CA1130669A - Fuel mixing device - Google Patents

Abstract

ABSTRACT
A mixer for forming a mixture of air and gaseous fuel for an internal combustion engine is disclosed. The mixer has an annular main body with a central outlet opening mountable on a conventional gasoline carburetor a peripheral flange around the outlet opening. An annular crown is mounted on top of the main body around the outlet opening to define with the main body an annular fuel distribution chamber. A fuel inlet chamber is provided in the main body for receiving fuel from a source of fuel and passing it tangentally into the distribution chamber. A flat crown plate is mounted above the crown and the outlet opening to define with the top of the crown a narrow, horizontal air inlet gap. Fuel orifices in the top of the crown discharge fuel from the distribution chamber into the narrow gap.
The mixer may be provided with a movable crown plate for dual fuel applications.

Description

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The present invention relates to fuel mixing devices and more particularly to devices for producing mixtures of air and gaseous fuel for use with internal combustion engines, either alone or in combination with the conventional liquid fuel carburetors.
With substantial increases in the cost of gasoline, which is conventionally used for operating internal combustion engines increased attention has been paid to alternative fuels for this purpose, for example propane and natural gas which are gaseous at atmospheric temperature and pressure conditions and can be stored as liquids in appropriate containers. Various systems have been proposed for converting gasoline powered internal combustion to use such a fuel. The systems conventionally include some form of pressure regulator vaporizer for evaporating the liquid fuel and controlling the pressure of the resulting gas and a mixer for mixing the gaseous fuel with air in appropriate amounts for supply to the engine.
One known form of mixer for such a system is a fuel injection nozzle that is inserted into a drilled and threaded bore in the gasoline carburetor for the engine at the point of minimum venturi diameter. In another known system, an adapter including a venturi is mounted on top of the conventional gasoline carburetor to supply air-fuel mixture -to its air inlet. This latter form of mixer is in many ways more satisfactory in that it has much greater range of applicability and does not require the major modification of the gasoline carburetor.

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One significant problem with the adapter style of mixer is fitting it into the limited space available in the engine compartments of a modern car. Where the mixer is to be mounted on top of the conventional gasoline carburetor, the space available is usually limited to that necessary for the air cleaner. The relatively long venturi style adapter mixer clearly cannot be used under the circumstances. While attempts have been made to construct equivilent mixers that are shorter, they still have a significant height that limits their applicability. Reference is made, for example, to Middelton et al United States Patent 2,939,775 where the venturi passage is in the form of a frusto-conical annulus which is said to have an effective length approximating that of a theoretically perfect linear venturi.
Other problems that are encountered with the known systems are the contxol of the fuel flow rate to match the engine demand and the ability to use both liquid and gaseous fuels.
According to one aspect of the present invention there is provided a mixer for forming a mixture of air and gaseous fuel for an internal combustion engine comprising:
an annular main body with a central outlet opening for the mixture and a peripheral flange around the outlet opening;
an annular crown mounted on top of the main body around the outlet opening to define with the main body an annular fuel distribution chamber;
a fuel inlet chamber in the main body for receiving fuel from a source thereof and passing it into the distribution chamber tangentally thereof;

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a flat crown plate mounted above the crown and the outlet opening define with the top of the crown a narrow, horizontal air inlet gap; and fuel inlet orifices in the top of the crown for discharging fuel from the distribution chamber into the narrow gap.
With a mixer of this sort, the air flow into the mixer is perpendicular to the flow through the carburetor rather than coaxial with it. The mixer can be made of a sufficiently low height that lt can be located substantially within an air cleaner of lQ conventional dimensions. The narrow gap between the crown and the crown plate provides a high velocity air flow across the fuel inlet orifices that induces the fuel into the air flow in an amount depending upon the speed of the air flow. This effect can be angmented if the orifices discharge into the gap immediately downstream of a steplike notch in the crown. Alternative, the inner face of the crown may be convexly rounded and the inlet orifices sloped inwardly toward the axis of the crown.
Furthermore, with the fuel drawn directly into the air flow ~; through the narrow gap between the crown and the crown plate, the homogeniety of the mixture is much better than where fuel is - supplied to the periphery or to the center of a laminar flow such as in a venturi style mixer.
According to another aspect of the present invention ` there is provided a gaseous fuel mixer for a dual fuel supply system for an internal combustlon engine having a conventional liquid fuel carburetor having an air inlet, said mixer comprising:

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an annular housing adapted to be mounted on the air inlet of the carburetor with an annular fuel distribution chamber of the housing surrounding the carburetor air inlet, said housing including a gaseous fuel inlet into the annular distribution chamber and a plurality of fuel discharge orifices for discharging fuel from the distribution chamber in a direction away from the carburetor inlet;
a crown plate mounted over the housing for movement between a liquid fuel position spaced from the housing and a gaseous fuel position adjacent the housing and forming therewith a narrow annular gap into which the fuel discharge orifices discharge.
As is known, liquid fuels, such as gasoline, require a considerably greater volume of air for combustion than do gaseous fuels such as propane and natural gas. Thus, it is necessary to provide in a dual fuel system, some arrangement for increasing the air flow when changing the system over to operate on a liquid fuel. With the described system, the changeover is particularly simple and may be performed automatically. In one preferred embodiment, two vacuum operated diaphragms are used for retracting the crown plate from its gaseous fuel position to its liquid fuel position.
According to a further aspect of the present invention there is provided an apparatus for supplying a mixture of air and a gaseous fuel to an internal combustion engine comprising an annular fuel distribution crown, a crown plate positioned on one side of said crown and defining therewith a narrow, annular gap, a plurality fuel outlet orifices in the crown for discharging fuel into the gap in a response to an air flow therethrough and ~ ~3~

means for supplying gaseous fuel to said crown at atmospheric pressure in volumes dependent on the flow rate of fuel from said orifices.
The use of a "demand" type of fuel vaporizer-regulator with the annular fuel distribution chamber enables a reduction of the chamber size with a consequent reduction in the overall size and cost of the mixer. Where fuel is supplied to the mixer chamber under pressure, a large volume chamber in the nature of a plenum rather than a manifold is necessary to stagnate the flow of fuel in the plenum and produce a uniform distribution throughout. A
further improvement can be obtained if the fuel is supplied to the fuel distribution chamber so as to produce a cyclonic or swirling effect around the chamber to ensure uniform fuel distribution throughout.
According to a further aspect of the present invention there is provided, in a mixer for producing a mixture of air and gaseous fuel comprising an annular fuel distribution chamber, a plurality of fuel outlet orifices from the chamber and a crown plate extending over the chamber to form therewith a narrow gap 20 into which the fuel outlet orifices discharge, the improvement comprising a stepped recess on a face of the distribution chamber confronting the crown plate, with the fuel outlet orifices discharging into said gap downstream of the step.
There is a flow separation at the stepped recess generat-ing a low pressure, turbulent flow immediately downstream of the step. The discharge of fuel from the fuel inlet orifices into this low pressure turbulent flow improves the fuel induction and mixing effects.

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In the accompanying drawings, which illustrate exemplary embodiments of the present invention:
Figure 1 is a sectional view of a gaseous fuel mixer;
Figure 2 is an exploded view of the mixer of Figure l;
Figure 3 is a sectional view like Figure 1 of a mixer for dual fuel application;
Figure 4, found on the same sheet as Figure 1, is a sectional view through the fuel inlet chamber; and Figure 5, also found on the same sheet as Figure 1, is a diammetrical section of an alternative form of crown.
Referring to the drawings, and particularly to the embodiment illustrated in Figures 1 and 2, there is illustrated a mixer 1 for forming a mixture of air and gaseous fuel for an internal combustion engine. The mixer has an annular main body 2 including a central cylindrical mixture outlet opening 4 surrounded by a flange 6. The flange 6 is equipped with a crown seat 8 immediately around the upper end of outlet opening 4 for mounting a crown as will be described in the following.
Surrounding the crown seat, the flange 6 has a frusto-conical section 10 that slopes away from the crown seat. This isfollowed by a radial, annular, peripheral section 12 to form a seat for an air cleaner as will be described in the following.
An inlet chamber 14 is formed on one side of the main body, beneath the crown seat 8. As most particularly illlustrated in Figure 4, this includes a trapezodial recess 16 open at the top to the crown seat and two threaded bores 18 opening into the ~3~

inlet chamber tangentially to the crown seat and sloping up-wardly toward the open top of inlet chamber 14. These two bores are identical. One oE them receives a fuel inlet fitting 20 connected to a gaseous fuel line 22 and the other is fitted with a plug 24. The plug 24 and fitting 20 are interchangeable so that the fuel line 22 can be led in rom either side of the mixer.
The main body 2 of the mixer also has a threaded bore 26 radially outside of the inlet chamber 14. This receives a vaporexhaust fitting in the form of elbow 28 that is in use, connected to the valve cover of the engine so that vapors generated in the valve cover will be led into the mixer and ultimately burned in the engine to prevent their escaping to the atmosphere.
As will be appreciated, a single main body will not be able to fit all carburetors in use. To adapt the mixer to various carburetor sizes, an adaptor 30 is fitted to the central outlet opening 4. This adapter consists of a radial flange 32 with a notch 34 along its outer periphery to receive the end of the central outlet opening 4 of the main body 2. At the center of the flange 32 is a cylindrical element 36 sized to fit a given size of carburetor.
An annular crown 38 with the general shape of an invented U in radial section is fitted to the crown seat 8 to provide an annular fuel distribution chamber 40 immediately surrounding the central opening 4 of the main body. The crown has a convexly curving face 42 that forms a continuation of the inner cylindrical face of the central outlet opening in the main body and curves outwardly to form a bell like entry for the main body outlet opening. A stepped notch 44 ~3~!~6~

is formed in the crown at the top of the inner face 42.
Immediately inside of this stepped notch are a plurality of fuel outlet orifices 46 oriented parallel to the axis of the crown and extending from the distribution chamber 40 to the base of the stepped notch 44.
A crown plate 48 is mounted above the crown 38 so as to form a narrow annular gap 50 between the top of the crown and the crown plate. The crown plate, crown and main body are secured together by means of cap screws 52 passing through the crown plate, the crown and the main body and nuts 54 fitted onto the cap screws beneath the main body. Spacers 56 are located on the cap screws 52 between the crown plate and the crown to maintain the desired gap 50.
As discussed in the foregoing, the main body 2 has a radial peripheral section 12 that forms a seat for an air cleaner 58. This cleaner is of conventional annular form with a pleated annular filter element 60 faced on either side with a plastic seat 62. The preferred filter has a filter element of fiberglass material since this is noncombustable and reusable.

A flat, circular cover plate 64 extends over the top of the cleaner 58 and is secured in place by means of a threaded rod 66 threaded into the conventional fitting on the gasoline carburetor (not shown) and a wing nut 68.
In operation, the gaseous fuel is supplied at atmospheric pressure (0 pressure gage~ through the inlet chamber 14 to the distribution chamber 40. The orientation of the bores 18 and the fuel inlet fitting 20 ensures that the fuel is introduced into the distribution chamber 40 tangentally to produce a cyclonic 3L~ 3r~

or swirling motion around the distribution chamber 40, to ensure uniform fuel distribution within the chamber. ~ecause -the fuel is supplied at atmospheric pressure there will be no flow into the distribution chamber or through the fuel orifices 46 unless there is a pressure less than atmospheric at the outlet of each orifice 46. The desired subatmospheric pressure is generated when the engine draws fuel through the gap 50 between the crown plate 48 and the crown 38. As the air flow passes the stepped notch 44, the abrupt change in flow cross section produces a low pressure, turbulent zone immediately at the outlet of each of the fuel orifices which will induce the flow of fuel from the distribution chamber 40 through each orifice 46 and mix the fuel thoroughly with all of the air entering the central mixing zone bounded by the crown plate, crown and main body. As the engine demand increases, the air flow through the gap 50 increases, the air pressure at the outlets of orifices 46 decreases and fuel is drawn more rapidly into the mixer from the distribution chamber 40.
It will be observed that the crown is recessed into the surrounding air cleaner and ~hat the overall height of the complete mixer unit, including air cleaner, is very little more than the total height of the air cleaner.
Turning now to Figure 3, this Figure illustrates a gaseous fuel mixer for a dual fuel supply system for an interal combustion engine. This mixer differs from that of Figures 1 and

2 in that it employs cap screws 70 that do not pass through the crown plate 48 but provide the desired gap using a specified cap thickness of the screw head or may also retain the spacers 56, the crown 38 and the main body 2 together. In this embodiment, two frustoconical diaphragms 72 are mounted on the underside of the cover plate 64 by means of respective annular retainers 74 which compress annular lips extending from the maximum diameter ends of the frusto-conical diaphragms 72 against the underside of cover plate 64 in an air tight manner.
Within each diaphragm 72 is a plate 76 conforming to the inside of the smaller diameter end of the diaphragm. ~hat end of the diaphragm is compressed between the respective plate 76 and the top face of the crown plate by a rivet 78 passing through the crown plate, the diaphragm and the plate.
A spiral coil spring 80 is positioned within each diaphragm with one end bearing on the underside of the cover plate 64 and the other end bearing on the associated plate 76 so as to bias the crown plate 48 into engagement with the spacers 56 so as normally to provide a fixed air gap 50 between the crown and the crown plate. The conical shape of the spring allows it to compress flat. A pair of fittings in the form of elbows 82 are connected to the cover plate 64 to communicate with the chambers on the insides of the respective diaphragms 72. The elbows 82 are connected to respective vacuum hoses 84 that are connected via a Y fitting 86, into a main vacuum conduit 88. The conduit 88 contains, in series, an operated solenoid vacuum valve 90 and a check valve 92. It is ultimately ~3~

connected to a manifold coupling 94 so as to be exposed at that point to manifold vacuum. A tee 96 is inserted in the line 88 between the check valve 92 and the manifold connection and is connected to a vacuum line 98 to a vaporizer lG0.
The vaporizer 100 is also connected to a fuel inlet line 102 which contains a solenoid operated fuel valve 104. Two coolant lines 106 supply heated engine coolant to the vaporizer to supply the heat of vaporization of the fuel being evaporated, so as to maintain the temperature of the vaporizer. A fuel outlet line 108 leads from the vaporizer to supply gaseous fuel to the inlet chamber 14 of the main body 2. A flow regulator 110 is inserted in the line 108.
As illustrated, the mixer is mounted on a gasoline carburetor supplied with gasoline through a line 114. Flow through the gasoline line 114 is controlled by a solenoid operated gasoline valve 116. The gasoline valve 116, the gaseous fuel valve 104 and the vacuum valve 90 are all connnected to a switch 118 for switching the system from liquid fuel to gaseous fuel or vice versa. The gaseous fuel valve 104 is connected to the switch 118 via a vacuum switch 120 operated by a vacuum in line 98, derived by an appropriate tee fitting 122 and a vacuum line 124.
Any "zero governor" style vaporizer may be used with the present mixer. A vaporizer of this type supplies fuel in response to a vacuum in the fuel outlet line 108. Fuel supply : is prevented in the absence of a vacuum in line 98.

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The switch 118 is a five position switch. When the switch knob is pressed, one set of contacts is closed to open a priming valve so as to supply pressurized fuel to the third stage of the vaporizer.
The switch knob also has four rotary positions.
One of these is for running on gaseous fuel wherein the solenoids of vacuum valve 90 and gasoline valve 116 are not energized so that the valves are closed, and the solenoid of gaseous fuel valve 104 is energized and the valve open provided the vacuum switch 120 senses a vacuum in the engine manifold.
A second position of the switch 118 is for running on gasoline. When the switch is in that poisition, the solenoid valve of gasoline 116 and the solenoid valve vacuum of 90 are energized to open -the associated valves. The gaseous fuel valve 104 is not energized and the valve is closed. Opening the gasoline valve permits the supply of gasoline to the carburetor 112 while opening the vacuum valve 90 permits the application of manifold vacuum to the collapsible chambers within diaphragms 72, so that the crown plate 48 is withdrawn to an upper position in engagement with the retainers 74 to enable the supply of adequate combustion air to the carburetor.
The check valve 92 acts as a vacuum retainer to retain the vacuum in the conduits 88 and 84 and the chambers of diaphragms 72 dispite any momentary loss of manifold vacuum. When closed, the vacuum valve 90 vents conduit 88 to atmosphere.

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The remaining two posi~ions on the switch 118 are change over positions. To change over to gasoline from gaseous fuel operation, the switch is turned to one of these positions where both the gasoline and gaseous fuel valve solenoids are energized and the valves open. This enables the enyine to operate on gaseous fuel until the carburetor float bowl is full. At that time, the switch is turned to the gasoline position to close the gaseous fuel valve.
To reverse this operation, the switch knob is turned to the remaining position in which both valves are closed.
This allows the engine to run on the gasoline in the carburetor float bowl until it is empty. At that time, the valve is turned to the gaseous fuel position for operation. The switch knob turns clockwise only to ensure proper operation.
The flow regulator 110 in the gaseous fuel line 108 is a variable flow restriction in this line. It is a "fine tuning"
adjustment on the amount of gaseous fuel supplied to the mixer in response to a given air flow into the mixer through the gap 50.
Turning to Figure 5, this illustrates an alternative form of crown that may be employed in the mixer. This crown 126 has an inner face 128 that is convexly curved from a vertical orientation adjacent the central opening of the mixer main body up to a horizontal orientation at the top of the crown adjacent the radially outer face. There is no stepped notch in the crown and the fuel orifices 46 slope inwardly towards ~3~i6fi9 the axis of the crown. It has been found that an angle of 27 is particularly suitable.
In either embodiment of the crown, the number and size of the fuel orifices can be varied according to engine displacement, athough it is preferred to provide a crown configuration that will suit a range of engine displacements and to tune the system using the flow regulator 110.
While specific embodiments of the invention have been described in the foregoing, it is to be understood that the present invention is not limited to the specific constructions illustrated. The scope of the invention is defined in the appended claims.

Claims (9)

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

1. A gaseous fuel mixer for a dual fuel supply system for an internal combustion engine having a liquid fuel car-burettor with an air inlet, the mixer comprising an annular housing mountable on the carburettor air inlet and having an annular fuel distribution chamber which surrounds the air inlet of the carburettor when mounted thereon, the fuel dis-tribution chamber having gaseous fuel inlet means and gaseous fuel outlet means, a crown plate mounted over the housing, and means for moving the crown plate towards and away from the housing between a liquid fuel position and a gaseous fuel position, the crown plate being spaced from the housing in the liquid fuel position by a relatively large predetermined distance to enable an adequate amount of air to flow between the crown plate and the housing into the carburettor air inlet when liquid fuel is supplied to the carburettor, the crown plate being spaced from the housing in the gaseous fuel position by a relatively small distance to enable a desired amount of air to pass between the crown plate and the housing into the carburettor air inlet during gaseous fuel operation, and the gaseous fuel outlet means being positioned adjacent the crown plate to cause air passing between the crown plate and the housing during gaseous fuel operation to induce flow of gaseous fuel from the fuel distribution chamber through the fuel outlet means for mixture with the air and subsequent passage into the car-burettor air inlet.

2. A fuel mixer according to claim 1 wherein the crown plate is flat from its outer periphery inwardly to at least a substantial distance beyond the fuel outlet means of the housing.

3. A fuel mixer according to claim 1 or claim 2 wherein the housing has step-like notch means adjacent the fuel outlet means to enhance inducement of flow of gaseous fuel from the fuel outlet means by air flowing between the crown plate and the housing.

4. A fuel mixer according to claim 1 wherein the fuel inlet is positioned to direct fuel into the distribution chamber tangentially thereof.

5. A fuel mixer according to claim 1 wherein the fuel outlet means comprises a series of orifices spaced around the housing.

6. A fuel mixer according to claim 1 wherein the crown plate moving means is operable from a position remote from the mixer.

7. A fuel mixer according to claim 6 including resilient means biasing the crown plate towards its gaseous fuel position.

8. A fuel mixer according to claim 7 wherein the crown the crown plate moving means comprises means providing at least one collapsible chamber associated with the crown plate and means for supplying a vacuum pressure to the collapsible chamber means to move the crown plate against the bias of the resilient means to the liquid fuel posi-tion.

9. A fuel mixer according to claim 8 including a liquid fuel supply line for supplying liquid fuel to the carburettor, a gaseous fuel supply line for supplying gaseous fuel to the mixer, a vacuum supply line for apply-ing a vacuum pressure to the collapsible chamber means, valve means for each of said lines, and means for selectively operating the valve means simultaneously to a liquid fuel supply condition wherein the liquid fuel line is open, the gaseous fuel line is closed and the vacuum line is open, and to a gaseous fuel supply condition wherein the liquid fuel line is closed, the gaseous fuel line is open, the vacuum line is closed and the collapsible chamber means is vented to atmosphere.