WO2006079172A1

WO2006079172A1 - Fuel injection system for internal combustion engine

Info

Publication number: WO2006079172A1
Application number: PCT/AU2006/000097
Authority: WO
Inventors: David James Caley
Original assignee: Orbital Engine Company (Australia) Pty Limited
Priority date: 2005-01-27
Filing date: 2006-01-27
Publication date: 2006-08-03

Abstract

The invention provides a fuel injection system for an internal combustion engine (20) which includes at least one port or manifold injector (26); and at least one direct injector (12) for each combustion chamber (60) of the engine (20). A control means (100) controls the direct injector (12) to deliver fuel to the combustion chamber (60) when engine speed and load are above low load speed operating conditions. Control means (100) controls the port injector to deliver fuel to the combustion chamber (60) of the engine (20) under low load, low speed operating conditions.

Description

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINE

This invention relates to fuel injection systems for internal combustion engines and methods of operating engines incorporating such fuel injection systems. Port injection systems, such as manifold port injected (MPI) systems, are often employed in internal combustion engines. Port injection systems involve fuel injection into an intake manifold or inlet port of the engine, with port injector(s) delivering fuel from a fuel supply system into each inlet port of the engine. Single or multi-point port injection may be employed. Port fuel injection, because of the relatively large window of timings available for fuel injection, is well adapted to providing the wide range of fuelling required from idle conditions to maximum power conditions (which for high performance engines can be a relatively wide range). However, port fuel injection systems, particularly in 2-stroke cycle engines employing piston controlled exhaust ports, suffer from poor fuel economy due to what is commonly referred to as short-circuiting of the air-fuel charge. These engines also tend to suffer from poor exhaust emissions. Other engines, for example 4-stroke cycle engines, can also suffer from poor fuel consumption and/or increased emissions as a result of the use of port fuel injection systems, for example as described in US Patent No. 4934329, the contents of which are hereby incorporated by reference.

To overcome some of these deficiencies, direct fuel injection has been developed and successfully applied to these engines. The Applicant has developed such engines which utilize a dual fluid direct fuel injection system. However, economical provision of a direct fuel injection system that has the required turn-down ratio to control and deliver fuel from idle conditions right through to high power conditions may be a challenge. One way to overcome this challenge involves coupling of direct injection (or Dl) with port injection (or Pl) system to augment the Dl system to provide the required additional fuelling range to meet the required power and torque targets. Such augmentation may be achieved by operation of the Pl system under high speed-high load operating conditions while the Dl system is operated under other engine operating conditions, particularly low engine speed - low engine load or part load conditions. Such operation is disclosed in US Patent No. 5092287, the contents of which are hereby incorporated by reference. In such engines, at lower speeds and loads, the Dl system provides emissions control/driveability and fuel efficiency benefits whilst at high engine speeds and loads, the Pl system either complements or acts as the complete fuel source, thus effectively increasing the turn down ratio of the system.

Such a strategy may not be readily adopted for certain types of engine currently under development by the Applicant in which such a strategy may not be able to meet certain operating requirements. For example, for gaseous fuels, using a Pl system for high speeds and loads may lead to a loss in power due to the air being displaced as a result of the delivery of gaseous fuel into the intake system. In the case of use of hydrogen gas, power loss of the order of 30% would be expected as a result of intake air displacement. For compressed natural gas (CNG), the power loss can amount to about 10%.

It is therefore an object of the present invention to provide a fuel injection system which enables improved engine performance in engines under development by the Applicant.

With this object in view, the present invention provides, in one aspect, a fuel injection system for an internal combustion engine comprising at least one combustion chamber, at least one direct fuel injector for directly injecting fuel into the combustion chamber; at least one port injector for delivering fuel to the combustion chamber of the engine; and control means for controlling said at least one direct fuel injector to deliver fuel to the combustion chamber when engine speed and load are above low load low speed operating conditions and controlling said at least one port injector to deliver fuel to the combustion chamber of the engine under low load, low speed operating conditions.

The fuel injection system may be controlled by the control means, such as an engine control management system, such that fuel is delivered to the combustion chamber of the engine by port injector(s) only or direct injector(s) only. Alternatively, an engine control management system may enable fuel to be delivered by a combination of port injector(s) and direct injector(s) or port injector(s) or direct injector(s) alone. The engine control management system may set transition engine demand or engine demand ranges at which fuel delivery by port injector(s) is ceased with fuel delivery being achieved through the direct injector(s); fuel delivery by port injector(s) is overlapped with fuel delivery by direct injector(s), or fuel delivery is only by the port injector(s) without any fuel delivery by the direct injector(s).

Typically, a single port injector (Pl) and single direct injector (Dl) would be provided for each cylinder of the engine. However, such a correspondence is not required. A single Pl injector may supply multiple cylinders. Port and direct injectors may be of conventional design, avoiding complexity and cost. Port injector(s) may be located in the intake manifold or inlet port of the engine. Throttle body injectors may be adopted. The Pl injector may be configured so that full load fuel can be supplied with a duty cycle of approximately 80%. The Dl injector may be configured so that the full load fuel can be supplied during a compression phase of the engine.

The control means may be an engine management control system, such as an electronic control unit (ECU), which controls fuelling at any transition between injection regimes selected from the group consisting of port injection, direct injection or combined port and direct injection operation such that the overall effect, at such transitions, at least as far as the operator is concerned, is as transparent as possible, and no perceptible difference in engine speed or power is observed. The ECU may also regulate the quantity of fuel metered to and/or apportioned between the Pl and Dl injectors, as a function of the particular engine operating conditions where Pl and Dl injectors are operated in combination, in such a way that correct fuelling of the engine is achieved while maintaining good driveability. Pl and Dl injection events, during the combined regime of operation, may be scheduled and timed in duration by the ECU to avoid over-fuelling and rich misfire of the engine. In this case, the ECU outputs an appropriate schedule of Pl and Dl fuel injection events dependent on engine operating conditions.

The ECU may control pressure differential across the fuel injector(s) as a way to effect the fuel metering; this differential being the difference between the supply pressure of the gaseous fuel and the pressure within the combustion chamber during the injection process, the pressure differential being such that the flow through the injector is not "choked" or "sonic". The fuel injection system may be applied to both single fluid fuel injection or injection of a dual fluid mixture of fuel and air or like gas, in which case "fuel" includes a fuel/air charge.

The fuel injection system of the invention is particularly suitable for engines fuelled by gaseous fuels, such engines being currently under development by the Applicant. The term "gaseous fuels" is defined herein as referring to both compressed gas fuels, such as compressed natural gas (CNG) or hydrogen (H₂), and liquefied gas fuels such as liquid petroleum gas (LPG). There are numerous potential advantages in using gaseous fuels. For example, exhaust emissions from an engine using gaseous fuel can be lower than for a comparable engine using liquid fuels. Cost savings may also be achieved.

However, gaseous fuel injection only into the inlet manifold or inlet port of a reciprocating engine displaces air resulting in reduced trapped air and reduced maximum engine torque. Direct injection, alone, of gaseous fuel into the cylinder of an engine after inlet port closure avoids the displacement of air but imposes strict timing limitations on the injection event. For a typical automotive four stroke engine, the fuel for full load operation should be injected in <4.0 m/sec to avoid displacing air at high engine speeds. The injection system must also provide controlled fuel metering at idle and low load operating conditions. Such requirements are, surprisingly, better met by the fuel injection system of the invention, involving port and direct injector(s), as above described. In such engines, the direct injectors(s) would advantageously be operated during the compression stroke of a cylinder for improved engine torque.

In some instances, stratified charge operation may be desirable. These instances will be dependent on the nature of the gaseous fuel and other specific parameters. For example, the use of hydrogen gas may offer an opportunity to use some stratified combustion at certain operating points. The operation of the Pl injector(s) may be limited to only low load/low speed operation with the Dl system providing some stratification effects in the medium load/medium speed operating region and then becoming homogeneous in the higher load/higher speed region to maximum power output.

The gaseous fuel injection system may include a fuel supply means for storing and supplying the gaseous fuel. In one arrangement, the pressure of the gaseous fuel supply means may be unregulated. Alternatively, the gaseous fuel may be delivered to the fuel injector(s) at a regulated pressure, optionally relatively constant pressure. The port injector(s) and direct injector(s) would preferably operate on a common injection pressure of between 1.2 and 3.5 MPa. However, the fuel supply pressure to port injector(s) and direct injector(s) may be regulated separately allowing individual operating pressures of between 0.8 and 5.0 MPa. A flow control valve or valves may be included in the fuel supply means to control the fuel supply to the fuel injector(s), the flow control valve(s) preferably being operated by an actuating means. Certain control and design aspects as applied to an engine direct injected with gaseous fuel and described in the Applicant's US Patent No. 5941210, the contents of which are hereby incorporated by reference, may also be implemented.

Further, it may be desirable - in some instances - to use water injection to control knock and/or NO_x emissions. For instance, hydrogen gas combustion can cause particularly high combustion chamber temperatures which could lead to increased knock. Water injection, by metering water into the delivery injector using a metering unit (such as described in the Applicant's US Patent No. 4934329 the contents of which are hereby incorporated by reference), is particularly convenient. In this case, water rather than fuel is metered into the delivery injector, and the pressurised gas atomises and delivers the water to the combustion chamber for knock/NO_x emission control.

Alternatively, a further additive such as a gas or liquid fuel could be delivered by the metering injector. Injection of a further combustible substance, such as hydrogen, may be conducted to enhance combustion efficiency.

An engine incorporating the fuel injection system of the present invention may be spark-ignited and operate on a two or four stroke cycle. The engine may be single or multi-cylinder.

In another aspect, the present invention provides a method of operating an internal combustion engine having a combustion chamber and a fuel injection system comprising at least one direct fuel injector for directly injecting fuel into the combustion chamber; and at least one port injector for delivering fuel to the combustion chamber of the engine wherein said at least one direct fuel injector is controlled to deliver fuel to the combustion chamber when engine load and speed are above low load, low speed engine operating conditions and said at least one port injector is controlled to deliver fuel to the combustion chamber of the engine under low load, low speed operating conditions. An engine control system may embody components necessary to enable and control the method.

The fuel injection system of the present invention will be more readily understood from the following exemplary description of one practical arrangement of the fuel injection system of the present invention as illustrated in the accompanying drawings in which: Figure 1 is a schematic sectional view of an internal combustion engine incorporating one embodiment of the fuel injection system of the present invention;

Figure 2 is a schematic of an internal combustion engine incorporating a fuel injection system of a second embodiment of the fuel injection system of the present invention; and

Figure 3 is an engine speed -engine load diagram illustrating injector control strategy for the fuel injector(s) of the fuel injection system of the present invention.

Figure 1 shows one cylinder 21 of a multi-cylinder internal combustion engine 20. The engine 20 is spark ignited and is fuelled, in this case, with a gaseous fuel such as LPG. The cylinder 21 has a combustion chamber 60, a cylinder head 40 and an air intake manifold 22. A fuel injector 26 is located in the air intake manifold 22 to inject gaseous fuel into the air intake manifold 22. This injector 26 is a port injector of conventional type. A fuel injector 12 is also located in the cylinder head 40 of cylinder 21.

Fuel injector 12 is a direct injector arranged to deliver fuel directly into the combustion chamber 60 of cylinder 21. Fuel injector 12 has a housing 30 with a cylindrical spigot 31 defining an injection port 32 in communication with a fuel rail unit 11 described below. The injection port 32 includes a solenoid operated selectively openable poppet valve operating in a manner similar to that as described in the Applicant's US Patent No. 4934329, the contents of which are hereby incorporated by reference, and which relates to a dual fluid injection system. A fuel metering unit is not needed for gaseous fuel operation; nevertheless a fuel metering unit 120, as described in US Patent No. 4934329, is employed to meter water to fuel injector 12 for knock and/or NO_x emissions control as shown in Figure 2.

Fuel rail unit 11 is supplied with pressurised LPG from a fuel tank and vaporiser unit (both not shown). Fuel rail unit 11 has pressure regulated between 1.2 and 3.5 MPa and supplies LPG to fuel injectors 12 and 26 at common pressure as required for particular engine operating conditions. Operation of fuel injectors 12 and 26 is under control of an electronic control unit (ECU) 100. ECU 100 may compensate for any temperature, pressure and/or composition variations in the fuel rail unit 11.

ECU 100 can control the duration of the opening period of each fuel injector 12 and 26 as well as the point at which each fuel injector 12 and 26 is opened during an engine cycle. It will be understood that fuel injectors 12 and 26 need not be operated simultaneously. This will depend on engine operating conditions. ECU 100 obtains input signals from various sensors providing information on the operating conditions of engine 20 as well as the driver demand and outputs control signals to certain engine components. The driver demand can be determined either as a load demand or a speed demand depending on the control strategy used. For example, a determination of the driver demand may be obtained from a throttle position sensor which provides a driver demand input signal to the ECU 100. Numerous other sensors are used to provide information to ECU 100 on the operating conditions of the engine 20. For example, the ECU 100 receives input signals relating to the air temperature and the engine speed. The ECU 100 may also receive other inputs such as crankshaft position inputs (e.g TDC pulses) depending on the particular engine application or configuration. Conversely, the ECU 100 outputs control signals to, for example, the electronic driver of the fuel injectors 12 and 26.

Operation of engine 20 will now be described. At low engine demands, speeds and loads, port fuel injector 26 supplies the entire fuel requirement of engine 20. ECU 100 enables fuel injector 26 to operate accordingly (Pl operation). As engine demand, speed or load increases above a transition point, ECU 100 initiates direct fuel injection from fuel injector 12. The fuel delivered by fuel injector 26 may be reduced to some extent. In this regime, fuel is delivered by both fuel injectors 12 and 26 (PI/DI operation). ECU 100 may control the amounts of fuel delivered on a fuel per cycle of engine operation basis. In this case, ECU 100 determines the total fuel per cycle requirement of the engine 20 and the contribution, on a fuel per cycle basis, of each fuel injector 12 and 26, to this total fuel per cycle requirement.

As engine demand, speed or load increases above a further transition point, delivery of fuel from the Pl fuel injector 26 is ceased altogether. At this point, corresponding with the onset of high speed, high load engine operation, fuel is delivered only directly to engine 20 through the fuel injector 12 (Dl operation).

Dl fuel injector 12 may be operated, for example during medium load/medium speed operating region to provide stratification in combustion chamber 60. In the higher load/high speed region, homogeneous charge operation is preferred to maximise power output of the engine 20. The operation of the fuel injector(s) through the engine speed - engine load range is illustrated by Figure 3, showing which injector(s) operate during the engine speed and load range of the engine 20.

ECU 100 operates the control strategy as above described for the direct and port injectors 12 and 26 of each cylinder of engine 20. ECU 100 may compensate for variations between cylinders. ECU 100 also times the operation of the direct and port injectors 12 and 26 in the engine cycle. ECU 100 may enable direct injector 12 to deliver full load fuel during the compression stroke of the engine.

Modifications and variations to the fuel injection system of the invention will be apparent to the skilled reader of this disclosure. Such modifications and variations are considered to be within the scope of the present invention.

Claims

CLAIMS:

1. A fuel injection system for an internal combustion engine comprising at least one combustion chamber; at least one direct fuel injector for directly injecting fuel into said combustion chamber of the engine; at least one port fuel injector for delivering fuel to the combustion chamber of the engine; and control means for controlling operation of said fuel injectors wherein said control means controls said at least one direct fuel injector to deliver fuel to the combustion chamber when engine speed and load are above low load low speed operating conditions and said control means controls said at least one port fuel injector to deliver fuel to the combustion chamber of the engine under low load, low speed operating conditions.

2. The fuel injection system of claim 1 wherein fuel is delivered to said combustion chamber by said at least one port fuel injector only.

3. The fuel injection system of claim 1 wherein fuel is delivered to said combustion chamber by said at least one direct fuel injector only.

4. The fuel injection system of claim 1 wherein fuel is delivered to said combustion chamber by a combination of said at least one direct fuel injector and said at least one port fuel injector.

5. The fuel injection system of any one of the preceding claims wherein said control means sets engine demand ranges for fuel delivery by an injection regime selected from the group consisting of port injection, direct injection and combination of port injection and direct injection; and controls transitions between said injection regimes.

6. The fuel injection system of claim 5 wherein each combustion chamber of said engine has one direct fuel injector and one port fuel injector.

7. The fuel injection system of claim 6, wherein said direct fuel injector delivers fuel, optionally full load fuel, during a compression phase of said engine.

8. The fuel injection system of claim 4 comprising at least one port fuel injector and at least one direct fuel injector wherein said control means controls the proportion of fuel delivered to said combustion chamber by each of said port fuel injector and said direct fuel injector.

9. The fuel injection system of claim 8 wherein said proportion of fuel delivered by each of said port fuel injector(s) and said direct fuel injector(s) is controlled as a function of engine operating conditions.

10. The fuel injection system of any one of the preceding claims wherein fuel is delivered to said combustion chamber in a fuel injection event, said control means scheduling the timing and duration of said fuel injection event.

11. The fuel injection system of claim 10 as dependent from claim 4 wherein said control means schedules a series of fuel injection events, being port fuel injection and direct fuel injection events, scheduling of said fuel injection events being dependent on engine operating conditions.

12. The fuel injection system of any one of the preceding claims wherein said fuel is a gaseous fuel.

13. The fuel injection system of claim 12 wherein said control means controls pressure differential across a direct fuel injector to effect fuel metering.

14. The fuel injection system of any one of the preceding claims wherein at least one fuel injector injects a single fluid.

15. The fuel injection system of any one of claims 1 to 13 wherein at least one fuel injector injects a dual fluid mixture.

16. The fuel injection system of claim 9 wherein said control means controls said direct fuel injector(s) to deliver fuel to said combustion chamber to form a stratified charge in said combustion chamber.

17. The fuel injection system of claim 9 wherein said control means controls said port fuel injector and said direct fuel injector to deliver fuel to said combustion chamber to maximize power output of the engine.

18. The fuel injection system of claim 12 wherein a fuel supply means for supplying fuel to said fuel injectors has unregulated pressure.

19. The fuel injection system of claim 12 wherein a fuel supply means for supplying fuel to said fuel injectors has at least one regulator for regulating pressure of fuel supplied to said fuel injectors.

20. The fuel injection system of claim 19 wherein said regulator regulates pressure at a relatively constant pressure.

21. The fuel injection system of claim 20 wherein fuel is supplied to a port fuel injector and a direct fuel injector at a common pressure.

22. The fuel injection system of claim 20 comprising regulators for separately regulating pressure of fuel supplied to port fuel injector(s) and direct fuel injector(s) by said fuel supply means.

23. The fuel injection system of any one of claims 18 to 22 wherein said control means compensates for at least one of temperature, pressure and composition variations in said fuel supply means.

24. The fuel injection system of any one of the preceding claims comprising a metering injector for delivering at least one of water and an additive to at least one of said fuel injectors.

25. The fuel injection system of claim 24 wherein said additive is a combustible substance for enhancing combustion efficiency.

26. An engine comprising the fuel injection system of any one of the preceding claims.

27. The engine of claim 26 comprising spark ignition means and being operated on the two or four stroke cycle.

28. The engine of claim 26 or 27 being a multi-cylinder engine.

29. A method of operating an internal combustion engine having a combustion chamber and a fuel injection system comprising at least one direct fuel injector for directly injecting fuel into the combustion chamber; and at least one port fuel injector for delivering fuel to the combustion chamber of the engine wherein said at least one direct fuel injector is controlled to deliver fuel to the combustion chamber when engine speed conditions are above low load, low speed operating conditions and said at least one port fuel injector is controlled to deliver fuel to the combustion chamber of the engine under low load, low speed engine operating conditions.