AU751916B2 - Pressure balanced gas injection valve - Google Patents

Description

WO 98/26168 PCT/AU97/00842 PRESSURE BALANCED GAS INJECTION VALVE Field of the invention The present invention relates generally to a valve, especially but not exclusively suitable for use as a gas valve, and to a gas injection system incorporating the valve. Such a system has application to internal combustion engines such as may be used e.g. for motor vehicles, generators, pumps, air conditioning and compressors.

Background of the invention Modern petrol engines with electronic multi-point fuel injection systems operate with relatively lean mixtures, particularly during cruise and deceleration. Liquid petroleum gas (LPG) and compressed natural gas (CNG) engine systems widely in use today are of carburettor design, which does not give even distribution of gas to each cylinder of multi-cylinder engines.

Because of this, such engines cannot operate on relatively lean mixtures to the same extent as petrol engines without causing problems, including hard starting, backfiring when starting, and backfiring when travelling in cruise mode or on deceleration when the throttle is opened suddenly. This is caused by the presence of gas in the inlet manifold. Some of these problems are presently overcome by having the engine start using a petrol injection system. Whereas the others of these problems are presently overcome by running a richer mixture during cruise mode and during deceleration. However. this approach to one problem creates other difficultieshigher emissions and poor fuel economy. Moreover, because carburettor systems have a venturi or mixing valve, the volumetric efficiency of the engine is affected when operating on gas as well as petrol, reducing maximum power.

One approach to addressing these problems with LPG (described in Australian patent application 90192/91) is to inject liquid phase LPG through an injection system similar to that used with petrol, in which a high pressure pump is mounted in the gas tank. Very high pressures are used to prevent vaporisation in the fuel rail and injectors in the engine under hot conditions. This type of system has the disadvantage of very high pressure build up in the LPG tank such that refilling the tank is impossible unless the tank is cooled or vented.

Another approach, for CNG, is to substitute the conventional carburettor or mixing valve configuration with a gas metering valve. However, existing gas valve designs have proven unreliable for this purpose. For example, in a prior art electro-magnetic gas injection valve, a valve seat and a valve closure means which engages the seat are both metallic, requiring WO 98/26168 PCT/AU97/00842 2 precision manufacturing for good sealing. Such precision manufacturing can also include complex shapes such as toroidal cuneiform shapes and others. Such a valve usually has a body which includes a valve seat between an inlet and outlet passage and an armature which carries the valve closure means. A high lift distance is imparted to the armature and thus to the valve closure means so as to allow for maximum gas flow. Such high lifting, however, increases noise and wear. Particularly for motor vehicle applications, such noise is a severe disadvantage, and the wear decreases the life of the valve.

To have two metal components creating an effective seal requires fine tolerances on the valve seat and valve closure means. These types of valves can become clogged with residual oil carried in a gaseous fuel such as LPG, and with a dry gas like CNG there is excessive wear through lack of lubrication. The orifice size and the valve seat width are limited because the solenoid has to lift the armature and valve closure means from the valve seat against the pressure differential which exists across the valve closure means and the outlet side of the valve.

The object of the invention, therefore, is to provide an improved valve which may be adapted to serve as a metering valve in a gas injection system, especially for an internal combustion engine.

Summary of the invention The invention provides, in a first aspect, a valve including a body which defines an inlet chamber with an inlet port and an outlet chamber with an outlet port, valve means movably mounted in the body, and means defining at least two separate flow paths between the inlet and outlet chambers, which paths include respective valve seat means at which flow is controlled in tandem by the valve means.

The valve means preferably includes a valve stem supported in the body for operative movement parallel to its longitudinal direction, which stem carries respective seal means engageable with the valve seat means.

The flow paths preferably include respective means that apply static fluid pressure in the inlet chamber to the valve means whereby to apply respective forces which at least partly counterbalance. In one such arrangement, the valve seat means is disposed at ports from the inlet chamber at which the static fluid pressure therein is oppositely directed. In another, one of the flow paths includes a third chamber arranged whereby static fluid pressure therein acts on WO 98/26168 PCT/AU97/00842 3 the valve means to oppose static fluid pressure in the inlet chamber acting on the valve means prior to moving the valve means to allow flow at the respective valve seat means. This flow path may include a passage in the valve stem communicable with the inlet chamber and the third chamber.

Preferably, one or more of the valve seat means are of annular form, defining respective annular flow ports.

In a second aspect, the invention provides, a gas injection system for an internal combustion engine including: a valve according to the first aspect of the invention, the inlet chamber thereof being arranged to receive gas from a storage tank thereof; conduit means to deliver gas from the valve to the engine separately of air for the air/fuel mixture in the engine; and means to control the valve in response to actual or desired engine conditions whereby the valve meters gas delivery to the engine.

Preferably, the system is a multi-point injection system configured for delivering gas separately to each engine cylinder.

The invention further provides a kit of components configurable to form the aforedescribed gas injection system and including the valve, the conduit means and the control means.

Brief description of the drawings An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a gas injection metering valve according to a first embodiment of the invention, incorporating an electromagnetic actuator; Figure 2 is an axial cross section of the valve, shown in its closed condition; Figure 3 is a view similar to Figure 2, but showing the valve in its open condition; Figure 4 is an exploded perspective view of the principal components of the valve; Figure 5 is a side elevational view of the valve stem of the valve; Figure 6 is a view similar to Figure 2 of a second embodiment of valve according to the invention; WO 98/26168 PCT/AU97/00842 4, Figure 7 is an axial cross section of part of a valve according to a further embodiment; Figure 8 is a diagram of a multi-point gas injection system for a six-cylinder internal combustion engine, suitable for use with LPG; Figure 9 is an alternative configuration of an LPG injection system; and Figure 10 is a diagram of an alternative single point LPG injection system.

Detailed description of the embodiments The illustrated valve 2 includes a main valve body 4 housing the principal operational components of the valve, and an attached electromagnetic actuator 5. Valve body 4 is typically formed in aluminium and has a generally cylindrical blind bore which is multiply counterbored to define three principal diameters 62,64,66. The diameter 66 at the open end of the bore defines an inlet chamber 65 with a radial inlet port 54, while the intermediate diameter 64 defines an outlet chamber 67 with a radial outlet port 56. Valve means in the form of a generally tubular valve stem 6 is aligned coaxially with diameters 62,64 and 66, extending through chambers 67,65 from adjacent the end 116 of the bore within valve body 2, and is formed in a ferromagnetic material whereby it is also the armature of the electromagnetic actuator. To this end, the valve stem 6 projects from the valve body 2 into the actuator 5 in an arrangement which will be further described subsequently. The valve stem 6 is moved to open the valve by energising actuator Two separate flow paths are defined between inlet chamber 65 and outlet chamber 67. The first is a direct annular passage 71 about the valve stem 6. Passage 71 is ported by the cooperation of a stainless steel separation ring 78 defining a valve seat 84 with a sealing ring 30 carried by valve stem 6. The other flow path is via the interior 18 of hollow tubular valve stem 6 and an annular third chamber 70 defined by a valve insert 68. Interior passage 18 of valve stem 6 communicates respectively with inlet chamber 65 and third chamber 70 by respective rings of ports 16,14 in the valve stem 6. There may be, four ports in each ring.

Chamber 70 is ported to outlet chamber 67 between a valve seat 69, at the end of insert 68 about the rim of chamber 70, and a sealing ring 28 retained on valve stem 6. Sealing rings 28,30 are substantially identical in size, being chamfered profiled rings retained between respective pairs of integral peripheral flanges 20,22 and 24,26 of the valve stem 6. The chamfered annular formation of the seals 28,30 helps to reduce the weight of the seals and yet provides sufficient integrity for performance of the sealing task.

WO 98/26168 PCT/AU97/00842 A suitable material for the seals is known by the generic term FMK, which is a fluoro-carbon rubber or a fluoro-elastomer. Such an elastomer is also designated ASTM D2000 HK, and is currently available under the brand name VitonTM. Any elastomeric material with suitable chemical and or mechanical and or material properties to be in service in high temperature environments related to modem day engines. Such elastomers should be sufficiently chemically resistive to petro-chemicals. Preferably the elastomers chosen also have suitable hardness and wear characteristics to survive for modem day warranty periods, which for motor vehicles is generally 100,000kms.

Preferably the elastomer chosen for the seal has a hardness of some 50 duro to 90 duro and more preferably at the upper ranges of approximately 80 duro to 90 duro. The hardness of a polymer or material such as Viton

T

M is inversely proportional its elasticity and the hardness range described above will provide a relatively elastic seal, which will compensate for any differences in tolerances which result from manufacture, between the valve seats 68 and 84.

Whilst the valve 2 and its components can be machined to close tolerances, the providing of elastic seal members ensures that the tolerances do not have to be close as close tolerance are always hard to reproduce during manufacturing.

Valve insert 68 is typically stainless steel and is an interference press fit in the inner diameter 62 of valve body 2 on shoulder 72. Insert 68 also carries, within an inner groove 74, a split curl bearing 73 which serves as the inner lower) bearing for valve stem 6. A sealing ring may be provided for insert 68 if the interference fit is an insufficient seal.

Separation ring 78 locates on shoulder 76 between intermediate and outer diameters 64,66 of the valve body 2, and includes a peripheral underside rebate 80 to mount an O-ring 82 at the corner of the shoulder to serve as a seal between the inlet chamber 65 and outlet chamber 67.

It will be seen that the arrangement is such that the static pressure in the third chamber communicated from inlet chamber 65 via ports 16, passage 18 and ports 14 acts on flange and an adjacent portion of valve sealing ring 28 in the opposite direction to that of the pressure in inlet chamber 65 on flange 26 and sealing ring 30, whereby the static fluid pressure in the third chamber opposes the action on the valve stem 6 of the static fluid pressure in the inlet chamber, when the valve is closed. This arrangement is effective to reduce the force required to move the valve stem 6 when opening the valve 2 by energising actuator The valve stem 6 is biased to the closed position by a conical compression spring 34 acting between flange 26 on the valve stem 6 and an inner flanged portion 92 of an annular sleeve 86 disposed within the larger counterbored diameter 66 of valve body 4. The assembly of the valve WO 98/26168 PCT/AU97/00842 6.

is maintained by an annular cover plate 98 fixed to the valve body 2 by plural screws 160. The sleeve 86 is of a length to seat between the cover plate and the separation ring 78 so as to compress O-ring 82. A further O-ring 90 is disposed in a groove 88 at the outer cylindrical surface of sleeve 86.

The opening limit of valve stem 6 is defined by a stop ring 40 retained between a further integral external flange 36 of the valve stem 6, and a shoulder 41 at the boundary between a smaller diameter inner portion of the valve stem 6 and a larger diameter outer portion. Stop strikes the inner flange 92 of sleeve 86. It is found that, even where the movement of the valve stem 6 defined at the stop is a relatively small lift, for example of say 0.5mm, the fact that there are two flow paths between the inlet and outlet chambers and that the controlled ports at the valve seats are a relatively large annulus about the valve stem 6, means that the flow is sufficient for engine injection purposes.

Turning now to the detail of the electromagnetic actuator 5. Around a bobbin 121 is coiled nylon encapsulated wire to form a solenoid coil assembly 8. The bobbin 121 is subsequently encapsulated by a casing 120 to seal the nylon encapsulated wire within the bobbin 121 and the casing 120 assembly. The coil assembly 8 is disposed about a central bore 123 in the bobbin 121. In the bore 123 is disposed a stainless steel ferrule 52. Ferrule 52 provides the structural link to the valve body 4 and in turn receives valve stem 6 to about the mid point of the coil, and a pole 48 of ferromagnetic material. At its end within actuator body 120, ferrule 52 has an inward lip 52a about gasket 110 and a cold formed pressing 102 by which it grips the pole. At the valve end, ferrule 52 is out-turned to form an end flange 100 that is retained in a shallow seat defined on inner flange 94 of sleeve 86, being also locked in position by cover plate 98. A further sealing ring 92 retained in groove 96 further seals this connection, and therefore the valve chambers from the exterior.

The outer upper) bearing for valve stem 6 with respect to ferrule 52 is provided by a split curl bearing 51 in groove 50 in the outer surface of stem 6. Split curl bearings 51,73 are formed from thin rod or thin teflon or nylon sheeting and it will be noted that the two bearings are identical to reduce manufacturing inventory. The split curl bearings 51,73 also serve as a nonmetallic spacer to prevent metal-to-metal contact of relatively moving parts. Whilst reduction of friction and wear is highly desirable, so too is reduction of noise.

The actuator assembly further includes a U-shaped coil bracket 105 which is made of a ferromagnetic material. The assembly is maintained by a cover ring 106 and by a split ring 108 which engages a peripheral groove in the protruding head of pole 48.

WO 98/26168 PCT/AU97/00842 7 Interior passage 18 of valve stem 6 is in fact a blind bore extending over almost the whole length of the valve stem 6. At its inner end, a bleed hole 44 communicates this passage with a narrow gap 46 between the facing ends 42,114 of valve stem 6 and pole 48. This spacing provides a narrow air gap, for example in the order of 0.2mm at the open position of the valve, which serves both to minimise hysteresis effects and to prevent direct contact between the valve stem 6 and the pole, thus guarding against noise generation.

Upon energising of the solenoid 8, the pole 48 becomes magnetic with end 114 being one pole of a magnet. The armature/valve stem 6 also becomes magnetic with end 42 being a pole but an opposite magnetic pole to the pole 48. thereby generating a force of attraction between the armature 6 and the pole 48. This force of attraction needs be sufficient to overcome the force of the spring 34 and any friction forces present. This will force the armature 6 to move towards the pole 48 thereby allowing the seals 28 and 30 to lift off from their respective valve seats 69,84 to the position shown in Figure 2.

Upon the armature 6 reaching its limit of travel, which is determined by the stop ring engaging the flange 92 of the annular sleeve 86, the valve 2 will be in its fully opened state.

To achieve the open state, the armature 6 travels approximately 0.5mm. The 0.5mm of travel will also lift the seals 28 and 30 a distance of 0.5mm off from their respective seats. This will create an opening between the seals 30 and 28 and their respective seats allowing gas to pass out of the chamber 70 into the outlet chamber 67 and from the inlet chamber 65 into the outlet chamber 67 and thus out of the outlet 56. The surface area for both ports or openings formed between the valve seats 69 and 84 and the seals 30 and 28 is about 25mm in this embodiment.

At approximately 150 kilopascals of inlet gas pressure, for example, this has been determined to provide sufficient gas flow and volume of gas for engine injection purposes.

To ensure that no restriction is formed in the valve preferably the total surface area of the ports 16 and 14 respectively, is equal to or greater than the surface area of the port or opening formed when the valve seals lift off the valve seats. Whilst there are illustrated 4 ports 16 and four ports 16, there could be any number shape or size providing the total port area is equal to or greater than the surface area of the port or opening formed when the valve seals lift off the valve seats.

When the solenoid 8 is de-energised the armature/valve stem 6 returns the seals 28 and 30 into sealing contact with their respective valve seats by the force generated from return spring 34, as illustrated in Figure 1.

WO 98/26168 PCT/AU97/00842 8 It will be noted that the residual end of the bore formed in valve body 4 and defined by diameter provides a shallow cavity 63 which serves the purpose of allowing for wear of the valve seals 28,30. As the seals, and/or the associated valve seats, wear, there is a gradual increase in the displacement of the valve stem 6 as it moves from the open to the closed position. Wear of this level will effect the operation of the valve, and cause a deterioration in its performance.

The end 12 of valve stem 6 will progressively move towards the base 116 of the cavity 63.

This arrangement allows wear to be detected earlier, preferably prior to the wear significantly damaging the performance of the valve.

While the communication between the interior passage 18 of valve stem 6 and the respective chambers 65,70 is by sets of four ports, it will of course be appreciated that other arrangements are possible. It will be further understood that the third chamber 70 may well be defined by a formation on the valve stem 6, and that, while the successive coaxial and annular arrangement of the chambers 65,67,70 is convenient, a variety of configurations are of course possible.

Figure 6, in which like parts are indicated by like reference numerals presented as a "200" series, illustrates an alternative embodiment. Here, the seals 228,230 and stop ring 240 are of a toroidal or O-ring formation, and the valve insert 268 is secured by a spigot 268a in a bore opening 268b in the end of the valve body 204. Instead of a conical spring, this embodiment has an internal helical compression spring 234 housed within a counterbore of the valve stem 6 and acting against the end of the solenoid pole 248.

Figure 7 illustrates in part a further embodiment in which the inlet chamber 365 is ported directly to both the outlet chamber 367 and the third chamber 370 at the respective seals 330,328. The outlet port 356 is open to chambers 367,370 via stem interior 318 and ports 316,314. In effect, this embodiment is operated in reverse, with the static inlet pressure in chamber 365 acting oppositely on stem 306 at seals 328,330.

In the embodiment of figure 7, the stop ring 340 is located in the sleeve 386, with the stop flange 392, mounted on the valve stem 306. This arrangement limits the travel or movement of the valve stem 306 when the valve stem 306 is moved to the open condition, in same way as stop ring 40 on valve stem 6 interacts with stop surface 92 in the embodiment of figure 2.

If desired the stop rings 40 and 240 may be provided on the sleeves 86 and 286 respectively in figures 2 and 6 rather than on the respective valve stems 6 or 206 themselves.

The illustrated valve may be utilised in a multi-point gas injection system 170 illustrated diagrammatically in Figure 8. The system 170 includes a gas tank 140 to hold liquid phase LPG t WO 98/26168 PCT/AU97/00842 9 at a pressure typically of the order of 700kPa, depending on the ambient temperature. The gas tank 140 is connected via a pipe 144 to a converter/pressure regulator 148 which is also supplied with engine coolant. Safety shut-off valves 142,146 are respectively provided in pipe 144 close to the tank and to the regulator. In the regulator 148, the liquid phase LPG from tank 140 is converted to gas and the pressure regulated so that the gas in the outlet line 150 is at approximately 150kPa or other appropriate pressure above the inlet manifold pressure of engine 168. This is preferably achieved by the use of a rising rate pressure regulator 148 vented to the engine inlet manifold 169 by a conduit 149 instead of to atmosphere. Line 150 delivers the gas to the inlet port 54 of the gas injection metering valve 2 of one of the forms illustrated in Figures 1 to 7. A gas safety shut-off valve 152 is located upstream of the metering valve 2. Gas passes to a distribution manifold 158 under the control of a digital signal from an LPG electronic control unit (ECU) 154 which in turn receives a digital signal from a petrol ECU 156 for controlling valve 2 in response to actual or desired engine conditions. LPG ECU 154 also controls safety shut-off valves 142,146,152, and the shut-off of the petrol injectors. From manifold 158, gas is delivered via individual gas lines 160 with respective metering orifices 162 and non-return diaphragm valves 164 to respective inlet ports for the cylinders of engine 168.

Figure 9 illustrates a modified gas injection system in which, instead of a single metering valve ahead of the manifold, each cylinder delivery line 160' has a gas injection metering valve 2' as well as metering orifices 162' and non-return diaphragm valves 164'.

A gas injection system for compressed natural gas (CNG) is not illustrated but would typically be generally similar to the system shown in Figure 8 or 9. In this case, however, the tank would hold compressed natural gas at approximately 20Mpa. Instead of a single regulator 148, there would be a first stage regulator in which the pressure was reduced to approximately 700kPa. The gas at this pressure then proceeds to a second stage pressure regulator which is preferably a rising rate regulator in which the regulator is vented to the engine inlet manifold rather than to atmosphere.

Figure 10 illustrates a single point injection system for LPG for injection at 180 below the throttle valve 167 of engine 168", preferably using a spray bar for injection. A similar alternative is of course available for a CNG injection system.

The invention has provided, in each of the preferred embodiments of Figures 1 to 7, a gas injection valve with features that make it highly suitable for use as a fast response gas metering valve, including dual porting of a relatively large cross-section allowing a very small lift and the opposing pressure configuration to reduce the force initially necessary to open the valve.

WO 98/26168 PCT/AU97/00842 The fast response can be further optimised by using a low inductance coil, i.e. low turns and high current draw, combined with a lightweight armature with a small residual air gap to minimise hysteresis effects. Another factor contributing to a high speed of operation is the light spring.

The advent of a valve satisfactory for this application, such as one of the above embodiments, renders practicable a multi-point gas injection system for an LPG or CNG fuelled internal combustion engine, along the lines of the systems depicted in Figures 8 to 10. A multi-point gas injection system, with such a valve of the above described above, gives equal distribution of gas to all cylinders of a multi-cylinder engine with improved gas/air mixing. Because the gas is injected into the inlet ports and there is no gas in the inlet manifold, the engine can be started on gas, or when the throttle is opened suddenly during cruise mode or deceleration, with no backfiring problem, even though the engine is running on a leaner mixture.

As the engine can operate on a leaner mixture at all times, better fuel economy and lower emissions result. As there is no venturi or mixing valve in the inlet duct, greater volumetric efficiency is achieved, giving greater power.

As the system uses a digital valve, a petrol ECU of well established and reliable form, and all its built-in sophistication, is used to control fuel flow or metering, using an interface to improve fuel economy and emissions. The ignition advance curve can be optimised for gas injection to give further improvements of economy and power.

The valves of figures 2, 6 and 7 should in principle be able to be operated by reversing the connections previously described so as to produce reverse flow through the valve from that indicated in the above description. However, it has been found that in tests conducted on the valves, that the valves will or have a tendency to leak under reverse flow conditions. Whilst this result is thought to be a function of the relationship between tolerances of the appropriate parts, it is not known if this is the only reason.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

The forgoing describes embodiments of the present invention, and modifications, obvious to those skilled in the art, can be made thereto, without departing from the scope of the present invention.

Claims (13)

1. A valve including: A body which defines an inlet chamber with an inlet port and an outlet chamber with an outlet port; Valve stem means moveably mounted in the body; and means defining at least two separate flow paths between said inlet and outlet chambers, one said flow path includes a passage in said valve stem communicable with said inlet chamber and said third chamber and which said paths include respective valve seat means at which flow is controlled in tandem by the valve means.

2. A valve according to claim 1 wherein said valve means includes a valve stem supported in said body for operative movement parallel to its longitudinal direction, which stem carries respective seal means engageable with the valve seat means.

3. A valve according to claim 1 wherein said flow paths include respective means that apply static fluid pressure in the inlet chamber to the valve means whereby to apply respective forces which at least partly counterbalance. oooe

4. A valve according to claim 1 wherein one of said flow paths includes 20 a third chamber arranged whereby static fluid pressure therein acts on the valve means to oppose static fluid pressure in the inlet chamber acting on the valve means prior to moving the valve means to allow said flow at said respective valve seat means. A valve according to claim 1 wherein said valve stem is generally tubular to provide said passage and has one or more ports communicating said passage with said inlet chamber and said third chamber.

6. A valve according to claim 1 wherein said body includes a body segment which defines said third chamber about said valve stem and further mounts or provides the valve seat means of said one flow path, and wherein said valve stem includes oppositely facing surface 51856/98 12 portions respectively exposed to pressure in the inlet and third chambers.

7. A valve according to claim 1 wherein said third chamber opens to said outlet chamber at its respective valve seat means.

8. A valve according to claim 1 wherein said inlet chamber and said outlet chamber are disposed about said valve stem, and said body further defines an annular passage at which the valve seat means of the other flow path is disposed.

9. A valve according to any one of the previous claims further including an electromagnetic actuator for operating said valve means, wherein said valve stems is an armature of said actuator. A valve according to claim 9 wherein said actuator includes a solenoid coil about a chamber which mounts a magnetically susceptible pole member and slidably receives said armature, and means defining an air gap between the pole and armature to minimize hysteresis effects and to prevent direct contact between the armature and the pole. A valve according to any one of the previous claims further including .spring means to bias the valve means to shut off flow at the respective :valve seat means, and wherein the third chamber is arranged so that fluid pressure therein substantially counterbalances fluid pressure in S the inlet chamber acting on the valve means when said flow at the S* respective valve seat means is shut off.

12. A valve according to any one of the preceding claims, wherein one or more of any valve seat means are of annular form, defining respective annular flow ports. 51856/98 13

13. A valve as claimed in any one of the preceding claims, wherein said valve means includes a seal constructed from chamfered profile rings.

14. A gas injection system for an internal combustion engine including: a valve according to any preceding claim, said inlet chamber thereof being arranged to receive gas from a storage tank thereof; conduit means to deliver gas from the valve to the engine separately of air for an air/fuel mixture required in the engine; and means to control the valve in response to actual or desired engine conditions whereby the valve meters gas delivery to the engine.

15. A gas injection system according to claim 14 wherein said system is a multi-point injection system configured for delivering gas separately to each engine cylinder.

16. A kit of components configurable to form a gas injection system according to claim 14 or 15, wherein said components include said valve, said conduit means and said control means. S" oS o r