US1972374A - Carburetor - Google Patents

Description

P 1934. R. BRANNIGAN 1,972,374

CARBURETOR Filed Aug. 11, 1930 F gj BY QM ATTORNEY Patented Sept. 4, 1934 1,972,374 CARBURETOR Robert -A. Brannigan, New York, N. Y.; Gladys Brannigan, New York, N. Y., executrix-oi' said Robert A. Brannigan, deceased Application August 11, 1930, Serial No. 474,571

11 Claims.-

My invention pertains to carburetors for internal combustion engines and more particularly has reference to the use of superheated liquid fuel for obtaining more uniform and homogeneous 6 mixtures.

The two principal functions of a carburetor are the maintenance of the desired mixture ratio between the air and liquid fuel components and the suflicient atomization of the liquid fuel to insure 10 a homogeneous gaseous mixture.

The only sources of energy available to do this in an ordinary carburetor are: first that which is due to the difference between the atmospheric pressure in the float chamber and the subatmosl5 pheric pressure at the carburetor jet; and second, the energy coming from the stream of air flowing past the jet. As the throttle is closed,

this first source of energy diminishes, and yet that is the very time it is most needed. The air velocity giving the second source of energy is controlled by the wide open throttle, full speed, condition of the engine. The degree of pressure drop permissible is thus limited as, otherwise, the volumetric emciency of the engine would be adversely aifected. For all speeds lower than highest speed and all throttle positions below the wide open, this velocity drops off. So the sources of energy for atmozing the liquid fuel vary in the ordinary carburetor. They are at minimum at idling speeds of the engine, and the amounts of these two energies are controlled by the external factors. In the early days of very volatile fuel, however, these sources of energy were sufficient, but with the heavy ends in modern fuels they have proven to be insufficient and what is now needed is to bring to'bear upon the liquid fuel, as it is discharged into the air stream, some additional energy whose amount is not affected by other considerations. My solution of this problem is the superheating of liquid fuel.

In producing a combustible mixture from air and liquid fuel, complete gasification of the liquid fuel is theoretically desirable. To do this by ordinary heating means. raising the temperature of the entire mixture which is fatal to volumetric eiliciency of an engine. Fortunately, it is not necessary to go that far. I have found that if the liquid fuel is subdivided into small enough particles, then under the law of the ratio of volume to surface of a sphere, there is a liquid particle so small that it will maintain itself in suspension in the gaseous medium and the two will flow along as a homogeneous mixture. Thus, in the fire box of a boiler, the radiant heat of the flame will vaporize these fuel particles so combustion is complete. In an internal combustion engine, such a mixture will maintain its homogeneous state through the manifold and past the inlet vlaves and, on the compression stroke of the engine, the resulting temperature causes these particles to gasify so that combustion again is satisfactory.

,When a liquid is subjected to a certain pressure, be it the ordinary atmospheric pressure or something above or below that and heat is applied, then for any given pressure there is a certain boiling point temperature, the higher the pressure the higher this temperature. So, to cause gasification of a liquid for any given pressure, it has to be raised to a certain temperature, that is to say, for each boiling temperature there is a certain corresponding pressure which has to be taken into consideration. If the liquid at a a given temperature is held at a pressure in excess of this it remains liquid, but if then the pressure is dropped below this critical pressure for that temperature, gasification occurs.

The boiling points of various liquids are usually rated at atmospheric pressure, and if liquid is raised above this temperature andthe pressure is raised so as to retain the liquid in a liquid form, the liquid is said to be superheated. Now, if liquid in a superheated state is released into a lower pressure atmosphere, vaporization to some extent occurs, and this occurs immediately and with violence. The extent of the vaporization depends upon the amount of heat available. To take an example, water boils at atmospheric pressure at 212 F. If it is held in a boiler and the temperature raised to say 222 F., and it is held under pressure in the liquid state, the raising of this temperature from 212 to 222 represents the addition each unit of liq-. uid of a certain number of heat units. That is, for every pound of water there would be ten British thermal units. Now, if a pound of this water is allowed to escape, ten British thermal units represent the latent heat of vaporization of some portion of this pound, and that Wili be the portion which will flash into steam. This Vaporization will occur throughout the mass of the liquid allowed to escape. It will be in nature of local explosions throughout the mass. The temperature of the steam and the fog of the unvaporized water will be lowered to 212 degrees. The liquid portion of the water will be atomized into small particles. This is what occurs in a boiler carrying a head of steam when one of the water level try cocks below the water level is opened. A solid stream of hot water does not escape, but a mass of steam and water, the latter in a fine stage of subdivision, is what is discharged. The violence of this atomization depends upon the degree of superheat.

As a matter of physics, it is possible to raise the temperature and the corresponding pressure of the water in a steam boiler so that the super- Where there is a fuel which is made up of a,

series of fractions of various boiling points, and this is superheated and discharged in the liquid state into an atmosphere of lower pressure, there would be the same vaporization and atomization of the fuel, and this is true even though some of the heavier ends of the fuel may not be raised to their particular superheated condition. The lighter ends which are in a superheated condition will vaporize suddenly and atomize the remaining liquid.

But to apply this principle of atomization to an automobile carburetor presents another problem because the demands vary rapidly with speed and load on the engine. It would be impossible to put upon the operator of the car the burden of accomplishing this process by manual adjustments.

hEy invention has for its fundamental object the complete atomization of the liquid fuel by super-heating under pressure and then suddenly releasing the liquid fuel in the carburetor air stream.

portion of which is raised above its atmospheric boiling point, but which is kept under such a pressure that it is in a liquid state until it passes the jet orifice and'this condition is maintained '15 the butterfly throttle valve 3 can be omitted and irrespective of the rate of discharge through the carburetor jet.

With these and other objects in view which may be incident to my improvements, my inven- ,tion consists in the combination and arrangement of elements hereinafter described and illustrated in the accompanying drawing, of which:

Figure l is'a vertical longitudinal section of a carburetor embodying a preferred form of my invention;

Figure 2 is a fragmentary vertical section of a modified form of needle valve operating mechanism;

Figure 3 is a similar view of still another modincation of the same;

Figure & is a vertical section, of a heating iagret for supplying controlled heat to the liquid The carburetor body consists of a cylindrical casing 1 constituting a mixing chamber 2 whose outlet to the engine is controlled by the usual butterfly throttle valve 3, and a Venturi throat 4 which is secured to the lower end of casing 1 by any ordinary means such as screws 5. If desired the throttle valve operator can be applied direct- 1y to the element 9. Positioned in the lower.

end of casing 1 is an annular bushing 6 whose inner wall 7 is rounded to form a smooth stream line surface with the wall of casing 1. This bushing is screwed in place by screws 8 and forms a seat for an air valve 9 which controls the entrance of air into mixing chamber 2. Valve 9 is mounted by a stem 10 which slides freely in a bushing 11 carried by a bridge 12 across the Venturi throat 4. Stem l terminates at its lower end in a tapered needle valve 13 which controls the orifice 14 of a nozzle 15 which is supported in the center of Venturi throat 4 by a horizontal arm 16 integral with the wall thereof. Fixedly attached to the stem about needle valve 13 is a small cup 17 in which is seated a helical spring 18 which bears against bushing 11 and normally holds valves 9 and 13 on their seats. The valve 9, bushing 6, needle 13, spring 18 and throat 4 are so proportioned that as the suction of the engine draws the air through the carburetor, the valve 9 will open the needle valve 13 to the desired amount so the resulting liquid flow will maintain the desired mixture ratio.

' Nozzle is fed by a fuel passageway 19 which is of considerably larger cross, section than the orifice 14 in the nozzle. Passageway 19 communicates with a fuel heating chamber 20 in which is suspended a thin metallic diaphragm 21 forming a separate compartment 22 for the heating medium which enters by pipe 23 and leaves by pipe 24.

Liquid fuel is fed into chamber 20 by a pressure pump 25 geared to the engine and a constant pressure is maintained by a regulating valve 26 which is adapted to. open when the pressure exceeds a predetermined amount and returns the liquid fuel through an overflow pipe 27 back to 5119 of spring 28 by nut 29.

Near the top of chamber 20 is a passageway 30 which. communicates with mixing chamber 2 through a regulating valve 31 for a purpose which will hereinafter appear.

As shown in Figure 1, chamber 20 is located immediately adjacent carburetor body 1 so that heat is applied to the fuel as close to the jet as possible. The source of heat supplied to chamber 20 is preferably that of the exhaust of the engine, with an electric heating coil 32 to facilitate starting and to be automatically cut out as soon as the engine is warmed up by a thermostat 33.

As exhaust heat is variable, the'fuel heater is made in the form of a chamber 20 with the fuel entering and leaving from the bottom and another chamber 22 extending downward into this first chamber, with the exhaust heat entering and leaving this inner chamber 22 by the pipes 23 and 24. Thus, if the exhaust heat is too great, the liquid fuel in chamber 20 is raised above its boiling point under the pressure of the pump 25 and vaporization occurs in the top of chamber 20. The

liquid level is thus lowered and decreases the area 3' of the diaphragm 21 which is in contact with the of entrained particles of air, it is necessary to provide a means for slowly and continuously evacuating the space in chamber 20 above the liquid level, as otherwise, -a quantity of air would gradually accumulate therein and prevent the temperature regulating means from functioning as described. The top of chamber 20 is, therefore, placed in re-' stricted communication with mixing chamber 2 by means of pipe 30 and valve 31. This valve is opened only a very small amount so as first to permit any air released from the liquid fuel in chamber 20 to escape but not enough to permit any appreciable amount of vaporized fuel to escape or even to appreciably affect the pressure in chamber 20 caused by the pump 25 or the vaporization of fuel as above described.

The passage 19 from the heater chamber 20 to the jet orifice 14, as stated above, should be rather large in cross-section to prevent wire drawing and any drop in pressure which would allow vaporization in this passage because that would interfere with the mixture ratio control. Pressure and temperature control are not at all delicate, nor the amount of energy to supply pressure and temperature great, as the whole liquid fuel is not raised to a superheated stage, but only a portion of the light end of the fuel. The higher the degree of superheat, the more energy is applied to atomize the fuel at the jet orifice, but it is not necessary to do any more than to produce that minimum degree of atomization which is necessary.

If the pump pressure should vary materially the resulting variations in the rate of fuel discharge to air fiow would produce variations in mixture ratio, so the pressure control on the pump is held within such limits as not to disturb the mixture ratio. But as positively driven by-pass pumps have been used for this purpose in various arts successfully, this presents no problem.

By selecting a'pressure sufficiently uniform an having the degree of heat to produce the required superheat in a portion of liquid, the device will give the degree of atomization desired. A higher degree of atomization results if the superheat is high, and less if the superlieat is low, but if the lesser limit is sufiicient to produce atomization, the greater degree of superheat producing greater atomization will do no harm;

As a rough example, let it be assumed that the liquid is held under two pounds pump pressure, and that the corresponding temperature which is just short of vaporization at this pressure would give adequate pulverization is A degrees. Then if the device was operated under a ten pound pressure, and the vaporization temperature at that pressure is B degrees, there would be a permissible temperature variation of from A to B, because while anything under A would not produce a superheated liquid at the jet orifice and any temperature above B would develop gas in the feed line and interfere with the mixture ratio, between these limits the superheated liquid would be discharged correctly according to the demands of the carburetor. These pressures 2 and 10 pounds are just illustrative.

With certain types of engines where the temperature variation in exhaust gases was not so great, exhaust gases can be utilized without any particular temperature control. It is then possible to substitute for the heater in Figure 1 a double wall heater as shown in Figure 4 with exhaust gas in an inner chamber 40 and the liquid -fuel in an outer chamber 41, with this outer chamber having a water or air cooling jacket 42 so that although there was a variation in the temperature of exhaust gases, the excess heat could be wasted through this air or water cooling system with the result that the liquid fuel is not subjected to a temperature ,range beyond that permissible.

with this type of heater the fuel outlet would be at the top and .therefore air-binding would not have tobe guarded against.

It isflt'o be appreciated that this superheated fuel carbureting arrangement would work on any volatile fuel whether homogeneous or a mixture of components of various boiling points. As a practical matter any given carburetor designed to work on a mixed fuel that had a certain component of a lower boiling point would operate on any fuel that had that component in it, even though the rest was of higher boiling point. That is to say, very heavy fuels could be used in a carburetor designed to use lighter fuel, if these heavy ones were spiked with a small percentage of a component which had the proper low boiling point.

Of course it is appreciated that when fuel is atomizedinto particles. of any size evaporation of the surface of the particles is going on all the time. In a fog mixture of very small particles whose total exposed surface is large, this evaporation is substantial. This phenomenon is helpful to the fog mixture because it tends to make the particles even smaller and thus the mixture tends more and more to become a true gas flowing through the manifold.

In the above described type of carburetor with the inverted needle valve opened by the air flow past the disc on its stem, it is to be appreciated that the area ofthe needle valve subjected to the liquid fuel pressure is very small so that the device is calibrated solelyas regards the air flow. That is to say, thepressu're of the liquid cannot have any material effect in lifting the valve off the seat.

If this disc were put in a straight conical divergent throat of the venturi, the device might be somewhat delicate. One way of producing a more rugged and less sensitive device would be to have a quite long and slightly tapering needle valve giving a longer travel. Or a shorter valve can be used and instead of the disc being secured directly to the needle valve stem, it could act upon it through a spring 50 as in Figure 3 and the movement :of the needle valve in turn resisted by another spring 51, between it and a fixed abutment 11. Or a multiplying linkage can be used between the disc and the valve as in Figure 2 wherein a lever 60 is pivoted at 61 and connected at one end to valve 9 and. at the other end to a link 62 which in turn is connected to a second lever 63 pivoted at 64 and bearing against a flange 65 on needle stem 10, with of course suitable restraining springs. The mixture ratio for a given flow can be controlled either by a calibrated tapering of the needle valve 13 or by a calibrated variant in the cross-section of the air passage in which the disc was located, that is to say, if the passage is conical a given flow would give a certain movement of the disc against the spring resistance. If this passage departed from a true cone as by changing the contour of walls '7, calibration could be effected, or a combination of these two schemes could be used.

While I have shown and described the preferred embodiments of my invention, I desire it to be understood that I do not limit myself to the constructional details shown as the invention may be practiced by a variety of forms of apparatus and changes in arrangement and combination of elements may be made by those skilled in the art without departing from the spirit of my invention or exceeding the scope of the appended claims.

I claim: v

1. A carburetor for automotive engines comprising means for atomizing liquid fuel consisting of mediately converted into ,a highly dispersed vapor.

3. A carburetor for automotive engines comprising means for metering liquid fuel and air in a controlled ratio and means for vaporizing the liquid fuel comprising means for subjecting it to a substantially constant superatmospheric temperature and pressure and means for suddenly releasing it into the metered air.

- i 4. A carburetor comprising means for heating liquid fuel to a substantially constant superatmospheric temperature, said means including inezlins for eliminating air bubbles in said liquid 5. A carburetor comprising a mixing chamber, a liquid fuel nozzle in said chamber, a suction responsive valve controlling the flow of air into said chamber, and a valve co-operating with said nozzle and adapted to maintain liquid fuelin .said nozzle under a superatmospheric pressure and to release it-into said mixing chamber iiLa controlled ratio to the air entering same.

6. A carburetor comprishag ;ajmixing chamber, a liquid fuel nozzle in said sihamber, a suction responsive air valve controlling the flow of air into said chamber and a fuel valve actuated by 4 said air valve and adapted to maintain liquid fuel in said nozzle under a superatmospheric pressure and to release it into said mixing chamber in a controlled ratio to the air entering same.

,7. A carburetor comprising a. pressure responsive air valve, 8. liquid fuel valve controlled by the air valve through a yielding connection so that the air valve is free to move through a limited distance without moving the fuel valve, and means for supplying fuel under relatively high pressure to the fuel valve.

8. In a carburetor, a. mixing chamber having fuel and air inlets, a fuel valve in said fuel inlet, means for supplying fuel thereto under pressure and at superatmospheric temperature, a pressure responsive air valve positioned posterior to the fuel valve, and a mechanical connection between the air valve and fuel valve.

9. In a carburetor, a mixing chamber having fuel and air inlets, a fuel valve in said fuel inlet, means for supplying fuel thereto under pressure, a pressure responsive air valve, and an overrunning mechanical connection between the air valve and the fuel valve to permit the air valve to move through a limited distance without mov-' ing the fuel valve.

10. The process of preparing a fuel mixture for an internal combustion engine which comprises passing an air stream along a predetermined path, varying the velocity of the air stream at will, introducing into said air stream a stream of volatile liquid fuel under superatmospheric pressure and at a temperature above its boiling point, varying the rate of introduction of said fuel with variations in the velocity of the air stream, and releasing the pressure on the fuel stream at the instant of introduction with suflicient suddenness to cause the fuel to flash into vapor.

, 11. In the process of carbureting a volatile fuel,

"the step of atomizing the fuel by subjecting it to superatmospheric pressure and to a temperature above its boiling point without the addition of noncombustible ingredients, suddenly releasing it in the air to be carbureted to cause it to flash into vapor, and causing the rate of air flow tocontrol the rate of release of'the fuel.

ROBERT A. BRANNIGAN.

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