Fuel-efficient injector testing system

Abstract

The invention relates to a system or testing fuel gas injectors (1, 2, 3, 4, 5, 6) designed to be used for supplying an internal combustion engine with gaseous fuel initially stored in a replenishable storage tank (100), The system according to the invention includes:. a recycling loop (103, 104, 105, 106) for collecting, filtering and recompressing the gaseous fuel outputted by the injectors, and injecting the recompressed gaseous fuel into the storage tank (100); and. a leakage detection module (103) configured to detect and signal by means of an alarm signal (ALM) substantial drops of a gaseous fuel pressure value measured within the injection rail (102).

Description

[0001] FUEL-EFFICIENT INJECTOR TESTING SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to a system for testing fuel gas injectors designed to be used for supplying an internal combustion engine with gaseous fuel, particularly hydrogen.

[0004] BACKGROUND OF THE INVENTION

[0005] It is well known within the art that, in internal combustion engines, a crucial function is implemented by injectors through which gaseous fuel is supplied to cylinders enclosing the engine’s combustion chambers. Consequently, it is of great importance to collect as much data as possible on the injectors’ physical and functional characteristics in order to be able to plan for necessary maintenance operations during the lifetime of the engine, but also to fine tune various operational parameters of the engine such as the optimal scheduling of actuating pulses driving the opening and closing of the injectors when the engine is running, etc.

[0006] In the current state of the art, injectors are tested by having them mounted within real engines and letting said engines run as long as necessary for the collection of all data relevant for the testing purposes.

[0007] TECHNICAL PROBLEM

[0008] This known method consisting in testing the injectors generally involves a very important fuel gas consumption. As an example, a thorough testing of an injector requires approximately 500 million operating cycles, which in turn represent a consumption of 1500kg of gaseous fuel amounting to 9000 Euros at a value of 6 Euro / kg for Green Hydrogen. A validation campaign of a 12-hydrogen injector system thus involves spending an amount of 300.000 Euros for hydrogen consumption purposes only, which is prohibitive for economic as well as for environmental reasons.

[0009] The inventors have thus aimed at designing an injector testing system allowing to perform a great number of operating cycles, with a gaseous fuel consumption reduced with respect to that of known testing systems. GENERAL DESCRIPTION OF THE INVENTION

[0010] The invention enables to overcome the above-mentioned drawbacks, by providing a system for testing fuel gas injectors designed to be used for supplying an internal combustion engine with gaseous fuel, said system comprising, according to a first of its aspects:

[0011] . at least one storage tank for storing said fuel gas at a first pressure;

[0012] . at least one pressure regulator for reducing the fuel gas pressure to a second predetermined pressure; and

[0013] . an injection rail for supplying said fuel gas a series of injectors, said system being characterized in that, said at least one tank being replenishable, the system includes: a recycling loop for collecting, filtering and recompressing the gaseous fuel outputted by the injectors, and injecting the recompressed gaseous fuel into the storage tank; and

[0014] . a leakage detection module configured to detect and signal substantial drops of a gaseous fuel pressure value measured within the system.

[0015] In the system according to the invention, the gaseous fuel which is used during a given iteration of the operational testing cycle of an injector is not burned within the engine, nor alternately flushed towards the atmosphere. It is instead collected and subjected to a recycling process allowing it to be recirculated for a reuse in a future iteration of an injector testing cycle.

[0016] Accordingly, the system is generally designed as a closed loop system, as the fuel gas that is taken from the storage tank for injector testing will be recompressed to be stored back into the storage tank. The recycling loop comprises means for collecting, filtering and recompressing the gas discharged by the injectors during testing. In practice, the various components of the system (storage tank, pressure regular(s), injection rail, compressor, filter etc. are connected in series by piping.

[0017] Simultaneously, the leakage detection module ensures an integrity of the recycling loop and enables to prevent gaseous fuel loss due to potential leaks occurring within the testing circuit, and, consequently, to keep the testing system running in optimal conditions by maintaining an overall constant operational pressurization. The leakage detection module operates based on a pressure sensor signal and is configured to detect pressure drops. As the system operates with gaseous fuel, and in particular H2, leak detection is important, at any position in the system.

[0018] Accordingly, the pressure sensor feeding the pressure signal to the leakage detection module may be positioned at any appropriate location within the system. In particular, the pressure sensor feeding the pressure signal to the leakage detection module may be arranged to detect the fuel gas pressure in the fuel rail, which is close to the parts under tests and hence that are ‘temporarily in the system’ (i.e. replaced after testing, compared to the parts of the system which are rather ‘permanent’). Other possible locations for the pressure sensor are storage tanks, e.g. the storage tank (high pressure) upstream of the injectors and the low-pressure storage tank in the recycling loop.

[0019] In an advantageous embodiment of the invention, the leakage detection module includes a computing unit configured to compare a real-time value of the gaseous fuel pressure measured within the injection rail to a predetermined pressure reference value.

[0020] This embodiment of the invention enables at a relatively low cost to monitor the operating pressure of the injection rail.

[0021] In a preferred embodiment of the invention, the computing unit is further configured to:

[0022] . launch a countdown when a difference between the predetermined pressure reference value and the real-time value of the gaseous fuel pressure value measured within the injection rail becomes greater than a predetermined threshold; and

[0023] . transmit an alarm signal if, at the end of the countdown, a difference between the predetermined pressure reference value and the updated real-time value of the gaseous fuel pressure value measured within the injection rail is again greater than the predetermined threshold.

[0024] This preferred embodiment of the invention enables to discount as flukes substantial but short-lived variations in the operating pressure of the injection rail, which will have no long-term impact on the outcome of the injector testing process. In this embodiment, an alarm condition will only be declared if a pressure discrepancy lasts longer than a significant time period associated with the countdown value. The alarm condition is signaled by the transmission of the alarm signal. The alarm signal may take any appropriate form, e.g. as a flag, a change of variable, a visual signal, a sound, or a combination thereof. The control unit and / or user may take any appropriate measure if an alarm condition is present, e.g. shutting down the system and closing all valves.

[0025] The predetermined pressure reference value may be a constant value, but, according to a variant of the above-described embodiments of the invention, the predetermined pressure reference value is preferably an instantaneous value computed in real time as being equal to an average value of a predetermined number of samples of the gaseous fuel pressure value within the injection rail, stored at regular intervals prior to the instant at which the comparison is made with the actual real-time value of the gaseous fuel pressure measured within the injection rail.

[0026] This variant of the invention takes into account the fact that, during the normal operation of the testing system, the real-time value of the gaseous fuel pressure measured within the injection rail may be subject to variations which will not be indicative of functional anomalies. In such a situation, a comparison of the gaseous fuel pressure measured within the injection rail with a fixed value could trigger a false alarm, which is prevented by using a variable predetermined pressure reference value computed instantaneously in close and continuous correspondence with past measured values of the gaseous fuel pressure within the injection rail.

[0027] According to a second of its aspects, the invention also relates to a system for testing fuel gas injectors designed to be used for supplying an internal combustion engine with gaseous fuel, said system comprising an instrumentation module (120) for testing a plurality of injectors placed in a row along a first direction, a light emitting module configured to output a light beam in a direction essentially parallel to the first direction and a light receiving module arranged across from the emitting module, said light receiving module (being intended to receive said light beam and to output an electric signal representative of an intensity of the light actually received by the light receiving module, the injectors being each provided with a pintle and being arranged in such a way that each pintle at least partially obstructs said light beam when its respective injector is actuated. This second aspect of the invention, which may be used alternatively of cumulatively with the first aspect described hereinbefore, is particularly interesting in that it enables to test in a single operation a plurality of injectors arranged in a row parallel to the light beam. The injectors being alternately actuated in sequence, each event during which a pintle will obstruct the light beam will produce electric variations in the electric signal outputted by the light receiving module, said variations being equivalent to an electric print associated with the injector associated with the considered pintle, which electric print will enable to measure interesting functioning parameters inherent to this injector, such as its opening and closing delays with respect to related rising and falling edges of the injector’s control signal pulses.

[0028] According to a third of its aspects, the invention also relates to a system for testing fuel gas injectors designed to be used for supplying an internal combustion engine with gaseous fuel, said system comprising an oil injection device for adding oil to the gaseous fuel supplied to the injectors, said injection device including a solenoid controlling the opening of an oil delivery valve upon reception of a control pulse, the oil injection device further comprising a controlling module for sending to the solenoid a train of sub-pulses having a duration inferior to the minimum duration required for said control pulse, said train of pulses including a number of pulses, preferably varying as a function of a difference between the temperature of the oil to be injected and a predetermined reference temperature.

[0029] This second aspect of the invention, which may be used alternatively of cumulatively with the first and / or the second aspect described hereinbefore, is particularly interesting in that it enables to use as a heating element the solenoid normally intended to control the opening of the oil delivery valve. By varying the number of sub-pulses included in successive trains of such sub-pulses, it is possible to tune the heat produced by the solenoid by these cumulated sub-pulses and thus to regulate the temperature of the oil adding oil to the gaseous fuel supplied to the injectors.

[0030] According to a functional aspect, the invention also relates to a method for testing fuel gas injectors designed to be used for supplying an internal combustion engine with gaseous fuel, said system comprising: . at least one replenishable storage tank for storing said fuel gas at a first pressure;

[0031] . at least one pressure regulator for reducing the fuel gas pressure to a second predetermined pressure; and

[0032] . an injection rail for supplying said fuel gas to a series of injectors, said method being characterized in that it includes:

[0033] . a recycling step for collecting, filtering and recompressing the gaseous fuel outputted by the injectors, and injecting the recompressed gaseous fuel into the storage tank; and

[0034] . a leakage detection step for detecting and signaling substantial drops of a gaseous fuel pressure value measured within the system.

[0035] According to an advantageous embodiment of this functional aspect, the leakage detection step includes a comparing step for comparing a real-time value of the gaseous fuel pressure P(ti) measured within the injection rail to a predetermined pressure reference value Pref(ti).

[0036] According to a preferred embodiment of this the functional aspect, the leakage detection step further includes:

[0037] . a temporizing step during which a countdown is launched when a difference between the predetermined pressure reference value Pref(ti) and the real-time value P(ti) of the gaseous fuel pressure value measured within the injection rail becomes greater than a predetermined threshold THR; and

[0038] . an alarm signaling step during which an alarm signal ALM is transmitted if, at the end of the countdown, a difference between the predetermined pressure reference value and the updated real-time value P(ti+T0) of the gaseous fuel pressure value measured within the injection rail is again greater than the predetermined threshold THR.

[0039] The predetermined pressure reference value may be a constant value, but, according to a variant of the invention, a method as described above further includes a step for computing in real time an instantaneous predetermined pressure value as being equal to an average value of a predetermined number of samples P(tj, for j=i- n to i-1 ) of the gaseous fuel pressure value within the injection rail, stored at regular intervals prior to the instant (ti) at which the comparison is made with the actual realtime value P(ti) of the gaseous fuel pressure measured within the injection rail.

[0040] Brief Description of the Drawings

[0041] Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings, wherein:

[0042] Fig. 1 is a schematic diagram of a fuel gas injector testing system according to a first aspect of the invention;

[0043] Fig. 2 is a graph illustrating the operation of a leakage detection module included in the system shown in the previous figure;

[0044] Fig. 3 is a schematic diagram of a leakage detection method according to a preferred embodiment of the invention;

[0045] Fig. 4 is a schematic diagram of an instrumentation module according to a second aspect of the invention;

[0046] Fig. 5 is a set of graphs illustrating the operation of a the leakage detection module shown in the previous figure;

[0047] Fig. 6 is a detailed view of portions of the previous figure;

[0048] Fig. 7 is a schematic diagram of an oil injection device according to a third aspect of the invention;

[0049] Fig. 8 is a screen shot illustrating the operation of an oil injection device according to this third aspect of the invention; and

[0050] Fig. 9 is a schematic diagram of a temperature regulation method carried out with such an oil injection device.

[0051] Description of Preferred Embodiments

[0052] Fig. 1 illustrates a system for testing fuel gas injectors designed for supplying an internal combustion engine with gaseous fuel. Conventionally fuel injectors comprise an elongate body that defines an axial fuel passage extending from an inlet opening to an outlet opening. The outlet opening is typically controlled by means of a pintle having a shaft moveable with the injector body and a head that cooperates with a valve seat surrounding the outlet opening. The pintle is spring biased against the valve seat, i.e. in closed position. The pintle is typically controlled by an electromechanical actuator that allows lifting the pintle from the valve seat into an open position in which fuel gas is discharged through the outlet opening. In particular, the actuator includes a solenoid coil that cooperates with a magnetic armature mechanically coupled to the pintle. When energized, the solenoid creates a magnetic field that attracts the armature and thereby moves the pintle in open position. In fuel gas injectors the pintle is preferably in outwardly open configuration. That is the valve seat faces downstream and the pintle head is outside of the fuel passage in the injector body. Hence, in certain injector configurations, the opening movement of the pintle can be observed outside of the body, the pintle head protruding beyond the tip of the injector body in open position. These are known injector structures that need not be further detailed herein.

[0053] According to a first aspect of the invention, this system comprises:

[0054] . at least one replenishable storage tank (100) for storing said fuel gas at a first pressure;

[0055] . at least one pressure regulator (101 ) for reducing the fuel gas pressure to a second predetermined pressure; and

[0056] . an injection rail (102) for supplying said fuel gas a series of injectors (1 , 2, 3, 4, 5, 6).

[0057] In this embodiment of the invention, the system SYST includes:

[0058] . a recycling loop (118, 104, 105, 106) for collecting, filtering and recompressing the gaseous fuel outputted by the injectors, and injecting the recompressed gaseous fuel into the storage tank (100); and

[0059] . a leakage detection module (103) configured to detect and signal by means of an alarm signal (ALM) substantial drops of a gaseous fuel pressure value. In this embodiment the pressure is measured within the injection rail (102).

[0060] In fig.1 , reference sign 118 designates a collecting box that comprises a collecting chamber in which the injector tips protrude (see Fig.4). The injectors are sealing fixed in openings of the collecting box 118. When the injectors are actuated (injection events), the gas is discharged into the collecting chamber, which has an outlet port connected to the recycling loop.

[0061] In this embodiment of the invention, the recycling loop includes cooling means, e.g. a heat exchanger (14), for cooling down the gaseous fuel outputted by the injectors and collecting it in low pressure storage means (tank 104) at a pressure of a few bars, e.g. lower than 4 barA. The recycling loop further includes compressing means (105) for bringing the low-pressure gaseous fuel stored in storage means (104) to a higher pressure, e.g. 350 bar, and filtering means (106) for removing from the high pressure gaseous fuel outputted by the compressor (106) the oil and the impurities it may contain, before injecting / forwarding the high pressure gaseous fuel into the replenishable tank (100).

[0062] In this particular embodiment, the testing system SYST further includes temperature pre-conditioning means (107) coupled to an optional second pressure regulator (108) by means of a cut-off valve (109), and low-pressure filtering means (110) coupled with injection rail (102) by means of a cut-off valve (11 1 ).

[0063] The system comprises a control unit CTL that is configured to operate the various components. CTL generally includes a processor and a memory. In use, the CTL operates the injectors to perform the desired series of operating cycles. The injectors are typically operated serially to perform injection events one after another in predetermined order. The fuel injectors are thus alternately operated by applying a drive current during a predetermined time period (Pulse Width) to open the injector. The leakage detection module (103) can be integrated to the CTL or may be implemented as an independent module.

[0064] The fuel rail 102, situated above the injectors, may generally comprise a body defining an elongate plenum chamber 102.1 for gas accumulation and comprising transverse outlet channels 102.2, extending downward towards the injectors. The injectors are connected via individual pipes 102.3 to the respective outlet channels 102.2, as visible in Fig.7

[0065] A pressure sensor P is mounted to the fuel rail 102 to detect pressure therein. Fig.1 is a simplified diagram; various additional elements can be present in the testing system according to the invention that are not represented here in order to simplify the description (e.g. Pressure Relief Valves, Purge valves, etc.). Furthermore, although the injection rail supplies six injectors in the present example, in other embodiments, the number of injectors may be different, e.g. ranging from four to twelve.

[0066] In the embodiment of the invention shown here, the testing system SYST further comprises an instrumentation module (120) and an oil injection device (130, 131 ) for adding oil to the gaseous fuel supplied to the injectors (1 , 2, 3, 4, 5, 6).

[0067] Fig.2 explains the operational principle of the leakage detection module, which includes a computing unit configured to compare a real-time value P(ti) of the gaseous fuel pressure measured within the injection rail to a pressure reference value Pref(ti).

[0068] In embodiments, the pressure reference value may be a constant value, but, in the advantageous variant of the invention depicted here, the predetermined pressure reference value Pref(ti) is an instantaneous value computed in real time as being equal to an average value of a predetermined number of samples of the gaseous fuel pressure value within the injection rail, stored at regular intervals prior to the instant (ti) at which the comparison is made with the actual real-time value of the gaseous fuel pressure measured within the injection rail. In other words, Pref (ti) is a moving average of the pressure measured during a time period of predefined duration that ends with the last measure before instant (ti). This predefined duration may represent range from 0.5 s up to 1 .0 or 2.0 s.

[0069] This variant of the invention takes into account the fact that, during the normal operation of the testing system, the real-time value of the gaseous fuel pressure measured within the injection rail may be subject to variations which will not be indicative of functional anomalies. In such a situation, a comparison of the gaseous fuel pressure measured within the injection rail with a fixed value could trigger a false alarm, which is prevented by using a variable predetermined pressure reference value Pref(ti) computed instantaneously in close and continuous correspondence with past measured values of the gaseous fuel pressure within the fuel rail. In the preferred embodiment of the invention depicted here, the computing unit is further configured to:

[0070] . launch a countdown at an instant (t3) when a difference between the pressure reference value Pref(ti) and the real-time value P(ti) of the gaseous fuel pressure value measured within the injection rail becomes greater than a predetermined threshold; and

[0071] . transmit an alarm signal ALM if, at an instant (t3+T0) when the end of the countdown is reached, a difference between the pressure reference value Pref(ti) and the updated real-time value P(ti) of the gaseous fuel pressure value measured within the injection rail is still greater than the predetermined threshold.

[0072] This preferred embodiment of the invention enables to discount as flukes (or artefacts) substantial but short-lived variations in the operating pressure of the injection rail, which will have no long-term impact on the outcome of the injector testing process. In this embodiment, an alarm condition will only be declared if a pressure discrepancy lasts longer than a significant time period TO associated with the countdown value.

[0073] The duration of the countdown may range from 20 s to 60 s, or up to 90 s.

[0074] Indeed, as can be seen in Fig.2, a first countdown was launched at an instant t1 when a difference between the pressure reference value Pref(ti) and the real-time value P(ti) of the gaseous fuel pressure value measured within the injection rail had already become greater than the predetermined threshold, but, since said difference Pref(ti)-P(ti) had again become lower than said threshold at an instant (t2) prior to the end of the countdown at (t1 +T0), no alarm signal was then transmitted.

[0075] For ease of implementation, the comparison to the threshold can be implemented in absolute value, i.e. | Pref(ti)-P(ti) | is compared to the threshold.

[0076] Fig.3 explains in greater detail the operation of the above described leakage detection module, by disclosing a leakage detection method which includes:

[0077] . a sampling step (301 ) configured for continuously sampling values of the gaseous fuel pressure (P) measured within the injection rail, at a rhythm set by a clock signal Ck having for example a frequency of 40MHz; . a storing step (302) that memorizes the continuously sampled values P(ti) in a memory which may or may not be included within the leakage detection module;

[0078] . a calculating step (303) that calculates an instantaneous pressure reference value Pref(ti); and

[0079] . a comparison step (304) that compares said instantaneous pressure reference value Pref(ti) to a real-time value P(ti) of the gaseous fuel pressure measured within the injection rail.

[0080] In the presently disclosed leakage detection method, the instantaneous pressure reference value Pref(ti) is advantageously computed in real time as being equal to an average value of a predetermined number (n) of samples P(tj, for j=i-n to i-1) of the gaseous fuel pressure value within the injection rail, stored at regular intervals prior to the instant (ti) at which the comparison is made with the actual real-time value P(ti) of the gaseous fuel pressure measured within the injection rail.

[0081] This leakage detection method further comprises:

[0082] . a temporization step (305) in the course of which a countdown is launched when a difference between the instantaneous pressure reference value Pref(ti) and the real-time value P(ti) of the gaseous fuel pressure value measured within the injection rail becomes greater than a predetermined threshold THR; and

[0083] . an alarm signal transmission step (307) for sending an alarm signal (ALM) if, at the end of the countdown, a difference between an updated instantaneous pressure reference value Pref(ti+T0) and the updated real-time value P(ti+T0) of the gaseous fuel pressure value measured within the injection rail is again greater than the predetermined threshold THR.

[0084] It may be noted that the leakage detection module (103) can be implemented to operate leakage detection for other system components that are provided with a pressure sensor. Preferably, the high-pressure storage tank (100) and the low- pressure tank (104) are both provided with a pressure sensor, which is connected to the leakage detection module (103), as represented by the dashed lines in Fig.1. The leakage detection module (103) is preferably configured to operate the same leakage detection principle / method for those sensors, as for the sensor fitted on the fuel rail. Fig. 4 depicts an instrumentation module (120) according to a second aspect of the disclosure. This instrumentation module (120) is incorporated to the collecting box 118 and designed testing a plurality of injectors (1 , 2, 3, 4, 5, 6) placed in a row along a first direction (D1 ), a light emitting module (12), for example a laser generator / source that is configured to output a light beam (121 ) in a direction essentially parallel to the first direction. This instrumentation module (120) further includes a light receiving module (22), for example a photodiode, arranged across from the emitting module, said light receiving module (22) being intended to receive said light beam (121 ) and configured to output an electric signal (122) representative of an intensity of the light actually received by the light receiving module (22). As explained before, the injectors (1 , 2, 3, 4, 5, 6) are typically of the outward opening type, whereby the pintle (13) moves outwardly (distally from the pintle tip) in open position. In the fig. the injectors are shown in closed position and their pintles (13) do not interfere with the light beam (121 ); they are spaced therefrom. However, it should be appreciated that the injectors are arranged in such a way that each pintle (13) at least partially obstructs / interrupts the light beam (121 ) when its respective injector (3) is actuated.

[0085] This second aspect, which may be used alternatively of cumulatively with the first aspect described hereinbefore, is particularly interesting in that it enables to test in a single operation a plurality of injectors (1 , 2, 3, 4, 5, 6) arranged in a row parallel to the light beam (121 ).

[0086] Fig.5 depicts (for k=1 to 6) of the respective injectors (1 , 2, 3, 4, 5, 6), each control signal PLSk featuring a pulse (here the logic pulse) intended to be applied to the solenoid actuator incorporated in the injector in order to generate an magnetic field allowing the displacement of the pintle in the injector. When thusly displaced, the pintle frees the outlet orifice through which the gaseous fuel may pass.

[0087] As shown in the previous figure, the injectors (1 , 2, 3, 4, 5, 6) being alternately actuated in sequence, each event during which a pintle will obstruct the light beam will produce electric variations in the electric signal (122) outputted by the light receiving module, said variations being equivalent to an electric print associated with the injector associated with the considered pintle, which electric print will enable to measure interesting functioning parameters inherent to this injector, such as its opening and closing delays with respect to related rising and falling edges of the injector’s control signal pulses.

[0088] Fig.6 is a detailed view of portions of the previous figure, which enables to better observe the real aspect of the electric print, in the electric signal (122) outputted by the light receiving module, associated with the crossing of the light beam by the corresponding pintle. The current plot below corresponds to the drive signal actually applied to the injector during pulse PLS in Fig.5.

[0089] Of particular interest are the opening and closing slopes (OPS, CLS) of output signal (122), as well as the opening delay (OD) which can be precisely measured between the start of the rising edge of the control pulse (PLS) and the start of the rise of output signal (122), and the closing delay (CD) which can be precisely measured between the start of the falling edge of the control pulse (PLS) and the start of the decline of output signal (122). For this, it is preferred that the light beam is as close as possible to the injector tips.

[0090] Furthermore, the instrumentation module enables to precisely quantify the maximal stroke value of the pintle, which corresponds to the peak value of the output signal (122), which also features oscillations following the closing of the pintle representing a bouncing behavior of the pintle trigger upon closure.

[0091] Fig. 7 schematically shows a part of an oil injection device included in an injector testing device according to a third aspect of the disclosure. This oil injection device is intended to add oil to the gaseous fuel supplied to an injector (IN Jk), which is of particular importance when the gaseous fuel is hydrogen, since this fuel is inherently devoid of any lubricant and won’t be able to contribute, in its natural pristine state, to the smoothing of interactions between mobile parts located within the injector. Preferably, one such injector INJk is provided per fuel injector (1 ...6) and arranged on the fuel rail, to inject oil into in a respective outlet channel 102.2, preferably in an enlarged section102.4 of the outlet channel 102.2.

[0092] The oil injector INJk is here designed as a gasoline fuel injector, i.e. having a body with a nozzle portion including a valve member that controls injection holes. The valve member is operated directly by a solenoid actuator, as is known in the art. The various oil injector INJk are connected to a source of pressurized oil. In such oil injector IN Jk, the discharged amount of oil is proportional to the opening time, i.e. actuating duration, piloted by the Control signal CNS below.

[0093] However, the addition of oil to the gaseous fuel may change the temperature of the latter, and thus alter the operating conditions of the injector. The purpose of the third aspect of the invention is to regulate the temperature of the oil before its injection into the gaseous fuel flow. To this end, a controlling module CNT will monitor and regulate the temperature Tdoz of the oil to be injected by means of the control signal CNS applied to the solenoid controlling the operation of the oil delivery valve allowing the actual injection. CNT can be integrated in CTL.

[0094] Similar to the PLS applied to the fuel injectors, the control signal CNS is the logic signal defining the actuating / opening time of the oil injection device IN Jk. The signal CNS is represented in Fig.8. Reference sign 80 designates actuating pulses that are designed to open injection device I N Jk to discharge a predetermined amount of oil, i.e. lubricating pulses. In order to heat up oil that may be at lower temperature, CTL generates trains of pulses in CNS, indicated 82, before the actual lubricating pulse 80. A temperature sensor is arranged at the IN Jk fixture and generates temperature signal Tdoz. These trains of pulses 82 consist of a plurality of pulses that each have a duration inferior to the minimum duration required for a regular control pulse intended to trigger an opening of the oil delivery valve. That is, each individual pulse in the train of pulses 82 has a duration that is too short to open I N Jk. Preferably, each train of pulses includes a number (N) of pulses varying as a function of a difference between the temperature (Tdoz) of the oil to be injected and a predetermined reference temperature (Tref), which may be the ambient temperature. Hence, the module CNT may store a mapping that relates the number of pulses N, Tdoz and Tref.

[0095] Hence, a warm up effect of the oil if achieved by applying before each lubricant pulse a train of pulses at rapid frequency (e.g. 25 to 250 Hz), that does not open the injector be will heat up the injector body by joule effect, and hence the oil contained in the injector. The time period Ts between the end of a train pulse 82 and corresponding lubrication pulse 80 may be of about 1 .0 to 3.0 s.

[0096] Fig.9 shows how the number (N) of pulses may advantageously be regulated. After an initial step (600) during which a train of N pulses has been applied to the solenoid, the temperature Tdoz of the oil to be injected is measured during a measuring step (601 ). During a following comparison step (602), the oil temperature Tdoz is compared to reference temperature Tref. If the oil temperature Tdoz is lower than the reference temperature Tref, the number N of pulses to be included in each pulse train is increased during an increasing step (603). Conversely, if the oil temperature Tdoz is higher than the reference temperature Tref, the number N of pulses to be included in each pulse train is decreased during a decreasing step (604).

Claims

Claims1 . A system for testing fuel gas injectors configured for supplying an internal combustion engine with gaseous fuel, said system comprising:. at least one storage tank (100) for storing said fuel gas at a first pressure;. at least one pressure regulator (101 ) for reducing the fuel gas pressure to a second predetermined pressure; and. an injection rail (102) for supplying said fuel gas to a series of injectors (1 , 2,3, 4, 5, 6), characterized in that, said at least one tank (100) being replenishable, the system includes:. a recycling loop for collecting, filtering and recompressing the gaseous fuel outputted by the injectors, and injecting the recompressed gaseous fuel into the storage tank (100); and. a leakage detection module (103) configured to detect and signal substantial drops of a gaseous fuel pressure value measured within the system, in particular within the injection rail (102).

2. The system as claimed in claim 1 , wherein the leakage detection module (103) includes a computing unit configured to compare a real-time value of the gaseous fuel pressure measured within the injection rail to a predetermined pressure reference value.

3. The system as claimed in claim 2, wherein the computing unit is further configured to:. launch a countdown when a difference between the predetermined pressure reference value and the real-time value of the gaseous fuel pressure value measured within the injection rail becomes greater than a predetermined threshold; and. transmit an alarm signal if, at the end of the countdown, a difference between the predetermined pressure reference value and the updated real-time value of the gaseous fuel pressure value measured within the injection rail is again greater than the predetermined threshold.

4. The system as claimed in any one of claims 2 or 3, wherein the predetermined pressure reference value is an instantaneous value computed in real time asbeing equal to an average value of a predetermined number of samples of the gaseous fuel pressure value within the injection rail, stored at regular intervals prior to the instant at which the comparison is made with the actual real-time value of the gaseous fuel pressure measured within the injection rail.

5. The system as claimed in any one of claims 1 to 4, further comprising an instrumentation module (120) for testing a plurality of injectors (1 , 2, 3, 4, 5, 6) placed in a row along a first direction (D1 ), a light emitting module (12) configured to output a light beam (121 ) in a direction essentially parallel to the first direction and a light receiving module (22) arranged across from the emitting module, said light receiving module (22) being intended to receive said light beam (121 ) and configured to output an electric signal (122) representative of an intensity of the light actually received by the light receiving module (22), the injectors (1 , 2, 3, 4, 5, 6) being each provided with a pintle (13) and being arranged in such a way that each pintle at least partially obstructs said light beam (121 ) when its respective injector (3) is actuated.

6. The system as claimed in any one of claims 1 to 5, further comprising an oil injection device for adding oil to the gaseous fuel supplied to the injectors (1 , 2, 3, 4, 5, 6), said injection device (130, 131 ) including a solenoid controlling the opening of an oil delivery valve upon reception of a control pulse, the oil injection device further comprising a controlling module (CNT) for sending to the solenoid a train of pulses having a duration inferior to the minimum duration required for said control pulse, said train of pulses including a number (N) of pulses, preferably varying as a function of a difference between the temperature (TDOZ) of the oil to be injected and a predetermined reference temperature (Tref).

7. A method for testing fuel gas injectors designed to be used for supplying an internal combustion engine with gaseous fuel, said system comprising:. at least one replenishable storage tank (100) for storing said fuel gas at a first pressure;. at least one pressure regulator (101 ) for reducing the fuel gas pressure to a second predetermined pressure; and. an injection rail (102) for supplying said fuel gas to a series of injectors (1 ,2, 3, 4, 5, 6),said method being characterized in that it includes:. a recycling step for collecting, filtering and recompressing the gaseous fuel outputted by the injectors, and injecting the recompressed gaseous fuel into the storage tank (100); and. a leakage detection step for detecting and signaling substantial drops of a gaseous fuel pressure value measured within the system.

8. The method as claimed in claim 7, wherein the leakage detection step includes a comparing step (304) for comparing a real-time value of the gaseous fuel pressure P(ti) measured within the injection rail to a predetermined pressure reference value Pref(ti).

9. The method as claimed in claim 8, wherein the leakage detection step further includes:. a temporizing step (305) during which a countdown is launched when a difference between the predetermined pressure reference value Pref(ti) and the real-time value P(ti) of the gaseous fuel pressure value measured within the injection rail becomes greater than a predetermined threshold (THR); and. an alarm signaling step during which an alarm signal (ALM) is transmitted if, at the end of the countdown, a difference between the predetermined pressure reference value and the updated real-time value P(ti+T0) of the gaseous fuel pressure value measured within the injection rail is again greater than the predetermined threshold (THR).

10. The method as claimed in any one of claims 8 or 9, further comprising a step for computing in real time an instantaneous predetermined pressure value as being equal to an average value of a predetermined number of samples P(tj, for j=i-n to i-1 ) of the gaseous fuel pressure value within the injection rail, stored at regular intervals prior to the instant (ti) at which the comparison is made with the actual real-time value P(ti) of the gaseous fuel pressure measured within the injection rail.

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