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 2,4 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 gas pressure and temperature within each section. The system may have a computing unit 50 which provided comparison means for comparing a first fuel gas mass within at least one section at a first time with a second fuel gas mass in the same at least one section at a second time. 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 gas-powered 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, 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 an engine re-start is about to happen after said engine has been turned off. In such a case, an electric repowering for igniting the engine may generate a spark which may in turn ignite a pocket of escaped supply gas generated during the engine’s inactive state by an undetected leak within the gas supply system, and thus damage the vehicle and even cause it to explode. In the context of Internal combustion engine usage, hydrogen can leak to compartments inappropriate for usage of conventional H2 leakage detectors, which are only working under ambient conditions, and not in hot nor wet conditions. It is therefore very important to be able to detect leaks occurring during inactive states of the engine, in order to inhibit its re-start as soon as such a leak is detected, as a mechanism complementary with the detection currently performed by the ambient H2 leakage detectors. 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. 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 (1) including at least one tank for storing said fuel gas at a predetermined 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 injectors, said system being characterized in that each section is separated from an adjacent section by a at least one pressure separator (11, 21, 31), the system being further provided with a plurality of sensors for assessing fuel gas pressure and temperature values (P, T) within said section. In the system according to the invention, temperature information pertaining to each section is gathered in addition to pressure information, which enables taking into account the effects of possible fuel gas expansion and compression occurrences which are currently overseen in known gaseous fuel supply / delivery systems. 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 like valves (11,31), or in the form of a pressure regulator (21). In an advantageous embodiment of the invention, the above defined system further comprises a computing unit (50) for computing a value of fuel gas mass enclosed within at least one section at a given instant on the basis of fuel gas pressure and temperature values (P, T) established at said given instant for said at least one section. 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 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. In another advantageous embodiment of the invention, the computing unit further comprises comparison means for comparing a first value of fuel gas mass enclosed within at least one section at a first instant with a second value of fuel gas mass enclosed within said at least one section at a second instant. This embodiment of the invention enables to accurately analyze a situation in which the fuel gas temperature of a given section has changed between the first and the second instant, for example between the shutting off of the engine and a later keying-on of said engine. In conventional systems, the temperature change will usually generate a pressure change and thus trigger an alarm signal preventing the actual re-powering of the engine, whereas the fuel gas mass within said given section may actually have remained constant, in which case no leakage alarm should have been raised. In such a situation, the invention will prevent the generation of a false alarm signal, but will still enable leakage detection and signaling in cases of fuel gas mass variation between the first and second instants. In a preferred embodiment of the invention, the computing unit further comprises compilation means for computing a first sum of values of fuel gas masses enclosed within at least two adjacent sections at a first instant and a second sum of values of fuel gas masses enclosed within said at least two adjacent sections at a second instant, and means for comparing said first and second sum of values. This embodiment of the invention enables to compute aggregate values of fuel gas masses enclosed within a plurality of sections of the system. Indeed, in certain situations, a given quantity of fuel gas may have exited a given section towards an another, adjacent section and still be trapped within said other section. The computation of an aggregate mass value for both sections, considered as a whole, will then enable to assert that no outside fuel gas leakage has occurred between the first and second instants, but that the shut-off valve separating the given section from its other, adjacent section may have developed a leak and should be closely examined and possibly repaired or replaced. 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 or mapping, each density value thus being addressed by a couple of pressure and temperature values acting as access coordinates to this matrix / mapping. 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 functional aspect, the invention also relates to a method for detecting leaks in a gaseous fuel supply system that comprises: . a first section (1) including at least one tank for storing fuel gas at a first predetermined pressure; . a second section (2) including at least one pressure regulator for reducing the fuel gas pressure to a second predetermined pressure; and . a third section (4) including an injection rail for alternatively supplying said fuel gas to one of a series of injectors, each section being separated from an adjacent section by a shut-off valve. The method is 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). The method according to the invention advantageously comprises a computing step (602) for computing a value of fuel gas mass enclosed within at least one section at a given instant on the basis of fuel gas pressure and temperature values established at said given instant for said at least one section. Advantageously, the above method further comprises a comparison step (603) for comparing a first value of fuel gas mass enclosed within at least one section at a first instant with a second value of fuel gas mass enclosed within said at least one section at a second instant. Preferably, the method according to the invention further comprises a compilation step (604) for computing a first sum of values of fuel gas masses enclosed within at least two adjacent sections at a first instant and a second sum of values of fuel gas masses enclosed within said at least two adjacent sections at a second instant, and comparing said first and second sum of values. In an advantageous application of the invention, the first instant corresponds to a shutting off of the engine and the second instant corresponds to a keying on of said engine. 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 a first embodiment of the invention; Fig. 2 is a schematic diagram of a method for detecting leaks in a gaseous fuel delivery 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 gaseous fuel delivery system SYST according to a first 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 predetermined, 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). 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 is predetermined 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) included in the second section (2) is here a mechanical pressure regulator and is 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). In this particular embodiment, the system SYST further includes a fourth section (4) comprising a hydraulic line connecting the pressure regulator (21) included in the second section (2) to the third section (3). Each section (1, 2, 3 and 4) 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 said section. 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 SYST further comprises a computing unit (50) for computing and storing in a memory (52) a value of fuel gas mass enclosed within at least one section at a given instant on the basis of fuel gas pressure and temperature values (P, T) established at said given instant for said at least one section, which values (P,T) have been stored over time in said memory (52) which cooperates with a processor (51) enclosed within the processing unit (50). The functionalities operated by the computing unit (50) in the context of the present invention are typically implemented by software. The processor (51) embodies comparison means for comparing, in cooperation with memory (52), a first value of fuel gas mass enclosed within at least one section at a first instant with a second value of fuel gas mass enclosed within said at least one section at a second instant. In this embodiment, The processor (51) enclosed within the computing unit (50) further embodies compilation means for computing, in cooperation with memory (52), a first sum of values of fuel gas masses enclosed within at least two adjacent sections at a first instant and a second sum of values of fuel gas masses enclosed within said at least two adjacent sections at a second instant, and means for comparing said first and second sum of values. As will be explained hereinafter, in predefined circumstances, if a difference between the first and second sum of values exceeds a given threshold, the computing unit (50) will recognize the existence of a leak within at least one of the considered sections and will hence generate an alarm signal 54 which will trigger an inhibition of the re-powering of the engine in order to prevent any possibility of igniting a pocket of leaked fuel gas. 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, a given section may find itself deprived of such sensors, in which case the temperature of the fuel gas enclosed within said section may be estimated, e.g. may 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. Fig.2 illustrates a method for operating the system described hereinbefore. 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 sections (i for i=1 to 3) at various instants (tj), and more particularly at a first instant t1 corresponds to a shutting off of the engine and at a second instant t2 corresponding to a keying on of the engine, all pressure separators (11, 21, 31) being intended to be activated when the engine is stopped. In this embodiment, the method further comprises a computing step (602) for computing values of fuel gas mass (M@t1, M@t2) enclosed within each section at instants t1 and t2 on the basis of fuel gas pressure and temperature values ((P,T)@t1, (P,T)@t2) established at said instants t1 and t2 for each section. 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 the 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. The computation of said 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 a mapping (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 the respective 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. The method according to this embodiment further comprises a comparison step (603) for comparing a first value of fuel gas mass (M@t1) enclosed within at least one section at a first instant t1 with a second value of fuel gas mass (M@t2) enclosed within said at least one section at a second instant t2. The present method allows to accurately analyze a situation in which the fuel gas temperature of a given section has changed between the first and the second instant (t1, t2), i.e. between the shutting off of the engine and a later keying-on of said engine. By contrast, in conventional systems, the temperature change will usually generate a pressure change and thus trigger an alarm signal preventing the actual re-powering of the engine, whereas the fuel gas mass within said given section may actually have remained constant, in which case no leakage alarm should have been raised. In such a situation, the inventive method will prevent the generation of a false alarm signal, but will still enable leakage detection and signaling in cases of fuel gas mass variation between the first and second instants (t1, t2). The method shown in the figure 2 further comprises a compilation step (604) for computing a first sum of values of fuel gas masses enclosed within at least two adjacent sections at a first instant and a second sum of values of fuel gas masses enclosed within said at least two adjacent sections at a second instant, and comparing said first and second sum of values. This embodiment enables to compute aggregate values of fuel gas masses enclosed within a plurality of sections of the system. Indeed, in certain situations, a given quantity of fuel gas may have exited a given section towards an another, adjacent section and still be trapped within said other section. The computation of an aggregate mass value for both sections, considered as a whole, will then enable to assert that no outside fuel gas leakage has occurred between the first and second instants, but that the shut-off valve separating the given section from its other, adjacent section may have developed a leak and should be closely examined and possibly repaired or replaced. 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), an absence of fuel gas leakage may be transcribed by the equation: (M1 @t1 )+(M2@t1 )+(M3@t1)+(M4@t 1) = (M1 @t2)+(M2@t2)+(M3@t2)+(M4@t2) Conversely, if (M1 @t1 )+(M2@t1 )+(M3@t1 )+(M4@t1) - [(M1 @t2)+(M2@t2)+(M3@t2)+(M4@t2)] >THR, where THR is a predetermined threshold value, the computing unit will send an alarm signal which will trigger an inhibition of the re-powering of the engine in order to prevent any possibility of igniting a pocket of leaked fuel gas. The knowledge of the fuel gas mass value of each section for both instants t1 and t2 enables to 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 t1 and t2, while the aggregate value of the fuel gas mass in sections (2) and (3) has remained constant, which may be written as: (M1@t1) - (M1@t2) >THR and (M2@t1)+(M3@t1) - [(M2@t2)+ (M3@t2)] <THR 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.: (M1@t1) - (M1@t2) >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 value THR may be a constant value, but it may also vary as predetermined function of the time elapsed between the first and second instants t1 and t2, e.g. the value of THR could be proportional to said elapsed time, which would then be written THR=THR0.(t2-t1) where THRO is a constant value. Fig. 3 illustrates a gaseous fuel delivery system SYST according to a second 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 predetermined 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) for connecting the second and third sections together via a further shut-off valve (41). In this variant, the gaseous fuel, for example hydrogen, is stored within tanks (101, 102...1 On) 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 configured to decrease the fuel gas pressure to an intermediate value which will be around 50 bar, the second pressure regulator (37) being an electronically driven regulator (i.e. controllable) configured to output a fuel gas stream at reduced pressure, e.g. at a a working pressure ranging from 20 to 40 bar. In this embodiment, 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), an absence of fuel gas leakage may be transcribed by the equation: (M1@t1)+(M2@t1)+(M3@t1)+(M4@t1) = (M1@t2)+(M2@t2)+(M3@t2)+(M4@t2) Conversely, if (M1@t1)+(M2@t1)+(M3@t1)+(M4@t1) - [(M1@t2)+(M2@t2)+(M3@t2) )+(M4@t1)] >THR the computing unit will send an alarm signal which will trigger an inhibition of the repowering of the engine 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 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 predetermined pressure, a third section (3) including an electronically driven pressure regulator (37) for reducing the fuel gas pressure 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 4) at instant j, (for j=1 or 2), an absence of fuel gas leakage may be transcribed by the equation: (M1@t1)+(M2@t1)+(M3@t1) = (M1@t2)+(M2@t2)+(M3@t2) Conversely, if (M1@t1)+(M2@t1)+(M3@t1) - [(M1@t2)+(M2@t2)+(M3@t2))] >THR the computing unit will send an alarm signal which will trigger an inhibition of the re-powering of the engine 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 predetermined 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 injectors,said system being characterized in that each section is separated from an adjacent section by a at least one pressure separator (11, 21, 31), the system being further provided with a plurality of sensors for assessing fuel gas pressure and temperature values (P, T) within each section.

2. The system as claimed in claim 1, characterized in that it further comprises a computing unit (50) for computing a value of fuel gas mass enclosed within at least one section at a given instant on the basis of fuel gas pressure and temperature values (P, T) established at said given instant for said at least one section.

3. The system as claimed in claim 2, characterized in that the computing unit further comprises comparison means for comparing a first value of fuel gas mass enclosed within at least one section at a first instant with a second value of fuel gas mass enclosed within said at least one section at a second instant.

4. The system as claimed in claim 3, characterized in that the computing unit further comprises compilation means for computing a first sum of values of fuel gas masses enclosed within at least two adjacent sections at a first instant and a second sum of values of fuel gas masses enclosed within said at least two adjacent sections at a second instant, and means for comparing said first and second sum of values.

5. The system as claimed in any one of claims 1 to 4, characterized in that it further includes a memory (52) for storing fuel gas density values, each of whichcorresponding to a given combination of fuel gas pressure and fuel gas temperature.

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

7. The system as claimed in any one of claims 1 to 6, 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.

8. A method for detecting leaks in a gaseous fuel delivery system comprising: . a first section (1) including at least one tank for storing fuel gas at a first predetermined pressure;. a second section (2) including at least one pressure regulator for reducing the fuel gas pressure to a second predetermined pressure; and. a third section (3) including an injection rail for alternatively supplying said fuel gas to one of a series of injectors,each section being separated from an adjacent section by a pressure separator, 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).

9. The method as claimed in claim 8, characterized in that it comprises a computing step (602) for computing a value of fuel gas mass enclosed within at least one section at a given instant on the basis of fuel gas pressure and temperature values established at said given instant for said at least one section.

10. The method as claimed in claim 9, characterized in that it further comprises a comparison step (603) for comparing a first value of fuel gas mass enclosed within at least one section at a first instant with a second value of fuel gas mass enclosed within said at least one section at a second instant.

11. The method as claimed in claim 10, characterized in that it further comprises a compilation step (604) for computing a first sum of values of fuel gas massesenclosed within at least two adjacent sections at a first instant and a second sum of values of fuel gas masses enclosed within said at least two adjacent sections at a second instant, and comparing said first and second sum of values.

12. A method as claimed in any one of claims 8 to 12, wherein the first instant corresponds to a shutting off of the engine and the second instant corresponds to a keying on of said engine, all pressure separators being intended to be activated when the engine is stopped.

13. The method as claimed in any one of claims 8 to 12, 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.

14. The method as claimed in any one of claims 8 to 13, wherein the pressure separator is a shut-off valve or a pressure reducer.

15. The method as claimed in any one of claims 8 to 14, 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.

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