US2417604A - Heater having means for diverting and igniting a fuel-air mixture - Google Patents

Description

March-18,1941 H. J. DE N.Mcco|.1.uM 2,417,604

HEATER HAVING'IIEANS FOR DIVERTIENG AND IGNITING A FUEL-AIR MIXTURE Filed l larch e, 1943 2 Sheets-Sheet 1 1 Q lav ws- March 18, 1947,

H. J. DE N. MCCOLLUM HEATER HAVING MEANS FOR DI-VERTING AND IGNITING A FUEL-AIR MIXTURE Filed March 6, 1943 2 Sheets-Sheet 2 2kmw Patented Mar. 18, 1947 UNITED, sures PATENT- OFFICE HEATER HAVING: MEANS FOR- DIVERTING AND IGNITIN G A FUEL-AIR MIXTURE Henry J. De N. McCollum, Chica o, [1].; Thelma McCollum, executrix of said Henry J. De N.

McCollum,

deceased, assignor to Stewart- Warner Corporation, Chicago, 111., a corporation of Virginia Application March 6, 1943, Serial No. 478,258

Another object ofv my invention is to provide a heater having igniting means which is efiective atextremely low temperatures.

Another object of my invention is to provide a new and improved heater which can be easily started in all positions.

Another object of my invention is to provide a heater having improved igniting means which is particularly effective with heavy fuels.

Other objects and advantages will become apparent as the description proceeds.

In thedrawings:

suitably attached to its inner wallfa series of U-shaped copper strips 2| providing inwardly projecting fins forming longitudinally extending gas passages 22 for gases traveling from the combustion chamber 14 to an outlet chamber 24 from which these gases are discharged to atmosphere through anexhaust pipe 26. u-shaped strips 28 of copper or other suitable material have their bases brazed or otherwise suitably secured to the outer wall of the shell I 9 and form outwardly projecting longitudinally extending fins.

A muiiler 3D is located in the heat exchanger and serves to direct the hot gases of combustion into the lefthand or inlet ends of the gas passages 22. This muiller comprises a sheet metal shell 32 provided with metal partitions 34 which divide the shell into a plurality of compartments filled with sound absorbing material 36, such as stainless steel wool or glass wool. Each compartment has an annular series of openings 36 providing acoustic coupl ngs between the interior of the compartment and the gas passages 22. The lefthand end of the mufller is provided with a heat insulating disc 40 of fire clay or other suitable material Fig. 1 is a longitudinal, sectional view through Fig. 4 is a partiaLsectional view of a detail and is taken on the line 4-4 of Fig. 3; and

Fig. 5 is a view showing a partial, transverse section taken on the line 5-5 of Fig. l.

The heater shown in the drawings comprises a cylindrical casing 10 connected to an air inlet l2 supplied with air by a ram, blower, or any other suitable means. The air flowing into the inlet l2 passes over and around a combustion chamber l4 and into the ventilating air passages formed between a heat exchanger 16 and the casin l0. As the air passes over the heat exchanger. l6, its temperature is raised by absorption of heat from the heat exchanger and the heated ventilating air passes from the heat exchanger l6 and into the outer or righthand end of the casing II] which is illustrated as communicating with a duct l8 leading to a cabin or other space or spaces to be heated.

' secured in place by screws 42.

The muffier is freely slidable in the heat exchanger l6 and is held in place by a pin 44 attached to the righthand' end of the muffler and having a threaded extension 46 passing through the sleeve 48. welded or otherwise secured in a wall of the exhaust pipe 26. A nut 50 is threaded to the end of the extension 46 and firmly secures the mufiler in fixed position. This muiller is claimed in my co-pending application, Serial No. 478.259, filed March 6, 1943, and requires no further description herein. Part of the heated air leaving the heat exchanger enters the inlet 52 of a combustion air pipe 54 leading to a carburetor 56. The particular carburetor shown is of the altitude compensating type and has the usual float bowl 58 connected by a pipe 60 with any suitable source of fuel. A jet 62 located in the throat of the Venturi tube 64 supplies fuel to the air flowing through this Venturi tube. As best shown in Fig. 3, the inlet 52 of the combustion air pipe 54 is considerably higher than the carburetor float bowl 58 and Venturi tube 64. This arrangement makes it impossible for fuel to flow from the carburetor through the combustion pipe 54 to the ventilating air duct [8 andcasing I0 if flooding of the carburetor should occur. This is an important feature of my invention, since discharge of fuel into the ventilating air might result in explosions or fire which would destroy or damage the aircraft and its occupants or might result in the discharge of unhealthy fumes into the aircraft cabin.

The Venturi tube 68 delivers a mixture of fuel and air to the inlet end of an induction pipe 68 having a relatively long port on 68 extending lengthwise of the casing l8. The induction pipe 66 is provided with an elbow I8 connecting the long straight portion 68 with a short straight portion 12 passing through the casing l8 and cylindrical wall 14 of the combustion chamber I4 and connecting with a preheating portion I6 wh ch is curved about the axis of the combustion chamber and lies closely adiacent th wall 14 of this chamber. The induction tube 68 is preferably of uniform diameter and has an internal surface free from obstructions and interruptions. The outlet end 18 of this induction tube delivers the combustible mixture to the combustion chamber in a direction tan ential to the cylindrical wall of this chamber whereby the combustible mixture whirls about the axis of the combust on chamber, as fully explained and cla med in my co-pending a plication, Serial No. 477,080, filed February 25,

combustion chamber and to draw the hot gases formed in th s chamber through the passages 22 in the heat exchanger. The pressure drop across the carburetor which is available for discharging fuel through the jet 62 is very sli ht. with the result that the fuel is not discharged by this jet in a cont nuous un form spray. Instead this spray is interrupted and irregular. althou h of un form volume over anv appreciable period of time. However, the lack of uniform ty in this sprav makes the mixture of fuel and air delivered to the induction pipe 86-vary somewhat in richness and where such a varying mixture is delivered to t e combustion chamber. the heater ooerates w th a sputtering noise which is difficult to muflle.

A feature of my present invention lies in the particu ar arran ement of the carburetor and the pipes 54 and 66 whereby the carburetor is close to the inlet of the combustion air supply pipe 54 and remote from the outlet of the induction pipe 86. The long induct on pipe 68 permits the variable fuel and air mixture sup lied to it by the carburetor to mix more thoroughly and acquire a more homo eneous composition before entering the combust on chamber. This thinning out of the fuel and airmixture is aided by the preheating of the combustion air which is supplied to the carburetor 56 through the elevated inlet 52.

The combust on mixture supplied to the combustion chamber I4 is ignited by an electrical igniter 88 to form a ring of flame in the combustion chamber. This igniter may be of the conventional type having a hot wire 82 located in the lower end of a sleeve 84 and is screwed into a housing 86 projecting to one side of the combustion chamber and attached to the cylindrical wall of this chamber by weld ng or in any suitable manner. The hous ng 86 has a. cylindrical passage 88 of slightly larger. diameter than the sleeve 84. An inlet 98 connects the upper end of passage 88 with the interior of the combustion chamber and an outlet 92 connects the lower end of the passage 88 with this chamber.

When the heater is first started, the igniter wire 82 attains ignition temperature in a very few seconds and the sleeve 84 almost immediately reaches a fairly high temperature. The fuel and air mixture delivered to the combustion chamber by the induction pipe 68 is unheated and any liquid fuel contained in this mixture flows along the cylindrical wall of the combustion chamber and passes through inlet 98 into passage 88 where it is vaporized by the hot sleeve 84. A certain amount of air also enters the inlet 98, as indicated by the arrows, and flows downwardly between the sleeve 84 and walls of the passage 88. The vaporization of the liquid. fuel in this passage produces a rich mixture of fuel and air which is readily ignited by the hot wire 82. The resulting combustion produces a torch-like flame which is blown out of the outlet 92 along the adjacent wall of the portion 16 of the induction tube to meet this tube and ignite the mixture in the combustion chamber I4. After the heater has attained normal operating temperature, the ring of flame formed in the combustion chamber suffices to maintain combustion therein and the igniter 88 is disconnected from its source of electrical current by the usual thermostatic switch.

In some instances, all of the fuel in the mixture delivered to the combustion chamber will be mixed with air and there will be no liquid fuel to flow along the wall of the combustion chamber and through the inlet 98 to the passage 88 around the igniter 88. However, the richer part of the mixture of fuel and air is the heaviest part of this mixture and tends to follow around the wall of the combustion chamber, whereas that portion of the entering air which contains little fuel is less responsive to centrifugal force and more readily flows toward the center of the combustion chamber. The rich mixture of fuel and air following along the wall of the combustion chamber enters the inlet 98 and flows downwardly between the igniter 88 and walls of the passage 88 to be ignited by the hot wire 82.

The particular arrangement of the igniter illustrated and described has proved particularly advantageous with all sizes of heaters to which extremely cold air is supplied, for example, where an airplane is operating under atmospheric temperatures of 30 to 60 below zero. This arrangement has also proved particularly advantageous in heaters of large capacity even where these heaters are supplied with air at relatively mild temperatures. In heaters of large capacity, a single electrical igniter is usually incapable of creating sufflcient heat in the combustion chamber to ignite the fuel and air mixture therein and it has been common practice to provide such large heaters with a plurality of igniters which operate simultaneously. Such an arrangement is costly and the several igniters consume an undesirably large amount of current, whereas my novel arrangement utilizes a single igniter of conventional size and is more effective in starting combustion in large heaters than are the several igniters heretofore used.

While my igniter is located in a pocket outside of the combustion chamber proper, this pocket is so arranged that it can not become filled with liquid fuel. The lower end of this pocket or passage 88- communicates with the combustion chamber through outlet 92 so that any liquid fuel supplied to this pocket and not ignited therein flows back into the combustion chamber through outlet 92 instead of forming a pool ofvliquid in the lower end of the pocket.

' Where the heater is intended to be used with kerosene or other relatively heavy fuel, it is desirable to establish a heat transfer path between the lower end of the housing 86 and the adjacent portion 12 of the induction tube. In Figs. 3 and mitted to the inlet end of the heater. The heat from the hot wire 82 causes the entire igniter 80,

' .housingfl-S and portion 72 of the induction tube to become quite hot and as soon as these parts have reached the desired temperature, air is admitted to the heater inlet. The resulting flow of fuel and air mixture to the combustion chamber is sufficiently preheated by the section 12 of the induction tube to ignite readily upon entering the combustion chamber and coming in contact with the igniter 80. with gasoline or other light fuels, air is ordinarily admitted to the heater at the same time the isniter switch is closed and the silver solder 94 maybe dispensed with.

Where the heater-is used in the horizontal position shown in Fig. 1, .there isa tendency for any liquid fuelentering the combustion chamberto pass from the righthand end of this cham-v ber before it travels along the cylindrical wall of this chamber a suflic'ient distance to enter the Where the heater is operatedinlet 90 leading to the igniter 80. I, therefore, Y

provide the outlet end of the combustion chamber with a ring 96 which causes liquid fuel entering the combustion chamber from the induction pipe to follow along the circular wall of this chamber and pass through inlet 90 and into the space around the igniter 80. As previously explained, the heat of the igniter vaporizes this liquid fuel and produces a rich fuel and air mixture which is readily ignited by the hot wire 82.

Where the. heater is operated in an inclined position with the righthand end of the heater substantially elevated, the force of gravity prevents liquid fuel from leaving the combustion chamber before it has followed around the walls of this chamber suflicientl'y to enter the passage around the igniter 90. Under these conditions,

the ring 96 is unnecessary and is preferably, butnot necessarily, omitted.

From the foregoing description taken in connection with the accompanying drawings, it will be apparent that the advantages which I,have described are provided by a simple, lightweight structure whichis economical to manufacture and which is sturdy and capable of long, troublefree service. While my heater is particularly adapted for use on aircrafts, it is not limited to such use, but may be used for general application. Although I have illustrated and described only a single embodiment of my invention, it is to be understood that my invention is not lim ited to-the details shown and described, but may assume numerous other forms and that the scope of my invention is defined in the following claims:

1. In a heater of the class described, means forming a combustion chamber having a cyllndrical wall, a housing attached to said wall exteriorly thereof, said housing including a passage which extends in circumferential direction with relation to said cylindrical wall, saidwall having an inlet therethrough connecting one end of saidpassage with said combustion chamber and an outlet therethrough connecting the other end of said passage with said combustion chamber,

2. In a heater of the class described, means.

forming a combustion chamber having a wall provided with/an arcuate segment, means for delivering a combustible mixture of fuel and air at one end of said segment and in a direction to flow along said segment, means providing a passage outside of said combustion chamber but in communication with said chamber adjacent said end of said segment whereby fuel and air flowing along said segment enters said passage by the action of centrifugal force, and an igniter for vaporizing liquid fuel in said passage and igniting combustible mixture therein, said passage having an outlet communicating with said combustion chamber at the other end of said segment through which outlet the ignited mixture flows into the combustion chamber.

ing an induction tube intersecting the cylindrical wall of the combustion chamber and having its terminal portion curved around the inner surface of said wall whereby the mixture flowing through said curved portion of the tube absorbs heat from the combustion proceeding in said chamber.

4. In a heater as defined in claim 1, said means for supplying the combustible mixture comprising an induction tube intersecting the cylindrical wall of the combustion chamber and having its terminal portion curved around the inner surface of said wall, said combustion chamber having an end wall and an annular flange extending inwardly from its cylindrical wall in spaced relation to said end wall, said curved terminal portion of the induction tube and said inlet and outlet of the igniter housing being disposed between said end wall and said flange.

HENRY J. DE N. McCOLLUM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES ra'ran'rs

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