Method for operating a gaseous fuel engine

Abstract

The invention relates to a method for operating an internal combustion engine, the engine comprising a fuel delivery system comprising a plurality of fuel injectors, each fuel injector being configured to deliver fuel to a corresponding cylinder of the engine, means for selectively delivering controlled water amounts in respective cylinders, and further comprising a lambda sensor arranged to generate a signal responsive to oxygen concentration in the exhaust gases. The method comprises the steps of operating combustion events in the cylinders whereby injection events are performed to inject predetermined fuel amounts in respective cylinders; and corresponding water events are performed to introduce predetermined water amounts based on a demand water rate. The method comprising further comprises: determining an injected water content present in the exhaust gas and / or an actual water rate, which are due to water event(s); and controlling operation of the engine based on said injected water content in the exhaust gas and / or the actual water rate.

Description

[0001] P-DELPHI-439 / WO 1

[0002] METHOD FOR OPERATING A GASEOUS FUEL ENGINE

[0003] Technical field

[0004] The present invention generally relates to method for operating a gaseous fuel engine. More specifically to a method for operating a hydrogen internal combustion engine (H2 ICE) with ported water injection.

[0005] Background Art

[0006] In internal combustion engines, precise control of the air-fuel ratio is critical for optimizing combustion efficiency, reducing emissions, and ensuring engine durability. The lambda value (A), defined as the ratio of the actual air-to-fuel ratio to the stoichiometric air-fuel ratio, serves as a key metric for combustion optimization. A lambda value of 1 represents an ideal balance of air and fuel, ensuring complete combustion. In traditional liquid-fuel engines, lambda values typically range from 0.9 (slightly rich) to 1.1 (slightly lean), depending on operating conditions and emission requirements.

[0007] In such engines, the effective lambda value is determined using an oxygen sensor located in the exhaust, which measures residual oxygen in the exhaust gases. This oxygen concentration provides an indirect indication of the combustion efficiency and, by extension, the air-fuel ratio. The lambda value derived from this sensor data is used by the engine control unit (ECU) to regulate fuel injection and maintain optimal combustion.

[0008] In contrast, hydrogen combustion engines, known for their reduced greenhouse gas emissions, typically operate in a lean-burn mode, with lambda values significantly greater than 1 , often in the range of 2.3 to 2.6. This lean operation maximizes thermal efficiency and reduces harmful emissions, particularly nitrogen oxides (NOx). However, conventional oxygen sensors, originally designed for liquid-fuel engines, fail to provide accurate oxygen concentration readings in gaseous-fuel environments like hydrogen combustion. This leads to inaccurate air-fuel ratio estimations, resulting in suboptimal performance, higher emissions, and potential engine wear over time. P-DELPHI-439 / WO 2

[0009] The challenges associated with oxygen measurement are exacerbated in hydrogen internal combustion engines employing ported water injection (PWI). PWI is a critical technique used to enhance engine durability, suppress knocking, and further reduce NOx emissions. However, the introduction of water into the intake port creates complications for conventional oxygen sensors. Specifically, the water injected during the intake phase has been found to cause misleading sensor readings when estimating the oxygen concentration resulting from an injection event.

[0010] Technical problem

[0011] It is an object of the present invention to provide a method for operating a gaseous fuel engine which overcomes the aforementioned drawback, and accurately estimates the O2 concentration resulting from an injection event.

[0012] General Description of the Invention

[0013] This object is achieved by a method for operating a gaseous fuel engine as claimed in claim 1 .

[0014] The present invention relates to a method for operating an internal combustion engine, the engine comprising a fuel delivery system comprising a plurality of fuel injectors, each fuel injector being configured to deliver fuel to a corresponding cylinder of the engine, means for selectively delivering controlled water amounts in respective cylinders, and further comprising a lambda sensor arranged to generate a signal responsive to oxygen concentration in the exhaust gases, wherein the method comprises the steps of operating combustion events in the cylinders whereby

[0015] - injection events are performed to inject predetermined fuel amounts in respective cylinders; and corresponding water events are performed to introduce predetermined water amounts based on a demand water rate.

[0016] The method further comprises: P-DELPHI-439 / WO 3

[0017] - determining an injected water content present in the exhaust gas and / or an actual water rate, which are due to water event(s);

[0018] - controlling operation of the engine based on said injected water content in the exhaust gas and / or the actual water rate.

[0019] The present invention relates to fuel control strategies in internal combustion engines that are equipped for water injection. It has been developed in the context of hydrogen combustion engines, but it is generally applicable to lean-burn engines. Accordingly, the inventive method is applicable, i.a., to gaseous fuel engines, in particular those operating on hydrogen (substantially pure) or containing a given proportion of hydrogen, and to diesel engines. Depending on the fuel, the combustion event will comprise a spark event, to ignite the fuel air mixture.

[0020] The invention is applicable to both port fuel injection configurations and to engines equipped for direct injection. Likewise, the water injection may be done by water injectors that may be arranged for discharging water in the intake port (PWI), or arranged for directly introducing water into the combustion chamber.

[0021] A merit of the invention is indeed to have observed that the presence of water in the exhaust gas due to water injection can lead to issues in engine control and reliability, such as erroneous lambda readings and high humidity putting at risk the lambda sensors and other heated sensors that may be present in the exhaust line. These problems did not arise in the past essentially because the engines were usually not configured for water injection.

[0022] The present invention thus proposes techniques / strategies to determine injected water content present in the exhaust gas and an actual water rate, which can be advantageously used for engine control.

[0023] For example, an oxygen concentration, respectively a lambda value (or lambda number), may be determined based on said lambda sensor, and the operation of the engine may be controlled based on the oxygen concentration or the lambda value.

[0024] A first strategy proposes correcting the lambda sensor reading for the injected water content. This strategy uses a mapping that relates the lambda, referred to as actual lambda value, to the lambda sensor current and the actual water rate. P-DELPHI-439 / WO 4

[0025] The term water rate, as used herein, refers to a ratio of injected water mass over injected fuel mass. As will be discussed below, the water and fuel amounts are not necessarily determined together, and control strategy may thus require determination of an actual water rate, i.e. the water rate that has been effectively applied to the relevant cylinder.

[0026] In embodiments, the demand water rate is defined in function of engine speed and load; and for a current injection event by which a current fuel quantity is injected, the corresponding water event is performed by injecting a predetermined water amount that is determined based on a fuel quantity corresponding to a previous injection event and on said demand water rate. The actual water rate may then be computed as the ratio of the predetermined water amount (mass) and the current fuel quantity (mass).

[0027] Advantageously, an actual lambda value may be determined based on the lambda sensor signal and the actual water rate, in particular from a mapping relating the actual lambda value with the lambda sensor current and the actual water rater. The operation of the engine is then preferably based on this actual lambda value.

[0028] Another strategy is disclosed, whereby the injected water content whithin the exhaust gas is determined in order to be able to determine, correct or update water content dependent parameters.

[0029] In this context, controlling operation of the engine may further be based on a determined combustion water content resulting from fuel combustion, in particular wherein the combustion water content is determined from an air fuel ratio of the combustion event.

[0030] In embodiments, the combustion water content is determined from

[0031] MM_exh / MM_H2 * 1 / (1 + AF) where MM_exh is the molar mass of the exhaust gas, MM_H2 is the molar mass of hydrogen, and AF is the air fuel ratio of the combustion event P-DELPHI-439 / WO 5

[0032] The injected water content may be determined from an air fuel ratio of the combustion event AF.

[0033] In embodiments, the injected water content is determined from

[0034] MM_exh / MM_H20 * WR * 1 / (1 + AF), where MM_exh is the molar mass of the exhaust gas, MM_H20 is the molar mass of water, AF is the air fuel ratio of the combustion event, and WR is the actual water rate.

[0035] The molar mass of the exhaust gas MM_exh may be determined from a demand lambda value.

[0036] The air fuel ratio AF may correspond to a demand lambda value or to a measured lambda value (actual lambda) for the combustion event.

[0037] The water estimation approach according to embodiments of the invention, taking into account the proportion / concentration of water in the exhaust, due in part to combustion and in part to water injection, can be used to determine parameters dependent on this water content.

[0038] In embodiments, a liquid water estimator function determines the amount of liquid water within the exhaust line based on the injected water content in the exhaust gas; and wherein the lambda sensor and / or another sensor in the exhaust line is enabled when the temperature around the respective sensor is higher than a predetermined threshold and the estimated liquid water content is zero or below a predetermined threshold. Enabling the sensor means that the sensor can be activated, and in particular in the context of heated sensors, the sensor heater can be supplied without risk of moisture / water damage.

[0039] Conversely, if the temperature around the respective sensor is lower than the predetermined threshold or the estimated liquid water content is above the predetermined threshold, then the sensor is not enable (is switched off or remains switched off).

[0040] The present invention has been particularly developed in the context of hydrogen powered internal combustion engines, but is generally suitable for gaseous fuel engines and learn bum engines (also with liquid fuel). P-DELPHI-439 / WO 6

[0041] These and other embodiments are also recited in the appended dependent claims.

[0042] According to another aspect, the invention relates to a computer program product comprising instructions which, when the program is executed by a control unit comprising a processor, cause the control unit to carry out the method according to the present disclosure.

[0043] According to yet another aspect, the invention relates an internal combustion engine according to claim 14.

[0044] Brief Description of the Drawings

[0045] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

[0046] Fig. 1 is a flowchart of an engine control strategy according to an embodiment of the invention;

[0047] Fig. 2 is a flowchart of another engine control strategy according to another embodiment of the invention;

[0048] Fig. 3 is a functional diagram representing various engine components and control modules;

[0049] Fig. 4 is a schematic diagram of an exhaust system;

[0050] Fig. 5 is a plot of the lambda error for different values of water rate.

[0051] Description of Preferred Embodiments

[0052] The present invention relates to fuel control strategies in internal combustion engines that equipped for water injection.

[0053] The techniques according to the present invention are generally applicable to lean bum engines, i.e. engines operating mostly with excess air, and particularly to diesel or gaseous fuel engines, specifically hydrogen.

[0054] In the following, embodiments of the invention are described in the context of a hydrogen internal combustion engine (H2-ICE). The structure of an H2-ICE and general fueling concepts will first be summarized P-DELPHI-439 / WO 7

[0055] In an H2-ICE, the fuel delivery system typically comprises a fuel tank, e.g. containing pressurized gaseous hydrogen, a fuel rail and a plurality of fuel injectors for selective fuel injection into the engine. The fuel injectors may be coupled directly to the fuel rail via so-called sockets, or indirectly via tubes. Conventionally, one fuel injector is provided per cylinder, either in direct injection (DI) configuration (fuel is introduced directly into the cylinder / combustion chamber) or in PFI configuration (the injector is arranged to discharge fuel upstream of the intake valve(s)).

[0056] As is known in the art, the engine comprises an engine block with a plurality of cylinders with associated reciprocating pistons mechanically coupled to a crankshaft. At least one fuel injector is provided per cylinder -according to the mentioned configuration PFI or DI- to inject fuel to be combusted in the respective combustion chamber and generate torque. Each cylinder comprises at least one intake valve for admitting fresh air and at least one exhaust valve for discharging combustion gases.

[0057] Introduction of fuel in a given cylinder, i.e. cylinder fueling, is performed during an injection event, by applying a drive signal to the fuel injector to activate an electromechanical actuator, e.g. a solenoid actuator, to cause the injector to open during a predetermined time period. Much simplified, injection control strategies use mappings (known as calibrated flow curves) that relate the fuel quantity to the injector actuation time that is referred to as pulse width, PW. To perform an injection event, a drive pulse is applied during a time period PW to discharge a corresponding fuel amount.

[0058] Conventionally, injection control strategies are programmed in the Engine Control Unit, ECU, that receives various signals indicating the state of the engine from various sensors, and is, inter alia, configured to determine a fuel quantity to be injected and a corresponding timing of injection. More specifically, the ECU is configured to determine a desired fuel quantity to be injected to achieve a given demand (e.g. of torque or engine speed), and subsequently determines the injector control signal (injector actuation PW) corresponding to the desired fuel quantity.

[0059] In general, the method according to the present disclosure can be implemented by hardware and / or software. In practice, it may conveniently be implemented by a control unit comprising a processor and a memory, such as e.g. the Engine Control P-DELPHI-439 / WO 8

[0060] Unit. In such case the memory may contain instructions which, when executed by the ECU / processor, cause the latter to carry out the present method.

[0061] Turning now to Fig.3, engine components are represented in box 10 and comprise:

[0062] - fuel injectors 12 with associated drive unit, configured to selectively inject / discharge predetermined gaseous fuel quantities into the associated cylinders. The drive unit is conventionally designed to apply the control signals to the injectors to discharge a fuel gas quantity based on the respective fuel command for each cylinder combustion cycle;

[0063] - an engine 14 with cylinders defining the combustion chamber;

[0064] - an exhaust system 16 with an exhaust manifold and exhaust pipe, which collects and directs exhaust gases from the engine cylinders out of the vehicle, aiding in efficient engine performance and emission control. As shown on Fig. 4, the exhaust system may comprise a hydrogen oxidation catalyst 16a for burning unburnt hydrogen, a particle filter 16b, and / or an SCR catalyst 16c. These components are widely known in the art and will not be discussed in detail;

[0065] - an oxygen sensor 18 (also referred to as lambda sensor) responsive to the airfuel ratio in exhaust gasses in the exhaust system 16. The oxygen sensor 18 may conventionally be a wide-range oxygen sensor (also wide range - WRAF - or UEGO sensor) where the sensor signal corresponds to the sensor current (known as pumping current). The sensor signal / current correlates (generally monotonically) with the oxygen concentration. As shown on Fig. 4, the oxygen sensor 18 may be positioned in the exhaust system upstream of the hydrogen oxidation catalyst 16a. Reference signs 18’ and 18” indicate typical positions for sensors such as oxygen sensor or NOx sensors, which may be arranged after the particle filter 16b, and / or the SCR catalyst 16c. In embodiments, there can be one, two or three sensors 18 associated with a respective treatment device.

[0066] It may be noted that sensors 18, 18’ and 18” may typically be so-called heated sensors. That is, they include a heating element (e.g. resistor) that is, in use, powered to heat the sensor within a predetermined working temperature range for its nominal operation. Such sensors are sensitive to moisture and water presence, which can cause severe damage. P-DELPHI-439 / WO 9

[0067] Reference sign 20 indicates a fuel adjusting function, which outputs the fuel command Qc to the injectors drive unit 12. The drive unit 12 operates each injector by applying control signals thereto in such a way as to discharge the fuel amount Qc through one or more injection events for a given combustion cycle. In case cylinder fueling is done in one injection event, then Qc is converted into a drive signal having a duration PW using the above-mentioned flow-curves.

[0068] The fuel command Qc is computed in module 20 based on a base fuel amount QB. The base fuel amount QB is advantageously adjusted based on a global correction (here a global correcting factor) CG determined in module 24, and optionally on an ICFC (Individual Cylinder Fuel Control) correcting factor Ci determined in module 22. The fuel determination can e.g. be written as:

[0069] Qc = QB x CG x Ci [Eq.1 ]

[0070] The base fuel amount QB may typically originate from a conventional fuel determination structure, not shown here. Typically, a driver torque function or a speed control function receives demands from various components, for example direct demand from the driver (accelerator pedal) or indirect demand via cruise control, demands from the transmission system, from driving dynamics, from the gearbox or demands related to specific components (e.g. accessory torque). The driver demand function coordinates these various demands and generates a global demand TD. This global demand TD may be limited / capped by a maximum demand Tmax that may depend on various factors. This function outputs a gross indicated demand Togross.

[0071] A desired fuel mass QD (or fuel demand) is then determined to meet the request Togross, typically by calculation based on IMEP (Indicated Mean Effective Pressure), cylinder volume and combustion efficiency coefficients. This is typically based on calibrated mappings.

[0072] In parallel, a lambda set point is determined, referred to as desired lambda AD, in function of the current operating point (engine speed, load... ). As is known, the Lambda value determines the mass ratio of air and fuel in the combustion chamber, in regards to the stoichiometric air-fuel ratio. The lambda setpoint may be determined to optimize combustion efficiency, combustion stability and pollutant emissions (NOX). P-DELPHI-439 / WO 10

[0073] A desired air mass MD (representing the air mass desired in the cylinder) is computed based on the desired fuel mass QD and taking into account the desired lambda AD. The throttle and turbocharger gate positions are adjusted on the basis of the desired air MD.

[0074] It may be noted that since the air loop is typically much slower than the fuel loop, the calculation of the fuel mass to be injected is done on the basis of lambda desired AD as well as, advantageously, on the basis of the air mass MF (or fresh air flow) actually entering the cylinder (hence not on the MD). Air mass MF can be estimated based on the intake manifold pressure and temperature and volumetric efficiency. This logic privileges the respect of the air / fuel ratio and is advantageous during transitory regimes where the inducted air mass can significantly vary from the computed air mass MD.

[0075] Finally, the base fuel amount QB is determined as the fuel quantity to be injected in the next scheduled injection event I combustion (for the upcoming cylinder in firing order). The base fuel amount QB is advantageously determined from the lambda setpoint (desired lambda AD) and from the fresh air flow MF.

[0076] Conventionally, the global correcting factor CG may be a factor determined from an average closed loop lambda control module based on an actual lambda value determined from the oxygen sensor signal. The global correcting factor CG may be determined by a proportional integral (PI) controller function based on the deviation of the actual lambda value from the lambda setpoint. This global correcting factor CG determination is implemented in module 24.

[0077] Computation of the ICFC correcting factor Ci is known in the art and is not the focus of the invention; it will thus not be further discussed herein.

[0078] Box 15 represents a set of water injectors, which may be arranged in port fuel configuration (for water injection in the intake duct) or in direct configuration (for water injection directly into the combustion chamber).

[0079] As is known in the art, in some engine designs it is desirable to introduce water in the combustion chamber to lower the temperature in the combustion chamber, to thereby limit the generation of NOx and knocking. P-DELPHI-439 / WO 11

[0080] The present inventors have found that in lean burn engines, and particularly in an H2-ICE, that implement water injection, the injected water may cause misleading oxygen sensor readings. Indeed, as shown on Fig. 5, which represents the lambda error for different values of water rate, higher water rates lead to larger absolute errors. These lambda errors may then result in inaccurate global correcting factor CG determinations, thereby negatively affecting operation of the engine.

[0081] The present inventors have devised improved control strategies which account for the water injection for operation of the engine.

[0082] In the following, two strategies are present where the added water content is determined and taken into account in the engine operation control.

[0083] < Lambda determination >

[0084] In one embodiment, the invention proposes a strategy to correct the lambda determination to take into account the water injection.

[0085] As explained above (see Fig.3), the engine control strategy typically uses a lambda sensor to monitor the exhaust gases and update / adjust the fuel quantity. The lambda sensor generates a signal that correlates (may be linear or not, or partially linear, and is generally monotonic) with the quantity or concentration of oxygen in the exhaust gases. Such sensor typically responds to molecular oxygen, not to bound oxygen (like H2O). Accordingly, the addition of water in the cylinder, which results in water vapor in the exhaust gases, tends to dilute the free oxygen concentration.

[0086] To correct the lambda sensor reading, the following strategy is proposed, wherein the lambda sensor signal is corrected in function of the injected water content, namely in function of the water rate.

[0087] In reference to Fig.1 , let us now take the example for the combustion event scheduled for the current cylinder N (step S10).

[0088] This typically requires the performance of an injection event - step S16- whereby a fuel quantity Qc is injected into cylinder N - noted QC(N) - which may e.g. be determined based on the strategy shown in Fig.3. P-DELPHI-439 / WO 12

[0089] The strategy also involves injecting water into the cylinder, step S14, whereby a predetermined amount of water, noted Mass.H2O is injected into cylinder N.

[0090] The water content for a combustion event is set by a so-called demand water rate WRD, which is stored in a calibrated map noted WRD_MAP, in function of engine load and speed. The term water rate is defined as mass ratio of water over fuel.

[0091] So, in step S12 the water rate WRD is determined for the current engine speed and load.

[0092] The water mass to be injected may then be calculated as

[0093] Mass.H2O = WRD X QC(N-I) [Eq.2] and this water quantity is injected in the cylinder at step S14.

[0094] It may be noted that in the calculation of Mass.H2O, the fuel amount of the previous injection cycle is used, instead of the current fuel quantity. This will be explained below.

[0095] In step S16, the injection event is performed: fuel mass Qc is discharged into cylinder N.

[0096] Next, step S18, a spark event is performed at a scheduled timing, which will trigger the combustion of the mixture in the combustion chamber.

[0097] At following step S20 the actual water rate is then computed as

[0098] WRact = MassH2O I QC(N) [Eq.3]

[0099] The actual lambda Lact can then be determined from a calibrated mapping Lact-MAP in function of the lambda sensor signal (pumping current) and the water content expressed as WRact.

[0100] Finally, the actual lambda value can be used to control the engine at step S24.

[0101] The water amount is based on the WRD, determined from map WRD_MAP, hence with the current engine speed and load.

[0102] It should be noted that the fuel and water injection events can be performed together, but not necessarily. To perform the water injection event, the mass of water P-DELPHI-439 / WO 13 to be injected is calculated from the water rate WRD by multiplication by the fuel amount.

[0103] However, at the moment where Mass.H2O must be computed for cylinder N, the fuel quantity Qc to be injected in cylinder N is often not available. So, in practice, the water event for cylinder N is typically triggered before the fuel injection event for same cylinder.

[0104] Therefore, in the present strategy the water mass to be injected is computed as the product of the current water rate WRD and the fuel amount corresponding to the previous injection event (typically in the directly preceding cylinder (N-1 ), in firing order). This is written as

[0105] Mass. H2O = WRD x Qc(N-i) [Eq.4]

[0106] Then an actual water rate is computed as

[0107] WRact = Mass.H2O I QC(N) [Eq.5]

[0108] At step 22, the lambda value, noted actual lambda Lact, is then determined from mapping Lact-MAP, which relates the lambda value with the lambda sensor signal (current) and the measured water rate WRact.

[0109] Finally, engine can be controlled based on the actual lambada value Lact, for example in module 24 of Fig.3.

[0110] < Water content determination >

[0111] Fig. 2 shows a flowchart of another strategy implementing the inventive method. This strategy is adapted to compute the water content in order to determine, correct or update a water-dependent parameter, such as e.g. the dew point.

[0112] In an injection event SO, hydrogen fuel is delivered to a cylinder of the engine. Around the same time, water is delivered at the intake port of said cylinder in water event step S1 at a demand water rate WRD. Water may be delivered using conventional PWI techniques, typically using port fuel water injectors. P-DELPHI-439 / WO 14

[0113] As explained before, the water rate represents a ratio of water amount over fuel amount. The strategy may use a calibrated mapping that defines the water rate in function of engine speed and load, as the map WRD_MAP described above.

[0114] Subsequently, a spark event is triggered in step S2, igniting the in-cylinder mixture, thereby consuming hydrogen and oxygen and generating exhaust gases. At step S3, the water content in the exhaust gas is determined. Specifically, the injection water content due to the delivery of water at the intake port, and the combustion water content due to the water produced during the combustion event are determined.

[0115] In the inventive method, the water content [H20_inj] (concentration) in the exhaust gas due to water injection is determined / estimated from the air fuel ratio of the combustion event using the following formula: where MM_exh is the molar mass of the exhaust gas, MM_H20 is the molar mass of water, AF is the air fuel ratio of the combustion event; and WR is the water rate, in particular the actual water rate WRact as explained in the previous section. MM_exh is preferably determined from the combustion equation and taking into account the demand lambda value. The air fuel ratio AF may correspond to a demand lambda value or to an actual lambda value for the combustion event.

[0116] In the inventive method, the combustion water content [H2O_comb] (concentration) may also be determined from an air fuel ratio of the combustion event using the following formula: where MM_exh is the molar mass of the exhaust gas, MM_H2 is the molar mass of hydrogen, and AF is the air fuel ratio of the combustion event. The engine is subsequently controlled at step S4 based on the water content in the exhaust gas and / or the predetermined water rate. In particular, controlling the engine may involve computing different engine parameters from the exhaust water content in the exhaust gas and / or the predetermined water rate, and controlling the engine based on said engine parameters. P-DELPHI-439 / WO 15

[0117] In that context, step S4.1 illustrates the case where a parameter dependent on the water content is determined for a given section of the exhaust line. Specifically, the water content is estimated to determine whether enabling conditions are met for the oxygen sensor 18 and / or other sensors 18’, 18”.

[0118] A function, referred to as liquid water estimator, is configured to estimate the liquid water content within the exhaust line, by estimating the engine out water content based on [H2O_inj] and [H2O_comb] (as explained above), and calculating how much water accumulates due to condensation. The function uses input from a thermal model that estimates the temperature in the exhaust line (e.g. wall temperature), which enables predicting the conditions under which water vapor condenses on the internal surfaces. It also determines how the accumulated water evaporates as the wall temperature rises during engine operation, providing a comprehensive evaluation of water condensation and evaporation dynamics within the exhaust system.

[0119] A comparison is performed at step C1 to determine whether the temperature in the exhaust line section is larger than a predetermined threshold temperature TENL based on the dewpoint (basically corresponding to the dewpoint plus an offset) and whether the liquid water content (estimated with the liquid water estimator) is below a predetermined threshold (and preferably equal to zero).

[0120] At step S5, the lambda sensor 18 is switched on or off based on the result of the comparison. If the temperature in the exhaust line is larger than the threshold TENL and the liquid water content meets the threshold Tiw (i.e. zero or below threshold), the oxygen sensor 18 is enabled. However, if the temperature of the exhaust is smaller than TENL or the liquid water content is above the threshold TLW, the lambda sensor 18, and possibly other heated sensors (18’, 18”) of the exhaust line, is / are switched off (or remain switched off), thereby preventing possible damages to these sensors due to the deposit of droplets.

Claims

P-DELPHI-439 / WO 16Claims1 . A method for operating an internal combustion engine, the engine comprising a fuel delivery system comprising a plurality of fuel injectors, each fuel injector being configured to deliver fuel to a corresponding cylinder of the engine, means for selectively delivering controlled water amounts in respective cylinders, and further comprising a lambda sensor arranged to generate a signal responsive to oxygen concentration in the exhaust gases, wherein the method comprises the steps of operating combustion events in the cylinders whereby injection events are performed to inject predetermined fuel amounts in respective cylinders; corresponding water events are performed to introduce predetermined water amounts based on a demand water rate; the method further comprising:• determining an injected water content present in the exhaust gas and / or an actual water rate, which are due to water event(s);• controlling operation of the engine based on said injected water content in the exhaust gas and / or the actual water rate.

2. The method according to claim 1 , wherein a lambda value is determined based on the lambda sensor signal and corrected based on at least one of the injected water content and the actual water rate; and wherein operation of the engine is based on said corrected lambda value.

3. The method according to claim 1 or 2, whereby said demand water rate is defined in function of engine speed and load; and whereby for a current injection event by which a current fuel quantity is injected, the corresponding water event is performed by injecting a predetermined water amount that is determined based on a fuel quantity corresponding to a previous injection event and on said demand water rate; andP-DELPHI-439 / WO 17 the actual water rate is computed as the ratio of the predetermined water amount and the current fuel quantity.

4. The method according to claim 3, wherein an actual lambda value is determined based on the lambda sensor signal and the actual water rate, in particular from a mapping relating the actual lambda value with the lambda sensor current and the actual water rater; and wherein preferably operation of the engine is based on said actual lambda value.

5. The method according to any of the preceding claims, wherein controlling operation of the engine is further based on a determined combustion water content resulting from fuel combustion, in particular wherein the combustion water content is determined from an air fuel ratio of the combustion event.

6. The method according to the previous claim, whereby the combustion water content is determined from MM_exh / MM_H2 * 1 / (1 + AF), where MM_exh is the molar mass of the exhaust gas, MM_H2 is the molar mass of hydrogen, and AF is the air fuel ratio of the combustion event.

7. The method according to any of the preceding claims, whereby the injected water content is determined from an air fuel ratio of the combustion event AF.

8. The method according to any of the preceding claims, whereby the injected water content is determined from MM_exh / MM_H20 * V / / ? * 1 / (1 + AF , where MM_exA is the molar mass of the exhaust gas, MM_H20 is the molar mass of water, AF is the air fuel ratio of the combustion event, and WR is the actual water rate.

9. The method according to claim 6 or 8, whereby the molar mass of the exhaust gas MM_exh is determined from a demand lambda value.

10. The method according to any of claims 6 to 9, whereby the air fuel ratio AF corresponds to a demand lambda value or to a measured lambda value for the combustion event.P-DELPHI-439 / WO 1811 . The method according to any of the preceding claims, whereby a liquid water estimator function determines the amount of liquid water within the exhaust line based on the injected water content in the exhaust gas; and wherein the lambda sensor and / or another sensor in the exhaust line is enabled when the temperature around the respective sensor is higher than a predetermined threshold and the estimated liquid water content is zero or below a predetermined threshold.

12. The method according to any of the preceding claims, wherein the engine is configured to operate on gaseous fuel, and in particular on hydrogen.

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

14. An internal combustion engine comprising a fuel delivery system including a plurality of fuel injectors, each fuel injector being configured to deliver fuel to a corresponding cylinder of the engine, means for selectively delivering controlled water amounts in respective cylinders, a lambda sensor arranged to generate a signal responsive to oxygen concentration in the exhaust gases; and a control unit configured to implement a method according to any one of the preceding claims.

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