Patent Description:
Liquid fuels such as diesel and, more recently, gaseous fuels have been used to fuel vehicle engines for many years now. Such gaseous fuels include, among others, natural gas, propane, hydrogen, methane, butane, ethane or mixtures thereof. The engine fuel injection system generally comprises a plurality of fuel injectors fluidly connected to a fuel supply conduit. Generally, in the case of a direct injection system, each fuel injector is located in a bore formed in the cylinder head of the engine and the fuel supply conduit, commonly referred to as the fuel rail, can be either located in a bore formed in the cylinder head or can be an external pipe which is fluidly connected to each of the injectors through bores provided in the cylinder head. Each injector operates as a fuel valve which opens and closes to inject fuel into the combustion chamber of each engine cylinder and respectively, to stop fuel flow into the combustion chamber. Such opening and closing of the fuel injectors generates pressure pulsations at the injector fuel inlet which cannot be dampened during the time the injector is closed because of the short interval between the injection events. Such pressure pulsations can generate a fuel pressure increase or a pressure drop at the injector nozzle which affects the amount of fuel injected into the combustion chamber during an injection event. Such pressure pulsations can also be transmitted from one injector back to the fuel rail and through the rail to the next fuel injector of the engine. Furthermore, if the pressure in the fuel rail fluctuates the pressure pulsations in the rail can be transmitted to the inlet of the fuel injector and further to the injector nozzle.

In the past, the problem described above has been addressed by incorporating a bush in the fuel rail which supplies fuel to an injector of diesel engine, as described for example in <CIT>, such bush providing an orifice which restricts fuel flow from the fuel rail to the injector, thereby dampening the pressure pulsations in the fuel passage which connects the fuel rail to the fuel injector. Several other similar solutions have been disclosed in the prior art to address the problem of pressure pulsations in conventional liquid fuels such as diesel fuel or gasoline supplied to an injector of an internal combustion engine. In gaseous fuels, the pressure pulsations caused by the opening and closing of the injectors behave differently than in liquid fuels, because of the physical composition of the gaseous fuel which tends to prolong the pressure oscillations.

In other variants, at least one dampening element is disposed in an opening of the fuel injector through which fuel flows from the fuel rail such as described in <CIT>.

The design solutions presented in the prior art do not consider the problem of determining the location of the pulsation dampening orifice relative to the injector nozzle for controlling the dampening of the pressure pulsations between the fuel rail and the fuel injector and for controlling the fuel pressure within the nozzle chamber before fuel is injected into the combustion chamber. This problem becomes even more relevant for dual fuel engines which inject a gaseous fuel and a liquid fuel directly into the combustion chamber through a dual fuel injection valve which comprises a dual needle assembly having concentric needles for separately and independently injecting the liquid fuel and the gaseous fuel, as described for example in applicant's <CIT>. In such fuel injectors a predetermined bias has to be maintained between the liquid fuel pressure and the gaseous fuel pressure within the body of the injector, with the liquid fuel pressure being higher than the gaseous fuel pressure, to prevent gaseous fuel leakage into the liquid fuel. Gaseous fuel, due to its physical state, can more easily leak past the sealing arrangements within the fuel injector and can leak into the liquid fuel or can compromise the hydraulic function of the valve actuators if it leaks from the gaseous fuel passage into the hydraulic fluid control chamber inside the fuel injector.

<CIT> discloses an accumulator fuel injection device.

Accordingly there is a need for a solution for a better control of dampening the pressure pulsations at the fuel injector nozzle while controlling the pressure drop between the fuel rail and the fuel injector nozzle to prevent leakage and to control the fuel pressure at the injector nozzle before it is injected into the combustion chamber.

A first aspect of the present invention provides an improved fuel supply system for a gaseous fuelled internal combustion engine as recited in claim <NUM>.

A second aspect of the present invention provides a fuel supply method for a gaseous fueled internal combustion engine as recited in claim <NUM>.

<FIG>, schematically illustrates the present fuel supply system for a gaseous fuelled internal combustion engine having an external gaseous supply conduit <NUM>, also known as a gaseous fuel rail. The fuel supply system comprises a fuel injector <NUM> for injecting gaseous fuel into the combustion chamber <NUM> of engine cylinder <NUM>. Fuel injector <NUM> has a body <NUM> which comprises nozzle <NUM> provided with a plurality of injection holes <NUM> through which fuel is injected into combustion chamber <NUM>, an inlet <NUM> which is fluidly connected to the gaseous fuel supply conduit and an internal fuel passage <NUM> for fluidly connecting fuel inlet <NUM> to nozzle chamber <NUM> within the fuel injector body. The fuel injector further comprises needle <NUM> which can be lifted from its seat <NUM> to open the fuel injector and allow fuel to be injected from nozzle chamber <NUM> through fuel injection holes <NUM> into combustion chamber <NUM>. When the injector is closed, needle <NUM> is seated in its seat <NUM> forming an injection valve seal that stops the fuel injection. As illustrated in <FIG> needle <NUM> can be actuated by a hydraulic actuator, more specifically needle <NUM> moves within needle bore <NUM> inside body <NUM> of the fuel injector being actuated by the hydraulic fluid pressure in hydraulic control chamber <NUM> of the hydraulic actuator which is controlled by the engine controller. To avoid any gaseous fuel leakage from nozzle chamber <NUM> to hydraulic control chamber <NUM> fluid seals <NUM> are provided between the needle and the needle bore in the body of the injector. Sealing fluid is supplied to the seals through sealing fluid passage <NUM>. Furthermore, to prevent any further leakage, needle <NUM> is match fit with needle bore <NUM> between hydraulic control chamber <NUM> and nozzle chamber <NUM>.

In the embodiment illustrated in <FIG>, the fuel injector is mounted in the cylinder head <NUM> and fuel is injected directly into combustion chamber <NUM>. Gaseous fuel is supplied to fuel injector <NUM> from gaseous fuel supply conduit <NUM> which is mounted on the cylinder head <NUM> and which comprises a body <NUM> and a gaseous fuel supply passage <NUM> through which fuel flows. Fuel is supplied from the gaseous fuel supply passage <NUM> of the gaseous fuel supply conduit through restricted fluid flow passage150 (that is, the dampening orifice) and gaseous fuel flow passage <NUM> to nozzle chamber <NUM>. Gaseous fuel flow passage <NUM> comprises a first fuel flow passage <NUM> within cylinder head <NUM> through which fuel is supplied from the gaseous fuel supply conduit <NUM> to injector inlet <NUM> and internal fuel passage <NUM> within the body of the injector through which fuel is supplied from injector inlet <NUM> to nozzle chamber <NUM>. Gaseous fuel flow passage <NUM> fluidly connects restricted fluid flow passage <NUM> to nozzle chamber <NUM>.

When gaseous fuel is supplied from gaseous fuel supply conduit <NUM> to nozzle chamber <NUM> the pressure pulsations from the gaseous fuel supply conduit can be transmitted to the fuel injector inlet and downstream to nozzle chamber <NUM>. Similarly the pressure pulsations in nozzle chamber <NUM> caused by the opening and closing of the injector can be transmitted back to the gaseous fuel supply conduit amplifying the pulsations therein. Such pressure pulsations within the gaseous fuel flow passage and within the nozzle chamber can cause variations in the amount of fuel injected in the combustion chamber during an injection event, more specifically within a predetermined injection pulse width which is commanded by the engine controller according to the engine operating condition. Furthermore, such pressure pulsations can cause the pressure in nozzle chamber <NUM> to become higher than the pressure of the sealing fluid or of the hydraulic fluid in hydraulic control chamber <NUM>. In such situations, gaseous fuel can leak through the match fit into the sealing fluid and/or into the hydraulic fluid which is not desirable. There is therefore a need to limit the magnitude of the pressure pulsations within nozzle chamber <NUM> within predetermined limits.

In the present disclosure, restricted fluid flow passage <NUM> and the volume of first fuel flow passage <NUM> between restricted fluid flow passage <NUM> and fuel injector inlet <NUM> are dimensioned to reduce the pressure pulsations within gaseous fuel flow passage <NUM> and implicitly within nozzle chamber <NUM>. The volume of the first fuel flow passage <NUM> and implicitly the volume of the gaseous fuel flow passage <NUM> which comprises the first fuel flow passage <NUM> are calculated to reduce the pressure pulsations at the injector inlet and within the nozzle chamber and the fluid flow area of the restricted fluid flow passage <NUM> is selected as a function of the predetermined (calculated) volume of the first fuel flow passage <NUM> and implicitly as a function of the volume of entire gaseous fuel flow passage <NUM> to maintain the pressure pulsations with gaseous fuel flow passage <NUM> and within nozzle chamber <NUM> within a predetermined pressure range while maintaining the gaseous fuel pressure within the nozzle chamber above a predetermined threshold that is needed to inject a commanded amount of gaseous fuel within a predetermined injection pulse width for each engine operating condition.

In general, injection accuracy is improved by reducing the range of inlet pressure variation that a fuel injector sees at the time of injection. Injector inlet pressure is not constant due to the creation of pressure waves within the fuel injector (due to the pulsed nature of fuel injection) that get transmitted to the fuel rail. A fuel injector creates a lower pressure wave at the injection valve when opening and a high pressure wave when closing. These pressure waves originate at the injection valve and travel upstream initially. To achieve a reduction in the range of inlet pressure variation an injector sees, it is useful to isolate the fuel injectors from the fuel rail such that the pressure waves generated during the injection events do not get transmitted to the fuel rail and thus to other injectors. There is a limit to this isolation in regard to the size of the orifice (that is, the size of the restricted fluid flow passage). The orifice cannot be too small, since this will reduce the flow through the injectors during the injection event. The location of the orifice relative to the injection valve, and more particularly to the injection valve seal, is also important. The orifice size will have no impact on the flow through the injector during the injection event when the orifice is far enough away from the injection valve seal such that there is no fuel flow through the orifice while the injection valve is opened, that is during the injection event. The orifice can be placed at a distance such that fuel flow is just about to begin therethrough as the injector is closed. Then the only effect from the size of the orifice is if the orifice is too small that it cannot "re-fill" the volume between the orifice and the injection valve seal in between injection events. In an exemplary embodiment restricted fluid flow passage <NUM> is located a predetermined distance away from the injection valve seal of fuel injector <NUM> such that there is no flow through passage <NUM> during injection events. Flow through restricted fluid flow passage <NUM> begins when the low pressure wave created upon opening the injection valve reaches the passage. The pressure waves between passage <NUM> and the injection valve travel at the speed of sound, and the predetermined distance can be at least equal to the value calculated according to Equation <NUM>, where D is the predetermined distance (measured in meters), SOS is the speed of sound (measured in meters per second) through the gaseous fuel between the injection valve and passage <NUM>, and PW is the pulse width of the injection event (measured in seconds), also referred to as the opened time herein.

The speed of sound through gaseous fuel is directly related to gaseous fuel pressure and increases as the pressure increases. In an exemplary embodiment the predetermined distance is calculated according to Equation <NUM> when gaseous fuel pressure is equal to the maximum gaseous fuel pressure and the pulse width is equal to the maximum pulse width employed by engine <NUM>, which will thereby effectively remove the effect of the orifice during injection events under this and any other engine operating condition. Typically, the maximum gaseous fuel pressure and the maximum pulse width are employed during maximum engine load conditions.

In another exemplary embodiment, the predetermined distance can be at least equal to the distance calculated according to Equation <NUM> below. When the low pressure wave (a trough) created during an injection event reaches restricted fluid flow passage <NUM> it gets reflected as a high pressure wave (a crest) that begins travelling back towards the injection valve. As long as the injection valve is closed before the crest wave reaches the starting position of the low pressure wave front (in the vicinity of the injection valve seal) then the amount of fuel injected will not substantially be affected by the pressure wave within the fuel injector, even though gaseous fuel flow has begun through restricted fluid flow passage <NUM> due to the low pressure wave creating as the injection valve was opened. Similar to Equation <NUM>, Equation <NUM> can be calculated using parametric values for the variables determined under maximum engine load conditions.

<FIG> is a schematic representation of second embodiment of the present fuel supply system for a gaseous fuelled internal combustion engine. This embodiment has many components that are equivalent to like components of the embodiment presented in <FIG> and like components are identified by like reference numbers. In this disclosure like-numbered components function in substantially the same way in each embodiment. Accordingly if like components have already been described with respect to the first embodiment illustrated in <FIG>, the purpose and the function of such components will not be repeated here in connection with <FIG>.

The difference between the embodiment illustrated in <FIG> and the embodiment illustrated in <FIG> is that in this second embodiment the restricted fluid flow passage is not integrated within the body of the fuel supply conduit. Instead, a separate body <NUM> is placed within injector body <NUM>, between gaseous fuel supply conduit <NUM> and nozzle chamber <NUM> and body <NUM> is provided with a restricted fluid flow passage <NUM>. The gaseous fuel flow passage <NUM> fluidly connecting restricted fluid flow passage <NUM> to nozzle chamber <NUM> in this embodiment is a portion of internal fuel passage <NUM> which is provided with an enlarged portion <NUM>. The volume of gaseous fuel flow passage <NUM> between the restricted fluid flow passage and the nozzle chamber is calculated to reduce the pressure pulsations within the nozzle chamber <NUM>. The fluid flow area of restricted fluid flow passage <NUM> is selected as a function of the volume of this gaseous fuel flow passage to maintain pressure pulsations within internal fuel passage <NUM> and nozzle chamber <NUM> within a predetermined pressure range while maintaining gaseous fuel pressure within nozzle chamber above a predetermined threshold that is needed to inject a commanded amount of gaseous fuel within a predetermined injection pulse width for each engine operating condition. In some embodiments, body <NUM> can be integrated in the injector body <NUM>. Restricted fluid flow passage <NUM> is located the predetermined distance (as defined in the embodiment of <FIG>) from an injection valve seal that is formed when needle <NUM> abuts seat <NUM>. In the illustrated embodiment internal fuel flow passage <NUM> is shown connecting restricted fluid flow passage <NUM> in a direct path with nozzle chamber <NUM>, in other embodiments passage <NUM> can comprise multiple sections that form a path that is not direct between the restricted fluid flow passage and the nozzle chamber such that the restricted fluid flow passage is located the predetermined distance away from the injection valve seal. In an exemplary embodiment, there can be multiple side by side fluid passage sections like enlarged portion <NUM> that are connected in series, such that the path between restricted fluid flow passage <NUM> and nozzle chamber <NUM> reciprocates back and forth.

Modelling conducted on different sizes of dampening orifices have shown that pressure pulsations within the nozzle chamber of the injector are reduced by reducing the size and implicitly the flow area of restricted fluid flow passage as illustrated in <FIG>. The pressure pulsations within the nozzle chamber of the injector before opening and after closing the injector for a fuel system comprising a restricted fluid flow passage having a <NUM> and respectively a <NUM> diameter are reduced compared to the pressure pulsations within the nozzle chamber when there is no restricted fluid flow passage in the fuel supply system. More specifically it was observed that the maximum peak to trough magnitude "A" of fuel pressure pulsations within the nozzle chamber before the start of fuel injection (SOI) for a fuel supply system having a dampening orifice of a <NUM> diameter is smaller than the maximum peak to trough magnitude "B" of fuel pressure pulsations for a fuel supply system that has no dampening orifice and at the same time it is larger than the maximum peak to trough magnitude "C" of the fuel pressure pulsations for a fuel supply system that has a dampening orifice of <NUM>. If the maximum peak to trough magnitude of the pressure pulsations is larger than a predetermined range, the pressure within the nozzle chamber at the start of injection can vary beyond a predetermined acceptable limit and this causes too big a variation in the amount of fuel injected into the combustion chamber. This means that for reducing the variation of the amount of fuel injected into the combustion chamber during an injection event the mean pressure within the nozzle chamber before an injection event is preferably maintained within a predetermined range. Data plotted in <FIG> proved that pressure pulsations can affect engine performance if not dampened. The modelling results have shown that the mean pressures within the nozzle chamber for a fuel supply system having a dampening orifice with respective <NUM> and <NUM> diameters, for this particular modelled engine, were within a predetermined acceptable range Pacc while the mean pressure for a fuel system having no pressure dampening orifice was outside of the predetermined range. The mean pressure within the present disclosure is interpreted to be the average pressure measured within the nozzle chamber between two injection events. The modelling done on the same engine has also shown that the pressure drop within the nozzle chamber during an injection event varies depending on the size of the restricted fluid flow passage, more specifically that the pressure drop increases for restricted fluid flow passages with a smaller diameter. As illustrated in <FIG>, the pressure drop "D" during an injection event for a restricted fluid flow passage having a diameter of <NUM> was larger than a pressure drop "E" for a restricted fluid flow passage having a diameter of <NUM>. This alone is not surprising but it demonstrates a trade off in selecting the size of the restricted fluid flow passage to balance between dampening and managing the pressure drop so that the final pressure in the fuel injector nozzle is above the minimum pressure needed to inject the desired amount of fuel within a predetermined injection pulse width for each engine operating conditions.

Therefore based on the modelling results the flow area of the restricted fluid flow passage is preferably selected to reduce the fuel pressure pulsations within the nozzle chamber and to keep the mean fuel pressure and the pressure drop at the injector nozzle during an injection event within predetermined ranges so that a predetermined amount of fuel is introduced into the combustion chamber.

Similarly the volume of the flow passage between the restricted fluid flow passage and the fuel injector inlet and respectively between the restricted fluid flow passage and the nozzle chamber influences the magnitude of the pressure pulsations and the pressure drop at the fuel injector inlet during an injection event. Therefore the volume of the fuel flow passage between the restricted fluid flow passage and the nozzle chamber is also calculated based on the desired range for the maximum peak to trough magnitude and consequently based on the desired range for the mean pressure and for the pressure drop within the nozzle chamber. The fluid flow area of the restricted fluid flow passage is therefore selected as a function of the predetermined volume of fuel flow passage as calculated above to maintain the pressure pulsations within the injector's nozzle chamber within a predetermined pressure range while maintaining gaseous fuel pressure within the nozzle chamber above a predetermined threshold that is needed to inject a commanded amount of gaseous fuel within a predetermined injection event.

Another embodiment of the present disclosure is illustrated in <FIG> which shows a gaseous fuel supply system for a dual fuel internal combustion engine fuelled with a liquid fuel and a gaseous fuel having an internal gaseous fuel rail which is mounted within the cylinder head. The gaseous fuel supply system comprises fuel injector <NUM> for injecting the gaseous fuel and the liquid fuel into combustion chamber <NUM> of engine cylinder <NUM>.

Fuel injector <NUM> has a body <NUM> which comprises a nozzle <NUM> provided with a plurality of injection holes <NUM> through which gaseous fuel is injected from gaseous fuel plenum <NUM> into the combustion chamber <NUM>. The injector comprises an outer needle <NUM> which can be lifted from its seat <NUM> by an actuator to allow gaseous fuel injection through injection holes <NUM> into combustion chamber <NUM>. The injector also comprises an inner needle <NUM> which is seated inside the outer needle <NUM> and can be lifted from its seat by an actuating mechanism to allow the injection of the liquid fuel supplied through liquid fuel passage <NUM> from a liquid fuel rail (not illustrated) into the combustion chamber through injection holes <NUM> provided in outer needle <NUM>. Needle <NUM> can be actuated by a hydraulic actuator, more specifically needle <NUM> moves within needle bore <NUM> inside body <NUM> of the fuel injector being actuated by the hydraulic fluid pressure in hydraulic control chamber <NUM> of the hydraulic actuator which is controlled by the engine controller. To avoid any gaseous fuel leakage from nozzle chamber <NUM> to hydraulic control chamber <NUM> fluid seals <NUM> are provided between the needle and the needle bore in the body of the injector. Sealing fluid is supplied to the seals through a sealing fluid passage (not illustrated). Furthermore, to prevent any further leakage, needle <NUM> is match fit with needle bore <NUM> between hydraulic control chamber <NUM> and nozzle chamber <NUM>.

Gaseous fuel is supplied to nozzle chamber <NUM> from the gaseous fuel supply conduit <NUM> which is at least partially mounted in cylinder head <NUM>. Gaseous fuel supply conduit <NUM> comprises a body <NUM> and a fuel supply passage <NUM> from which gaseous fuel is supplied through supply channel <NUM> provided in a separate component <NUM>, and through restricted fluid flow passage <NUM> and gaseous fluid flow passage <NUM> to nozzle chamber <NUM>. Gaseous fuel flow passage <NUM> comprises first fuel flow passage <NUM> which is located within the cylinder head and internal fuel passage <NUM>. As illustrated in <FIG>, restricted fluid flow passage <NUM> is not placed in the gaseous fuel supply conduit, but in a component that is separate from it. This might have manufacturability advantages over the embodiment presented in <FIG> because a separate component can be more easily customized to the required dimensions of the dampening orifice. Gaseous fuel is supplied from injector inlet <NUM> to nozzle chamber <NUM> through internal fuel passage <NUM>.

As in the previous embodiment, the volume of first fuel flow passage <NUM> and implicitly the volume of the gaseous fuel flow passage <NUM> are calculated to reduce the gaseous fuel pressure pulsations within the nozzle chamber before the start of fuel injection such that the maximum peak to trough magnitude of the fuel pressure pulsations and the pressure drop within the nozzle chamber is maintained within a predetermined range. In some embodiments, the volume of first fuel flow passage <NUM> may be restricted by the space available in the cylinder head. As in the previous embodiments, the fluid flow area of the restricted fluid flow passage <NUM> is selected as a function of the volume of gaseous fuel flow passage <NUM> to maintain the gaseous fuel pressure within the nozzle chamber above a predetermined threshold that is needed to inject a commanded amount of gaseous fuel within an injection event and may be further selected to preferably maintain a mean gaseous fuel pressure and the gaseous fuel pressure drop within the nozzle chamber within predetermined ranges. Restricted fluid flow passage <NUM> is located the predetermined distance from an injection valve seal, which is formed when needle <NUM> abuts seat <NUM>.

In an injector which injects both the gaseous fuel and the liquid fuel into the combustion chamber, as the one illustrated in <FIG>, there are additional requirements regarding the pressure of the gaseous fuel and respectively the pressure of the liquid fuel being injected into the combustion chamber. A certain bias has to be maintained between the gaseous fuel pressure and the liquid fuel pressure to reduce or preferably avoid any gaseous fuel leakage into the liquid fuel. If the pressure of the gaseous fuel within nozzle chamber <NUM> is not dampened and raises to a pressure higher than the liquid fuel, gaseous fuel can leak into the liquid fuel by travelling between the match fits between needle <NUM> and bore <NUM> and can leak into the needle control chamber <NUM> through fluid seals <NUM> that normally fluidly isolate the gaseous fuel from the hydraulic fluid. In many cases the hydraulic fluid used for actuating the needle is the liquid fuel used for igniting the gaseous fuel. Therefore the gaseous fuel pressure is normally maintained lower than the pressure of the liquid fuel to reduce and preferably prevent such leakage.

<FIG> and <FIG> show the modelling results for the gaseous fuel pressure within the nozzle chamber ("local GRP") and for the liquid fuel supply pressure within the injector ("local DRP") for a fuel supply system without a restricted fluid flow passage ("No Orif") and respectively for a fuel supply system with a restricted fluid flow passage having a <NUM> diameter. The modelling shows that for the fuel supply system that does not comprise a restricted fluid flow passage, the gaseous fuel pressure (local GRP) during an injection event which comprises a liquid fuel injection <NUM> and a gaseous fuel injection <NUM> becomes higher than the liquid fuel pressure (local DRP) for a prolonged period of time, as illustrated in <FIG>. The plotted data shows that a gaseous fuel supply system that comprises a restricted fluid flow passage the gaseous fuel pressure (local GRP) within the nozzle chamber stays lower than the liquid fuel supply pressure for almost the entire injection event, the occasional spikes of gaseous fuel pressure being of a very short duration which reduces the risk of gaseous fuel leakage into liquid fuel. The modelling results illustrated in <FIG> and <FIG> have been obtained for an existing conventional internal combustion engine and for this particular engine, the size of the restricted fluid flow passage was calculated such that the pressure of the gaseous fuel within the nozzle chamber was maintained lower than the liquid fuel pressure by a predetermined value (bias) during the entire engine operation. Another aspect that was considered during the calculations of the fluid flow area of the restricted fluid flow passage was that the shape of the trace of the pressure within the nozzle chamber was preferably maintained the same as the trace of the pressure within the nozzle chamber for a fuel supply system that does not have a restricted fluid flow passage such that substantially the same amount of fuel is injected into the combustion chamber during an injection event and substantially the same injection timing is preserved.

In dual fuel engine systems, the size of dampening orifice <NUM> and the volume of flow passage <NUM> are calculated based on the requirements related to providing a predetermined amount of gaseous fuel into the combustion chamber and taking in consideration that the peak pressure of the gaseous fuel within the nozzle chamber has to be maintained lower than the liquid fuel supply pressure by a predetermined bias.

Another embodiment of the present gaseous fuel injection system is schematically illustrated in <FIG> which represents a dual fuel direct injection internal combustion system <NUM>. Gaseous fuel is supplied from gaseous fuel storage vessel <NUM> through gaseous fuel rail <NUM> to the six engine injectors 310a - 310f which each inject the gaseous fuel directly into a respective combustion chamber of an engine cylinder, the six engine cylinders being illustrated with reference numbers 300a to 300f. Liquid fuel is supplied from liquid fuel storage tank <NUM> through liquid fuel rail 381to injectors 310a to 310f which each also inject the liquid fuel directly into the combustion chamber of respective ones of the six engine cylinders 300a to 300f. Injectors 310a to 310f can have a similar construction to the dual fuel injector illustrated in <FIG> and are located at least partially in the cylinder head <NUM>. Air is supplied through intake port <NUM> to intake manifold <NUM> and exhaust gases are directed out of the combustion chambers through exhaust manifold <NUM>.

Gaseous fuel is supplied from rail <NUM> to each of the injectors 300a to 310f through restricted fluid flow passages 350a to 350f, each restricted fluid flow passage being fluidly connected to the gaseous fuel rail and is also connected to an injector (one of injectors 300a to 300f) through a flow passage of a predetermined volume (one of flow passages 360a to 360f).

In a preferred embodiment, each of the restricted fluid flow passages 350a to 350f has a different size which is calculated based on the pressure pulsations within the nozzle chamber for each one of the six injectors.

In some embodiments the volume of each of the flow passages that fluidly connect each restricted fluid flow passage to each of the fuel injectors is different and it is based on the pressure pulsations within the nozzle chamber of the respective injector to which it is connected.

Modelling results have also shown that the mean gaseous fuel pressure and the pressure drop within the nozzle chamber for each one of the engine injectors can vary from one injector to another according to the size of the restricted fluid flow passage. Therefore the size of the restricted fluid flow passage for each injector is preferably selected to maintain the pressure pulsations within the nozzle chamber of each injector within predetermined ranges.

In the illustrated embodiments herein the gaseous fuel passage connections at injector inlets (<NUM>, <NUM>, <NUM>) are shown as gallery connections where an annular volume extends around respective fuel injectors (<NUM>, <NUM>, <NUM>) and where the annular volume is fluidly connected with respective gaseous fuel passages (<NUM>, <NUM>, <NUM>). In alternative embodiments direct metal-to-metal fuel connections can be employed between respective gaseous fuel passages (<NUM>, <NUM>, <NUM>) and injectors inlets (<NUM>, <NUM>, <NUM>), such as disclosed in <CIT>, and co-owned by the Applicant.

For all embodiments described here, the fluid flow area of flow passage which fluidly connects gaseous fuel supply conduit to the injector inlet and the cross-sectional area of fuel passage which connects the injector inlet to the nozzle chamber are each larger than a cross-sectional area of restricted fluid flow passage. This allows a smooth fuel flow between from the restricted fluid flow passage and the injection holes.

Claim 1:
A fuel supply system for a gaseous fueled internal combustion engine comprising:
a gaseous fuel supply conduit (<NUM>);
a fuel injector (<NUM>) for injecting gaseous fuel into said internal combustion engine, said fuel injector (<NUM>) having a first body (<NUM>) comprising an inlet (<NUM>), and a nozzle chamber (<NUM>) fluidly connected to said inlet (<NUM>) and from which said gaseous fuel is injected into said internal combustion engine, and comprising a needle (<NUM>) and a seat (<NUM>), an injection valve seal formed when said needle (<NUM>) abuts said seat (<NUM>);
a second body formed for installation between and fluidly connecting said gaseous fuel supply conduit (<NUM>) and a gaseous fuel flow passage (<NUM>) of a predetermined volume through which said gaseous fuel supply conduit (<NUM>) is connected to said nozzle chamber (<NUM>), said second body defining a restricted fluid flow passage (<NUM>) for delivering said gaseous fuel to said nozzle chamber (<NUM>); and
wherein a cross-sectional area of said restricted fluid flow passage (<NUM>) is a smallest effective area between said gaseous fuel supply conduit (<NUM>) and said nozzle chamber (<NUM>) and wherein said cross-sectional area of said restricted fluid flow passage (<NUM>) is selected as a function of said predetermined volume to maintain pressure pulsations within said gaseous fuel flow passage (<NUM>) within a predetermined pressure range while maintaining gaseous fuel pressure within said nozzle chamber (<NUM>) above a predetermined threshold which is needed to inject a commanded amount of gaseous fuel within a predetermined injection pulse width for each engine operating condition.