas to supply a circular flame projecting upwardly and inwardly into the combustion chamber, and a third outer concentric series of air holes in the upper outer flat portion of the main plate and directed upwardly and outwardly.

4. A gas burner comprising a main metallic plate adapted to separate an air-supply chamber from a combustion chamber, said plate being centrally dished so that the plate comprises a central substantially circular horizontal portion surrounded by an upwardly and outwardly sloping rim extending to a main outer horizontal portion, an upper substantially circular metallic plate having downwardly projecting radial ribs which rest on the at central portion of the main plate within the dished recess and support the upper plate in spaced position above the main plate, a covering of refractory material mounted on the upper surface of the upper circular plate, the main plate having an opening in its central portion for receiving gas from a supply-pipe said gas flowing outwardly between the radial ribs and upwardly around the circumferential edge of the upper plate and cover, a circular series of upwardly directed air-holes adjacent the edge of the upper plate, a second concentric circular -to be positioned transversely in a housing so as to separate a lower air-inlet chamber from an upper combustion chamber, -said assembly comprising a main metallic plate, a substantially circular upper burner plate supported on and spaced from said main plate by a plurality oi substan- 4vtially radial ribaand means communicating with the central portionv of the space between the plates for supplying gas thereto under substantially atmospheric pressure, there being a'substantially circular series of upwardly directed air-openings formed through the main plate and leading from the air inlet chamber into the com'- bustion chamber at locations adjacent the outer edge of the upper plate so that jets ot air directed upwardly from these openings will draw gas from between the plates into the combustion chamber, and means including a conduit communicating with said air openings for creating said upwardly directed air jets.

6. In combination, a burner assembly adapted to be positioned transversely in a housing `so as to separate a lower air-inlet chamber from an upper combustion chamber, said assembly comprising a' main metallic plate, a substantially circular upper burner plate supported on and spaced from said main plate by a plurality oi substantially radial ribs, a top covering of refractory material on said upper plate, and means communicating with the central portion of the space between the plates tor supplying gas thereto under substantially atmospheric pressure, there being a substantially circular series of upwardlyv directed air-openings iormedthrough the main plate and leading from the air inlet chamber into the combustion chamber at locations adjacent the outer edge oi the upper plate so that jets of air drawn upwardly through these openings will now across the space between the plates to draw gas from said space into the combustion chamber, and suction means including a conduit com municating with said air openings for drawing said jets of air upwardly therethrough.

7. In lcombination, a. burner assembly adapted to be positioned transversely in a housing so as to separate a lower air-inlet chamber from an upper combustion chamber, said assembly comprising a main metallic plate, a substantially circular upper burner plate supported on and spaced from said main plate by a plurality of substantially radial ribs, and means communieating with the central portion oi the space beforced upwardly through both series of openings will impinge against one another to retard their rate of movement and f orm with the gas drawn from between the plates a circular flame projecting upwardly and inwardly into the combustion chamber above the upper plate and suction means communicating with said air openings for drawing air upwardly therethrough.

8. In combination, a burner assembly adapted to be positioned transversely in a housing so as to separatea lower air-inlet chamber from an upper combustion chamber, said assembly comprising a main metallic plate, a substantially circular upper burner plate supported on and spaced from said main plate by a plurality of substantially radial ribs, and means communicating with the central portion of the space between the plates for supplying gas thereto under substantially atmospheric pressure so that this gas will ilow evenly between the ribs into the combustion chamber, therebeing a substantially circular seriesl of upwardly directed air-openings formed through the main plate and leading into the com. bustion chamber at locations adjacent the cir-f cumference of the upper plate a second series oi air-openings 'concentric with the irst series and tween the plates for supplying gas thereto under substantially atmospheric pressure so that this gas will ilow evenly between the ribs into the combustion chamber, there being a substantially circular series of upwardly directed air-openings formed through the main plate and leading into the combustion chamber at locations adja cent the circumference oi the upper plate, a second series of air-openings concentric with the irst series and being spaced outwardly in radial alignment with and inclinedtoward the open= inge or the nrst series so that the air streams being spaced outwardly in radial alignment with and inclined toward the openings of the ilrst series so that the air streams forced upwardly through both series of openings will impinge against one another and form with the gas drawn from between the plates a circular llame projecting upwardly and inwardly into the combustion chamber above the upper plate. there being a third circular' series of air-openings through the mainfplate, outside-oi the second series. and directed upwardly and outwardly and suction means for drawing air upwardly through said air openings. l

9. In combination, a gas burner comprisinga main plate adapted to separate an air supply chamber from a combustion chamber andV including a centrally dished circular portion having a nat bottom portion connected by an upwardly sloping wall to an outer horizontal. flange portion, 'an upper plate arranged in the dished portion of the main plate and having downwardly projecting radial ribse-wlnch rest on the flat bottom portion oi the marrlate and denne shallow passages for directing gas from a central supply. opening to the outer edge of the upper plate,y

means for delivering gas into said shallow passage at substantially atmospheric pressure there being a series oi upwardly directed air holes formed in the main plate adjacent to the edge or the upper plate so that upwardly directed thereof and to mix therewith, and means for causing vsaid streams of air to ilow from said air holes. l

l0. En combination, a gas burner positioned transversely in a housing so as to separate a lower air inlet chamber from an upper combustion chamber, there being a gas inlet passage in the burner for delivering gaslaterally at a location above the bottom of the burner. means assise 1l for vdelivering gas to said las inlet passage at substantially atmospheric pressure and the burn er having also concentric rows of upwardly di- "rected air openings, the inner row of which is positioned below the gas inlet, whereby Jets of air directed upwardly from said air openings across said inlet withdraw gas therefrom to form an aerated gaseous mixture, and another row of said air openings being positioned with their axes inclined in a direction toward the iirst'inenV tioned row of openings, whereby the air jets from said concentricrows of openings impinge at a location above the gas inlet to reduce their ve iocity and eilect further aeration ot the mixture, and suction means communicating through said housing with said air inlet openings for drawing said iets of air upwardly therethrough 1l. In combination, a burner assembly having a gas inlet passage therein and a series of air inlet openings positioned to direct .iets of air across the discharge end oi the Zas passage, means for delivering gas to said gas inletpassage at substantially atmospheric pressure, and air jet producing means communicating with said air openings for forcing jets of air therefrom, whereby the gas is withdrawn from said passage by the inspirating action of the air jets; the 'sumeer assembly being also provided with. a second series of air openings communicating with seid air jet producing means and inclined toward the tlrst mentioned series of openings so that the air jets from the second series of air openinssinr pinge against the jets from the first mentioned series of openings to retard the velocity thereof and spread thegaseous mixture at a location beyoud the ses passage.

l2. In a heat generator in which a partial vacuum created in the upper portion oi' the gener-' ator creates a suction to draw air and fuel into a combustion space thereof; a casing enclosing; said combustion. space and an air supply chamber andhaving a door opening leading into said combustion space; a closure for said opening pivotally supported normally in a partially open position and adapted to be drawn to a closed f ens le. newness.

REFERENCES @li'liib The following references are oi record 'me of this patent:

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