GB2438456A

GB2438456A - I.c. engine fuel injection system with a fuel injector functioning as a positive displacement pump, and a mixing chamber

Info

Publication number: GB2438456A
Application number: GB0522068A
Authority: GB
Inventors: Jeffrey Allen
Original assignee: Scion Sprays Ltd
Current assignee: Scion Sprays Ltd
Priority date: 2005-08-05
Filing date: 2005-10-28
Publication date: 2007-11-28
Anticipated expiration: 2025-10-28
Also published as: GB2423119A; GB0606104D0; CN101238279A; CN101238282B; GB2438456B; GB2421543B; GB0516235D0; GB2423119B; CN101238282A; GB2421543A; GB0522068D0

Abstract

The fuel injection system delivers fuel to be mixed with charge air for subsequent combustion in a combustion chamber (630) of an internal combustion engine. The fuel injection system comprises a fuel injector (210) which functions as a positive displacement pump and dispenses in each operation thereof a set quantity of fuel; ```a mixing chamber (218) into which the fuel injector dispenses fuel; and a gas supply passage (601) for supplying gas to the mixing chamber (218) to entrain the fuel dispensed into the mixing chamber in a flow of gas which passes through the mixing chamber into the combustion chamber (630). The mixing chamber (218) is connected to the combustion chamber (630) to deliver fuel and gas into the combustion chamber separately from the charge air and a depression in the combustion chamber (630) is used to draw gas through the gas supply passage (601) into the combustion chamber (630). An inlet valve (614) controls flow of charge air into the combustion chamber (630) and the inlet valve (614) is kept closed for an initial part of an intake stroke of the engine so that the depression is created in the combustion chamber (630).

Description

* 2438456

A FUEL INJECTION SYSTEM FOR

AN INTERNAL COMBUSTION ENGINE

The present invention relates to a fuel injection system for an internal combustion engine.

Most internal combustion engines in automobiles currently use fuel injection systems to supply fuel to the combustion chambers of the engine. Fuel injection systems have replaced the earlier technology of carburettors because they give more control of delivery of fuel and enable the engine to meet emission legislation targets as well as improving the overall efficiency of the engine.

Figure 1 schematically illustrates a conventional internal combustion engine 100 comprising a cylinder 102 in which reciprocates a piston 104 with the piston 104 and the cylinder 102 defining between them a combustion chamber 106.

The piston 104 is connected by a connecting rod 108 to a crankshaft 110. The crankshaft 110 drives a camshaft 112 which in turn drives an inlet valve 114 and an exhaust valve 116. The inlet valve 114 and the exhaust valve 116 are driven in timed relationship to the movement of the piston 104 in the cylinder 102, with return springs (not shown) biasing the valves 114, 116 back into their valve seats.

The fuel injection system of the engine 100 comprises a fuel injector 118 arranged to deliver fuel 120 into an inlet passage 122 upstream of the inlet valve 114. A throttle valve 124 is placed in the inlet passage 122 to control the flow of charge air through the inlet passage 122. The fuel and air mix together in the inlet passage. The inlet valve 114 then controls the flow of the mixture into the combustion chamber 106.

An engine control unit 126 controls the time at which the fuel 120 is injected into the charge air present in the inlet passage 122 and also controls the quantity of fuel 120 that is injected. The engine control unit 126 receives a signal from the throttle valve 124 via a control line 128, the signal indicating the rotational position of the throttle valve 124 and hence the engine load. Additionally, the engine control unit 126 receives a timing signal from a camshaft sensor 128 (which could be replaced by a crankshaft sensor) via a control line 130. The engine control unit 124 can determine, from the timing signal received from the camshaft sensor 132, the speed of the engine 100 and the position of the piston 104 within the cylinder 102. Having regard to the timing signal produced by the camshaft sensor 132 and the load signal produced by the sensor attached to the throttle valve 124, the engine control unit 126 generates a control signal which is relayed to the injector 118 via a line 134 and controls the operation of the injector 118.

As is well known, the pressure within the inlet passage 122 varies during the engine cycle. Current fuel injection systems typically use a combination of a fuel pump 131 and a pressure regulator 132 to supply fuel from a fuel tank 133 to the fuel injectors at a constant positive pressure differential with respect to the pressure within the inlet passage 122. The pressure regulator 132 is connected by a passage 134 to the air inlet passage 122 downstream of the throttle 124, to receive a pressure reference signal. The injectors function as on/off valves, which can be activated for a predetermined time period under the control of the electronic control unit 126. The result of such a combination of known pressure differential and variable, but controlled opening times gives an injection of known quantities of fuel 120 into the combustion chamber 106 of the engine. However, because the pressure differential between the fuel and the charge air determines the rate at which fuel is dispensed by the injector, such systems require tight control and monitoring of the fuel pressure, as well as precise monitoring of the pressure of the charge air. The opening times of the on/off valves must also be accurately controlled or the amount of fuel dispensed will not be precisely known. Conventional fuel injection systems therefore typically require a fuel pump as well as pressure regulation, and fuel pressure adjustment devices thereby making these systems complex, heavy, and expensive. Some fuel injection systems also use an air pump and air pressure regulator which increases the complexity further.

Most fuel injection system are designed to meter fuel accurately and are not fuel atomisation devices. It is recognised that a finely atomised fuel spray will improve air fuel mixing and will help reduce engine emissions. It is therefore advantageous to incorporate an atomisation feature into the fuel injector. This is difficult with conventional injectors as we have seen if the atomisation process has any variable effect on the pressure difference across the injector it will dramatically alter the flow rate of fuel through the injector and cause incorrect fuel quantities to be delivered to the engine. Therefore, choosing an effective atomisation process is very limited with the conventional fuel injection systems and the current "state of the art" injection systems overcome this problem by using a complex highly controlled high pressure fuel system where the high kinetic energy in the fuel can aid atomisation.

The sophisticated and highly developed fuel injection systems currently available are ideal for use in internal combustion engines in automobiles. However, there are many other applications for internal combustion engines where such a level of sophistication is not appropriate and too costly. For instance, small single cylinder engines as used for lawn mowers, chain saws, small generators, mopeds, scooters, etc are built to very tight cost targets and so cannot afford the cost of a sophisticated fuel injection system nor the additional power required to run a fuel pump.

To date, such small engines have used traditional carburettor technology and relied on a gravity fed fuel supply. However, it is now the case that such small engines will face the same type of exhaust gas emission legislation as the engines in automobiles and so must be modified in such a way as to meet emissions targets. Therefore, a cheap and simple system of fuel injection is required for such small engines.

According to a first aspect of the invention, there is provided a fuel injection system for delivering fuel into charge air for combustion therewith, the fuel injection system comprising: a fuel injector which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector; and an atomising nozzle in fluid communication with the fuel injector, the fuel from the fuel injector being dispensed through the atomising nozzle into the charge air, the dispensed fuel atomising upon exiting the atomising nozzle and entering the charge air.

According to a second aspect of the invention, there is provided a fuel injection system for an internal combustion engine which delivers fuel into charge air for mixing therewith for subsequent combustion in a combustion chamber of the internal combustion engine, the fuel ignition system comprising: a fuel injector which functions as a positive displacement pump and dispenses in each operation thereof a set quantity of fuel; a mixing chamber into which the fuel injector dispenses fuel; and a gas supply passage for supplying gas to the mixing chamber to entrain the fuel dispensed into the mixing chamber in a flow of gas which passes through the mixing chamber into the charge air.

Internal combustion engines that make use of embodiments of the invention can do away with complicated, heavy and expensive fuel injection systems. Instead, they may make use of a cheaper and simpler system that does not require the pressure within the inlet passage to be monitored or the provision of a fuel pump and pressure regulator to maintain a constant pressure differential between the fuel and the charge air. Rather, the fuel injector of the current invention dispenses a known quantity of fuel at a fixed flow rate independent of the pressure of the charge air. The ability to deliver fuel in this way also allows a simpler apparatus for dispersing the fuel in the charge air and the use of low cost effective atomisation processes without effecting the accurate fuel quantity being delivered, so allowing simple small engines to benefit from well atomised accurate full flow rates.

Embodiments of the invention shall now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a conventional internal combustion engine; Figure 2 is a schematic representation of the inlet passage of an internal combustion engine which encompasses a fuel injector embodying the present invention; Figure 3a shows a cross-sectional view of a nozzle of the fuel injector of Figure 2; Figure 3b shows a cross-sectional view of the fuel injector of Figure 2; Figures 4a-4d show alternative nozzle orifice shapes; Figure 5 shows a further embodiment of the present invention in which the inlet passage includes a venturi; Figure 6 is a schematic representation of a fuel injector of the present invention arranged for direct injection into the combustion chamber; and Figure 7 is a schematic representation of a fuel injector of the present invention arranged for direct injection into the combustion chamber wherein the sonic nozzle is of the pintle type.

Turning to Figure 2, there is shown a throttle body 202 of an internal combustion engine. The throttle body 202 includes an inlet passage 200 similar to the inlet passage 122 of Figure 1, and contains charge air 203. The inlet passage 200 communicates at one end 204 with the engine combustion chamber 106 via inlet valve 114, and at the other end 206 with atmospheric air, possibly via an air filter (not shown) . Within the inlet passage 200 is located a throttle valve 208 while downstream of the throttle valve, between the throttle valve 208 and the inlet valve 114 is a fuel injector 210. The fuel injector comprises a fuel inlet 212, a fuel outlet 214, and a fuel chamber 216. The fuel outlet is arranged to protrude into the inlet passage 200 of the throttle body 202.

The fuel inlet 212 of the fuel injector 210 is connected to a supply of fuel and communicates via spring-loaded one-way valve 222 with the fuel chamber 216. A second spring-loaded one-way valve 224 controls the flow of fuel out of the fuel chamber 216 to the fuel outlet 214.

The fuel chamber itself is defined by a piston 220 which is slidably located within a body of the fuel injector 210. The piston 220 is acted upon by a biasing spring 211 and surrounded by a solenoid 213. An end plate 215 is connected to the piston 220 at an end remote from the final chamber 216 and extends radially outwardly from the piston across an end face of the solenoid 213. The solenoid 213 is connected by a line (not shown) to an engine control unit (also, not shown) Starting from a condition in which the piston 220 is biased to its lowermost point within the body of the fuel injector 210 by the biasing spring 211 (i.e. the point at which the fuel chamber 216 has its greatest volume), the fuel chamber 216 will be primed with fuel ready for injection. Energisation of the solenoid 213 then acts to pull the end plate 215 into contact or near contact with the solenoid 213. The piston 220 moves upwards against the force of the basing spring 211 to reduce in volume the fuel chamber 216. This causes the positive displacement of fuel from the fuel chamber 216, the one-way valve 224 opening to allow the piston 220 to expel fuel from the fuel chamber 216 towards the fuel outlet 214 while the one-way valve 222 remains closed.

Once the solenoid 213 is de-energised, the biasing spring 211 will force the piston 220 downwardly and the end plate 215 away from the solenoid 213. The downward motion of the piston 220 will cause the fuel chamber 216 to increase in volume and this will have the effect of closing the one-way valve 224 and opening the one-way valve 222.

The moving piston 220 draws fuel from the fuel inlet 212 into the fuel chamber 216 to fully charge the fuel chamber 216 ready for the next dispensing of fuel.

The fuel injector 210 is constructed so that the piston 220 has a set distance of travel in each operation. The piston 220 moves between two end stops. Thus, in each operation of the fuel injector 210, the piston 220 displaces a predetermined quantity of fuel and a predetermined quantity of fuel is dispensed out of the fuel outlet 214.

The amount of fuel dispensed by the fuel injector 210 is constant for each and every operation.

Having been dispensed from the fuel chamber 216, the fuel is forced towards the fuel outlet 214 which comprises in turn a mixing chamber 218 and an atomising nozzle 226.

To assist in the production of a fuel and charge air mixture that will be burn rapidly when ignited in the combustion chamber, the fuel must be effectively mixed with the charge air. Conventional carburettors and fuel injectors achieve this by having a number of holes at the end of the injector nozzle to form a fine spray of fuel from the nozzle into the charge air. The atomising nozzle 226 of the present invention is a sonic nozzle (also known in the art as a critical flow venturi, or critical flow nozzle) The atomising nozzle could also be an air-blast nozzle.

Sonic nozzles are often used as fluid flow standards as they provide a constant volumetric flow rate, provided that the pressure differential across them exceeds a predetermined threshold valve. A schematic diagram of a sonic nozzle is shown in Figure 3a. The nozzle comprises a throughbore 350, the internal dimensions of which narrow to provide a throat or venturi 302. The fluid upstream 352 of the venturi is provided at a higher pressure than that downstream 354 of the venturi. The fluid flows into the nozzle and is accelerated in the narrowed region. The velocity of the fluid in the narrowed region approaches the speed of sound. Once this condition has been realised the flow rate through the sonic nozzle will remain constant even if the downstream pressure varies significantly, provided, of course, that the pressure differential across the nozzle continues to exceed the threshold valve. Thus in the present case a constant fuel flow rate into the charge air is achieved. It should be noted that a sonic nozzle will provide a constant flow rate regardless of the abruptness of the change in downstream pressure provided that the -10 -downstream pressure remains at less than about 85-90% of the upstream pressure.

In the current invention the passage of fuel through the sonic nozzle 226 also aids in dispersing the fuel into the charge air. In fact, since the velocity of the fuel passing through the venturi 302 approaches the speed of sound, the nozzle 226 acts as a highly efficient atomizer breaking the liquid fuel up into a mist of tiny particles.

Generally, the finer the spray of fuel in the charge air, the better the combustion process achieved. While the exact operation of sonic nozzles in atomizing fuel is not well understood, it is thought that the passage of the liquid fuel through the shock waves in the high velocity region of the sonic nozzle produces very high shear stresses on the liquid surface and cavitation bubbles within the liquid, both of these processes leading to very fine atomisation and dispersion of the fuel into the charge air.

In conventional fuel injection systems the pressure differential between the fuel and charge air must be constantly regulated to allow the amount of fuel dispensed by the injectors to be accurately determined. This prevents the use of sonic nozzles. However, in the current invention the fuel injector does not require the fuel-to-charge air pressure ratio to be precisely controlled. Hence, the use of sonic nozzles becomes possible.

As mentioned above, in conventional fuel injection systems, the fuel is pressurised and the or each fuel injector simply acts as an on/off switch to control the amount of fuel dispensed. In contrast, the present fuel -11 -injector is intended to be operated using a pulse. In particular the fuel injector 210 comprises a piston 220 which dispenses a fixed volume of fuel. However, due to changing load conditions on the engine, the amount of fuel to be injected for combustion may have to be increased or decreased. To meet this requirement the pulse count injector method uses multiple operations of the fuel injector in each engine cycle. When the engine is at the part of the cycle at which fuel injection must occur, multiple operations of the fuel injector take place. To increase or decrease the amount of fuel dispensed, the number of operations of the injector is adjusted accordingly. For example, under normal loading conditions the number of operations may be, say, ten. For higher load conditions the number is increased to fourteen, for example, or for reduced load conditions the number of pulses may be reduced to, say, six.

As mentioned above, for a conventional engine with a fuel injection system the timing of the fuel injection is critical. Both the duration for which the on/off valves are open, and the point in the engine cycle at which the fuel is dispensed must both be accurately controlled. The combination of a pulse count injection system with a sonic nozzle overcomes many of the timing problems associated with the prior art. In a pulse count injection system using a sonic nozzle the length of time of each individual operation of the injector is easily determined. A sonic nozzle has a constant flow rate, and since the volume of fuel delivered in each operation is fixed and known, the duration of each fuel injection operation can be accurately determined and reliably predicted. This allows successive operations of -12 -the fuel injector (in a single engine cycle) in a pulse count injection system to be easily provided for. Once the timing of the first pulse has been set, the delay until the next pulse of fuel is dispensed can also be easily set.

Moreover the timing of the injection within the engine cycle does not have to be as precisely set as in a conventional engine as the pressure inside the inlet passage is not so critical.

In an alternative embodiment, the piston 220 may be configured to deliver a number of different volumes of fuel.

This may be achieved by only partially retracting the piston 220. There are other ways of implementing such a variable volume injection device, for example a diesel fuel injector with a variable stroke can be used to give a variable, but known quantity of fuel.

A further aspect of the fuel injector 210 relates to the mixing chamber 218. As mentioned above, this is located between the fuel chamber 216 and the nozzle 226. As can be seen in Figure 2, and in the enlarged view in Figure 3b, the throttle body 202 also comprises an air bypass 240. This consists of a further passage which communicates with both the mixing chamber 218 and a region where air is at atmospheric pressure.

During operation of the fuel injector 210, the piston 220 moves to expel the fuel from the fuel chamber 216. The fuel then passes through the mixing chamber 218 and on through the sonic nozzle 226. The fuel is expelled under the pressure provided by the piston. The dispensing of the fuel is timed to coincide with low pressure conditions -13 -inside the inlet passage 200. As the fuel is expelled, the low pressure conditions in the inlet passage 200 helps to draw the fuel from the mixing chamber 218 into the inlet passage. The low pressure in the inlet passage 200 also helps to draw air from the air bypass 240. Thus air flows through the air bypass tube 240 and entrains the fuel in the mixing chamber 218. The air in the air bypass 240 is at a higher pressure than the air in the inlet passage 200, and hence as the fuel is dispensed from the nozzle 226 into the inlet passage 200, this air creates the high velocity region in the nozzle and causes the stream of fuel to be broken up.

This acts in cooperation with the fuel vapour (caused by cavitation), previously mentioned, to improve the break up and atomisatjon of the stream of fuel as it is ejected from the sonic nozzle 226.

Clearly, the air bypass 240 is not limited to supplying air but could alternatively be connected to a gas supply to provide an alternative gas to aid in atomisation or combustion. One such example of another gas that could be used is exhaust gas from the engine (i.e. exhaust gas recirculatjon) Further embodiments of the present invention use nozzle orifices of different shapes as shown in Figure 4 to improve the atomisation of the fuel in the inlet passage. The orifice of a standard sonic nozzle, when a cross-section is taken perpendicular to the flow direction, is circular (see Figure 4a) . Alternative shapes of the nozzle orifices may be provided, for example a linearly extending orifice (Figure 4b), a cruciform shape (Figure 4c) or alternatively a plurality of smaller dispersed nozzles, each having a -14 -circular orifice (Figure 4d) . All of these allow the control of the fuel mist 230. The plurality of smaller dispersed nozzles provides improved atomisation.

Figure 5 shows a further embodiment of the present invention. At wide open throttle conditions the pressure of the charge air in the inlet passage 200 is not as low as under other throttle conditions (i.e. the pressure is closer to atmospheric pressure) . As mentioned above, although sonic valves are less sensitive to variations in pressure differential than convention fuel injection systems, nonetheless, they still need the pressure differential between the input and output sides to exceed a predetermined threshold.

The fuel injection system of Figure 5 is similar to the fuel injection system of Figure 2 but additionally comprises means to create a low pressure region in the inlet passage to allow the fuel injector to operate effectively even at wide open throttle positions. In particular, there is provided a passage 300 inside the inlet passage 200 parallel to the normal direction of flow of the charge air. The internal dimension of the tube 300 narrow downstream from the start of the passage, and then broadens out again creating a venturi. The fuel outlet 214 is arranged perpendicular to the flow direction of the venturi. The exit from the fuel outlet 214 through the sonic nozzle 226 is provided at the narrowest point of the venturi.

The venturi 300 ensures that even at wide open throttle positions where the pressure of the charge air in the inlet passage 200 is relatively high, a low pressure region is created where the fuel is injected. This low pressure -15 -region ensures the fuel leaving the sonic nozzle 226 is atomised sufficiently. These "secondary venturis" are known in carburettors but their purpose is to draw fuel and control the fuel rate rather than aid in atomising the fuel or allowing the sonic nozzle to operate correctly.

A further embodiment of the invention uses a fuel injector 210 and nozzle 226 similar to that shown in Figure 2, but does not inject the fuel into the inlet passage 200 of the throttle body 202. Instead the fuel injector causes direct injection of fuel into the combustion chamber of the engine. Figure 6 shows this embodiment in which a piston 620 cooperates with a cylinder to define a combustion chamber 630 similar to that shown in Figure 1. Also shown are inlet valve 614 and exhaust valve 616. As can be seen, the fuel inlet pipe 214 and sonic nozzle 226 of the fuel injector 210 are arranged to dispense fuel directly into the combustion chamber 630 of the engine. However, in this case the pressure inside the combustion chamber may be too high to allow air to be drawn through the air bypass 240 and entrained with the fuel in the mixing chamber 218. To overcome this problem an air pump may be used to provide air at an increased pressure. Alternatively, if the opening of the inlet valve 614 is delayed, an air pump may not be required. Instead the movement of the piston 620 may be used to create a partial vacuum in the combustion chamber 630. The fuel can then be dispensed into the combustion chamber 630 and the partial vacuum would assist in drawing air from the air bypass 240. An electrically operated valve 600 (comprising a spring biased member 602 and an electrical coil 603) is used to control flow of air.

-16 -Figure 7 shows a further embodiment of the invention.

This is similar to the embodiment shown in Figure 6. The fuel injector is located for direct injection of fuel into the combustion chamber of the engine. However, this embodiment includes a different type of sonic nozzle. In this case, the sonic nozzle consists of an outer tube 710 through which fuel entrained in air (or exhaust gases) flows. A pintle 720 is provided across the end of the tube inside the combustion chamber. The closure is connected to an actuating rod 730 located centrally of the outer tube 710. Importantly, the pintle 720 abuts against the outer tube 710. The abutting surfaces of both the pintle 720 and the outer tube 710 are chamfered.

Fuel supplied by supply line 742 is dispensed from the mixing chamber 216 of the injector 210. At the same time the pintle closure is opened allowing fuel and air to be dispensed into the combustion chamber 630. Air (or exhaust gases) flows through passage 741 to entrain the dispersed fuel in mixing chamber 743 and deliver it to the combustion chamber. Either the air/exhaust gas is pressurised or the pintle 720 is opened only when the piston in the combustion chamber is moving to draw air into the cylinder. The chamfered shape of the pintle causes a spray of fuel forming a conical shape 750 extending outwards from the pintle.

Actuation of the pintle may be by means of a solenoid 740 or other means. Again, in this embodiment there is no requirement to monitor and tightly regulate the pressure in the mixing chamber or the combustion chamber. A sonic velocity is achieved as the fuel is forced through the narrow gap between the closure 720 and the tube 710.

Claims

-17 -CLAIMS: 1. A fuel injection system for delivering fuel into charge

air for combustion therewith, the fuel injection system comprising: a fuel injector which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector; an atomising nozzle in fluid communication with the fuel injector, the fuel from the fuel injector being dispensed through the atomising nozzle into the charge air, dispensed fuel atomising upon exiting the sonic nozzle and entering the charge air.

2. The fuel injection system of claim 1, further comprising a mixing chamber in fluid communication between the fuel injector and the atomising nozzle, the mixing chamber further receiving a supply of gas, wherein the fuel is delivered by the injector into the mixing chamber and then entrained in a flow of gas to pass through the atomising nozzle.

3. The fuel injection system of claim 2 wherein the supply of gas comprises a supply of air.

4. The fuel injection system of claim 2 or claim 3 wherein the supply of gas comprises a supply of combusted gases.

5. The fuel injection system of any preceding claim, wherein the atomising nozzle is a sonic nozzle.

-18 - 6. The fuel injection system of any one of claims 1 to 5 further comprising an atomising chamber disposed within said charge air, the atomising chamber containing a venture and the atomising nozzle being arranged to dispense fuel into a throat of said venturi.

7. The fuel injection system of any one of claims 1 to 5 wherein the atomising nozzle dispenses the fuel directly into a combustion chamber of an engine.

8. A fuel injection system for an internal combustion engine which delivers fuel to be mixed with charge air for subsequent combustion in a combustion chamber of the internal combustion engine, the fuel injection system comprising: a fuel injector which functions as a positive displacement pump and dispenses in each operation thereof a set quantity of fuel; a mixing chamber into which the fuel injector dispenses fuel; and a gas supply passage for supplying gas to the mixing chamber to entrain the fuel dispensed into the mixing chamber in a flow of gas which passes through the mixing chamber into the charge air.

9. The fuel injection system of claim 8 wherein the mixing chamber is connected to an air inlet passage of the engine downstream of an air inlet throttle and a depression downstream of the throttle is used to draw gas through the gas supply passage, bypassing the throttle.

-19 - 10. The fuel injection system of claim 9 wherein a venturi device is provided in the air inlet passage through which a part of the charge air flow passes and the mixing chamber is connected to a throat of the venturi device whereby the depression used to draw gas through the gas supply passage is a depression in the venturi throat.

11. The fuel injection system of claim 8 wherein the mixing chamber is connected to the combustion chamber to deliver fuel and gas into the combustion chamber separately from the charge air and a depression in the combustion chamber is used to draw gas through the gas supply passage into the combustion chamber.

12. The fuel injection system of claim 11 wherein an inlet valve controls flow of charge air into the combustion chamber and the inlet valve is kept closed for an initial part of an intake stroke of the engine so that the depression is created in the combustion chamber prior to delivery of charge air into the combustion chamber.

13. The fuel injection system of any one of claims 8 to 12 wherein the gas supply passage supplies air drawn from atmosphere.

14. The fuel injection system of any one of claims 8 to 12 wherein the gas supply passage supplies combusted gases drawn from an exhaust of the engine.

15. The fuel injection system of any one of claims 8 to 12 wherein the gas supply passage supplies a mixture of air -20 -drawn from atmosphere and combusted gases drawn from an exhaust of the engine.

16. The fuel injection system of any one of claims 8 to 15 wherein the fuel injector dispenses an amount of fuel which is fixed for each and every operation of the injector.

17. The fuel injector system of any one of claims 8 to 16 wherein fuel and gas leaving the mixing chamber pass through an atomising nozzle prior to mixing with the charge air.

18. The fuel injection system of any one of claims 1 to 7, 17 or 18, wherein the atomising nozzle is a sonic nozzle and the velocity of the fuel passing through the sonic nozzle into the charge air is substantially constant throughout the period during which the fuel is dispensed.

19. The fuel injection system of any one of claims 1 to 7, 17 or 18, wherein the atomising nozzle comprises a non-circular orifice through which the fuel exits into the charge air.

20. The fuel injection system of any one of claims 1 to 7, 17 or 18, wherein the atomising nozzle comprises a plurality of orifices through which the fuel exits into the charge air.

21. The fuel injection system of any one of claims 1 to 7, 17 or 18, wherein the atomising nozzle further includes a pintle, the pintle being operated simultaneously with the fuel injector.

-21 - 22. The fuel injection system of any preceding claim further comprising an electronic control unit for controlling the member of times the fuel injector is actuated in a given engine cycle to control the quantity of fuel mixed with the charge air.

23. A fuel injection system substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.

24. An internal combustion engine comprising a fuel injection system in accordance with any previous claim.

25. An internal combustion engine substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.

26. An engine powered device comprising an internal combustion engine according to claim 24 or claim 25.

27. A device according to claim 26 wherein the device is a gardening device.

28. A device according to claim 26 wherein the device is selected from the list comprising: a lawn mover; a hedge trimmer; a chain saw; a strimrner; a rotavator; a lawn aerator; a scarifier; and

I

-22 -a shredder.

29. A device according to claim 26 wherein the device is an engine driven vehicle.

30. A method of delivering fuel into charge air for combustion therewith, the method comprising the steps of: dispensing a set quantity of fuel from a fuel injector to an atomising nozzle; and dispensing the fuel from the fuel injector through the atomising nozzle into the charge air, the dispensed fuel atomising upon exiting the atomising nozzle and entering the charge air.

31. The method of claim 30 further comprising the step of entraining the fuel dispensed from the fuel injector in a flow of gas with the gas and fuel mixture flowing through the atomising nozzle.

32. The method of claim 30 or claim 31 further comprising the step of using a depression in a low pressure region within the charge air to draw through the atomising nozzle the gas used to entrain the dispensed fuel.

33. The method of any of claims 30 to 31 wherein the atomising nozzle is disposed so as to dispense the fuel from the fuel injector directly into a combustion chamber of an engine.

34. The method of claim 33 wherein a depression is created in the combustion chamber in an early part of an intake stroke of the engine and the depression is used to draw -23 -through the atomising nozzle the gas used to entrain the dispensed fuel.

/521 AWP CTF Amendments to the claims have been filed as follows CLJIMS: 1. A fuel injection system for an internal combustion engine which delivers fuel to be mixed with charge air for subsequent combustion in a combustion chamber of the internal combustion engine, the fuel injection system comprising: a fuel injector which functions as a positive displacement pump and dispenses in each operation thereof a set quantity of fuel; a mixing chamber into which the fuel injector dispenses fuel; and a gas supply passage for supplying gas to the mixing chamber to entrain the fuel dispensed into the mixing chamber in a flow of gas which passes through the mixing chamber into the charge air; wherein: the mixing chamber is connected to the combustion chamber to deliver fuel and gas into the combustion chamber separately from the charge air and a depression in the combustion chamber is used to draw gas through the gas supply passage into the combustion chamber; and an inlet valve controls flow of charge air into the combustion chamber and the inlet valve is kept closed for an initial part of an intake stroke of the engine so that the depression is created in the combustion chamber.

2. The fuel injection system of claim 1 wherein the gas supply passage supplies air drawn from atmosphere.

3. The fuel injection system of claim 1 or claim 2 wherein the gas supply passage supplies combusted gases drawn from an exhaust of the engine.

4. The fuel injection system of claim 1 wherein the gas supply passage supplies a mixture of air drawn from atmosphere and combusted gases drawn from an exhaust of the engine.

5. The fuel injection system of any one of claims 1 to 4 wherein the fuel injector dispenses an amount of fuel which is fixed for each and every operation of the injector.

6. The fuel injector system of any one of claims 1 to 5 wherein fuel and gas leaving the mixing chamber pass through an atomising nozzle prior to mixing with the charge air.

7. The fuel injection system of claim 6, wherein the atomising nozzle is a sonic nozzle and the velocity of the fuel passing through the sonic nozzle into the charge air is substantially constant throughout the period during which the fuel is dispensed.

8. The fuel injection system of claim 6 or claim 7 wherein the atomising nozzle comprises a non-circular orifice through which the fuel exits into the charge air.

9. The fuel injection system of claim 6 or claim 7, wherein the atomising nozzle comprises a plurality of orifices through which the fuel exits into the charge air.

10. The fuel injection system of claim 6 or claim 7, wherein the atomising nozzle further includes a pintle, the pintle being operated simultaneously with the fuel injector.

11. The fuel injection system of any preceding claim further comprising an electronic control unit for controlling the member of times the fuel injector is actuated in a given engine cycle to control the quantity of S fuel mixed with the charge air.

12. A fuel injection system substantially as herein described with reference to Figures 5 and 6 of the accompanying drawings.

13. An internal combustion engine comprising a fuel injection system in accordance with any previous claim.

14. An internal combustion engine substantially as herein described with reference to Figures 5 and 6 of the accompanying drawings.

15. An engine powered device comprising an internal combustion engine according to claim 13 or claim 14., 16. A device according to claim 15 wherein the device is a gardening device.

17. A device according to claim 16 wherein the device is selected from the list comprising: a lawn mover; a hedge trimmer; a chain saw; a lawn aerator; a scarifier; and a shredder.

18. A device according to claim 16 wherein the device is an engine driven vehicle.

19. A method of delivering fuel into charge air for combustion therewith, the method comprising the steps of: dispensing a set quantity of fuel from a fuel injector to an atomising nozzle; and dispensing the fuel from the fuel injector through the atomising nozzle into the charge air, the dispensed fuel atomisirig upon exiting the atomising nozzle and entering the charge air; wherein: a depression is created in the combustion chamber in an early part of an intake stroke of the engine and the depression is used to draw through the atomising nozzle the gas used to entrain the dispensed fuel.