This invention relates to an evaporation carburetor.

Generally speaking, evaporation carburetor systems have met with little or no success and have been generally abandoned. One reason for this is that evaporation carburetors have tended to- provide too lean a mixture and have tended to become easily gummed-up. The carburetor of the invention, on the other hand, satisfactorily and very efficiently operates otherwise conventional automobiles without evidence of gumming.

Some evaporation carburetors pass the engine's air through a fuel-soaked wick in order to enrich the fuel-air mixture and attempt to provice a more uniform charge. This charge is then delivered to a conventional carburetor which controls the overall mixture to the engine. An object of the instant invention, however, is to provide a carburetor which can operate an engine in lieu of a conventional carburetor. In this respect, however, one of the advantages of the invention is that it can be used on a conventional automobile to retrofit its conventional carburetor without re¬ quiring modification of the engine itself.

Another advantage of the invention is that it is adapted to make use of the engine's exhaust-gas

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energy that is otherwise wasted. This, of course, also reduces exhaust-gas temperature so as to reduce both thermal pollution and the corrosive effects of the exhaust. In this connection, exhaust gases have previously been used to preheat carburetor air and to heat fuel. In such cases, however, varnish buildups have been detrimental; energy losses have resulted; and, the charge has not been sufficiently dense for adequate engine operation. In the structure about to be described, however, it is not necessary to directly heat the fuel. Indeed, the vaporizing fuel cools the previously heated portion of the engine's air so that an initial fuel-vapor-laden portion of the engine's charge is relatively cool when it is further mixed with additional air prior to being delivered to the engine's intake manifold.

Another advantage of the invention is that the fuel in the charge is substantially completely vaporized, whereas most of the fuel of a conventional carburetor is merely atomized to droplets not much smaller than about 7-10 microns. Hence, since fuel vapcr has about three times the usable heat value of the liquid, the vapor-laden charge is far more efficient. Moreover, the combustion mixture is more uniform from cycle to cycle and cylinder to cylinder; there is more complete use of the fuel; the exhaust is cooler; and, the air pollutants are far less.

Additionally, in a conventional carburetor there is a tendency toward a- fuel-flow lag as additional air is drawn into the carburetor during acceleration. Hence, conventional carburetors employ acceleration pumps to inject additional fuel into the charge during acceleration. The carburetor of the invention, how¬ ever, provides increased fuel-vapor flow at the same time the engine's air flow increases. Consequently, there is no need for an acceleration pump; less fuel

is wasted; and, pollutants are further reduced.

SUMMARY

The formation of a charge for an internal combustion engine includes the circulation of fuel over an air permeable element to saturate the element with fuel. Ambient air is then drawn through the air permeable element by the engine after having first been heated in a heat exchanger for picking up some o i:-P the otherwise wasted heat from the engine's exhaust. As the heated air passes through the air permeable element, it vaporizes the fuel which cools the now vapor-laden air to about one-third the temperature at which it entered the air permeable element. Each volume of the resultingly cooled vapor-laden air is then mixed with about 10 to 20 volumes of air that are drawn into the carburetor by conventional means prior to delivery to the engine's intake manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings, wherein reference characters refer to the same parts throughout the various views. The drawings are not necessarily drawn to scale.

Instead, they are merely presented so as to illustrate principles of the invention in a clear manner.

FIG. 1 is a schematic, vertical, partially cross-sectional, view of an embodiment of the invention;

FIG. 2 is a plan view of the FIG. 1 structure taken along the lines 2-2 thereof;

FIG. 3 is a fragmentary plan view of a portion

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of a fuel manifold for the FIG. 1 structure;

FIG. 4 is a bottom fragmentary view of an outer chamber of the carburetor illustrated in FIG. 2;

FIG. 5 is a fragmentary pictorial view of a slide valve used in the FIG. 1 carburetor.

FIG. 6 is a schematic, vertical, partially cross-sectional view of an alternate embodiment of the invention;

FIG. 7 is a schematic flow diagram illustrating the flow of the engine's exhaust gases through heat exchanger portions of FIG. 6;

FIG. 8 is a schematic sectional view of the heat exchanger portions taken along the line 8-8 in FIG. 7; ^'

FIG. 9 is a schematic vertical sectional view of the heat exchanger portion taken along lines 9-9' in FIG. 7;

FIG. 10 is a schematic, vertical, partially cross-sectional view of yet another embodiment of the invention; and,

FIG. 11 is a sectional view taken along the lines 10-10 in FIG. 9.

DETAILED DESCRIPTION

FIG. 1 is a schematic cross-section of an embodiment of -the invention mounted by a means not shown onto the upper portion 11 of a conventional carburetor having its own independent fuel supply not shown. The structure includes a first annular chamber 13 which surrounds a multi-section heat exchanger 15 and is

connected by a plurality of ports 17 to a housing 19 for an accordian-folded air permeable element 21. The housing 19 is, in turn, actively connected to a second chamber 23 by means of ports 25 in a slide valve 27.

Fuel is delivered to a sump 29 through a needle valve 31 connected to a fuel line 33 by a coupling 35. In this regard, fuel to Ine 33 is provided by a separate fuel pump, not shown, that is independent from that of the automobile's conventional carburetor. The automobile's conventional fuel pump can be used for this purpose, however, by merely directing the conventional pump's output. In either event, the level of the fuel in the sump 29 is controlled by a float 37 in a conventional manner.

An electric fuel pump 39 runs continuously during operation of the engine and pumps fuel from the sump.through a line 40 to a fuel manifold 41 on top of the housing 19 and covered by a plate 43. In this regard, the fuel is distributed to orifices 44 at a pressure of about 1 to 5 psi., through concentric grooves 45 and radial grooves 47 (FIG. 3) . The orifices 44 should be equally distributed around the top of the manifold 41; and, if desired, can be combined with flow-balancing screws 51 as illustrated in FIG. 1 to adjust the fuel passing through individual orifices.

The air permeable element 21 is covered by a fuel distribution pad 53 and receives the fuel from the orifices 44. The fuel then runs down over the element 21 and saturates it with fuel—the excess dripping off of the bottom thereof and back into the sump 29. In this manner, the fuel is continually circulated by gravity and the electric pump 39 so that the element 21 remains saturated at all times. This, however, is also somewhat of a function of the size of

the element 21. For a 250 cubic inch engine, for example, the surface area of an air permeable element was about

750 square inches and it remained continually saturated throughout the engine's range of operation. Too small a surface area, however, would have resulted in dry areas on the element; too little vaporization of fuel; and too lean a mixture for the engine. In this respect, even if the element 21 is properly saturated, too small an area causes too great a suction ^' which results in liquid fuel being drawn into the engine (as opposed to the desired vapor) . In this embodiment of the invention 0.95 square inches of element surface for each cubic inch of engine displacement is about the smallest acceptable ratio of element surface to displacement.

In the above regard, since the fuel manifold 41 is pressurized to about 1-5 psi, the more volatile fuel fractions are prevented from boiling off at too rapid a rate. Similarly, it has been found that the continuous circulation prevents heavier elements and varnish from being deposited on the bottom of the sump 29 and gumming up the valve mechanism 31. Also, this circulation maintains a balanced fuel composition in the fuel system.

The heat exchanger 15 is comprised of upper and lower chambers 15a and 15b as shown in the right hand side of FIG. 1. In this regard, hot exhaust gases from the engine are controlled by a butterfly valve 55 to be passed into either the upper annular portion 15a of the heat exchanger ^• or directed to the engine's regular exhaust system. The exhaust gases that pass the butterfly valve are then directed through the upper portion 15a of the heat exchanger in the direction of arrows 57 and 59 in FIG. 2.

When the gases reach the left side of the heat exchanger in FIGS. 1 and 2 the two streams 57 and 59 converge and enter the lower chamber 15b to return to the right side in the direction of arrows 61 and 63

in FIG. 2. When the gases reach the right side of por¬ tion 15b, they are directed into the engine's con¬ ventional exhaust system not shown.

The bottom side of chamber 13 includes a plurality of closely spaced holes 64 as illustrated in FIG. 4. When the slide valve 27 is open, therefore, the engine pulls air through the ambient air ports 64. ThJ s air picks up heat from the heat exchanger 15 and enters the housing 19 through the ports 17. In this regard, the double-layered, counterflow aspects of the heat exchanger 15 ensure that the temperature of the air entering the ports 17 is substantially uniform throughout the various ports. The temperatures in the heat exchanger 15 typically run between about 800°F and 1200°F during normal engine operation. The carburetor of the invention will operate at higher heat exchanger temperatures, but the heat exchanger is preferably made of copper, which, perferably, should not exceed its annealing temperature of about 1200°F. If higher heat exchanger temperatures are desired, therefore, a dif¬ ferent heat exchanger material should be used.

A slide valve control mechanism, not shown, has one or more ther isters 65 (FIG. 2) as control elements located at one or more of the ports 17. In this .manner, the slide valve control mechanism causes an actuator assembly 67 and an actuator arm 69, to rotate the slide valve 27 when the ^' temperature at the thermister reaches a selected level depending upon the engine and operating conditions. In one of the embodi- ments of the invention the preferred temperature was found to be about 400°F. As a practical matter, how¬ ever, the preferred temperature range is about 375- 406°F depending, among other things, upon the pressure differential across the element 21.

In the above regard, a cylindrical wall 71 forms the upper and inner wall of the chamber 19 and

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has a plurality of ports 73 therein; and, when the slide valve 27 is fully rotated by the arm 69, the ports 25 and 73 are brought into alignment as shown in FIG. 5 so that air from ports 64 can pass through the air permeable element 21 and into the inner chamber 19. At the same time, outside air is also drawn in through a conventional air filter 75 and directed radially in¬ wardly and. then downwardly into the second chamber 23.

In operation, the cold engine is started by using its conventional carburetor. At that time, the exhaust gases are cool; the heat exchanger 15 is cool; and, air passing through ports 65 would not pick up sufficient fuel from the air permeable element 21 to properly operate the engine. Hence, the slide valve 27 is preferably closed at this time and the engine is started and warmed up by means of the conventional carburetor.

When the temperature at thermister 65 reaches a desired level depending upon the engine and operating conditions, the conventional carburetor's fuel supply is shut off; and, after a sufficient time for the con¬ ventional carburetor's bowl to empty, the slide valve actuating mechanism causes the slide valve to rotate; the ports ^" 25 and 73 to .be aligned; and, the ambient. air from ports 64 to pass through the carburetor.

Alternatively, the output from the carburetor can be simply blocked at the desired temperature so that there is no necessity for the bowl to be emptied.

Once the heat exchanger has reached its desired temperature and the slide valve is opened, the thusly heated air from chamber 13 passes through the ports 17 and the saturated element 21. As the heated air passes through the element, it becomes cooled by the fuel which is vaporized into the pas- sing air. In this regard, in the embodiment of the invention which opened the sli e valve 27 at a teimo-

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erature of 400°F, the temperature of the fuel-vapor- laden air passing through ports 73 and 25 into chamber 23 was no more than about 135°F-145°F. This portion of the engine's charge, however, is then mixed with the ambient outside air entering through conventional filter 75 in a proportion of ^" about one volume of fuel- apor-laden air to 19 volumes of ambient air from the filter 75. Hence, the air from chamber 13 is still further cooled.

In the above regard, it is preferable to maintain low heat exchanger temperatures and avoid stratification between the outside air and the fuel- vapor-laden air. Hence, it is preferred that the temperature of the air entering ports 73 and 25 be close to that of the ambient air from the filter 75.

In other embodiments of the invention; and, in other ambient conditions, the above proportions can change to as little as one volume of fuel-vapor-laden air to about nine volumes of ambient air through the air filter 75. It should also be noted that if supplemental means are used to heat air passing through the port 17, the cold engine can be started by the evaporative carburetor itself.

The pressure drop across element 21 is preferably about five inches of water for elements that are mounted on a wire frame and comprised of a relatively absorbant fabric of rayon, or other suitable synthetic material. The element 21 can be made of other suitable materials, however, such as thin felt. The desired speed of air through the element 21 varies with the size of the engine and the size and type of element, but speeds as high as 175 inches per second have been found to be satisfactory even though speeds of 15-20 inches per second at an engine speed of 4000 RPM were preferable for embodiments of the invention employed with test automobiles.

_B UREΛTT

Perhaps the most important of the above variables is the temperature at which heated air enters the housing 19 for impingement upon the element 21. In this respect, a relatively small increase in temperature at the thermister 65 resulted in twice as much fuel being vaporized into the air as it passed through element 21. Hence, relatively small changes in temperature can cause significant changes in fuel economy and pollution. This temperature, however, is easily controlled to suit the individual engine requirements by selectively adjusting the butterfly valve 55 and the amount of rotation of slide valve 27 so that the fuel air ratio entering the engine's intake manifold is that which is desired under any given conditions. This has been accomplished in the past by any one of several electronic sensing and control circuits in order to obtain relatively automated control; but, the butterfly valve 55 and the slide valve 27 have also been controlled by simple manual choke-type cables and satisfactory adjustments of engine operation were obtained nevertheless.

Similarly, the thermister 65 (or other temperature sensing device) can be used in conjunction with a suitable circuit to provide a continuing indication of the temperature of the air at ports 17. If temperatures become excessive, therefore, it is merely necessary to adjust the butterfly valve 55 and reduce the amount of exhaust gases that are directed to the heat exchanger 15.

FIG. 6 illustrates an alternative embodiment of the structure described above. Therein, a first annular chamber 81 surrounds a multi-section heat exchanger 83. A chamber 85 for an air permeable element 21', however, is connected to the chamber 81 by means of a continuous annular opening 87 extending between ends 89 and 91 of generally circular baffle elements 93 and 95 respectively. The air permeable

element 21' , therefore, is directly exposed to radiant heat from the heat exchanger assembly 83 rather than merely being connected to the first chamber by means of ports such as 17 in the FIG. 1 embodiment.

The lower portions of the chambers 81 and 85 are formed by a spun member 97 having a substantially circular support bracket 99 welded thereto so that the heat exchanger assembly 83 rests on the top of the support bracket 99 as shown. The tops of the chambers 81 and 85 are covered by a cylindrical plate 101 corresponding to plate 42 in FIG. 1 and suitably affixed to a flange 103 on the spun member 97. In this regard, an upper support bracket 105 is affixed to the plate 101 such as at 107. In this manner, when the plate 101 is thusly affixed, the heat exchanger assembly 83 is held in place between points 109 and 111 on the upper support bracket 105 and the lower support bracket 99 respectively.

The heat exchanger assembly 83 is comprised of a first lower chamber 112; a second lower chamber 113; a first upper chamber 115; and, a second upper chamber 117. In this respect, hot exhaust gases from the engine are delivered to the first lower chamber 112 through a butterfly valve, not shown, in substantially the same manner as described above in connection with the FIG. 1 embodiment. As shown in FIGS. 7, 8, and 9, the hot exhaust gases enter the first lower chamber 112 at point 119 in the FIG. 7 flow diagram and are free to flow in the direction of the arrows 121. Part of the incoming exhaust gases, however, strike a baffle 123 to move in the direction of arrows 125 in the second lower chamber 113—chambers 112 and 113 being joined at the inlet point by walls 127 and 129 as shown in the FIG. 7 flow diagram and FIG. 8.

When the hot gases in the first lower chamber reach portion 131, they move upwardly into the second

upper chamber 117; and, the gases from the second lower chamber 113 move similarly upwardly at portion 133 into the first upper chamber 115. From these locations the hot gases return to the exhaust outlet 135 in the direction of arrows 137 and 139 in the FIG. 7 flow diagram. In other respects , the heat exchanger assembly 83 operates in a manner similar to the FIG. 1 embodiment, and, therefore, will not be further described.

The lower portion of the spun member 97 includes a large plurality of openings 141 similar to those illustrated in FIG. 4. In this regard, when a valve assembly 143 (to be described shortly) is open, the engine pulls air through the openings 141. This air is directed by the support bracket 99 upwardly around the outside of the first lower chamber 112 and the second upper chamber 117. The air from openings 141 is then directed downwardly between the first and second upper chambers 115 and 117 by the upper support bracket 105 in the direction of arrow 145. After passing between -the chambers 112 and 113, .the air is then directed toward the continuous annular opening 87 by the ^' upper side of the support bracket 99 in the direction of arrow 147. The thusly heated air is then directed over the element 21' in the same manner as described above in connection with the first embodi¬ ment; and, then through valve assembly 143 which will now be described.

A cylindrical wall 149 (corresponding - to member 71 in FIG. 1) and a valve seat member 151 are suitably affixed to a lip 153 of the spun member 97 to form a cylindrical chamber 155 corresponding to chamber 23 in the initial embodiment; and, a cylindrical valve 157 has closure surfaces 159 for engaging corresponding surfaces of a seat 161.

A series of annular grooves 163 extend around the cylindrical valve 157 to act as a seal with the

inner portion of the cylindrical wall 149. In this manner, air flowing through ports 165 from the air permeable member 21' is not permitted to escape between the valve 157 and the inner portion of cylin- drical wall 149.

The valve 157 has an internal groove 167 for accommodating a spring 168 between the lower portion of the groove and an upper ring 169 having stanchions 171 and 173 extending upwardly therefrom. The stanchions have openings therei ' for accommodating a slide bar 175 having cam 177 thereon.

A bar 179 extends across the upper portion of the cylindrical valve 157 and has a cam follower 181 on a vertical bracket 183 affixed thereto by adjustable fasteners 185 threadably mounted through ears 187 which are biased by springs 189 surrounding the adjustable fasteners 185 and located between the ears 187 and the bar 179.

The slide bar 175 is movable back and forth in FIG. 6 by a solenoid 191 in the same manner that the actuator arm 69 is controlled by the actuator assembly 67 in FIG. 2. When the solenoid 191 moves the slide bar 175 to the right in FIG. 6, therefore, the cam surface 177 forces the cam follower 181 up- wardly against the bias of spring 168 to raise the valve closure surfaces 159 from the seat 161 to permit fuel-vapor-laden air from the element 21' to enter the cylindrical chamber 155.

A float chamber 195 is located under and contiguous to the right side of the spun member 97 in FIG. 6 and contains a needle valve and float mech¬ anism 196 corresponding to similar structure in FIG. 1. Fuel from the chamber 195 is delivered to the lower portion of chamber 85 for delivery to an electric fuel

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pump (not shown) similar to pump 39 in FIG. 1, which, in turn, delivers fuel through a suitable line to a fuel distribution chamber 197. In this regard, the fuel distribution chamber is comprised of an annular recess 199 in the cylindrical plate 101 covered by an annular plate 201 having a corresponding recess 203 therein and sealed by O-rings 205 and 207 to form the chamber 197.

The fuel distribution chamber 197 is con- nected to the chamber 85 above the element 21' by a plurality of orifices 209 corresponding to orifices 44 in FIG. 1. Hence, the air permeability element 21' has fuel delivered thereto in the same manner as was described above in connection with the initial embodi- ment. That is, the fuel runs down over the element

21' and saturates it with fuel--the excess fuel drip¬ ping off of the bottom thereof for recirculation by the pump similar to 39. It should be noted, however, that the baffle 95 is operative to direct any outwardly dripping fuel downwardly into the bottom of the spun member 97 and also to prevent fuel from flashing up¬ wardly therefrom and onto the heat exchanger elements .

The operation of the FIG. 6 embodiment is substantially the same as that of the FIG. 1 embodi- ment. Hence, the following operational description will be quite brief.

When the temperature of the air passing through annular opening 87 is determined by a suitable sensor 65' to have arrived at the desired temperature, the cylindrical valve 157 is opened as described above. Air from port 141 is then permitted, after being heated by heat exchanger assembly 83, to pass through element 21' to be cooled by the fuel which is vaporized into the passing air. The fuel-vapor-laden air then passes into the chamber 155 as described above. This

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portion of the engine's charge is then mixed with ambient outside air entering through an opening 215 in a cover 217 after having been filtered by a suit¬ able means not shown. That is, the ambient outside air is directed downwardly through the open central portion of the cylindrical valve 157 for admixture with the fuel-vapor-laden air in the chamber 155. Thereafter, the thusly mixed charge is drawn into the engine through an adaptor ring 219 for affixing the carburetor of the invention to the upper portion of a conventional carburetor, not shown.

In other respects, the FIG. 6 embodiment is similar to that of FIG. 1. Hence, those aspects of this particular embodiment will not be further discussed.

FIGS. 10 and 11 illustrate yet another embodi¬ ment of the invention which has been particularly adapted for use with small engines. In this respect, a bowl 241 is fabricated from stainless steel and shaped according to a surface of revolution such as a parabola. Circular heat transfer tubes 243, 245, 247 and 249 are made of copper and located inside the bowl 241 at the sides thereof where entrance and exhaust pipes 251 and 253 are affixed to the tubes. In this regard, ports 255 connect each of the -circular heat transfer tubes to the entrance and exhaust pipes as illustrated. In this manner, the engine's exhaust is delivered to pipe 251; passed into the heat transfer tubes through ports 255 on the left side of the bowl 241 in FIG. 9; and, circulated through the tubes around the inside of the bowl 241 for exit through exhaust pipe 253 via ports 255 on the right side of FIG. 10.

A circular aluminum plate 257 is affixed to the top of the bowl at 259 and has a hemi-torroidal member 261 affixed thereto along circles of contact 263 and 265. The member 261 extends downwardly into

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the bowl adjacent the heat transfer tubes as shown and accommodates an air permeable element 21" similar to the corresponding elements in the foregoing embodi¬ ments.

The circular plate 257 is provided with a plurality of ports 267 located in a circle thereabout and is covered by a flat circular ring 269 which is slidably mounted on top of '.he plate 257 within circular brackets 271 and 273 so as to be rotated by a handle member 275 which extends out of a slot 277 in the left side of the bowl 241 in FIG. 10. In this manner, motion of the handle 275 permits selective rotation of the ring 269 to adjust the alignment of ports 267 with corresponding ports 279 in the ring 269. That is, by moving the handle 275 back and forth, the ports 267 can be selectively adjusted to any position between fully closed or fully opened so that fuel-vapor-laden air can flow into the structure's upper portion which will now be described.

A lid 281 has a plurality of holes 283 spaced along a circle therearound. Circular upper and lower brackets 285 are located about the inner sides of the lid for holding a cylindrical ring 289 having an extension 291 thereof extending through a slot 293 in the upper portion of the lid 281. In this manner, back-and-forth motion of the extension 291 permits selective alignment of the holes 283 with corresponding holes 295 in the cylindrical ring 289 in order to regulate the amount of ambient air entering the structure as will be described shortly.

Fuel from a device not shown (similar to needle valve 31 and float 37 in FIG. 1) is delivered to the lower portion 296 of the bowl 241 for passage out of a tube 297 to a suitable pump or the like (not shown) similar to pump 39 in FIG. 1 for delivering fuel into line 299 and a manifold 301 located above

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the element 21". This fuel saturates the element 21" in the manner described above; and, excess fuel drips from the bottom of the element where it is collected in the lower portion 303 of the hemi-torroidal member 261 and drips out of a plurality of ports 305 into the lower portion 296 of the bowl 241 for recirculation through tube 297 and the fuel pump in the same manner as has been described above in connection with the other embodiments.

The outer wall of the hemi-torroidal member

261 is provided with cut-out portions 307 so that the element 21" receives direct radiation from heat trans¬ fer tube 247 and a portion of tube 245. Tube 243 is located above the openings 307, however, and tube 249 is located below the openings. The tube 249, therefore, radiates heat toward the lower portion 296 of the bowl 241 and the lower portion of the hemi- torroidal member 261, but its radiation does not directly impinge upon the element 21" , nor does the radiation from tube 243.

The general operation of the structure illustrated in FIGS. 10 and 11 is similar to that of the earlier-described embodiments. Hence, this embodiment:' s operation will only be briefly described. In this regard, the structure is mounted upon an engine's carburetor by means of a tube 309 which is connected to the aluminum plate 257 and surrounded by the stainless steel bowl 241 and the aluminum hemi-torroidal member 261.

Air from ports 311 on the sides of bowl

241 is drawn into the structure's interior for passage over the heat transfer tubes and, after being thusly heated, passes through the openings 307 into the interior of the hemi-torroidal member 261. The heated air then passes through the fuel-saturated element 21" to vaporize fuel therefrom and be cooled

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during the evaporation process. In this respect, the amount of air that is permitted to pass through the element 21" is controlled by the degree of alignment between the holes 267 and 279 as described above.

The fuel-vapor-laden air passes out of the ports 267 and 279 into the upper lid portion where it mixes with ambient air which is drawn into the lid through ports 283 and 295 in accordance with the degree of their alignment. In this regard, however,, it will be appreciated that the lid 281 can be surrounded by a suitable air filter if desired in order to filter the air entering the lid. In any event, the ambient air and the fuel-laden-air are drawn downwardly through the tube 309 and into the engine's conventional carburetor.

It will be appreciated by those skilled in the art that the above-described structure provides efficient carburetion producing low exhaust temperatures , low pollutant levels, and high gas mileage. In this connection, carburetors of the invention have regularly obtained a 200 percent and more increase in gas mileage at legal speeds. Moreover, the structure is relatively simple and standard engines are easily retrofited with carburetors of the invention.

Additionally, the above-described carburetor does not require any particular skill by the operator. As indicated above, an automobile, for example, is started in the same manner as a conventional car using its conventional carburetor. Somewhat before the slide valve opens to let the evaporation carburetor take over, the fuel pump for the conventional carbure¬ tor is turned off; and, after its bowl is emptied (or the output blocked) , the slide valve is auto- matically opened and the vehicle's charge is provided by the evaporative carburetor.

Insofar as engine speed is concerned, the same throttle valve is used as with a conventional carburetor. Hence, except for experiencing an almost instantaneous pickup upon acceleration, the operator need not even be aware of the difference.

As to pollutants, it should be noted that one test vehicle was run with both a conventional carburetor and an evaporative carburetor. The eva¬ porative carburetor however, resulted in a decrease of carbon monoxide pollutants of up to 58 percent; a decrease in hydrocarbons of up to 75 percent; and, moreover, was entirely capable of meeting pollution standards set by the Environmental Protection Agency without additional catalytic convertors or the like.

Similarly, it might be noted that tests on a 455 cubic inch Oldsmobile engine employing an evaporative carburetor obtained certified gas mileage in the 30-40 mile per gallon range depending upon driving conditions; and, uncertified tests on a Chrysler Motors automobile resulted in gas mileage ^• of as high as 60 miles per gallon. The results obtained therefore, have been satisfactory indeed.

While the invention has been particularly- shown and described with reference to preferred embodiments there-of, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the ^* spirit and scope of the invention. For example, a first stage of heating to the heat exchanger can come from the engine's cooling system; or, water might be converted to steam at the engine's exhaust manifold and this steam can be circulated in exchanger 15 in order to heat ambient air being drawn through chamber 13, Similarly, a fire screen 77 can be inserted across the bottom of chamber 23 to reduce fire hazards in the

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event of a backfire. These and other modifications, however, will be apparent to the skilled artisan. Hence, the scope of the present invention should only be measured by the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: