GB2182096A - I.C. engine fuel injection control - Google Patents

Abstract

In order to produce an ignitable mixture in the vicinity of a spark plug in an i.c. engine combustion chamber the fuel-air ratio of fuel and air cylically delivered through a valve 43 into the combustion chamber or air intake is controlled during the delivery at least under low load engine operating conditions. The valve 43 controls delivery from a chamber 32 connected to a supply of air under pressure and receiving fuel metered by a device 30. Control of fuel delivery into the chamber 32 when the valve 43 is open provides for variation of the fuel-air ratio of the mixture being discharged by the valve. <IMAGE>

Description

SPECIFICATION Control of fuelling rate for internal combustion engines This invention is directed to the delivery of fuel to the combustion chamberofan internal combustion engine.

Fuel injection systems have been proposed wherein fuel is injected to an engine combustion chamber or air induction system by a compressed gas. An example of such systems is described in ourAustralian patent application No. 32132/84. In that example fuel is supplied to what may be termed a scheduling chamberwhich is pressurized buy a gas, preferably air, and thescheduling chamber is selectively communicated with a combustion chamber or air induction system by the opening of an injection nozzle. The fuel is projected as a fuel-gas mixture spray th rough the nozzle into the combustion chamber, orthe airflow to the combustion chamber.

In the previously described systems the rate of flow offuel, also termed thefuelflux, through the injection nozzle is controlled by the flow area ofthe injection nozzle, the pressure drop acrossthe nozzle, andthe ratio offuel to air in the mixture being propelled from the nozzle.

In the case of the injection system described in the above patent application, the rate of flow of fuel through the injection nozzle rises rapidly as the injection nozzle opens, remains generally steady until the metered amount of fuel is largely expelled from the scheduling chamber, and then drops as the scheduling chamber is stripped of fuel.

In the efforts to control the harmful components in the exhaust gases from engines, it has been found that control ofthefuel distribution in the combustion chamber can be beneficial. One method proposed to achieve the control is to provide flow directors in association with the inlet port ofthe cylinderto thereby inductthe desired gas flow in the cylinder, into which the fuel is injected. The provision of flow directors in the inlet port naturally constitutes an obstruction to the airflow and as a consequence is detrimental to volumetric efficiency. In addition flow directors give rise to difficulties and additional costs in manufacture.

There have been previous proposals to operate internal combustion engines with multiple fuel deliveries per cycle, with the view to obtaining a degree offuel stratification in the axial direction ofthe combustion chamber. One proposal is found in U.S.

Patent No. 3154059 by Witzky et al which discloses a four stroke cycle engine wherein respective injectors are provided to deliver metered quantities of fuel to the air induction system and directly into the combus tion chamber. In addition it is proposed to dividethe direct injection to the combustion chamber into two or more pulses. Howeverthis proposal requires a swirling motion to also be induced in the gas charge in the combustion chamber as a major contribution to the fuel stratification. Also the liquid fuel is delivered as a single fluid to the combustion chamber by the direct injector, the fuel not being entrained in a gas, and relies on a resonant condition inthe liquid fuel line to establish the multiple fuel pulses.

Another proposal isfound in U.S. Patent No.

4446830 Simko,wherein two distinct injections offuel are effected each engine cycle, one injection occuring nearthe start ofthe induction stroke and the second shortly before the end of the compression stroke. This proposal is specifically directed to engines operating with high latent heat fuels such as methanol, the majority of which is injected at the start ofthe induction stroke to provide sufficient heat and time to vapourisethefuel before ignition. The second injection isto provide the fuel rich mixture atthespark plug at the time of ignition.

Other prior U.S. patents relating to multiple fuel injection per engine cycle known but considered not to be directly relevantto this invention are: LLoyd 4187825 Eckert 4022165 Araya et al 3722490 Eyzat 3216407 and 3439655 It is the object of the present invention to provide a method of delivering fuel to an engine to control the fuel distribution in the engine combustion chamber to improve combustion efficiency.

With this object in view there is provided a method of delivering fuel to an engine comprising introducing a meteredquantityoffuel into a body of gas to provide a fuel-gas mixture, delivering said fuel-gas mixture to the engine in timed relation to the engine cycle, and controlling the introduction of the fuel to the gas to obtain a predetermined fuel distribution in the combustion chamber ofthe engine at ignition.

Preferablythe predetermined fuel distribution includes a fuel rich mixture in that portion ofthe combustion chamberwhere ignition ofthe charge is initiated. Conveniently the fuel distribution is such that the combustion charge is fuel rich at the cylinder head end ofthe combustion chamber and decreases in fuel density as the distance form the cylinder head increases. This distribution may be considered as axial fuel stratification in the combustion chamber.

The control of the rate of introduction of the fuel into the gas which conveys the fuel to the engine, both prior to and/or during admission ofthe fuel-gas mixturetothe engine, maybe usedto obtainthe required fuel distribution in the engine combustion chamber. In one embodiment the fuel is introduced into a scheduling chamber charged with air, the scheduling chamber being selectively communicable with the induction manifold or combustion chamber oftheengine.Partofthetotal meteredquantityoffuel may be introduced to the scheduling chamber priorto establishing communication of the scheduling cham berwiththeinduction manifold or combustion chamber, and the remainder of the fuel introduced to the scheduling chamber over a selected portion ofthe period during which communication exists between the scheduling chamber and the combustion chamber or induction manifold.

The quantity of fuel introduced during the respective periods maybe adjusted to achievethe required fuel distribution in the combustion chamber at the time of ignition. In particular, the introduction offuel to the scheduling chamber after commencement of delivery therefrom is a convenient control sequence to provide a fuel rish mixture adjacentthe cylinder head where ignition occurs.

An alternative means of controlling the fuel distribu tion in the combustion chamber is to modulate the pressure differential across the portthrough which the fuel-air mixture is delivered to the combustion chamber or manifold, and so control the velocity, and hence the degree of penetration, ofthefuel-gas mixture.

Itwill be appreciated that both of the above discussed specific modes of controlling fuel distribution in the combustion chamber may be combined to achieve the required fuel distribution.

There is also provided by the present invention a method of injecting fuel, to the combustion chamber or air induction system of an internal combustion engine comprising introducing a metered quantity of fuel into a scheduling chamber, selectively communicating the scheduling chamberwith the combustion chamber or air induction system in timed relation to the engine cycle, supplying airto the scheduling chamberata pressureabovethe pressure in the combustion chamber or air inducting system during said communication, to inject a fuel-air mixture, and controlling the rate and/ortime of introduction ofthe fuel to the scheduling chamber in relation to the period of communication of the scheduting chamber with the combustion chamber or induction system to achieve a predetermined fuel distribution in the combustion chamber at ignition.

Conveniently the control is arranged so the fuelling rate duringthe iater part ofthe injection into the combustion chamber or air induction system is increased. In thisway a fuel rich combustion mixture can be located adjacentthe pointofignitionto provide ease of ignition. This increased fuelling rate may be in contrast to a generally steady fuelling rate during the whole ofthe earlier part ofthe injection ofthefuel.

Alternatively there may be a decline in the fuelling rate during the earlier part ofthe fuel injection followed by an increasefrom said declined rate at the later part of the fuel injection. Preferably the fuel/gas ratio of fuel-gas mixture during the latter part of delivery to the engine is not less than the ratio during the remainder ofthe delivery.

It is to be understood that the total quantity of fuel delivered to the engine per cycle is determined in accordance with the engine load and speed and the presentinvention does not propose a departurefrom this determined quantity. The present invention controls the rate of introduction ofthe determined quantities offuel to the engine combustion chamber to obtain the efficient distribution ofthe fuel within the combustion chamber. Arising from the effective fuel distribution greaterfuel economy may result; howeverthe major advantage is the reduction of undesirable contaminants in the engine exhaust gas.

In this regard it is to be understood thatthe optimum fuel distribution in the combustion chamberwill vary with engine operating conditions. In particular it is more important to have a non-uniform fuel distribution at low loads where the distribution should be restricted to provide a readily ignitable mixture, preferably richerthan a stoichometric mixture, atthe point of ignition. At high engine loads it is important to more evenly distribute the fuel throughout the gas charge in the combustion chamber, to exposethefuel to sufficient oxidantto combust all ofthe fuel.

Accordingly the controlling ofthefuel distribution to achieve a non-uniform fuel distribution may not be effected over the complete load range ofthe engine, but is preferably effected over at least the low load range ofthe engines operation.

Low and high loads are relative termsthatwill be generally understood by the skilled person. However, as a general guide, in the context of modern automotive engines high loads can be considered asthose greaterthan 75% ofthe maximum load attainable at the particular engine speed, and low loads are those less than 25% ofthe maximum load at that particular speed.

The invention will be more readily understood from the following description of one practical arrangementofthefuel injection method and apparatusfor carrying out the method.

In the drawings: Figure 1 shows a portion of an engine utilising the invention.

Figure 2 shows a fuel injector utilised in the engine shown in Figure 1.

Figure 3 shows graphically injector valve positions and fluid flow rates against engine crank angle when the injector is operated in a prior art mode.

Figure 4 shows injector valve positions and fluid flow rates against crank angle when the injector is operated in a mode according to the present invention.

Figures 5 to 10 show comparative performance characteristics of present invention againstthe prior art.

Referring now to Figure 1 the engine 9 is a single cylindertwo stroke cycle engine, of generally conventional construction, having a cylinder 10, crankcase 11 and piston 12 that reciprocates in the cylinder 10. The piston 12 is coupled by the connected rod 13 to the crankshaft 14. the crankcase is provided with air induction ports 15, incorporating conventional reed valves 19, and three transfer passages 16 (only one shown) communicate the crankcase with respective transfer ports, two of which are shown at 17 and 18, the third being the equivalentto 17 on the opposite side of port 18.

The transfer ports are each formed in the wall ofthe cylinder 10 with their respective upper edge located in substantially the same diametral plane of the cylinder.

An exhaust port 20 is formed in the wall ofthe cylinder generally opposite the central transfer ports. The upper edge of the exhaust port is slightly above the diametral plane ofthe transfer ports' upperedges, and will accordingly close later in the engine cycle.

The detachable cylinder head 21 has a combustion cavity 22 into which the spark plug 23 and fuel injector nozzle 24 project. The cavity 22 is located substantially symmetrically with respect to the axial plane ofthe cylinder extending through the centre ofthe transfer port 18 and exhaust port 20. The cavity 22 extends across the cylinder from the cylinderwall immediately above the transfer port 18 to a distance past the cylinder centre line.

The injector nozzle 24 is located at the deepest part of the cavity 22, while the spark plug 23 projects into the cavity 22 at the face of the cavity remote from the transferport18.Accordinglytheairchargeentering the cylinderwill pass along the cavity past the injector nozzle 24 towa rd the spark plug and so carries the fuel from the nozzleto the spark plug.

Further details ofthe form ofthe cavity 22 and ofthe combustion process derived therefor are disclosed in British Patent Application No 8612601 and the corres- ponding United States Patent Application No 866427 lodged on the 23rd May 1986, the disclosures of each being hereby incorporated herein by this reference.

The injector nozzle24is an integral partofthefuel metering and injection system wherein the fuel is entrained in air and delivered to the combustion chamber of the engine by the pressure of the air supply. Oneparticularform of such a fuel metering and injection unit is illustrated in Figure 2 ofthe drawings.

The fuel metering and injection unit incorporates a suitable commercially available metering device 30, such as an automotivetypethrottle body injector, coupled to an injector body 31 having a holding or scheduling chamber 32 therein. Fuel is drawn from the fuel reservoir35 by the fuel pump 36 and delivered via the fuel pressure regulator37through fuel inlet port 33 to the metering device 30. The metering device operating in a known manner meters an amount of fuel into the chamber32 in accordance with the engine fuel demand. Excess fuel supplied to the metering device is returned to the fuel reservoir 35 via the fuel return port 34. The particularconstruction ofthe fuel metering device 30 is not critical to the present invention and any suitable device may be used.

In operation,thescheduling chamber 32 is maintained at a selected pressure supplied from the air source 38 via air pressure regulator 39 to air inlet port 45 in the body31. Delivery ofthe fuel into the chamber 32 is effected against the pressure of the airtherein, and accordingly the pressure differential between the fuel and air is relevantto the rate of delivery of the fuel into the chamber. Injectorvalve 43 is actuated to permitthe pressure oftheair inthe chamber32 to discharge the fuel through injector nozzle 42 into a combustion chamberofthe engine. Injector valve 43 is ofthe poppet valve construction opening inwardly to the combustion chamber, that is, outwardly from the sequencing chamber 32.

The injector valve 43 is coupled, via a valve stem 44, which passes through the chamber32, to the armature 41 of solenoid 47 located within the injector body 31.

The valve 43 is biased to the closed position by the disc spring 40, and is opened byenergisingthesolenoid 47.

Further details ofthe operation of this fuel injection system are disclosed in Australian Patent Application No.32132/84 and the corresponding United States Patent Application No 740067 filed 2nd April 1985, the disclosures ofwhich are incorporated herein by reference.

The energising of the solenoid 47 is timed in relation to the engine cycle by a suitable electronic processor 50.The processor receives an input signal from the speed sensor 51 which signal is indicative ofthe engine speed and also identifies a reference point in the engine cycle in respect of which operations may be timed in relation to the engine cycle. The processor 50 also receives a signal from the load sensor 52 indicative ofthe airflow rate in the engine air induction system which is directly related to engine load. The processor is programmed to determine from the airflow rate signal the load demand on the engine, and hence the requiredquantityoffuelto be delivered by the metering device 30 into the chamber 32.

The processor 50 is further programmed to deter mine from the speed and load conditions of the engine the required timing oftheinjection ofthefuel into the combustion chamber. Conveniently the processor incorporates multi-point maps designating thereto quired injection timing for a range of engine loads and speeds, these having been determined from tests carried outto obtain required engine power and exhaust emission levels.

The processor 50 provides appropriate signals two the actuator 55 of the fuel metering device 30, and to theinjectoractuator53thatcontrolstheenergising of the solenoid 47, in accordance with the processor's determinations, to effect metering ofthe required amountoffuel intothe chamber32 and to energisethe solenoid 47 at the required time in the engine cycle for injection of the fuel into the combustion chamber. The general construction ofthe load and speed sensors suitable for use as above indicated are well known in the industry, as are processors for performing the functions required by the processor 50.

Itwill be understood that the timing of ignition ofthe fuel will preferably be varied as the timing of injection of the fuel is varied, and this may also be controlled by the processor 50. The principle of variation of ignition timing with injection timing is well known and practised in the field offuel injected engines and is not further discussed herein in detail.

As previously referred to the pressure ofthe air supplytothe chamber32 is controlled bythe air pressure regulator 39, and the pressure of the fuel supply to the metering unit 30 is controlled by the fuel pressure regulator 37. As the pressure differential between those fuel and air supplies is related to the metering function ofthe metering unit 30, it is desirable that this differential be maintained constant.

Accordingly it is proposed that the fuel supply pressure be regulated relative to atmospheric pressure, and the air supply pressure be regulated with respecttothefuel pressuretothereby maintain the required pressure differential between the fuel and air supplies independently of the fuel pressure.

An integrated fuel and air pressure regulatorthat will regulate the fuel and air pressures in the above proposed manner is disclosed in ourAustralian Patent Application No PH1560 and the corresponding International Application No PCT/AU86/00203 lodged on the 18th July1986. The disclosure in each ofthese applications is hereby incorporated in this specification by reference. The regulator disclosed in the applications just referred to incorporate provision for varying the fuel regulated pressure in response to a selected engine operating condition, and this feature may be used in the practice of the present invention. It isto be noted that as the air pressure is regulated with respect to the fuel pressure, any variation in the regulated fuel pressure will not affect the fuel-air pressure differential and hence the fuel metering.

An increase in the air pressure, resulting from an increase in fuel pressure, will increase the mass of air delivered with the fuel to the combustion chamber, in a fixed time interval. Thus at high engine loads the air available to deliverthe fuel may be increased by increasing the air pressure while maintaining the same injection period, and without necessitating adjustmentto the fuel metering function. Also an increase in the air pressure will increase the degree of penetration ofthefuel into the engine combustion chamberwhich is desirable at high engine loads.

In the previously discussed fuel metering and injection equipment, the total metered quantity of fuel, as determined by the processor 50 to be required per engine cycle to meetthe engine load demand, is delivered into the chamber32 priortothe opening of the valve 43. Accordingly the metered quantity of fuel is entrained in the generally stationary mass of air within the chamber 32. Upon opening ofthe valve 43 the air in the chamber 32 and the fuel entrained therein is displaced through the valve 43 into the cavity 22 in the engine cylinder head. As the quantity of air delivered through the valve 43 while open is greater than that quantity of air initially within the chamber 32, the air delivered immediately after opening of the valve will be richer in fuel than that later delivered air.

This mode of operation is graphically illustrated in Figure 3 ofthe drawings, being the prior art mode of operation. Figure 3 plots against crank angle measured after piston top dead centre position (ATDC), fuel delivery to the chamber 32, plot 61, valve 43 position, plot62,and rateoffuel deliverytothe combustion chamber 32, plot 63. These plots are for the engine operating at a fixed speed in the medium area ofthe engine speed range.

As seen from plot 61 the metering device 20 commences to introduce fuel into the scheduling chamber 22 at about 1S"AfterTop Dead Centre (ATDC) and finishes at about 70" ATDC, the rate of delivery being substantially uniform overthis period. Plot 62 showsthatthe injection valve33commences opening at about 2500ATDC, is fully opened by about 260 ATDC, commences closing at about 305" ATDC and completely closes at about 320 ATDC.The rate of fusel flow through injection valve 33 into the combustion chamber as shown by plot 63, rises rapidly as the injection valve opens, remains generally steady for about 200 of crank rotation, and then progressively reduces as the quantity offuel in the scheduling chamber 32 decreases until substantially only air remains two pass into the combustion chamber. It will be appreciated that the above described time relationship between fuel metering and fuel injection will result in a relatively large proportion ofthe metered quantity offuel being delivered early in the injection period which would tend to lead to a relatively fuel lean mixture being delivered atthe end of the injection period.

Itwillfurtherbeappreciatedthatthefuel injected earlywill penetrate and/or be mixed further into the combustion chamberthan the later injected fuel.

Accordingly use of the priorartinjection mode (as represented by Figure 3) when a low fuelling rate is required (at low engine loads) results in a relatively lean mixture in the immediate vicinity of the spark plug and hence poorignitability. This condition contributes to increased unburntfuel in the exhaust gases which in turn produces increased fuel consump tion and hydrocarbon (HC) emissions.

One mode of operation of the fuel injector in accordance with the present invention is illustrated by Figure4, in a similarfashion to Figure3, Plot 71 shows the flow of fuel from the metering device30 into the scheduling chamber 32. Plot 72 shows the position of injection valve 43, and plot 73 shows the rate offuel flowthrough the injection valve 43. The metering device 30 introduces fuel into the scheduling chamber from l50ATDCto400ATDCandagaininasecond metering period from 2700 to 3000ATDC. The injection valve 43 opens and closes atthesametiming as in plot 61 in Figure 3.The rate offuel flowthrough injection valve 43 rises as the injection valve initially opens, and commences to decrease as the fuel previously me teredintothescheduling chamber32 during the period from 1 50to 400 ATDC is used up. However at 270 ATDC the second metering period commences as further fuel entersthe scheduling chamber 32 increasing the fuel delivery rate to the engine during the secondary fuelling period. Thereafter the fuel delivery rate again decreases as the quantity of fuel in the scheduling chamber 22 is exhausted.

The redistribution in the fuel flow rates, provided by the present invention as illustrated in Figure 4, thus provides an avenueforthe production of a richer fuel-air mixture around the region of the spark plug, than would otherwise have been available. This is achieved without an increase inthetotal metered quantity offuel per cycle, and without effecting two or more separate injections of fuel within the one engine cycle. This richer mixture is located high in the combustion chamber, in comparison with the region adjacent the piston, and so provides a readily combustible mixture at the spark plug, and also a stratification of the fuel in the direction of the axis of the cylindrical combustion chamber.The stratified form ofthefuel distribution provides improved combustion conditions, particularly under low loads, with improved fuel consumption and reduced exhaust emissions, particularly HC.

The control ofthetiming ofthe introduction ofthe fuel intothechamber32 can readily be achieved by suitable programming ofthe electronic processor controllingthefuel metering unit30.The particular metering unit previously referred to, like a large number of fuel metering devices in current use infuel injection systems, has a solenoid operated meteetirg valve. When energised, the solenoid opensth.evaive to permit fuel to flow into the chamber 32 and so, by controlling the period of energisation ofthesolenoid, and the time relation thereof to the operating of the injection valve 43, it is possible to deliverthefuel to the chamber32 in the mode as illustrated in Figure4 or any similar divided delivery It will be appreciated thatthe processor 50 responds to the signal, indicating the engine load condition, to determine the required total fuel quantity to be supplied to the chamber 32 each injection cycle.The processor in order to carry outthe present invention, then divides that determined fuel quantity into the two components represented by "a" and "b" in Figure 4 and energisesthe solenoid of the metering device 30 for the respective periods oftime, and at the required times in the engine cycle. In this manner the predetermined fuel distribution in the cylinder is obtained.

The processor may be arranged to divide the determined fuel quantity into two or more components in a fixed ratio, independent of engine load or speed, or maybe arranged to varythe ratio in response to engine load and/orspeed. In this regard the processor may be arranged to only divide the fuel quantity into components when the engine is operating within a selected load and/or speed range, such as the low load range. Also similarly the processor may bearrangedtovarythetiming ofthedeliveryofthe respective components of the fuel quantity, both in regard to the time intervals between the delivery of the respective components and theirtiming with relation to the engine cycle-and/or injection cycle.

In the previous discussion with respect of Figures 1 to 4, the present invention has been in the form of controlling the direct injection ofthe fuel into the combustion chamber of the engine. However, as indicated in the early part of this specification, the invention is also applicable to the injection of fuel into the air induction system of an engine. This is particularly applicable to engines operating on the four stroke cycle, and it has been noted that in afour stroke cycle engine similar improvements in engine performance are obtained by the application ofthe present invention to deliverthefuel into the air induction system close to the inlet valves or directly into the combustion chamber.

In applying the invention to injection offuel into the air induction system the fuel metering and scheduling equipment as described with reference to Figure 2 may be used to meterthe required quantity of fuel in accordance with the engine demand, and schedule the timing and the rate ofthe delivery ofthe fuel into the induction manifold.

It will be appreciated that by appropriate programming ofthe processorthe fuel delivery timing and rate tothe induction manifold may be arranged to obtain the required.fuel distribution in the engine combustion chamber at the time of ignition. At least under low load condihons this distribution is preferably a richer fuel charge nearthe ignition point (axially nearthe cylinder headY relative to the rest ofthe fuel charge (axiallyspacedfrornthecylinderhead).Thusagain an axially stratifiedfuel charge is provided in the cylinder.

Comparativetests have been carried out using one cylinder ofafourstrokefourcylinder engine having an engine capacity of 1.6 litres, and known as the "Kent" engine, manufactured by Ford in Great Britain.

In one test a comparison was made between the direct injection of fuel into the cylinder using an injectorofthetype shown in Figure 2 and a singlefluid injector known as the L-JETRONIC (Trade Mark) type injector as manufactured by Bosch GMBH.

The air-fuel ratio maps obtained from these tests are shown in Figures 5 and 6. Figure 5 being the air-fuel ratio map obtained by operating the injector in Figure 2 in accordance with the present invention, and Figure 6thatobtained using the Bosch injectorsystem. ltcan be clearly seen thatthe present invention allowed the use of substantially higher air-fuel ratiosthan the Bosch injector system as most loads and speeds, and particularly at low and medium speeds.

Figure 7 shows the improved combustion stability achieved with the present invention over the Bosch injector system by the respective plots of percent coefficient of variation of indicated mean effective pressure in the cylinder against air-fuel ratio. Plot 81 represents the stability ofthe engine using the fuel injectorofthetype in Figure 2, and operated in accordance with the present invention as compared with plot 82 obtained with the Bosch injection system.

Plot 83 represents the stability ofthe engine using the fuel injector of Figure 2 but without controlling the fuel deliveries to the scheduling chamber as proposed by the present invention.

Figure 8 shows the fuel octane rating requirements of the engine with each of the injection systems. The direct fuel injection system of Figure 2 permitted the engineto run at loweroctane ratings as represented by plot 91 than the Bosch injector system as represented by plot 92. The ability to influence the octane sensitivity of an engine as indicated in Figure 8 is particularly significant in the transition of the engine from low to high loads.

In the tests above referred to in regard to Figures 5 to 8, injection of the fuel by the injector as described with reference to Figure 2 was effected with a fixed injection period of 15 ms. howeverthetiming ofthe injection in the engine cycle was varied to obtain optimum results. The actual injection timing variation with speed is shown in Figures 9 and 10. In this regard itwasfound that variation ofthetiming ofthe injection in relation to the engine cycle has only marginal effect on the performance ofthe Bosch injection system, and in the above tests injection timing was not varied but setatthe generally preferred timing forthe engine load and speed range ofthe test.

The lean combustion condition obtainable with the Figure 2 fuel injection system, in addition to providing low fuel consumption, provides a reduction in oxides of nitrogen in the exhaust gases. The tests demons trated that with the Figure 2 fuel injection system it was possible to calibratethe processor to provide improved fuel economy and lower oxides of nitrogen oxide emissions without a sacrifice in hydrocarbon emission.

Forfour stroke engines there are substantial similarities in the fuel flux control effects, in relation to axial stratification of the fuel charge, using fuel injection into the air induction system as is achieved with direct injection into the combustion chamber. The same basic metering and injection equipment as previously discussed for use in direct injection may be used to inject into a manifold.The injector nozzle is positioned in the manifold close to the inlet port communicating the manifold with the combustion chamber. In a multi-cylinder engine a separate injector nozzle is provided for each cylinder. The timing of injection is selected so the fuel is delivered to the manifold while the inlet port is open so the fuel is carried immediately into the combustion chamber. It has been found that thefuel distribution established during deliveryofthe fuel into the air in the induction manifold issubstan- tially maintained to establish a stratified fuel distribu tion in the combustion chamber, provided there is not extreme turbulence in the combustion chamber.

Accordingly by increasing the fuelling rate in the air entering the combustion chamber shortly before the inlet port is closed, will intensifythefuel stratification gradient in the combustion chamber and thus lean combustion can be extended to higher air-fuel ratios, without loss of combustion stability.

The invention is applicable to internal combustion engines for all uses but is particularly useful in contributing to fuel economy and control of exhaust emissions in engines for vehicles, including automobiles, motorcycles and boats including outboard marine engines.

Claims (19)

1. A method of delivering fuel to an engine having a combustion chamber in which fuel is ignited and burnt, comprising introducing a metered quantity of fuel into a body of gas to provide a fuel-gas mixture, admitting said fuel-gas mixture to the engine in timed relation to the engine cycle, and controlling the introduction offuel to the gas as the fuei-gas mixture is delivered to the engine to obtain a predetermined fuel distribution in the combustion chamber at ignition over at least part of the load range of the engine.

2. A method of delivering fuel to an engine as claimed in claim 1 wherein said control is arranged so that over said part ofthe load range, the fuel/gas ratio ofthe fuel-gas mixture at the latter portion of the deliverythereofto the combustion chamber is not less than during the remainder ofthe deliveryforthe particular engine cycle.

3. A method of delivering fuel to an engine as claimed in claim 1 wherein the metered quantity of fuel is delivered into a scheduling chambercontaining gas to form the fuel-gas mixture, a first part said metered quantityoffuel being delivered into the scheduling chamber priorto commencing delivery of the fuel-gas mixture to the engine, and the balance of the metered quantity offuel is delivered into the scheduling chamber during delivery ofthe fuel-gas mixture to the engine.

4. A method of delivering fuel to an engine as claimed in claim 3 wherein the delivery ofthefuel-gas mixture to the engine is effected by selectively communicating the scheduling chamberwiththe engine and maintaining a supply of gas to the chamber during said communication at a pressure sufficient to displace the fuel-gas mixture from the scheduling chambertothe engine.

5. A method as claimed in any one of claims 1 to 4 wherein the fuel-gas mixture is delivered directly into the engine combustion chamber.

6. A method of delivering fuel to a spark ignited internal combustion engine having a combustion chambercomprising,foreachfuelling cycleofthe combustion chamber, introducing a metered quantity offuel into a body of gas to provide a fuel-gas mixture, delivering said fuel-gas mixturefor admission to the combustion chamber as a single delivery, and at least over part ofthe operating load range of the engine controlling the fuel-gas ratio of said mixture during the period ofdeliveryto obtain a predetermined fuel distribution in the combustion chamber at ignition.

7. A method as claimed in claim 6 wherein for each fuelling cycle ofthe engine part ofthe metered quantity offuel is introduced to the gas priortothe commencement of delivery of the fuel-gas mixture and the balance ofthe metered quantity offuel is introduced to the gas during said delivery ofthe fuel-gas mixture.

8. A method as claimed in claim 6 or7 wherein the control is arranged so that at least over part ofthe load range,the fuel/gas ratio of the fuel-gas mixture at the latter portion of delivery thereof to the combustion chamber is not less than during the remainder ofthe delivery for the particular engine cycle.

9. A method as claimed in claim 6,7 or 8 wherein the control offuel-gas ratio is such that at ignition the fuel-gas ratio in the combustion chamber atthe ignition location is about stoichometric.

10. A method as claimed in any one of claims 6 to 9 wherein the control ofthefuel-airratio ofthe mixture is effected over the low load portion ofthe engine load range.

11. A method of injecting fuel to the combustion chamber of induction system ofan internal combus- tion engine comprising introducing a metered quantity offuel into a scheduling chamber, selectively communicating the scheduling chamberwith the combustion chamber or induction system in timed relation to the engine cycle, supplying gas to the scheduling chamber at a pressure above the pressure in the combustion chamber or inducting system during said communication,to delivery a fuel-gas mixture thereto, and controlling the rate and/or time of introduction ofthe fuel to the scheduling chamber in relation to the period of communication ofthe scheduling chamber with the combustion chamber or induction system to achieve a predetermined fuel distribution in the combustion chamber at ignition.

12. A method as claimed in claim 11 wherein for each fuelling cycle ofthe engine part ofthe metered quantity of fuel is introduced to the gas prior to the commencement of delivery ofthefuel-gas mixture and the balance ofthe metered quantity of fuel is introduced to the gas during said deliveryofthe fuel-gas mixture.

13. A method as claimed in claim 11 wherein the metered quantity offuel is delivered into said scheduling chamber containing gas to form the fuel-gas mixture, a first part of said meteredquantityoffuel being delivered into the scheduling chamberpriorto commencing delivery ofthe fuel-gas mixtureto the engine, and the balance ofthe metered quantity offuel is delivered into the scheduling chamber during delivery of thefuel-gas mixtureto the engine.

14. An internal combustion engine including means to deliver fuel thereto, said means being adapted to operate in accordance with the method as claimed in any one of claims 1 to 13.

15. In an automotive vehicle an internal combustion engine including means to delivery fuel thereto, said means being adapted to operate in accordance with the method as claimed in any one of claims 1 to 13.

16. An outboard marine engine including means to deliver fuel thereto said means being adapted to operate in accordance with the method as claimed in any one of claims 1 to 13.

17. A method of delivering fuel to a spark ignited internal combustion engine comprising introducing airto a combustion chamber to support combustion of fuel, introducing a metered quantity of fuel into a body of gas to provide a fuel-gas mixture independent of the induced air, admitting said fuel-gas mixture to the combustion chamber in timed relation to the engine cycle, and controlling the introduction of the fuel to the gas as the fuel-gas mixture is delivered to the engine to obtain a predetermined fuel distribution in the combustion chamber at ignition over at least part of the load range of the engine.

18. A method of delivering fuel to an engine as claimed in claim 17 wherein the fuel-gas mixture is admitted to the air as the air is being introduced to the combustion chamber.

19. A method of delivering fuel to an engine as claimed in claim 17 wherein the fuel-gas mixture is admitted directly into a combustion chamber ofthe engine.