US2374569A - Heater - Google Patents

Description

' A Pl'il 24 1945 v. N. TRAMoN'nNl 2,374,569

HEATER Filed Nov. 15., 1943 v 2 sheets-sheet 2 Patented Apr. 24, 1945 HEATER `Vernon N. Tramontini, Chicago, Ill., assignor to Stewart-Warner Corporation, Chicago, Ill., a

corporation of Virginia Application November 15, 1943, Serial No. 510,280 i '12 claims. (criss- 77) My invention relates generally to heaters, and more particularly to improvements in liquid hydrocarbon burners especially adapted for use in aircraft heaters of the sealed combustion type.

It is an object of my invention to provide improved means for atomizing the fuel supplied to a sealed combustion chamber and to control the rate of supply of air for combustion.

A further object is to provide a liquid hydrci carbon burner with improved means responsive to variations in atmospheric pressure to control the rate of admission of combustion air to the combustion chamber.

A further object is to provide an improved burner and combustion chamber construction in Y which the rate of flow of air into the combustion chamber is automatically controlled conjointly by the pressure drop across the heater and the absolute pressure.

Other objects will appear from the following description, reference beingV had to the accompanying drawings, in which Fig. 1 is a central vertical sectional view of the combustion chamber and air and fuel admission the combustion chamber, it will be clear that of Fig. 1, rotated Y the apparatus may be used in any desired position, provided the igniter is appropriately located in the combustion chamber. l

In heaters, particularly those designed for use on aircraft, considerable difiiculty has been encountered in maintaining an adequate but not excessive supply of'air for combustion Ain the combustion chamber. This -diiiiculty has been more pronounced in heaters in which the mixing of the fuel and air takes place substantially in the combustion chamber, that is, in which the fuel is sprayed directly into the combustion chamber. These diliculties areovercome in the burner of my invention by varying the effective size of the inlet port through which air is supplied to the combustion chamber in accordance with the velocity of air flow, and in addition, controlling the effective size of the air inlet port in response to variations in atmospheric pressure. Thus, when the heater is used in an airplane, the volumetric flow is'increased with increased altitude, while the gravimetric rate of air ow to the combustion chamber is kept substantially constant- As shown in Fig. 1, the burner comprises a :gen-

erally elbow-shaped induction pipe casting lil` having flanges l2 and il. The casting lil may have a tubular extension it for connection to a ram' or blower, or other means for supplying air under pressure. A tubular sheet metal casing it is secured to the flange l2 and to the extension it. The upper portion of the casing ill, together with a tapering sheet metal section 2b, forms a combustion chamber 22. The upper end of the section 2i) isfwelded or otherwise suitably secured to the end wall 24 of a, heat exchanger 26. The latter may be of any suitable construction adapted to receive the products of combustion from the combustion chamber 22 4and to transfer heat to Ventilating air-which flows upwardly past the combustion chamber and associated parts and through or around the heat exchanger 26.

An igniter supporting tube 2B projects through the section 2l! and is suitably welded thereto, this tube having a threaded ring 30 secured thereto to receive an igniter shell 32. Within the igniter shell 32 is the usual hot, wire igniter 34, the inner end of which is secured to the shell 32 and the outer endl of which is suitably connected to a wire 36 which is insulated from the shell 32 and supplies energizing current to the igniter. Suitable thermostatic control means are preferably provided to cause energization of the igniter during starting, and in the event that the llame in the burner becomes extinguished.

Al baille 38, having4 a central opening surrounded by a flange 40, is secured to the ange I4 by a plurality of cap screws 42, being spaced there- `from by tubularseparators 44 surrounding the cap screws. The peripheral edge of the baille 38 has long narrow arcuate notches therein, t0 provide auxiliary ports y,for admitting air to the co-mbustion chamber. y

Fuel is supplied from a constant pressure source connected to the outer end of a nozzle member 48 which is rigidly secured to the casting l0 by a nut 50. The nozzle member 48 forms a spindle and has a central fuel conducting passageway 52 which terminates in' a small diameter passageway 54 having. a sidewardly directed portion registering with a iiow metering discharge port 56 formed.

in a sleeve 58 surrounding the reduced diameter end portion 60 of the nozzle member 48. The sleeve 58 is clamped to the end portion 60 by means of a self-locking'nut 62, which also serves t secure in place a, shield 84. 'Ihe shield 64 is welded to a supporting spider 66, and the latter is clamped in position by the self-locking nut 62.

A rotor. 88 includes a flaring atomizing cup 10, an impeller flange 12 carrying a plurality of impeller blades 14, and a sleeve portion 16. Within the sleeve portion 16 are located a ballbearing assembly 18 and a needle bearing assembly 80,

thus providing for free rotation of the rotor 68 annular space between the impeller ange 12 and 'Ihe bore 88 and beveled surface 90 of the sleeve 84 form part of a valve mechanism for controlling the rate of flow of air into the combustion chamber. I'he remaining portion of this control means is provided by a `plurality of segmental shutters 92 which, as best shown in Fig. 3, are six in number and overlap one another. Each of the `shutters 92 has a slbt 94 formed therein for the reception of a prestressed leaf spring 96. The ends of the leaf springs 96 project into guiding and motion limiting recesses 98 formed in the impeller flange 12. The leaf springs 96 are preferably formed as arms of a spider-like element, and

are clamped to the sleeve 16 by a bushing |00 which is threaded in the end of the sleeve.

The position of the sleeve 84 is determined by a plurality of aneroid bellows I 02, one end of each of which is rigidly secured to the flange I2, and each of which carries at its other end an arm |04 which projects through a suitable elongated slot |06 formed in the wall of the casting I0, the extremity of each of the arms |04 fitting into a groove |08 formed in the outer surface lof the sleeve 84, Thus, as the atmospheric pressure decreases, the bellows |02 will expand and move the sleeve 84 upwardly.

In the operation of the apparatus. air under pressure is supplied to the inlet extension I6 of the casting I4 and ows in the direction of the arrows past the impeller blades 14. causing the rotor assembly 68 to commence rotation. At the same time, fuel under relatively constant pressure, is supplied through the passageways in the nozzle member 48 and is discharged through the port 56 in the sleeve 58. Due to the centrifugal force resulting from the rotation of the rotor assembly the conical atomizing cup 10 in a thin nlm, and will be flung from the brim of the' atomizing cup 10 in very small droplets. These atomized particles of fuel will traverse the combustion air flowing through the annular space between the flange 40 and the external wall of the atomizing cup 10, andY will be thoroughly and substantially uniformly mixed with the incoming air to prov. .de `a combustible mixture. This mixture will be ignited proportioning of the air and fuel. substantially complete combustion will take place, within the combustion chamber 22 and within the inlet endA portion of the heat exchanger 28.

the wall of the bore 88. Such outward movement of the shutters 92 will reduce the rate of air flow to the combustion chamber, and thus cause a reduction in the speed of rotation of the rotor assembly'68. The shutters 92 will thus tend to assume a position in whichthe ,air ow into the combustion chamber is maintained at a predetermined rate. Since the shutters 92 overlap one another, and since they are pressed against each other and against the lower surface of the impeller flange 12, there will be a certain amount o1' friction impeding their movement, and these frictional forces will operate to damp the'movement of the shutters and prevent hunting.

Since the energy available for the rotation of the rotorv assembly 68 is proportional to the density of the air and the square of the velocity, it will be apparent that at higher altitudes the air would be supplied to the heater at a reduced gravimetric rate if no means were provided to make compensation for the reduction in density due to altitude. In the apparatus disclosed herein, such compensation is obtained by moving the sleeve |34 upwardly as .the atmospheric pressure decreases. Upward movement of the sleeve 84 brings the beveled surface 90 of the sleeve into f thev plane of the shutters 92. Since the outward movement of the shutters is limited by the engagement of the ends of the leaf springs 96 with the ends of the recesses 98, it willl be clear that the shutters will be progressively less eective v to reduce the air ow as the sleeve 8,4 is raised. The slope of the aring surface 90 of the sleeve 68, the fuel will ow upwardly along the walls of Aby the electricigniter 34, and due to the accurate If the pressure of the air supplied to the inlet Y extension I6 of the casting |0 is higher than that reduired to produce the flow of a weight of air adequate for'complete combustion of the fuel. thev 84 and the dimensions of the bellows |02 are such as to compensate correctly for the reduced density of the air at lower atmospheric pressure, with the ultimate lresult; that irrespective of the pressure drop across the heater, and irrespective of reductions in atmospheric pressure, the air will be supplied to the combustion chamber at a substantially constant gravimetric rate adequate to secure complete combustion of the fuel, which is likewise supplied at a constant rate.

Due to the preloading of the leaf springsl 96, the rotor assembly 68.will have to attain a predetermined minimum speed before the shutters commence moving outwardly partially to obstruct the air inlet passageway. For example, the preloading of the springs may be such. relative to the mass of the shutters 92, that outward movement of the shutters will not take place until a speed of 9,000 R. P. M. is attained. By way of further illustration, the springs 96 may be of such dimensions that they will continue to ex outwardly as the speed of rotation increases to 10,500 R. P. M.; at which speed the shutters will have moved outwardly to the maximum extent.l Thus, thel speed range of the rotor assembly may be relatively limited, thereb.v to secure accurate regulation of the rate vof air ow into the combustion chamber.

It will be noted that all of the air owing into the combustion chamber flows past the impeller blades, thus improving the response of the apparatus to changes in air flow rate, as

peller blades flows through the annular space inside the ange 40 of the baille 38. The baille 38 is provided with long narrow arcuate notches along its periphery, so that a limited quantity shield is connected to the nozzle member by,

three arms of the spider 66, the rate of heat conduction to the nozzle extension 60 .and its sleeve 58, will be relatively low. Thus the end portion 60 and the sleeve 58 remain sufficiently cool to prevent vaporization of the fuel flowing through the passageway 54' and port l58. Likewise, the transmission of excessive heat to the bearing assembly `'i8 is prevented. The 'flow of cool air past the outer surface of the atomizing cup I keeps the latter from becoming overheated.

Since the tendency of the fuel is to break up into droplets at the rim of the atomizing cup, and, due to centrifugal force, the droplets tend to traverse the annular space through `which the majority of combustion air is' flowing, a very intimate and uniform mixture of the atomized fuel and air is obtained.

Due to the segmental shape of the shutters 92, and due to the fact that they overlap one another, they are effective, as they are swung radially outwardly, progressively to decrease the effective cross sectional area of the air inlet passageway. Because of their simplified construction and arrangement, the shutters may move independently of one another and thus provide an averaging effect'shouldone of the shutters fail to move outwardly smoothly as the speed increases.

While I have shown and described a particular embodiment of my invention, it will be apparent that numerous variations and modications thereof may be made without departing from the underlying .principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention, all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the.

same or equivalent means.

I claim:

1. In a liquid hydrocarbon fuel burner, the combination of a` source for supplying liquid fuel at a substantially constant pressure, a nozzle member having a flow metering outlet port, an atomizing cup of generally conical conformation surrounding said nozzle adjacent said port, antifriction'. means for mounting said atomizing cup for rotation, means having a passageway to direct ow of air past the outer surface of said atomizing cup, impeller blades located in the path of flow of air, said impeller blades being secured to said atomizing cup to cause rotation thereof upon flow of air, and means rotated with said atomizing cup and operable in response to centrifugal force to decrease the eifective size of said passageway, said means being restrained by preloaded resilient means so as to have 'a limited e'ective operating lllllge.

2. In a heater adapted for the heating of aircraft in which the pressure and density of the combustion air may vary considerably due to variation in speed and altitude of the aircraft,

the combination of means forming a combustion chamber, an" inlet passageway for conducting air for combustion to said combustion chamber, a fuel supply nozzle, an atomizing element mounted forrotation with respect to said nozzle and receiving fuel therefrom, means forming a passageway for conducting combustion air past said atomizing element into said combustion chamber, an impeller in said passageway carriedv ply fuel at a constant rate to said nozzle.l

3. The combination set forth in claim 2y in which said shutter mechanism comprises a plurality of segment shaped sheets overlapping one another in normal position and said preloaded resilient means comprises a plurality of leaf springs each operatively connected to one of said shutter sheets resiliently to hold the latter toward the axis of rotation of said atomizing element.

4. In an aircraft heater, the combination of a fixed nozzle member having a spindle portion provided with a discharge port, an atomizing cup mounted for `free rotation on said spindle portion, means forming a combustion air conducting passageway around said atomizing cup, a pluralityof impeller blades secured to said atomizing cup and extending across said passageway, speed responsive means for decreasing the effective area of said passageway as the speed of rotation of said atomizing cup exceeds a predetermined minimum value, and atmospheric pressure respon'- sive means for increasing the effective area of said passageway as the atmospheric pressure decreases.

5. The combination set forth in claim 4, in which a movable sleeve having a. non-uniform diameter bore forms the external Wall of said passageway, and in which said atmospheric pressure responsive means comprises aneroid bellows operatively connected to said sleeve formovlng the` latter upon changes in atmospheric pressure.`

6. The combination set forth in claim 4, in

which the external wall of a portlon'of said passponsive means comprises a plurality of centrifugally operating shutters cooperating with said sleeve to determine the cross sectional area of the'passageway through said sleeve, and in which said atmospheric pressure responsive means comprises an aneroid bellows connected to said,sleeve for moving the latter upon changes' in atmospheric pressure.

7. In a liquid hydrocarbon fuel burner, the combination of a source for supplying liquid fuel at a substantially constant pressure, a nozzle member having a flow metering outlet port, an atomizing cup of generally conical conformation surrounding said nozzle adjacent said port, antifriction means for mounting said atomizing cup for rotation, an air passageway surrounding said cup, a. source of air under pressure connected to said passageway, impeller blades located in the pathl of flow of air, said impeller blades vbeing secured to said atomizing cup to cause rotation thereof upon now of air from said source through said passageway, and means conjointly responsive to the atmospheric air pressure and the speed of rotation of the atomizing cup for controlling the flow of air to said passageway.

8. In a heater having a combustion chamber, means -forming an annular passageway for conducting air under pressure to said combustion chamber, an atomizing cup having impeller blades in said annularV passageway, said atomizing cup being mounted for free rotation, means to supply fuel to the inside of said atomizing cup, means to shield said atomizing cup from the heated gases in said combustion chamber, and a baille extending across said combustion chamber and having an opening to provide an annular port surrounding the combustion chamber end of said atomizing cup, and having aplurality of openings along its periphery for admitting air for combustion to said combustion chamber.

9, In an aircraft heater, the combination of'- a nozzle member having a spindle portion provided with a discharge port, an atomizing cup mounted for free rotation on said spindle portion, means forming a combustion air conducting passageway around said atomizing cup,` a plurality of impeller blades secured to said atomizing cup and extending across said passageway, and speed responsive means for decreasing the effective area of said passageway as the speed of rotation of said atomizing cup exceeds a predetermined minimum value.

10. In an aircraft heater, the combination of a nozzle member having a spindle portion provided with a discharge port, an atomizing cup mounted for free rotation on said spindle portion, means forming a combustion air conduct- Y ingpassageway around said atomizing cup, a plurality of impeller blades secured to said atomizing cup and extending across said passageway, and atmospheric pressure responsive means for increasing the effectvie area of said passageway as the atmospheric pressure decreases.

1v1. In an aircraft heater, the combination 0f a'nozzle member having a spindle portion provided with a discharge port, an atomizing cup mounted for rotation on said spindle portion, means forming a combustion air conducting passageway, an impeller in said passageway rotated at a speed changing with the rate of mass flow of air through said passageway, a driving connecticn between said impeller and said atomizing cup to rotate the latter, and means responsive to the speed of rotation of said impeller for decreasing the effective cross sectional area of said passageway as the speed of rotation of said impeller exceeds a predetermined minimum value.

A12. In an aircraft heater, the combination of a nozzle member having a spindle portion provided with a discharge port, an atomizing cup mounted for rotation on said spindle portion, means forming a combustion air conducting passageway, an impeller in said passageway rotated at a speed changing with the rate of mass flow of air through said passageway, a driving connection between said impeller and said atomizing cup to rotate the latter, and means to increase the effective cross sectional area of said passageway as the atmospheric pressure decreases.

lVERNON N. TRAMONTINI.

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