Fuel systems including auto-adaptation to gaseous fuel variation

Abstract

A system includes an engine including combustion cylinders, a fueling system including a fuel rail configured to receive a gaseous fuel mixture from a fuel supply, fuel injectors in operative communication with the fuel rail and the combustion cylinders, and a pressure sensor system operatively coupled with the fuel rail and configured to provide output indicative of fuel pressure of the fuel rail. An electronic control system is in operative communication with the fueling system and controls on times of the plurality of fuel injectors to provide injections of the gaseous fuel mixture, determines a fueling control parameter in response to output of the pressure sensor system, changes the fueling control parameter in response to a change in average molecular mass of the gaseous fuel mixture, and in response to the change in the fueling control parameter, adjust an injector operation parameter.

Description

FUEL SYSTEMS INCLUDING AUTO-ADAPTATION TO GASEOUS FUEL VARIATIONCROSS-REFERENCE

[0001] The present disclosure claims priority to and the benefit of U.S. Application No. 63 / 520,390 filed August 18, 2023, and the same is hereby incorporated by reference.TECHNICAL FIELD

[0002] The present application relates to fuel systems including auto-adaptation to gaseous fuel variation, fuel systems including gaseous fuel identification, and related apparatuses, controls, diagnostic, processes, systems, and techniques.BACKGROUND

[0003] Gaseous fueling systems for internal combustion engines and controls for such systems suffer from a number of shortcomings including those respecting accuracy, complexity, computational burden, dedicated hardware requirements, precision, reliability, and robustness, among other shortcomings. There remains a significant need for the unique apparatuses, processes, systems, and techniques disclosed herein.DISCLOSURE OF EXAMPLE EMBODIMENTS

[0004] For the purposes of clearly, concisely, and exactly describing example embodiments of the present disclosure, the manner, and process of making and using the same, and to enable the practice, making and use of the same, reference will now be made to certain example embodiments, including those illustrated in the figures, and specific language will be used to describe the same. It shall nevertheless be understood that no limitation of the scope of the invention is thereby created, and that the invention includes and protects such alterations, modifications, and further applications of the example embodiments as would occur to one skilled in the art.SUMMARY OF THE DISCLOSURE

[0005] Some embodiments include unique gaseous fueling system controls. Further embodiments include unique apparatuses, systems, and processes comprising or embodying such controls. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Fig. 1 is a schematic diagram illustrating certain aspects of an example engine system including an example fueling system.

[0007] Fig. 2 is a schematic diagram illustrating certain aspects of an example fueling system.

[0008] Fig. 3 is a schematic diagram illustrating certain aspects of an example fueling system.

[0009] Fig. 4 is a flow diagram illustrating certain aspects of an example process.

[0010] Fig. 5 is a graph illustrating certain aspects of an example gaseous fuel sonic speed determination.

[0011] Fig. 6 is a graph illustrating certain aspects of an example gaseous fuel sonic speed determination.

[0012] Figs. 7-12 are graphs illustrating certain aspects of an example gaseous fuel sonic speed determination.

[0013] Figs. 13-18 are graphs illustrating certain aspects of an example gaseous fuel sonic speed determination.

[0014] Fig. 19 is a schematic diagram illustrating certain aspects of example controls.

[0015] Fig. 20 is a schematic diagram illustrating certain aspects of example controls.

[0016] Fig. 21 is a schematic diagram illustrating certain aspects of example controls.

[0017] Figs. 22 and 23 are graphs illustrating certain aspects of example controls.DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0018] With reference to Fig. 1, there is illustrated a system 11 comprising an engine 10 and agaseous fueling system 9. Gaseous fueling system 9 is configured to supply a gaseous fuel, such as such as natural gas, hydrogen, bio-derived gaseous fuels, mixed gases fuels, or other gaseous fuels or mixtures of gaseous fuels for combustion by engine 10. Engine 10 comprises combustion chambers 13 (also referred to as cylinders) of a reciprocating piston-in-cylinder-type engine which are configured to generate mechanical power from the combustion of gaseous fuel supplied by fuel injectors 12. Fuel injectors 12 are in fluid communication with respective combustion chambers 13 of the engine 10 and are structured to inject gaseous fuel which is provided to their respective combustion chambers 13.

[0019] In the illustrated embodiment, fuel injectors 12 are configured and provided as port fuel injectors configured to inject fuel directly into respective ports of intake manifold 37 leading to respective combustion chambers 13 of engine 10. Other embodiments may include other types and configurations of injectors such as direct fuel injectors configured to inject fuel directly into respective combustion chambers 13 of engine 10. In the illustrated embodiment, four fuel injectors 12 and four combustion chambers 13 are depicted, it being appreciated that engine 10 may include fewer or greater numbers of fuel injectors 12 and combustion chambers 13. System 11 may be provided in a number of forms including as a prime mover system (or component of a prime mover system) of vehicle, a genset, other power systems configured to drive or supply power to various loads.

[0020] In the illustrated embodiment, the gaseous fueling system 9 includes a gaseous fuel supply and injection system 17 and a gaseous fuel supply 32. Gaseous fuel supply and injection system 17 includes one or more rails 30 and one or more sets of injectors 12 operatively coupled with and supplied with gaseous fuel from a respective one of the one or more rails 30. The one or more rails 30 are, in turn, configured to receive pressurized fuel from gaseous fuel supply 32.

[0021] The gaseous fuel supply 32 may include a high pressure tank configured to store a supply of gaseous fuel at high pressure. In some embodiments, gaseous fuel supply 32 may include additional elements such as a compressor configured to compress gaseous fuel received from the fuel tank supply compressed gaseous fuel to the one or more rails 30, and / or and accumulator as well as filters, and mechanically or electronically controllable valves configured to control supply of gaseous fuel to and from the accumulator and / or the one or more rails 30.

[0022] It shall be appreciated that the illustrated form of gaseous fueling system 9 is but oneexample of a fueling system according to the present disclosure. In other embodiments, the gaseous fueling system 9 may be configured and provided as another type of gaseous fueling system, for example, as a gaseous hydrogen fueling system. In other embodiments, gaseous fueling system 9 may be configured and provided in other forms.

[0023] System 11 further includes electronic control system (ECS) 20 in communication with engine 10 and configured to control one or more aspects of engine 10, including controlling the injection of fuel into engine 10 via the fuel injectors 12. Accordingly, ECS 20 may be in communication with the fuel injectors 12 and configured to command each fuel injector 12 on and off at prescribed times to inject fuel into the engine 10 as desired. ECS 20 typically include at least one electronic control unit (ECU) 22 configured to execute operations of ECS 20 as described further herein and, in some embodiment, may include additional ECUs configured to execute operations of ECS 20 as described further herein.

[0024] ECS 20 may be further structured to control other parameters of engine 10, which may include aspects of engine 10 that may be controlled with an actuator activated by ECS 20. For example, ECS 20 may be in communication with actuators and sensors for receiving and processing sensor input and transmitting actuator output signals. Actuators may include, but not be limited to, fuel injectors 12. The sensors may include any suitable devices to monitor operating parameters and functions of the system 11. For example, the sensors may include one or more pressure sensors 16 and one or more temperature sensors 18. The one or more pressure sensors 16 are in communication with the one or more rails 30 and structured to communicate a measurement of the pressure of gaseous fuel in the one or more rails 30 (also referred to as fuel rail pressure or rail pressure) to the ECS 20. The one or more temperature sensors 18 are in communication with the one or more rails 30 and structured to communicate a measurement of the temperature of gaseous fuel in the one or more rails 30 (also referred to as fuel rail temperature or rail temperature) to the ECS 20. System 11 include an intake manifold pressure (IMP) sensor 38 in communication with and configured to sense a pressure of intake manifold 37.

[0025] As will be appreciated by the description that follows, the techniques described herein relating to fuel injector or fuel injection parameters can be implemented in ECS 20, which may include one or more controllers for controlling different aspects of the system 11. In certain embodiments, the ECS 20 comprises one or more electronic control units (ECU) such as an enginecontrol unit or engine control module. The ECS 20 may be comprised of digital circuitry, analog circuitry, or a hybrid combination of both of these types. Also, the ECS 20 may be programmable, an integrated state machine, or a hybrid combination thereof. The ECS 20 may include one or more Arithmetic Logic Units (ALUs), Central Processing Units (CPUs), memories, limiters, conditioners, filters, format converters, or the like which are not shown to preserve clarity. In one form, the ECS 20 is of a programmable variety that executes algorithms and processes data in accordance with operating logic that is defined by programming instructions (such as software or firmware). Alternatively or additionally, operating logic for the ECS 20 may be at least partially defined by hardwired logic or other hardware.

[0026] In addition to the types of sensors described herein, any other suitable sensors and their associated parameters may be encompassed by the system and methods. Accordingly, the sensors may include any suitable device used to sense any relevant physical parameters including electrical, mechanical, and chemical parameters of the engine system 11. As used herein, the term sensors may include any suitable hardware and / or software used to sense or estimate any engine system parameter and / or various combinations of such parameters either directly or indirectly.

[0027] With reference to Fig. 2, there are illustrated further details of an example embodiment of gaseous fueling system 9. In the illustrated example of gaseous fueling system 9, gaseous fuel supply 32 is configured to supply pressurized gaseous fuel to rail 30i which is supplied with pressurized gaseous fuel from gaseous fuel supply 32 and is configured and operable to supply pressurized gaseous fuel to a plurality of injectors 12 which are configured to inject gaseous fuel to particular ones of a plurality of cylinder intake ports 14 associated with a plurality of cylinders 13.

[0028] In the illustrated example, the plurality of cylinders 13 comprises the first, second, third, fourth, fifth, and sixth cylinders formed in a block of an in-line six-cylinder engine lOi. The plurality of injectors 12 comprises injectors 1A, IB, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A, and 6B. Injectors 1 A and IB are configured to supply gaseous fuel to a first intake port of intake manifold 37 leading to a first combustion cylinder. Injectors 2A and 2B are configured to supply gaseous fuel to a second intake port of intake manifold 37 leading to a second combustion cylinder. Injectors 3 A and 3B are configured to supply gaseous fuel to a third intake port of intake manifold 37 leading to a third combustion cylinder. Injectors 4A and 4B are configured to supply gaseousfuel to a fourth intake port of intake manifold 37 leading to a fourth combustion cylinder. Injectors 5 A and 5B are configured to supply gaseous fuel to a fifth intake port of intake manifold 37 leading to a fifth combustion cylinder. Injectors 6A and 6B are configured to supply gaseous fuel to a sixth intake port of intake manifold 37 leading to a sixth combustion cylinder.

[0029] In the embodiment of Fig. 2, the one or more pressure sensors 16 comprise pressure sensor 16a and may in some forms further comprise pressure sensor 16b which is provided at a separate location of rail 30i. Pressure sensors 16a, 16b are in communication with rail 30i and are structured to communicate a measurement of the pressure of gaseous fuel in rail 30i (also referred to as fuel rail pressure(s) or rail pressure(s)) to the ECS 20.

[0030] In the embodiment of Fig. 2, the one or more temperature sensors comprise temperature sensor 18a. In some forms, the one or more temperature sensors may further comprise additional or alternate temperature sensor(s) which is or are provided at a separate location of rail 3 Oi or other locations of gaseous fueling system 9. Temperature sensor 18 is in communication with rail 30i and is structured to communicate a measurement of the temperature of gaseous fuel in rail 30i (also referred to as fuel rail temperature(s) or rail temperature(s)) to the ECS 20.

[0031] It shall be appreciated that rail 3 Oi is one example of a form in which the one or more rails 30 illustrated and described in connection with Fig. 1 comprise a single rail. Other embodiments in which the one or more rails 30 comprise multiple separated or divided rails are also contemplated. Likewise, while the illustrated example pertains to an engine including six cylinders, other embodiments relate to other engines including more or less than six cylinders.

[0032] With reference to Fig. 3, there are illustrated further details of an example embodiment of gaseous fueling system 9’. In the illustrated example of gaseous fueling system 9’, gaseous fuel supply 32 is configured to supply pressurized gaseous fuel to front rail 30f and rear rail 30r. Front rail 30f and rear rail 30r are configured and provided as physically separated or divided gaseous fuel containment structures which may be provided in a number of forms including, for example, as physically separated or divided tubular fuel rails or pipes or physically separated or divided bores formed in an engine component such as an intake manifold or cylinder head. Front rail 30f and rear rail 3 Or preferably are supplied with pressurized gaseous fuel from gaseous fuel supply 32 at separate and distinct locations effective to provide a degree of isolation between their respective pressures.

[0033] Front rail 30f is configured and operable to supply pressurized gaseous fuel to a front plurality of injectors 12f which are configured to inject gaseous fuel to particular ones of a plurality of front cylinder intake ports 14f associated with a first plurality of cylinders 13f. In the illustrated example, the first plurality of cylinders 13f comprises the first, second, and third cylinders formed in a block of an in-line six-cylinder engine 10i’. In the illustrated example, front plurality of injectors 12f comprises injectors 1A, IB, 2A, 2B, 3A, and 3B. Injectors 1A and IB are configured to supply gaseous fuel to a first intake port of intake manifold 37 leading to a first combustion cylinder. Injectors 2A and 2B are configured to supply gaseous fuel to a second intake port of intake manifold 37 leading to a second combustion cylinder. Injectors 3A and 3B are configured to supply gaseous fuel to a third intake port of intake manifold 37 leading to a third combustion cylinder.

[0034] Rear rail 30r is configured and operable to supply pressurized gaseous fuel to a rear plurality of injectors 12r which are configured to inject gaseous fuel to particular ones of a plurality of rear cylinder intake ports 14r associated with a second plurality of cylinders 13r. In the illustrated example, the second plurality of cylinders 13r comprises the fourth, fifth, and sixth cylinders formed in a block of an in-line six-cylinder engine 10i’. In the illustrated example, rear plurality of injectors 12r comprises injectors 4A, 4B, 5A, 5B, 6A, and 6B. Injectors 4A and 4B are configured to supply gaseous fuel to a fourth intake port of intake manifold 37 leading to a fourth combustion cylinder. Injectors 5 A and 5B are configured to supply gaseous fuel to a fifth intake port of intake manifold 37 leading to a fifth combustion cylinder. Injectors 6A and 6B are configured to supply gaseous fuel to a sixth intake port of intake manifold 37 leading to a sixth combustion cylinder.

[0035] In the illustrated example, the plurality of cylinders 13 comprises the first, second, third, fourth, fifth, and sixth cylinders formed in a block of an in-line six-cylinder engine lOi. The plurality of injectors 12 comprises injectors 1A, IB, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A, and 6B. Injectors 1 A and IB are configured to supply gaseous fuel to a first intake port of intake manifold 37 leading to a first combustion cylinder. Injectors 2A and 2B are configured to supply gaseous fuel to a second intake port of intake manifold 37 leading to a second combustion cylinder. Injectors 3 A and 3B are configured to supply gaseous fuel to a third intake port of intake manifold 37 leading to a third combustion cylinder. Injectors 4A and 4B are configured to supply gaseous fuel to a fourth intake port of intake manifold 37 leading to a fourth combustion cylinder. Injectors5 A and 5B are configured to supply gaseous fuel to a fifth intake port of intake manifold 37 leading to a fifth combustion cylinder. Injectors 6A and 6B are configured to supply gaseous fuel to a sixth intake port of intake manifold 37 leading to a sixth combustion cylinder.

[0036] In the embodiment of Fig. 3, the one or more pressure sensors 16 comprise pressure sensor 16f and pressure sensor 16r. Pressure sensor 16f is in communication with font rail 30f and is structured to communicate a measurement of the pressure of gaseous fuel in front rail 30f (also referred to as fuel rail pressure(s) or rail pressure(s)) to the ECS 20. Pressure sensor 16r is in communication with font rail 30r and is structured to communicate a measurement of the pressure of gaseous fuel in front rail 30r (also referred to as fuel rail pressure(s) or rail pressure(s)) to the ECS 20. It shall be appreciated that in some forms the one or more pressure sensors 16 may comprise one or more additional pressure sensors in communication with font rail 30f or rear rail 30r and structured to communicate a measurement of the pressure of gaseous fuel in front rail 30f or rear rail 3 Or.

[0037] In the embodiment of Fig. 2, the one or more temperature sensors comprise temperature sensors 18f, 18r. In some forms, the one or more temperature sensors may further comprise additional or alternate temperature sensor(s) which is or are provided at a separate location of rail 30f, rail 30r, or other locations of gaseous fueling system 9. Temperature sensor 18f is in communication with rail 30f and is structured to communicate a measurement of the temperature of gaseous fuel in rail 30f (also referred to as fuel rail temperature(s) or rail temperature(s)) to the ECS 20. Temperature sensor 18r is in communication with rail 30r and is structured to communicate a measurement of the temperature of gaseous fuel in rail 30r (also referred to as fuel rail temperature(s) or rail temperature(s)) to the ECS 20.

[0038] It shall be appreciated that front rail 3 Of and rear rail 3 Or are one example of a form in which the one or more rails 30 illustrated and described in connection with Fig. 1 comprise a first rail and a second rail separated or divided from the first rail. Other embodiments in which the one or more rails 30 comprise a first rail and a second rail separated or divided from the first rail are also contemplated. Such embodiments include, for example, systems comprising relative arrangements and positioning of multiple fuel rails servicing a set of in-line cylinders other than front and rear, systems wherein the one or more rails 30 comprise three or more rails, and / or systems wherein the one or more rails 30 comprise two or more rails configured to supply gaseousfuel to the same set or group of cylinders. Likewise, while the illustrated example pertains to an engine including six cylinders, other embodiments relate to other engines including more or less than six cylinders.

[0039] The present disclosure contemplates a number of embodiments, including apparatuses, processes, and systems wherein real-time, on-engine measurements of the sonic speed of the operating gaseous fuel mixture may be utilized in determining the molecular mass (sometimes referred to as average molecular weight) of the gaseous mixture, the gaseous flow rate, the injected quantity and the energy content of the gaseous mixture. Some such embodiments may make determinations of these parameters based in whole or in part on relationships according to one or more of equation (1), equation (2), equation (3), equation (4), equation (5), and equation (6):

[0040] In equation (1), equation (2), equation (3), equation (4), equation (5), and equation (6), as applicable, c = sonic speed, y = ratio of specific heats of the gaseous mixture, R = universal gas constant, T = absolute temperature, M = the average molecular mass of the gaseous mixture, —= the choked flow rate of the gas, Cd= the effective discharge coefficient of the injector, AT=the effective flow area of the injector, Ps= the average supply pressure to the injector during the injection event, and Pd= the average downstream pressure to the injector during the injection event. It shall be appreciated that equation (4) accounts for and models a choked flow condition, and equation (6) account for and model conditions which are non-choked with a Mach number of less than 1. Furthermore, equation (5) may be utilized to test for choked and non-choked system conditions. If the state of a fueling system is such that equation (5) is true, then the flow is choked and equation (4) is used to calculate the mass flow rate. If the state is such that equation (5) is false, then the flow is not choked and equation (6) is used to calculate the mass flow rate.

[0041] With reference to Fig. 4, there is illustrated an example process 100 for operating an electronic control system e.g., ECS 20 or another electronic control system), in operative communication with a fueling system (e.g., gaseous fueling system 9 or another fueling system). Process 100 may be implemented in and performed by one or more components of an electronic control system such as one or more electronic control units (e.g., ECU 22 and / or other electronic control units) and / or by other electronic control system components.

[0042] Process 100 begins at start operation 102 and proceeds to operation 104 which operates an engine system. In some modalities, operation 104 may operate the engine system in-mission, such that no special or dedicated operating mode is required, although some modalities may utilize a special or dedicated operating mode such as a test mode or calibration mode. Operation 104 may control a number of aspects of operation of the engine system including, for example, controlling on times of a plurality of fuel injectors to provide injections of a gaseous fuel mixture for combustion by the engine, controlling rail pressures, and controlling injection timing, among other aspects of.

[0043] From operation 104, process 100 proceeds to operation 106 which determines a engine control parameter in response to output of fuel pressure sensor system. It shall be appreciated that an engine control parameter may comprise any one or more of a plurality of parameters including, for example, a fuel quantity, an injection timing, a number of injection events, a fuel system pressure, an ignition timing, an intake manifold pressure, and an air flow rate to name several examples. Additionally, one or more engine control parameters may be utilized to determine one or more injector operation parameters which directly act on a fuel injector such as an injector on time (for example, the total time that an injector is command to be on and / or the initial time thatan injector is first command to be on for a given injection event).

[0044] It shal also be appreciated that parameters such as fuel quantity and injection timing on the one hand and injector on time on the other hand may be correlated but distinguishable in that fuel quantity and injection timing comprise parameters stored in memory of an electronic control system and injector on time comprises an operational state which may be externally observed without direct access to or knowledge of parameters stored in memory of an electronic control system, for example, by measuring a signal, such as a voltage or current, provided to a fuel injector by an electronic control system. In some respects and instances, an engine control parameter and an injector operation parameters may directly related or substantially the same, for examine, in controls where injection timing is utilized to directly determine an initiation of injector on time. In some respects and instances, an engine control parameter and an injector operation parameters may be indirectly related or influenced by multiple or additional factors, for example, in a control structure where a total injector on time for a given injection event is determined in response to a fuel quantity, a fuel system pressure, and potentially other control parameters

[0045] Operation 106 may utilize a number of techniques in connection with determining the engine control parameter in response to output of fuel pressure sensor system. In some embodiments, operation 106 may determine a sonic speed parameter of the gaseous fuel mixture in response to output of the pressure sensor system, and may determine a gaseous fuel characteristic indicative of a molecular mass of the fuel in response to the sonic speed parameter. In some embodiments, operation 106 may determine a gaseous fuel characteristic indicative of a molecular mass directly without necessarily determining or calculating the sonic speed parameter.

[0046] Operation 106 may utilize a number of techniques to determine a sonic speed parameter of the gaseous fuel mixture in response to output of the pressure sensor system. Such techniques may include, for example, the differential time techniques, natural frequency techniques, Fourier transform techniques, oscillation decay techniques and other techniques disclosed and revealed by the present disclosure. Operation 106 may also utilize a number of techniques to determine a gaseous fuel characteristic indicative of a molecular mass of the fuel. Such techniques may include, for example, the sonic speed calculation techniques disclosed herein, the molecular mass determination techniques discloser herein, and / or calculations based on any of equation (1), equation (2), equation (3), equation (4), equation (5), and equation (6). It shall be appreciated thatoperation 106 may be repeated conducted for purposes such as gaining increasing confidence in the accuracy and precision of the estimate of engine control parameters and to get estimates for the determinations of the engine control parameters at differing pressure or temperature states.

[0047] From operation 106, process 100 proceeds to operation 108 which the operating engine system receives and operates using a changed gaseous fuel mixture. The operating engine system may receive a changed gaseous fuel mixture under a number of conditions including, for example, a refueling event, a change in pipeline gas composition, a change in wellhead gas composition, admixture of multiple gaseous fuel sources or changes in such admixture, among other conditions. It shall be appreciated that the change in gaseous fuel mixture may involve a change in average molecular mass of the gaseous fuel mixture due to changes in molecular constituents of the gaseous fuel being supplied to an engine system. It shall also be appreciated that the change in gaseous fuel mixture may not be known in advance by operation 108, process 100, or the apparatuses or systems in which they are implemented and executed.

[0048] From operation 108, process 100 proceeds to operation 110 which changes the engine control parameter in response to a change in average molecular mass of the gaseous fuel mixture. Operation 110 may utilize number of techniques in connection with changing the engine control parameter in response to a change in average molecular mass of the gaseous fuel mixture including, for example, the techniques disclosed and referenced in connection with operation 106. In some embodiment, operation 110 may determine a new value of the sonic speed parameter of the fuel in response to output of the pressure sensor system, and may determine a new value of the gaseous fuel characteristic indicative of a molecular mass of the fuel in response to the new value of the sonic speed parameter.

[0049] From operation 110, process 100 proceeds to operation 112 which adjusts an injector operation parameter effective to mitigate a change in engine output in response to the change in average molecular mass. Operation 112 may adjust one or more injector operation parameters and may utilize number of techniques is such adjustment including, for example, the techniques disclosed in connection with Fig. 20 and the techniques disclosed elsewhere herein.

[0050] From operation 112, process 100 proceeds to operation 114 at which processes ends, repeats, or returns to a prior operation, such as operation 104.

[0051] The present disclosure contemplates a number of techniques which can be utilized todetermine the sonic speed of the gaseous mixture on-engine at the current operational pressure and temperature state. Some embodiments may determine a sonic speed parameter of a gaseous fuel utilizing differential time techniques. Such embodiments may measure the difference in pressure sensor response time following one or more injection events and compare the difference in the response time to distances between the operating injector(s) and the pressure sensor(s). As with a number of other techniques disclosed herein, differential time techniques can determine the sonic speed of the operating gaseous fuel mixture unobtrusively, on-engine, and in real time.

[0052] In some differential time techniques, an electronic control system may receive a first output from a first pressure sensor of the pressure sensor system corresponding to an injection event. The first pressure sensor may be configured to sense fuel pressure associated with a first location of the fuel rail. The electronic control system may receive a second output from a second pressure sensor of the pressure sensor system corresponding to the same injection event. The second pressure sensor may be configured to sense fuel pressure associated with a second location of the fuel rail spaced apart from the first location. In the example embodiment illustrated and described in connection with Fig. 2, the first pressure sensor may be pressure sensor 16a of gaseous fueling system 9 and the second pressure sensor may be pressure sensor 16b of gaseous fueling system 9, and the injector may be any of the injectors. In the example embodiment illustrated and described in connection with Fig. 3, the first pressure sensor may be pressure sensor 16f of gaseous fueling system 9’ and the second pressure sensor may be pressure sensor 16r of gaseous fueling system 9’.

[0053] The electronic control system may determine the sonic speed parameter in response to a difference between the first output and the second output (the differential time), and an inverse relationship between sonic speed of a gaseous fuel and the differential time. Fig. 5 illustrates a graph depicting an example of such an inverse relationship between sonic speed of a gaseous fuel on the vertical axis and differential time on the horizontal axis. The inverse relationship depicted in Fig. 5 is associated with a particular gaseous fuel temperature and supply pressure. It shall be appreciated that as gaseous fuel temperature and supply pressure vary, the slope of the inverse relationship between sonic speed of a gaseous fuel and differential time may vary. A plurality of inverse relationships at multiple gaseous fuel temperatures and supply pressures may be established and stored as one or more equations, maps, tables, or other data structures via which an electronic control system may utilize to determine a gaseous fuel sonic speed parameter inresponse to a differential time, gaseous fuel pressure, and gaseous fuel temperature.

[0054] In some differential time techniques, an electronic control system may receive a first output from a pressure sensor of the pressure sensor system corresponding to a first injection event performed by a first injector of the fueling system, the first injector being spaced apart from the pressure sensor by a first distance. The electronic control system may receive a second output from the pressure sensor corresponding to a second injection event performed by a second injector of the fueling system, the second injector being spaced apart from the pressure sensor by a second distance different from the first distance. The electronic control system may determine the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

[0055] It shall be appreciated that differential time sonic speed determination techniques according to the present disclosure may account for a potential difference in the response times of the pressure sensors by a number of methods. One example method may perform injection with injectors 2A and 2B and measure the differential time for the resulting pressure disturbance to be at observed at the rear pressure sensor 16r which is further from the operating injectors at a known distance along the flow path from the operating injectors 2A and 2B as compared to the front pressure sensor 16f which is close to operating injectors at a known distance along the flow path from the operating injectors 2A and 2B. The method may then perform injection with injectors 5 A and 5B and measure the differential time for the resulting pressure disturbance to be at observed at the front pressure sensor 16f which is further from the operating injectors at a known distance along the flow path from these operating injectors 5 A and 5B as compared to the rear pressure sensor 16r which is close to these operating injectors at a known distance along the flow path from the operating injectors 5 A and 5B. The average of the differential time for these two events provide a method for the control system to mitigate the effect of any pressure sensor to sensor response time differences.

[0056] Some embodiments may determine a sonic speed parameter of a gaseous fuel utilizing natural frequency techniques. As with a number of other techniques disclosed herein, natural frequency techniques can determine the sonic speed of the operating gaseous fuel mixture unobtrusively, on-engine, and in real time.

[0057] Example natural frequency techniques may determine one or more natural frequencies of output of a pressure sensor of a pressure sensor system following an injection event, and may determine a sonic speed parameter may in response to the one or more natural frequencies. For example, an electronic control system may command an injection event from one or more of a set of injectors associated with an engine cylinder at a time when the pressure in the rail is relatively stable at a near quasi-static condition such as when the engine is in a motoring state. The free response of the pressure in one or both of the rails may be measured by one or more pressure sensors following a single injection command. A frequency analysis of the free response following the single injection event is then calculated from the measured pressure signal using one of many possible methodologies including a discrete Fourier transform (DFT), a sinusoidal based curve fit estimation or any other similar method.

[0058] Fig. 6 illustrates an example natural frequency technique, using the system of Fig. 3 wherein injector 2A was commanded to inject. The calculated natural frequencies of the system as measured at the front rail pressure sensor was calculated and is shown in the abscissa of Fig. 8 for differing gaseous fuel mixtures. The ordinate of the illustrated graph is the sonic speed of the differing gaseous fuel mixtures at the time and state of the injection event. As shown in the graph of Fig. 6, there is a near linear relationship between the natural frequencies and the sonic speed which can be used to calculate the sonic speed. A similar methodology could be used for system configurations such as shown in Fig. 2.

[0059] Some embodiments may determine a sonic speed parameter of a gaseous fuel utilizing a peak amplitude, discrete Fourier transform (DFT) technique. As with a number of other techniques disclosed herein, peak amplitude DFT techniques can determine the sonic speed of the operating gaseous fuel mixture unobtrusively, on-engine, and in real time.

[0060] Figs. 7-12 illustrate certain aspects of a peak amplitude, DFT technique utilizing a DFT peak amplitude of rail pressure at the 1.5 engine firing frequency harmonic. The system configuration, the engine operating conditions and the fuel pressure and temperature are identical for the graphs shown in Figs. 7, 8, and 9; however, as can be observed by a comparison of these graphs, the DFT amplitudes at the 1.5 engine firing frequency harmonic differ with different gaseous fuel mixtures. The fuel mixture properties similarly affect all DFT harmonics.

[0061] One peak amplitude, DFT technique which can be utilized to identify the operating fuelis to compare the engine operational speeds at which the maximum DFT amplitudes are observed at the 1.5 engine firing frequency harmonic. For the present example, the maximum calculated DFT amplitudes at the 1.5 engine firing frequency harmonic are shown in Fig. 10 as a function of the engine speed for differing gaseous mixtures. As illustrated by the graph of Fig. 11, the engine speed at which the maximum calculated DFT amplitudes at the 1.5 engine firing frequency harmonic for the example embodiment for the differing gaseous mixtures is shown to have a relationship to the sonic speed of the gaseous mixtures at the gas operating conditions as defined by equation (1). As illustrated in Fig. 12, the control structure of the engine and fuel system can utilize the DFT results to estimate the sonic speed of the gaseous mixture. This sonic speed can then be used in conjunction with equation (2) to estimate the molecular mass of the gaseous mixture.

[0062] Peak amplitude DFT techniques such as the foregoing example may implemented in an electronic control system being configured to determine the sonic speed parameter by determining a maximum amplitude of a Fourier transform of output of the pressure sensor system, and determine the sonic speed parameter in response to the maximum amplitude. The Fourier transform of output of the pressure sensor system comprises a Fourier transform at a 1.5 engine firing frequency harmonic or other suitable multiples of engine firing frequency.

[0063] Some embodiments may determine a sonic speed parameter of a gaseous fuel utilizing decaying oscillation techniques. As with a number of other techniques disclosed herein, decaying oscillation techniques can determine the sonic speed of the operating gaseous fuel mixture unobtrusively, on-engine, and in real time.

[0064] Figs. 13, 14, and 15 illustrate example supply pressure measurements. Fig. 13 illustrates a supply pressure measurement when the fuel system is operating with 100% methane. Fig. 14 illustrates a supply pressure measurement when the fuel system is operating with a gaseous mixture which has a mass ratio of 90% methane and 10% hydrogen. Fig. 15 illustrates a supply pressure measurement when the fuel system is operating with a gaseous mixture which has a mass ratio of 80% methane and 20% hydrogen. Figs. 13. 14, and 15 each show the injected quantity rate shapes, injected quantities, the pressure at the supply pressure sensor associated with the injectors operating in a six cylinder engine with cylinders 1, 2, and 3, and the filtered supply pressure. For the representative example, all three figures show an engine operating condition of 800 rpm andan individual injected quantity of approximately 40 mg. All three figures show a gaseous fuel supply temperature of 40C before the injectors.

[0065] The sonic speed of a gaseous mixture (c) may be determine in accordance with equation (1) Fig. 16 shows the relationship between the sonic speed of a gaseous mixture to the period of time associated with oscillations in filtered supply pressure following an injection event for the example data shown in Figs. 13, 14, and 15. As can be seen in Fig. 16, there is a significant correlation between the sonic speed at the measurement conditions and the oscillation time period. The data shows the inverse relationship between the oscillation time period and the sonic speed. Therefore, data from a measurement of the oscillation time period at engine speed, injected quantity, and temperature can be used to sonic speed which can then be used to estimate the gaseous fuel’s components and properties.

[0066] The data from multiple measurements at differing fuel supply temperature, fuel supply pressures, injected quantities and engine speeds can improve the accuracy of the measurements and to estimate the fuel’s properties and component percentages. The average molar mass of gaseous mixtures (M) may be calculated in accordance with equation (7) from the mole fractions xtof the components and their molar masses:(7)

[0067] The average molar mass of gaseous mixtures M can also be calculated in accordance with equation (8) from the mass fractionsof the components and their molar masses(8)

[0068] Fig. 17 shows example molar masses for several gases and gaseous mixtures. As is shown in Fig. 17, there can be a large difference between the molar masses even for gaseous blends which are identified as natural gas. Fig. 17 also shows the adiabatic ratio, also called the ratio of specific heats for differing gases and gas mixtures at a temperature of 40C and an absolute pressure of 6 bars.

[0069] Fig. 18 shows an example of how the adiabatic ratio, also called the ratio of specific heats for an example gas, 100% methane varies with the fuel temperature and pressure. By using measured data and information during the engine’s operation at differing supply pressures andtemperatures, an estimate of the molecular mass and the adiabatic ratio as a function of the pressure and temperature can be made. This information can then be used to estimate the relative component percentages in the operating gas. The relationship for the mass flow rate for a choked flow condition of a gaseous injector is given in equation (9):

[0070] In equation (9), Cd is the effective discharge coefficient, AT is the effective flow area at the temperature, Ps is the average supply pressure during the injection event, c is the sonic speed, and y is the adiabatic ratio. As can be seen in equation (9), the mass flow rate is inversely proportional to the sonic speed. Therefore, an estimate of the sonic speed based on the period of oscillation of the supply pressure following an injection event can be readily utilized to compensate for the change in the mass flow rate as a function the sonic speed of the gas at the fuel system’s current operating state in an operating engine.

[0071] There are additional methods which could be used to estimate the sonic speed and gas properties. One alternative method is measuring the period of oscillation following a single isolated injection event during times where the engine is not otherwise commanding fuel for combustion such as during engine motoring. Another additional method is using the change in the magnitude of the amplitude of the supply pressure oscillations following the injection event. As is shown in equation (9), a lower sonic speed results in a higher mass flow rate.

[0072] According to some decaying oscillation techniques an electronic control system may be configured to determine a sonic speed parameter by determining a period of decaying oscillation of output of a pressure sensor of the pressure sensor system following an injection event, determining the sonic speed parameter in response to the period of decaying oscillation. In such embodiments, the electronic control system may perform at least one of: determining the period of decaying oscillation for a single injection event and determining the sonic speed parameter using an inverse relationship between the sonic speed parameter and the period of decaying oscillation, and / or determining the period of decaying oscillation during transient operation of the engine.

[0073] With reference to Fig. 19, there are example controls 200 which may be implemented in and executed by an electronic control system (e.g., ECS 20 or another electronic control system),in operative communication with a fueling system (e.g., gaseous fueling system 9 or another fueling system). Controls 200 may be implemented in and performed by one or more components of an electronic control system such as one or more electronic control units (e.g., ECU 22 and / or other electronic control units) and / or by other electronic control system components. Controls 200 are one example of a controls wherein pressure and temperature measurements of a gaseous fuel are used to estimate the gaseous fuel and the fuel’s characteristics based on measuring the period of time associated with oscillations in supply pressure following an injection event.

[0074] Controls 200 may be executed during operation of an engine system in-mission, such that no special or dedicated operating mode is required, although some modalities may utilize a special or dedicated operating mode such as a test mode or calibration mode.

[0075] Operator 202 obtains one or more measurements of a gaseous fuel supply pressure (also referred to herein as the “supply pressure”) using one or more pressure sensors, such as one or more of the pressure sensors illustrated and described in connection with Figs. 1-3. Operator 202 optionally provides the one or more pressure measurements to operator 204 which filters the supply pressure. Alternatively, operator 202 may provide the one or more pressure measurements to operator 205 and operator 206. For systems with more than one pressure sensor, a method such as an averaging method of the two response pressures can be used to correct the pressure signals for offset biases of each of the pressure sensors.

[0076] Operator 204 filters the supply pressure. Operator 204 may utilize a filtering technique such as a moving average filter to improve the accuracy and precision of the measurement and to improve the signal to noise ratio of the measurement. Operator 204 provides the one or more filtered pressure measurements to operator 205 and operator 206.

[0077] Operator 205 calculates the average supply pressure associated with the one or more filtered pressure measurements received form operator 204 or, alternatively, the one or more pressure measurements received form operator 202.

[0078] Operator 206 calculates a sonic speed parameter in response to one or more pressure measurements. It shall be appreciated that the sonic speed parameter may comprise a sonic speed value or a value correlated with or from which a sonic speed value may be determined. Operator 206 may utilize any of the techniques disclosed herein in calculating a sonic speed parameter based upon a relationship between pressure and sonic speed including, for example, a differential timetechnique, a natural frequency technique, a decaying oscillation technique, and a DFT maximum amplitude technique. In some embodiments, operator 206 may calculate the oscillation period based on a peak to peak duration or time of an oscillating pressure waveform. In some embodiments, operator 206 may calculate the differential response time between two pressure sensors to the same injection event. In some embodiments, operator 206 may calculate the free response to one or more natural frequencies. In some embodiments, operator 206 may calculate the maximum DFT amplitude.

[0079] Operator 207 obtains one or more measurements of a gaseous fuel supply temperature (also referred to herein as the “supply temperature”) using one or more temperature sensors, such as one or more of the temperature sensors illustrated and described in connection with Figs. 1-3.

[0080] Operator 208 calculates the sonic speed of the fuel for the measurement in response to the sonic speed parameter determined by operator 206. Fig. 16 illustrated shows the relationship between the sonic speed of a gaseous mixture to the period of time associated with oscillations in fdtered supply pressure following an injection event for the example data shown in Figs. 13, 14, 15. As can be seen in Fig. 8, there is a correlation between the sonic speed at the measurement conditions and the oscillation time period, namely an inverse relationship between the oscillation time period and the sonic speed. Therefore, data from a measurement of the oscillation time period at engine speed, injected quantity, and temperature can be used to determine sonic speed which can then be used to estimate the gaseous fuel’s components and properties.

[0081] Operator 210 updates one or more model(s), equations(s), map(s), table(s), and / or other data structures or controls which are used to represent the gaseous fuel’s sonic speed as a function of the gaseous fuel temperature and gaseous fuel pressure.

[0082] Operator 211 estimates the gaseous fuel’s effective molecular mass. Operator 211 may calculate the effective molecular mass (M) of the gaseous mixture as approximated by ratio of the adiabatic ratio (y), the universal gas constant (R), and the absolute temperature (T), divided by the square of sonic speed (C2), for example, in accordance with Equation (2) or equivalent or similar equations.

[0083] Operator 212 estimates the gaseous fuel’s effective adiabatic ratio at differing pressures and temperatures for example, in accordance with a form of one of equations (1) through equation(6) solved for adiabatic ratio gamma (y) or equivalent or similar equations.

[0084] Operator 214 sets the fuel system and engine control commands such as the injected mass and injection timing and other affected algorithms or controls based on the effective molecular mass of the fuel determined by operator 211 and the gaseous fuel’s effective adiabatic ratio at differing pressures and temperatures determined by operator 212.

[0085] Operator 216 optionally appends to a data log and storage of the gaseous properties history of the engine or otherwise stores such information.

[0086] With reference to Fig. 20, there are illustrated example controls 900 which may be implemented in and operated by one or more components of an electronic control system such as ECS 20 or another electronic control system configured for operative communication with a fueling system. In some forms, at least a portion of controls 900 may be implemented in one or mode electronic control units of an electronic control system such as ECU 22 or additional or alternative electronic control units.

[0087] Controls 900 include injector controls 910 which are configured to determine and output at least one injector control signal 919 to control operation of an injector 12i in response to one or more inputs. In the illustrated example, injector controls 910 are configured to determine and output injector commands for a particular individual injector 12i. Controls 900 may include additional instances of injector controls the same as or similar to injector controls 910 which are configured to determine and output injector commands for other particular individual injectors.

[0088] In the illustrated example, injector controls 910 are configured to receive a plurality of inputs including fueling command 902, engine speed 903, and intake manifold pressure (IMP) 904, rail pressure 906, and rail temperature 908. In other embodiments, injector controls 910 may be configured to receive additional or alternative inputs.

[0089] Fueling command 902 may include a fueling quantity (Q) and a fueling pressure (P). Fueling command 902 may be determined and provided to injector controls 910 in response to an operator input such as an accelerator pedal position or in response to automated operation of an electronic control system such as an adaptive cruise control system. Engine speed 903 may be provided by an engine speed sensor. Engine speed 903 may be provided to injector controls 910 via a dedicated connection or via one or more communication networks.

[0090] IMP 904 may be provided by pressure sensor 38 which is in operative communication with and configured to sense a pressure of intake manifold 37. IMP 904 may be provided to injector controls 910 via a dedicated connection or via one or more communication networks. IMP 904 may be utilized as a pressure of an intake manifold described above in connection with controls 200 or may be utilized in determining the pressure of the intake manifold.

[0091] Rail pressure 906 may be provided by pressure sensor 16 which is in operative communication with and configured to sense a pressure of fuel rail 30 which is configured to supply fuel to injector 12i and may also be configured to supply fuel to other injectors. Rail pressure 906 may be provided to injector controls 910 via a dedicated connection or via one or more communication networks. Rail pressure 906 may be utilized as a rail pressure measurement described above in connection with controls 200 and may be sampled repeatedly to determine multiple points or values of a rail pressure measurement.

[0092] Rail temperature 908 may be provided by temperature sensor 18 which is in operative communication with and configured to sense a temperature of fuel rail 30. Rail temperature 908 may be provided to injector controls 910 via a dedicated connection or via one or more communication networks. Rail temperature 908 may be utilized as a rail temperature described above in connection with controls 200 and may be sampled repeatedly to determine multiple points or values of a rail temperature measurement.

[0093] Injector controls 910 comprise control circuitry configured to implement and execute control logic for processing the inputs received by injector controls 910 and to determine and output injector control signal 919. In the illustrated example the circuitry of injector controls 910 is configured to provide and execute pressure measurement processing logic 912, gaseous fuel characterization logic 914, injection control logic 916, and injection control modification logic 918. In other embodiments, the control logic provided by injector controls 910 may be differently organized with the aspects of one or more of the illustrated logic blocks being combined in a single block or units, divided into multiple blocks or units, and / or provided with additional or alternative blocks or units.

[0094] In the illustrated example, pressure measurement processing logic 912 and gaseous fuel characterization logic 914 are configured to implement and execute one or more operations such as the gaseous fuel sonic speed determination and gaseous fuel molecular mass determinationtechniques described herein. Pressure measurement processing logic 912 is configured to perform a plurality of operations relating to the receipt and processing of a rail pressure 906. Gaseous fuel characterization logic 914 is configured to perform a plurality of operations relating to calculation of an injected fuel quantity estimate using the output of pressure measurement processing logic 912. In other embodiments, the foregoing operations may be differently distributed between or among pressure measurement processing logic 912, gaseous fuel characterization logic 914, and / or additional logic injector controls 910.

[0095] Injection control logic 916, is configured to determine injector commands to provide output including injector control signal 919. Injector control logic 916 may be configured to determine an injector on-time command effective to set injector control signal 919 to an injector- on state or value for a duration corresponding to a commanded injector on time. Injector control logic 916 may determine the injector on-time command in response to fueling command 902, engine speed 903, and intake manifold pressure (IMP) 904, rail pressure 906, and rail temperature 908 and may utilize a number of techniques to perform this determination.

[0096] In some embodiments, injector control logic 916 may be configured and provided as one or more lookup tables, maps or response surfaces which are configured and operable to provide an injector on-time command in response to the aforementioned inputs. In some embodiments, a set of tables according to which injector control logic 916 may be configured to determine an injector on-time commanded for a give input values of engine speed 903, intake manifold pressure (IMP) 904, rail pressure 906, and rail temperature 908. It shall be appreciated that interpolation between a set of two or more tables, between a set of two or more curves of a given table may be utilized to determine intermediate values.

[0097] In some embodiments, injector control logic 916 may be configured and operable to solve one or more equations to determine an injector on-time command in response to the aforementioned inputs. Equation (10) provides an example of an equation which may be so utilized:(_ Qr ref -C0+ C1Ps+ C2Pd + C3Ps +C4Pd+ C5PsPd(10) C comm and C6+ C7PWherein t is the commanded injector on time, Qr ref is injection quantity at a defined reference temperature, Psis the pressure of gaseous at the fuel rail, Pdis the intake manifold pressure, andCo, CltC2, C3, C4, C5, C6, and C7are coefficients which may be empirically determined or derived from a physics based model and which may be tuned to vary the effect of equation (1).

[0098] The injector on-time command could also be determined using the equation (11) and equation (12) where the opening and closing time delays of the injector can be represented in forms including equations or tables.

[0099] The relationship for the mass flow rate for the gaseous injector is given in equation (10) for a choked flow state of the ratio of the downstream pressure to the supply pressure or in equation (11) for a non-choked flow state of the ratio of the downstream pressure to the supply pressure. The actual open flowing duration of the injector is shown in equation (12).

[0100] The injector-on state of injector control signal 919 may be effective to actuate switch 934. Switch 934 is operatively coupled with a system voltage source (V supply) and configured to selectably supply an injector current (l inj) a solenoid 124 of an injector 12. The injector current (l inj) is effective to energize solenoid 124 to induce lifting motion of injector armature 122 (sometimes referred to as an injector needle) in the direction generally indicated by arrow L. In the lifted position (illustrated in phantom as denoted by dashed lines), injector armature 122 allows fuel supplied to injector gallery 126 to exit one or more apertures of a tip of injector 12 as an fuel injection (F inj) into a port of intake manifold 37 leading to an associated combustion chamber of engine 10.

[0101] Injection control modification logic 918 is configured to modify a relationship between an injector on-time command and a commanded injection quantity which is utilized by injector control logic 916 as described above. In some embodiment injection control modification logic 918 may be configured to modify one or more tables defining one or more relationships between commanded on-time as a function of injection quantity at a given gaseous fuel temperature and a given engine speed such as described above in connection with injector control logic 916. In some embodiment injection control modification logic 918 may be configured to modify one or more coefficients of an equation defining one or more relationships between commanded on-time as afunction of injection quantity at a given gaseous fuel temperature and a given engine speed such as described above in connection with injector control logic 916. In some embodiments injection control modification logic 918 may be configured to modify one values in adaptive tables or equations defining one or more relationships between commanded on-time as a function of injection quantity at a given gaseous fuel temperature and a given engine speed such as described above in connection with injector control logic 916.[00102J Injection control modification logic 918 may modify one or more of the foregoing relationships between an injector on-time command and a commanded injection quantity by comparing a calculated injected fuel quantity estimate, such as the estimate determined in operator 214 of controls 200, with an existing model of the relationship. The existing model of the relationship may comprise a set of look-up tables or equations.

[0103] Injection control modification logic 918 may compare a calculated injected fuel quantity estimate with a predicted injected quantity for an engine speed and fuel rail temperature corresponding to one or more tables, for example, by determining a difference between the calculated injected fuel quantity estimate and the predicted injected quantity. The comparison of difference may be utilized to modify the relationship between an injected quantity (Q) and a moving average pressure change (AP_avg) or the amplitudes of discrete Fourier transforms at differing firing frequency ratios at given engine speed and fuel rail temperature. The relationship between an injected quantity (Q) and a moving average pressure change (AP_avg) or the amplitudes of discrete Fourier transforms at differing firing frequency ratios at given engine speed and fuel rail temperature may be a part of gaseous fuel characterization logic used 914 to estimate the injected quantity. A comparison of difference between the commanded injected quantity and the estimated injected quantity may be utilized to modify the relationship or relationships which are used to determine the commanded on-time for an injected quantity (Q) as a function of characteristics of variables such as the rail pressure, the intake manifold pressure, the engine speed, the fuel temperature, and the operating gaseous fuel. In some embodiments, the modified relationship may be incorporated into or utilized to modify one or more of the set of tables or equations utilized by injector control logic 916. In some embodiments, the modified relationship may be incorporated into or utilized to modify one or more coefficients of an equation utilized by injector control logic 916.

[0104] It shall be appreciated that additional tables for combinations of other gaseous fuel temperatures and engine speeds may also be provided in tables according to the present disclosure. It shall also be appreciated that interpolation between a set of two or more tables, between a set of two or more curves of a given table may be utilized to determine intermediate values.

[0105] With reference to Fig. 21, there are example controls 300 which may be implemented in and executed by an electronic control system (e.g., ECS 20 or another electronic control system), in operative communication with a fueling system (e.g., gaseous fueling system 9 or another fueling system). Controls 300 may be implemented in and performed by one or more components of an electronic control system such as one or more electronic control units (e g., ECU 22 and / or other electronic control units) and / or by other electronic control system components. Controls 300 are one example of a controls wherein pressure and temperature measurements of a gaseous fuel are used to estimate the gaseous fuel and the fuel’s characteristics based on measuring the period of time associated with oscillations in supply pressure following an injection event.

[0106] Controls 300 may be executed during operation of an engine system in-mission, such that no special or dedicated operating mode is required, although some modalities may utilize a special or dedicated operating mode such as a test mode or calibration mode.

[0107] Operator 200’ determines one or more gaseous fuel sonic speed parameters fuel in response to gaseous fuel and pressure. Operator 200’ may include or utilize operations substantially similar to those described in connection with controls 200. For example, operator 200’ may include operators substantially similar to operator 202, operator 204, operator 205, operator 206, operator 207, operator 208, operator 210, operator 211, and operator 212 of controls 200. Furthermore, operator 200’ may determine and provide a gaseous fuel effective molecular mass parameter 311, for example, a parameter substantially similar to that determined by operator 211 of controls 200, and a gaseous fuel adiabatic index parameter 312, for example, a parameter substantially similar to that determined by operator 212 of controls 200.

[0108] Operator 320 receives gaseous fuel effective molecular mass parameter 311 and may determine a lower heating value parameter, partially or entirely, in response to gaseous fuel effective molecular mass parameter 311. Operator 320 may make this determination using a predetermined relationship between the gaseous fuel effective molecular mass parameter 311 and the lower heating value parameter, for example, a predetermined relationship between a relativechange in the lower heating value of a gaseous fuel and an average molecular mass of the gaseous fuel.

[0109] It shall be appreciated that the lower heating value parameter may comprise a lower heating value per se, an estimated lower heating value, or a parameter correlated to a lower heating value or from which a lower heating value is readily ascertainable. The lower heating value parameter may additionally or alternatively be predetermined using physical relationships of different gaseous fuel mixtures. Furthermore, regardless of the particular provenance of a predetermined relationship between gaseous fuel effective molecular mass parameter and the lower heating value parameter, such predetermined relationship may be stored in one or more lookup tables, operating maps, equations, or other data or computational structures of controls 300.

[0110] Fig. 22 illustrates a graph depicting an example predetermined relationship between the gaseous fuel effective molecular mass parameter 311 and the lower heating value parameter. The graph of Fig. 22 illustrates relative (percent) change in the lower heating value (LHV) of a choked flow rate of gaseous fuel on its vertical axis as a function of gaseous fuel average molecular mass on its horizontal axis for several example gaseous fuel mixtures under steady state choked flow conditions at the same pressure, temperature, and percentage of diluent gases.

[0111] In Fig. 22, data point 402 corresponds to EPA Natural Gas Certification Fuel ASTM DI 954. Data point 404 corresponds to a blend of 90% of the fuel of data point 402 and 10% hydrogen. Data point 406 corresponds to a blend of 80% of the fuel of data point 402 and 20% hydrogen. As indicated by curve 401, there is a proportional relationship between the LHV percent change and average molecular mass of the example gaseous fuel mixtures. It shall be appreciated that predetermined relationships may be determined based on more extensive example gaseous fuel mixtures and that such relationships may comprise a number of types of relationships between a lower heating value parameter and an average molecular mass parameter.

[0112] Fig. 23 illustrates a graph depicting an example predetermined relationship between the gaseous fuel effective molecular mass parameter 311 and the lower heating value parameter. The graph of Fig. 23 illustrates gaseous fuel mixture lower heating value (LHV) on its vertical axis as a function of gaseous fuel mixture mass on its horizontal axis for several example gaseous fuel mixtures. Curve 502 depicts the relationship for a gaseous fuel mixture with a molar percentage of N2 of less than 0.3%. Curve 504 depicts the relationship for a gaseous fuel mixture with a molarpercentage of N2 of about 4%. Curve 506 depicts the relationship for a gaseous fuel mixture with a molar percentage of N2 of about 5.5%.

[0113] Operator 320 may also receive one or more engine output sensor measurements 318 which may be provided by one or more sensors configured to sense parameters indicative of engine output varying with a lower heating fuel parameter of the gaseous fuel mixture being combusted. For example, an engine torque sensor or an engine exhaust gas oxygen (EGO) sensor or lambda sensor may be utilized to provide inputs indicative of engine torque or engine exhaust oxygen content (which is correlated with engine torque as an indication of the completeness or incompleteness of combustion). A variance between an actual engine torque or an actual exhaust oxygen content from an expected engine torque or expected exhaust oxygen content may be utilized to determine a percentage of diluent gasses in a combustion air fuel mixture above the percentage expected for the intake air thus ultimately indicating the percentage of diluent gasses in the gaseous fuel mixture. Operator 320 may utilize the determined percentage of diluent gasses in the gaseous fuel mixture to adjust determination of the lower heating value parameter, for example, adjusting on a percentage or pro-rata basis to account for a percentage of one or more diluent gases which may be non-combustible or inert and therefore do not contribute to heat of combustion.

[0114] Operator 320 provides the determined lower heating value parameter to operator 322 which also receives the gaseous fuel effective molecular mass parameter 31 1, and the gaseous fuel adiabatic index parameter 312. In response to these inputs, operator 322 sets more or more fuel system and engine control commands such as the injected mass, injection timing, ignition timing, intake manifold pressure, air flow rate and other and operating control parameters. Operator 324 may optionally store gaseous fuel mixture parameters (e.g., the determined lower heating value parameter, the gaseous fuel effective molecular mass parameter, and the gaseous fuel adiabatic index parameter) and / or the determined operating control parameters for use in analytics, diagnostics, and prognostics, for example, by appending such data to a data log storing a gaseous fuel properties history of the engine. In some embodiments, for example, the operator 324 may store a gaseous properties history of the engine including an estimate percent hydrogen history, which may be utilized in connection with analytics, diagnostics and prognostics of performance and durability issues. Logging of percentage hydrogen may be based on the fact that hydrogen has a low molecular weight of around 2 grams / mole and, therefore, will reduce the average molecularweight of natural gas mixtures. Since typical blends of natural gas are not less than 16.043 grams / mole which is the molecular weight of its normal lowest molecular weight component, methane, a low molecular weight estimate measurement may be utilized to indicate the presence of hydrogen in the gaseous mixture.

[0115] As illustrated by this detailed description, the present disclosure contemplates multiple and various embodiments, including, without limitation, the following example embodiments. A first example embodiments is a system comprising: an engine comprising a plurality of combustion cylinders; a fueling system including a fuel rail configured to receive a gaseous fuel mixture from a fuel supply, a plurality of fuel injectors in operative communication with the fuel rail and the plurality of combustion cylinders, and a pressure sensor system operatively coupled with the fuel rail and configured to provide output indicative of fuel pressure of the fuel rail; and an electronic control system in operative communication with the fueling system and configured to: control on times of the plurality of fuel injectors to provide injections of the gaseous fuel mixture, determine a fueling control parameter in response to output of the pressure sensor system, change the fueling control parameter in response to a change in average molecular mass of the gaseous fuel mixture, and in response to the change in the fueling control parameter, adjust an injector operation parameter.

[0116] A second example embodiments include the features of the first example embodiment, wherein the electronic control system is configured to: determine a sonic speed parameter of the gaseous fuel mixture in response to output of the pressure sensor system, determine a gaseous fuel characteristic indicative of a molecular mass of the fuel in response to the sonic speed parameter, and modify one or more of the injector on times in response to the gaseous fuel characteristic.

[0117] A third example embodiments include the features of the second example embodiment, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: receive a first output from a first pressure sensor of the pressure sensor system corresponding to an injection event, the first pressure sensor configured to sense fuel pressure associated with a first location of the fuel rail; receive a second output from a second pressure sensor of the pressure sensor system corresponding to the injection event, the second pressure sensor configured to sense fuel pressure associated with a second location of the fuel rail spaced apart from the first location; and determine the sonic speedparameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

[0118] A fourth example embodiments include the features of the third example embodiment, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: receive a first output from a pressure sensor of the pressure sensor system corresponding to a first injection event performed by a first injector of the fueling system, the first injector being spaced apart from the pressure sensor by a first distance; receive a second output from the pressure sensor corresponding to a second injection event performed by a second injector of the fueling system, the second injector being spaced apart from the pressure sensor by a second distance different from the first distance; and determine the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

[0119] A fifth example embodiments include the features of the second example embodiment, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: determine one or more natural frequencies of output of a pressure sensor of the pressure sensor system following an injection event; and determine the sonic speed parameter in response to the one or more natural frequencies.

[0120] A sixth example embodiment includes the features of the fifth example embodiment, wherein the electronic control system is configured to determine the one or more natural frequencies using at least one of a discrete Fourier transform (DFT) and a sinusoidal based curve fit.

[0121] A seventh example embodiment includes the features of the fifth example embodiment, wherein the electronic control system is configured to determine the sonic speed parameter using a linear relationship between the sonic speed parameter and the one or more natural frequencies.

[0122] An eighth example embodiment includes the features of the fifth example embodiment, wherein the electronic control system is configured to determine the one or morenatural frequencies during operation of the engine in a quasi-static condition.

[0123] A ninth example embodiment includes the features of the second example embodiment, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: determine a period of decaying oscillation of output of a pressure sensor of the pressure sensor system following an injection event; and determine the sonic speed parameter in response to the period of decaying oscillation.A tenth example embodiment includes the features of the ninth example embodiment, wherein the electronic control system is configured to at least one of: determine the period of decaying oscillation for a single injection event; determine the sonic speed parameter using an inverse relationship between the sonic speed parameter and the period of decaying oscillation; and determine the period of decaying oscillation during transient operation of the engine.

[0124] An eleventh example embodiment includes the features of the second example embodiment, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: determine a maximum amplitude of a Fourier transform of output of the pressure sensor system, and determine the sonic speed parameter in response to the maximum amplitude.

[0125] A twelfth example embodiment includes the features of the eleventh example embodiment, wherein the Fourier transform of output of the pressure sensor system comprises a Fourier transform at a 1.5 engine firing frequency harmonic.

[0126] A thirteenth example embodiment includes the features of the first example embodiment, wherein the electronic control system being configured to adjust an injector operation parameter is effective to mitigate a change in engine output in response to the change in average molecular mass of the gaseous fuel mixture.

[0127] A fourteenth example embodiment includes the features of the first example embodiment, wherein the electronic control system being configured to adjust an injector operation parameter is effective to reduce an difference between a commanded engine output and an actual engine output in response to the change in average molecular mass of the gaseous fuel mixture.

[0128] A fifteenth example embodiment is a process for controlling a system including an engine including a plurality of combustion cylinders and a fueling system including a fuel rail configured to receive a gaseous fuel mixture from a fuel supply, a plurality of fuel injectors in operative communication with the fuel rail and the plurality of combustion cylinders, and a pressure sensor system operatively coupled with the fuel rail and configured to provide output indicative of fuel pressure of the fuel rail, the process comprising: controlling on times of the plurality of fuel injectors to provide injections of the gaseous fuel mixture, determining a fueling control parameter in response to output of the pressure sensor system, changing the fueling control parameter in response to a change in average molecular mass of the gaseous fuel mixture, and in response to the change in the fueling control parameter, adjusting an injector operation parameter.

[0129] A sixteenth example embodiment includes the features of the fifteenth example embodiment, comprising: determining a sonic speed parameter of the gaseous fuel mixture in response to output of the pressure sensor system, determining a gaseous fuel characteristic indicative of a molecular mass of the fuel in response to the sonic speed parameter, and modifying one or more of the injector on times in response to the gaseous fuel characteristic.

[0130] A seventeenth example embodiment includes the features of the sixteenth example embodiment, wherein the determining the sonic speed parameter comprises: receiving a first output from a first pressure sensor of the pressure sensor system corresponding to an injection event, the first pressure sensor configured to sense fuel pressure associated with a first location of the fuel rail; receiving a second output from a second pressure sensor of the pressure sensor system corresponding to the injection event, the second pressure sensor configured to sense fuel pressure associated with a second location of the fuel rail spaced apart from the first location; and determining the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

[0131] A eighteenth example embodiment includes the features of the seventeenth example embodiment, wherein the determining the sonic speed parameter comprises: receiving a first output from a pressure sensor of the pressure sensor system corresponding to a first injection event performed by a first injector of the fueling system, the first injector being spaced apart from the pressure sensor by a first distance; receiving a second output from the pressure sensorcorresponding to a second injection event performed by a second injector of the fueling system, the second inj ector being spaced apart from the pressure sensor by a second distance different from the first distance; and determining the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

[0132] A nineteenth example embodiment includes the features of the sixteenth example embodiment, wherein the determining the sonic speed parameter comprises: determining one or more natural frequencies of output of a pressure sensor of the pressure sensor system following an injection event; and determining the sonic speed parameter in response to the one or more natural frequencies.

[0133] A twentieth example embodiment includes the features of the nineteenth example embodiment, wherein the determining the one or more natural frequencies uses at least one of a discrete Fourier transform (DFT) and a sinusoidal based curve fit.

[0134] A twenty-first example embodiment includes the features of the nineteenth example embodiment, wherein the determining the sonic speed parameter utilizes a linear relationship between the sonic speed parameter and the one or more natural frequencies.

[0135] A twenty-second example embodiment includes the features of the nineteenth example embodiment, wherein the determining the one or more natural frequencies is performed during operation of the engine in a quasi-static condition.

[0136] A twenty-third example embodiment includes the features of the sixteenth example embodiment, wherein the determining the sonic speed parameter comprises: determining a period of decaying oscillation of output of a pressure sensor of the pressure sensor system following an injection event; and determining the sonic speed parameter in response to the period of decaying oscillation.

[0137] A twenty-fourth example embodiment includes the features of the twenty-third example embodiment, comprising to at least one of: determining the period of decaying oscillation for a single injection event; determining the sonic speed parameter using an inverse relationship between the sonic speed parameter and the period of decaying oscillation; and determining the period of decaying oscillation during transient operation of the engine.

[0138] A twenty-fifth example embodiment includes the features of the sixteenth exampleembodiment, wherein the determining the sonic speed parameter comprises: determining a maximum amplitude of a Fourier transform of output of the pressure sensor system, and determining the sonic speed parameter in response to the maximum amplitude.

[0139] A twenty-sixth example embodiment includes the features of the twenty-fifth example embodiment, wherein the Fourier transform of output of the pressure sensor system comprises a Fourier transform at a 1.5 engine firing frequency harmonic.

[0140] A twenty-seventh example embodiment includes the features of the fifteenth example embodiment, wherein the adjusting an injector operation parameter is effective to mitigate a change in engine output in response to the change in average molecular mass of the gaseous fuel mixture.

[0141] A twenty-eighth example embodiment includes the features of the fifteenth example embodiment, wherein the adjusting an injector operation parameter is effective to reduce a difference between a commanded engine output and an actual engine output in response to the change in average molecular mass of the gaseous fuel mixture.

[0142] It shall be appreciated that the present disclosure contemplates a number of gaseous fuel system including capabilities of identifying characteristics of gaseous which affect engine and fuel system operation. In certain embodiments, the gaseous fuel identification methodology may be conducted during normal engine operation in the field. In certain embodiments, the measurements utilized for purposes of gaseous fuel identification can be unobtrusive to normal or ex-measurement operation. In certain embodiments, the gaseous fuel estimate can be used for purposes such as on-engine adaption of the engine and fuel system commands to account for the performance differences between alternative gaseous fuels, closed loop injection quantity control, and engine and fuel system prognostics and diagnostics.

[0143] It shall be appreciated that terms such as “a non-transitory memory,” “a non-transitory memory medium,” and “a non-transitory memory device” refer to a number of types of devices and storage mediums which may be configured to store information, such as data or instructions, readable or executable by a processor or other components of a computer system and that such terms include and encompass a single or unitary device or medium storing such information, multiple devices or media across or among which respective portions of such information are stored, and multiple devices or media across or among which multiple copies of such information are stored.

[0144] It shall be appreciated that terms such as “determine,” “determined,” “determining” and the like when utilized in connection with a control method or process, an electronic control system or controller, electronic controls, or components or operations of the foregoing refer inclusively to any of a number of acts, configurations, devices, operations, and techniques, individually or in combination, including, without limitation, calculation or computation of a parameter or value, obtaining a parameter or value from a lookup table or using a lookup operation, receiving parameters or values from a datalink or network communication, receiving an electronic signal (e.g., a voltage, frequency, current, or pulse-width modulation (PWM) signal) indicative of the parameter or value, receiving output of a sensor indicative of the parameter or value, receiving other outputs or inputs indicative of the parameter or value, reading the parameter or value from a memory location on a computer-readable medium, receiving the parameter or value as a run-time parameter, and / or by receiving a parameter or value by which the interpreted parameter can be calculated, and / or by referencing a default value that is interpreted to be the parameter value.

[0145] While example embodiments of the disclosure have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain example embodiments have been shown and described and that all changes and modifications that come within the spirit of the claimed inventions are desired to be protected. It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicates that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the scope being defined by the claims that follow. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and / or “a portion” is used the item can include a portion and / or the entire item unless specifically stated to the contrary.

Claims

CLAIMS1. A system comprising: an engine comprising a plurality of combustion cylinders; a fueling system including a fuel rail configured to receive a gaseous fuel mixture from a fuel supply, a plurality of fuel injectors in operative communication with the fuel rail and the plurality of combustion cylinders, and a pressure sensor system operatively coupled with the fuel rail and configured to provide output indicative of fuel pressure of the fuel rail; and an electronic control system in operative communication with the fueling system and configured to: control on times of the plurality of fuel injectors to provide injections of the gaseous fuel mixture, determine a fueling control parameter in response to output of the pressure sensor system, change the fueling control parameter in response to a change in average molecular mass of the gaseous fuel mixture, and in response to the change in the fueling control parameter, adjust an injector operation parameter.

2. The system of claim 1, wherein the electronic control system is configured to: determine a sonic speed parameter of the gaseous fuel mixture in response to output of the pressure sensor system, determine a gaseous fuel characteristic indicative of a molecular mass of the fuel in response to the sonic speed parameter, and modify one or more of the injector on times in response to the gaseous fuel characteristic.

3. The system of claim 2, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: receive a first output from a first pressure sensor of the pressure sensor system corresponding to an injection event, the first pressure sensor configured to sense fuel pressure associated with a first location of the fuel rail;receive a second output from a second pressure sensor of the pressure sensor system corresponding to the injection event, the second pressure sensor configured to sense fuel pressure associated with a second location of the fuel rail spaced apart from the first location; and determine the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

4. The system of claim 3, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: receive a first output from a pressure sensor of the pressure sensor system corresponding to a first injection event performed by a first injector of the fueling system, the first injector being spaced apart from the pressure sensor by a first distance; receive a second output from the pressure sensor corresponding to a second injection event performed by a second injector of the fueling system, the second injector being spaced apart from the pressure sensor by a second distance different from the first distance; and determine the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

5. The system of claim 2, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: determine one or more natural frequencies of output of a pressure sensor of the pressure sensor system following an injection event; and determine the sonic speed parameter in response to the one or more natural frequencies.

6. The system of claim 5, wherein the electronic control system is configured to determine the one or more natural frequencies using at least one of a discrete Fourier transform (DFT) anda sinusoidal based curve fit.

7. The system of claim 5, wherein the electronic control system is configured to determine the sonic speed parameter using a linear relationship between the sonic speed parameter and the one or more natural frequencies.

8. The system of claim 5, wherein the electronic control system is configured to determine the one or more natural frequencies during operation of the engine in a quasi-static condition.

9. The system of claim 2, wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: determine a period of decaying oscillation of output of a pressure sensor of the pressure sensor system following an injection event; and determine the sonic speed parameter in response to the period of decaying oscillation.

10. The system of claim 9, wherein the electronic control system is configured to at least one of: determine the period of decaying oscillation for a single injection event; determine the sonic speed parameter using an inverse relationship between the sonic speed parameter and the period of decaying oscillation; and determine the period of decaying oscillation during transient operation of the engine.

11. The system of claim 2 wherein the electronic control system being configured to determine the sonic speed parameter comprises the electronic control system being configured to: determine a maximum amplitude of a Fourier transform of output of the pressure sensor system, and determine the sonic speed parameter in response to the maximum amplitude.

12. The system of claim 11, wherein the Fourier transform of output of the pressure sensorsystem comprises a Fourier transform at a 1 .5 engine firing frequency harmonic.

13. The system of claim 1, wherein the electronic control system being configured to adjust an injector operation parameter is effective to mitigate a change in engine output in response to the change in average molecular mass of the gaseous fuel mixture.

14. The system of claim 1, wherein the electronic control system being configured to adjust an injector operation parameter is effective to reduce an difference between a commanded engine output and an actual engine output in response to the change in average molecular mass of the gaseous fuel mixture.

15. A process for controlling a system including an engine including a plurality of combustion cylinders and a fueling system including a fuel rail configured to receive a gaseous fuel mixture from a fuel supply, a plurality of fuel injectors in operative communication with the fuel rail and the plurality of combustion cylinders, and a pressure sensor system operatively coupled with the fuel rail and configured to provide output indicative of fuel pressure of the fuel rail, the process comprising: controlling on times of the plurality of fuel injectors to provide injections of the gaseous fuel mixture, determining a fueling control parameter in response to output of the pressure sensor system, changing the fueling control parameter in response to a change in average molecular mass of the gaseous fuel mixture, and in response to the change in the fueling control parameter, adjusting an injector operation parameter.

16. The process of claim 15, comprising: determining a sonic speed parameter of the gaseous fuel mixture in response to output of the pressure sensor system, determining a gaseous fuel characteristic indicative of a molecular mass of the fuel in response to the sonic speed parameter, andmodifying one or more of the injector on times in response to the gaseous fuel characteristic.

17. The process of claim 16, wherein the determining the sonic speed parameter comprises: receiving a first output from a first pressure sensor of the pressure sensor system corresponding to an injection event, the first pressure sensor configured to sense fuel pressure associated with a first location of the fuel rail; receiving a second output from a second pressure sensor of the pressure sensor system corresponding to the injection event, the second pressure sensor configured to sense fuel pressure associated with a second location of the fuel rail spaced apart from the first location; and determining the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

18. The process of claim 17, wherein the determining the sonic speed parameter comprises: receiving a first output from a pressure sensor of the pressure sensor system corresponding to a first injection event performed by a first injector of the fueling system, the first injector being spaced apart from the pressure sensor by a first distance; receiving a second output from the pressure sensor corresponding to a second injection event performed by a second injector of the fueling system, the second injector being spaced apart from the pressure sensor by a second distance different from the first distance; and determining the sonic speed parameter in response to a difference between the first output and the second output, and a difference in distance between the first pressure sensor and an injector performing the first injection event and the second pressure sensor and the injector performing the first injection event.

19. The process of claim 16, wherein the determining the sonic speed parameter comprises: determining one or more natural frequencies of output of a pressure sensor of the pressure sensor system following an injection event; and determining the sonic speed parameter in response to the one or more natural frequencies.

20. The process of claim 19, wherein the determining the one or more natural frequencies uses at least one of a discrete Fourier transform (DFT) and a sinusoidal based curve fit.

21. The process of claim 19, wherein the determining the sonic speed parameter utilizes a linear relationship between the sonic speed parameter and the one or more natural frequencies.

22. The process of claim 19, wherein the determining the one or more natural frequencies is performed during operation of the engine in a quasi-static condition.

23. The process of claim 16, wherein the determining the sonic speed parameter comprises: determining a period of decaying oscillation of output of a pressure sensor of the pressure sensor system following an injection event; and determining the sonic speed parameter in response to the period of decaying oscillation.

24. The process of claim 23, comprising to at least one of: determining the period of decaying oscillation for a single injection event; determining the sonic speed parameter using an inverse relationship between the sonic speed parameter and the period of decaying oscillation; and determining the period of decaying oscillation during transient operation of the engine.

25. The process of claim 16, wherein the determining the sonic speed parameter comprises: determining a maximum amplitude of a Fourier transform of output of the pressure sensor system, and determining the sonic speed parameter in response to the maximum amplitude.

26. The process of claim 25, wherein the Fourier transform of output of the pressure sensor system comprises a Fourier transform at a 1.5 engine firing frequency harmonic.

27. The process of claim 15, wherein the adjusting an injector operation parameter is effective to mitigate a change in engine output in response to the change in average molecularmass of the gaseous fuel mixture.

28. The process of claim 15, wherein the adjusting an injector operation parameter is effective to reduce an difference between a commanded engine output and an actual engine output in response to the change in average molecular mass of the gaseous fuel mixture.

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