US2165447A

US2165447A - Pressure metering carburetor

Info

Publication number: US2165447A
Application number: US94534A
Authority: US
Inventors: Kenneth A Browne
Original assignee: Wright Aeronautical Corp
Current assignee: Wright Aeronautical Corp
Priority date: 1936-08-06
Filing date: 1936-08-06
Publication date: 1939-07-11
Anticipated expiration: 1956-07-11

Description

July 11', 1939. K, A, BROWNE 2,165,447

PRES SURE METERING CARBURETOR Filed Aug. e, 1956 INVENTOR. Kenneth A. Browne.

BY I

Patented July 11, 1939 UNITED "STATES PRESSURE METERING OABBUBETOB Kenneth A. Browne. Bidgewcod, N. 1., asaignor to Wright Aeronautical Corporation, a corporation of New York Application A!!! 8; 1938, Serial No. 94,534 15 Claims. (Cl. 2131-69) This invention relates to carburetors of the type used in conjunction with internal combustion engines, the carburetor of this invention being particularly adapted for use in aircraft engines and engines subject to operation in atmospheres of varying density.

The conventional type of carburetor utilizes a constant level float chamber from which liquid fuel is delivered to the throat of the carburetor,

10 due to the low pressure obtained thereat by the use of a restriction or Venturi. Ordinarily, the throttle valve is placed upon the downstream side of the carburetor throat, and carburetors of this type, particularly in aircraft service, have certain disadvantages in that the throttle valve and fuel discharge nozzle are apt to accumulate ice .when operated in atmosphere where the relative humidity is high. Such ice accumulation is very detrimentalto proper engine performance, since it up- .0 sets the fuel-air ratio and restricts the air flow capacity to an undue extent. The constant level float chamber'of the conventional carburetor introduces an undesirable characteristic in that changes in position of the carburetor have a detrimental eflect upon the constancy of the fuel-air ratio. The plain Venturi suction carburetor does not maintain a constant fuel-air ratio with changes in atmospheric density, but meters the fuel in proportion to the square root of the air density, whereby richness of mixture is increased unless compensating devices of some mechanical nature are applied in an attempt to maintain constancy of the mixture. This invention provides a carburetor which overcomes these disadvantages by eliminating constant level. float chambers and by eliminating the direct metering of fuel into the Venturi throat in response to the' of these improvements, the carburetor can operate properly in any position and will maintain no a constant fuel-air ratio in the engine regardphere in which the engine is operating. Control of the weight 'of fuel feed is accomplished by controlling the fuel pressure diiferential on a meter- 5 ing orifice, rather than by establishing a volu- 7 less of the pressure or temperature of the atmosmetric control as is done in some types of fuel injection systems.

Objects'of the invention are to provide a carburetor which will under all conditions maintain a desired proportion of fuel to air; to provide a carburetor, free from constant level float devices, wherein fuel is fed under pressure to the carburetor, the pressure differential on the fuel metering orifice being governed by the mass flow of air in the-carburetor throat in order that the amount of fuel delivered is controlled directly in proportion to the weight of air flowing through the carburetor throat; to provide a carburetor having a throttle upstream, with respect to the venturi and fuel metering nozzles to prevent ice from accumulating thereon by condensation from the mixture. As the liquid fuel introduced by the carburetor is in direct proportion to the weight of air actually being drawn into the engine, the carburetor is unaffected by appurtenances intro- 20 duced in the engine intake system such as superchargers and the like, and is independent of the position of the throttling means.

Further objects are to provide piston and mechanical linkage devices by which the pressure of 25 fuel on the carburetor is governed in accordance with engine operating conditions, and whereby the ratio offuel to air entering the intake system is variable in proportion to the amount of fuel entering the system as dictated by particular engine 30 requirements. I

An outstanding difference between the carburetor of this invention and the conventional type lies in the source of the pressure by which fuel is metered into the airstream. The change in air 3.3 flow velocity head across a carburetor venturi is ordinarilymsed to draw fuel from a float chamber, but in this invention, the velocity head differential pressure across the venturi is used solely for mechanically producing a pressure diiferential across 40 the fuel metering orifice, the basic fuel head on the orifice being provided by an engine-driven fuel pump or other suitable means. Variations in the air pressure surrounding the fuel discharge nozzles have no effect upon fuel flow through the 46 nozzle, nor does the pressure in the fuel system per se affect the amount of fuel metered into the carburetor so long as the fuel pressure supplied by the fuel pump is more than the air pressures existing in the various elementscf the carburetor. 50

In a carburetor having a venturi, the pressure drop across the venturi is proportional to the air velocity squared times the air density. Thus:

' Pa varies as VaD where Pa is the pressure drop, Va is the velocit of air and D is the density. In the liauid l orifice Pr varies as Vi Since it is essential to proportion V 1)" (or Web to P: to efiect the desideratum, it is necessary to apply a single density factor to the VGD relation resultant from the Venturl pressure drop whereby;

P1 varies as W! varies as We varies as Va l) To accomplish the desired result, the Venturi pressure drop is mechanically linked to a fuel pressure control valve, and an air density responsive device is mechanically connected to the linkage to bias the fuel pressure control valve directly. Thereby the ultimate fuel pressure upon the fuel orifice is that pressure necessary to proportion, consistently, the fuel-air ratio. The controls are positive and definite, each functioning independently on the fuel pressure valve, avoiding the indefinite back suction control and analogous means appearingin the prior art.

The density factor (D above) is affected by pressure and temperature in a well known manner. The correction is applied in the present invention by means of a flexible bellows containing a fixed weight of air or gas, which may expand or contract due to temperature change and due to ambient air pressure to which the bellows is exteriorly subject.

In the drawing, the figure is a section through a preferred embodiment of the invention as applied to a single barrel engine carburetor.

It will be obvious to those skilled in the art that the metering control devices of the invention may be equally well applied to multi-barrel carburetors. The carburetor barrel is represented as i I! and incorporates a venturi if provided with a plurality of holes l2 at the throat thereof. The barrel also is provided with a butterfly throttle valve iii in the conventional manner, except that said valve is on the upstream side of the venturi. To the barrel is suitably attached a housing comprising component elements l4, l5 and I8 formed to define certain chambers which will presently be described. A fuel inlet pipe I! delivers liquid fuel from the conventional fuel supply source or pump, not shown, to a chamber I8 having a duct l9 leading to a chamber 20. This latter chamber is separated from an adjacent chamber 2| by means of a flexible diaphragm 22 which carries a tube 23 in which is formed a fuel metering orifice 24. Said tube is free to move axially, and

one end thereof, as at 25, is formed as a head slidable in a cylinder 26. The housing l5 carries a screw 21 on which is a tapered metering pin 23 engaging within the orifice 24 so that, as the tube 23 moves axially, the effective opening of the orifice 24 is varied. It will be seen that fuel passes from the chamber 20 through the cylinder 26, through the orifice 24, within the tube 23 and into the chamber 2|. conducts fuel to a chamber 33 defined on one side by a flexible diaphragm 3|. Said diaphragm Thence, a conduit 23 may be subject to atmospheric or any other order of relatively constant pressure. To the diapa at is attached a fuel tube 34 having openings 35 for entering of fuel thereto from the chamber 30, the left hand end of the tube 34 seating against a part 38 of a main fuel nozzle 31?. The tube is freely axially slldable in a bore of the housing member i4 and is normally pressed into contact with the part 38, to prevent fuel flow therefrom, by a light spring 38 which will be of such character as to have a relatively constant pressure gradient within the normal range of movement of the tube 34.

From the apparatus thus far described, it may be readily appreciated that when fuel is supplied under pressure through the tube fuel will pass through the passage i3, the chamber 20, the orifice 26, the chamber 2|, the conduit 23, the chamber 30 and into the tube 34. As soon as the fuel pressure in the chamber 30 is sufliciently great to overcome the resistance of the spring 38, the tube 34 will move to the right and permit fuel flow from the left hand end of the tube 34 and through the nozzle 31 into the carburetor barrel. So long as there is the necessary pressure to slightly compress the spring 38, fuel will flow into the nozzle regardless of any other factor. Thus, this device, including the tube 34 and the diaphragm 3|, merely acts as a check valve and is not effective in actually metering fuel. However, the orifice 24 and its position relative to the metering pin 28 does have an actual effect in metering the amount of fuel which is supplied to the chamber 30. The pressure differential between the chambers 20 and 2| will determine the position of the orifice 24 with respect to the metering pin 28, thereby governing the amount of fuel flow through the orifice. Presuming that the pressure in the chamber 2| is substantially equal to that in the chamber 30, and which pressure in turn is substantially constant in an amount just sufficient to permit of fuel flow into the nozzle 31, the amount of fuel flow through the nozzle will be a function of the actual fuel pressure in the chamber 20 and correspondingly, in the chamber l3.

Now, it becomes necessary to control the pressure of fuel in the chambers l8 and 20 in proportion to the pressure differential of air passing throughthe venturl II and in accordance with the air density. This is accomplished by a bypass valve 33 permitting of fuel by-pass from the pressure pipe I! to the exit pipe 33 which, as

before mentioned, is under either atmospheric or some relatively fixed pressure condition. The valve 33 is provided with a stem 40 backed up by a light spring 4| seated upon a manually adjustable seat 42, said seat 42 being carried on a rod 43 which may be turned for adjustment by any suitable means. Ordinarily, for idling conditions, the amount. of fuel fed to the carburetor may be at a constant rate, and in this carburetor, thisrate is determined by the difference in pressure between the springs 4| and 38. The spring 4| may be fixed at a pressure of, for example 1.6 pounds, whereas the spring 33 may be fixed at a pressure of, for example 1.5 pounds. This differential is constant. This will hold a fuel pressure of 1.6 in the chambers l3, l9 and 20. To obtain fuel flow through the tube 34, it is necessary to have a pressure of 1.5 pounds in the chamber 30, and consequently in the chamber 2|. The 0.1 pound pressure differential is absorbed as pressure drop across the orific 24 as a funca,1ec,447 3 is, of course, less in proportion to the relative density. The pressure differential between the tion of the amount of fuel flowing therethrough.

' munication, through a passage 41, with the Venturi openings l2, while the chamber 46' is in communication, through a passage 48, with the carburetor barrel in. Thus, in operation, a pres- I sure difierential exists between the chambers 44 and 46, which differential has the eifect of moving the diaphragm '45 to the right as the velocity and amount of air flowing through the barrel increases. The diapliigagfif 15 is connected by a link 49 to a pivot 50.1% which in turn are pivoted links 5| and 52 connected respectively with a slide 52 and a bellows 54. The slide 53 is movable vertically as shown,,i'n a guide 55 The bellows 54 comprises a non-reactive membrane 56 encompassing a fixed quantity of air or other elastic I fluid which will vary inwolume with changes" in pres ure and temperature'in' swell-known manner. Since the bellows 54 is non-reactive, the link 52 will be moved vertically downward upon increases in temperature of the fluid within the bellows, and will be movedvertically upward in response tol increases in; pressure within the chamber 44. The link 5i rests against an abutment 51 on the valve stem 40 so that, as the link 5| is moved to the right, it tends to hold the valve 29in a closed position. Such movement would be governed by a large pressure differential between the chambers 44 and .46, which in turn would be resultant from the flow of a large amount of air through the carburetor barrel. Temperatureand pressure compensation of the force on the valve 39, which is necessary, for instance, in high altitude operation, and/or throttled operation will be governed by the bellows 54 whereby the leverage of the link 49 toward closure of the valve 39 will be reduced for either or both increase in temperature or reduction in pressure.

The results flowing from the operation of the carburetor may be visualized from the following examples of operating conditions. If we assume full throttle operation at ground level, (normal density) the mass of air flowing through the carburetor barrel will be at a maximum and consequently, a maximum pressure differential will exist between the chambers 44 and 46. Thus, a

maximum effect will be produced in increasing the fuel pressure in the chamber l8 whereby there will be a maximum of fuel passed through the orifice 24 and into the discharge nozzle 31.

Now, we may assume full throttle operation at.

high altitude where the ambient air is less dense than at sea level, and where the temperature is usually lower. In this case, the power produced by the engine at the same R. P. M. as ground level is less than in the first case, which means that a a lesser weight of air will be consumed and a correspondingly lesser weight of fuel will berequired. In the operation of the carburetor, this reflects itself in the following manner. The actual velocity of air passing through the carburetor barrel will be substantially the same as in the first instance, but the weight of air passing therethrough stantially greater.

to the relative density squared, whereby the fuel pressure in the chamber II is maintained at the same proportional pressure and therefore gives a fuel flow proportional to the relative density. The result of the carburetor action is therefore to produce a constant fuel-air ratio regardless of altitude and throttle opening.

Temperature of the air entering the engine will have a corresponding efiect upon fuel metering as produced by pressure changes-when air temperature is high, a lesser amount of fuel will be permitted to flow per unit of volume of air entering the engine, while, if the temperature is low, a greater amount of fuel will be permitted to enter the carburetor barrel. Temperature compensation is taken care of in the same manner as above when the bellows 54 is maintained at the temperature of air entering the carburetor.

I provide a by-pass 59 between the passages 41 and 48, which by-pass may be manually adjusted by a valve 60." The by-pass when opened has the effect of reducing the pressure differential between the passages 44 and 46 which will therefore provide an adjustment for the mixture ratio of the carburetor.

I also provide a hole 6i open to the atmosphere communicating with the space 82 within the fuel nozzle 3'] and surrounding the tube 34. This serves as an air bleed to provide air for the engine under idling conditions, and also provides air for emulsifying the fuel emanating from the nozzle 31 to assist in more perfectly atomizing the liquid fuel as it passes'into the manifold system.

The shape of the metering pin 28 will determine the change in fuel-air mixture ratio which.

ly, for cruising power conditions and conditions where maximum economy is desired, the metering pin will have a cross-section to leavethe net orifice area at a minimum. Adjustment. as to thepoint of minimum 'fuel-air ratio may be effected by adjustment of the screw.2|. Springs 63 and 64 are respectively contained within the chambers 2| and 20 to hold the .diaphragm 22 in a central position, and the respective pressure which these springs exert upon the diaphragm may be selected so as to obtain the desired motion of the diaphragm with respect to fuel pressure differential to control the orifice opening in accordance wih the amount of fuel consumed.

' It might well be pointed out here that the orifice opening might be fixed, is which event the fuelair-ratio would be constant from substantially closed throttle to open throttle engine operation as a result .of the Venturi and density control of the fuel pressure. The variable area orifice proing chamber for fuel under pressure, a spring loaded relief valve for maintaining a pre-set pressure in said chamber, a fuel metering jet having an orifice fed from said chamber, and an outlet valve from said Jet having spring loading to normally close said outlet valve, the

spring loading thereof having a lesser force than the spring load of said relief valve, whereby the difference in force of said springs is effective as an idling fuel control in determining the idling pressure drop across said fuel jet orifice.

2. A pressure metering carburetor for operation in atmosphere of variable density comprising a barrel having a venturi, a housing having therein a flexible diaphragm defining within said housing separate chambers connected respectively to the Venturi throat and to the ambient air, wherefore force on the diaphragm is proportional to the Venturi pressure drop, i. e., the function VQD wherein Va is air velocity and D is air density, a sealed hollow element in ofie of said chambers having a wall responsive in its movement to D or air density, multiplying linkage connected to said diaphragm and said wall whereby the linkage imposes a force proportional to VJD, a liquid fuel metering orifice, a conduit connecting the discharge side thereof to the carburetor barrel, a source of fuel under pressure connected with the inlet side of said orifice, and a fuel pressure control valve actuated by the linkage and responsive in its operation to the force imposed thereby to control the fuel pressure on the inlet side of said fuel orifice in direct proportion to vtD as air mass flow through the barrel increases and decreases.

3. A. pressure metering carburetor for operation in atmosphere of variable density comprising a barrel having a venturi, a housing having therein a flexible diaphragm defining within said housing separate chambers connected respectively to the Venturi throat and to'the ambient air, wherefore force on the diaphragm is proportional to the Venturi pressure drop, i. e., the function VsD wherein Va is air velocity and D is air density, a sealed hollow element in one of said chambers having a wall responsive in its movement effect to D or air density, multiplying linkage connected to said diaphragm and said wall whereby the linkage imposes a force proportional to VaD, a liquid fuel metering orifice, a conduit connecting the discharge side thereof to the carburetor barrel, a source of fuel under pressure connected with the inlet side of said orifice, a fuel pressure control valve actuated by the linkage and responsive in its operation to the force imposed thereby to control the fuel pressure on the inlet side of said fuel orificev in direct proportion to VJD as air mass flow through the barrel increases and decreases, and means in said discharge conduitto isolate the discharge side of said orifice from the eflect of barrel air pressure.

4. A pressure metering carburetor for opera- 7 tion in atmosphere of variable density comprising a barrel having a venturi a housing having therein a flexible diaphragm defining within said housing separate chambers connected respectively to the Venturi throat and the ambient air wherefore force on the diaphragm is proportional to the Venturi pressure drop, i. e., the function VtD wherein V- is air velocity and D is air density, a sealed hollow element in one of said chambers having a wall responsive in its movement effect to D or air density, multiplying linkage connected to said diaphragm and said well whereby the linkage imposes a force proportional to VJD, a liquid fuel metering orifice, a conduit connecting the discharge side thereof to the carburetor barrel, a source of fuel under pressure connected with the inlet side of said orifice, a fuel pressurecontrol valve actuated by thelinkage and responsive in its operation to the force imposed thereby to control the fuel 'pressure on theinlet side of said fuel orifice in direct proportion to V-FD as air mass flow through the barrel increases and decreases,

means in said discharge conduit to isolate the discharge side of said orifice from the effect of barrel air pressure, said means including an air bleed to emulsify fuel discharged from the orifice during its passage through said conduit.

5. A carburetor including a barrel having a venturi, an inlet fuel passage adapted to receive fuel under pressure, a fuel metering orifice connected therewith and discharging to said barrel, a relief valve in said passage for controlling the fuel pressure therein; and means including a diaphragm device subject on its opposite sides ,to the dynamic pressure of said venturi and to the static pressure of the barrel, respectively, to impose upon said valve a force directly proportional to the square of the air velocity times the air density passing through said barrel and venturi.

6. A carburetor including a barrel having a venturi, an inlet fuel passage adapted to receive fuel under pressure, a fuel metering orifice connected therewith and discharging to said barrel, a by-pass valve in said passage for controlling the fuel pressure therein; and means including a device movable in response to Venturi pressure drop to impose upon said valve 9. force proportional to the square of the air mass passing through said barrel and venturi. said means comprising a housing having a flexible element defining chambers connected respectively to the ambient air and the Venturi throat wherefore the force on said flexible element is proportional to the velocity squared times the density of air from the working atmosphere passing through fixed mass of elastic fluid andsubject to the pressure and temperature of the working atmosphere wherefore the said second element movement is proportional to the density of the working atmosphere, and linkage multiplying the force and movement from said flexible elements for application upon said by-pass valve.

7. In a carburetor for an internal combustion engine, a barrel for airfiow, a fuel metering orifice, a pressure fuel supply to which the inlet side of said orifice is connected, a fuel pressure control device, a conduitto which the discharge side of said orifice is connected including valve means exerting a back pressure on said orifice 7 aroma-r toisolatetheorificefromtheeifectofbarrelalr pressure,- means actuated by barrel air pressures for producing a force proportional .to barrel airfiow velocity. a means movable in response to the barrel air density, and a multiplying linkage responsive to the force and movement exerted by said means and actuating said fuel pressure control device for increasing the fuel pressure drop across said orifice with increases in barrel air velocity and density, whereby the fuel 'fiow through said orifice increases with the .mass airfiow through the barrel.

8. In a carburetor for an internal combustion engine, a barrel for airflow, a fuel metering orifice, a pressure fuel supply to which the inlet side of said orifice is connected, a fuel pressure control device, a conduit to which the discharge side of said orifice is connected including valve means exerting a back pressure on said orifice of theri'uel-air ratio. actuated by the pressure drop across the orifice.

9. In a carburetor foran internal combustion engine, a barrel for airflow, a-fuel metering orifice, a pressure fuel supply to which the inlet side of said orifice is connected, a fuel pressure control device, a conduit to which the discharge side of said orifice is connected including valve means exerting a back pressure on said orifice to isolate the orifice from the effect of barrel air pressure, means. actuated by barrel air pressure for producing a force proportional to barrel airfiow velocity, 9. means movable in response to the barrel air density, a multiplying linkage responsive to the force and movement exerted by said means and actuating said fuel pressure control device for increasing the fuel pressure-drop across said orifice with increases in barrel air velocity v and density, whereby the fuel flow through'said orifice increases with the mass airflow through the barrel; and metering means in said orifice for controlling the richness of the fuel-air ratio actuated by the pressure drop across the orifice comprising a metering pin,

movable within said orifice, and means controlled by the pressure drop across the orifice for relatively moving said orifice and pin.

10. In a carburetor having a barrel,.in combination, a fuel pressure source, means to control the fuel pressure thereof proportionally to the square of the air mass flowing through the barrel, a metering orifice fed from said source, a

delivery jet in the barrel fed,fromvsaid orifice, and -means to substantially isolate the downstream side of said orifice from the influence of barrel air pressure at the jet comprising a piston type valve between the orifice and jet and a diaphragm operable to open said valve acted upon, on one side, by fuel pressure existent between the valve and orifice, and acted upon on its opposite side by a substantially constant valve closing force.

11. In a carburetor having a nation, a fuel pressure source, means to control barrel, in combi-.

the fuel pressure thereof proportionally to the square of the air mass flowing through the barrel, a metering orifice fed from said source, a

delivery jet in the barrel fed from said orifice, and means to substantially isolaterthe downstream side of said orifice from the influence of barrel air pressure at the jet comprising a valve between the orifice and jet, resilient means to hold said valve closed, and a diaphragm carried by the valve having an area substantially greater than that of the valve subject on one side to substantially constant pressure'and on its other side to fuel pressure from the downstream side of said orifice, said latter pressure acting on said diaphragm to overcome the closing effect of said constant pressure and of said resilient means, to open the valve and admit fuel to the jet.

12. In a carburetor in combination, an airstream venturi, a throttle upstream thereof, a fuel jet in the airstream remote from said venturi, a fuel metering orifice discharging to said jet: means to impose fuel pressure on the orifice; a controldevice actuated by the air mass passing through the venturi comprising means acted upon by the pressure resultant from air velocity in the venturi and airdensity to produce a force proportional to the product of the squares of air velocity and air density, and mechanism to apply said force to control the fuel pressure on said orifice in proportion thereto; and valve means independent of actuation by barrel air pressure, between said orifice and Jet, openable by fuel pressure downstream of said jet to pass fuel from theprifice to the jet.

13. In a carburetor in combination, an air-.

stream venturi, a throttle upstream thereof, a

- proportional to theproduct of the squaresof air velocity and air density, and mechanism to apply said force to control the fuel pressure on said orifice inproportion thereto; and valve meahs independent of actuation by barrel air pressure, between said orifice and jet openable by fuel pressure downstream of said jet to pass fuel from the orifice to the jet, and means responsive to the pressure drop across the orifice to alter the effective area thereof. a

14. In a carburetor subject tovarying air density, a fuel metering orifice having the normal characteristic that the weight of fuel flow therethrough is proportional to the square root of the fuel pressure drop thereacross, a barrel for air flow into which said orifice discharges, means between the orifice and barrel comprising a valve independent in its opening to barrel pressure but responsive in its opening to pressure at the downstream side of the orifice, a source of fuel under pressure communicating with the upstream side of the orifice, means actuated by air passing through the barrel to generate a force proportional to the square of the weight of air passing therethrough, and valve means controlling said fuel pressure responsive in its operation to said force, said valve means serving to control the fuel pressure on said orifice proportionally to the square of the indicated air weight.

-15. In a carburetor, .a hollow housing, a barrel having a venturi adjacent to the housing, a yielda-ble diaphragm within the housing dividing same into two chambers, means connecting one chamber to the throat of said venturi'by which the dynamic pressure due to the velocity of air passing through the venturi is communicated to said 5' chamber, means connecting the other chamber to the barrel for establishing in the latter chamber the static pressureexistent in the barrel; a

s'trut projecting from and substantially normal to said diaphragm, a lever on an end of which said strut is pivoted, the other end of said lever having a pin-slot connection with the housing to 1 permit of substantial axial movement of the lever relative to the housing; a yieldable closed diaphragm confining a fixed amount of elastic fluid secured to'the housing and acting substantially axially along said lever for moving the lever in said pin-slot connection, said closed diaphragm being subject exteriorly to the atmosphere; a source of fuel under-pressure, said housing havdng a cavity withwhich said source communicates, a conduitleajding from said cavity to the barrel, a fuel metering orifice in said conduit, a

valve downstream of said orifice in said conduit including substantially constant pressure means for holding same closed, means embodied in said valve; subject to pressure of fuel downstream of the orifice for opening said valve to establish communication and fuel flow from the orifice to the barrel, and ,a poppet type relief valve openelastic diaphragm, exerting a-force on the valve stem urging the valve toward a closing position for increasing fuel pressure in said cavity,-said second closed diaphragm serving to adjust the eifective lever length, in response to atmospheric air density, to alter the closing force upon said valve as exerted by said first diaphrag KENNETH A. BROWNE.