Fuel gas supply system with enhanced leak detection

Abstract

A gaseous fuel supply system comprising a first section 1 including at least one fuel tank 101 at a predetermined first pressure. The system also has a second section 2 including at least one pressure regulator 21 for reducing the fuel pressure to a predetermined second pressure. The system has a third section 3 including an injection rail 32 for supplying fuel to a series of injectors 33-36. The system is arranged such that each section is separated from an adjacent section by at least one pressure separator (11,21,31). The system has a plurality of sensors for monitoring fuel pressure and temperature within each section. The system has a computing unit 50 which calculates a cumulative quantity of fuel injected in the engine through the injectors between a first and second instant. The computing module may be configured to calculate an input value defined as the difference between fuel enclosed within said system at the first and second instants. An output value may be calculated defined by the cumulative quantity. The computing module may issue an alarm if the difference between the input and output values is above a threshold. A method for detecting leaks is also claimed.

Description

FIELD OF THE INVENTION The present invention generally relates to a system for supplying a combustion engine with fuel gas, particularly hydrogen. BACKGROUND OF THE INVENTION It is well known within the art that gas leakage is an important concern for designers of vehicles powered by combustion engines, and particularly hydrogen combustion engines. Indeed, the hydrogen fuel gas is usually stored at high pressures ranging from 350 bars to 700 bars and above, before having its pressure reduced by means of various components to 5 to 40 bars in order to enable its injection within the actual engine, such a supply process creating multiple situations in which fuel gas leakage may occur. Furthermore, hydrogen is intrinsically very volatile and inflammable as past catastrophes have amply demonstrated, so that early and accurate detection of any kind of fuel gas leakage is of paramount importance in terms of user safety, which is in turn crucial for the commercial success of hydrogen-powered vehicles. The detection of fuel gas leakage is of special importance in situations where the engine is running, i.e. when electrical power is applied to certain of its parts, in which situations random sparks may ignite a pocket of escaped supply gas generated by an undetected leak within the gas supply system, and thus damage the vehicle and possibly even cause it to explode. It is therefore very important to be able to detect leaks occurring during the operation of the engine, in order to trigger an alarm an enable the vehicle’s user to shut down said engine as soon as possible after such a leak is detected. TECHNICAL PROBLEM In the current state of the art, pressure measurement means are used in different sections of known fuel gas supply systems in order to monitor the pressure specific to each section and detect any substantial variation which could be caused by a leak within said section. However, the inventors have observed that a substantial pressure variation between two successive measurements may be explained by a variation in temperature in the time interval between said measurements, so that the accuracy and the general reliability of the known leakage detection techniques is insufficient. The inventors have thus aimed at designing a fuel gas supply system in which leaks can be detected and pinpointed with greater precision and reliability than in known systems, even while the engine is running. GENERAL DESCRIPTION OF THE INVENTION The invention aims at overcoming the above-mentioned drawbacks, by providing a gaseous fuel delivery system for supplying a combustion engine with fuel gas, said system comprising: . a first section including at least one tank for storing said fuel gas at a first pressure; . a second section including at least one pressure regulator for reducing the fuel gas pressure to a predetermined second pressure; and . a third section including an injection rail for supplying said fuel gas a series of fuel gas injectors associated with respective engine cylinders, characterized in that each section is separated from an adjacent section by at least one pressure separator, and in that it further includes: . a plurality of sensors for assessing fuel gas pressure and temperature values (P, T) within each of said sections; and . a computing module configured to calculate a cumulated quantity of fuel gas injected in the engine through the injectors between a first and a second instant. A pressure separator is a component which is able to establish a separation between two hydraulic sections which contain fluid at two different respective pressures. A pressure separator may be embodied in the form of a shut-off valve, or in the form of a pressure reducer. The sections are preferably connected in series and the pressure separators are then arranged at the interface between adjacent sections, whereby gas may only flow from one section to an adjacent section via a respective pressure separator. In the delivery system according to the invention, temperature information pertaining to each section is gathered in addition to pressure information, which enables to take into account the effects of possible fuel gas expansion and compression occurrences which are currently overseen in known supply systems. The invention thus allows an accurate computing of the quantity of fuel gas outputted by the delivery system between the first and second instants and to compare this outputted value to the calculated quantity of fuel gas injected in the engine through the injectors between these first and second instants. Any significant difference between both quantities will indicate a high probability of leakage and trigger the generation of an alarm signal. In an advantageous embodiment of the invention, the computing module included in the above defined system is further configured to: .compute an input value defined as a difference value between a first and a second value of fuel gas mass enclosed within said system at a said first and second instants on the basis of fuel gas pressure and temperature values (P, T) established at said first and second instants for each section; . determine an output value defined as a value of fuel gas mass injected through the injectors between said first and second instants on the basis of the calculated cumulated quantity; and . issue an alarm signal if a difference between said input and output values is greater than a predetermined threshold value. This embodiment of the invention is advantageous because, unlike its pressure, the mass of the fuel gas included in a closed circuit should remain invariant even if the temperature of said fuel gas is varying. The computation and use of fuel gas mass values will enable to assess the state of the supply system in terms of mass conservation, which is physically more accurate and error-proof than comparisons of pressure values. According to a specific embodiment of the invention, a system as described above further includes a memory for storing fuel gas density values, each of which corresponding to a given combination of fuel gas pressure and fuel gas temperature. In this specific embodiment, the density values can advantageously be stored in the form of a matrix, each density value thus being addressed by a couple of pressure and temperature values acting as access coordinates to this matrix. The mass of fuel gas enclosed within any given section at any given instant may then be easily computed as being equal to the multiplication of a known volume value of said given section by the density value memorized in combination with the fuel gas pressure and fuel gas temperature corresponding to said given instant. According to a preferred embodiment of the invention, sensors intended to measure fuel gas pressure and temperature values (P, T) pertaining to a given section are arranged in the vicinity of a central location intrinsic to said given section. In this preferred embodiment of the invention, the measured fuel gas pressure and temperature values (P, T) will have a high probability of being representative of the operating conditions of the given section in consideration, although local gas pressure and temperature values of outer parts of this given section may differ from the measured value because of possible external parasitic factors, the influence of which thus being downplayed. According to a another aspect, the invention also relates to a method for detecting leaks in a gaseous fuel supply system of an internal combustion engine, the system gaseous fuel delivery comprising: . a first section including at least one tank for storing said fuel gas at a first pressure; . a second section including at least one pressure regulator for reducing the fuel gas pressure to a predetermined second pressure; and . a third section including an injection rail for supplying said fuel gas to a series of fuel gas injectors associated with respective engine cylinders; wherein each section is separated from an adjacent section by at least one pressure separator; said method being characterized in that it includes: . an assessing step and a memorizing step for assessing and memorizing fuel gas pressure and temperature values (Pij, Tij) within at least two adjacent sections (i for i=1 to 4) at a given instant (tj); and . an injection calculating step for calculating a cumulated quantity of fuel gas injected in the engine through the injectors between a first and a second instant (t1, t2). The injection calculating step may conveniently involve summing the fuel quantities between instants (t1, t2) that are used by the ECU (engine control unit) for controlling the injection events. These are typically fuel masses determined from a mapping relating torque demand and fuel mass (also generally in function of fuel pressure). This is however only an example; other approaches may be used to calculate the cumulated quantity of fuel gas injected into the engine, e.g. where the individual injector quantities are determined based on pressure drop in the fuel rail. The method according to the invention advantageously comprises a computing step for: .computing an input value defined as a difference value between a first and a second value of fuel gas mass enclosed within said system at a said first and second instants on the basis of fuel gas pressure and temperature values (P, T) established at said first and second instants for each section. In this step, the fuel mass within the system at two different instants is considered based on pressure and temperature, to determine a change of mass over a time period. . determining an output value defined as a value of fuel gas mass injected through the injectors between said first and second instants on the basis of the calculated cumulated quantity. In this step, the injected fuel mass is determined based on injection control information. When the calculated cumulated quantity is based on summing fuel mass from the (Torque; Fuel gas quantity) maps, the calculated cumulated quantity is thus readily expressed in mass and the output value may thus directly correspond to the calculated cumulated quantity (output value = calculated cumulated quantity). If the calculated cumulated quantity is determined using other information, for example expressed in fuel volume, then this step may involve converting the fuel quantity into fuel mass. . a comparison step for issuing an alarm signal if a difference between said input and output values is greater than a predetermined threshold value. According to a specific variant of the invention, the temperature of the fuel gas enclosed within at least one section is computed on the basis of at least one temperature value related to an engine component which is adjacent to said at least one section. In this variant of the invention, it is not necessary to equip each section of the supply system with both pressure and temperature sensors. Indeed, a temperature information pertaining to a given section may be calculated by pondering a value measured in the vicinity of said given section on the basis of a temperature variation gradient. For example, the temperature of the injection rail can be calculated on the basis of an already measured motor temperature value. Brief Description of the Drawings 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: Fig. 1 is a schematic diagram of a gaseous fuel delivery system according to an advantageous embodiment of the invention; Fig. 2 is a schematic diagram of a method for detecting leaks in a gaseous fuel supply system; Fig. 3 is a schematic diagram of a gaseous fuel delivery system according to another embodiment of the invention; and Fig. 4 is a schematic diagram of a gaseous fuel delivery system according to yet another embodiment of the invention. Description of Preferred Embodiments Fig. 1 illustrates a first embodiment of the present gaseous fuel delivery system SYST comprising: . a first section (1) including a plurality of tanks (101, 102... 10n) for storing said fuel gas at a first pressure; . a second section (2) including at least one pressure regulator (21) for reducing the fuel gas pressure to a predetermined second pressure; and . a third section (3) including an injection rail (32) for alternatively supplying said fuel gas to one of a series of injectors (33, 34, 35, 36), each injector configured to provide a cylinder of a combustion engine with fuel gas. Fig. 1 is a simplified diagram; various additional elements can be present that are not represented here in order to simplify the description (e.g. circuit to fill the tank, filters, Pressure Relief Valves, Purge valves, etc.). Furthermore, although the engine includes four injectors in the present example, in other embodiments, the number of injectors may vary, e.g. ranging from three to eight. In this embodiment of the invention, the gaseous fuel, for example hydrogen, is stored within tanks (101, 102... 10n) at a relatively high pressure ranging from 350 to 700 bar. The first pressure is the pressure within the first section and varies in use. It may be referred to as predetermined pressure in the sense that it is typically filled up to a filling pressure, but the pressure will drop as the gas is consumed by the engine. The pressure regulator (21) is here a mechanical pressure regulator and configured to decrease the fuel gas pressure to a range of 30 to 50 bar, which corresponds to an exemplary working pressure of the injection rail (32). Remarkably, each section (1,2, 3) is separated from an adjacent section by at least one pressure separator, which can be either embodied by a shut-off valve (11,31) or a pressure regulator (21), the system SYST being further provided with a plurality of sensors for assessing fuel gas pressure and temperature values (P, T) within the respective sections. It may be noted that, as seen on the figures, the sections are connected in series. Advantageously, the pressure separators are arranged at the interface between adjacent sections. In other words, gas may only flow from one section to an adjacent section via a respective pressure separator. Regarding the shut-off valves, they allow flow from one section to an adjacent section when in open state. In closed state, the gas cannot flow through the shut-off valve, which prevents flow from the current section to the adjacent section. In other words, closing the shut-off valve of a respective section allows to isolating (fluidically) that section from an adjacent section. The system further includes a computing module (50) configured to calculate a cumulated quantity of fuel gas injected in the engine through the injectors between a first and a second instant, on the basis of injection data (ID) provided by the Engine control unit (ECU). This cumulated quantity is typically computed from the fuel masses determined in accordance with the injection control schemes, based on mappings relating torque demand with fuel quantities (ref. 60 in Fig.2). These fuel masses can thus be seen as theoretic or reference quantities, in that they represent the fuel masses that are used by the ECU to perform / control the injection events. In other words, the computing module is configured to sum the reference fuel mass quantities used to perform the injection events performed between the first and second instants. In the present delivery system SYST, temperature information pertaining to each section (1, 2, 3) is gathered in addition to pressure information, which enables to take into account the effects of possible fuel gas expansion and compression occurrences which are currently overseen in known supply systems. The invention then allows an accurate computing of the quantity of fuel gas outputted by the delivery system between the first and second instants and to compare this outputted value to the calculated cumulated quantity of fuel gas injected in the engine through the injectors between these first and second instants. The outputted quantity of fuel gas refers to the quantity (mass) of fuel gas that is discharged / withdrawn from the system. Accordingly, the computing unit (50) is configured to compute and store in a memory (52) values of fuel gas mass enclosed within each section at given instants on the basis of fuel gas pressure and temperature values (P, T) established at said given instants for said section, which values (P,T) are stored over time in said memory (52) which cooperates with a processor (51) enclosed within the processing unit (50). The processor (51) embodies computing means for: .computing an input value defined as a difference value between a first and a second value of fuel gas mass enclosed / contained within the system at a first and second instant on the basis of fuel gas pressure and temperature values (P, T) established at the first and second instants for each section; . computing an output value defined as a value of fuel gas mass injected through the injectors between said first and second instants on the basis of the calculated cumulated quantity . In general, where the calculated cumulated quantity is determined in mass, we have: output value = calculated cumulated quantity. . issuing an alarm signal (54) if a difference between said input and output values is greater than a predetermined threshold value. The functionalities operated by the computing module (50) in the context of the present invention are typically implemented by software. They can be integrated in the Engine control unit. In this embodiment, each section is provided with sensors for measuring its fuel gas pressure and temperature values (P, T). In other embodiments of the invention however, a given section may find itself deprived of such sensors, in which case the temperature of the fuel gas enclosed within said section will be computed on the basis of at least one temperature value related to an engine component which is adjacent to said at least one section, e.g. an adjacent section or a component of the motor itself. Indeed, a temperature information pertaining to a given section may be calculated by pondering a value measured in the vicinity of said given section on the basis of a temperature variation gradient. For example, the temperature of the injection rail (32) can be calculated on the basis of an already measured motor temperature value. According to a preferred embodiment of the invention, sensors configured to measure fuel gas pressure and temperature values (P, T) pertaining to a given section (1,2, 3) are arranged in the vicinity of a central location intrinsic to said given section. In this preferred embodiment of the invention, the measured fuel gas pressure and temperature values (P, T) will have a high probability of being representative of the operating conditions of the given section in consideration, although local gas pressure and temperature values of outer parts of this given section may differ from the measured value because of possible external parasitic factors, the influence of which thus being downplayed. Fig. 2 illustrates an embodiment of a method for detecting leaks in a gaseous fuel delivery according to the present disclosure.. This method includes an assessing step (600) and a memorizing step (601) for assessing and memorizing fuel gas pressure and temperature values (Pij, Tij) within at least two adjacent sections at a given instant (tj). Preferably, the (Pij, Tij) are computed for all sections, i.e. for i=1 to N, where N is the total number of section. In figs. 1 and 4 we have N=3, whereas in Fig.3 N=4. An injection calculating step (602) involves calculating a cumulated quantity of fuel gas injected into the engine through the injectors between a first and a second instant (t1, t2). As indicated before, the cumulated quantity determined in step (602) may typically be obtained by computing a sum of all quantities of fuel used for injector control, i.e. to build the injector control signals in order to perform the injection events between the first and second instants (t1, t2). Conventionally, injector control signals are defined based on mappings relating torque and fuel mass, as represented by reference sign 60. As will be understood, this cumulated quantity may slightly differ from the sum of all quantities of fuel actually injected by the injectors due to part to part variations and calibrations issues. However, the cumulated quantity represents a nominal or reference fuel quantity that can be easily computed from available data generated by conventional injection control schemes. The resulting value of step (602) is referred to as output value and indicated IM(t1,t2) in Fig.2, which is thus defined as a value of fuel gas mass injected through the injectors between said first and second instants (t1, t2) on the basis of the calculated cumulated quantity. The method further comprises the step (603) of computing an input value (M@t1-M@t2) defined as a difference value between a first (M@t1) and a second (M@t2) value of fuel gas mass enclosed within the system SYST at said first and second instants (t1, t2) on the basis of fuel gas pressure and temperature values (P, T) established at said first and second instants (t1, t2) for each section. Finally, a comparison step (604) is configured for issuing / generating an alarm signal (54) if a difference between the input and output values is greater than a predetermined threshold value. As explained above, this embodiment of the invention is advantageous because, unlike its pressure, the fuel gas mass included in a closed circuit should remain invariant even if the temperature of said fuel gas is varying. The computation and use of fuel gas mass values will enable to analyze the state of the supply system in terms of mass conservation, which is physically more accurate and error-proof than comparisons of pressure values. In step 603, the computation of the values of fuel gas mass (M@t1, M@t2) is here performed by using the fuel gas pressure and temperature values ((P,T)@t1, (P,T)@t2) as access coordinates for obtaining corresponding fuel density values (D@t1, D@t2) stored within matrix (53). For each section, the values of fuel gas mass (M@t1, M@t2) at a given instant t1 or t2 will then be computed as being equal to the multiplication of a known volume value V of said given section by the density value (D@t1) or (D@t2) memorized in combination with the fuel gas pressure and fuel gas temperature ((P,T)@t1) or (P,T)@t2) corresponding to said given instant t1 or t2. Considering the system SYST as a whole, if (Mi@tj) is the mass of fuel gas enclosed within section i (for i=1 to 3) at instant j, (for j=1 or 2), the total input value (M@t1 -M@t2) defined as a difference value between a first (M@t1) and a second (M@t2) value of fuel gas mass enclosed within the system at a said first and second instants (t1, t2) is computed as: (M@t1 -M@t2) = (M1 @t1 )+(M2@t1 )+(M3@t1) - [(M1 @t2)+(M2@t2)+(M3@t2)] An absence of fuel gas leakage may be transcribed by the equation: (M@t1-M@t2) = IM(t1,t2) Conversely, if (M@t1-M@t2) - IM(t1,t2) >THR1, where THR1 is a first predetermined threshold value, the computing unit will send an alarm signal which will should cause the user of the vehicle to shut off the engine as soon as possible in order to prevent any possibility of igniting a pocket of leaked fuel gas. Once the engine has been stopped, the invention may enable to help pinpoint the leak thanks to a continuing assessment of pressure and temperature values pertaining to each section between a given instant t3 and a later instant t4. Indeed, after engine shut-off, an absence of fuel gas leakage in the fuel gas delivery system may be transcribed by the equation: (M1@t3)+(M2@t3)+(M3@t3) - [(M1@t4)+(M2@t4)+(M3@t4)]=0 In such a case, the leak is to be searched outside the fuel gas delivery system, for example at the level of the injection rail or within one or several injectors. Conversely, if (M1@t3)+(M2@t3)+(M3@t4) - [(M1@t4)+(M2@t4)+(M3@t4)] >THR2, a leak is located within the fuel gas delivery system, THR2 being a second predetermined threshold value, which may or may not be equal to the first predetermined threshold value THR1. The knowledge of the fuel gas mass value of each section for both instants t3 and t4 enables to further pinpoint the component of the system where a leakage has occurred. Indeed, if there is a significant difference in the value of the fuel gas mass in section (1), i.e. in the tanks, between instants t3 and t4, while the aggregate value of the fuel gas mass in sections (2) and (3) has remained constant, which may be written as: (M1 @t3) - (M1 @t4) >THR2 and (M2@t3)+(M3@t4) - [(M2@t3)+ (M3@t4)] <THR2 the leak is most probably located within at least one of the fuel tanks, for example within a dysfunctional tank shut-off valve. This operating principle may be generalized for pinpointing possible leaks: If there is a significant difference in the value of the fuel gas mass in section (i), i.e.: (Mi@t3) - (Mi@t4) >THR and no significant difference in the value of the fuel gas mass in the other sections, there is a high probability of leakage within section i. It should be noted here that the threshold values THR1 and THR2 may have a same constant value, but they may also vary as predetermined function of the time elapsed between the first and second instants t1 and t2, and the third and fourth instants t4, respectively. As an example, the value of THR1 could be proportional to the elapsed time between first instants t1 and t2, which would then be written THR=THR0.(t2-t1) where THRO is a constant value. Another interesting application of the invention is worthy of note: As explained hereinbefore, the output value IM(t1,t2) is based on the calculated cumulated quantity which can for example be obtained by computing a sum of all quantities of fuel scheduled for injection via each injector between the first and second instants (t1, t2). The value of the calculated cumulated quantity of injected fuel gas thusly obtained may slightly differ from the sum of all quantities of fuel actually injected by each injector between said first and second instants (t1, t2). However, a significant difference between the cumulated calculated value and the actually injected value may indicate a problem located within at least one of the injectors. Therefore, the invention advantageously also enables to monitor the following comparison: IM(t1 ,t2) - (M@t1-M@t2) >THRI, where THRI is a predetermined threshold value specific to injector leakage and (M@t1-M@t2) represents the total fuel gas mass delivered to the injectors in the absence of leakage within the fuel delivery system. Fig. 3 illustrates a gaseous fuel delivery system SYST according to another embodiment of the invention, which comprises: . a first section (1) including a plurality of tanks (101, 102... 10n) for storing said fuel gas at a first pressure; . a second section (2) including a first pressure regulator (21) for reducing the fuel gas pressure to an intermediate pressure; . a third section (3) including a second pressure regulator (37) for further reducing the fuel gas pressure from said intermediate pressure to a working pressure suitably adjusted for the optimal operation of an injection rail (32) intended to alternatively supply said fuel gas to one of a series of injectors (33, 34, 35, 36); and . a fourth section (4) that connects the second and third sections together via a further shut-off valve (41). In this embodiment of the invention, the gaseous fuel, for example hydrogen, is stored within tanks (101, 102... 10n) at a relatively high pressure ranging from 350 to 700 bar, the pressure regulator (21) being a mechanical pressure regulator incorporating a shut-off valve and intended to decrease the fuel gas pressure to a intermediate value which will be close to 50 bar, the second pressure regulator (37) being an electronically driven regulator able to reduce the fuel gas pressure from said intermediate pressure to an optimal working pressure ranging from 20 to 40 bar. In this embodiment of the invention, considering the system as a whole, if (Mi@tj) is the mass of fuel gas enclosed within section i (for i=1 to 4) at instant j, (for j=1 or 2), the total input value (M@t1-M@t2) defined as a difference value between a first (M@t1) and a second (M@t2)value of fuel gas mass enclosed within said system at a said first and second instants (t1, t2) is computed as: (M@t1 -M@t2) = (M1 @t1 )+(M2@t1 )+(M3@t1 )+(M4@t1) - [(M1 @t2)+(M2@t2)+(M3@t2)+(M4@t1)] and an absence of fuel gas leakage may be transcribed by the equation: (M@t1-M@t2) = IM(t1,t2) Conversely, if (M@t1-M@t2) - IM(t1 ,t2) >THR1, where THR1 is a first predetermined threshold value, the computing unit will send an alarm signal which will should cause the user of the vehicle to shut off the engine as soon as possible in order to prevent any possibility of igniting a pocket of leaked fuel gas. Fig.4 illustrates a gaseous fuel delivery system SYST according to yet another embodiment of the invention, which comprises a first section (1) including a plurality of tanks (101, 102... 10n) for storing said fuel gas at a first pressure, a third section (3) including an electronically driven pressure regulator (37) for reducing pressure of the fuel gas from the first predetermined pressure to a working pressure suitably adjusted for the optimal operation of an injection rail (32) intended to alternatively supply said fuel gas to one of a series of injectors (33, 34, 35, 36), and a second section (2) linking the first (1) and third (3) sections together. In this embodiment of the invention, considering the system as a whole, if (Mi@tj) is the mass of fuel gas enclosed within section i (for i=1 to 3) at instant j, (for j=1 or 2), the total input value (M@t1-M@t2) defined as a difference value between a first (M@t1) and a second (M@t2)value of fuel gas mass enclosed within said system at a said first and second instants (t1, t2) is computed as: (M@t1-M@t2) = (M1@t1)+(M2@t1)+(M3@t1) - [(M1@t2)+(M2@t2)+(M3@t2)] and an absence of fuel gas leakage may be transcribed by the equation: (M@t1-M@t2) = IM(t1,t2) Conversely, if (M@t1-M@t2) - IM(t1 ,t2) >THR1, where THR1 is a first predetermined threshold value, the computing unit will send an alarm signal which will should cause the user of the vehicle to shut off the engine as soon as possible in order to prevent any possibility of igniting a pocket of leaked fuel gas.

Claims

1. A gaseous fuel delivery system for supplying a combustion engine with fuel gas, said system comprising:. a first section (1) including at least one tank for storing said fuel gas at a first pressure;. a second section (2) including at least one pressure regulator for reducing the fuel gas pressure to a predetermined second pressure; and. a third section (4) including an injection rail for supplying said fuel gas a series of fuel gas injectors (33, 34, 35, 36) associated with respective engine cylinders, characterized in that each section is separated from an adjacent section by at least one pressure separator (11, 21, 31), and in that it further includes:. a plurality of sensors for assessing fuel gas pressure and temperature values (P, T) within each of said sections; and. a computing module (50) configured to calculate a cumulated quantity of fuel gas injected in the engine through the injectors between a first and a second instant.

2. The system as claimed in claim 1, characterized in that the computing module (50) is further configured to:.compute an input value defined as a difference value between a first and a second value of fuel gas mass enclosed within said system at a said first and second instants on the basis of fuel gas pressure and temperature values (P, T) established at said first and second instants for each section;. determine an output value defined as a value of fuel gas mass injected through the injectors between said first and second instants on the basis of the calculated cumulated quantity; and. issue an alarm signal if a difference between said input and output values is greater than a predetermined threshold value.

3. The system as claimed in any one of claims 1 to 2, characterized in that it further includes a memory (53) for storing fuel gas density values, each of which corresponding to a given combination of fuel gas pressure and fuel gas temperature.

4. The system as claimed in any one of claims 1 to 2, characterized in that sensors configured to measure fuel gas pressure and temperature values (P, T) pertaining to a given section are arranged in the vicinity of a central location intrinsic to said given section.

5. The system as claimed in any one of claims 1 to 4, wherein the pressure separator is a shut-off valve or a pressure reducer.

6. The system as claimed in any one of claims 1 to 5, wherein the sections are connected in series and the pressure separators are arranged at the interface between adjacent sections, whereby gas may only flow from one section to an adjacent section via a respective pressure separator.

7. A method for detecting leaks in a gaseous fuel delivery system of an internal combustion engine, the system gaseous fuel delivery comprising:. a first section (1) including at least one tank for storing said fuel gas at a first pressure;. a second section (2) including at least one pressure regulator for reducing the fuel gas pressure to a predetermined second pressure; and. a third section (4) including an injection rail for supplying said fuel gas to a series of fuel gas injectors (33, 34, 35, 36) associated with respective engine cylinders;wherein each section is separated from an adjacent section by at least one pressure separator (11,21, 31);said method being characterized in that it includes:. an assessing step (600) and a memorizing step (601) for assessing and memorizing fuel gas pressure and temperature values (Pij, Tij) within at least two adjacent sections (i for i=1 to 4) at a given instant (tj);and. an injection calculating step (602) for calculating a cumulated quantity of fuel gas injected in the engine through the injectors between a first and a second instant (t1, t2).

8. The method as claimed in claim 7, characterized in that it comprises a computing step (603) for:.computing an input value defined as a difference value between a first and a second value of fuel gas mass enclosed within said system at a said first and second instants on the basis of fuel gas pressure and temperature values (P, T) established at said first and second instants for each section;. determining an output value defined as a value of fuel gas mass injected through the injectors between said first and second instants on the basis of the calculated cumulated quantity; and. a comparison step (604) for issuing an alarm signal if a difference between said input and output values is greater than a predetermined threshold value.

9. The method as claimed in any one of claims 7 to 8, characterized in that the temperature of the fuel gas enclosed within at least one section is computed on the basis of at least one temperature value related to an engine component which is adjacent to said at least one section.

10. The method as claimed in any one of claims 7 to 9, wherein the pressure separator is a shut-off valve or a pressure reducer.

11. The method as claimed in any one of claims 7 to 10, wherein the sections are connected in series and the pressure separators are arranged at the interface between adjacent sections, whereby gas may only flow from one section to an adjacent section via a respective pressure separator.

12. The method as claimed in any one of claims 7 to 11, wherein said cumulated quantity of fuel gas injected in the engine is determined based on the fuel quantities used for injection control and obtained from a mapping relating torque demand and fuel gas quantity.

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