US2212061A - Fuel combustion - Google Patents

Description

Aug. 2o, 1940. G@ LEN Er AL 2,212,061

Y FUI-:L -coMBUsTIoN Original Filed Feb. 6, 19.35 2 Sheets-Sheet 1 F, 22 Fafv mme? l BY WWM MATORNEY Original Fild Fb. 6, 1955 G. DALEN ET AL FUEL colBUsTIon 2 Shee'ts-Sheet 2 vlm /NTORS l Il BY WWW 47227 14u/ATTORNEY Patented Aug. 20,1940

y UNITED STAT-Es PATENT OFFICE FUEL COMBUSTION Application February 6,

193s, serial No. 655.334.

' Renewed December 29, 1938. In Sweden February 13, 1932 4 Claims.

Our invention relates to combustion, and more particularly to combustion of hydrocarbon fuels, and still more particularly heavy hydrocarbons, such as what is commonly termed fuel oil. In one phase, our invention relates to cook stoves and, more specifically, to stoves including heataccumulating mass in the form of a large block of metal or the like.

The object of our invention is to provide a reliable combustion apparatus for fuel oil or the like and particularly adapted for continuous burning at a relatively slow rate. v

Further objects and the nature and advantages of our invention will become apparent from a consideration of the following specification considered in connection with the accompanying drawings illustrating the invention and forming. a part of this specification, and of which:

Fig. 1 is a vertical, cross-sectional view of a cook stove embodying the invention;

Fig. 2 is a cross-sectional view showing, in detail, one form of combustion apparatus usable in the cook stove of Fig. l;

Fig. 3 is a. cross-sectional view of a combustion apparatus constituting a modification of the structure shown in Fig. 2.

Liquid hydrocarbon fuel or fuel oil, for example, the kind supplied generally for house heating, herein generally termed oil, is supplied to the stove of Fig. 1 by means of the pipe or conduit I. 'This pipe is connected to and discharges into a vaporizer 2, the detailed structure of which is shown in Fig. 2. In the vaporizer, the oil is converted to vapor form. The vaporizer is in direct heat transfer relation with a large mass of metal 3, which serves for the accumulation of heat. The vaporizer 2 should be so intimately associated with the accumulating mass 3 that they are at the same, or substantially the same, temperature. The accumulating mass 3 may be made of cast-iron or a cast-steel alloy. The vaporizer is maintained at so high a temperature that the oil is vaporized substantially instantaneously upon its introduction therein. We contemplate the operation of our stove at high temperature, for example, 900 F.

From the vaporizer 2, the vapgrized oil passes to a mixer 4 supplied with fresh air by means of a pipe or conduit 5. Pipe 5 is connected to the surrounding atmosphere and the air passing therethrough may be preheated before reaching the mixerV 4. The extent of preheating may be determined by the extent of the pipe 5 within the insulation. The vapor and air mixed therewith are then fed through pipe or conduit 6 to the (ci. 15s-s3).

burner 1, where the* combustible mixture is ignited.

'Ihe gases or products of combustion in the channel or combustion zone 8 give up their heat to the accumulating mass 3 and thence pass through the off-take or channel 9 to the chimney or ue I0. 'I'he upper surface II of the accumulating mass 3 is horizontal and nat and constitutes a cooking surface or hot-plate surface. The accumulating mass is surrounded by a thick bed, preferably several inches thick, of insulation such as asbestos mixed` with kieselguhr, and preferably a sheet metal cover is placed around the insulation. A well-insulated cover I2 is preferably provided which is hinged to the top of the stove and folds down to cover the cooking surface II. The stove may be provided with several cooking surfaces and may be provided with a high temperature oven in direct heat-transmitting relation with the accumulating mass or a low temperature oven receiving heat essentially through insulation or both, as is illustrated in U. S. Patent No. 1,862,009, granted June 7, 1932, to Gustaf Daln.

Referring more particularly to Fig. 2, thelower end of pipe i is shown as providing a fuel feeding member having the shape of a nozzle I1 the opening of which is downwardly directed so as` to allow the liquid fuel to drip therefrom in drops in free falling condition. The oil drops from the tip of nozzle II onto a hot surface I8 at the bottom of the vaporizer 2 and in the main or vaporizing chamber 2a thereof. The vaporizer structure enclosing the chamber 2a is secured in good heat-conducting relation with the metal mass 3 as by being bolted thereto on a smooth surface I8. This connection is made to the lower partd of the heat-accumulating mass which is adjacent the burner 1. We call the surface I8 a hot surface because, in operation, it is heated to a very high temperature due to the direct heat transfer relation with the wall structure of the combustion zone. Due to the suction produced by the hot gases leaving the combustion zone 8 through thestack or chimney, gases are drawn from the channel E into the combustion zone 8. This in turn draws fresh air in through the pipe 5 to the mixer 4 and draws the vaporized oil into the mixer from the vaporizer 2. The mixer 4 is formed in the shape of a contracting and expanding nozzle with a slit 20 between the contracting and expanding parts, and the fresh air from the conduit 5 enters the contracting part of the nozzle and the vaporized oil from the vaporizer 2 enters the mixer through the slit 20.

Gas of such quantity or nature as to be essenvapor is supplied to the upper part of auxiliary .chamber 24 of the vaporizer surrounding the drip nozzle I1 by means of conduit I5. The pipe I5 is connected to a chamber I4 which may be embedded in the insulation and which we will term a. cooler. 'I'he chamber I4 is connected by means of a pipe I3 with the off-take 9 to receive products of combustion therefrom, and is also connected by means of the small diameter pipe 28 to atmosphere. The essentially inactive gas thus constitutes products of combustion with which are mixed a relatively small quantity of air which provides in the mixture delivered to the pipe I5. an extremely small percentage of oxygen. The chamber I4 is surrounded by a cooling water jacket 22 to which cooling water is supplied by pipe 2| and from which cooling water leaves through pipe 23.

I'lie drops of oil fall freely under the influence of gravity alone from the tip ofv nozzle I1 onto the surface I8 in the vaporizer. It will be understood from the above description that this sur-` face I8 is extremely hot since it is in direct heat-transmitting relation with the high temperature metal mass 3. Consequently, the oil is very rapidly vaporized as soon as it hits this surface I 8. Small quantities of coke are formed at I8 as indicated in Fig. 2 and the oil falls onto the 'small mound of coke rather than directly onto the vaporizer surface, wherefore the surface of the coke may be said to constitute the surface I8. On account of the high temperature of the vaporizer, this coke will be red hot or practically so.

By introducing a small amount of oxygen into the gas passing through pipe I5, the coke at I8 can be consumed. The amount of oxygen supplied by means of the gas mixture admitted through conduit I5 is preferably sufficient only to consume the coke and not sufflcientto cause pre-ignition or at least to cause very little preignition of the vaporized oil in the vaporizer ahead of the mixer. In view of the high temperature of the coke and the temperature and quality of the vapor, the coke will be combusted before the oxygen effects any ignition of oil vapor.

It is one of the objects-of the present invention to prevent the vaporization of oil until it strikes the extremely hot surface I8. Gradual vaporization in any path of ilow is extremely undesirable,

as the light hydrocarbons are first vaporized and,

low temperature, vaporization is prevented from taking place until the moment when the oil touches the vapcrization surface. The latter is kept at such high temperature that even the pitch-like particles of oil are vaporized. There remain only thin layers of coke, which can be disposed of by the supply of what we have termed the essentially inactive gas above referred to.

Furthermore, on account of the rapid vaporization, the vaporized oil acquires so high a temture of the light hydrocarbons.

perature, while maintaining low pressure,'that its viscosity diminishes considerably. This, however, involves both advantages and disadvantages. The high temperature, as used .by us in this stove. exceeds that of the iiash-point of the oil and thus would cause immediate ignition of the gas in the vaporizer if there were sufficient oxygen in it. On the other hand, the reduced viscosityand consequent ready flow of gas tends to make the oil vapor mix very well with foreign additional gases in order toform a homogeneous gas mixture. The dilliculties in obtaining a homogeneous gas mixture have been recognized for a long time. At lower temperature, the oil vapors do not ow smoothly and are little inclined to mix with air.` Consequently, the mixture which is burned as a rule includes oxygen-free, cloud formations of oil vapors. `These burn imperfectly and are the cause of soot collection.

In the present case, the disadvantages are overabove described inactive gas containing a small amount'of free oxygen. It is important that the inactive gas carry into the vaporizer oxygen only of such small quantities or proportions that no, or substantially no, ignition of the 4vaporized oil can take place in the vaporizer. The low quantity of oxygen contained in the mixed. gas thus prevents ignition. On the other hand, due to the dilution, the iiash point of the mixed gas rises so that it can be mixed with fresh air in a cham, ber separat and communicating with the vaporizer, namely, the mixer 4, without risk of pre-ignition.

Furthermore, the inactive gas is preferably introduced adjacent the drip point of the nozzle and directed toward `the hot or vaporization surface in the same direction as the dropping liquid oil, that is, downwardly through the auxiliary chamber 24. Thus, the inactive gas constitutes an envelope for, or enshrouds, the dripping oil and prevents vaporization until the oil strikes the hot surface and furthermore prevents any tendency for vaporized oil to back *up into the oil supply pipe and cause cracking or distillation before the oil reaches the vaporizer. It may be said that this inactive gas is an insulator for the oil supplied to the vaporizer.

y Preferably, the distance of fall of the oil from the nozzle I'I to the hot surface I8 is relatively small, for example,two or three inches.

The gas which we have termed essentially inactive gas, is cold, and and thus will cool the nozzle I1 and the oil supply conduit leading up to the nozzle. If these parts are not cold, there is likely to be pre-volatilization in them and, consequently, light hydrocarbons will ow as vapor and heavy hydrocarbons will flow slowly in the supply pipe or in the nozzle. This might result in dry-distillation giving off hydrogen and leaving coke or other carbon in the pipe.

The essentially inactive gas owing in the same direction as the drops of oil in the chamber 24 prevents any back-condensation. If this inactive gas is not introduced., oil vapor would fill the whole vaporizer including the chamber 24 surrounding the nozzle. The walls of the chamber 2a are warmer than the vaporization temperature of the heavy hydrocarbons in the oil, and the nozzle is colder than the vaporizatlon tempera- The danger, therefore, of formation of coke adjacent the nozzle is present and this danger is entirely eliminated by the introduction of the essentially inactive gas moving in the same direction as the dropping oil in the auxiliary chamber 24. 'I'his prevents condensation on the insider wall of chamber 24, which would result in such formation of coke. Thus. it is an important characteristic of our invention that the cold nozzle is heatinsulated from the hot vaporizer by means of moving inactive gas. Some diffusion of oil vapor into the essentially inactive gas will, of course, take place, but the auxiliary chamber 24 is narrow horizontally and the movement of the inactive gas is therefore (and due to the rate of supply) such that there is not sufiicient time for oil vapor to diifuse through the stream of enshrouding fluid so that it might condense on the wall of chamber 24.

'I'he mixture of oil vapor and dilution or inactive gas is drawn from the vaporizer into the injector or jet device 4 as above described. Aithough there is oxygen contained in the vapor in the vaporizer 2, the mixture thus Iformed is not a combustible mixture. It becomes a combustible mixture when the additional air is added thereto from the conduit 5. As above stated, the combustible mixture then passes through conduit 5 and to the burner 1. The quality of the mixture might be improved if conduit 6 contains means such as a spiral baille indicated at' 6a to cause turbulence and mixing of the combustible mixture. Preferably, a grid 21 is supplied subdividing the gas flow at the place of ignition. The conduit 6 (all the conduits are made of metal) is in heat-transmitting relation with the burner, whereas the burner is insulated from the wall structure of the combustion zone 9 by means of a ring 28 of asbestos or other heat-insulating material. 'I'his permits the heat of the burner to be dissipated through the pipe 6 and in this manner the temperature of the burner can be kept below the flash-point and thus spontaneous ignition of the gas under the grid 21 is avoided.

'I'he vacuum obtained by the low speciiic weight oi' the gas column in the combustion zone 3 and the stack is utilized to draw in the fresh air through the pipe 5 so that it can mix with the gas mixture obtained from the vaporizer. 'I'he oil vapor is conveyed to the mixer 4l by means of injector action, which injector action produces a slight vacuum in the vaporizer. Due to this vacuum, the dilution gas mixture or essentially inactive gas is drawn from the off-take iiue 9 through the pipe I3, cooler I4, and pipe I5 to the vaporizer 2. The cooling of the combustion gas in the cooler I4 increases the specific weight of the gas in the downfiow leg of the circuit and thereby assists in producing the circulation of the combustion gas downwardly in pipe I5 and through the vaporizer and the conduit 5 and upwardly through the combustion zone.

'Ihe liquid fuel supply may be controlled automatically by a temperature-responsive element which may consist of a valve operated by a liquidcontaining bulb of the usual type in heat-transmitting relation with the metal mass 3.

In Fig. 3 we propose to utilize excess of pressure for forcing the essentially in active gas into the vaporizer. This we accomplish by placing a throttling device 29 in the off-take ue 9 and thus by excessive pressure the combustion gas is forced into the pipe I3, through cooler I4 and pipe I5 to the vaporizer. In this case we propose to cool the cooler I4 by air. It will be appreciated that if the throttling device 29 were not in the ue 9, and without injector action, the stack would pull a vacuum up through the pipe I5 and cooler I4 unless the cooler were sumciently cool to offset this. The placing of the orice plate 29 in the flue 9 permits downiiow through parts I4 and I 5 with air cooling.

Consequently, in the arrangement shown in Fig. 3, the mixer 4 n eed not take the form of an injector, although, however, in certain circumstances it might prove of advantage to do so. For

- the purpose of insuring proper mixture of the oil vapor supplied from chamber 2a with the air for combustion supplied through pipe 5, the mixer 4 in this embodiment is advantageously provided with a plurality of bailies 49 forcausing tortuous and turbulent iiow through the mixer. In this arrangement, fresh air cannot be added to the cooler I4 due to the existence of excess pressure. If required, an excess of oxygen in the dilution gases can readily be obtained by firing the .stove with surplus of air so that all the air is not consumed in the combustion zone and some air passes downwardly through conduit I3. In the hereinbefore described embodiments of the invention showing the application thereof to a domestic cook stove of the heat accumulating type, the rate at which fuel is supplied in normal operation is such that it falls to the vaporizing surface in the form of drops. As will be readily understood, the invention may be applied to and is equally applicable to heating apparatus of such size that fuel must be supplied thereto in a continuously iiowlng stream rather than by separated drops.

It will be understood that the invention is not limited to the structures shown nor is our invention hunted to accumulator type stoves, although there are special advantages in connection with the -accumulating mass as maintaining at all times the desired very high temperature of the vaporizer.

The broad subject matter of the present invention is claimed in our co-pending continuation-in-part application Serial No. 166,916, filed October 2, 1937, the claimed subject matter in the present application being restricted to the features of species not disclosed in said continuation-in-part application.

What we claim is:

1. Liquid fuel combustion apparatus comprising wall structure forming a combustion zone, a vaporizer disposed in heat-receiving relationship to said wall structure and having a main chamber and an auxiliary chamber above and in communication with said main chamber, a liquid feeding member in said auxiliary chamber disposed to have liquid drop or pour therefrom'into said main chamber, means to supply liquid hydrocarbon fuel to said feeding member, means to introduce into the upper part of said auxiliary chamber at a temperature relatively cool with respect to the temperature of said vaporizer, to have downward movement in the same direction as liquid falling from the feeding member, products of combustion from said combustion zone thereby forming with vapor of the hydrocarbon fuel anon-combustion supporting mixture in said main chamber, said auxiliary chamber being relatively narrow horizontally to provide suicient flow of the gaseous fluid to prevent condensation on the wall thereof of vapor of the hydrocarbon fuel, a mixer, means to supply air to said mixer, means to conduct uid from said main chamber to said mixer, and means to conduct uid from said mixer to said combustion zone.

2. Liquid fuel combustion apparatus comprising wall structure forminga combustion zone and a metal heat-accumulatlng mass in heat-receiving relation with said combustion zone, a vaporizer disposed in heat-receiving relationship with said mass having a chamber, a liquid feeding member disposed to have liquid drop or pour therefrom into said chamber, means to supply liquid hydrocarbon fuel to said feeding member, an off-take flue leading fromsaid combustionzone, meansA to conduct products of combustion from said off-take flue to said vaporizer, means to' cool the products of combustion so conducted, a mixer, means to supply fresh air to said mixer, means toconduct fluid from said vaporizer to said mixer, andv means to conduct fluid from said mixer to said combustion zone.

3. Liquid fuel combustion apparatus comprising wall structure forming a combustion zone, a vaporizer disposed in heat-receiving relationship to said wall structure and having a vaporizing chamber, a liquid feeding member disposed to have liquid fall therefrom into said chamber,

' means to supply liquid hydrocarbon fuel to said the vaporizer, and means for supplying combustion air to said non-combustion supporting gas mixture subsequent to its withdrawal from the vaporizer to provide a combustion supporting mixture for combustion in said combustion zone.

4. Liquid fuel combustion apparatus comprising wall structure forming a combustion zone, a vaporizer disposed in heat-receiving relationship to said wall structure and having a main chamber and an auxiliary chamber above said main chamber and in .communication therewith, a liquid feedingmember in said auxiliary-chamber disposed to have liquid fall therefrom into said main chamber, means to supply liquid hydrocarbon fuel to said feeding member, said vaporizer having a hot surface in said main chamber vertically below said feeding member, means to introduce an essentially inactive gaseous fluid containing products of combustion into said auxiliary chamber to enshroud the falling fuel, the

-last mentioned means including a cooler for cooling said gaseous-huid to a. temperature very much lower than thatof said vaporizing surface, means for withdrawing from said main chamber the non-combustion supporting mixturev formed in said main chamber, and means for supplying combustion air to said non-combustion support- GUs'rAF' aan; BJRKmND.

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