GB2540532A

GB2540532A - Injector

Info

Publication number: GB2540532A
Application number: GB1509754.6A
Authority: GB
Inventors: John Gregory Dingle Philip
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-06-05
Filing date: 2015-06-05
Publication date: 2017-01-25
Also published as: GB201509754D0

Abstract

Dual fuel injector 2 for an internal combustion engine, comprising concentrically arranged needles 6, 8, an inner needle 8 for controlling a flow of a high reactivity fuel such as diesel / DME received via a pilot piston shuttle, and an outer needle 6, in which the inner needle 8 is arranged and guided, for controlling a flow of a lower reactivity gaseous fuel; the inner and outer needles both being controlled by a single actuator 102 and control valve 82, wherein the injector can operate in a dual fuel operational mode, or in a high reactivity fuel only mode, as required for example on depletion of gaseous fuel. The injector may be used in a fuel injection apparatus 100 or a fuel system with two distinct fuel sources, and may be applied in the heavy duty trucking sector.

Description

Injector

TECHNICAL FIELD

The present invention relates to a fuel injector, and specifically to a dualfuel direct injector.

BACKGROUND OF THE INVENTION

The development of “fracking” technologies for the extraction of gas and oil from otherwise trapped resource locations is leading to a situation particularly in North America where there is an abundance of natural gas and thus a prospect of low prices as one looks to the future.

In the heavy duty trucking sector where fuel costs form a large portion of fleet operating costs, there is strong interest in technologies that allow a base diesel engine to be converted to run on natural gas (NG), and many conversion systems are available on the market, some of which are intended for OE (original equipment) installation, and some intended for in-service retrofit.

Because a conventional diesel engine operates on the compression ignition (Cl) principle, it requires a fuel that ignites readily under these conditions, and such a fuel will therefore have a high cetane value. NG, however, has a high octane number and a low cetane value and is therefore not readily suitable for use in a Cl engine without significant adaptation.

Of the available techniques for converting a Cl engine to run satisfactorily on NG, the most technologically sound requires direct injection of the gas late on the compression stroke against the rising cylinder pressure, and typically in conjunction with a small pilot injection of a reactive fuel such as diesel or dimethyl-ether (DME) for use as an ignition source. This results in a diffusion combustion process which closely duplicates normal diesel combustion and which therefore delivers similar performance as the base engine. This concept is well disclosed in the prior art, for example in US patent application no. US5996558A (Westport Research Inc.). A known fuel system in this area is a High Pressure Direct Injection (HPDI) system. However, this injector is complex, bulky, difficult to manufacture, is based on electronic unit injector architecture, has very limited limp-home capability in the event of gaseous fuel depletion, and is only appropriate for OE installation. These factors limit the applicability of the injector and system to specific engines and truck fleets that are able to work within these constraints.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved dual fuel injector which at least mitigates the problems encountered with known embodiments.

Accordingly the present invention provides, in a first aspect, an injector according to claim 1.

The present invention provides a high pressure gaseous dual-fuel direct injection injector which is less complex and easier to manufacture than prior art embodiments. The injector of the present invention is dimensionally compact, has a robust limp-home capability on liquid fuel, and is appropriate for installation in the in-service retrofit market.

Preferably, the injector is operable to effect an injection event in either a first operational mode or a second operational mode; wherein in the first operational mode, the second fuel is injected through the or all second fuel spray holes as a pilot fuel, and the first fuel is injected through the or all first fuel spray holes as a main fuel; and wherein in the second operational mode, the injector operates injects only the second fuel as a main fuel.

The injector may further comprise an intermediate fuel gallery located between the first fuel gallery and the second fuel gallery, wherein in use of the injector, the intermediate fuel gallery captures leakage of either first fuel from the first luel gallery, and/or leakage of second fuel from the second fuel gallery.

The first fuel may be gaseous, and the second fuel may be diesel or DME.

In a further aspect, the present invention comprises luel injection apparatus, comprising an injector as above, and further comprising a pilot shuttle piston to control a flow of second fuel into the second fuel gallery from a second fuel inlet.

The fuel injection apparatus may further comprise a bypass valve arranged in parallel with the pilot shuttle piston wherein, in use of the injector, in the first operational mode, the bypass valve is closed, and in the second operational mode, the bypass valve is open.

In a further aspect, the present invention also comprises a fuel system for a vehicle comprising the fuel injection apparatus as above, and further comprising a first fuel source and a second fuel source.

The fuel system may further comprise a jet pump or venturi which is connected to the intermediate fuel gallery; wherein any leakage fuel collected in the intermediate gallery is drawn out to a cyclone separator, wherein any leakage of second fuel is returned to the second fuel source, and any leakage of first fuel is fumigated into a turbocharger inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional schematic representation of an injection system in accordance with the present invention;

Figures 2 and 3 are partial detailed cross-sectional views of the injection system of Figure 1; and

Figure 4 is a schematic representation of the bypass valve and shuttle piston valve of Figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is described below in relation to the orientation of the figures. Terms such as upper, lower, above, below, top, bottom, horizontal and vertical are not intended to be limiting.

Referring to the figures, the present invention comprises a common rail injection apparatus 100, for a fuel system for a vehicle. The apparatus 100 comprised an injector 2, the injector 2 comprising a nozzle body 4, a first, outer needle 6, and a second, inner needle 8, wherein the inner needle 8 is arranged within a bore 14 of the outer needle 6, such that the inner and outer needles 6, 8 are arranged concentrically with one another.

As explained in greater detail below, the outer needle 6 controls a flow of first fuel, and the inner needle 8 controls a flow of a second fuel.

The first fuel is a low reactivity gaseous fuel, and is supplied from a first fuel gallery 10. The first fuel gallery 10 is supplied with the first fuel from a first fuel source 32, via a first fuel supply channel 34.

The second fuel is of a higher reactivity relative to the first fuel. The second fuel could be, for example, diesel or DME. The second fuel is supplied from a second fuel gallery 12, which in turn is supplied from a second fuel source 42, and enters the injector 2 in a second fuel supply channel 44.

The inner needle 8 comprises a main shaft 20, and towards the top of the inner needle 8, an increased diameter section 22. The increased diameter section 22 of the inner needle 8 is guided within a guide portion 16 of the bore 14 of the outer needle 6 wherein the guide portion 22 has a bore diameter matching that of section 22.

The outer needle 6 is provided with axial drillings 18 in the vicinity of the second fuel gallery 12. The drillings 18 provide fluid communication between the second fuel gallery 12 and an inner needle seat 52, provided inside and towards a lower end of the outer needle 6, via an inner annular passage 30 provided between the outer and inner needles 6, 8.

Fluid communication is provided between the first fuel gallery 10 and an outer needle seat 54, via an outer annular passage 28 provided between the outer needle 6 and the nozzle body 4.

The increased diameter section 22 of the inner needle 8 projects into a control chamber 50 which is normally pressurised at rail pressure from a common rail pump (not shown), and thus the inner needle 8 is loaded down onto the inner needle seat 52, and therefore the outer needle 6 is also loaded onto the cooperating outer needle seat 54, provided by annular surface within and at a lower end of the nozzle body 4. A piston shuttle valve 84 is provided, through which second fuel is supplied to the injector 2, when the injection apparatus 100 is run in either a first or a second operational mode, as explained in greater detail below.

In the first operational mode (dual fuel mode), both fuels are used in an injection event, the second, higher reactivity fuel being used as a pilot injection source. In the second operational mode, the injection apparatus 100 is run solely on the second, higher reactivity fuel.

In the first operational mode, wherein the second fuel is used as a pilot injection source, a flow of the second fuel from the second fuel source 42, is supplied at a rail pressure (for example, approximately 400 bar), and enters the injector 2 via a second fuel inlet 74. The second fuel inlet 74 subsequently splits the flow of the second fuel between a first channel 76 and a second channel 78.

The first channel 76 communicates with the control chamber 50, via a control valve 82; second fuel in control chamber thereby becomes pressurised. The pressure of the second fuel within the control chamber 50 urges the inner needle 8 into a closed position, wherein it is in contact with the inner needle seat 52.

The second channel 78 communicates with and supplies second fuel from the inlet 74 to a spring-biased pilot shuttle piston 84.

On initiation of an injection event, an actuator 102 (shown schematically in Figure 1) is actuated to switch the control valve 82, thereby causing the control chamber 50 to depressurise. Fuel pressure acting on a differential area, formed by a shoulder at a junction of the main shaft 20 of the inner needle 8 and the increased diameter section 22, provides an upwardly urging force on the inner needle; when the control chamber 50 is pressurised, this force is overcome, however when the control chamber 50 depressurises, the upward force on the differential causes the inner needle 8 to move upwardly, into the control chamber 50. The inner needle 8 thereby opens, i.e. lifts from the inner needle seat 52.

For the duration of the fixed stroke of the pilot shuttle piston 84, the inner needle 8 is open, i.e. second fuel in the inner annular passage 30 is able to pass the seat 52 of the inner needle 8, and a pilot injection 92 of second fuel is injected from the injector 2 to a combustion chamber (not shown), via one or more second fuel spray holes 96.

During the fixed stroke of the pilot shuttle piston 84, second fuel at rail pressure within the inner annular passage 30 continues to maintain the outer needle 6 in a closed position, i.e. wherein the outer needle 6 is in contact with the outer needle seat 54.

Once the pilot fuel quantity (as determined by the stroke of the pilot shuttle piston 84) has been exhausted, and the pressure of second fuel in the inner annular passage 30 acting on the outer needle 6 therefore reduces. The outer needle 6 is then free to open under the action of first fuel pressure of, for example, approximately 250 bar, acting on a outer needle differential area 88 towards the bottom of the outer needle 6, i.e. to lift from the outer needle seat 54, and an injection 94 of the first fuel from the injector 2 to the combustion chamber, via one or more first fuel spray holes 98, commences.

Depending upon factors such as the choice of pilot fuel used, and upon the temperature of the combustion chamber, there will be differences in the ignition delay which must be accommodated. The second, pilot fuel is selected to be sufficiently responsive such that a multi-pulse point pilot will be available, so that a situation in which a large volume of the gaseous fuel is injected during the pilot ignition delay leading to high rates of pressure change (DP/DT), can be overcome.

After injection of the first and second fuels, to end an injection event, the control valve 82 re-pressurises the control chamber 50, so that the inner needle 8 serves to close both needles 6, 8. The pilot shuttle piston 84 comprises a calibrated orifice 62 (indicated on Figure 4), which allows pilot fuel to pass through at calibrated rate from the rail. The calibrated rate is selected to be adequate to pressurise the injector 2 between injections, but low enough that it does not fully re-pressurises the injector 2 during an injection event (which would have the effect of terminating the injection of first fuel).

An intermediate fuel gallery 70 located between the first fuel gallery 10 and the second fuel gallery 12. The intermediate fuel gallery 70 is positioned to capture leakage of either first fuel from the first fuel gallery 10, and/or leakage of second fuel from the second fuel gallery 12.

The intermediate fuel gallery 70 can be connected to a jet pump or venturi (not shown in the figures), and is therefore configured to be under a constant depression. Any leakage fuel collected in the intermediate gallery 70 can be drawn out to a cyclone separator (not shown in the figures), where the leakage of second fuel is returned to the second fuel tank / second fuel source 42, and any small leakage amount of the gaseous first fuel can be fumigated into a turbocharger inlet (not shown in the figures).

When the injection apparatus 100 is operating in the first operational mode, i.e. a dual-fuel operational mode, a bypass valve 86 comprising a bias spring 80 and being provided in parallel with the pilot shuttle piston 84, is not operational, i.e. the bypass valve 86 remains closed.

It may be required for the injection apparatus 100 to run in a second operational mode, wherein the injector runs on the second fuel alone (e.g. in a diesel-only operation where rail pressure would be much higher, e.g. approaching 2000 bar). The second operational mode may be necessary, for example, if the supply of the first, gaseous fuel has been depleted.

In the second operational mode, the bypass valve 86 is operational.

To enable the injection apparatus 100 to run on the second fuel alone, the rail pressure is increased to a value which is sufficient to open the bypass valve 86 against its bias spring 80, so that the nozzle 4 has full flow access to the second fuel being supplied from the rail. In this operational mode, the injection apparatus 100 behaves as a conventional common rail injector apparatus. A suitable bypass valve 86 could be a differential-area type, such that a high pressure is required to open the valve 86, however a lower pressure will maintain the valve 86 in an open position.

The injection apparatus of the present invention comprises a concentric valve arrangement for direct in-cylinder injection of two different fuels, such as gas and diesel fuel. The dual-fuel application of the present invention enables diffusion combustion, and gas knock is obviated. As a result, high BMEP can be developed and thus a similar power rating on NG (with diesel pilot) is available from the engine, as with diesel fuel alone.

The present invention is a common rail based system, as opposed to the currently available unit injection based system. Furthermore, the present invention requires only one actuator to regulate both diesel and gaseous fuel, representing a cost and complexity saving compared to prior art systems requiring two actuators.

REFERENCES injector 2 nozzle body 4 first, outer needle 6 second, inner needle 8 first fuel gallery 10 second fuel gallery 12 outer needle bore 14 outer needle bore guide portion 16 inner needle main shaft 20 inner needle increased diameter section 22 outer annular passage 28 inner annular passage 30 first fuel source 32 first fuel supply channel 34 second fuel source 42 second fuel supply channel 44 control chamber 50 inner needle seat 52 outer needle seat 54 nozzle body lower end 60 pilot shuttle piston calibrated orifice 62 intermediate fuel gallery 70 second fuel inlet 74 second fuel inlet first channel 76 second fuel inlet second channel 78 bypass valve bias spring 80 control valve 82 pilot shuttle piston 84 bypass valve 86 inner needle differential area 88 outer needle differential area 90 pilot injection of second fuel 92 first fuel injection 94 second fuel spray holes 96 first fuel spray holes 98 common rail injector apparatus 100 actuator 102

Claims

1. A fuel injector (2) for injection of a first fuel and second fuel, the injector (2) comprising a nozzle body (4), an outer needle (6), and an inner needle (8); wherein the inner needle (8) is arranged within a bore (14) of the outer needle (6), and the inner and outer needles (6, 8) are arranged concentrically with one another; wherein in use of the injector, the outer needle (6) controls a flow of first fuel from a first fuel gallery (10), via an outer passage (28) provided between the outer needle (6) and the nozzle body (4), and an outer needle seat (54), to one or more second fuel spray holes (96); and wherein the inner needle (8) controls a flow of a second fuel from a second fuel gallery (12), via an inner passage (30) provided between the inner needle (8) and the outer needle (6) and an inner needle seat (52), to one or more first fuel spray holes (98); wherein the injector further comprises a control valve (82), wherein a pressure of second fuel within the control chamber (50) is varied by a control valve (82), thereby to selectively open the inner needle (8) by moving the inner needle (8) away from the inner needle seat (52), and the outer needle (6) by moving the outer needle (6) away from the outer needle seat (54); wherein one actuator (102) is operable to control the control valve (82) and thereby to selectively open the inner needle (8) and the outer needle (6).

2. An injector (2) as claimed in claim 1 wherein the injector (2) is operable to effect an injection event in either a first operational mode or a second operational mode; wherein in the first operational mode, the second fuel is injected through the or all second fuel spray holes (96) as a pilot fuel, and the first fuel is injected through the or all first fuel spray holes (98) as a main fuel; and wherein in the second operational mode, the injector (2) operates injects only the second fuel as a main fuel.

3. An injector (2) as claimed in claim 1 or claim 2, further comprising an intermediate fuel gallery (70) located between the first fuel gallery (10) and the second fuel gallery (12), wherein in use of the injector (2), the intermediate fuel gallery (70) captures leakage of either first fuel from the first fuel gallery (10), and/or leakage of second fuel from the second fuel gallery (12).

4. An injector (2) as claimed in any one of the preceding claims wherein the first fuel is gaseous, and wherein the second fuel is diesel or DME.

5. Fuel injection apparatus (100), comprising an injector (2) as claimed in claim 1, and further comprising a pilot shuttle piston (84) to control a flow of second fuel into the second fuel gallery (12) from a second fuel inlet (74).

6. Fuel injection apparatus (100) as claimed in claim 5, further comprising a bypass valve (86) arranged in parallel with the pilot shuttle piston (84) wherein, in use of the injector (2), in the first operational mode, the bypass valve (86) is closed, and in the second operational mode, the bypass valve (86) is open.

7. A fuel system for a vehicle comprising the fuel injection apparatus (100) of claim 4, and further comprising a first fuel source (32) and a second fuel source (42).

8. A fuel system as claimed in claim 7, further comprising a jet pump or venturi which is connected to the intermediate fuel gallery (70); wherein any leakage fuel collected in the intermediate gallery (70) is drawn out to a cyclone separator, wherein any leakage of second fuel is returned to the second fuel source (42), and any leakage of first fuel is fumigated into a turbocharger inlet.