EP2279339A1

EP2279339A1 - A method of and system for improving the fuel efficiency of electronically controlled fuel injected internal combustion engines

Info

Publication number: EP2279339A1
Application number: EP09721783A
Authority: EP
Inventors: Edward Christopher Zyla; Mark Vincent Howarth; Gary Michael Mcmahon
Original assignee: Hybrid Combustion Ltd
Current assignee: Hybrid Combustion Ltd
Priority date: 2008-03-20
Filing date: 2009-03-19
Publication date: 2011-02-02
Also published as: WO2009115845A1; GB2458500A; GB0805221D0

Abstract

A method of improving the fuel efficiency of electrically controlled fuel injected internal combustion engines, and including a system adapted to interrupt a control signal from an engine management computer or powertrain control module (PCM) (15) to a fuel injector (11) comprising a current sensor (17) adapted to measure the duration of a pulsed supply of fuel to the injector, a switching block (18) to interrupt the supply if required, and a microprocessor (22) to actuate the switching block and to produce a signal which may be used to effect injection into the engine of a secondary fuel of shorter molecular structure thus to achieve, as far as possible, homogenous combustion within the engine.

Description

A METHOD OF AND SYSTEM FOR IMPROVING THE FUEL EFFICIENCY OF ELECTRONICALLY CONTROLLED FUEL INJECTED INTERNAL COMBUSTION ENGINES

[0001] This invention is concerned with improving the fuel efficiency of fuel injected diesel or petrol engines in order to effect within the engine the principle of homogenous combustion, i.e., to ensure that fuel is utilised (burnt) as fully as possible thus improving the efficiency of the engine and bringing about a reduction of harmful exhaust emissions. Of course, "homogenous" implies complete burn of all fuel, which is not achievable in practical terms, but nevertheless this is to be desired to avoid emission of unburnt fuel that may be harmful to the environment.

BACKGROUND

[0002] It is known that hydrocarbon fuels such as diesel have a molecular structure which is long, complex and slow to combust which prevents some hydrocarbon fractions from burning fully. Again in the case of diesel engines this is largely responsible for smoke and particulate matter issuing from the exhaust system of the engine.

[0003] Typically, a conventional diesel engine on a heavy commercial vehicle has an effective diesel burn of between 75% and 80% of its total capability and it is a further object of the present invention to increase this to a level much closer to 100%.

[0004] It is known to employ a secondary fuel in gasoline and diesel engines. US-A- 4463734 discloses a diesel engine in which increasing proportions of liquefied petroleum gas (LPG) are metered to the engine as power demand increases, starting from as little as 20% gas and increasing to about 80% gas, where the percentage is given in calorific value. By volume, the calorific value of LPG is about 60% that of diesel so that, in terms of liquid volume, the percentage range is between 30% and 87% of gas. Different gases have different calorific values.

[0005] US-A-4641625 discloses a range of gaseous fuel in a liquid gas mixture of between 0 and 95% gas. [0006] US-A-6026787 and US-A-2005/0205021 both disclose dual fuel engines, but without specifying the proportions of the fuels.

[0007] It is an object of the present invention to improve the efficiency of a diesel engine whereby better fuel economy and/or greater power is available while at the same time improving the emissions standard of the engine. BRIEF SUMMARY OF THE DISCLOSURE

[0008] According to a first aspect of the present invention, there is provided a method of improving the fuel efficiency of an electronically controlled fuel injected internal combustion engine, comprising the steps of controlling the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and sequentially supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the amount by calorific value of the second fuel injected is limited to between 5 and 25% of the total fuel employed. Preferably, the amount in liquid form of the second fuel injected is limited to between 5 and 25% of the total fuel employed in liquid form.

[0009] The present invention ensures a more complete burn of the hydrocarbon fuel by introducing said second fuel or fuels to act as an accelerant within the combustion chamber.

[0010] The invention recognises several facts. The first is that only a small amount of gas (which is used herein interchangeably with the term "second fuel" - indeed, "fuel" should be interpreted to include a mixture of more than one fuel, as well as a single fuel) is needed to improve the combustion of the first fuel, which may be diesel or petrol or any long chain fuel that is liquid at ambient temperatures and pressures. The gas mixes easily with the air and gets to all corners of an engine's combustion chamber. Moreover it burns easily so that it, at least, is entirely combusted and in doing so ensures that all the heavier first fuel ignites also. At least, a greater majority of the fuel is combusted. Accordingly, the efficiency of the engine is enhanced.

[0011] However, what the present invention does not seek to do, and which the prior art seems to have attempted universally, is maximise the quantity of gas introduced. This might be done because gas is frequently a less expensive form of fuel. However, in a diesel engine, the engine is set up for burning diesel fuel, and lighter LPG or other small molecule fuel is not especially suitable. Furthermore, it is believed that by increasing the quantity of gas injected, oxygen available for burning the diesel is diminished so that the improved efficiency peaks at a relatively low level of introduced gas. Of course, it may be that overall emissions continue to improve with increasing gas usage because a) gas is an inherently cleaner fuel and b) less diesel fuel is being used, which is the source, at least, of particulate emissions. However, this masks the reality that the gas, in burning quickly, robs the combustion chamber of available oxygen, which might in any event be diminished by introducing gas into the combustion chamber. Of course, at any given engine speed and torque, the engine is designed to aspirate

(boosted or otherwise) more air than is needed to burn the diesel injected. However, if a proportion of this air is depleted by gas injection, and the gas uses a proportion of the oxygen in its own combustion, the available oxygen for combustion of the diesel will be depleted.

[0012] Indeed, preferably, when the arrangement is provided as a bolt-on system to an existing engine, the amount of gas injected is so small that the overall engine management control system is not adversely affected, whereby the gas added is simply additional to the diesel injected for the engine operational conditions responsive to the throttle position determined by the operator or the control system. That is to say, the improved efficiency is simply seen by the management system as a reduced load on the engine, leading to increased speed, and is not perceived as an error condition. However, this depends to some extent on the system in which the engine is fitted,

[0013] The controlled quantity of the first fuel injected into the combustion chamber may be determined by a microprocessor which produces a signal to determine the proportional quantity of the second fuel and the sequential timing of injection thereof into the combustion chamber.

[0014] The controlled quantity of the first fuel may be determined by measuring the normal duration of a pulsed supply of the first fuel by an injector as determined by an engine management computer or powertrain control module (PCM).

[0015] If required, for example in systems expecting a certain level of performance for a given level of diesel fuel injected, the pulsed supply of the first fuel may be interrupted at a predetermined point in time, the proportional quantity of the second fuel being introduced into the combustion chamber at a subsequent point in time coincident with a combustion stroke of the engine.

[0016] Said introduction of the second fuel may be by direct injection into the combustion chamber, during the induction stroke, compression stroke or combustion stroke of the engine. Preferably, however, said injection is into an inlet manifold of the engine behind an inlet valve of each combustion chamber of the engine during the induction stroke of the chamber in question. In that event, the proportion of said second fuel injected during said induction stroke is determined on the basis of the amount of first fuel injected in a preceding combustion cycle of the engine, ideally an immediately preceding cycle.

[0017] Preferably, injection into said inlet manifold begins after all outlet valves of the chamber in question have closed in or following the preceding exhaust stroke of the engine. Preferably, injection into said inlet manifold ceases before the inlet valve of the chamber in question closes in or following said induction stroke of the engine. [0018] The controlled quantity of the first fuel may be determined by monitoring the duration of the supply of the first fuel by an injector in relation to a signal representative of the instantaneous fuel pressure derived from a fuel pump, and interrupting the supply at a predetermined point in time. [0019] A signal may be sent to the fuel pump to modify the fuel pressure in addition to, or as an alternative to, modification of the duration of a pulsed fuel supply to the combustion chamber of the engine.

[0020] The second fuel may be liquefied petroleum gas (LPG). The second fuel may be hydrogen. The second fuel may comprise two or more different fuels of different molecular structures. The second fuel may be injected into the air stream supplied to the combustion chamber of the engine. Preferably, there is between 5 and 15% of the second fuel, in calorific value, or in liquid form by volume.

[0021] According to a second aspect of the present invention, there is provided a method of improving the fuel efficiency of an electronically controlled fuel injected internal combustion diesel engine, comprising the steps of controlling the quantity of a first diesel fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and sequentially supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the amount of the second fuel injected is limited so that the calorific value of the combined fuels injected into the engine for a given level of performance is less than the calorific value of the first fuel needed to achieve the same level of performance when injected alone.

[0022] While the definition employed above is based on the result to be achieved it is predicated on the proposition that there is both a minimum and maximum level of injection of the second fuel that results in a reduction in the required calorific value of the total fuel employed compared with use of the first fuel alone. However, the absolute values of the minimum and maximum will vary both from one engine set up to another, as well as from one, (first or second), fuel to another. However, there is no uncertainty for the skilled person because it is based on a given engine, a given first fuel and a given second fuel.

[0023] Thus, the aim of the second invention is not to maximise the use of a second, gaseous, fuel, but only to improve the efficiency of the engine, particularly a heavy diesel engine, and its emissions. A corollary benefit of the invention is precisely that it does not employ a substantial quantity of the gas. Firstly, this means that a large reservoir of the gas is not required in order to provide a significant range of dual-fuel use before replenishment of the gas is needed. It is to be remembered that in most countries the supply of gas is not universally available, for example in all (or even, many) garage filling-station forecourts. Secondly, while gas is presently less expensive than diesel fuel, this is primarily a present tax policy matter and there is no guarantee that it will remain the case in the future and generally it will not if gas becomes a significant fuel source for vehicles.

[0024] In US-A-6026787 mentioned above, an engine system for dual fuel has the OEM injector lines from the vehicle control module supplied to a processor which chops the pulse length to reduce the quantity of diesel injected. However, the gas is controlled simply by engine vacuum.

[0025] US-A-2005/0205021 , also mentioned above, discloses independent control of the gas injection by a Flow Control Unit that is controlled by an integrated control unit that takes all parameters into account and determines the appropriate proportion of gas to diesel. Hence it is an integrated system and cannot be a bolt-on system to an existing vehicle. It is hence a relatively complex system.

[0026] EP-A-1281850 discloses a controller that determines pulse widths and timings for engine injectors, which pulse width and timings are used for either diesel or gas. When employed to control diesel injection, there is one algorithm in the control unit. However, when it is used to control gas injection, a different algorithm is employed. [0027] It is a further object of the present invention to provide a convenient method of control of gas injection in a fuel employing both gas and liquid fuel simultaneously. Particularly it is desirous a) to have a system that is easily bolted onto many existing engines to convert them from single liquid fuel to combined fuel use without extensive modification either of the engine or the bolt-on system, and b) to enable vehicle and other engine manufacturers to render engines more easily convertible. Indeed, it is an object of the invention to provide a system that enables vehicle manufacturers (and other engine suppliers) relatively straightforwardly to modify their existing engines to dual-fuel use without the necessity to re-map the engine management system

[0028] According to a third aspect of the present invention there is provided a system for improving the fuel efficiency of an electronically controlled fuel injected internal combustion engine, comprising: means for supplying a first quantity of a first fuel having a first molecular structure for injection into to a combustion chamber of the engine during a combustion cycle; means for supplying a second quantity of a second fuel of a shorter molecular structure into the combustion chamber; and a first microprocessor controlling said first quantity of fuel according to multiple parameters of the engine; wherein a second microprocessor determines the quantity of the second fuel as a function of the quantity of the first fuel and causes injection of the second quantity sequentially with respect to the first quantity.

[0029] Preferably, said parameters are the normal parameters detected by an engine management system on the basis of which a fuel quantity is normally determined, such as engine speed and throttle position. Others are, of course, within the ambit of the skilled person. [0030] The first and second microprocessors may be a single, integrated processor or at least be contained within a single engine management computer or powertrain control module (PCM).

[0031] However, they may equally be separate and, indeed, added separately with the first microprocessor being part of an existing set up for the engine when running on a single first fuel, and subsequently modified by addition of a kit including the second microprocessor. Thus, the system may further comprise: means for measuring the duration of a pulsed supply of a first fuel to the injector; means to monitor the instantaneous pressure of the first fuel derived by a fuel pump; wherein said second microprocessor receives signals from the measuring means and monitoring means; and the second microprocessor is adapted to calculate said first quantity of the first fuel injected and produce and transmit a resultant signal to means for sequentially supplying said second quantity of the second fuel. [0032] The system may be adapted for connection between an engine management computer (ECU) and a fuel injector for the engine thus to intercept the signals issued by the PCM to the injector and to supply optionally modified signals to the injector. Indeed, the system may comprise means for modifying the pulsed length of the supply of the first fuel. [0033] Alternatively or additionally, the system may include means to modify the instantaneous pressure of the first fuel as a parameter of the supply of the first fuel to the engine.

[0034] The pressure monitoring means may be the second microprocessor adapted to receive signals from, and transmit signals to, a fuel pump for the first fuel. [0035] The second microprocessor may be connected to the PCM and adapted to transmit signals thereto representative of the overall fuel supply to the engine, thus to emulate normal engine operational conditions as monitored by the PCM.

[0036] The means for measuring the duration of the pulsed supply of the first fuel to the injector may be a Hall Effect current sensing device producing an analogue signal, and connected, via an analogue to digital converter, to the second microprocessor.

[0037] The means for modifying the pulsed length of the supply of the first fuel to the injector may be an optically coupled MOSFET switching block connected to the second microprocessor. [0038] The Hall Effect current sensor and the optically coupled MOSFET switching block may provide a low-resistance, electrically conductive path completing a circuit between the PCM and the injector.

[0039] An opto-coupler may be connected in parallel to the optically coupled MOSFET switching block to detect any potential difference during an "off" state of the switching block.

[0040] Said function is preferably a proportional function, optionally a linear function. Said second quantity of said second fuel may preferably be between 5 and 25% by calorific value of the total fuel employed. It may be between 5 and 25% by liquid volume of the total fuel employed. [0041] The invention also provides an electronically controlled fuel injected internal combustion engine, suitable for implementing the systems or methods described above, comprising an engine management computer or powertrain control module (PCM) and a fuel injector for the engine, wherein the engine management computer or PCM has an output for connection of a second fuel injection control system and indicative of the instantaneous quantity of fuel injected in each cylinder of the engine during each combustion cycle of the engine. The advantage of such an arrangement is that the subsequent conversion of the engine to duel fuel use according to the present invention is simplified. Indeed, provided it is not desired to interrupt and modify the first fuel supply, said outputs are all that a system according to the present invention needs in order to control the supply of the second fuel. Existing bolt-on LPG or other gaseous fuel conversion kit can be added to a vehicle (or other apparatus employing the engine) in a known manner, with its control arrangements employing said outputs. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] An embodiment of the invention, as applied to a diesel engine, is described hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a diagram representing the manner of operation of the system to be described; and

Fig. 2 is a circuit diagram of the system as applied to the PCM and each fuel injector of an engine.

DETAILED DESCRIPTION

[0043] The method of and system for improving the fuel efficiency of an electronically controlled fuel injected diesel engine, in accordance with the invention, is intended to bring about, as completely as possible, homogenous combustion within each cylinder or combustion chamber of the engine in order most effectively to burn the entire quantity of diesel fuel supplied to the combustion chamber and thus increase the effective diesel burn from between 75% to 80% as typically experienced in a conventional diesel engine, to something in the region of 98% to 99% ie, almost 100%.

[0044] This is achieved by electronically reading the signal to each fuel injector, as supplied by the engine management computer or powertrain control module (PCM) and, if necessary, cross-referencing data pulses derived from these signals with a pressure reading from the fuel supply pump, and then, optionally, controlling the exact amount of a primary fuel being supplied to the engine by each injector. This then triggers a second signal which is used to control a secondary fuel injector which proportionally injects a correct amount of a secondary fuel of a shorter molecular structure than the primary fuel to increase the optimum burn, i.e., to achieve, as far as possible, homogenous combustion. The secondary fuel system is a sequential injection system which applies the secondary pulse in an appropriate timing pattern.

[0045] The system imposes a control over the fuelling mechanism which, if required, can vary the fuel pressure and/or the duration of the pulsed supply of diesel fuel to the engine. Thus, the normal performance characteristics can be maintained while efficiency is increased.

[0046] Electronic fuel injection systems currently available vary considerably in characteristics according to different fuel types, and seek to address the ever increasing demands for improved performance, efficiency and lower exhaust emissions. While these systems share the same basic principle of injecting fuel into an internal combustion engine via an electronically controlled valve known as an injector, the control technology and the design of the injectors themselves vary considerably across the range of systems available. Therefore, in order to impose control over the efficiency of such an engine the present invention provides a system which can be applied universally to most, if not all, electronic fuel injection systems irrespective of the differences in their design and performance characteristics.

[0047] Referring now to Fig. 1 , the system of the present invention is illustrated diagrammatically at 3 and is adapted to receive signals monitoring the injection pulses 1 applied to each injector from the engine management computer (15 in Fig. 2). These may consist of individual pulses or groups of pulses per engine cylinder combustion stroke. The total injection duration is calculated in system 3 and multiplied by a relative voltage 2 representing the fuel pressure derived from a fuel supply pump (16a in Fig. 2). Output data is generated at 4 representing the total fuel quantity delivered to the combustion chamber, and this may consist of one or more of an individual pulse 4a, per combustion, of variable pulse width, a variable voltage/current analogue output 4b, a digital output 4c, or a combination of all three.

[0048] Referring now to Fig. 2, a dotted line X represents a point of connection of the system illustrated below the line X, to an engine management computer or powertrain control module (PCM) and the engine injectors, which are represented above the line X. [0049] Therefore, the engine to which this system is to be connected will include a series of fuel injectors 1 1 in the form of electrically operated valves, all connected to a common fuel supply rail 12, an engine management computer (PCM) 15 and a fuel pump 16a. A pressure sensor 13 produces a signal representative of the instantaneous fuel pressure in the rail 12 and transmits the signal to the PCM 15 which is connected also the fuel pump 16a.

[0050] The system of the invention is connected to the components above the line X by interrupting the normal circuit from the PCM 15 to each injector 1 1 as shown at 14, and so an entire system as illustrated below the line X is required and connected between the PCM 15 and each of the injectors 1 1. [0051] Therefore, the intercepted circuit 14 is replaced by a circuit including a Hall Effect current sensing device 17 and an optically coupled MOSFET switching block 18. The resultant circuit illustrated by thickened line Y provides a low-resistance, electrically conductive path thus completing the circuit and ensuring any changes made to the injector control circuit characteristics by its insertion are negligible, and completing the circuit between the PCM and the injector. [0052] An opto-coupler 19 is connected in parallel with the MOSFET switching block 18 to enable detection of any potential difference in the circuit during the MOSFET "off" state, during operation. The opto-coupler 19 is connected to a microprocessor 22, an output of which is also connected to the MOSFET switching block 18 while the analogue signal from the Hall Effect current sensor 17 is supplied via a multiplex analogue to digital converter (ADC) 20 to the microprocessor 22. The signal from the pressure sensor 13 is also connected to the microprocessor 22 via ADC 20.

[0053] Any or all external circuits having an affect upon or receiving effective signals from the system, are represented at 21 and are thus connected to the microprocessor 22 both to receive signals from and to transmit signals to the latter.

[0054] As shown at 17b, there is a connection between the fuel pump 16a and the microprocessor 22 which is also connected to the PCM 15.

[0055] In use, analogue signal voltages from the fuel pressure sensor 3, the Hall Effect current sensing device 7, and external control voltages are converted into digital signals by the ADC 20, while signals from the latter, from the opto-coupler 19, and from external control interface circuits 21 are received and monitored by the microprocessor 22.

[0056] The microprocessor 22 mathematically combines the fuel pressure reading from pressure sensor 13 and the duration of injection pulses as read by the Hall Effect current sensor 17 thus providing a proportional digital output signal from the microprocessor 22 representing the relative quantity of fuel injected into the engine.

[0057] The microprocessor 22 is programmed to enable a fuel injection pulse generated by the PCM 15 and transmitted to the injector 1 1 to be interrupted if necessary at a predetermined point in time by transmitting a signal to the MOSFET switching block 18 thus to turn off the supply pulse at a precise moment, thus prematurely stopping the injection of fuel into the combustion chamber. A resultant signal is then transmitted from the microprocessor 22 via the interface 21 to control a second set of injectors (not shown) arranged to inject a pulse or pulses of predetermined length of a second, lighter fuel such as LPG into the air stream supplied to the combustion chamber. The timing generated by the microprocessor 22 is such that the injection of secondary fuel coincides with the next induction cycle of the engine. Indeed, it can be arranged to occur in periods after the exhaust valve of the respective cylinder has closed, so as to ensure that secondary fuel entering the combustion chamber is not immediately washed into the exhaust contaminating the engine's emissions and wasting fuel. This is possible in engines that have valve overlap. Indeed, it may go further so that injection of the secondary fuel ends sufficiently in advance of the inlet valve closing, thereby to ensure that there is no fuel left in the intake manifold to potentially wash through the cylinder in the next cycle.

[0058] However, it is also possible for the gaseous fuel to be injected directly into the combustion chamber shortly after injection of the primary fuel. This has the advantage that the gaseous fuel injected is precisely matched to each stroke of the engine, whereas when the gas is injected into the inlet manifold it is only matched to the preceding combustion cycle, which means that it will always be out of step. However, the quantity of fuel to be injected from one combustion cycle to the next seldom changes, and, when it does change, it seldom changes very rapidly substantially or such that this out-of-step fuel injection has any discernible effect, either in acceleration or deceleration of the engine. In any event, a disadvantage of direct injection is that a) the cylinder head of the engine requires modification and b) the advantage of the gas mixing and disseminating reliably through the entire cylinder volume may be lost. There is the further problem that the fuel will need substantial pressurization to be injected during the compression or combustion stroke of the engine. Consequently, injection into the inlet manifold is preferred.

[0059] Accordingly, a predetermined and controlled injection of diesel fuel takes place during one combustion stroke, while a predetermined quantity of the second fuel is injected into the combustion chamber sequentially, so that the overall fuel supply to the combustion chamber is a sum of the first and second fuels in their predetermined and controlled proportions, the second fuel having a shorter molecular structure ensuring substantially complete combustion of the first fuel thus considerably increasing the efficiency of the engine and reducing carbon emissions from the exhaust as well as smoke and particulate matter.

[0060] The microprocessor 22 may also intercept the fuel pump pressure control signals 16b to cause the fuel pressure to be modified. This is not essential in all cases since the pressure can be a constant while the volume of the fuel supply is controlled and modified as appropriate to maximise efficiency. [0061] Since the system, in this example, is readily connected physically to and between the PCM 15 and injector 1 1 of any electronically controlled fuel injected engine, the microprocessor 22 can be programmed to bring about a control of a single or dual fuel supply to the engine to achieve improved efficiency and reduce emissions, irrespective of the design of the engine or the control imposed over it by the PCM 15. [0062] The system can be used for other purposes by imposing a control over the fuel supplied to the injectors 1 1. It can be used for electronic fuel injection fault diagnosis by providing an injected fuel quantity reference as a means of checking and confirming correct fuel delivery. It can be used to enhance engine performance by injecting a secondary fuel in proportions which serve to increase engine power output. [0063] The system is fully bi-directional so that it may be connected in either polarity and it is electrically isolated so that high voltages cannot enter the control circuit. The system may be used with both diesel and petrol (gasoline) direct injection engines. While in operation current sensing within the circuit is monitored by the Hall Effect sensor 17, and any improper current flow conditions within the circuit can be rectified by switching off the MOSFET switching block 18 thus protecting the circuit from damage.

[0064] Indeed, the MOSFET switching block is certainly a preferred element of the present invention. However, when only detection of the pulse length applied to the diesel injectors is required, it could be that the MOSFET switching block 18 is omitted. Of course, it is still possible to adjust the volume of diesel injected without this feature by altering fuel rail pressure applied by the fuel pump. However, in many instances, it is not necessary to alter the injection volume of the diesel. The engine management system will do this to some extent automatically, recognizing the improved performance of the engine not as some fault condition but simply as a reduction in engine load. In this event, it is feasible to omit the MOSFET switching block 18 entirely. [0065] When used for the sequential supply of a secondary fuel any liquid/gaseous fuel may be used, provided that it is fuel of shorter molecular structure than the diesel or gasoline supplied as the primary fuel. Examples of lighter secondary fuels include liquefied petroleum gas (LPG), hydrogen, compressed natural gas, and bioethanol.

[0066] The improved thermal efficiency within the internal combustion engine afforded by dual-fuel control as described, serves to create a cooler, leaner burn, which will provide improved output in terms of power, torque and energy, while using less overall fuel and producing considerably less harmful emissions, particularly nitrogen oxides, as well as, in the case of diesel fuel, a considerable reduction in particulate matter and smoke. In the case of a large commercial engine, for example, this improvement in efficiency is interpreted by the engine's PCM as though it were a reduction in load carried by the vehicle, so the PCM will consequently retard the quantity of diesel fuel supplied and thus improve the economy of the engine in direct proportion to the improvement in engine efficiency.

[0067] Typical results on a large commercial engine are considered to provide a reduction in primary fuel consumption of around 20%, using only 5% to 10% of secondary fuel (by liquid volume) to achieve this improvement. Indeed, volume for volume, less fuel in total is used, and this ignores the fact that diesel fuel has about 1 .6 times more calorific value than LPG in liquid volume terms. Emission reductions are typically 40% to 70% reduction in nitrogen oxides, 80% to 90% reduction in smoke and particulate matter, and a reduction of carbon dioxide reflective of the reduction of overall fuel used and the efficiency of the engine.

[0068] These improvements are achieved in a non-invasive manner so that the engine life and/or periods between servicing will be extended due to the lower combustion temperatures achieved by substantially homogenous combustion, and the reduction in carbon deposits. It is found that the heavier the primary fuel, the greater is the improvement in engine efficiency and reduction in exhaust emissions.

Claims

1 . A method of improving the fuel efficiency of an electronically controlled fuel injected internal combustion engine, comprising the steps of controlling the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and sequentially supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the amount by calorific value of the second fuel injected is limited to between 5 and 25% of the total fuel employed.

2. A method of improving the fuel efficiency of an electronically controlled fuel injected internal combustion engine, comprising the steps of controlling the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle, and sequentially supplying to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure, wherein the amount of the second fuel injected is limited so that the calorific value of the combined fuels injected into the engine for a given level of performance is less than the calorific value of the first fuel needed to achieve the same level of performance when injected alone.

3. A method according to claim 1 or 2, wherein the second fuel is supplied to the combustion chamber during the same combustion cycle.

4. A method according to claim 1 or 2, wherein the second fuel is supplied to the combustion chamber during a subsequent combustion cycle.

5. A method according to any preceding claim, wherein the controlled quantity of the first fuel injected into the combustion chamber during a combustion cycle is determined by a microprocessor which produces a signal to determine the proportional quantity of the second fuel and the sequential timing of injection thereof into the combustion chamber.

6. A method according to any preceding claim wherein the controlled quantity of the first fuel is determined by measuring the duration of a pulsed supply of the first fuel by an injector as determined by an engine management computer or powertrain control module (PCM), the proportional quantity of the second fuel being injected directly into the combustion chamber at a subsequent point in time coincident with an induction, compression or combustion stroke of the engine.

7. A method according to claim 6, wherein the pulsed supply of the first fuel is interrupted at a predetermined point in time.

8. A method according to any of claims 1 to 5, wherein said injection of the second fuel is into an inlet manifold of the engine behind an inlet valve of each combustion chamber of the engine during the induction stroke of the chamber in question.

9. A method according to claim 8, wherein the proportion of said second fuel injected during said induction stroke is determined on the basis of the amount of first fuel injected in a preceding combustion cycle of the engine, preferably an immediately preceding cycle.

10. A method according to claim 8 or 9, wherein injection into said inlet manifold begins after all outlet valves of the chamber in question have closed in or following the preceding exhaust stroke of the engine.

1 1. A method according to claim 8, 9 or 10, wherein injection into said inlet manifold ceases before the inlet valve of the chamber in question closes in or following said induction stroke of the engine.

12. A method according to any preceding claim, wherein the controlled quantity of the first fuel is determined by monitoring the duration of the supply of the first fuel by an injector in relation to a signal representative of the instantaneous fuel pressure derived from a fuel pump, and, optionally, interrupting the supply at a predetermined point in time.

13. A method according to any preceding claim, further comprising the step of modification of the duration of a pulsed fuel supply of said first fuel to the combustion chamber of the engine.

14. A method according to any preceding claim, wherein the first fuel is diesel.

15. A method according to any one of claims 1 to 13, wherein the second fuel liquefied petroleum gas (LPG) or hydrogen.

16. A method according to any one of claims 1 to 13, wherein the second fuel comprises two or more different fuels of different molecular structures.

17. A method according to any one of claims 1 to 13, wherein the second fuel is a hydrocarbon fuel.

18. A method according to any preceding claim, wherein the amount of the second fuel injected is controlled to between 5 and 25% by volume of the total fuel in liquid form employed.

19. An electronically controlled fuel injected internal combustion engine to put the method of claims 1 to 18 into effect comprising: means to control the quantity of a first diesel fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle; means sequentially to supply to the combustion chamber a controlled proportional quantity of a second fuel of a shorter molecular structure; and means controlling the amount of the second fuel injected to between 5 and 25% by calorific value of the total fuel employed.

20. An engine as claimed in claim 19, wherein said controlling means controls the amount of the second fuel injected to between 5 and 25% by volume of the total fuel in liquid form employed.

21. A system for improving the fuel efficiency of an electronically controlled fuel injected internal combustion engine, comprising: means for supplying a first quantity of a first fuel having a first molecular structure for injection into to a combustion chamber of the engine during a combustion cycle; means for supplying a second quantity of a second fuel of a shorter molecular structure into the combustion chamber; and a first microprocessor controlling said first quantity of fuel according to multiple parameters of the engine; wherein a second microprocessor determines the quantity of the second fuel as a function of the quantity of the first fuel and causes injection of the second quantity sequentially with respect to the first quantity.

22. A system according to claim 21 , wherein said parameters include engine speed and throttle position.

23. A system according to claim 21 or 22, wherein the first and second microprocessors are a single integrated processor.

24. A system according to claim 21 , wherein the system further comprises: means for measuring the duration of a pulsed supply of a first fuel to the injector; means to monitor the instantaneous pressure of the first fuel derived by a fuel pump; wherein said second microprocessor receives signals from the measuring means and monitoring means; and wherein the second microprocessor is adapted to calculate said first quantity of the first fuel injected and produce and transmit a resultant signal to means for sequentially supplying said second quantity of the second fuel.

25. A system according to claim 24, adapted for connection between an engine management computer or powertrain control module (PCM) comprising said first microprocessor and a fuel injector for the engine thus to intercept the signals issued by the PCM to the injector and, optionally, to supply modified signals to the injector.

26. A system according to claim 25 comprising means for modifying the pulsed length of the supply of the first fuel.

27. A system according to claim 25 or 26 comprising means to modify the instantaneous pressure of the first fuel as a parameter of the supply of the first fuel to the engine.

28. A system according to any of claims 24 to 27, wherein said pressure monitoring means comprises the second microprocessor adapted to receive signals from, and transmit signals to, a pump of the engine for said first fuel.

29. A system according to claim 28, wherein the second microprocessor is connected to the PCM and adapted to transmit signals thereto representative of the overall fuel supply to the engine thus to emulate normal engine operational conditions as monitored by the PCM.

30. A system according to any of claims 24 to 29, wherein the means for measuring the duration of the pulsed supply of the first fuel to the injector is a Hall Effect current sensing device producing an analogue signal, and connected, via an analogue to digital converter, to the second microprocessor.

31. A system according to claim 26, or any of claims 27 to 30 when dependent on claim 26, wherein the means for modifying the pulsed length of the supply of the first fuel to the injector is an optically coupled MOSFET switching block connected to the microprocessor.

32. A system according to claims 30 and 31 , wherein the Hall Effect current sensor and optically coupled MOSFET switching block are connected to provide a low- resistance electrically conductive path completing a circuit between the PCM and the injector.

33. A system according to claim 32 including an opto-coupler connected in parallel to the optically coupled MOSFET switching block to detect any potential difference during an "off" state of the switching block.

34. A system according to any of claims 21 to 33, wherein said function is a proportional function, preferably linear.

35. A system according to any of claims 21 to 34, wherein said second quantity of said second fuel is between 5 and 25% by calorific value of the total fuel employed, optionally between 5 and 25% by liquid volume of the total fuel employed.

36. A method for improving the fuel efficiency of an electronically controlled fuel injected internal combustion engine, comprising the steps of: controlling the quantity of a first fuel having a first molecular structure injected into a combustion chamber of the engine during a combustion cycle; determining the quantity of the first fuel injected; determining a proportional quantity of a second fuel of a shorter molecular structure; and supplying said proportional quantity of said second fuel to the combustion chamber sequentially to the supply of said first fuel.

37. A method according to claim 36, further comprising the steps of: measuring the duration of a pulsed supply of a first fuel to the injector; monitoring the instantaneous pressure of the first fuel derived by a fuel pump; and making said determination of the quantity of the first fuel injected on the basis of said duration and said pressure.

38. An electronically controlled fuel injected internal combustion engine, suitable for implementing the method of any of claims 1 to 18 or claim 36 or 37, or suitable for implementing the system of any of claims 19 to 35, except when dependent on claim 23, comprising an engine management computer or powertrain control module (PCM) and a fuel injector for the engine, wherein the engine management computer or PCM has an output for connection of a second fuel injection control system and indicative of the instantaneous quantity of fuel injected in each cylinder of the engine during each combustion cycle of the engine.