Method for operating an indirect injection gaseous fuel engine

Abstract

The invention relates to a method for controlling indirect injections for a hydrogen powered internal combustion engine. The method comprising the steps of: • - determining a fuel demand Q p from an input torque demand T D; • - determining an initial fresh air flow M F, k based on a previous specific gas constant R mixing, kJ; • - determining a fast lambda value λ Fast based on the initial fresh air flow M F, k, • - determining an updated specific gas constant R mixing, k+i based on the fast lambda λ Fast ' • - determining a updated fresh air flow M F, k+1 based on the updated specific gas constant R mixing, k+ 1J • - determining a fuel quantity Q F based on the updated fresh air flow M F, k+1; • - performing an injection event by injecting said fuel quantity into an engine cylinder. The invention takes into account the mixed flow of air and hydrogen admitted into the cylinder via the inlet valves in case of indirect injection, the proportion of which is given by the lambda value A. The method uses a specific gas constant R of this mixing, which is defined by the following formula:

Description

[0001]P-DELPHI-404 / WO 1METHOD FOR OPERATING AN INDIRECT INJECTION GASEOUS FUELENGINE Technical field The present invention generally relates to a method for operating a gaseous fuel internal combustion engine, more specifically to a method of controlling indirect injections for a hydrogen powered internal combustion engine. Background Art The transition to cleaner and more sustainable energy sources has prompted astrong 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 control of torque in hydrogen combustion engines emerge as crucial factors in achieving optimal performance, efficiency, and emissions reduction. Today, hydrogen fueled engines are developed / designed based mainly on the knowledge and know-how gained with gasoline engines, making requiredadaptations and new developments. As is known, gasoline / gas operated enginesare conventionally controlled based on an ‘air lead’ approach, where lambda is mainly constant (stoichiometric), the air charge being adjusted in function of load and then the fuel being computed from the fresh air flow to meet the lambda setpoint. This control of the air fuel mixture is required for optimal operation of the catalytic converter. One drawback of this conventional approach, when applied to hydrogen combustion engines, is a lag in torque response, when the driver depresses the accelerator pedal to request a rapid change of torque. This lag is due to a combination of elements: boost lag from the turbocharger running with low enthalpy (lean lambda setpoint); lambda demand depends on actual torque to get consistent combustion setpoints (Air / spark / injection timing demand). A prior strategy developed by the present inventors is shown in Figure 1 and relatesto a method of operating a hydrogen combustion engine which alleviates the above-P-DELPHI-404 / WO 2mentioned drawback by computing a so-called fast lambda value, which is based on the current air flow rate and the current fuel demand. However, with gaseous fuels such as hydrogen, estimating air flow rates in indirectinjection systems is more challenging than in direct injection systems. Indeed, inindirect injection systems, fuel is injected into the intake manifold / upstream ofintake valves (also known as PFI application – for Port Fuel Injection), rather thandirectly into the combustion chamber where the air and fuel mixture ignites. As hydrogen density is very low, it occupies a considerable volume in the intakemanifold (PFI application), which must be considered to accurately estimate the airflow rate. Technical problemIt is an object of the present invention to provide a method of controlling indirectinjections for a hydrogen powered internal combustion engine which overcomes theaforementioned drawbacks. This object is achieved by a method as claimed in claim 1. General Description of the InventionThe present invention proposes a method for controlling injection in a hydrogenpowered internal combustion engine, wherein hydrogen is indirectly injected into the engine. The method comprises the steps of: -determining a fuel demand QD from an input torque demand TD;- determining an initial fresh air flow MF, k based on a previous specific gasconstant Rmixing, k; -determining a fast lambda value λ^^^^ based on the initial fresh air flow MF, k;- determining an updated specific gas constant Rmixing, k+1 based on the fastlambdaλ^^^^; -determining an updated fresh air flow MF, k+1 based on the updated specificgas constant Rmixing, k+1; -determining a fuel quantity QF based on the updated fresh air flow MF, k+1;P-DELPHI-404 / WO 3- performing an injection event by injecting said final fuel quantity in at leastone cylinder. This method has been developed to address lambda management during torque transients in indirect injected (PFI) engines. It is thus advantageously applied in case of a variation in torque demand. Compared to prior art strategies, the invention allows for an accurate trapped air estimation of PFI engine running with variable lambda setpoint, as is the case in H2- ICE engines, and thus for an improved combustion lambda control. Further benefits of the inventive method are the reduction of combustion issues (knock, pre-ignition) and pollutant emissions (NOx).The fast lambda value λ^^^^ is a lambda number that is used in torque transient andtypically computed based on the current air flow rate MF and advantageously further on current fuel demand QD. In steady state, for a given Torque Demand, a desired air mass MDis typically determined based on the fuel demand QD and on a standard lambda number (lambda desired), and at least one charge air parameter is adjusted based on saiddesired air mass MD. The fuel quantity QF to be injected is then determined basedon current (intake) air flow MF rate and on a lambda setpoint corresponding to the standard lambda number (lambda desired). In case of a variation in torque demand, the lambda setpoint is then the fast lambda value λ^^^^.In embodiments, the steps of determining a fast lambda value λ^^^^; Determining anupdated specific gas constant Rmixing, k+1; and Determining an updated fresh air flowMF, k+1 may be repeated one or more time for improving convergence. In embodiments, the fast lambda value λ^^^^is further determined based on the fuel demand QD. In embodiments, the fast lambda value λ^^^^is clamped to an interval centered ona desired lambda value λ^. The width of said interval may be determined from adifference in torque demand and the desired lambda value λ^.P-DELPHI-404 / WO 4In embodiments, λ^^^^ is clamped between a minimum lambda value λ^^^ and amaximum lambda value λ^^^that are calibrated in function of engine speed andengine load. For example, λ^^^ may be comprised between 1.5 and 1.8, and λ^^^is comprised between 2.2 and 3.5.Preferably, the fresh air flow MF, k (air mass) is computed based on a specific gas constant Rmixing,kand is derived from, resp. is done according to, the following formula: where ^^^^^^^ is the gas pressure in the intake port, ^^^^^^^^^ is the volume of acylinder, ^^^^^^is the volumetric efficiency, ^^^^^^^is the temperature in the intake port, and R^^^^^^,^is the specific gas constant. Preferably, the specific gas constant R^^^^^^,^is computed based on fast lambda λ^^^^and derived from, resp. is done according to, the following formula: where R is the ideal gas constant, ^^^^ is the molar mass of air, ^^^ is the molarmass of hydrogen, and λ^^^^is the fast lambda value. 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 flowchart illustrating a method for operating a direct injection systemusing a fast lambda value; andFigure 2 is flowchart illustrating an embodiment of the method according to thepresent invention.P-DELPHI-404 / WO 5Description of Preferred EmbodimentsFigure 1 shows a flowchart representing the method for operating a direct injectionsystem with a fast lambda value; this method has been described by the presentinventors in patent application GB 2213718.6, which is herein incorporated byreference. Reference sign 10 designates a torque structure module that receives torque demands from various components, for example direct torque demand from the driver (accelerator pedal) or indirect torque demand via cruise control, torque demands from the transmission system, from driving dynamics, from the gearbox ortorque demands related to specific components (e.g. accessory torque). The torquestructure module 10 coordinates these various demands and generates a global torque demand TD. A desired fuel mass QD (also referred to as fuel demand) is then determined to meet the desired torque demand TD, typically by calculation based on IMEP (Indicated Mean Effective Pressure), cylinder volume and combustion efficiency coefficients. At 12 a desired air mass MDis computed based on the desired fuel mass QDand on a desired lambda λ^. The throttle and turbocharger gate positions are adjusted onthe basis of the desired air mass MD.That is, in steady state, the predetermined lambda value is a desired Lambda number λ^. The fuel calculation module 14 determines a final fuel mass QF, i.e. the fuel quantity to be injected into the engine for the upcoming combustion cycle (total fuel for all cylinders) and used in the engine management scheme. The final fuel mass QF is determined on the basis of the fresh air flow MF and for a given lambdasetpoint corresponding to λ^.The method of Fig.1 applies a strategy whereby a different lambda value λ is usedfor the calculation of the final fuel mass in case of a change in torque demand.Roughly speaking, desired lambda λ^values are calibrated to be applied duringsteady state engine conditions, i.e. when little to no increase or decrease of torquedemand TD occurs. Desired lambda λ^ values typically correspond to a lean air / fuelratio. For example λ^ may be in the range of 3.5 to 2.5 at low-mid load and down to1.6 at full load (this is however only an example and rather depends on the engine).P-DELPHI-404 / WO 6When the driver presses the pedal, or in case of deceleration (i.e. where the engineis no longer in steady state operation), there is a difference (i.e. a variation) in torquedemand TD. A difference in torque demand TD can generally be determined bycomparing the new torque demand (e.g. TD) to a previous reference value of torquedemand. In case a variation in torque demand is present, then a different lambda(module 16) referred to as fast lambda value λ^^^^, which is different from the desiredlambda λ^, is used (as setpoint) for the fuel global mass calculation 14. The comparison can e.g. be done by subtraction or by computing a ratio, the result of which can then either be compared to a threshold or directly used as input toinfluence the value λ^^^^. In embodiments, the new torque demand is compared toa moving average of torque demand (for previous combustion events or cycles). The fast lambda value λ^^^^is computed based on the desired fuel mass QD, thefresh air flow MF (determined by module 18) and the desired lambda λ^ (module 20).More specifically, a quantity λ^^^may be computed as: ^ λ^^^^= ^^∙^^^^^^^^^^^[Eq.1]where AFRstoichH2 is the mass stoichiometric ratio of fuel to hydrogen (34.33 : 1).This λ^^^ is then subsequently clamped to an interval based on the desired lambdaλ^, the engine speed and the engine load to obtain the fast lambda value λ^^^^. The width of the clamping interval may depend on the difference in torque demand. For example, a table may be defined having:^ A maximum limit Lmax to avoid too “lean” combustion in order to keepacceptable combustion stability;^ A lower limit Lmin to avoid too rich combustion to control Nox emissions andabnormal combustions;where Lmax and Lmin depend on engine speed and load.Hence if Lraw is within the range [Lmin; Lmax] then the value Lraw is used as fast lambda value, i.e. as setpoint. This can be written as LFAST=Lraw. If Lraw exceeds Lmax, then LFAST takes the value Lmax (LFAST=Lmax).If Lraw is below Lmin, then LFAST takes the value Lmin (LFAST=Lmin).P-DELPHI-404 / WO 7The final fuel mass QF is then determined in module 14 based on the fresh air flowMF and the fast lambda value λ^^^^ (used as lambda setpoint). The final fuel massQF represents the fuel quantity to be injected into the engine for the upcoming combustion cycle (total fuel for all cylinders) and used in the engine management scheme. <Invention> Whilst the above method enables to address transient load operations in directinjection engines, it requires some adjustments to properly function with indirectinjection engines. Indeed, both the final fuel mass QFand the fast lambda value λ^^^^are determinedbased on the fresh air flow MF. However, with gaseous fuel such as hydrogen,estimating air flow rates in indirect injection systems is more challenging than indirect injection systems. Indeed, as hydrogen density is very low, it occupies a considerable volume in the intake manifold (PFI application), which must beconsidered to accurately estimate the air flow rate.The present invention thus proposes an improvement of the method of Fig.1, specifically adapted for indirectly injected hydrogen combustion engines, i.e. where hydrogen is introduced in the fresh air flow upstream of the cylinder. Hence, the functions modules operate in the same / similar manner, unless specified otherwise. As will be seen, the functional flow chart of Fig.2 is mostly identical to that of Fig.1, except for the new module 22 relating to the Gas constant Rmixing.Again, to recap, to generally operate a combustion event a predetermined fuelquantity QFneeds to be injected in an engine cylinder. Therefore, a fuel demand QDis determined from an input torque demand TD. Module 12 determines acorresponding desired air mass MD based on the fuel demand QD and on a desired lambda value λ^, whereby at least one charge air parameter is typically adjustedbased on said desired air mass MD. The predetermined fuel quantity QF based oncurrent (intake) air flow MFrate and on a lambda setpoint LSET. In steady state, LSETcorresponds to the desired lambda value λ^. However, in case of a variation inP-DELPHI-404 / WO 8torque demand, the lambda setpoint LSET will change to take the value of lambda fast λ^^^^. Furthermore, QF is then determined based on an updated fresh air mass. The fresh air flow MF (air mass) can generally be computed from the following formula: where ^^^^^^^is the gas pressure in the intake port, ^^^^^^^^^is the volume of a cylinder, ^^^^^^is the volumetric efficiency, ^^^^^^^is the temperature in the intakeport, and ^^^^^^^ is the specific gas constant.This air mass calculation is carried out by module 18 based on Eq.2. For direct injection, the composition of the gas volume admitted (trapped) into thecylinder is pure air, hence R=287 [J / kg.K] is constant.However, for indirect injection, the flow admitted into the cylinder via the inlet valvesis a mix of air and hydrogen, the proportion of which is given by the lambda valueλ. In this case, the specific gas constant R of this mixing is defined by the followingformula: where ^^^^ is the molar mass of air and ^^^ is the molar mass of hydrogen.Hence the lambda value λ depends on the fresh air flow MF, which itself dependson the specific gas constant ^^^^^^^, which itself depends on the lambda value λ. Inother words, for indirect injection engines, these quantities are highly mathematically coupled and thus difficult to accurately determine. The prior strategy of Fig.1 is thus modified by implementing modules 18 and 22 to determine the fresh air flow MF and the specific gas constant Rmix, to take into account the volume occupied by hydrogen in the case of PFI engine. To overcome this difficulty and accurately approximate these quantities, theinventive methods comprise the following steps in respect of an injection event:a) determining a fuel demand QD from an input torque demand TD;P-DELPHI-404 / WO 9b) determining an initial fresh air flow MF, k based on a previous specific gasconstant Rmixing, k; c) determining a fast lambda value λ^^^^ based on the initial fresh air flow MF,k;d) determining an updated specific gas constant Rmixing, k+1 based on the fastlambdaλ^^^^; e) determining an updated fresh air flow MF, k+1 based on the updated specificgas constant Rmixing, k+1; f) determining a final fuel quantity QF based on the updated fresh air flow MF,k+1.So, in step b) an initial value of MFis computed taking into account a previous value of Rmixing. The previous value of Rmixing is a known / stored value previously determined, typically for the previous injection event (e.g.180° of CA before, i.e. for the previously fueled cylinder). The computation of MFis done using Eq.2, withactual values of pressure and temperature (i.e. currently determined / measured).In step c) the value of fast lambda λ^^^^ is determined based on initial MF and Qd(module 16).At step d) an updated value of Rmixing is computed, and next an updated value of MFis computed with Eq.2 based on the updated Rmixing and the actual intake pressureand temperature values (same as in step b). Next, the fuel quantity QF is determined by module 14 based on updated MF andfast lambda λ^^^^.Subsequently, (step g) an injection event is performed by injecting said final fuel quantity QF in the respective engine cylinder.The inventive method enables to minimize possible errors and avoid running “toorich” when the torque demand increases. Hence the present method / strategy is beneficial in case of a variation in torque demand. In practice, steps c), d) and e) may be repeated at least one time, to improve convergence.The terms ‘previous’, as in previous specific gas constant Rmixing, k¸ refers to anexisting value, previously determined (and available in memory), for example for theP-DELPHI-404 / WO 10previous cylinder in fueling order or for a previous determination for upcoming cylinder to be fueled according to fueling order. < ECU > The present method is typically implemented by a control unit, e.g. an engine control unit, by means of appropriate software and hardware. In particular the control unit may comprise a data processing system storing instructions which, when executed by the system, cause the latter to perform the steps of the present method. In practice, an Engine Control Unit (ECU), as described herein, comprises one or more processor units, memory units, input / output (I / O) interfaces, and communication modules configured to execute control algorithms for regulating engine operation. The processor unit may include a microcontroller, microprocessor, digital signal processor (DSP), field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), or any combination thereof. The processor is configured to execute control logic, process sensor data, and generate actuation signals for engine components. The memory unit comprises non-volatile memory, such as read-only memory (ROM), flash memory, or electrically erasable programmable read-only memory (EEPROM), for storing firmware, calibration parameters, and control algorithms. Additionally, the ECU includes volatile memory, such as random-access memory (RAM), to facilitate real-time data processing and temporary storage of operating parameters. The input interfaces receive data from various sensors associated with engine operation, including but not limited to pressure sensors, temperature sensors, oxygen sensors, throttle position sensors, and crankshaft position sensors. The ECU processes these inputs to determine optimal fuel injection timing, ignition timing, and air-to-fuel ratio adjustments. The output interfaces are configured to transmit control signals to actuators, including fuel injectors, ignition coils, throttle control mechanisms, and Gas tanks shut off valves. These interfaces may include pulse-width modulation (PWM) drivers, digital-to-analog converters (DACs), or other signal conditioning circuits.P-DELPHI-404 / WO 11The communication module facilitates data exchange between the ECU and external systems, such as diagnostic tools, vehicle control networks, or cloud-based monitoring systems. Communication may occur via standard automotive protocols, including Controller Area Network (CAN), Local Interconnect Network (LIN), FlexRay, or Ethernet. In certain embodiments, the ECU may include additional co-processors or neural network accelerators to implement machine learning algorithms for adaptive engine control. The ECU may further incorporate security modules to ensure data integrity and prevent unauthorized access to control functions. Alternative implementations of the ECU may employ distributed architectures, wherein multiple interconnected control units collectively manage different aspectsof engine operation, fuel delivery, and emissions control.

Claims

P-DELPHI-404 / WO 12Claims1. A method for controlling indirect injections for a hydrogen powered internalcombustion engine, the method comprising the steps of:- determining a fuel demand QD from an input torque demand TD;- determining an initial fresh air flow MF, k based on a previous specific gasconstant Rmixing, k; -determining a fast lambda value λ^^^^ based on the initial fresh air flow MF,k;- determining an updated specific gas constant Rmixing, k+1 based on the fastlambdaλ^^^^; -determining a updated fresh air flow MF, k+1 based on the updated specificgas constant Rmixing, k+1; -determining a fuel quantity QF based on the updated fresh air flow MF, k+1;- performing an injection event by injecting said fuel quantity into an enginecylinder.

2. The method according to any of the preceding claims, wherein the steps of:- Determining a fast lambda value λ^^^^;- Determining an updated specific gas constant Rmixing, k+1;- Determining an updated fresh air flow MF, k+1;are repeated at least one time.

3. The method according to any of the preceding claims, wherein the fast lambdavalue λ^^^^is further determined based on the fuel demand QD.

4. The method according to any of the preceding claims, wherein the fast lambdavalue λ^^^^is clamped to an interval centered on a desired lambda value λ^.

5. The method according to the preceding claim, wherein a width of said interval isdetermined from a difference in torque demand and the desired lambda valueλ^.P-DELPHI-404 / WO 136. The method according to any of the preceding claims, wherein λ^^^^ is clampedbetween a minimum lambda valueand a maximum lambda valuethat are calibrated in function of engine speed and engine load.

7. The method according to the preceding claim, wherein λ^^^ is comprisedbetween 1.5 and 1.8, and λ^^^ is comprised between 2.2 and 3.5.

8. The method according to any of the preceding claims, wherein said fuel demandQD, respectively said fuel quantity QF, are determined in respect of an upcoming injection event in a respective cylinder.

9. The method according to any of the preceding claims, wherein computing afresh air flow MF, k based on a specific gas constant R^^^^^^,^is derived from the following formula:where ^^^^^^^is the gas pressure in the intake port, ^^^^^^^^^is the volume of a cylinder, ^^^^^^is the volumetric efficiency, ^^^^^^^is the temperature in the intake port, and R^^^^^^,^is the specific gas constant.

10. The method according to any of the preceding claims, wherein computing aspecific gas constant Rmixing, k based on the fast lambda is derived from thefollowing formula:where Rmixing, kis the specific gas constant, R is the ideal gas constant, ^^^^is the molar mass of air, ^^^is the molar mass of hydrogen, and λ^^^^is the fast lambda value.

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