AU6920281A - Water injection in internal combustion engines - Google Patents

Description

WATER INJECTION IN INTERNAL COMBUSTION ENGINES

Cross-Reference to Related Application

This application is a Continuation-in-part application of United States application, Serial Number 120,678, filed February 11, 1980.

Technical Field

This invention relates to improved methods and means for addition of water as vapor or droplets into the fuel/air mixture of internal combustion engines.

Background of the Invention

It has long been known that the addition of water vapor to the fuel/air mixture of an internal combustion engine can improve performance in the area of response to throttle opening and fuel economy. A number of schemes have been devised by which to accomplish the addition of water. However, except in connection with racing and a few other special applications, none of those schemes have enjoyed popular acceptance. It is apparent that the cost of water injection apparatus and the need to add a water supply have been too high a price to pay for a relatively small increase in performance, because of the availability of inexpensive fuel. Now that fuel costs have increased, and because antipollution apparatus has degraded engine performance, there is renewed interest in "water injection" as the processes of adding water were once called.

Amont the antipollution apparatus commonly found on automobiles and trucks is a positive crankcase ventilation (PCV) valve and a conduit which extends from the crankcase to the fuel/air intake manifold and in which the PCV valve is included in series. The most common form of PCV valve is a check valve which opens in response to negative pressure at the fuel/air intake side to permit flow of air and "blow-by" gasses and fuel from the crankcase to the intake manifold. At zero negative pressure, the valve is closed. As pressure becomes more negative the PCV valve opens, but at some even more negative pressure the valve closes in part. Thus arranged, the valve limits blow-by inflow during periods of high vacuum and permits high inflow during medium vacuum operation.

A third factor that has a bearing on this matter is the supplemental air inlet valve. The need to build automotive carburetors so that a single set of adjustment instructions could be issued to all mechanics without re¬gard to local climactic conditions has led to compromises in carburetor designs. Most carburetors have been arranged to provide uniform fuel/air ratio after warm-up that was optimum at only one intermediate speed and load range. The inclusion of a vacuum operated air inlet valve in the system results in significant improvement in many automobiles and trucks. These valves respond to negative intake manifold pressure to admit ambient air to the manifold in parallel with the carburetor. They are open at low vacuum and heavy load, and they close against spring pressure as load decreases and vacuum increases. At least for some engines and carburetors inclusion of the supplemental air valve permits carburetor adjustment to achieve a near optimum fuel/air ratio over a wider range of throttle openings and loads for a gain in efficiency and fuel economy.

With the advent of the PCV valve, a change in the spring bias of the supplemental air valve was required. The air valve became less important but was not made obsolete. When both the PCV valve and the supplemental air system are used, a carburetor adjustment can be made to improve system efficiency in a majority of automobiles.

Summary of the Invention

It is an object of this invention to provide improved methods and means for introducing water into the fuel/air mixture of internal combustion engines.

Another object is to utilize a positive crankcase ventilation system for engines in introducing water with the fuel and air that is supplied to the engine.

A further object is to utilize both the positive crankcase ventilation system and the supplemental air valve to facilitate the addition of water to the fuel mixture of internal combustion engines.

A mixing chamber is included in the positive crankcase ventilation system at the intake manifold side of the PCV valve. Water is drawn into this chamber where it is vaporized, atomized, and otherwise distributed more or less uniformly with the flow of air and blow-by gasses that proceeds to the intake manifold in response to negative pressure. That arrangement does more than provide a mechanism by which water is transported from a storage reservoir to the intake manifold. It provides a means for controlling the amount of water that is introduced as a function of load and throttle opening.

The variations in engine performance with climate and design and other factors, including driver technique, are such that optimizing water, air, blow-by gas, and fuel input requires continuous solution of a very complex algorithm. An object of this invention is to provide an inexpensive means, within existing antipollution law, for intro ducing water into the fuel flow system in a way that will provide a meaningful net benefit to the majority of users, if not all users. The embodiment of the invention that is now preferred introduces ambient air and water into the positive ventilation crankcase system at the same point in the system downstream from the PCV valve. The air and water and the flow from the PCV valve are mixed together in a chamber in that line. Consistent with the objective tominimize cost, neither the PCV valve nor the ambient air inlet valve is adjustable in the preferred embodiment. Adjustment is accomplished at the carburetor.

Experimentation and testing of the invention by federal and state environmental protection agencies have shown that it is preferable to supply water to the apparatus at which it is to be introduced into the PCV system. Moreover, it has been discovered that some of the "additive" chemicals that are added to gasoline producers and end users to enhance efficiency or to reduce emissions that are harmful to exhaust systems and the atmosphere provide better results when introduced with the water rather than when added directly to the gasoline. One of the features of the invention is an improved water storage container and improved apparatus for removing water from the container and delivering it to the PCV.

In this connection, it is an object of the invention to provide an improved apparatus and method for forming water droplets and for ensuring that the rate at which water is delivered to the PCV system is relatively uneffected by the level of water in the storage container. The Drawings

In the drawings:

Figure 1 is a schematic view of a gasoline engine that has been fitted with a water/air/ blow-by gas system according to the invention;

Figure 2 is a graph illustrating operation of the invention in one engine;

Figure 3 is a top view of a flow control device according to the invention;

Figure 4 is a cross-sectional view taken on line 4-4 of Figure 3;

Figure 5 is a view in side elevation of an air inlet valve, a water flow tube. and a water storage container assembly;

Figure 6 is a top view of the storage con tainer of Figure 5; and

Figure 7 is a cross-sectional view of the water container taken on line 7-7 of Figure 6 which includes a sectional view of part of the water flow tube. Detailed Description of the Invention

In Figure 1 the numeral 10 identifies a gasoline engine of conventional design. It includes a crankcase 12, a carburetor 14 and an intake manifold 16 by which a mixture of fuel and air are conducted from the carburetor 14 to the several cylinders of the engine.

During operation of the engine, rapid expansion of fuel in the cylinder forces gasses past the piston rings and pistons to the region below the cylinders which is enclosed by a crankcase housing or oil pan. The composition of blow-by gas varies with engine condition, and engine speed and load, but a large proportion is represented by unburned fuel. One of the antipollution measures that is required for motor vehicles is to draw the blow-by gasses from the crankcase region and return them to the fuel supply system of the engine. In practice, that is done by connecting a flow conduit from the crankcase of the engine to the intake manifold. Downward movement of the pistons within their cylinders produces a suction or negative pressure in the intake manifold. The negative pressure is often called vacuum or "a vacuum" and it results in withdrawal of blow-by gas from the ullage space in the crankcase to the intake manifold.

The same vacuum in the intake manifold is utilized to draw air through the carburetor where it is mixed with the fuel. Engine speed is controlled by controlling quantity of fuel/air mixture that is allowed to pass to the intake manifold. That quantity is controlled by a throttle which operates to change the volumetric rate of air flow or air and fuel flow. In practice, the volume of air and fuel supplied by the carburetor at full open throttle is enough to satisfy the suction whereby intake manifold vacuum is reduced to near zero.

When the throttle is closed, air flow through the carburetor is shut off. In this condition, the measured vacuum at the intake manifold is high. In Figure 2, the relation between throttle opening and negative pressure is represented as a straight line which extends from HI or open throttle and LO negative pressure to LO or closed throttle and HI negative pressure. Because measured negative pressure is a function of both engine speed which generates negative pressure and throttle opening which diminishes that negative pressure, the ordinate of the graph represents a combination of their effect. They have opposite effect. However, speed varies inversly with load. Thus, negative pressure is commonly thought of as a function of throttle opening and load. For that reason, the ordinate in Figure 2 is labelled "THROTTLE/LOAD."

Lest it limit the fuel intake, it is preferred to limit flow from the crankcase at full throttle. To permit control of the flow from the crankcase and to pre¬clude explosion of blow-by fumes in the crankcase in the event of a backfire, a valve is included in the flow passage from the crankcase to intake manifold. The combination of the valve and flow passage is called a positive crankcase ventilation system, and the valve is called a positive crankcase ventilation valve. They are usually called PCV system and PCV valve. In Figure 1, the PCV valve is designated 18. It is included in series in a flow passage or conduit which extends from a connection with the crankcase at point 20 to a connection with the intake manifold 16 at point 22. That portion of the flow passage which is upstream from the valve 18 is numbered 24. The downstream portion of the flow passage includes a device 26 to be des- cribed below. That part of the flow passage that extends between valve 18 and device 26 is numbered 28. The remaining part 30 extends from device 26 to point 22 at the intake manifold.

There are several kinds of PCV systems and valves. The system and valve shown here are like the most common system and valve, and they typify other systems and valves. In valve 18, the valve core 32 is normally closed. In the absence of inlet or outlet pressure, the spring 34 urges the core in a direction (downward in Figure 1) to close the inlet 36. Also, in the event of a backfire, pressure applied to the outlet 38 of the valve acts to force the core 32 to seal the inlet 36 and isolate the crankcase.

Negative pressure at the downstream side of the valve "pulls" the core 32 against the bias of spring 34 to open the inlet 36. Blow-by gasses flow around the core 32 and past the forward shoulder 40 of the valve housing. Gasses also flow to the outlet 38 through an opening 42 from a point behind the tapered forward end 44 of the core to the forward face of that forward end.

The shoulder 40 serves as a valve seat for the tapered forward end 44 of the valve core 32. At highly negative values of negative pressure the core is moved against spring bias until the core seats against the shoulder to foreclose flow around the core. At that value of negative pressure, and at more negative pressures, flow is confined to opening 42 through the core. An idealized graph of flow through the valve 18 as a function of negative pressure has been added to Figure 2 in the curve labelled "PCV FLOW." A primary function of the device 26 is to facilitate admission of water into the fuel/air mixture at the intake manifold. As in the case of the fule, the water must be vaporized or "atomized." Not much water is required. While the amount varies greatly with driving conditions, one pint per one thousand miles is typical, and the inclusion of alcohol antifreeze material is not harmful, although carburetor adjustment may be required. The water supply should be located below the device 26 to preclude gravity feed and syphoning. Water feed rate should be con¬trolled by negative pressure downstream from the PCV valve in the PCV system. A typical arrangement might include a one gallon water container mounted in the engine compartment eight or ten inches below the device 26, a one millimeter inside diameter hose which extends from a point close to the container bottom, leads to a 5.7 millimeter diameter orifice in device 26. Water emerging from the orifice enters a mixing chamber where it combines with the blow-by gas and air that flows through the PCV valve to the chamber.

It is not essential to the invention, in its broader sense, to introduce ambient air into the PCV flowpath. The PCV valve outflow can be used to vaporize and automize the water and the mixing chamber arrangement shown in the drawing will do that. The chamber shown is cylindrical with the inlet and outlet ports spaced around the side walls. Water and blow-by gas are directed into the central region of the chamber where they swirl around. It is a feature of the invention to add ambient air and to introduce it into this same mixing chamber. That feature is included in the embodiment shown. Ambient air is introduced at an angle to water and blow-by gas to air mixing and vaporization and atomization of the water at lower values of negative pressure. In this embodiment, ambient air is introduced at an end of the chamber. Idealized curves of ambient air inflow and water inflow have been added to Figure 2. They are the short dash curve and the solid line curve, respectively. Water being heavier, it is drawn in only small quantity at those negative pressures at which both the PCV valve and ambient air inlet valves are open. The inflow of supplemental ambient air is controlled by a normally, spring opened valve which closes as negative PCV system pressure is increased.

In Figure 1, the supplemental air inlet valve is incorporated in device 26. The mixing chamber is designated 46. Passages or flow lines 28 and 30 open to the chamber at diametric points. The water line 43 extends from a point in the ullage space of water container 50 to the orifice 52 midway on the chamber wall between the ports connecting to lines 28 and 30. The air inlet 54 opens at the upper end wall of the chamber. It communicates with a larger recess which contains a compression spring 56. The recess opens to the outwardly tapered lower, wall of another chamber. A ball 58 in that chamber cooperates with the tapered wall to form an air shut-ofrf valve. At low values of negative pressure in mixing chamber 46, spring 56 holds the ball 58 away from tapered wall 60 so that air may be admitted. As negative pressure increases, air flow past ball 58 forces it against the force of spring 56. At some higher value of negative pressure, the ball is forced against its tapered seat 60 and air flow ceases.

Returning to Figure 2, negative pressure at the intake manifold varies inversely with some combination of throttle opening and load so negative pressure is the dependent variable. However, negative pressure is indicated on the abscissa because it is the independent variable in the relationship between negative pressure and the flow of supplemental air, blow-by gas and water. As indicated above, negative prssure is assumed to have an idealized inverse relation to throttle opening and engine load. Ambient air intake increases with negative pressure until flow reaches a level at which it forces closure of the air valve. The flow of a blow-by gas is deferred until negative pressure reaches a value sufficient to open the PCV check valve. Thereafter, blow-by gas flow increases with negative pressure until the high side valve closes to limit flow to an intermediate value. Water flow is determined by negative pressure and weight of the water. Since air and gas flow more readily than does water, negative pressure tends to be overcome or "satisfied" by air and gas when the air and PCV valves are full open. Water flow increases when the air valve closes and the PCV valve moves to limited flow position.

It has been discovered that there is some advantage in delivering water to the mixing chamber as droplets or at least in small discrete quantities. That can be done by aerating the water so that a quantity of air bubbles moves through the tube with the water from the storage container to the mixing chamber. Thus, it is one feature of the invention to provide a means to dissolve air in the water. In Figure 1, that means is formed by the air inlet tube which extends from an opening above the liquid level in the water storage container to a point near the bottom of the container. Air is drawn into the container as water is removed and that air is made to bubble up through the body of water to the otherwise sealed ullage space.

A preferred form of the device 26 is the structure 70 shown in Figures 3 and 4. Except for the three ports that open into the mixing chamber 72 and the coupling elements associated with them, the unit is symmetrical about its vertical centerline. That centerline is perpendicular to the page in the case of Figure 3, and lies in the plane of the page in the case of Figure 4. The generally cylindrical housing 74 is made of metal to facilitate heat conduction. The upper half of the housing is formed with a series of closely spaced circumferential slots. The metal that remains forms a series of outwardly extending heat dissipating fins arranged in parallel spaced planes. Two fins, numbered 76 and 78, have been numbered for identification.

The upper end of the housing is bored axially for a distance about one-third the height of the unit. The lower end 80 of this bore, called the ball chamber, is tapered inwardly and downwardly to form a seat for the supplemental air valve ball 82. The upper end of the bore is enlarged to form a shoulder on which rests a ball retainer plate 84. It is foraminated to admit air and to exclude debris, and its function, is to retain ball 82. The plate is held in place by a convenient means such, for example, as spring retainer 86.

A second recess, cylindrical in shape in the preferred embodiment, is formed in the lower face of the housing. It is closed by an end plate 88 which is press fitted into the outer end of the recess to form the mixing cavity 72. There are three openings through the housing wall that open into cavity 72. Their respective axes lie on a common plane and intersect on the vertical axis of the unit. They are spaced two at diametric points and one midway between the other two. A tubular inlet coupling 90 is fitted into one opening and a similar tubular coupling 92 is fitted into the diametric opening. One of these fittings is arranged for connection to a flow line that extends to the intake manifold of an engine. The other is arranged for connection to a flow line that extends to the downstream side of the PCV valve of that engine. The third tubular inlet coupling 94 is mounted in the intermediate mixing chamber port. It is arranged for connection to a water inlet line and water source.

The ball chamber and the mixing chamber are connected by an axial bore which is large enough in diameter at the side toward the ball chamber to accommodate an axially arranged compression spring 96. The end of this axial bore toward the mixing chamber 72 is smaller in diameter than the diameter of the spring. A shoulder is formed at the step in the bore's diameter and the spring 96 is trapped between that shoulder and the ball 82.

Improved performance results when the water is delivered to the mixing chamber of the device 26 in the form of droplets. The use of humidified air provides significant improvement but the preferred form at the cylinder is a fine "atomized" mist of water rather than mere humidified air. The preferred mode of operation cannot be achieved if all of the water is evaporated into the air in the water storage container or the air injection device 26. Accordingly, the preferred form of the invention includes a means for delivering water in mist or droplet form to the mixing chamber of device 26.

A preferred form of that means is shown in Figures 5, 6 and 7. It includes a water storage container 98 and a water flow tube 100. Figure 5 illustrates how they are interconnected to one another and to the mixing device 26. The flow tube is fitted with a dividing means for dividing water and droplets into fine droplets at a point within the tube close to its end 102 at its connection to the container. In this embodiment, that means has the form of a small piece of fine metal screening 104. One of the advantages is that the screen does an excellent job whatever its specific shape. The only requirement is that the screen be quite fine and that it extend across the flow path. It is shown in Figure 7 to be inserted in the end 102 of the tube against the end of a tubular insert 106. Insert 106 strengthens the wall of the flexible tube to protect the screen against being crushed and to provide rigidity against buckling of the tube when assembled with the outlet fitting 110 of the container. A similar tubular insert 108 near the other end of tube 100 provides rigidity to facilitate assembly with the mixing chamber. In preferred form the tube is transparent. That is helpful during manufacture because it permits easy inspection of the condition and position of the inserts and the filter screen. After installation proper operation can be verified visually because the water droplets are visible through the flow tube wall.

The container 98 is made of a high impact plastic material in this case, and its inner surface does not wet. That,, while not essential, is a feature of the invention. At the fill end of the container, the right end in Figures 5 and 7, its shape is conventional and any convenient shape may be employed. The fill opening is formed on a sloping surface 112 and is surrounded by a fill neck 114 which slopes upwardly and forwardly. The rim of the neck is below the level of the upper wall 116 of the container so that it is impossible to completely fill the container. A fill level marker 118 (Figure 5) and written instructions to the user suggest filling to the level of the marker. The container is shown to be properly filled in Figure 7. The body of water is numbered 120 and the ullage space is identified by reference numeral 122.

Elements 130, 132 and 134 are provided to facilitate mounting the container. As best shown in Figures 6 and 7, these mounting elements are molded on the vertical centerline of the container. That is true, too, of the out- let nipple 110. Figure 6 illustrates that the side walls are parallel in this version. It is the outlet end, the left end in Figure 5 and Figure 7 and the end at the bottom of Figure 6, that is specially shaped. That end is curved in the vertical center plane as shown in Figures 5 and 7. the region of the center plane an elongated transverse bulg extends over the length of the outlet end. The numeral 136 identifies the bulge in Figures 5 and 6.

The bulge and the outlet end shape are formed as shown so that the droplet forming tube 140 will be positioned as it is shown to be in Figure 7 notwithstanding that it is fixed to the container only by having its end forced through an upper wall opening at 142 whose diameter is a little smaller than the outer diameter of the tube 140.

One end 144 of tube 140 opens to the atmosphere outside the container. The other end 146 opens to the ullage space 122. The length of the tube 140 is such that, when properly assembled in the container opening, end 146 of the tube is positioned just below the entry opening into outlet nipple 110 as shown. The outer diameter of the tube shown is one centimeter. Its inside diameter is just a little greater than 0.8 centimeters. At the end 146, a short length 150, 0.5 centimeters, of tubing has been forced into the tube 140. Its inside diameter is about 0.5 centimeters and the inner end has been cut off square in the transverse plane. Just below the insert 150, four perforations are formed through the wall of tube 140. Those perforations are more or less uniformly spaced around the periphery of tube 140 and one has been numbered 152 to iden tification.

The end of insert 150 presents an annular shoulder just above the perforations to a water and air bubble mixture that flows in the droplet forming tube. Water droplets and splashes that pass through the opening in the insert with substantial velocity strike the inner surface of thecontainer in the vicinity of the inlet of the nipple 110 or they strike the "splash board" surface of a V-shaped protrusion 156 that extends at least across the bulged region of the outlet. Because the container material does not wet, the water that passes through the insert 150 forms droplets and rivulets that become drops.

Both ends of the droplet forming tube are normally positioned above the water, but the tube will be filled to that level in the absence of engine vacuum because the tube 140 is punctured at or near its lowest point. A short length of small diameter tubing is threaded through the puncture so that a port 160 is disposed within the tube 140 while another port 162 is disposed without tube 140. Port 160 at the inside extends toward, and. has its opening toward, the end 146.

Flow of air and water droplets proceeds during those intervals in which engine operation results in development of a negative pressure in the chamber of device 26. Air is withdrawn from the ullage space. Outside air is drawn into the end 144 of tube 140. Tube water is forced out of end 146 and almost immediately, after air is first drawn .past the lowest point in the tube, it is a confusion of air and splashing water that reaches the shoulder at the end of insert 150 and the splash board at indent 156. Some of the water forms droplets as it emerges from perforations 152 and as it falls from the splash board. They are drawn into the flow tube 100 and may be seen traversing the length of the tube as drops or small streamers and variously shaped small quantities of water. In large degree the flow has adequate character for addition to the mixing chamber of device 26 as it flows along the flow tube. Any larger quantity of water arriving at the screen 104 is disbursed by the screen.

Inside the container the water that is removed from tube 140 is replenished through the small tube 160 and 162. The droplet forming action takes place in the droplet forming tube 140, and the inner wall of the container in th vicinity of outlet nipple 110. That action is substantiall independent of the depth of water in the container from the fill level until the water supply is almost exhausted. If the water supply becomes exhausted no harm results. Only the benefit of the invention is lost until more water is added.

A major advantage of the construction shown lies in its low cost and foolproof simplicity. Another is that the water that is added by this system reaches the engine when the operating conditions are those conditions at which some of the additive chemicals are most needed and most effective. The result is that it is more economical and efficient to introduce them with the water in this system than to add them to the gasoline directly.

In practice, the invention provides another benefit that can be very substantial. In most PCV systems, a substantial amount of vaporized oil is drawn from the crankcase through the PCV valve and is returned to the inle manifold where it mixes, as a vapor, with fuel and air. Burning oil accelerates build-up of carbon deposits. In this invention the oil tends to condense under most speed and load conditions. The oil condensate, which may be mixe with water, serves as a lubricant at the valves and in the cylinders. Even if it burns eventually, it will have been useful in minimizing friction in the process. Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art.

Claims (23)

The ClaimsI Claim:

1. Apparatus for adding water to the air/fuel mixture for gasoline engines comprising: a housing defining a mixing chamber; means defining an inlet passage and an outlet passage formed through the wall of said housing and opening to the mid-region of the length of said chamber at opposite sides of said chamber; coupling means for connecting said inlet passage to a flowpath extending from the outlet of a positive crankcase ventilation valve and for connecting said outlet passage to a flowpath extending to the intake manifold of a gasoline engine; and means for introducing water into said chamber in response to negative pressure in an intake manifold comprising a water inlet passage extending through said housing and opening to said mixing chamber at a point between said inlet and outlet passages.

2. The invention defined in Claim 1 which further comprises air inlet means in the form of an air inlet passage extending through said housing and opening at a point in said chamber between said inlet and outlet passage.

3. The invention defined in Claim 2 which further comprises a normally open, spring biased check valve connected in series in said air inlet passage.

4. The invention defined in Claim 3 in which said check valve is responsive to close at a negative pressure in said chamber more negative than a selected pressure.

5. The invention defined in Claim 1 which further comprises a container for water and means for connecting the ullage space of the container to said means for introducing water into said mixing chamber.

6. The invention defined in Claim 5 in which said container for water is fitted with a means for introducing ambient air to the interior of the container at a point which, in use, is below the water's surface.

7. The invention defined in Claim 6 which further comprises air inlet means in the form of an air inlet passage extending through said housing and opening at a point in said chamber between said inlet and outlet passage.

8. The method of introducing water into the fuel/air mixture of an internal combustion engine of the kind that is fitted with a PCV valve connected in a flowpath between the crankcase and the intake manifold which method comprises the steps of: introducing quantities of water into said flowpath at a position between the PCV valve and the intake manifold; utilizing negative pressure at said position to control the quantity of water so introduced as a function of the magnitude of said negative pressure.

9. The invention defined in Claim 8 which comprises the further step of introducing ambient air into said flowpath at a point between the PVC valve and the intake manifold when negative pressure at.that point is less negative than the amount required to actuate the PCV valve to its low flow position.

10. The invention defined in Claim 8 in which the ambient air and water are introduced at a common position in said flowpath.

11. The invention defined in Claim 8 in which a cavity is included in said flowpath at said common position and which comprises the further step of intermixing said water, said ambient air and the discharge from said PVC valve in said cavity.

12. Apparatus for adding water to the air/fuel mixture for gasoline engines comprising: a housing defining a generally cylindrically shaped mixing chamber; means defining an inlet passage and an outlet passage formed through the wall of said housing; coupling means for connecting said inlet passage to a flowpath extending from the outlet of a positive crankcase ventilation valve and for connecting said outlet passage to a flowpath extending to the intake manifold of a gasoline engine; and means for introducing water into said chamber in response to negative pressure in an intake manifold comprising a water inlet passage extending through said housing and opening to said mixing chamber at a point between said inlet and outlet passages.

13. The invention defined in Claim 12 which further comprises a normally open, spring biased check valve connected in series in said air inlet passage.

14. The invention defined in Claim 13 in which said check valve is responsive to close at a negative pressure in said chamber more negative than a selected pressure.

15. The invention defined in Claim 14 which further comprises a container for water and means for connecting the ullage space of the container to said means for introducing water into said mixing chamber.

16. The invention defined in Claim 15 in which said container for water is fitted with a means for intro ducing ambient air to the interior of the container at a point which, in use, is below the water's surface.

17. The invention defined in Claim 16 which further comprises air inlet means in the form of an air inlet passage extending through said housing and opening at a point in said chamber between said inlet and outlet passage.

18. The invention defined in Claim 1 which further comprises means for dividing the water into droplet sized quantities prior to entry into said mixing chamber.

19. The invention defined in Claim 18 in which said means for dividing the water comprises a screen in said means for introducing water.

20. The invention . defined in Claim 18 in which said means for introducing water includes a water storage container, a flow tube from the container to said mixing chamber, means including an air inlet tube in said container for forming droplets of water, and means for introducing the droplets so formed into said flow tube.

21. The invention defined in Claim 20 in which the container includes an ullage space, said flow tube affording communication between said ullage space and the mixing chamber.

22. The invention defined in Claim 21 in which said air inlet tube extends from an inlet at the exterior of said container, through said container at a point below its ullage space to an outlet in said ullage space, and which includes an inlet for container water at a point below said ullage space.

23. The invention defined in Claim 8 in which the water is introduced in the form of droplets.