GB2345089A

GB2345089A - A carburation device with a piezoelectric or heating means to atomise and eject fluid

Info

Publication number: GB2345089A
Application number: GB9828543A
Authority: GB
Inventors: Richard Anthony Kirk
Original assignee: Canon Research Centre Europe Ltd
Current assignee: Canon Technology Europe Ltd
Priority date: 1998-12-23
Filing date: 1998-12-23
Publication date: 2000-06-28
Also published as: GB9828543D0

Abstract

A carburation device 12 for supplying fluid e.g fuel to an air intake duct 11 of an internal combustion engine comprising comprises a passage 24 adapted at one end 25 to communicate with the air intake duct 11, fluid supply means 21, 22 to maintain fuel in the passage 24, and an electrically operable ejection means 26 to eject a single fluid droplet from the passage 24 into the duct 11 on receipt of a respective control signal. The ejection means 26 may be a heater and the activation of which causes a local vapour bubble to form in the passage 24 which results in the fluid, adjacent the open end 25 of the passage 24, being ejected into the duct 11 as a droplet. Alternatively the ejection means 26 may be a piezoelectric element the activation of which causes shock waves in the fluid resulting in ejection of the fluid adjacent to the end of the passage. The control signal may be provided by provided by a processor and based on engine operating parameters.

Description

Carburettor The present invention relates to carburettors for internal combustion engines, and is particularly concerned with a carburettor which allows accurate control of the size and quantity of individual fuel droplets to produce a uniform droplet size.

In an internal combustion engine, a mixture of air, fuel and optionally fuel additives, lubricants, etc. is admitted to a combustion chamber and therein compressed and ignited. The expansion of the heated gas drives a piston linked to a drive shaft to produce a rotary power output. The fuel and air mixture is conventionally formed using a venturi-type carburettor, or by means of a fuel injection system with additives pre-mixed in the fuel.

In a venturi-type carburettor, a restriction is placed in the flow duct carrying air to the engine, and the drop in static pressure of the air which this flow restriction causes is used to draw fuel from a float chamber through a jet. The fuel forms a spray into the intake air stream of the venturi and the resultant mixture of air and fuel droplets is led to the combustion chambers of the engine for ignition. The size of droplets varies greatly, and is not precisely controlled.

Furthermore, there is little scope for independent variation of fuel and air mass flow rates, since variations in the air flow give rise to corresponding changes in fuel flow rates.

To produce a practical carburettor, capable of providing an acceptable fuel and air mixture for all engine conditions, and capable also of providing rapid engine response to demands for increased power, a complex mechanical arrangement of pumps, valves and flow restrictors is usually required. The carburettor is thus an expensive and complicated sub-assembly to produce, and the fine jets and flow restrictors in the carburettor are susceptible to blockage and maladjustment which necessitates skilled labour to dismantle the carburettor and reassemble and adjust it after cleaning. Another disadvantage of conventional carburettors is that at idling speeds it is difficult to produce a low fuel flow rate by means of the venturi, and thus the fuel consumption at idle is often greater than is necessary to sustain idling speed.

In recent years, fuel injection systems have become available as an alternative to the conventional venturitype carburettor. In some such fuel injection-systems, there is provided a fuel pump which draws fuel from a tank. The outlet of the pump is led to a fuel manifold, in which the fuel is maintained at high pressure. A pressure relief valve controls the pressure in the fuel manifold, returning excess fuel to the tank. Solenoid operated valves are provided in communication with the high-pressure fuel in the fuel manifold, the solenoid operated valves being opened intermittently to emit a spray of high-pressure fuel into the inlet manifold of an engine, preferably immediately upstream of a cylinder intake port. Typically, each cylinder is provided with a respective solenoid operated valve or"injector". The operation of the solenoid valves is controlled electronically, to emit a spray of fuel for an interval synchronised with the intake stroke of the particular cylinder. The quantity of fuel injected at each interval during the induction stroke of the engine is controlled by varying the duration of the spray, but the sizes of individual droplets in the spray is not closely controllable, and thus the full efficiency potential of the engine is not realised. Furthermore the rate of fuel flow during the injection interval is not controllable beyond the simple"on"or"off"function of the injector solenoid valve.

The venturi-type carburettor and fuel injection systems outlined above are conventional in spark-ignition engines, wherein the compressed fuel and air mixture is ignited by a spark from a spark plug within the cylinder.

However, the size distribution of droplets produced by the conventional systems is not finely controllable, which results in the efficiency of the engine being less than its full potential.

In order to improve the efficiency of an engine, the present invention seeks to improve the production of the fuel/air mixture being fed to the engine by providing an individual control of the formation and delivery of each fuel droplet into the engine intake air stream. To achieve this, a plurality of"drop on demand"devices may be used, each of which produces a single fuel droplet in response to a respective electrical control signal. Such a"drop on demand"device may comprise an open-ended fuel-filled passage which communicates with the intake air duct, and an electrically operated ejection device associated with the passage which causes a single droplet of fuel to be expelled from the passage when a control signal is applied. The ejection device may be a piezoelectric element arranged to impart a movement to the fuel in the passage, or may be a heater element arranged to vaporise a part of the fuel in the passage to form a bubble which displaces fuel from the passage.

In yet another type of"drop on demand"device, a flexible membrane divides the passage into a fuel passage and a propellant chamber, and a liquid in the propellant chamber is vaporised by a heater to form a bubble which deflects the flexible membrane and ejects a droplet of fuel from the passage.

The present invention seeks to provide a carburation device and system in which each fuel droplet is produced and ejected into an intake air stream in response to a discrete control signal. The carburation device may be used in a first arrangement to deliver a substantially continuous stream of droplets into an air duct leading via a manifold to a plurality of cylinders.

Alternatively, in a second arrangement the carburation device may be placed in a duct supplying only a single cylinder, and the ejection of droplets may be effected in intermittent"bursts"tuned to coincide with the induction stroke of the cylinder. Clearly, in a multi-cylinder engine the number of carburation devices will usually correspond to the number of cylinders.

Since each droplet is ejected in response to a respective control signal, then in this second arrangement the system may provide control signals to the carburation device during only a part of the induction stroke of the respective cylinder, to define a"fuel injection interval". The device and system of this second arrangement thus provides for the production of a fuel droplet/air mixture wherein the distribution of fuel droplets and also optionally the size of each droplet is finely controllable during the interval of fuel injection.

A further object is to provide a carburation system which can be controlled to vary the amount and size of droplets in an air/fuel mixture entering a combustion cylinder over the interval of fuel injection during the intake stroke of the cylinder. By producing each fuel droplet in response to an individual control signal, the rate of fuel flow is precisely controllable by controlling the rate at which signals are given to the ejection devices. Thus the mixture strength can be varied within the fuel injection interval.

In an advantageous development, a carburation device and system are provided wherein a fuel and a performance enhancing fuel additive, or first and second alternative fuels, can be supplied separately or together to an engine.

A third arrangement of the device is contemplated for use in an engine having a conventional fuel delivery system, wherein the carburation device is used to deliver a fuel additive or lubricant or other engine performance modifier to the air intake of an engine. As in the previous arrangements, the additive may be delivered to a common air intake as a substantially continuous stream of droplets, or may be delivered to an individual cylinder in bursts timed to coincide with the cylinder's induction stroke.

According to a first aspect of the present invention, there is provided a carburation device for supplying fluid to an engine having an air intake duct, comprising: a fluid passage communicating at one end with the air intake duct; fluid supply means to maintain the passage filled with fuel; and electrically operable ejection means to eject a single droplet of fluid from the passage into the duct on receipt of a respective control signal.

The fluid may be a fuel, either with or without one or more performance modifiers pre-mixed in the fuel, or alternatively the fluid may be a fuel adjunct or an engine performance modifier such as an upper cylinder lubricant, anti'knock'agent or the like.

In an advantageous embodiment, a plurality of passages are provided to communicate with the air intake duct, each passage having an associated ejection means operable by a respective control signal to eject a fluid droplet from the passage.

According to a second aspect of the invention there is provided a carburation system for supplying fluid to an engine comprising a carburation device and a control means, wherein the carburation device includes an ejection means operable to eject a single fluid droplet from a fluid passage into an engine air intake duct on receipt of a respective control signal, and the control means is operable to provide one or more control signals to the ejection means. The control means preferably receives inputs from sensing devices which detect engine parameters such as engine speed, crankshaft position, and engine temperature, and operational parameters such as ambient temperature, humidity, altitude and engine control positions. The control means may produce control signals to operate the ejection means of one or more fluid passages to eject fluid droplets at a rate determined by the control means on the basis of sensor inputs received by it.

In an advantageous embodiment, the control signal provided to each ejection means may be variable to vary the size of the droplet ejected, and the frequency with which control signals are sent to a particular ejection means may be varied to vary the number of droplets ejected by the ejection means in a determined time.

A third aspect of the invention provides a method of supplying fluid to an engine having an air intake duct, comprising the steps of: providing a carburation device according to any of claims 1 to 13; sensing an engine parameter; applying at least one control signal to the fluid ejection means to eject at least one fluid-droplet from the passage into the air intake duct on the basis of the sensed parameter.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a vehicle engine fitted with the carburettor of the present invention; Figure 2 is a sectional view taken along the inlet duct axis of the carburettor; Figure 3 is an axial view of the carburettor of Figure 2; Figures 4A to 4E show stages in the emission of a fuel droplet; Figure 5 is a partial section view, similar to Figure 2, of a second embodiment of the invention; Figures 6A, 6B, and 6C illustrate the operation of the carburettor of Figure 5; Figure 7 is a schematic illustration of a control system for the carburettor of the present invention; Figure 8 is a schematic sectional view of a twostroke engine fitted with the carburettor of the present invention; and Figure 9 is a schematic plan view of a multicylinder engine fitted with multiple carburettors.

Referring now to Figure 1 there is shown schematically a vehicle engine E having an air filter (10) from which intake air is fed via an intake duct (11) through a carburation ring (12) to the engine E. Between the carburation ring (12) and the engine E is a butterfly valve (13) to control the amount of the fuel/air mixture entering the engine. In alternative embodiments, the butterfly valve 13 may be placed upstream of the carburation ring 12 in air intake duct 11. The engine E is a conventional internal combustion engine in all respects other than its fuel supply system.

The fuel supply system for the engine E comprises a fuel tank (F1), which supplies fuel via a pump (14) to the carburation ring (12). A second fuel tank (F2) and a second fuel pump (14A) may also be provided, to supply a second fuel or other performance improver such as water, to the carburation ring (12), as will be described later.

The purpose of the carburation ring (12) is to provide a supply of fuel droplets to the air stream passing along the intake duct (11). The manner in which fuel droplets are formed will now be described, with reference to Figures 2 to 4.

Figure 2 shows an axial section of the carburation ring (12) seen in Figure 1. The carburation ring (12) comprises an annular body (20) which surrounds the intake duct (11). An annular fuel reservoir chamber (21) extends concentrically with the inlet duct (11), and is supplied with fuel via fuel feed spigot (22), to which is connected a fuel line (23) leading from the pump (14).

As can be seen in Figures 3 and 4, extending radially inwardly from the annular reservoir (21) are a plurality of passageways (24) open at their radially inner ends (25) to the inlet duct (11). The passageways (24) may be circular or rectangular or any other convenient shape in cross-section, as may be the reservoir (21). The diameter or transverse dimensions of the flow passages 24 area made sufficiently small, and the pressure in the manifold 21 is controlled, so that the fuel is drawn into the passages 24, but does not emerge from the open ends 25 of the passages 24.

The body (20) of the carburation ring (12) may be integrally moulded from any suitable plastics material or formed from metal. It is foreseen that the carburation ring (12) may be constructed from an assembly of coaxial annular components.

Adjacent each of the passages (24) is a heating element (26), the purpose of which will be described with reference to Figures 4A to 4E.

In Figure 4A, the carburation ring (12) is shown in partial sectional view. The fuel reservoir (21) and the passageway (24) are filled with fuel from the fuel supply line (23) by the pump (14). The output of the pump is so arranged so that the fuel will fill the passageways (24) but will not flow out of the passageways (24) under the influence of the pump (14) alone. A pressure limiting device (not shown) such as a pressure relief valve or a float chamber arrangement may be provided to regulate the fuel pressure to a desired value.

In order to form a fuel droplet and project it into the intake duct (11), electrical heating element (26) is energised by applying one or more voltage pulses via conducting wires (30).

As is seen in Figure 4B, the localised heating of the fuel by the heating element (26) causes a fuel vapour bubble (27) to form in the passageway (24). The formation of the vapour bubble (27) causes the fuel adjacent the open end (25) of the passageway (24) to be ejected into the inlet duct (11). It is seen in Figures 4C and 4D, the vapour bubble (27) eventually fills the entire passageway (24) and exits from the end (25) of the passageway, ejecting the fuel droplet (28) into the inlet duct (11).

Heating element (26) is then de-energised, and the pressure of the fuel in the reservoir (21) and capillary forces causes the fuel to refill the passageway (24), as is shown in Figure 4E. The minimum time interval between the ejection of successive droplets 28 will depend on how quickly the fuel can refill the passageway after the ejection of a droplet. Typical cycle frequencies for the ejection of droplets may be up to 20kHz, with an optimum frequency of about 5kHz.

In a typical car engine, the fuel flow rate at an engine speed of 3500rpm may be, say, 5.4 litres/hour.

This corresponds to an average flow rate of 1. 5cc/second.

If the average droplet size produced by the ejector is 6 nanolitres, then the steady rate of production of fuel droplets to supply the engine will be some 250,000 droplets per second. This is easily achievable with 50 passages operating at a frequency of 5kHz.

Since this is an average flow rate, then a steady production of fuel droplets at this rate will be adequate to supply an inlet manifold of a multicylinder engine.

When the carburation device is to be used on a single cylinder engine, or to supply only one cylinder of a multicylinder engine, then the device will preferably be operated only during part or all of the intake or induction stroke of the cylinder. Thus, for a four stroke cycle, the actual rate of production of droplets will be about four times the average rate during the induction stroke, with no droplet production during the compression, power and exhaust strokes. By providing a sufficient number of passages operating at high frequency, the required fuel charge can be supplied during the induction stroke or during a part thereof.

As will be appreciated, the speed at which the fuel droplet (28) is ejected from the passageway (24) will depend on the amount of energy provided to the heating element (26) and the rate at which the energy is provided.

The volume of the fuel droplet ejected at each energisation of the heating element (26) will depend principally on the dimensions of the passageway (24) and the distance between the heating element (26) and the open end (25) of the passageway (24), in arrangements wherein the fuel vapour bubble is allowed to exit the passageway 24. A plurality of heating elements may be provided at different distances from the open end 25 of the passageway 24. By applying the electrical energy to a selected one or to a combination of two or more heating elements, the size of the fuel droplet ejected may be controlled. Larger droplets are ejected when heaters further from the open end 25 of the passage 24 are energised.

As an alternative to the ejection process described above, it is possible to eject a droplet of fuel without the vapour bubble reaching the end (25) of the passageway (24). The energy supplied to the heater (26) is controlled so that the vapour bubble collapses before exiting the passageway (24), but after a fuel droplet (28) has separated from the fuel in the passageway. In such arrangements, the fuel droplet size will be closely related to the amount of energy supplied to the heater.

Energisation of the heating elements (26) of the carburation ring (12) is effected under the control of a control system (40) shown schematically in Figure 1.

Control system (40) receives control inputs from a plurality of sensors associated with the engine E. In the arrangement shown in Figure 1, the inlet duct (11) is provided with a temperature sensing thermocouple (41) and an anemometer (42) to measure the temperature and the speed, respectively, of air flowing through the inlet duct (11). The relative humidity of the ambient atmosphere is measured by a hygrometer (43). A speed sensor (44) associated with the engine crank shaft provides a signal corresponding to the engine rotation speed, and a position detector (45) provides a signal corresponding to the position of the accelerator pedal of the vehicle. An engine temperature sensor (49) provides an engine temperature signal to the control circuit (40).

On the basis of these sensor inputs, the control circuit (40) determines the amount of fuel required by the engine, and energises the heating elements (26) associated with the fuel passageways (24) so as to expel fuel droplets into the inlet duct at the appropriate rate. The mixture of air and fuel droplets then passes the butterfly valve (13), enters the engine E and is burnt in the conventional manner.

The control circuit (40) may also include a manual input means (47), which the driver of the vehicle may use to select different modes of operation of the control circuit (40). For example, the control system (40) may be arranged to operate in an"economy"mode to minimise fuel consumption, in a"sport"mode in which engine power output is maximised, or in a"high altitude"mode wherein the fuel/air ratio is adjusted to compensate for the reduced oxygen content of the air. In each case, the manual input means may provide selectors for leaded or unleaded fuel, and for the use of a fuel additive such as water, to enhance performance.

Figure 7 illustrates in detail the control system (40). In the embodiment illustrated, the control system (40) comprises a central processor (50) which executes control programs stored in a memory (51), which is preferably a ROM chip. Also linked to the processor (50) is a RAM memory (52), providing working memory for the processor.

The processor (50) receives input signals from the various sensors associated with the engine. As shown in the arrangement of Figure 1, the sensors include temperature and speed sensors (41 and 42) placed in the engine inlet duct (11) to detect temperature and speed of the incoming air, temperature and speed sensors (49 and 44) which provide signals relating to the engine temperature and engine rotation speed, hygrometer (43) to detect ambient humidity, accelerator pedal position sensor (45) and mode selector (47). While all these sensors are illustrated in Figure 1 and shown in Figure 7, it will be appreciated that not all of the sensors may be necessary for the satisfactory control of the carburation of the engine. For example, measurement of the air speed of the inlet duct by sensor (42) may be unnecessary, since the air speed will be closely dependent on engine rotation speed and accelerator pedal position. The control circuit may also be provided with crankshaft or camshaft angle or position information, so that control circuit can determine the position of each piston and the particular stroke (induction, compression, power, or exhaust) being executed by it.

Also linked to the processor (50) are memories (53, 54 and 55) which correspond to the various modes of operation of the control system.

The processor (50) provides an output signal to a driver circuit (56) which controls the heater elements (26) of the carburation ring.

In operation, the driver first selects the mode in which the engine is to operate, and the fuel and additives if desired, using the mode selector (47). The other sensor inputs are also fed to the processor (50), which under control of the program stored in ROM (51) selects the appropriate mode memory area (53,54 or 55).

Each mode memory area (52,54,55) provides the data necessary for the processor to generate appropriate control signals for each combination of sensor input values to operate the engine in that mode. In the embodiment illustrated, each mode memory area is in the form of a look-up table (LUT) which provides information for the processor to command a value for the fuel flow rate required for each combination of sensor input values to operate the engine. Under control of the program stored in the ROM (51), this fuel flow output signal is provided to a driver circuit (56) which controls the heating elements in the carburation ring (12) so as to actuate the heating elements at the frequency required to provide the fuel flow rate necessary. The fuel flow rate signal may also be provided to a pump controller circuit (57) to control the operation of the fuel pump (14) to ensure an adequate supply of fuel to the carburation ring (12) and prevent over supply.

The driver circuit (56) may be linked to the carburation ring (12) so as to control each of the heater elements (26) individually. Alternatively, groups of heater elements (26) may be linked together for collective control by the driver circuit (56). The groups of collectively controlled heater elements (26) may correspond to a number of passageways (24) which are adjacent each other in the circumferential direction of the carburation ring (12), or may correspond to a group of passageways (24) which are evenly distributed around the circumference of the carburation ring (12).

In operation, the processor may sample the outputs of each of the sensors in turn, and store the sensed values in the RAM (52). At the next sampling time for each sensor, the value stored in RAM 52 is updated, and this value remains until the next sampling and updating.

On the basis of the stored values, the CPU may then access the appropriate look-up table (53,54 or 55) to retrieve the required fuel flow rate value. Sampling of the sensor output signals may take place many times per second so that the values stored in RAM (52) are constantly updated. The stored values in RAM (52) may be provided to vehicle instrumentation systems such as the dashboard instruments, to provide an indication to the vehicle driver of the engine performance parameters such as engine revolutions, engine temperature, and instantaneous fuel flow rate (fuel economy).

In an alternative embodiment of the thermal type of "drop-in-demand"ejector means, the passage may be partially defined by a flexible membrane, with the fuel in contact with one surface of the membrane. The other surface of the membrane is contacted by a fluid, for example water, which is evaporated by a heater under the control of the control signal to form a water vapour bubble which deforms the membrane towards the interior of the passage, and expels a droplet of fuel from the end of the passage into the inlet duct.

Figures 5 and 6 show an alternative embodiment of the carburettor of the present invention, wherein fuel droplets are formed by mechanical means rather than by electrical heating.

Figure 5 shows a partial axial section of a carburation ring similar to that shown in Figure 2. The carburation ring comprises a generally annular body (20A) in which an annular reservoir chamber (21A) is formed.

A number of radially extending passageways (24A) extend from a central bore (11A) to communicate with the annular reservoir chamber (21A). At the radially outer end of each of the passageways (24A) is a piezoelectric element (26A) to which electrical current can be supplied by wires (30A). The arrangement of the piezoelectric element (26A) is such that when a voltage is applied to the element, the piezoelectric element (26A) expands in the radial direction of the carburation ring. A shock wave travels radially inwardly along the passageway (24A) and causes a droplet of fuel to be discharged radially inwardly into the bore (11A) from the end (25A) of the passageway (24A).

Figures 6A to 6C show the sequence of operation of the piezoelectric element (26A). In Figure 6A, the piezoelectric element (26A) is not energised, and the reservoir chamber (21A) and passageway (24A) are filled with fuel. In Figure 6B a voltage is applied to a piezoelectric element (26A) and its sudden expansion in the radial direction sends a shock wave travelling down the passageway (24A), expelling fuel from the end (25A) of the passageway (24A). In Figure 6C the piezoelectric element is de-energised and contracts. A fuel droplet (28A) separates from the fuel in the passageway (24A) and is discharged in to the bore (11A). The passageway (24A) is then refilled by fuel from the reservoir chamber (21A), returning the passageway to the state shown in Figure 6A, ready for the next discharge.

Figure 8 shows the application of the carburation ring to a single-cylinder two-stroke engine. In this type of engine, an inlet port (50) leads into the crank case (51) of the engine. A transfer port (52) connects the crank case to the engine cylinder (53) and an exhaust port (54) leads out of the cylinder (53). The inlet port (50) is fitted with a valve (not shown) which prevents any outflow from the inlet port (50). In operation, starting from the bottom dead centre position shown in Figure 8, the piston (55) rises in the cylinder (53).

This causes the mixture in the cylinder (53) to be compressed, and causes a fresh charge of air to be drawn into the crank case through the inlet port (50). A valving arrangement (not shown) in the transfer port (52) will prevent flow from the cylinder (53) to the crank case (51) via the transfer port (52). When the piston reaches the upper end of the cylinder (53), the charge is ignited by the spark plug (56), and the power stroke commences. As the piston passes the end of the exhaust port (54), the burnt gases in the cylinder (53) are expelled. The downward movement of the piston (55) also compresses the air in the crank case (51), and this compressed air is then transferred to the cylinder via the transfer port (52).

In the embodiment shown in Figure 8, the carburation ring (12) is positioned so as to discharge fuel droplets into the air flowing from the crank case to the cylinder through the transfer port (52). The control system for the carburation ring is similar to that described in relation to the above embodiments. However the efficiency of the two stroke engine may be improved by controlling the fuel injection so as to vary the rate of fuel injection during each rotation o specifically, a sensor may provide an input to the CPU of the control system indicative of the crank shaft angle, so that the rate of injection of fuel can be varied as the crank shaft angle changes. Using such a system, it is possible to time the injection of fuel in synchronism with the transfer of air through the transfer port (52). The efficiency of the engine may be increased if the charge of air initially entering the cylinder (53) from the transfer port (52) has no fuel in it, so that any of this part of the charge which escapes through the exhaust port (54) does not take with it unused fuel.

Injection of the fuel into the incoming air can be timed so as occur only when the resulting air/fuel mixture will remain in the cylinder (53) and be effectively burnt.

In conventional two-stroke engines, a mixture of air, fuel and oil is admitted to the crank case through the inlet port (50), and is transferred from the crank case to the cylinder by a transfer port (52). Since this is a homogenous mixture of air, fuel and oil, any unburnt mixture which escapes through the exhaust port (54) results in a reduction of the engines efficiency due to fuel wastage. By avoiding this fuel wastage, the efficiency of the engine can be increased.

Figure 9 shows, in plan view, a schematic arrangement of a four cylinder four-stroke engine. Air is drawn into the engine through an air filter (60) and an inlet manifold (61), which has respective branches (61a) to (61d) for each of the cylinders. The engine construction is conventional with respect to its inlet and outlet valving arrangements, and has a conventional exhaust manifold (70) to collect exhaust gases from the cylinders. Spark plugs (80) are provided to ignite the mixture in the cylinders, in the conventional manner.

In the embodiment shown in Figure 9, each of the branches (61a) to (61d) of the inlet manifold is provided with a carburation ring (12), positioned immediately upstream of the inlet port to the respective cylinder.

The control of the carburation rings will be substantially as has been described above, but the control system will receive an input from a sensor which detects the angular position of the camshaft which operates the inlet valves for the cylinders, so that fuel droplets can be formed by each carburation ring in synchronism with the induction stroke of the cylinder to which its respective manifold branch is connected.

As discussed above with relation to the two-stroke engine, this synchronised control of the injection of fuel droplets during the induction stroke of the cylinder enables the rate of injection to be varied during the induction stroke. It is foreseen that the initial part of the induction stroke may be used to draw only air into the cylinder, with the carburation ring functioning during the latter part of the induction stroke to inject fuel droplets into the air flowing into the cylinder.

The ejection of droplets may also be used so that the initial part of the induction stroke draws a lean mixture into the cylinder, followed by normal or rich mixture at subsequent parts of the induction stroke; other alternatives include rich then lean mixture, rich mixture then air only, as required. The size of the fuel droplets may also be controlled to provide a fuel/air charge which ignites easily and burns smoothly.

In the above-described embodiments, the carburation ring is used to provide a fuel/air mixture to a sparkignition engine. It is foreseen that the close control of the size of the fuel droplets which is possible using the carburation device of the present invention enables the device to be applied to compression-ignition engines (Diesel engines). If the compression ratio in a conventional engine is sufficiently high, the adiabatic heating of the air-fuel mixture is enough to ignite it without the action of the spark plug. There is a known delay of a few microseconds between compression and ignition because the drops of fuel have to volatalize first. This delay depends on the density of fuel droplets and their size. Because the fuel drop size and distribution is not controlled in a conventionally carburated engine, the burn geometry and timing is unpredictable. The conventional fuel injection arrangement on Diesel engines comprises a high-pressure injector pump, which delivers a spray of fuel directly into the cylinder during the compression stroke. This prevents the risk of premature ignition. The uneven fuel distribution ensures the burn spreads smoothly through the cylinder instead of all happening at once, and so gives reduced engine noise and wear. Such pumps require considerable power from the engine in order to operate, and the presence of high-pressure fuel lines from the pump to the injector nozzles increases the overall weight of the engine significantly. The use of the electronic fuel injection devices of the present invention enable these expensive and heavy components to be dispensed with, to produce a lighter and cheaper engine.

While it is foreseen that the fuel injection device of the present invention will be principally applicable to small engines, and particularly to two-stroke engines, the fuel injection device is in principle applicable to any engine ranging from the small engines used in model aircraft and cars, up to heavy duty industrial Diesels.

In a further embodiment of the injection device (not illustrated) the carburation ring may be provided with two or more reservoirs and corresponding number of sets of radially extending passages. A first of the reservoirs may be provided with the principal fuel of the engine, while the second and subsequent reservoirs may be supplied with performance-enhancing agents such as a higher-octane fuel, or water. The control system will then be arranged to deliver a mixture of fuel and air, or a mixture of fuel, performance-enhancer and air as appropriate to the operating conditions of the engine.

Such a device may be used to operate an internal combustion engine so as to start the engine from cold using ordinary petrol, but to run the engine once warm on a mixture of petrol and paraffin (kerosene) or on paraffin alone, or to deliver a mixture of petrol and water droplets when short-term power enhancement is required. The fuels and additives may be supplied to the carburation elements by pumps, or by gravity feed arrangements, or through capillary action if the flow rates required are small. Gravity feed and capillary feed are more appropriate to static engines, such as are used in generator sets.

While the carburation device of the described embodiments is in the form of an annular ring with passages to project droplets radially inwardly into an air intake duct, it is foreseen that the carburation device may be embodied as an annular or part-annular structure with generally radially arranged passages or as a planar structure which forms part of a sidewall of an air intake duct and has a parallel array of passages leading into the intake duct. Two or more planar arrays of passages may be provided, on one side of a rectangular section intake duct, so that access only to one side of the duct is required for maintenance of the carburation element. The planes of the arrays of passages may be transverse to the airflow direction, or may be arranged obliquely or longitudinally of the flow. In a further alternative, the carburation element may be embodied as a probe which can extend axially in an intake duct with passages to project fuel droplets radially outwardly relative to the duct.

Although the above embodiments have been described in terms of fluid delivery, it is to be understood that the device may be used to deliver both fuel and fuel additives or adjuncts, either pre-mixed together or separately via respective fuel and additive passages.

Where the device of the present invention is used only to deliver fuel additives, it is to be understood that the fuel may be delivered by any conventional device.

Claims

Claims: 1. A carburation device for supplying a fluid in droplet form to an engine having an air intake duct, comprising: a fluid passage adapted to communicate at one of its ends with the air intake duct; fluid supply means to maintain the passage filled with fluid; and electrically operable ejection means to eject a single fluid droplet from the passage into the duct on receipt of a respective control signal.
2. A device according to claim 1, wherein the fluid comprises one or more of: a fuel; a fuel additive; and an engine performance modifier.
3. A carburation device according to claim 1 or claim 2, wherein the ejection means comprises a heater in heat transfer communication with the interior of the passageway, and wherein the control signal causes the heater to evaporate a part of the fluid in the passage.
4. A carburation device according to claim 1 or claim 2, wherein the ejection means moves a part of the wall of the passage to eject a fluid droplet.
5. A carburation device according to claim 4, wherein the ejection means comprises a piezoelectric element which forms part of the wall of the passage.
6. A carburation device according to claim 4, wherein the passage is defined in part by a flexible membrane, and the ejector means comprises a heater arranged to vaporise a fluid in contact with the membrane to deform the membrane towards the interior of the passage.
7. A carburation device according to any preceding claim wherein a plurality of passages are provided.
8. A carburation device according to claim 7, wherein the passages are arranged in a plane transverse to the direction of the air intake duct.
9. A carburation device according to claim 8, wherein the passages are arranged in two or more planar arrays, in planes transverse to the direction of the intake duct.
10. A carburation device according to claim 7, wherein the passages are arranged to extend substantially radially of the air intake duct.
11. A carburation device according to claim 8 or claim 9, wherein the passages are parallel to each other.
12. A carburation device according to any preceding claim, wherein a mixture control valve is provided in the air intake duct to control the flow of air/fluid mixture therethrough.
13. A carburation device according to claim 12, wherein the fluid passage is situated upstream of the mixture control valve.
14. A carburation device according to claim 12, wherein the fluid passage is situated downstream of the mixture control valve.
15. A carburation system for supplying fluid to an engine having an air intake duct, comprising: a fluid passage adapted to communicate at one of its ends with the air intake duct; fluid supply means to maintain the passage filled with fluid; and electrically operable ejection means to eject a single fluid droplet from the passage into the duct on receipt of a respective control signal; and the control means comprising means for providing control signals to the ejection means.
16. A carburation system according to claim 15, wherein the control means comprises at least one sensor to detect an engine operating parameter; means to generate control signals in dependence on the sensed parameter or parameters; and means to apply the control signal to the ejection means of at least one passage.
17. A carburation system according to claim 15 or claim 16, wherein the control means further comprises manual setting means for selecting a mode of engine operation, and wherein the control signal generated by the control means depends on the sensed engine operating parameters and on the selected mode of operation.
18. A carburation system according to any of claims 15 to 17, wherein the fluid supply means comprises a fuel tank, and means for supplying fuel from the tank to a reservoir in communication with the fluid passage.
19. A carburation system according to any of claims 15 to 17, wherein the fluid supply means comprises a tank for containing a fuel additive or performance modifier, and means for supplying a reservoir in communication with the fluid passage with a fluid from the tank.
20. A carburation system according to claim 19, wherein fuel is supplied to the engine by a separate fuel supply system.
21. A carburation system according to claim 20 wherein the fuel supply system is a carburation system according to any of claims 15 to 17.
22. A carburation system according to any of claims 15 to 19, wherein the means for supplying fluid from the tank or tanks to the respective passages comprise respective pumps.
23. A carburation system according to claim 22 wherein the or at least one of the pumps is controlled by the control means.
24. A method of supplying fluid to an engine having an air intake duct, comprising the steps of: providing a carburation device according to any of claims 1 to 14; sensing an engine parameter; applying at least one control signal to the fluid ejection means to eject at least one fluid droplet from the passage into the air intake duct one the basis of the sensed parameter.
25. A method according to claim 24 wherein a plurality of control signals are applied to the ejection means during each engine cycle to eject a corresponding plurality of fuel droplets from the passage.
26. A method according to claim 25, wherein the rate at which control signals are applied to the ejector means is varied during the engine cycle.
27. A method according to claim 25 or claim 26, wherein the nature of the control signals is altered to cause a corresponding change in the size of the respective fuel droplets ejected.
28. A data carrier carrying processor-implementable instructions for carrying out a method according to any of claims 24 to 27.
29. A device for supplying a liquid to a combustion engine, comprising: a duct through which an intake air stream for the engine may pass; at least one passage for containing a fluid, open at one end to the duct; a reservoir in fluid communication with the passage; and ejector means associated with the passage and operable to eject from said one end of the passage into the duct a single fluid droplet on receipt of a respective electrical control signal.
30. A device according to claim 29 wherein the ejector means is a heater in heat transfer communication with a wall of the passage and operable to vaporise a part of a liquid within the passage on receipt of a respective control signal.
31. A device according to claim 30, wherein the ejector means comprises a movable portion of the wall of the passage.
32. A device according to claim 31, wherein the ejection means comprises a piezoelectric element which forms part of the wall of the passage.
33. A device according to claim 29, wherein the passage is defined in part by a flexible membrane, and the ejector means comprises a heater operable to vaporise a part of a liquid in contact with the membrane to deform the membrane towards the interior of the passage.
34. A carburation device substantially as described herein with reference to Figures 2,3,4,5,6,8 or 9 of the accompanying drawings.
35. A method of supplying fuel to an engine, substantially as herein described.