GB2452767A

GB2452767A - A fuel injection system for an internal combustion engine

Info

Publication number: GB2452767A
Application number: GB0718017A
Authority: GB
Inventors: Paul Bartholomew Ravenhill; Richard Matthew Hoolahan
Original assignee: Scion Sprays Ltd
Current assignee: Scion Sprays Ltd
Priority date: 2007-09-14
Filing date: 2007-09-14
Publication date: 2009-03-18
Anticipated expiration: 2027-09-14
Also published as: GB0718017D0; GB2452767B

Abstract

There is provided an internal combustion engine comprising a variable combustion chamber 10, an air intake passage 18, a throttle 23, a bypass passage 28 which bypasses the throttle 23 and via which air and/or recirculated air and/or recirculated exhaust gas is supplied to the intake passage 18 via a delivery nozzle 27 located downstream of the throttle 23. A fuel injector 20 delivers fuel to a mixing tube 26 having a mixing chamber (30, Fig.7) and the bypass passage 28 is also connected to the mixing chamber so that air or recirculated exhaust gas flowing through the bypass chamber entrains fuel present in the mixing chamber and a resulting mixture is delivered to the intake passage 18 via the delivery nozzle 28. The mixing chamber is defined in part by a plurality of inlet apertures (60-63, Fig.6) on the walls via which air/recirculated gas can be drawn into the chamber. The apertures are sized such that the surface tension of the fuel will resist flow of fuel out of the chamber. Furthermore, two bars (120, 121, Fig.5) extend at right angles to each other to prevent fuel or gas from flowing immediately through the mixing chamber.

Description

A FUEL INJECTION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE

The present invention relates to a fuel injection system for an internal combustion engine. The system is particularly suited for use with small capacity engines such as used in garden equipment, e.g. lawnmowers.

In GB 2421543 the applicant has described a "pulse count" injection system in which the quantity of fuel delivered to a combustion chamber in each engine cycle is controlled by controlling the number of operations of an injector which delivers in each operation a set quantity of fuel. Most commonly available systems operate with pulse width modulation (PWM) which controls the opening period of an injector to control the quantity of fuel delivered, with a need for a high pressure fuel supply to the injector and a pressure regulator to ensure that variations in pressure to the inlet manifold do not affect the quantity of fuel delivered. The apparatus of GB 2421543 avoided this by the injector itself operating as a pump and delivering a set quantity of fuel regardless of changes in pressure in the inlet manifold; then the total amount of fuel becomes a function of the number of times the injector is operated.

In UK application No.0522068.6, a development of the system of GB 2421543 was described. In this a sonic nozzle was incorporated so that fuel delivered by the pulse count injector is entrained in air (or combusted gases) to be delivered to the inlet manifold via a sonic nozzle in which the gas flow reached or approached the speed of sound. This resulted in better atomisation of the delivered fuel.

-I

The present invention provides an internal combustion engine comprising: a variable volume combustion chamber; an air intake passage supplying air to the combustion chamber; a throttle provided in the air intake passage for throttling flow of air through the air intake passage; a bypass passage which bypasses the throttle and via which air and/or recirculated exhaust gas is supplied to the intake passage via a delivery nozzle located downstream of the throttle; a fuel injector; and emulsion means, wherein: the fuel injector delivers fuel to a mixing chamber in the emulsion means; and the bypass passage is connected to the emulsion means so that air or recirculated exhaust gas flowing through the bypass passage passes through the emulsion means, entrains fuel present in the mixing chamber of the emulsion means and the resulting mixture is delivered from the emulsion means to the intake passage via the delivery nozzle.

The present invention provides an alternative method of atomisation of the fuel delivered by the fuel injector. The use of an emulsion means (e.g. an emulsion tube) has been found surprisingly to achieve better atomisation and fuel delivery than a sonic nozzle. Also, the new design allows the use of the arrangement to deliver fuel downwardly into an inlet manifold, rather than just upwardly.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of an internal combustion engine having a first embodiment of fuel injection system according to the present invention; Figure 2 is an illustration of the throttle body of the fuel injection system of Figure 1, showing in greater detail an emulsion tube, pulse count injector and by-pass inlet passage; Figure 3 shows a variant of the Figure 2 embodiment, in which the by-pass inlet passage is connected to receive recirculated combusted gases rather than air; Figures 4a to 4d show operation of the Figure 2 fuel injection system during a single engine cycle; Figure 5 is a view in greater detail of the emulsion tube used in the fuel injection systems of Figures 2 and 3; Figure 6 is a side elevation view of the emulsion tube of Figure 5; Figure 7 is a cross-section through the emulsion tube of Figure 6; Figure 8 is an isometric view of the emulsion tube of Figures 5,6 and 7; Figure 9 is n end view of the emulsion tube of Figures 5to8, and Figure 10 is a schematic view of a second type of emulsion tube suitable for use in the fuel injection systems of the type illustrated in Figures 2 and 3; Figure 11 is a cross-sectional view taken along an alternative type of fuel delivery nozzle suitable for the fuel injector systems of Figures 1 to 4d; Figure 12 is a cross-sectional view across the Figure 11 fuel delivery nozzle; Figure 13 is an illustration of emulsion apparatus comprising a perforated plate; and Figure 14 is an illustration of emulsion apparatus for a downwardly directing injector, comprising a plurality of perforated plates.

Figure 1 shows an internal combustion engine having a variable volume combustion chamber 10 defined by a piston 11 reciprocating in a cylinder 12.

The piston 11 is connected by a connecting rod 13 to a crankshaft 14. A poppet valve 15 is an exhaust valve controlling flow of combusted gases out of the combustion chamber 10 to an exhaust passage 16. The valve 15 will be opened by a cam on a camshaft (not shown) which is connected to the crankshaft 14 to rotate with the crankshaft 14. The valve 15 will be closed by a valve spring (not shown) which biases the valve into abutment with its valve seat. A poppet valve 17 is an inlet valve controlling flow of fuel/air charge into the combustion chamber 10 from an inlet passage 18. The valve 17 will be opened by a cam on the aforementioned camshaft and closed by a valve spring (not shown) The fuel injection system of the present invention comprises a fuel injector 20 of the type described in GB 2421543. The injector 20 is controlled by an engine control unit (ECU) 21 attached to a throttle body 22. An inlet butterfly throttle 23 is pivotally mounted in the throttle body 22 to throttle flow of air through the inlet passage

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18. A sensor 24 will provide a signal indicative of throttle position to the ECU 21, which will also receive other signals such as a crankshaft position signal or a signal from a pressure sensor measuring air pressure in the inlet passage 18. The throttle body 22 incorporates a venturi 25, a narrowing in cross-sectional area of the inlet passage, which will induce a localised increase in flow velocity of air flowing through the inlet passage 18 and a consequent localised reduction in pressure. The injector 20 delivers fuel to an emulsion tube 26 from which fuel is delivered via a fuel delivery nozzle 27 into the venturi 25, the fuel being entrained in air passing from a bypass passage 28 through the emulsion tube 26 into the venturi 25.

This will be described in more detail below.

Figure 2 shows that the fuel injector 20 delivers fuel to a mixing chamber and accumulation volume 30 of the emulsion tube 26. This is shown in greater detail in Figure 5. The emulsion tube 26 is located in a chamber 31 defined in the throttle body 22 and two rubber 0-rings 32,33 are provided between the emulsion tube 26 and the surrounding chamber 31 to provide a fluid seal, respectively preventing flow of fuel along the exterior of nozzle 27 to the venturi and flow of fuel past the injector 20. The inlet passage 28 opens on to the chamber 31 and delivers air to the chamber 31 from atmosphere, bypassing the throttle 23. As an alternative and as illustrated in Figure 3, the bypass passage 28 can be connected to an exhaust gas recirculation passage 40 so that combusted gases can be delivered to the chamber 41 via the bypass passage 28. The hot gas will also aid fuel evaporation. A thermal barrier will be needed to prevent heat passing from the hot exhaust gases to the cool \ fuel supplied to the injector, but this can be achieved by careful positioning of passageways.

The emulsion tube 26 is shown in detail in Figures 5, 6, 7, 8 and 9. The emulsion tube 26 has four rows of four apertures; two rows 50, 51 are shown in Figure 8. The apertures 60, 61, 62, 63 of row 40 are shown in Figure 6.

The apertures of the four rows allow flow of air from the chamber 31 into the mixing chamber 30. The rows 60, 61, 62, 63 are disposed at 900 intervals around a lower cylindrical wall 55 of the emulsion tube. Three spaced rows 50, 51, 52 are shown in the cross-sectional view of Figure 7 and all four rows 50, 51, 52, 53 in the cross-sectional view of Figure 9. The fuel delivery nozzle 27 extends away from the lower part of the emulsion tube; the nozzle 27 is of a reduced diameter compared to wall 55 and an interior passage 59 in nozzle 27 is of a reduced diameter compared to chamber 30. A delivery aperture in the form of slot 90 is provided at a distal end of the nozzle 27 (distanced from chamber 30) via which fuel and air is delivered to the venturi 25. The slot 90 is elongate and aligned parallel with a central axis 91 of the nozzle 27.

Two pairs of aligned apertures are provided in the wall 55, spaced axially apart. One aperture 110 of a first pair and one aperture 111 of the second pair are shown in Figure 7. These allow two bars 120, 121 to be located extending across the chamber 30 as can be seen in Figure 9; the bars 120,121 extend at right angles to each other when viewed as seen in Figure 9. The two bars 120, 121 are also seen in part in Figure 5. When fuel is delivered by the injector 20 into the chamber 30 then the two bars 120, 121 prevent the

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fuel flowing immediately through the mixing chamber 30 and out of the nozzle 90 and instead ensure that the fuel accumulates in mixing chamber 30 for subsequent entrainment by air flowing through the bypass passage 28.

Operation of the fuel injection system is shown in Figures 4a to 4d. Figures 4a and 4b show operation at part throttle; the throttle 23 is rotated to partially close the inlet passage 18. Figure 4a shows the condition when the inlet valve 17 is closed. While the valve is closed the injector 20 is used to deliver fuel into the mixing chamber 30, which fills up as illustrated (if desired the injector could continue to inject fuel when the inlet valve 20 is open) . The apertures of the four rows 50, 51, 52, 53 are sized such that surface tension of the fuel will prevent fuel flowing out of the mixing chamber 30 via the apertures.

In Figure 4b the intake valve 17 has been opened and air is drawn into the combustion chamber by downward motion of piston 11. The air is drawn through inlet passage 18 past throttle 23. A depression will be occasioned downstream of the throttle 23 by the air flow past the throttle 23. This will cause air to be drawn from the bypass passage 28 through the chamber 31 and via the emulsion tube 22 and out of the nozzle 27. The air drawn from the bypass passage 28 will entrain the fuel in the mixing chamber 30 as it flows through the emulsion tube 30. This will give rise to an emulsion of fuel and air which is then delivered into the charge air in venturi 25 and is atomised in the air and the fuel/air charge is then delivered into the combustion chamber 10 for combustion.

Figures 4c and 4D show operation at full load: the throttle 23 is rotated to a wide open condition. Figure 4c shows the condition when the inlet valve 17 is closed.

Whilst the valve 17 is closed, the injector 20 delivers fuel to the chamber 30 of the emulsion tube, which fills as illustrated (the injector could continue to deliver fuel when the inlet valve 17 is open) . Then at 4d the inlet valve 17 has opened and the piston 11 draws air into the combustion chamber 10 via the intake passage 17. Since the throttle 23 is wide open it offers little resistance to air flow and so does not itself give rise to a depression in pressure downstream of the throttle 23. Instead a fast flow of air through the intake passage 18 at high engine speeds/loads gives rise to a drop in pressure in the venturi 25. This drop in pressure draws air from the bypass passage 28 into the intake passage 18 via the emulsion tube 26 and delivery nozzle 27. The air passing through the emulsion tube 26 entrains the fuel in the mixing chamber 30 and delivers the fuel to the intake passage 18. The air passing through mixing chamber 30 forms an emulsion and gives rise to good atomisation of the fuel delivered to the intake passage 18 and hence to the combustion chamber 16.

The embodiment described above has an injector 20 arranged to deliver fuel vertically upwardly into a venturi 25. However, it may be desired to arrange the injector 20 to deliver fuel vertically downwardly or laterally into the venturi 25. The design previously described must be modified to prevent fuel flowing under gravity out of the chamber 30 of the emulsion tube. One possible modification is shown in Figure 10, in which the injector 1020 is oriented to deliver fuel vertically downwardly into a chamber 1030 of an emulsion tube 2026; the fuel is shown at 1031. The emulsion tube 1026 comprises an inner tube 1010 and an outer tube 1011. The fuel 1031 fills an annular cavity defined between the tubes 1010 and 1011. Rows of apertures are provided in both tubes 1010 and 1011. The apertures are sized (as described above) such that surface tension of the fuel will prevent the fuel flowing through the apertures until entrained by air flowing through the bypass passage. The inner and outer tubes 1010, 1011 are co-axial. The inner tube 1010 extends vertically downwardly through an aperture in the outer tube 1011. The inner tube 1010 provides a delivery nozzle 1027 which extends vertically downwardly into a venturi 25 and has an orifice 1090 via which fuel is dispensed when entrained in air.

Recent work on fuel atomisation has indicated to the applicant that use of an emulsion tube gives better results than sonic atomisation. Although the introduction of an emulsion tube means that the air flow does not reach sonic velocities, the less restricted airflow has been found to better entrain the delivered fuel.

Instead of using two bars in an emulsion tube as described above, a perforated plate or other baffle could be used.

The emulsion tube could be made of brass or stainless steel both of which are corrosion resistant and are easy to machine. It is also possible that the emulsion tube could be injection moulded in plastic, but the heat of EGR may cause problems for this. j)

-10 -When the engine is idling or on start-up the air flow is slow and the emulsion tube can give very good atomisation in these circumstances, e.g. from when the engine is first cranked over. In most conventional engines, fuel is delivered onto the back of the intake valve(s) and then as the intake valve(s) open(s) the initially small annular clearance provides a restricted path for fuel/air flow which aids atomisation (the heat of the intake valve also aiding atomisation) . However, in small engines (e.g. started by a hand pull mechanism) then there is not a high starting speed and there will be no heat on start up and so injecting fuel in such a conventional manner gives very poor mixing of fuel and air. The present invention permits use of a special regime on start up. In the start-up regime, all the airflow will be through the bypass passage 28 (the throttle valve 23 will be closed) and there will thus be maximum atomisatjon of the fuel and also the atomised fuel is delivered straight to the combustion chamber 10 without residence time in the cold intake passage.

In an alternative start-up strategy, a second start up valve is provided in the air intake passage in addition to the throttle. The start up valve will either completely close the air intake passage or will open the passage fully.

On starting of the engine the start up valve will be closed so that all the intake air is drawn through the bypass passage. The start up valve will be opened once the engine has started.

The air intake passage need no be completely closed on start up; the passage could be mostly closed instead, by either or both of the throttle valve or the start up valve.

-11 -The majority of the air supplied to the combustion chamber would still be supplied via the bypass passage, but a minority would flow past the throttle. This can be advantageous for larger capacity engines and also can be advantageous when the bypass passage is connected to the exhaust system to receive recycled combusted gases.

Above the fuel delivery nozzle 27 ahs been illustrated with a single delivery aperture 90. However, the performance of the apparatus could be improved by configuring the nozzle with a plurality of apertures -this is shown in figures 11 and 12. Figure 11 shows a row of vertically spaced apart apertures 6000, 6001, 6002, 6003 and 6004 provided on the downstream facing side of the fuel delivery nozzle 27.

Figure 12 shows that a plurality of such rows, numbered 6010, 6011, 6012 and 6013 are provided in the downstream side of the nozzle 27. The arrows in the figures 11 and 12 indicate the direction of the airflow past the nozzle 27.

Above the embodiments have used an emulsion tube as emulsion apparatus, but the applicant envisages that alternative apparatus could be used an examples are given in figures 13 and 14.

In figure 13 a fuel injector 7000 of the type described previously delivers fuel upwardly into a mixing chamber 7001 defined between two plates 7002 and 7003 provided in a chamber 7004 defined in a throttle body 7005. The plates each have a plurality of apertures which allow a flow of air from a bypass passage 7006 into the mixing chamber 7001 and then a flow of fuel and air mixture out of the mixing chamber 7001 via a delivery nozzle 7007 into a venturi 7008 -12 -in the air flow passage. The nozzle 7007 is art aperture in the throttle body wall rather than a tube extending into the venturi 7008. The apertures in the plates 7002 and 7003 are sized such that liquid fuel delivered to and then resident in the mixing chamber 7001 will not flow out of the mixing chamber in the absence of a bypass air flow, due to surface tension. The plate 7003 does not have any apertures aligned with an outlet of injector 7000, in order that fuel delivered to the chamber 7001 under pressure by the injector 7000 does not flow directly out of nozzle 7007. Instead plate 7003 ensures that the injected fuel remains in the mixing chamber 7001 until entrained in a flow of bypass air.

Figure 14 shows an arrangement similar to figure 13, except in the figure 14 embodiment or'dy one apertured plate 8000 is used, rather than two plates and in figure 14 fuel in injected downwardly into a mixing chamber 8001 by an injector 8002 and then delivered downwardly via nozzle 8003 into venturi 8004. Gravity will hold liquid fuel on the upstream surface plate 8000 until there is a flow of bypass air through passage 8005. Like in figure 13, the plate 8000 does not have apertures aligned with the outlet of injector 8002.

The present invention could use any emulsion apparatus which comprises a mixing chamber into which fuel is delivered by a fuel injector for subsequent mixing with bypass gas flow to form an emulsion of fuel and gas for subsequent delivery to a combustion chamber.

The good atomisation provided by use of emulsion apparatus also allows the use of alternative fuels such as -13 -kerosene and diesel and also blended fuels (e.g. with ethanol) In the embodiments described the fuel injection system is conveniently provided in the form of a unit detachable from the engine, the unit comprising: the throttle body 22 having the throttle 23 mounted therein and the bypass passage 28 and bypass chamber 31 integrally formed therein; the emulsion tube 26 located in the bypass chamber 31; and the fuel injector 20 and associated electronics 21 provided as a unit attached to the throttle body 22. This eases repair/replacement and also facilitates incorporation of the fuel injection system in existing engine designs.

Claims

-14 - CLAIMS

1. An internal combustion engine comprising: a variable volume combustion chamber; an air intake passage supplying air to the combustion chamber; a throttle provided in the air intake passage for throttling flow of air through the air intake passage; a bypass passage whi.ch bypasses the throttle and via which air and/or recirculated exhaust gas is supplied to the intake passage via a delivery nozzle located downstream of the throttle; a fuel injector; and emulsion means, wherein: the fuel injector delivers fuel to a mixing chamber in the emulsion means; and the bypass passage is connected to the emulsion means so that air or recirculated exhaust gas flowing through the bypass passage passes through the emulsion means, entrains fuel present in the mixing chamber of the emulsion means and the resulting mixture is delivered from the emulsion means to the intake passage via the delivery nozzle.

2. An internal combustion engine as claimed in claim 1 wherein the fuel injector functions as a positive displacement pump and comprises: a fuel chamber; a one-way inlet valve allowing flow into the fuel chamber from a fuel inlet; a one-way outlet valve allowing flow of fuel out of the fuel chamber to the emulsion tube chamber; a piston; an electrical coil; and -15 -a spring; the piston moving under influence of forces applied by the coil and the spring to sequentially draw fuel into and expel fuel from the fuel chamber,and the piston moving between two fixed end stops in each piston stroke so that a volume of the fuel chamber swept by the piston is constant in each operation of the fuel injector.

3. An internal combustion engine as claimed in claim 1 or claim 2 wherein the emulsion means is provided in a bypass flow chamber which is connected to the bypass passage and the mixing chamber is defined in part by a surface provided with a plurality of inlet apertures via which air/recirculated gas can be drawn into the mixing chamber from the bypass chamber, the inlet apertures being sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber via the inlet apertures to the bypass flow chamber.

4. An internal combustion engine as claimed in any one of claims 1 to 3 wherein the emulsion means is provided in a/the bypass flow chamber which is connected to the bypass passage and the mixing chamber is defined in part by a surface provided with a plurality of outlet apertures via which a mixture of fuel and air/recirculated gas can be drawn from the mixing chamber, the outlet apertures being sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber via the outlet apertures to the delivery nozzle.

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5. An internal combustion engine as claimed in any one of the preceding claims wherein the emulsion means is an emulsion tube.

6. An internal combustion engine as claimed in claim 5, wherein a flow impediment is provided in the mixing chamber to prevent fuel injected by the fuel injector flowing straight through the mixing chamber to the fuel delivery nozzle, whereby fuel delivered by the fuel injector can accumulate in the mixing chamber for subsequent entrainment in flow of bypass air or bypass recirculated gas.

7. An internal combustion engine as claimed in claim 6 wherein the flow impediment comprises a plurality of bars extending across the mixing chamber.

8. An internal combustion engine as claimed in any one of claims 1 to 4 wherein the emulsion means comprises one or more apertured plates which each define in part the mixing chamber.

9. An internal combustion engine as claimed in claim 8 wherein the fuel injector delivers fuel on to a surface of the/one of the plates and the relevant plate has a portion aligned with an outlet of the fuel injector in which no apertures are present.

10. An internal combustion engine as claimed in claim 1 or claim 2 wherein: the emulsion means comprises an emulsion tube provided in a bypass flow chamber which is connected to the bypass passage; -17 -the emulsion tube comprises outer and inner tubes; at least a part of the mixing chamber is defined between the outer and inner tubes; the outer tube is provided with a plurality of apertures via which air/recirculated gas can be drawn into the mixing chamber from the mixing chamber and which are sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber to the bypass flow chamber; and the inner tube is provided with a plurality of apertures via which fuel entrained in a flow of bypass air/ recirculated gas can pass to the delivery nozzle and which are sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber to the delivery nozzle in absence of a flow of bypass air/recirculated gas flow.

11. An internal combustion engine as claimed in claim 10 wherein the fuel injector delivers fuel vertically downwardly or laterally into the mixing chamber.

12. An internal combustion engine as claimed in claim 11 where the fuel delivery nozzle extends vertically downwardly or laterally into the air intake passage.

13. An internal combustion engine as claimed in any one of the preceding claims comprising a venturi in the air intake passage and wherein the delivery nozzle delivers fuel to the venturi, whereby any pressure drop occasioned by air flow through the venturi will draw air or recirculated gas from the bypass passage through the emulsion means.

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14. A method of operation of the internal combustion engine claimed in any one of the preceding claims in which on starting of the engine the throttle is fully closed so that all or nearly all of the air drawn into the combustion chamber is drawn through the bypass passage and via the emulsion means.

15. A method of operation of the internal combustion engine claimed in any one of claims 1 to 13 in which on starting of the engine a start up valve is used to mostly or fully close the air intake passage so that all or nearly all of the air drawn into the combustion chamber is drawn through the bypass passage and via the emulsion means.

16. An internal combustion engine substantially as hereiribefore described with reference to and as shown in the accompanying drawings.

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16. An internal combustion engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS:-

CLAI MS

1. An internal combustion engine comprising: a variable volume combustion chamber; an air intake passage supplying air to the combustion chamber; a throttle provided in the air intake passage for throttling flow of air through the air intake passage; a bypass passage which bypasses the throttle and via which air and/or recirculated exhaust gas is supplied to the intake passage via a delivery nozzle located downstream of the throttle; a fuel injector; and fuel and air mixing means comprising a bypass flow chamber connected to the bypass passage and a mixing chamber situated in the bypass flow chamber, wherein: the fuel injector delivers fuel to the mixing chamber; and the bypass passage is connected to the fuel and air mixing means so that air or recirculated exhaust gas flowing through the bypass passage passes through the mixing chamber means, entrains fuel present in the mixing chamber and a resulting mixture is delivered from the mixing chamber means to the intake passage via the delivery nozzle; wherein the mixing chamber is defined in part by a surface provided with a plurality of inlet apertures via * * * ** which air/recirculated gas can be drawn into the mixing **S chamber from the bypass chamber, the inlet apertures being ** sized such that surface tension of the fuel will resist flow p.. 4 of fuel out of the mixing chamber via the inlet apertures to the bypass flow chamber.

2. An internal combustion engine as claimed in claim 1 wherein the mixing chamber is defined in part by a surface provided with a plurality of outlet apertures via which a mixture of fuel and air/recirculated gas can be drawn from the mixing chamber, the outlet apertures being sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber via the outlet apertures to the delivery nozzle.

3. An internal combustion engine comprising: a variable volume combustion chamber; an air intake passage supplying air to the combustion chamber; a throttle provided in the air intake passage for throttling flow of air through the air intake passage; a bypass passage which bypasses the throttle and via which air and/or re-circulated exhaust gas is supplied to the intake passage via a delivery nozzle located downstream of the throttle; a fuel injector; and fuel and air mixing means comprising a bypass flow chamber connected to the bypass passage and a mixing chamber situated in the bypass flow chamber, wherein: I *. S the fuel injector delivers fuel to the mixing chamber; and * * * ** * the bypass passage is connected to the fuel and air *.* mixing means so that air or re-circulated exhaust gas flowing through the bypass passage passes through the mixing chamber, entrains fuel present in the mixing chamber and a resulting mixture is delivered from the mixing chamber to the intake passage via the delivery nozzle; wherein the mixing chamber is defined in part by a surface provided with a plurality of outlet apertures via which a mixture of fuel and air/re-circulated gas can be drawn from the mixing chamber from the bypass chamber, the outlet apertures being sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber via the outlet apertures to the delivery nozzle.

4. An internal combustion engine as claimed in any one of claims 1 to 3 wherein the fuel injector functions as a positive displacement pump and comprises: a fuel chamber; a one-way inlet valve allowing flow into the fuel chamber from a fuel inlet; a one-way outlet valve allowing flow of fuel out of the fuel chamber to the mixing chamber; a piston; an electrical coil; and a spring; the piston moving under influence of forces applied by the coil and the spring to sequentially draw fuel into and expel fuel from the fuel chamber, and the piston moving between two fixed end stops in each piston stroke so that a volume of the fuel chamber swept by the piston is constant in each operation of the fuel injector. * * * S..

S 5. An internal combustion engine as claimed in any one of : claims 1 to 4, wherein a flow impediment is provided in the mixing chamber to prevent fuel injected by the fuel injector flowing straight through the mixing chamber to the fuel delivery nozzle, whereby fuel delivered by the fuel injector can accumulate in the mixing chamber for subsequent entrainment in flow of bypass air or bypass recirculated gas.

6. An internal combustion engine as claimed in claim 4 wherein the mixing chamber is provided in a tube.

7. An internal combustion engine as claimed in claim 6 wherein the flow impediment comprises a plurality of bars extending across the tube.

8. An internal combustion engine as claimed in any one of claims 1 to 5 wherein the mixing chamber is defined at least in part by one or more apertured p1ates.

10. An internal combustion engine as claimed in any one of claims 1 to 4 wherein: *... the mixing chamber is defined at least in part between inner and outer tubes; * * * ** e the outer tube is provided with the plurality of inlet apertures via which air/recirculated gas can be drawn into the mixing chamber from the mixing chamber and which are sized such that surface tension of the fuel will resist flow * of fuel out of the mixing chamber to the bypass flow chamber; and -Th the inner tube is provided with a plurality of apertures via which fuel entrained in a flow of bypass air/ recirculated gas can pass to the delivery nozzle and which are sized such that surface tension of the fuel will resist flow of fuel out of the mixing chamber to the delivery nozzle in absence of a flow of bypass air/recirculated gas flow.

11. An internal combustion engine as claimed in claim 10 wherein the fuel inlector delivers fuel vertically downwardly or laterally into the mixing chamber.

13. An internal combustion engine as claimed in any one of the preceding claims comprising a venturi in the air intake passage and wherein the delivery nozzle delivers fuel to the venturi, whereby any pressure drop occasioned by air flow through the venturi will draw air or recirculated gas from the bypass passage through the mixing chamber means.

14. A method of operation of the internal combustion engine claimed in any one of the preceding claims in which on *S * starting of the engine the throttle is fully closed so that *..

all or nearly all of the air drawn into the combustion chamber is drawn through the bypass passage and via the mixing chamber means.

15. A method of operation of the internal combustion engine claimed in any one of claims 1 to 13 in which on starting of the engine a start up valve is used to mostly or fully close the air intake passage so that all or nearly all of the air drawn into the combustion chamber is drawn through the bypass passage and via the mixing chamber.