US2445466A - Fluid fuel combustion device - Google Patents

Description

y 94 A. A. ARNHYM FLUID FUEL coiBus'rIonnEvIcE Filed Jun 2. 1944 2 Shasta-Sheet 1 Q\ R i O O O O O O O O a Ii 1: n kw v $N NW 0 m QM O O O O O. :1 9 mm a all! g mm my & o o o o 9 QM m \m w QM m H 2 mm p u t W W mm mm 1 if m\ \w MN vmw Q N a w MN [wan/roe. ALBEETA-AHVHY Arro July 20, 1948. A. A. ARNHYM I FLUID FUEL COIBUSTI QN DEVICE 2 Sheets-Sheet 2 Filed June 2, 1944 fvvewro. I A4esez-A.Amvuy/m /11W Aria NEY.

Patented July 20, 1948 FLUID FUEL COMBUSTION DEVICE Albert A. Arnhym, Los Angeles, Calif., as'llgnor to Solar Aircraft Company, San Diego, Call! a corporation of California Application June 2, 1944, Serial No. 538,517

This invention relates to combustion devices burning fluid fuels, such as gasoline, and is particularly useful for providin heated air on, gasoline powered vehicles such as aircraft.

An object of theinvention is to provide a fluid fuel combustion device that has a large heat capacity in proportion to its weight and bulk.

Another object is to provide a device for burning liquid fuel such as gasoline substantially completely so that the exhaustcontains no unburned and poisonous ingredients such as carbon monoxide.

Another object is to provide a combustion device that has substantially uniform heat capacity, and operates reliably over a wide rangeof air pressures corresponding to different altitudes.

Another object is to provide a, gasoline burning combustion device that is capable of burning aviation gasoline containing lead without the lead interfering with the operation of the heater or being discharged as a toxic ingredient with the exhaust gas.

Still another object is to provide a gasoline burning device suitable for operation on aircraft, in which the controlsare largely automatic so that it is only necessary to vary the rate of flow of fuel to the heater to vary the output, the control of the air supply being automatically effected to compensate for variations in the fuel supply and for variations in the atmospheric pressure due to altitude changes.

Various other more specific objects and features of the invention will become apparent from the detailed description to follow with reference to the drawings.

Essentially, the heater of the present invention comprises an elongated combustion chamber, into which a rich mixture of fuel and air is forced at one end and auxiliary air to complete the combustion' is introduced at successive points between the ends of the combustion chamber so as to completely burn a hydrocarbon fuel to water air heated to a temperature desirable for introduction either into passenger compartments or many portion of the airplane structure where heat is desired 3 Claims. (Cl. 26319) 2 In the drawings: Fig. l is a side view with portions broken away of an actual embodiment of the heater;

Fig. 2 is an end view looking at the right end of Fig. 1, with portions broken away;

Fig. 3.15 a schematic view showing, i addition to the structure of Figs. 1 and 2, certain auxiliary elements necessary in the complete system; and

Fig. 4 is a detail section of a portion of the per- 'forated tube through which the fuel-air mixture is discharged into the combustion chamber.

The elements of the heater and their functions will first be described with reference to Figs. 1

- and 2, after which the operationwill be described with reference to those figures in conjunction with the schematic diagram of Fig. 3.

The heater is largely self-contained within a housing which comprises a cylindrical casing l0 and an auxiliary casing H, the latter consisting of a pair of'end walls l2 and I3, side walls I4 and I5 and a top wall Hi. The end walls l2 and [3 have concave lower edges fitting against and secured to the cylindrical casing ill, a portion of which forms the bottom wall of the auxiliary casing. The side and top walls are secured to the end walls and are removable.

The cylindrical casing l0 contains a combustion chamber l'l therewithin, the combustion chamber being centrally disposed within the cylindrical casing and extending through almost the full length of the latter which serves as a conduit to conduct the air to be heated past the combustion chamber.

As shown, the heater is particularly adapted for burning gasoline which is supplied from a reservoir (not shown) through tubing [8 to an electrically driven.fuel pump 20, the pump 20 delivering the fuel at a rate of flow proportional to the pump speed so that the rate of flow can be varied by varying the current supplied to the pump in a manner to be described later, From the pump 20 the fuel flows through an electrically actuated safety shut-off valve l9 and through a feed line 22, from the end of which it is sprayed into an air stream flowing into the combustion chamber ll.

additional cold air to provide a large volume of Air is supplied from any suitable source, such as a blower 12, through a duct 23 and through a control valve 24 to a manifold 25, from which it flows to the combustion chamber through three fuel line 22 so that all of the air flowing through.

duct 26 is mixed with the fuel issuing from the line 22 to form a rich mixture which is conducted into a perforated tube 28 which extends into the left end of the combustion chamber and is provided with a large number of apertures 29, through which the mixture is discharged in numerous small jets into the combustion chamber. The mixture burns as it issues from the apertures 23 but since, as previously stated the mixture is over rich, the combustion is not completed at this point. To complete the combustion, auxiliar air enters the combustion chamber from the manifold 25 through a second duct 30 and through a third duct 3|. The duct 39 is juxtaposed to the inlet tube 28 and discharges directly into the combustion chamber through a single large orifice. On the other hand, the duct 3i communicates with the combustion chamber substantially at its middle and the air is distributed through an annular row of apertures 32 in a venturi member 33 which is provided in the combustion chamber. The outer surface of the venturi member 33 defines. with an annular collar 34, an annular manifold through which the air is distributed from the duct 3| to the apertures 32. I

The air is supplied to the manifold 25 by the control valve 24 at a relatively low pressure, only slightly above the pressure of the surrounding atmosphere, and the venturi member 33 reduces the pressure within the combustion chamber adjacent the apertures 32 so as to facilitate the entry of a sufficient amount of air through the holes 32 to complete combustion of the fuel. This combustion is substantially completed by the time the gases reach the right end of the combustion chamber where they are discharged laterally into an air stream which flows through the cylindrical casing in from right to left.

, The first or leftmost portion of the combustion chamber l1 acts in part as a generator in which primary combustion takes place, which combustion is facilitated by the spply of secondary air received through the duct 30. By. the time the gases leave the part of the combustion chamber adjacent the inlet tube 28, they are still burning but contain a considerable percentage of carbon monoxide. The mixture in the combustion chamber to the right of the venturi 33 consists of burned exhaust gases, carbon monoxide and air, and the air is supplied in suflicient amount to complete combustion of the carbon monoxide so that the final exhaust products contain neither carbon monoxide nor any other unburned toxic gas or fumes.

' As illustrated in Fig, l, the cylindrical casing III of the heater is open at both ends and flow of air (hereinafter referred to as ventilating air) therethrough from right to left is merely indicated by arrows. In practice, however, it is to be understood that the casing ill will be connected at its right end to a suitable source of air such as a scoop or a blower. If the heater is to be used only during flight, an air scoop suitably situated on the airplane will sufiice but if the heater is to be used on the ground as well as in the air it may be desirable to provide a power 4 lating air. As shown in Fig. 2,.this cylindrical bailie 38has vertically extending flanges at the top and bottom which connect it to the casing Ill. The combustion chamber itself is supported from the baffle 38 by numerous curved strips 31 which extend therebetween. By virtue of the curvature of these strips 31, they can readily yield to compensate for expansion and contraction of the combustion chamber as its temperature changes.

It will be observed from Fig. 1 that closely adjacent the outlet the combustion chamber is constricted to form a neck 33 of reduced diameter. This tends to increase the velocity of the ventilating air as it flows past the annular discharge oriflce 39, which decreases the static pressure at that point and facilitates the flow of the products of combustion into the ventilating air stream. The annular discharge orifice 39 is formed in part by the rear end of the combustion chamber proper and in part by a cap 43 of cup shape havingits concave side directed toward the end of the combustion chamber. This cap 40 serves not only as a deflector for deflecting the products of combustion laterally through the orifice 39 but also serves to accumulate a portion of the lead deposit that results from operation with high octane aviation fuel containing tetraethyl lead.

In addition to the functions recited, the cylindrical shroud 36 also aids in sound-proofing the assembly and the shroud is sufflciently cooled by the air stream flowing between it and the cylindrical casing Hi to cause further deposition of lead in it. A filter 42 at the extreme left end of the casing l0 abstracts what lead may be left in the air prior to its discharge from the heater.

It is to be noted particularly that the ventilating air flows through the heater in direction opposite to the flow of the burning gases within the combustion chamber. This construction has distinct advantages. burning gases into a duct used to convey the heated air away from the heater since any gases that might be still burning at the time they issued from the annular orifice 39 are blown back along the outer surface of the combustion chamber and quickly extinguished. Another advantage is that the ventilating air is applied while it is still relatively cold to the discharge end of the combustion chamber which gets considerably hotter than the inlet end, thereby preventing over-heating of the combustion chamber wall. The .arrangement also causes thorough mixing of the products of combustion issuing from the orifice 39 with the ventilating air within the shroud 38.

Heretofore when burning leaded gasoline in a heater having a perforated member such as the tube 28 through which a mixture of fuel and air is discharged and ignited, trouble has been encountered due to depositions of lead compounds adjacent the outer orifices of the apertures in the memberwhich eventually clog the apertures and render the device'inoperative. Such difficulties are prevented in the present construction by chamferlng or counter-sinking the outer orifices of the apertures 29 as shown in the detail view of Fig. 4. It is found that with this construction as soon as a slight deposit has formed in the outer portion of an aperture it breaks away and the apertures remain clean for a long period of service.

As has been previously indicated, the rate of combustion andthe quantity of heat generated is varied by varying the rate at which liquid fuel is delivered through the tubing 22 and the air It prevents leakage of any supply is automatically varied to correspond. This automatic control of the air supply is obtained with the valve 24 which is jointly responsive to the pressure of the fuel'in the feed line 22 and to the air in the manifold 25. This valve comprises a casing 43 deflning a straight-through air passage between the air supply duct 23 and the manifold 25, which passage is adapted to be variably blocked by a, butterfly 44 which is connected by a link 45 to a diaphragm 40 mounted in a case 41. The under side of the diaphragm is exposed to the pressure in the manifold 25 on the discharge side of the butterfly 44 through an aperture 48, the link 45 extending through this aperture and through a slot 49 in the butterfly 44. A small amount of leakage takesplace through the slot 40 but it is not important. The major portion of the upper surface of the diaphragm 46 forms one wall of a sealed chamber 50, the other walls of which chamber are constituted by the upper portion II of the diaphragm crease rather than increase the flow of air. avoid such a contingency, a limit control is provided which decreases the speed of the fuel pump 20 until its pressure balances the maximum available air pressure. This control includes a rheostat II which is varied inresponse to opening of the butterfly 44. 'Thus there is secured to one end of the shaft 51 of the butterfly the movable contact I! of the rheostat 58, which movable contact, through the initial portion of the opening movement of the butterfly 44, rides on a low resistance conductor 50 but during the final opening movement of the butterfly'rides over the housing and by a Sylphon bellows 52 which extends verticallybetween the diaphragm and a fitting 53 in the cover 5|, which fltting connects to the feed line 22. l I

By virtue of the construction described, the major portion of the upper area of the diaphragm 48 is exposed to the substantially constant pressure of the sealed chamber and the remainder of the area is exposed to the pressure of the liquid in the fuel line 22. A light spring 55 moves the diaphragm 46 upwardly and closes the butterfly 44 when the fuel pump 20 is not operating and there is no pressure in the fuel line 22. However, when the device is set in operation and fuel pressure is developed in the, feed line 22, this pressure acting on the upper portion of the diaphragm 48 that is within the Syiphon bellows 52,-moves the diaphragm 46 downwardly, thereby opening the butterfly 44 and admitting air for combustion into the manifold 25. The air pressure within the manifold is applied through the opening 40 to the under side of the diaphragm 48 opposing the force exerted on the upperside of the diaphragm by the fuel pressure, and the butterfly 44 assumes a position in which the opposing forces are in equilibrium.

The structure described functions to providethe proper mixture of fuel and air for good combustion despite variations in the fuelsupply resulting from variations in the speed (manually controlled) of the fuel pump 20 and variations register 86; As will be explained in detail later with reference to the schematic diagram of Fig. 3;

the rheostat l. is connected in'iseries with the motor ofrthe fuel pump 20 so that it does not affect the speed of the pump so long as'the movable contact 58 is on the low resistance conductor l0 but-substantially reduces the speed of the fuel pump in response to final movement of the butterfly 44 into fully open position.

Should the air pressure drop below the value necessary to fully open the butterfly 44, a pressure responsive switch ll (Fig. 2) connected to the valve casing ahead of the butterfly 44 operates to open" the circuit to the fuel pump and thereby shut the heater down. The circuit will in the absolute pressure of the air due to changes heat output and the altitude is such as to reduce the atmospheric pressure to the minimum value for which the heater is designed, the butterfly 44 is substantially wide open. At any lower altitude or at any lesser fuel pressure the butterfly is only partially open. At sea level with maximum fuel flow,-the butterfly is. about one-third open in a heater designed for use at a maximum altitude of 40,000 feet.

The air supply through the inlet duct 23 may come from a scoop on the surface of the airplane or from a blower. If desired, the same scoop or blower may be used for supplying both the com bustion air and the ventilating air.

If for any reason the pressure of the air supplied through the duct 23 should be insufficient to balance the fuel pressure or, in other words, there is not enough mass flow of air for a given fuel flow. the butterfly 44 will tend to move beyond the wide open position, which would debe describedin detail later with reference to the schematic diagram of Fig. 3.

In the event the air pressure within the valve casing 48 ahead of the butterfly should rise too high, it might interfere with the proper functioning of the butterfly 44 due to the creation of turbulence in the flow therepast and it is therefore desirable to provide a static relief valve 62 between the valve casing 43 and the cylindrical casing I! so that in case of excess pressure some air can be vented from the casing 43 into the venting air passage of the heater. As shown, this relief valve 42 consists of a butterfly, the shaft of which is eccentrically disposed so that air pressure on the upper side thereof tends to open it.

Opening movement is resisted by a torsion spring l2 surrounding one end of the butterfly shaft and connected between the shaft and the housing.

In addition to the electrical elements already mentioned. various other controls, both electrical and non-electrical, are incorporated into the system and they will now be described with reference to the schematic diagram of Fig. 3, in which parts corresponding to those of Figs. 1 and 2 bear the same reference numerals.

The system is usually operated from a source of direct current such as a battery 44, one terminal of which is grounded and the other terminal of which is connected to a supply lead it which extends to a combination rheostat and switch in a control unit 85 which may be remotely positioned from the heater proper if that is desirable. It will be observed that the lead 88 is connected through a fuse 01 to amovable arm or contact 68 which is adapted to ride over a low resistance contact 0! and also a resistor 10. The rheostat is shown in the oil position. When it is desired to start the heater, the arm 88 is moved clockwise to make contact with the elements 69 and Ill. Current thereupon flows through the contact 44 and through a lead Ii to an-electrically driven blower 12, it being assumed that in this instance such a blower is provided for upplying the combustion air to the heater. As soon as the blower l2 attains its normal operating speed, it produces a static pressure within the valve casing 42 (Fig.

1| 1) which actuates the pressure responsive switch 8| to close the contacts thereof and complete a circuit from the lead II over a lead 18 and thence through the winding of a relay 14, through a lead I8, through the winding of a thermal relay I8 and a lead 11 to an ignition wire 18. the other terminal of which is grounded. This ignition wire 18 is mounted on the exterior of tube 28 (Fig. l) and is normally heated to a temperature sufllcient to ignite fuel in the combustion chamber whenever the heater is in operation. To protect the ignition wire '18 from air currents that would tend to cool it excessively, a trough-like shield 18 is provided which is positioned substantially concentrically with respect to the wire, 18 and be tween it and the tube 28. i

The relay ll operates almost immediately upon closure of the circuit described and the thermal relay 18 operates shortly thereafter. Operation of relay l4 closes a first pair of contacts Ill, completing a circuit from lead 13 through the solenoid relay l9, opening the latter to permit fuel to flow from the fuel pump 20 to the feed line 22.

Movement of the movable contact 88 onto the left end of the resistor applies current directly overa lead 80 and to one contact of a pressure responsive switch 82 on the cylinder H).

To indicate to the operator whether or not the system is functioning, various signal lamps may be mounted on the control unit 85. Thus a lamp 84 is connected between the lead 88 and a lead 85 extending to a thermal switch 88 mounted within the casing H) to indicate whether or not heat is being supplied. A second lamp 8'! is connected directly to the contact 89 to indicate whether or not current is being supplied from the battery 84 when the switch has been turned on.

When the system described is in use on an airplane flying at varying altitudes, the density of the air supplied for combustion is substantially less at high altitudes than at low altitudes. In other words, the device forcing the combustion air into the heater, whether it be the blower 12 of Fig. 3 or a scoop on the exterior of the airplane, is not intended to develop a pressure equal to the actual variation in pressure between sea level and the higher altitude at which the plane may fly. The heater is designed to provide a predetermined amount of heat when supplied with relatively thin air at high altitude and then to reduce the volume of air supplied (for the same fuel supply) when flying at lower altitudes. This methodis distinct from that of designing the If there is a suflicient supply of ventilating air,

the pressure responsive switch 82 will be closed, completing a circuit to the low resistance side 88 of the rheostat 88 associated with the butterfly valve 48 and thence over the movable contact 58 and a lead 88 to a second pair of contacts 142 on the relay l4. Assuming'that this relay has been previously operated as described, current is supplied over the lead 83 and the contacts 142 and the contacts i8l of the thermal relay It to the fuel pump 20, causing the latter to operate at maximum speed. The purpose of the thermal relay 16 is to insure that the ignitor wire 18 has time to heat before the fuel pump 20 starts delivering fuel to the combustion chamber.

Operation of the fuel pump 20 develops'pressure in the feed line 22, which pressure acts on the diaphragm 46, as previously described, to open the butterfly 44 and admit the proper amount of air for combustion to the manifold 28, and the resultant mixture of fuel and air issuing from the apertures 29 into the combustion chamber is ignited by the ignition wire 18.

The heat output may be reduced manually by rotating the movable contact 68 in the control unit 5% to gradually introduce the resistor I0 into the circuit and thereby slow the fuel pump 20. Furthermore, if for any reason the blower 12 fails to supply sufllcient air for proper combustion for the amount of fuel delivered, the butterfly as is moved toward fully open position to introduce the resistor 56 into the circuit, thereby slowing down the fuel pump 20.

Should the supply of ventilating air fail at any time, pressure responsive switch 82 functions to shut down the fuel pump and if the supply of combustion air becomes insuflicient to support proper combustion even with the butterfly 44 fully open, then the pressure responsive switch 6| opens its contacts to de-energize the relays l4 and 18, which function to not only ole-energize the fuel-pump 20 but also to release the solenoid valve 18 and positively stop further supply of fuel.

By' virtue of the fact that the ignition wire 18 is connected in series with the thermal relay l8 and the relay 14, failure (burning out) of the ignition wire immediately results in shut down of the system.

heater for normal operation at sea level and then supercharging it to compensate for decreased air densities at higher altitudes. A particular advantage of the system is that it requires only a single control, the rheostat in the control unit 85, all'other controls being fully automatic.

An actual heater designed to produce a maximum heat output ,of 250,000 B. t. u. per hour at an elevation of 40,000 feet may be dimensioned and equipped as follows:

I 1 I P Diameter of the combustion chamber in the cylindrical portion at the left end 2%" Diameter at the throat of the venturi 88-..- 1

Length of the venturi 33 2" Maximum diameter of the combustion chamber between venturi 38 and the necl:

38 3" Diameter at the neck 38 1%" Diameter of the discharge end of the combustion chamber 2 Width of the annular discharge orifice 38-.. 1" Diameter of the shroud 88 5 Diameter of the casing l0 7 Diameter of air duct 3| Diameter of air duct 80 Diameter of air duct 28 1*" Approximate lengths of air ducts 80 and II. 8%" Diameter of Jet in end of feed line 22 drill Diameter of burner tube 28 1" Number of the holes 29 146 Diameter of the holes 29 dril1 #40 Diameter of the diaphragm 48 6" Effective diameter of the Sylphon bellows 5'2 I Maximum capacity of the fuel pump 20 gal/hour 4 Diflerential pressure (above atmospheric) required in duct 23 for full capacity operation water 8" Although for the purpose of explaining the invention a specific embodiment thereof has been described in great detail, many changes from the specific construction shown will be obvious to those skilled in the art. For example, although as described the device is primarily intended for 78 heating space on an airplane or other location,

it may also be employed in jet propulsion or as the combusting part of a gas turbine in which heat is incidental and the primary object is to produce a large volume of gas at high velocity.

It is also to be noted that although gasoline has been particularly mentioned as a fuel, other liquid fuels, such as kerosene or alcohol may be employed. Furthermore, gaseous fuels, such as propane, butane or natural gases may be used by substituting a pressure reducing valve for the fuel pump 20 and substituting a throttle valve for the control rheostat I0.

It is also to be particularly noted that although as shown in the drawing the gases passing from the left end of the passage between the combustion chamber and the baiile 36 are mixed with the gas (air) passing between the battle 36 and the outer case "I, it is not essential that they be so mixed for delivery together. The gas from within the baiiie 36 may. if desired, be transmitted separately and used for anti-icing and similar purposesonly while using only. the relatively pure hot air from the annular passage formed by the shroud or baflie 39 and the outer casing III for the heating of passenger compartments.

I claim:

1. In a combustion device: an elongated combustion chamber, means for introducing a mixture of air and fuel into said combustion chamber at one end thereof, the other end of said chamber being open for the discharge of products of combustion, a casing surrounding said combustion chamber and adapted to have a stream 01 airto be heated forced therethrough in direction opposite to the flow through said combustion chamber,-

a cap juxtaposed to the open end of said combustion chamber for deflecting products of combustion laterally into said air stream, said casing being fully open at the ends whereby the smallest cross-sectional area of said air stream occurs in the annular space between said casing and said combustion chamber.

2. Apparatus as described in claim 1 in which the combustion chamber tapers from a larger cross-sectional dimension at said open end to a smaller cross-sectional dimension at a point spaced longitudinally from said open end, whereby the cross-sectional area of said air stream is reduced at the area of ingress into said'stream of the products of combustion, to reduce the pressure of the stream and promote the ingestion into the stream of said products of combustion.

3. Apparatus as described in claim 1 in which that portion of said casing that is juxtaposed to said combustion chamber is substantially of uniform cross-sectional area,.and said combustion chamber tapers from a maximum cross-sectional area in the general region of its mid-portion to a minimum cross-sectional area a'short distance from its open end, and then tapers to a crosssectional area intermediate said maximum and minimum areas at said open end.

ALBERT A. ARNHYM.

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

UNITED STATES PATENTS Hennig -May 6, 1947

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