AU675208B2 - Gaseous fuel delivery system - Google Patents

Description

OPI DATE 21/05/93 APPLN. ID 27607/92 AOJP DATE 22/07/93 PCT NUMBER PCT/AU92/00542 AU9227607

(PCT)

(51) International Patent Classification 5 International Publication Number: WO 93/08398 F02M 13/08, 21/02, 21/04 Al F02D 19/02, F16K 3/24, 31/122 (43) International Publication Date: 29 April 1993 (29.04.93) (21) International Application Number: PCT/AU92/00542 (81) Designated States: AT, AU. BB, BG, BR, CA, CH, CS, DE, DK, ES, Fl, GB, HU. JP, KP, KR. LK, LU, MG, (22) Internat~nal Filing Date: 12 October 1992 (12.10.92) MN, MW, NL. NO, PL, RO, RU, SD. SE, US. European patent (AT, BE, CH, DE, DK, ES. FR. GB, GR, IE. IT, LU. MC, NL, SE), OAPI patent (BF. B)J CF, Priority data: CG, Cl, CM, GA, GN, ML, MR, SN, TD, TG).

PK 8950 16 October 1991 (16.10.91) AU Published (71) Applicant (for all designated States except US): GASRESE- With international search report.

ARCH AUSTRALIA PTY. LTD. [AU/AU]; 19 Clarice Road, Box Hill, VIC 3128 (AU).

(72) Inventor; and Inventor/Applicant (for US onl) SHARPLES, Leigh, William [AU/AU]; 19 Clarice Road. Box Hill. VIC 3128'

(AU).

(74) Agent: WATERMARK: 2nd Floor. The Atrium, 290 Burwood Road, Hawthorn, VIC 3122 (AU).

675208 (54) Title: FUEL DELIVERY SYSTEM 14 21 22 110A 12 S102 4 1Mr <k 2 To Engine (57) Abstract A carburettor for low-pressure gaseous fuel (11) comprising: a hollo\w body having a through bore. a venturi in said through bore, a throttle valve downstream of said venturi a jet positioned in the venturi said jet connected to a gaseous fuel supply a flow control valve (15) interposed between said jet and said fuel supply said control valve being operatively connected to the throttle valve such that movement of the throttle valve causes translation of a vale element (26) in a gas port whereby the area of the port is varied to regulate the flow of gaseous fuel (11) to the jet in direct proportion to movement of the throttle valve 11-2-ge 3r 31 PM ;WhT ilP.K 8138950B10;# FUEL DELIVERY SYSTEM FUEL DELIVERY SYSTEM

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The present invention relates to the field of fuel delivery systems, particularly for internal combustion engines. In particular, the present invention deals with a system for providing a fuel and air gaseous mixture ready for combustion.

BACKGROUND ART: In order to reduce fuel costs, many Internal combustion engines particularly those used in automotive vehicles, have been adapted to run on gaseous fuels, such as compressed natural gas (CNG) or liquid petroleum gas (LPG), rather than more expensive liquid fuels, such as petrol or diesel.

The engines are 'converted' to gaseous operation, usually by the addition of a regulator vaporiser, mixer and manifold(s). These components serve to convert the high pressure gaseous fuel stored in onboard fuel tanks to a lower a 15 pressure fuel which, when mixed with air, provides a fuel/air mixture ready for combustion by the engine.

A difficulty with existing converted engines is that a significant reduction in power output of the engine is noticed after the engine is converted to run LPG or CNG fuels. This is often due to poor fuel/air mixtures being fed to the engine.

Thus combustion of the fuel does not take place under optimum conditions, Also, the ratio of fuel to air in the mixture which is combusted by the engine is determined external of the engine carburettor or fuel injection system, where liquid fuels are usually mixed. Accordingly, little, if any, control of fuel/air ratios throughout the entire operating range of the engine is undertaken, 25 Prior art systems utilise manifold vacuum to control a diaphragm which regulates flow of gaseous fuel, Accordingly, when the engine is started, a vacuum must be created in the engine before the diaphragm allows fuel flow into the engine. This results in relatively lengthy engine cranking times. Restrictive hoses and connectors are used between the diaphragm and engine manifold in order to gain greater vacuum, and thus more responsive diaphragm control.

Prior art systems use engine manifold vacuum to suck gaseous fuel into the 7 carburettor.

7r 0 41 3;U, Pt.; ;W.-TEF.h .K 2 However, when the engine is running at relatively high speed, the restrictive hoses serve to reduce the amount of fuel flowing to the engine.

Furthermore, as the speed of the engine increases, the manifold vacuum decreases, which in turn serves to increase the richness of the fuel flow to the engine. A reduction in performance and economy is thus noticeable.

Poor engine performance may also be attributable to poor mixing or ratios of the fuei and air, In some known arrangements, the gaseous fuel is allowed to dribble down the inside surface of the carburettor venturi. The fuel remains in close proximity to the carburettor walls, and does not mix adequately with the air passing thru'qgh the carburettor venturi, Furthe ,ore, not an insignificant amount of fuel is wasted when the engine is decelerating as diaphragm control systems are relatively slow to reduce fuel/air mixture passing to a decelerating engine. A danger of fuel leakage may also occur when the engine has been switched off. Gaseous fuel 15 which is present in the conversion equipment may be allowed to bleed through the engine and out the engine exhaust uncombusted.

OBJECT:

An object of the present invention is to provide a fuel delivery system which alleviates at least one disadvantage of the prior art.

A further object of the present invention is to provide a fuel delivery i: system which enables satisfactory control of fuel and air ratios throughout the •entire operating range of the engine.

A still further object of the present invention is to provide a fuel delivery system which may be calibrated for each particular engine it is fitted to.

25 Yet another object of the present invention is to provide a fuel delivery e system which enables an engine to consume substantially less fuel than existing gaseous fuel systems, and/or alleviate the reduction in power output of the engine due to the conversion to gaseous fuels.

SUMMIARY OF INVENTION: To this end the present invention provides a device for use with a i carburettor of an internal combustion engine to mix gaseous fuel with air passing e\ through the carburettor, said device including: 11-25-36 3:31 PM ;WATERMARK 8138196010; 7/20 a bore passing through said device through which a first stream of said air passes;

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Air an induction tube extending into said bore for introducing gaseous fuel directly into said first air stream; an outer surface over which a second stream of said air passes, said outer surface adapted to act in conjunction with an Inner wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of said Induction tube to mix said gaseous fuel with said air.

The present invention pr7,vides the gaseous fuel directly to and for mixing in the carburettor of the engine; the fuel being mixed in the carburettor with air to an appropriate fuel/air mixture for combustion by the engine. In this way the invention provides a stream of combustible gaseous fuel material directly into the inlet air stream path in relatively close proximity to the engine, The invention utilizes air velocity to create a relatively low pressure area into which the gaseous fuel is drawn. The provision of the low pressure area is not directly proportional to or regulated by manifold vacuum.

Furthermore, it has been found that by Jetting the gaseous fuel directly into the air stream passing through the device, the mixing of fuel and air is enhanced 20 and in turn provides a substantial improvement in power output from the engine, Preferably the outer surface of the device is flared and acts in conjunction with the inner wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of the induction tube to mix the gaseous fuel with the air.

25 It is further preferable that the bore passing through the device is tapered.

The present inventio t h particular application in the mixing of methane, liquid petroleum gas (LPG) or compressed natural gas (CNG) fuels with air for combustion in an internal combustion engine, The present invention also provides a fuel delivery system for use with a carburettor of an Internal combustion engine to mix gaseous fuel with air passing through the carburettor, the system including a device with a bore passing through said device through which a first stream of said air passes; 11i265F, :31 ;YhTEN1'APKi eZs81sa0±c;# z8/20 .4r 4 0*4 4 0 044* 4 0 0* 9 4 44 4 4 ~ic.

an induction tube extending into said bore for introducing gaseous fuel directly into said first air stream; an outer surface over which a second stream of said air passes, said outer surface adapted to act In conjunction with an inner wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of said induction tube to mix said gaseous fuel with said air; and a fuel valve to regulate the supply of the gaseous fuel, said fuel valve being operatively coupled to a means for controlling the flow of gaseous fuel/air mixture to the engine.

It has been found that a significant improvement in the amount of fuel consumed is achievable by utilising the valve arrangement to regulate the amount of gaseous fuel delivered to the engine.

Preferably the fuel valve includes a valve member and a mating seat, the valve member including a projection contoured to permit a predetermined flow of 15 fuel through said fuel valve for a given position of said fuel valve.

It is further preferable that the projection extends into the flow path of the fuel.

Preferably the fuel supply valve is operatively coupled to a butterfly valve of the carburettor whlch controls the flow of gaseous fuel/air mixture to the engine for combustion. it has been found that by controlling the operation of the gas fuel valve in conjunction with the operation of the carburettor butterfly valve, a significant improvement in fuel economy and emissions is achieved through a reduction in the amount of unburnt gases passing through the engine and out to exhaust.

25 It is further preferable for the fuel supply valve to be operatively coupled to the butterfly valve of the carburettor by means of a gear coupled to the butterfly valve which engages a gear rack coupled to the fuel supply valve in order to control movement of the fuel supply valve in response to movement of the butterfly valve, Preferably the fuel supply valve undergoes translational movement In response to movement of the butterfly valve.

The configuration of the valve of the present invention further enables the valve to be located in relatively close proximity to the carburettor of the engine.

S1S19801; 9/20 This close fitment further reduces drag forces on the flow of gaseous fuel to the carburettor.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, wherein Figure 1 shows, in combination, the carburettor and valve of the present invention at an engine idle setting; Figure 2 shows the combination set for initial engine acceleration; Figure 3 shows the combination at a setting for higher engine RPM; Figure 3A shows an enlarged view of a component part of the valve of the present invention; Figure 4 shows torque and horse-power output from an engine fitted with the system of the present invention.

Figure 5 shows comparison torque curves of an engine; Figure 6 shows a preferred form of the gaseous fuel mixing device 15 according to the present Invention; Figure 7 shows a preferred jet positioning in the bore of the gaseous fuel mixing device; 'an" Figure 8 shows modifications relating to the structure of the carburettor and valve system disclosed in Figures 1, 2 and 3; Figure 9 relates to a modification of Figure 7; and Figures 10A and 10B show an air pass valve for use in conjunction with the present invention.

Like numerals in the drawings denote like component parts of the present invention.

25 In general, the figures show a preferred form of the present Invention in which the carburettor 1 has a hollow main body portion 2, within which is located a mixing device 3 in accordance with the present invention.

At the other end of the carburettor 1, there Is provided a butterfly valve 4, which serves to control the flow of gaseous fuel/air mixture to the engine for combustion, The butterfly valve 4 pivots about shaft 5. Gear 6 is also coupled to h'aft 5. In an automobile, the accelerator pedal (not shown) is usually coupled r P,4 via a cable mechanism to shaft 5, Acceleration and deceleration of the engine is 11-26-96 Z:31 PM ;WATE:RMARK e1381901010/20 6 controlled by movement of the butterfly valve 4, Operatively coupled to the gear 6 is a rack 18 which serves to proportionately control movement of fuel valve Fuel valve 15 serves to regulate the flow of gaseous fuel 11 into jet 9 for mixture with incoming air flow 8.

A bypass fuel path is provided by pilot line 12 and idle port 10 for fuel and air channel When the engine is off, fuel valve 15 is closed, thus preventing fue! 11 flowing into jet 9. Furthermore, butterfly valve 4 is closed.

Figure 1 shows the system of the present invention set for the engine to run at Idle speed. The butterfly valve 4 at an idle position, closes off the air flow 8 passing to the engine via the butterfly valve 4, The flow of air 8 at the idle position of valve 4 is considered too low to draw fuel from jet 9 and fuel valve is closed. Accordingly, an alternate path is provided to allow for gaseous fuel to enter the engine, comprising an idle port 10 which serves as a junction of fuel line 12 and air channel 10A, Air and fuel is mixed in the idle port proximate the junction of line 12 and channel 10A. Low pressure gaseous fuel 11 is derived from an onboard gaseous fuel tank (not shown) and passes via a converter to 11 and also pilot line 12, to the idle port 'Figure 1 shows the path of air flow 8 via channel 10A, fuel flow via line 12 and the flow of fuel/air mixture. The carburettor may contact the engine intake manifold directly or contact an intermediate passage.

An idle adjustment screw 14 provides an adjustment of the amount of fuel flow and hence the fuel/air ratio at low r.p.m. of the engine, S* A fuel valve of the present invention provides a means by which the 25 amount of gaseous fuel can be regulated and controlled over the entire operating range of the engine in order to optimise the fuel/air ratio of the combustible mixture entering the engine.

Fuel valve 15 serves to regulate the flow of gaseous fuel 11 by means of valve member 16 and seat 17. As shown in Figure 1, the valve member 16 abuts seat 17 and therefore no fuel is allowed to flow into jet 9. Fuel for engine idling only flows via pilot line 12, Figure 2 shows operation of the fuel delivery system of the present I--z5-2e 3: P" I W' TERAARK *04 p *5pp 00 p 0 0 *0pg *0 0P* 0 *0 p p p 0 p Oepp SepO p.

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p p ipepep p .0 r P p p p p p o~ inventio'n as tho butterfly valve 4 is moved to a slightly open position so as to accelerate the engine from idle to low speed Ojust above Idle speed), The flow of idle fuel/air mixture via Idle port 10, including fuel flow via line 12 and air flow via channel 10QA continues only as long as there is enough vacuum at port As shown in Figure 2, as the accelerator is depressed, the valve 4 is moved to beyond progression port 20. The vacuum at the progression port opeins valve 21 and provides more fuel 11 into the air flow passing by one opening created by movement Of butterfly valve 4, at point 13 in addition to the fuel mixture emanating from idle port '10. As the englne speed Increases from idle, this additional fuel supplied to port 20 is required to maintain the correct air/fuel mixture.

A port valve 21 comprising pressure sensitive needle and seat valve 22 senses the increased air flow 13 and opens to allow additional fuel into the 15 carburettor, which fuel is mix-ed with the passing air 13 for combustion by the engine.

The fuel valve 15 also includes a resilient mechanism 19 which serves to further control the operation of member 16 and the flow of fuel 11, thus at this time, valve 15 remains closed so that no fuel 11 passes through jet 9.

20 The gear 6 coupled to shaft 5 rotates as the butterfly valve 4 is opened.

The gear 6 moves rack *18 whioh in turn servos to move valve plunger 24 outwardly relative to valve body Thei resilent mechanism 19 serves to delay the flow of gaseous fuel into jet 9 at idle or low engine speeds.

25 Figure 3 illustrates a further step in the acceleration of the engine from low to higher speed, The resilient mechanism 19 serves to bias valve member 16 against seat 17 to close valve 15 when the butterfly valve 4 is at Idle or low speed positions. However, as the butterfly valve 4 is opened and gear 6 moves rack 18 further outwardly, the plunger 24 moves to engage the top 27 of ?rojeotion 26 and move the projection 26 further outwardly and move valve member 16 away from seat 17 to open valve 15 and permit fuel 11I to flow Into jet 9.

11-25-36 3351 PU ;WAT.ERMARK 613819e6010 #12 8 The velocity of air flow 8 over and through the gaseous fuel mixing device 7 is sufficient to draw fuel through induction tube or jet 9 and enable mixing of air and gaseous fuel downstream of the jet in region 28. The induction tube or jet 9 extends into the air stream passing through the bore of the mixing device. Air flow over the outer surface of the device is accelerated by passing through a constriction between the outer surface and the inner wall of the carburettor. In the preferred embodiment depicted the constriction Is provided by the flared outer surface of the device. The acceleration of the air stream over the mixing device acts to lower the air pressure downstream of the jet.

The low pressure area 28 created by the mixing device is relatively strong. ThL4 it is advantageous to directly or operatively cou;'le the regulation of gas supply, for example by a needle/seat arrangement, to engine in order to obtain metering of gas flow to air flow (into engine) throughout the engine's rev. range. The coupling can be achieved in many ways, by lever, cable, other 15 known mechanisms or rack and gear as herein preferred. The metering of gas to air flow enables precise ratios of fuel/air to be obtained and optimised for each particular engine.

v Figure 7 shows a preferred positioning of Induction tube/jet 9 in the mixing device 7. The upper figure shows a view looking down into the bore of the mixing device 3. The ratio of area occupied by jet 9 to the area available for air to pass by jet 9 is 1 to 0, preferably 1.8 to 2.2, and most preferably 2.0. That is, the jet occupies an area of between 1 to 3 times more than the area available for

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The lower figure shows In cross-section, an end view of jet 9. Preferably 25 the ratio of area occupied by jet 9 to the air area Is 0.5 to 2, preferably 1,1 to 1.3, Referring to Figure 3, as the butterfly valve 4 is opened further for higher engine speed, valve 15 is proportionately opened to allow more fuel into the mixing device for mixing with air to form a combustible air/fuel mixture. The projection 26 may be tapered or stepped to provide a larger orifice for fuel flow through valve In order to obtain correct or optimum ratios of fuel and air throughout Sengine operating range, projection 26 can be contoured and shaped to a !1-26-96 PI-4 P ;W .TERNI.

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4 9 69 44 04 9* 0 predetermined configuration. Thus a narrowing of projection 26 will enable more fuel 11 to flow into jet 9 for higher engine r,p.m, or richer air/fuel mixtures, The converse also applies.

Figure 3A shows an enlarged view of projection 26. The amount of fuel drawn In via jet 9 depends on engine speed, air flow through the bore of the mixing device past jet 9 due to reduced pressure, and the 'size of the orifice in valve 15 between valve 16 and seat 17, The size of the orifice in valve 15 may be increased for higher engine speed, or richer fuel mixtures, by tapering or stepping the diameter of projection 26, As the valve member 16 is moved further outward, more space is created between valve member 16 and seat 17, The size of this space determines the amount of fuel 11 entering jet 9. The amount of fuel 11 entering jet 9 is also determined inversely by the volume occupied by projection 26 in the opening defined by seat 17. Thus, if the projection 26 is contoured in its outer shape, more or less fuel 11 can pass by seat 17 and enter 15 jet 9, This is particularly so when the valve member 16 is moved outwardly beyond end 29 of jet 9, Accordingly, at an end 30 of projection 26, there is provided a narrowing as an example embodiment, In operation, when end 30 is moved so as to sit near seat 17, a larger gap for fuel 11 to flow through into jet 9 is provided between end 30 and seat 17.

It is anticipated that the projection 26 is to be contoured on its surface in such a way, for each make and size of engine, so as to provide optimum fuel/air ratio of combustible mixture ntering an engine throughout the engine's operating range, When the driver of the automobie lifts their foot from the accelerator pedal this serves to return butterfly valve 4 to its idle position and close valve 15 and the engine then decelerates as shown in Figure 1. The closure of valve reduces significantly the flow of fuel 11 into jet 9, and hence the quantity of unburnt gas passing to exhaust, It has also been found that if seat 17 is formed as a projection Into the path of the flow of fuel 11, more accurate control of fuel flow into jet 9 can be achieved. A turbulent flow is created in fuel flow proximate seat 17.

61S8: .I 010; 14/20 Furthermore, it has been found that the shape o' configuration of the mixinig device 7 serves to enhance the performance of the fuel delivery system of the present invention.

Figure 6 shows a preferred form of the mixing device 7. The solid shape is a most preferred form, whereas the shapes denoted by dotted lines have been found to work less efficiently. The solid shape has a slight taper on its internal surface and a flaring on the outer surface.

Figure 4 shows graphically horsepower (HP) and torque (rD rD) output of a 3.8 litre V6 GMH engine using the fuel delivery system of the present invention.

Figure 5 srows an approximate comparison of torque output of a 3.8 litre V6 GMH engine running on various fuels. At 3000 rp.m, a prior art LPG conversion unit branded IMPCO 225 produces 68 horsepower The engine running on petrol fuel injection produces 91 HP, whereas using the fuel delivery system of the present invention, the engine running on LPG fuel produces 105 15 HP, ****Modifications relating to the invention disclosed above will now be described.

With regard to Figure 8, the body 2 of the carburettor Is shown with relatively straight inner walls. That is, the thickening of the inner wall near the inlet of the carburettor as depicted in Figs 1, 2 3 is not essential to the Invention, Furthermore, the valve 21 as disclosed above may be deleted, however the port 20 still remains.

Idle adjustment screw 14 has been moved to channel 10A. It has been 25 found that the function f the idle adjustment is more effective if placed in the air flow path rather than the fuel flow path. Furthermore, it has been found that the adjustment screw, if placed in the fuel path, is not an accurate method of regulation of idle adjustment. The gas flow in path 12 has been found to be too small to affect accurate regulation.

It has also been found that, in general, with regard to the present invention, the air:fuel ratio should be of the order of 10:1 to 20:1 dependent on r the engine, and preferably 13:1 for most I.C. engines on the market today, It has 11-25-38 3:31 PM ;WATER:ARK e181960:0; #1/20 11 been found that there are a number of ways in which the air:fuel ratio can be effected. The air:fuel ratio is a function of factors such as the cross sectional area available for the flow of air through the mixing device, the cross sectional area available for the flow of air around the mixing device, and the cross sectional area occupied by the jet.

The present invention may be utilised in conjunction with many gaseous fuels, including in particular, methane, LPG and CNG.

With regard to Figure 9, it has been found not to be necessary to provide three legs holding the mixing device 3 in place, Furthermore, the jet or spud may extend through the one leg as shown in dotted lines. The end of the jet may terminate anywhere within the bore of the mixing device (shown in dotted lines).

Preferably the end of the spud is terminated at an angle extending from its upper most tip down to the inner wall of the bore of the device. The area, In plan view, of the angled end of the spud has relevance in determining air:fuel ratio. The 15 greater the angle of the spud end, the more area occupied by the spud in bore of the mixing device, therefore more fuel may be introduced into the air flowing through the mixing device.

Figures !0A and 10B show an air pass valve which may be used In conjunction with the present invention although is equally applicable to petrol or other fuelled engines. Figure 10A shows the valve In a closed position and Figure 10B shows the valve in an open (pass) position.

SThe valve may be placed in connection with the manifold (to engine In .0 Figure gas input (11) or high/low pressure fuel converter.

The purpose of the valve is to reduce fuel consumption in conditions of 25 deceleration of the engine. In Figure 2, when the butterfly 4 is closed, high manifold vacuum causes fuel to flow via bypass circuit 10 and 12. The valve as osed, in such conditions, will open to an air pass position and allow air to .ass through the fuel delivery system and thus provide air rather than fuel into the manifold of the engine in response to a condition of high manifold va:uum.

The quantity and timing of air must be regulated In order to avoid the engine stalling and this can be set in accordance with the fuel/air requirements of each engina type, v:n 'NU, IQY I, OU2' 12 Under conditions of high vacuumn, piston 100 is drawn down. The amount of piston movement Is dependent on the amount of vacuum and piston size. The example shows a piston of preferably 20 mm diameter and ports 10 1, 102 of 4 mnm diameter. Springs 103 and 104 also serve to regulate the amount of piston movement. Spring 103 also serves to return or bias piston 100 towards a 'home' (closed) position under reduced or nil manifold vacuum.

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Claims (7)

1. A device for use with a carburettor of an internal combustion engine to mix gaseous fuel with air passing through the carburettor, said devIce Including: a bore passing through said device through which a first stream of said air passes; an induction tube extending into said bore for 'introducing gaseous fuel directly Into said first air stream; an outer surface over Which a second stream of said air passes, said outer surface adapted to act in conjunction with an Inner wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of said induction tube to mix said gaseous fuel with said air,

2. The device as claimed in Claim 1 wherein said outer surface is flared and goo acts in conjunction With the Inner wall of the carburettor to accelerate the second &too stream of air and thereby create a lbw pressure zone downstream of said induction tube to mix said gaseous fuel with said air. The device as claimed in Claim 2 wherein the bore passing through said device is tapered.

4. The device as clalmed In Claim I wherein said gaseous fuel is methane, liquid petroleum gas (LPG) or compressed natural gas (ONG). 8,138.1960 i #(18/20 14 A fuel delivery system for use with a carburettor of an internal combustion engine to mix gaseous fuel with air passing through the carburettor, the system including a device with a bore passing through said device through which a first stream of said air passes; an induction tube extending into said bore for introducing gaseous fuel directly into said first air stream; an outer surface over which a second stream of said air passes, said outer surface adapted to act in conjunction with an inner wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of said induction tube to mix said gaseous fuel with said air; and a fuel valve to regulate the supply of the gaseous fuel, said fuel valve being operatively coupled to a means for controlling the flow of gaseous fuel/air mixture to the engine.

6. The fuel delivery system as claimed in Claim 5 wherein said outer surface of the device is flared and acts in conjunction with the inner wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of said induction tube to mix said gaseous fuel with said air. i 7, The fuel delivery system as claimed in Claim 6 wherein the bore passing through said device is tapered.

8. The fuel delivery system as claimed in Claim 5 wherein said fuel valve includes a valve member and a mating seat, said valve member including a projection contoured to permit a predetermined flow of fuel through said fuel valve for a given position of said fuel valve. 9, The fuel delivery system as claimed in Claim 8 wherein said projection extends into the flow path of the fuel. th is 'The fuel delivery system as claimed In Claim 5 wherein said fuel supply valve is operatively coupled to a butterfly valve of the carburettor which controls the flow of gaseous fuel/air mixture to the engine for combustion.

11. The fuel delivery system as claimed in Claim 10 wherein said fuel supply valve undergoes translationall movement in response to movement of the butterfly valve.

12. The fuel delivery system as claimed in Claim 11 Wherein said fuel supply valve is operatively coupled to tt ,b butterfly valve of the carburettor by means of a gear coupled to the butterfly valve which engages a gear rack coupled to the fuel supply valve In order to control movement of the fuel supply valve in response to movernent of the butterfly valve. ,:se 0#. 04S 16 ASTRJAQT The present Invention provides a device for use with a carburettor of an Internal combustion engine to mix gaseous fuel with air passing through the carburettor, the device including: a bore passing through tho device through which a first stream of the air passes; an Induction tube extending into the bore for introducing gaseous fuel directly into the first air stream; an outer surfwce over which a second stream of the air passea, the outer surface adapted to act in co~njunction with an inn wall of the carburettor to accelerate the second stream of air and thereby create a low pressure zone downstream of the Induction tube to mix said gaseous fuel with said air, *fee 0* S 9* 00' O. 00 0*8