Method for operating a gaseous fuel engine

Abstract

A method of operating a hydrogen powered internal combustion engine, the method comprising performing a torque estimation routine, wherein an actual torque is computed for an engine cycle by estimatin

Description

Technical field The present invention generally relates to a method for operating a gaseous fuel internal combustion engine, more specifically to a method of estimating torque in such an engine. The present invention proposes a strategy to estimate the torque produced by a hydrogen engine that is particularly suited for implementation in an ECU for safety diagnostic. Background Art The transition to cleaner and more sustainable energy sources has prompted a strong interest in hydrogen as a potential alternative fuel for combustion engines. Hydrogen combustion engines (H2-ICE) offer the prospect of significantly reducing greenhouse gas emissions and contributing to a more environmentally friendly transportation and industrial landscape. As hydrogen gains traction as a viable fuel, the precise monitoring and control of torque in hydrogen combustion engines emerge as crucial factors in achieving optimal performance, efficiency, and emissions reduction. Conventional torque monitoring techniques designed for traditional combustion engines may fall short in accurately measuring and managing torque in the unique context of hydrogen combustion. The characteristics of hydrogen fuel, including its rapid combustion rates and distinct combustion properties, require specialized monitoring solutions to ensure safe and efficient engine operation. Thus, there is an evident need for an innovative torque monitoring method tailored to hydrogen combustion engines, capable of delivering real-time insights, enhanced precision, and adaptability to the unique challenges posed by hydrogen-based combustion processes. Such capability of torque monitoring is particularly desirable in the context of ECU safety monitoring, i.e. a safety function operated by the ECU which estimates the actual torque and compares it to an expected / reference torque. Technical problem It is an object of the present invention to provide a method for operating a gaseous fuel engine, with a torque estimation strategy adapted for H2-ICE. This object is achieved by a method as claimed in claim 1. General Description of the Invention To achieve this object, the present invention proposes a method for operating a hydrogen powered internal combustion engine, the method comprising performing a torque estimation routine, wherein an actual torque Tactual is computed for an engine cycle by estimating cylinder pressures based on the intake air pressure and temperature and using a value of lambda Ades that is determined from a mapping based on an operating state for the engine. A benefit of the present invention is to provide an approach of torque estimation that is adapted to the specifics of hydrogen powered ICE, which operate with various lambda values contrary to conventional approaches where lambda is assumed to be stoichiometric. For this purpose, a mapping is used which relates lambda with an operating state for the engine. The proposed approach implements an estimation the cylinder pressure caused by the combustion in the various cylinders for a given engine cycle, based on measured parameters of intake air such a pressure and temperature. The lambda value Ades is obtained from the mapping which is calibrated on the basis of predetermined engine operating states. A relevant parameter for the engine operating state is engine coolant temperature. In embodiments, the mapping may be calibrated such thatAdes decreases as the engine coolant temperature increases. In the mapping, lambda Ades may be clamped between 1.0 and 5.0, in particular between 1.6 and 4.0. That is, the mapping of Ades defines different values for Ades, depending on the operating state. Within the ECU, for the sake of safety / integrity, access to the Ades mapping is advantageously restricted to the torque estimation routine, i.e. not used by other functions / modules. Using a dedicated 2desmapping also reduces the odds for computation failures. Other relevant parameters of engine operating state are engine speed and torque parameter. In the context of the mapping of Ades, the term torque parameter may be representative of a permissible torque for the engine cycle (threshold values for maximum torque) or of an actual torque for a preceding engine cycle (i.e. determined by the same torque estimation routine). Advantageously, the estimation of the cylinder pressure involves the estimation of air mass using the ideal gas law, where the gas constant is modified to consider the volume taken by hydrogen, referred to as Rmix. Rmix is advantageously dependent on the amount of hydrogen and may thus be mapped in function of lambda Ades. In particular, gas constant Rmix may decrease as lambda Xdes increases. Rmix is preferably equal to R in case of fuel cut off (pedal is released) or in a pure air condition. Different approaches may be adopted by those skilled in the art to estimate the average cylinder pressure due to the combustion (average pressure over all cylinders for one combustion cycle). In particular, such calculation may involve efficiency factors and fuel heating value. However, the inventive approach is characteristic in that the average pressure depends on the ratio intake air pressure over (intake air temperature xAdes x Rmix). The intake air pressure and temperature may be measured in the intake manifold. Advantageously, the actual torque can be calculated using the following formula: _ Emanifold * H * Effvol * Efftherm * EffSpar]f Inactive cylinder dispeng actual rp D 1 Z7D * * 4 1 manifold * ^mix * ^des * ^stoich ’’-cylinder First tests have shown that whereas this formula only requires few signals from the engine, it provides a robust torque estimation in operation. The present torque estimation routine is particularly useful in the context of ECU safety diagnostic. In particular, the torque estimation routine may be implemented within the ECU, in an isolated process (which may be referred to as level 2), which comprises modules configured for monitoring operation of the standard ECU operating functions. In embodiments, the torque estimation routine is periodically executed at a frequency of 20 Hz or more, preferably 25 Hz or more. In that context, the actual torque may be compared to a permissible torque. The permissible torque is generally a reference or expected value that is conventionally determined based on inputs such as accelerator pedal position, and / or torque demand from cruise control or external modules (gearbox, ESP...). Different strategies can be implemented to determine the permissible torque, as will be known by those skilled in the art. If the actual torque is compared to a permissible torque, the operation of the engine may be switched to a safe mode, whereby the torque output of the engine is limited. A flag may be raised to signal a fault, and to indicate that operation of the engine has been switched to a safe mode. The invention further provides a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method as described above. The invention further provides a processing unit configured to execute the method as described above. Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a data flow diagram according to an embodiment of the invention applied to EMS with continuous torque monitoring. Description of Preferred Embodiments An embodiment of the inventive method for operating a hydrogen powered internal combustion engine is disclosed below. The method is preferably implemented by a control unit (or module) which may be part of the Engine Control Unit of the vehicle. The control unit comprises a processor and a memory and is configured to implement the method according to the present disclosure. A. Principle of torque estimation In the context of safety torque monitoring, it is desirable to use robust calculations with low computational costs in order to estimate torque multiple times per second. Conventionally, torque is estimated from the cylinder pressures caused by combustion, typically represented by IMEP (Indicated mean effective pressure) and engine displacement. As is known in the art, IMEP is a parameter that summarizes the net effect of all the pressure changes within combustion chambers during a power stroke. However, ICE vehicles are typically not equipped with torque sensors or cylinder pressure sensors and torque must therefore be estimated. The conventional relationship between torque and IMEP is written: Tae.ua> = IMEP * * Effspar» • [Eq. 1 ] •levtinder Where dispeng is the engine displacement and Effspark is the spark efficiency. IMEP itself depends on the energy released by the combustion, and its thus a function of fuel quantity, calorific value and air-fuel ratio. However, fuel quantity cannot be easily measured in the engine. However, the present approach considers that fuel quantity can be determined from the air quantity. Furthermore, intake air pressure and intake air temperature are easy to measure. We thus have the following relationships: Where the fuel quantity mfuei is expressed in function of the total air mass mair, the stochiometric air fuel ratio AFRstoich for hydrogen (about 34:1 for H2), and the lambda value A (ratio AFR to AFRstoich). and Pma.nifold*Vcylinder*Effvol ^manifold^^ [Eq. 3] this equation applies the ideal gas law where the mass of air mair is expressed in function of the intake manifold pressure Pmanifoid and temperature Tmanifoid, the cylinder volume VcyUnder, the volumetric efficiency Effvot and the gas constant R (in J / Kg / K). With some simplifications and approximations, the IMEP can be written as IMEP Pmanifold*M*E ff vol*Ef f therm*Ef f spark fEO 41 Tmanifold*R*^*AFRstoich Where El is the Lower Heating value (e.g. equals to 120,21 MJ / Kg), Efftherm is the thermal efficiency, Effspark is the spark efficiency, and nactlve cylmder jS the ratio of ilcy Under the number of active cylinders over the total number of cylinders in the engine. The volumetric, thermal, and spark efficiency may be pre-calibrated quantities as is conventional in the art. The values may be constant or variable, depending on the desired accuracy. In particular, the volumetric efficiency Effvot may be obtained from a pre-calibrated mapping based on engine speed, manifold pressure and / or temperature. Likewise, the thermal efficiency Efftherm may be obtained from a pre-calibrated mapping based on estimated thermal losses, manifold / engine temperature and engine speed. Finally, the spark efficiency Effspark may be determined from a pre-calibrated mapping based on the actual spark angle and the spark angle at Maximum Best Torque (MBT). Said mappings may be implemented as a mathematical function, a calibrated look-up table, or a trained neural network. B. Torque estimation As previously mentioned, the invention provides a method for estimating torque in a hydrogen ICE, which accounts for the specifics of the gaseous fuel. First, lambda is not assumed to be stoichiometric, but is variable (i.e. non-constant). Secondly, the ideal gas law is applied with a variable R, noted Rmix, that accounts for the mixture of air and hydrogen (occupying a greater volume than liquid fuel in the combustion chamber). The IMEP can thus be expressed as: IMEP = pmanifoM*H*Eff vol*Eff therm p manifold* pmix*^des* AF pstoich where Ades is the variable, desired lambda value and Rmix is the mixing parameter. Hence the actual torque may be determined from: erm* Ef f spark nactive cylinder dispeng [Eq. 6] Tmanifold*Rmix*^des*AFRstoich ncylinder The desired lambda value Xdes can be advantageously determined from an operating state of the engine. Said operating state of the engine may be defined by the temperature of the engine coolant, and further by the engine speed, and a torque parameter. The torque parameter may correspond e.g. to the permissible torque associated with the current engine load (for the current engine cycle) or to the actual torque estimated for the previous cycle. More specifically, a mapping may be used to draw a relationship between Ades, the engine coolant temperature, the engine speed, and the torque parameter. Said mapping outputs a desired lambda value Ades from an input engine coolant temperature, engine speed, and torque parameter. Said mapping may be implemented as a mathematical function, a calibrated lookup table, or a trained neural network. Preferably, Ades decreases as the coolant temperature increases. Likewise, Rmix may be determined from Ades using any form of mapping (e.g. mathematical function, look-up table, neural network, ...). Preferably, Rmix decreases as the Xdes increases. In other words, Xdes and Rmix may be expressed as: 'Ales f^coolant’ Spe6deng, ^demand}’ ^-mix 9 (Ades) Where f and g are mappings. C. Torque monitoring Fig. 1 shows a diagram implementing the present torque estimation approach in the context of ECU safety monitoring (ESM). The purpose of ESM is to avoid unintended accelerations in vehicles that would lead to unsafe driving. Reference sign 10 indicates an Engine control unit, ECU, which is conventionally an electronic device with processors and modules to implement control functions and strategies relating to engine operation, by software and hardware. Fig. 1 is much simplified and only shows the functions of relevance in the context of the ESM. The ECU 10 includes a main torque module 12 that is conventionally configured to determine a main torque demand from the accelerator pedal position and / or other input signals (including e.g. other torque demands from cruise control or external modules - e.g. gearbox, ESP controller, etc.). The main torque demand is a reference or expected value that can be determined based on any conventional strategy, as known in the art. This main torque demand will then be used as basis to determine the fuel quantity to be injected into the engine and to operate the various actuators (e.g. throttle, fuel injectors, etc.). This is within the Level 1 part of the ECU. Continuous torque monitoring is implemented in a Level 2 section of the ECU. It is preferably operated on processing means independent from Level 1 to ensure freedom of interference. A permissible torque function 14 is configured to determine a maximum allowable torque value using methods known in the art, which is referred to as permissible torque tperm. This function may determine torque demands based on the various inputs. The permissible torque Tpermrnay then be determined from a mapping in function of the accelerator pedal and the torque demands. A torque estimator function 16 implements a torque estimator routine using the approach described in the previous section and specifically based on Equation 6. Torque estimator 16 hence computes a value of actual torque t actual that estimates the engine torque output. For this purpose, Pmanifoid, Tmanifoid, Tcooiant and RPM are determined by means of sensors, like pressure and temperature sensors in the intake manifold, a temperature sensor in the engine coolant circuit and a crankshaft rotation sensor. In parallel, Xdes and Rmix are determined from the respective mappings. The volumetric efficiency Effvoi, the thermal efficiency Efftherm, the spark efficiency Effspark, the number of active cylinder on a given engine cycle ^active cylinder, the total number of cylinder in the engine ncylinder, and the engine displacement dispeng are determined using conventional means and methods. The actual torque Tactuai for a given engine cycle is then computed with Eq. 6. At 18, the permissible torque tpermis compared to the actual Torque tactual- If the actual torque is lower than the permissible torque, no fault is detected and operation of the engine proceeds as normal. However, if the actual torque is greater than the permissible torque (Tactuai >^perm}, a flag signaling a fault is raised and the engine is switched to operate in a safe mode 20 wherein torque is reduced. In practice, to ensure continuous monitoring, the actual and permissible torques, 5 and the comparison 18, may be implemented several times per second, e.g. with a frequency of about 20 to 25 Hz.

Claims

1. A method of operating a hydrogen powered internal combustion engine, the method comprising performing a torque estimation routine, wherein an actual torque Tactual is computed for an engine cycle by estimating cylinder pressures based on the intake air pressure and temperature and using a value of lambda Ades that is determined from a mapping based on an engine operating state.

2. Method according to claim 1, wherein the actual torque (Tactual) is computedbased on the following formula:7-actualEmanifold * H * Effvoi * * EffsparkT ■ i* R • * * AFR +- ■ j,1 manifold lxmix / vdes lYstoich^active cylinder ^^Peng*----------------*---------^■cylinder 4 / 1where Pmanifoid is the manifold pressure, H is the fuel lower heat value, Tmanifold is the manifold temperature, Rmix is the mixing gas constant, AFRstochio is the stoichiometric air-fuel ratio, EffvoL is the volumetric efficiency, Efftherm is the thermal efficiency, Effspark is the spark efficiency, nactive cylinder's the number of active cylinder on a given engine cycle, ncyUnder is the total number of cylinder in the engine, and dispeng is the engine displacement.

3. The method according to any of the preceding claims, wherein the engine operating state is defined by an engine coolant temperature.

4. The method according to claim 3, wherein lambda Ades decreases as the engine coolant temperature increases.

5. The method according to any of the preceding claims, wherein the engine operating state is defined by an engine speed.

6. The method according to any of the preceding claims, wherein the engine operating state is defined by a torque parameter, the torque parameter being representative of a permissible torque under the current engine load or of an actual torque for a preceding engine cycle.

7. The method according to any of the preceding claims, wherein the cylinder pressure is further estimated using a gas constant Rmix that is mapped in function of lambda Ades.

8. The method according to claim 7, wherein the gas constant Rmix decreases as lambda Ades increases.

9. Method according to any of the preceding claims, wherein lambda Ades is clamped between 1.0 and 5.0, preferably between 1.6 and 4.0.

10. Method according to any of the preceding claims, wherein the intake pressure, respectively manifold pressure, and the intake temperature, respectively manifold temperature, is measured.

11. Method according to any of the preceding claims, wherein the actual torque is periodically computed at a frequency of 20 Hz or more, preferably 25 Hz or more.

12. Method according to any of the preceding claims, wherein the actual torque is compared to a permissible torque.

13. Method according to claim 12, including operating the engine in a safe mode if the actual torque is greater than the permissible torque.

14. Method according to claim 13, wherein operating the engine if a safe mode includes limiting the torque output of the engine.

15. Method according to claim 12 to 14, including raising a flag signaling a fault if the actual torque is greater than the permissible torque.

16. Method according to claim 12 to 15, wherein the permissible torque is computed based on torque demand and / or inputs from the driver, said inputs preferably including the driver’s pedal position.

17. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any of the preceding claims.

18. A processing unit configured to execute the method according to any one of claims 1 to 16.

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