Method for controlling operation of hydrogen combustion engine system

Abstract

The present invention relates to a method for controlling operation of a hydrogen combustion engine system (10) comprising a hydrogen combustion engine (15, 15 ') and an exhaust aftertreatment system (EATS) (20) configured to reduce emissions of engine exhaust. The EATS includes a selective catalytic reduction (SCR) catalyst (40) and an ammonia escape catalyst (ASC) (50) disposed downstream of the SCR catalyst (40). The method comprises: determining (S10) a temperature of the SCR catalyst (40); determining (S20) a temperature of the ASC (50); in response to determining that the temperature of the SCR catalyst (40) is below a predetermined SCR temperature threshold and the temperature of the ASC (50) is below a predetermined ASC temperature threshold, operating (S30) the hydrogen combustion engine (15, 15 ') in an H2 exhaust excess mode defined by an amount of unburned H2 in the engine exhaust being at least 0.2 mol%, 15 ') and using (S40) the unburned H2 in the engine exhaust as a reducing agent for NOx conversion in the ASC (50).

Description

Technical Field

[0001] The present invention relates to a method for controlling the operation of a hydrogen combustion engine system of a vehicle, the hydrogen combustion engine system comprising a hydrogen combustion engine and an exhaust gas aftertreatment system EATS, the EATS being configured to reduce emissions of the engine exhaust. The present invention also relates to a hydrogen combustion engine system of a vehicle, a vehicle comprising such an engine system, and a computer program and a computer readable medium carrying the computer program.

[0002] The present invention is applicable to vehicles, in particular heavy vehicles, such as trucks, for example. However, although the present invention will be described primarily with respect to trucks, the hydrogen combustion engine system is also applicable to other types of vehicles, such as buses, passenger cars, industrial construction machines, wheel loaders, etc. Background Art

[0003] The demand for internal combustion engines has been growing steadily over the years and engines are constantly being developed to meet the various demands of the market. Reduction of exhaust gases, increased engine efficiency (i.e. reduced fuel consumption) and reduced noise levels of the engine are some of the criteria that are important aspects when selecting an engine for a vehicle. Furthermore, in the field of trucks there are applicable legal directives which, for example, have determined the maximum amount of exhaust gas pollution permitted. Furthermore, reducing the overall cost of the vehicle is important and, since the engine accounts for a relatively large part of the total cost, a reduction in the cost of the engine components is also desired.

[0004] In order to meet the described needs, various engine concepts have been developed over the years, in which conventional engine cylinders have been combined with, for example, a pre-compression stage and / or an expansion stage. Other engine concepts relate to the fuel used and burned in the combustion engine. For example, gasoline and diesel can be replaced with more environmentally friendly fuels, for example biofuels, such as ethanol. In some cases, when the fuel is changed, the combustion engine needs to be adapted to operate optimally with the new fuel. Recently, clean combustion engines (such as, for example, near-zero emission combustion engines) have become increasingly popular. For example, by changing the fuel to hydrogen or a hydrogen-based fuel, the combustion of hydrogen with oxygen only produces water as a by-product (in theory).

[0005] However, even if the engine is adapted for operation with the new fuel, NOx is typically formed during the high temperature combustion process, thus requiring cleaning of the engine exhaust. Therefore, there is a need in the industry for an engine system that includes an adapted exhaust gas aftertreatment system EATS to treat emissions from a hydrogen combustion engine. This is particularly important in situations where the EATS is in a cold state (e.g., during a cold start of a combustion engine). Summary of the invention

[0006] It is an object of the present invention to at least partially alleviate the disadvantages discussed above with respect to known exhaust gas aftertreatment systems and to provide an improved system.

[0007] According to a first aspect of the present invention, there is provided a method for controlling the operation of a hydrogen combustion engine system of a vehicle, the hydrogen combustion engine system comprising a hydrogen combustion engine and an exhaust gas aftertreatment system EATS configured to reduce emissions of engine exhaust, the EATS comprising a selective catalytic reduction SCR catalyst and an ammonia slip catalyst ASC arranged downstream of the SCR catalyst. The method comprises:

[0008] - determining the temperature of the SCR catalyst;

[0009] - determining the temperature of the ASC;

[0010] In response to determining that the temperature of the SCR catalyst is below a predetermined SCR temperature threshold and the temperature of the ASC is below a predetermined ASC temperature threshold, operating the hydrogen combustion engine in an H2 exhaust excess mode defined by an amount of unburned H2 in the engine exhaust being at least 0.2 mol%, and using the unburned H2 in the engine exhaust as a reductant for NOx conversion in the ASC.

[0011] Thus, NOx emissions in the engine exhaust can be reduced. That is, even if the temperature of the SCR catalyst is lower than a predetermined SCR temperature threshold, meaning that the NOx conversion capacity of the SCR catalyst is low, the ASC can still provide additional NOx conversion by using unburned H2 as a reductant in the ASC. In other words, if the temperature in the SCR catalyst is low (i.e., lower than a predetermined SCR temperature threshold, typically lower than the normal operating temperature of the SCR catalyst), the ASC can be used together with the unburned H2 in the engine exhaust to reduce the NOx emissions of the hydrogen combustion engine. That is, since the SCR catalyst is not operating at full load, the ASC can be used together with the unburned H2 in the engine exhaust to promote the reduction of NOx. Without being bound by any theory, the NO in the engine exhaust is catalytically converted into N2 (and N2O) in the ASC, where the unburned H2 reacts with excess oxygen, thereby promoting the NOx conversion in the ASC. In addition, by providing NOx conversion capacity in both the SCR catalyst and the ASC, the reduction of NOx emissions can be achieved in an effective manner. Therefore, during the operation of the EATS, NOx emissions in the engine exhaust are reduced.

[0012] It should be understood that the term "using" unburned H2 in the engine exhaust as a reductant for NOx conversion in the ASC means using unburned H2 as a reductant in NOx conversion in the ASC to convert NOx. Therefore, the method generally includes the step of converting NOx in the engine exhaust in the ASC, wherein the unburned H2 acts as a reductant for NOx conversion.

[0013] According to at least one exemplary embodiment, the predetermined SCR temperature threshold is defined as being lower than the normal operating temperature of the SCR catalyst, or even lower than the operating temperature of the SCR catalyst. Since the temperature of the SCR catalyst is lower than its normal operating temperature, or lower than the operating temperature of the SCR catalyst, the SCR catalyst is not operating at full load. For example, the predetermined SCR temperature threshold is set to a value between 200°C and 250°C, such as 200°C.

[0014] According to at least one exemplary embodiment, the predetermined ASC temperature threshold is set to a value between 200° C. and 250° C., for example 250° C. Below this temperature, H2 can act as a reductant in NOx conversion instead of burning at excessively high temperatures. However, it should be noted that at least a portion of the H2 (a minority) may still be burned in the ASC.

[0015] According to at least one exemplary embodiment, the H2 exhaust excess mode is included in the combustion mode of the hydrogen combustion engine. The combustion mode is a mode in which the engine cylinder of the hydrogen combustion engine performs at least one combustion during the operating cycle. For example, in the four-stroke cycle of the hydrogen combustion engine, four different piston strokes can be defined in the engine cylinder to complete an operating cycle: intake, compression, power (combustion) and exhaust. In such an example, the piston completes two complete strokes in the engine cylinder to complete an operating cycle. The hydrogen combustion engine may include one or more engine cylinders configured to operate in the same manner. For example, each of the engine cylinders may be configured to operate according to the aforementioned four-stroke cycle.

[0016] According to at least one exemplary embodiment, the H2 exhaust excess mode includes operating the hydrogen combustion engine by injecting H2 into engine cylinders during the exhaust stroke.

[0017] Thus, H2 is injected into the engine cylinder after combustion (compared to the same operating cycle), and can therefore be delivered to the engine exhaust without combustion, at least up to the amount of unburned H2 as defined above. For example, H2 is injected into the engine cylinder after the exhaust valve opens, such as, for example, at least 10 crank angle degrees after the exhaust valve opens. According to at least one exemplary embodiment, H2 is injected into the engine cylinder between 90 crank angle degrees before TDC and TDC, or between 130 crank angle degrees before TDC and 60 crank angle degrees. The exhaust stroke is typically the exhaust stroke in a four-stroke cycle in the combustion mode of the above-mentioned hydrogen combustion engine.

[0018] According to at least one exemplary embodiment, the H2 exhaust excess mode is defined by an amount of unburned H2 in the engine exhaust being at least 0.5 mol%.

[0019] Thus, even more NOx can be converted in ASC. According to at least one exemplary embodiment, the amount of unburned H2 in H2 exhaust excess mode is changed from a minimum level of 0.2 mol% to a minimum level of 0.5 mol%. This can be performed, for example, in response to an increase in torque demand or in response to the amount of NOx in the engine exhaust exceeding a NOx threshold value (e.g., 1000 ppm). The amount of NOx can be defined in terms of molar fractions, or based on weight, such as weight-to-volume (W / V) concentration. In addition, the amount of NOx can also be determined per unit driving distance, or per unit operating time or per unit energy weight (g / kWh). H2 can be injected during the exhaust stroke of the engine cylinder so that the amount of unburned H2 in the engine exhaust reaches at least 0.5 mol%.

[0020] According to at least one exemplary embodiment, the H2 exhaust excess mode is defined by the amount of unburned H2 being at most 4 mol%. Thus, the H2 exhaust excess mode may be defined by the amount of unburned H2 being between 0.2 mol% or 0.5 mol% and 4 mol%.

[0021] It should be noted that the expression “the amount of unburned H2 is at least X mol%” refers to the mole fraction of H2 in the exhaust gas (i.e., the mole percentage of H2 in the exhaust gas), and can be simply referred to as “the amount of H2 is at least X mol%”.

[0022] According to at least one exemplary embodiment, the H2 exhaust excess mode includes operating a hydrogen combustion engine by injecting H2 into engine cylinders during a compression stroke to achieve a target lambda.

[0023] Thereby, combustion of H2 in the engine cylinder is achieved.

[0024] Therefore, and according to at least one exemplary embodiment, H2 can be injected into the engine cylinder at least twice during one operating cycle (e.g., the four-stroke cycle described previously), namely a main H2 injection during the compression stroke and a secondary H2 injection during the exhaust stroke. In a normal operating mode of a hydrogen combustion engine (such as a default combustion mode), only the main H2 injection is used because an excess of H2 is not required in the engine exhaust. In the normal combustion mode, the amount of H2 in the engine exhaust is typically between 0.02 mol% and 0.15 mol%. Therefore, the H2 exhaust excess mode can be distinguished from the default combustion mode by the secondary H2 injection, and can therefore be referred to as an H2 secondary injection mode.

[0025] Target λ refers to a target air-fuel equivalence ratio and can be determined by the ratio of the actual air-fuel ratio (mass ratio of air to fuel) of a given mixture to the stoichiometric air-fuel ratio. According to at least one exemplary embodiment, target λ is higher than 1, such as, for example, between 1.5 and 3. Thus, NOx in the engine exhaust can be kept low.

[0026] According to at least one exemplary embodiment, the hydrogen combustion engine includes a fuel injector for each engine cylinder for injecting H2 into the engine cylinder. According to at least one exemplary embodiment, the fuel injector is used for both the main H2 injection and the secondary H2 injection as described above. In other words, the method may include performing a main H2 injection (to achieve a target λ) into the engine cylinder by the fuel injector during the compression stroke, and performing a secondary H2 injection into the engine cylinder by the fuel injector during the exhaust stroke. As an alternative embodiment, the fuel injector is a main fuel injector configured to perform a main H2 injection, wherein the hydrogen combustion engine also includes a secondary fuel injector configured to perform a secondary H2 injection. In other words, the method may include performing a main H2 injection (to achieve a target λ) into the engine cylinder by the main fuel injector during the compression stroke, and performing a secondary H2 injection into the engine cylinder by the secondary fuel injector during the exhaust stroke. For example, the secondary fuel injector may be arranged to inject H2 closer to the exhaust valve in the engine cylinder than the main fuel injector.

[0027] As a further alternative, a secondary fuel injector may be arranged downstream of the exhaust valve of at least one of the engine cylinders in a hydrogen combustion engine. Thus, secondary H2 injection may be performed outside the engine cylinder (and therefore less dependent on the operating cycle of the engine cylinder) and directly into the engine exhaust to achieve an amount of unburned H2 in the engine exhaust of at least 0.2 mol%. The secondary fuel injector may, for example, be arranged somewhere between the exhaust valve downstream of at least one of the engine cylinders and the inlet upstream of the EATS, such as at the engine outlet or at the exhaust passage downstream of the exhaust valve. Thus, secondary H2 injection may be achieved by injecting H2 into the engine exhaust somewhere between the exhaust valve downstream of at least one of the engine cylinders and the inlet upstream of the EATS.

[0028] According to at least one exemplary embodiment, the H2 exhaust excess mode includes operating the hydrogen combustion engine by injecting H2 downstream of an exhaust valve of at least one of the engine cylinders in the hydrogen combustion engine.

[0029] Thus, as described above, the injection of H2 can be performed external to the engine cylinder and therefore less dependent on the operating cycle of the engine cylinder and directly into the engine exhaust so as to achieve an amount of unburned H2 in the engine exhaust of at least 0.2 mol%. Furthermore, by injecting H2 downstream of the exhaust valve of at least one of the engine cylinders in a hydrogen combustion engine, the H2 is less likely to be combusted by hot surfaces inside the hydrogen combustion engine.

[0030] According to at least one exemplary embodiment, a hydrogen combustion engine system includes an H2 storage tank containing H2 fuel (typically pressurized H2). For example, both the main fuel injector and the secondary fuel injector are configured to supply H2 from the H2 storage tank. That is, both the main fuel injector and the secondary fuel injector are configured to supply H2 fuel from the same H2 storage tank. For example, the method may include performing a main H2 injection into an engine cylinder (to achieve a target λ) by a main fuel injector using H2 fuel from an H2 storage tank during a compression stroke, and performing a secondary H2 injection by a secondary fuel injector using H2 fuel from (the same) H2 storage tank so as to achieve an amount of unburned H2 in the engine exhaust of at least 0.2 mol%. Therefore, the unburned H2 in the engine exhaust originates from the H2 storage tank and is not burned in the hydrogen combustion engine.

[0031] According to at least one exemplary embodiment, the H2 exhaust excess mode includes operating the hydrogen combustion engine by injecting water into the engine cylinders during the intake stroke.

[0032] This is particularly advantageous when the target lambda value is relatively low, for example lambda between 1.5 and 2, in order to reduce NOx in the engine exhaust.

[0033] According to at least one exemplary embodiment, in response to receiving an instruction to reduce the target lambda to a predefined level (e.g., below 1.8), H2 is injected into the engine cylinders at a target lambda above a predetermined level during the exhaust stroke of at least five operating cycles of the engine cylinders (e.g., four stroke cycles as described above) prior to reducing lambda to the predefined level. Thus, unburned H2 in the engine exhaust can be provided to the ASC prior to reaching operation of the hydrogen combustion engine at the predefined target lambda level. In other words, EATS is prepared in advance prior to reaching the predefined target lambda level.

[0034] According to at least one exemplary embodiment, the method further comprises:

[0035] - delivering unburned H2 from an engine outlet of a hydrogen combustion engine to the ASC such that the mole fraction of H2 in the exhaust gas reaching the ASC is at least 80% of the mole fraction of H2 at the engine outlet.

[0036] Thus, a majority of the unburned H2 from the engine outlet may be received by the ASC. For example, at least a majority of the unburned H2 from the engine outlet is received by the ASC. Unburned H2 is typically delivered from the engine outlet to the ASC via exhaust gas in the EATS. By making the EATS temperature from the engine outlet to the ASC below a predetermined temperature (e.g., below 250° C.), combustion of a majority of the unburned H2 may be prevented.

[0037] It should be noted that the engine outlet and the exhaust inlet (or EATS inlet) constitute the interface between the hydrogen combustion engine and the EATS. Typically, the engine exhaust at the engine outlet continues to move as the exhaust in the EATS downstream of the exhaust inlet. According to at least one exemplary embodiment, the exhaust inlet defines an interface between the hydrogen combustion engine and the EATS. Therefore, the exhaust inlet is the most upstream part of the EATS, and is therefore the end point of the EATS. Accordingly, the engine outlet is the most downstream part of the hydrogen combustion engine. The EATS typically includes a fluid path for the exhaust gas received from the engine outlet of the hydrogen combustion engine, and the fluid path extends from the exhaust inlet to the outlet of the EATS.

[0038] According to at least one exemplary embodiment, the ASC is a monolithic catalyst comprising an oxidation catalyst and a metal zeolite coating, and the method comprises:

[0039] - Converting ammonia into NOx in the ASC using an oxidation catalyst; and

[0040] - Conversion of NOx to N2 in ASC using metal zeolites.

[0041] As previously described, unburned H2 in the exhaust gas reaching the ASC is used as a reductant for NOx conversion. The oxidation catalyst may be, for example, palladium, platinum or rhodium, and the metal zeolite may be, for example, a copper zeolite or an iron zeolite. The metal zeolite may, for example, be arranged on top of the oxidation catalyst. The conversion of NOx to N2 using a metal zeolite is typically promoted by the presence of ammonia in the exhaust gas. The oxidation catalyst and / or the metal zeolite may be applied to the monolith by a corresponding powder coating. According to at least one exemplary embodiment, the monolith may be a flow-through monolith or a wall-flow monolith. The monolith of the ASC may be referred to as a monolithic substrate, and may, for example, be a ceramic monolith.

[0042] Therefore, the ASC is configured to reduce emissions by ammonia oxidation and NOx conversion. In use, ammonia enters the ASC with the exhaust gas and is at least partially oxidized to NO (or NOx). Therefore, the oxidized NO and the unoxidized ammonia inside the ASC are converted into N2 by a catalytic conversion reaction using a metal zeolite (i.e., following a conventional SCR reaction scheme).

[0043] According to at least one exemplary embodiment, the method is performed during a cold start of a hydrogen combustion engine.

[0044] Therefore, in response to the cold start of the hydrogen combustion engine, the method of the first aspect of the present invention is performed. For example, during the initial operation of the vehicle, or at least during the initial operation of the hydrogen combustion engine, for example, until the time point at which the (normal) operating temperature of the hydrogen combustion engine system has been reached, or the time point at which the normal operating temperature of the EATS has been reached, the emissions from the EATS, such as the emissions per unit driving distance, or the emissions per unit operating time or the emissions per unit energy (g / kWh) are generally higher than when the operating temperature of the EATS has been reached. Such emissions are referred to as cold start emissions, and they generally include undesirable amounts of undesirable compounds (such as NOx) in the exhaust gas from the EATS due to the cold start of the hydrogen combustion engine system. The initial operation of the vehicle or the initial operation of the hydrogen combustion engine can, for example, span the near future of the start of the hydrogen combustion engine, for example, spanning a time span of, for example, 0 seconds or 1 second to 30 minutes, or 0 seconds or 1 second to 20 minutes, or 0 seconds or 1 second to 15 minutes, or 0 seconds or 1 second to 10 minutes. Therefore, the cold start dynamic emission of the hydrogen combustion engine system is the emission (such as NOx) of the exhaust gas that goes out from EATS during such initial operation of the hydrogen combustion engine. However, there are other vehicle operating conditions that result in the operating temperature (or normal operating temperature) of the hydrogen combustion engine system or at least the operating temperature of the EATS or SCR catalyst not being reached. Such vehicle operating conditions may also increase emissions, or at least result in unnecessary high emissions going out of EATS. For example, when the normal operating temperature of the SCR catalyst has been reached, it can be considered that the normal operating temperature of EATS is met. According to at least one exemplary embodiment, the normal operating temperature of EATS is defined by the temperature of the SCR catalyst being higher than a predetermined SCR temperature threshold. According to at least one exemplary embodiment, the normal operating temperature of EATS is defined by the temperature of the SCR catalyst being higher than a predetermined SCR temperature threshold and the temperature of the ASC being higher than a predetermined ASC temperature threshold. As previously described, each of the predetermined SCR temperature threshold and the predetermined ASC temperature threshold can be a value between 200°C and 250°C.

[0045] According to a second aspect of the present invention, a hydrogen combustion engine system is provided. The hydrogen combustion engine system comprises a hydrogen combustion engine and an exhaust gas aftertreatment system EATS configured to reduce the emission of engine exhaust, the EATS comprising a selective catalytic reduction SCR catalyst and an ammonia slip catalyst ASC arranged downstream of the SCR catalyst, wherein the hydrogen combustion engine system comprises a control unit, the control unit being configured as follows:

[0046] - determining the temperature of the SCR catalyst;

[0047] - determining the temperature of the ASC;

[0048] - In response to determining that the temperature of the SCR catalyst is below a predetermined SCR temperature threshold and the temperature of the ASC is below a predetermined ASC temperature threshold, commanding the hydrogen combustion engine to operate in an H2 exhaust excess mode defined by an amount of unburned H2 in the engine exhaust being at least 0.2 mol% to use the unburned H2 in the engine exhaust as a reductant for NOx conversion in the ASC.

[0049] The effects and features of the second aspect of the invention are largely similar to those described above in conjunction with the first aspect of the invention. The embodiments mentioned with respect to the first aspect of the invention are largely compatible with the second aspect of the invention, some of which are illustrated below.

[0050] According to at least one exemplary embodiment, the control unit is configured to cause the hydrogen combustion engine system to perform the steps of the method of the first aspect of the invention.

[0051] According to at least one exemplary embodiment, the hydrogen combustion engine is configured to operate via an Otto cycle.

[0052] According to at least one exemplary embodiment, a hydrogen combustion engine is an internal combustion engine configured to burn hydrogen in one or more engine cylinders of the engine. The engine cylinders mentioned throughout the application text may be referred to as combustion cylinders. It should be understood that when the configuration or operation of the engine cylinders is mentioned in the application text, the configuration or operation refers to at least one or all of the engine cylinders of the hydrogen combustion engine.

[0053] For example, a hydrogen combustion engine is configured to operate with a four-stroke combustion in the engine cylinders. Typically, a hydrogen combustion engine is configured to operate with a lambda between 1.5 and 3.

[0054] For example, a hydrogen combustion engine system includes a delivery conduit defining a fluid path for delivering exhaust gas from an exhaust inlet of an EATS to an EATS outlet. Therefore, unburned H2 from the engine exhaust can be delivered to the ASC and used there as a reducing agent for NOx conversion. According to at least one exemplary embodiment, the EATS does not have any oxidation catalyst arranged downstream of the exhaust inlet and upstream of the ASC. Therefore, typically, the delivery conduit defining the fluid path does not contain any oxidation catalyst.

[0055] This way, unburned H2 from the engine exhaust can more easily reach the ASC without being burned.

[0056] According to a third aspect of the present invention, there is provided a vehicle comprising a hydrogen combustion engine system according to the second aspect of the present invention.

[0057] According to a fourth aspect of the invention there is provided a computer program comprising program code means comprising instructions which, when the program is run on a computer, cause the hydrogen combustion engine system of the second aspect of the invention to perform the steps of the method of the first aspect of the invention.

[0058] According to a fifth aspect of the present invention, there is provided a computer-readable medium carrying a computer program including program code means, wherein the program code means includes instructions for causing the hydrogen combustion engine system of the second aspect of the present invention to execute the steps of the method of the first aspect of the present invention when the computer program is run on a computer.

[0059] The effects and features of the third to fifth aspects of the present invention are largely similar to those described above in conjunction with the first and second aspects of the present invention. The embodiments mentioned with respect to the first and second aspects of the present invention are largely compatible with the third to fifth aspects of the present invention.

[0060] It should be understood that the SCR catalyst and the ASC form different abatement modules in the EATS. For example, each abatement module may include a container or tank that houses abatement components such as various catalysts and substrates.

[0061] According to at least one exemplary embodiment applicable to any one of the first to fifth aspects of the present invention, the EATS further comprises at least one particulate filter. The particulate filter may be arranged between the SCR catalyst and the ASC, or downstream of the ASC. According to at least one exemplary embodiment, the particulate filter is integrated with the SCR catalyst (i.e., contained in the same container or tank) and arranged upstream of the SCR catalyst.

[0062] According to at least one exemplary embodiment applicable to any one of the first to fifth aspects of the present invention, the EATS further comprises:

[0063] - an injector configured to inject a reducing agent for supplying ammonia to the SCR catalyst, wherein the injector is arranged upstream of the SCR catalyst and downstream of the exhaust gas inlet.

[0064] Therefore, during the operation of EATS, the reducing agent is injected upstream of the SCR catalyst. Therefore, the injected reducing agent is delivered to the SCR catalyst by the exhaust gas flow of EATS. The injector can be arranged at any position between the exhaust gas inlet and the SCR catalyst. The reducing agent used by the injector can be at least one of the following: anhydrous ammonia, aqueous ammonia, urea, aqueous urea and diesel exhaust treatment fluid. According to at least one exemplary embodiment, the reducing agent is urea or liquid urea. As previously mentioned, the ASC is configured to process the excess ammonia that is not utilized in the SCR catalyst.

[0065] According to at least one exemplary embodiment, applicable to any one of the first to fifth aspects of the present invention, the SCR catalyst is a metal zeolite SCR catalyst, such as copper zeolite or iron zeolite. As an alternative, the SCR catalyst may include a vanadium oxide-based coating. Therefore, the SCR catalyst is configured to convert nitrogen oxides NOx into diatomic nitrogen N and water with the help of an SCR catalyst coating (i.e., a metal zeolite or a vanadium oxide-based coating). During the operation of EATS, the injected reductant (or the resulting ammonia) reacts on the SCR catalyst coating. The SCR catalyst coating can be applied to the carrier of the SCR catalyst (i.e., applied to the carrier by an aqueous slurry) through a basecoat, dried and calcined. Thus, it is beneficial to apply the SCR catalyst coating on the carrier. As an alternative, the SCR catalyst coating can be applied by a powder coating. The carrier of the SCR catalyst can be a monolith, such as a ceramic monolith.

[0066] According to at least one exemplary embodiment applicable to any one of the first to fifth aspects of the present invention, the hydrogen combustion engine system also includes various sensors at various positions in the EATS known to those skilled in the art. For example, the NOx sensor can be located at the exhaust inlet and / or outlet of the EATS, or near the exhaust inlet and / or outlet of the EATS. In addition, the temperature sensor and / or the pressure sensor can be located before and / or after any one of the emission reduction modules (such as SCR catalysts and ASC). In addition, the hydrogen combustion engine system can include one or more sensors for measuring the amount of H2 in the hydrogen combustion engine system. For example, an H2 sensor can be arranged at the engine outlet for measuring the amount of H2 in the engine exhaust. In addition or alternatively, an H2 sensor can be arranged upstream of the ASC for measuring the amount of H2 in the exhaust gas entering the ASC. The hydrogen combustion engine system can also include a controller, which is configured to control, for example, the introduction of a reducing agent into the fluid path of the exhaust gas.

[0067] Additional advantages and features of the present disclosure are disclosed and discussed in the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Embodiments of the invention cited as examples will be described in more detail below with reference to the accompanying drawings. In the drawings:

[0069] Figure 1 is a schematic side view of a vehicle including a hydrogen combustion engine system and an exhaust aftertreatment system of the hydrogen combustion engine system according to an exemplary embodiment of the present invention,

[0070] Figure 2is a schematic diagram of a hydrogen combustion engine system of a vehicle and an exhaust gas aftertreatment system of the hydrogen combustion engine system according to an exemplary embodiment of the present invention;

[0071] Figure 3A is a schematic diagram of at least a portion of a hydrogen combustion engine according to an exemplary embodiment of the present invention;

[0072] Figure 3B is a schematic diagram of at least a portion of a hydrogen combustion engine according to yet another exemplary embodiment of the present invention; and

[0073] Figure 4 is a flow chart illustrating the steps of a method according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0074] refer to Figure 1 , a vehicle 1 is shown, here embodied as a heavy truck 1, for which a hydrogen combustion engine system 10 of the type disclosed in the present disclosure is advantageous. However, the hydrogen combustion engine system 10 may also be implemented in other types of vehicles, such as in buses, light trucks, passenger cars, marine applications, etc. Figure 1 The hydrogen combustion engine system 10 of the vehicle 1 includes a hydrogen combustion engine 15 and an exhaust aftertreatment system EATS 20, which is configured to reduce the emission of engine exhaust from the hydrogen combustion engine 15. However, according to at least one exemplary embodiment, the vehicle can be a hybrid vehicle that also includes a motor or a fuel cell 16 (optional). The hydrogen combustion engine 15 is powered by hydrogen fuel (also called H2 fuel), which is usually contained in a fuel tank (also called H2 storage tank), and any motor is usually powered by electricity supplied from at least one energy storage or conversion device (such as a battery (not shown) or a fuel cell), and any fuel cell is usually powered by hydrogen fuel (such as hydrogen fuel from the fuel tank). The hydrogen combustion engine 15 is preferably configured to operate by an Otto cycle or another four-stroke cycle. The operation of the hydrogen combustion engine system 10 can be controlled, for example, by a control unit 18.

[0075] exist Figure 1 In the embodiment, the EATS 20 includes an exhaust inlet (such as Figure 2 The emission reduction modules 30 are configured to reduce the emission of the engine exhaust. The plurality of emission reduction modules 30 include at least a first emission reduction module 40 (here a selective catalytic reduction SCR catalyst 40) and a second emission reduction module 50 (here an ammonia slip catalyst ASC). Figure 1In the embodiment, the SCR catalyst 40 is arranged upstream of the ASC 50. The SCR catalyst 40 is configured to convert nitrogen oxides (also referred to as NOx) into diatomic nitrogen, N2 and water with the help of the SCR catalyst coating, and the ASC 50 is configured to reduce emissions through ammonia oxidation and NOx conversion, as will be referred to in Figure 2 EATS 20 typically includes additional components (such as, for example, piping) and may include additional abatement components ( Figure 1 not shown).

[0076] exist Figure 2 In more detail, Figure 1 The hydrogen combustion engine system 10 includes a hydrogen combustion engine 15 and an exhaust aftertreatment system EATS 20, wherein the EATS is configured to reduce the emissions of the engine exhaust, as shown in FIG. Figure 1 Brief Description. The engine exhaust gas entering the EATS is hereinafter referred to as exhaust gas.

[0077] The EATS 20 includes an exhaust inlet 22 for receiving engine exhaust from an engine outlet 17 of a hydrogen combustion engine 15; an EATS outlet 24 for discharging at least partially cleaned exhaust from the EATS 20; and a fluid path 26 for conveying exhaust from the exhaust inlet 22 to the EATS outlet 24. The EATS outlet 24 may, for example, be connected to or include an exhaust tail pipe of the vehicle 1. The EATS 20 also includes a plurality of emission reduction modules 30 arranged downstream of the exhaust inlet 22. The emission reduction modules 30 are configured to reduce emissions of the engine exhaust along the fluid path 26. Figure 2 In the embodiment of the present invention, the plurality of emission reduction modules 30 are composed of the aforementioned first emission reduction module as the selective catalytic reduction SCR catalyst 40 and the aforementioned second reduction module 50 as the ammonia slip catalyst ASC. The ASC 50 is arranged downstream of the SCR catalyst 40. In addition, Figure 2 In the embodiment of FIG. 5 , an optional third emission reduction module 60 , here a particulate filter, is arranged between the SCR catalyst 40 and the ASC 50 .

[0078] The SCR catalyst 40 preferably includes an SCR catalyst coating, which is a metal zeolite SCR catalyst, such as copper zeolite or iron zeolite. As an alternative, the SCR catalyst coating is a vanadium oxide-based coating. The SCR catalyst 40 is designed to convert nitrogen oxides NOx into diatomic nitrogen N and water with the help of the SCR catalyst coating. The SCR catalyst 40 generally includes a carrier, such as a monolith, on which the SCR catalyst coating is arranged.

[0079] The ASC 50 preferably includes an oxidation catalyst and a metal zeolite. That is, the ASC 50 preferably includes a first ASC coating as an oxidation catalyst and includes a second ASC coating as a metal zeolite (i.e., having an SCR catalyst function). The ASC 50 is designed to convert ammonia into NOx with the help of the oxidation catalyst and to convert NOx into N2 with the help of the metal zeolite. The ASC 50 generally includes a carrier, such as a monolith, on which the first ASC coating and the second ASC coating are arranged.

[0080] The particulate filter 60 is configured to remove particulates, such as particulate emissions or soot, from the exhaust. Figure 2 In the exemplary embodiment, the particulate filter 60 is disposed between the SCR catalyst 40 and the ASC 50, but according to an alternative exemplary embodiment, the particulate filter may be disposed upstream of the SCR catalyst 40. In such an embodiment, particulate emissions (such as, for example, sulfur-containing emissions) are filtered from the exhaust gas upstream of the SCR catalyst 40, thereby reducing degradation of the SCR catalyst coating disposed downstream.

[0081] In addition, in order to provide ammonia to the SCR catalyst 40 and the ASC 50, the EATS 20 includes an injector 34, which is configured to inject a reductant into the fluid path 26 upstream of the SCR catalyst 40 and downstream of the exhaust gas inlet 22. The reductant can be, for example, urea. Therefore, the injector 34 can be configured to inject urea. During the operation of the EATS 20, the injected reductant (or generated ammonia) is delivered to the SCR catalyst 40 through the exhaust gas and reacts on the SCR catalyst coating. The reductant or ammonia that does not react through the SCR catalyst 40 is processed in the ASC 50, as described above.

[0082] Figure 2 The EATS 20 of the hydrogen combustion engine system 10 is generally operated in the following manner: the engine exhaust or exhaust gas (to be cleaned) from the hydrogen combustion engine 15 leaves the engine outlet 17 and enters the EATS 20 via the exhaust inlet 22, and encounters the SCR catalyst 40. Upstream of the SCR catalyst 40 and downstream of the exhaust inlet 22, the reductant is injected via the injector 34. The injected reductant is therefore mixed with the exhaust gas. Typically, the reductant is evaporated and hydrolyzed into ammonia (by a heater or by being heated by the exhaust gas). In the SCR catalyst 40, catalytic reduction is performed on the NOx in the exhaust gas with the help of ammonia and the SCR catalyst coating. Thereafter, the exhaust gas passes through the particulate filter 60 (which is optional). Thereafter, at least part of the cleaned exhaust gas encounters the ASC 50. In the ASC 50, emissions are further reduced by ammonia oxidation and NOx conversion, and then the exhaust gas is discharged from the EATS 20 via the EATS outlet 24.

[0083] Likewise Figure 2 As shown, the EATS 20 may include means for providing determination / measurement of various parameters, such as, for example, providing determination / measurement of the temperature of the SCR catalyst 40 and / or the ASC 50 via temperature sensors 33, 35. In addition, the amount of NOx, such as the mole fraction of NOx, or the weight of NOx per unit distance traveled, the weight per unit operating time, or the weight per unit energy (g / kWh), may be determined / measured at the EATS outlet 24 via a NOx sensor 37. Figure 2 In the embodiment of the present invention, the first temperature sensor 33 is arranged to directly measure the temperature of the SCR catalyst 40, and the second temperature sensor 35 is arranged to directly measure the temperature of the ASC 50. However, it is noted that the temperature of the SCR catalyst 40 can be determined by an estimate using at least one temperature sensor arranged upstream and / or downstream of the SCR catalyst 40, and / or the temperature of the ASC 50 can be determined by an estimate using at least one temperature sensor arranged upstream and / or downstream of the ASC 50 (e.g., a temperature sensor arranged at the EATS outlet 24).

[0084] In addition, the hydrogen combustion engine system 10 may include one or more sensors for measuring the amount of H 2 in the hydrogen combustion engine system 10. For example, Figure 2 As shown in the exemplary embodiment of , a first H2 sensor 39a is arranged at the engine outlet 17 for measuring the amount of H2 in the engine exhaust, and a second H2 sensor 39b is arranged upstream of the ASC 50 for measuring the amount of H2 in the exhaust entering the ASC 50. As previously mentioned, the operation of the hydrogen combustion engine system 10 can be controlled by the control unit 18.

[0085] Now refer to Figure 3A Exemplary embodiments of the configuration of the hydrogen combustion engine 15 and its operation are described in greater detail. Figure 3A An engine cylinder (or combustion cylinder) 310 of a hydrogen combustion engine 15 housing a piston 312 is schematically shown. Typically, the hydrogen combustion engine 15 includes a plurality of such engine cylinders and corresponding pistons. In more detail, the piston 312 is configured to reciprocate within the engine cylinder 310, wherein a combustion chamber 314 is contained in the engine cylinder 310 above the piston 312. The hydrogen combustion engine 15 also includes a spark plug 309 disposed in the combustion chamber 314. The piston 312 may be a double-acting piston, wherein the engine cylinder 310 is a combustion cylinder, and the hydrogen combustion engine 15 also includes a compressor cylinder (not shown).

[0086] The hydrogen combustion engine 15 includes an air intake passage 315, which is arranged downstream of the air chamber, for example, in fluid connection with a compressor (not shown). Air or compressed air is supplied to the combustion chamber 314 via the intake passage 315 and is regulated by an intake valve 316. In addition, the hydrogen combustion engine 15 includes an exhaust passage 317 regulated by an exhaust valve 318.

[0087] like Figure 3A As shown, the hydrogen combustion engine 15 includes an injection system 420, which includes a fuel injector 403, which is configured to supply H2 (usually as a gaseous fuel) to the combustion chamber 314. The fuel injector 403 is fluidly connected to at least one H2 storage tank 405, which contains pressurized H2 fuel or hydrogen-based gas (or a fuel that can easily form hydrogen). The injection system 420 can also include a water inlet device 404, which is configured to supply a water-based fluid medium 404a to the combustion chamber 314.

[0088] The hydrogen combustion engine 15 can be operated according to the Otto cycle or another four-stroke combustion mode. Therefore, the four-stroke cycle of the hydrogen combustion engine includes four different piston strokes within the engine cylinder 310 to complete an operating cycle: intake or compression of air via the air intake passage 315 and the intake valve 316 when the piston 312 reciprocates away from TDC, compression when the piston 312 reciprocates toward TDC, power or combustion when the H2 fuel is burned using the spark plug 309, and exhaust of the engine exhaust from the combustion chamber 314 via the exhaust passage 317 and the exhaust valve 318.

[0089] Now refer to Figure 4 A method for controlling the operation of a hydrogen combustion engine system of a vehicle is described in the flowchart of FIG. 1 , which schematically shows the steps of such a method. Figure 1 and Figure 2 The hydrogen combustion engine system 10, and Figure 3A The hydrogen combustion engine 15 is shown. Therefore, the hydrogen combustion engine system 10 suitable for the method includes at least a selective catalytic reduction SCR catalyst 40 and an ammonia slip catalyst ASC 50 arranged downstream of the SCR catalyst 40. Figure 4 The method described by the flowchart of FIG. 1 may be performed, for example, in response to or during a cold start of the hydrogen combustion engine 15 .

[0090] In step S10, for example as a first step S10, the temperature of the SCR catalyst 40 is determined. For example, the temperature of the SCR catalyst 40 may be determined based on a temperature measurement. This may be done, for example, by measuring the temperature of the SCR catalyst 40 using a temperature sensor (e.g., reference 1). Figure 2The temperature of the SCR catalyst 40 may be determined by modeling the temperature of the EATS 20 in response to a known thermal model of the EATS or by estimating the temperature of the SCR catalyst 40 using temperature sensors disposed upstream and / or downstream of the SCR catalyst 40. Alternatively, the temperature of the SCR catalyst 40 may be determined by modeling the temperature of the EATS 20 in response to a known thermal model of the EATS.

[0091] In step S20, for example as a second step S20, which may be performed before step S10, simultaneously with step S10 or after step S10, the temperature of the ASC 50 is determined. For example, the temperature of the ASC 50 may be determined based on a temperature measurement. This may be done, for example, by measuring the temperature of the ASC 50 using a temperature sensor (e.g., reference 1). Figure 2 The temperature of the ASC 50 may be determined by estimating the temperature of the ASC 50 using temperature sensors disposed upstream and / or downstream of the ASC 50. Alternatively, the temperature of the ASC 50 may be determined by modeling the temperature of the EATS 20 in response to a known thermal model of the EATS.

[0092] In step S27, which is performed after at least steps S10 and S20, the determined temperature of the SCR catalyst 40 is compared with a predetermined SCR temperature threshold, and the determined temperature of the ASC 50 is compared with a predetermined ASC temperature threshold. For example, the predetermined SCR temperature threshold is set to a value between 200° C. and 250° C., for example, to 200° C., and the predetermined ASC temperature threshold is set to a value between 200° C. and 250° C., for example, to 250° C.

[0093] In response to the result of step S27 that the temperature of the SCR catalyst 40 is below the predetermined SCR temperature threshold and the temperature of the ASC 50 is below the predetermined ASC temperature threshold, the hydrogen combustion engine 15 is operated in a H2 exhaust excess mode in step S30, and in step S40, unburned H2 in the engine exhaust is used as a reductant for NOx conversion in the ASC 50. The H2 exhaust excess mode is defined by the amount of unburned H2 in the engine exhaust being at least 0.2 mol% or at least 0.5 mol%.

[0094] In step 31, the hydrogen combustion engine 15 is operated by injecting H2 into the engine cylinder 310 during the exhaust stroke of the piston 312. Typically, the H2 exhaust excess mode is included in the combustion mode of the hydrogen combustion engine, such as the four-stroke combustion mode described previously, wherein the exhaust stroke is the exhaust stroke of the four-stroke cycle described previously. Thus, H2 is injected into the engine cylinder 310 after combustion, and can therefore be delivered to the engine exhaust via the exhaust passage 317 without combustion, at least to an excess of unburned H2 as defined above. For example, after the exhaust valve 318 opens, such as, for example, at least 10 crank angle degrees after the exhaust valve 318 opens, H2 is injected into the engine cylinder 310 and the combustion chamber 314. Additionally or alternatively, H2 is injected into the engine cylinder 310 and the combustion chamber 314 between 90 crank angle degrees before TDC and TDC.

[0095] In step S32, the hydrogen combustion engine 15 is operated by injecting H2 into the engine cylinder 310 during the compression stroke of the piston 312 to achieve the target λ. Thus, combustion of H2 in the engine cylinder 310 and the combustion chamber 314 is achieved. The target λ is typically higher than 1, such as, for example, between 1.5 and 3. It should be noted that the order of steps S31 and S32 can be reversed, and / or looped.

[0096] As can be seen from steps S31 and S32, H2 can be injected into the engine cylinder 310 at least twice during one operating cycle (e.g., the aforementioned four-stroke cycle), namely the main H2 injection during the compression stroke in step S32 and the secondary H2 injection during the exhaust stroke in step S31.

[0097] like Figure 3A As shown, the same fuel injector 403 can be used for both the primary H2 injection and the secondary H2 injection. In other words, both steps S31 and S32 can be implemented by the fuel injector 403.

[0098] Figure 3B A further alternative is shown in . Figure 3B is with Figure 3A The same engine cylinder 310 and piston 312 are schematically shown and therefore the same reference numerals are used to indicate the same or corresponding features. Figure 3B The hydrogen combustion engine 15', Figure 3A The fuel injector 403 also shown in FIG. 1 is a primary fuel injector 403 configured to perform a primary H2 injection. In addition, the hydrogen combustion engine 15′ includes a secondary fuel injector 406 configured to perform a secondary H2 injection. Figure 3BAs shown, the secondary fuel injector 406 may be arranged downstream of the exhaust valve 318 of the engine cylinder 310. Thus, the secondary H2 injection may be performed external to the engine cylinder 310 (and thus less dependent on the operating cycle of the engine cylinder) and directly into the exhaust passage 317 to achieve an amount of unburned H2 in the engine exhaust of at least 0.2 mol%. Figure 3B As shown, the secondary fuel injector 406 may alternatively be located at the engine outlet 17, as indicated by the dashed box 406. The engine outlet 17 is, for example, a common outlet for a plurality of engine cylinders before the engine exhaust is diverted to the EATS 20. Other locations for the secondary fuel injector 406 are contemplated, for example, somewhere between downstream of the exhaust valve 318 of at least one of the engine cylinders 310 and upstream of the exhaust inlet 22 (e.g., Figure 2 As shown in Figure 3B In a further alternative embodiment not disclosed in , the secondary fuel injector is arranged and configured to inject secondary H 2 into the engine cylinder 310 .

[0099] Preferably, both the primary fuel injector 403 and the secondary fuel injector 406 are part of the injection system 420 ′ and are configured to supply H 2 from the H 2 storage tank 405 .

[0100] Back to Figure 4 In step S33, the hydrogen combustion engine 15 is operated by injecting water into the engine cylinder 310 during the intake stroke of the piston 312. This is typically achieved by the water intake device 404 mentioned above.

[0101] In step S34, in the H2 exhaust excess mode, the amount of unburned H2 is changed from a minimum level of 0.2 mol% to a minimum level of 0.5 mol%. This may be performed, for example, in response to an increase in torque demand of the hydrogen combustion engine 15 or in response to the amount of NOx in the engine exhaust exceeding a NOx threshold.

[0102] like Figure 4 As shown, steps S31, S32, S33 and S34 may be sub-steps of step S30 of operating the hydrogen combustion engine in the H2 exhaust excess mode. That is, steps S31, S32, S33 and S34 may be performed during operation of the hydrogen combustion engine 15 in the H2 exhaust excess mode.

[0103] In step S36, unburned H2 is transported from the engine outlet 17 of the hydrogen combustion engine 15 to the ASC 50. The transport is preferably performed such that the mole fraction of H2 in the exhaust gas reaching the ASC is at least 80% of the mole fraction of H2 at the engine outlet.

[0104] As mentioned above, the ASC 50 preferably includes an oxidation catalyst and a metal zeolite. Therefore, the step S40 of using unburned H2 in the engine exhaust as a reducing agent for NOx conversion in the ASC 50 may include a sub-step S40a of converting ammonia into NOx in the ASC 50 using the oxidation catalyst; and a sub-step S40b of converting NOx into N2 in the ASC using the metal zeolite.

[0105] like Figure 4 As shown, in response to the result of step S27 that the temperature of the SCR catalyst 40 is higher than the predetermined SCR temperature threshold, and / or the temperature of the ASC 50 is higher than the predetermined ASC temperature threshold, in step S50, the hydrogen combustion engine 15 is operated in a default (or normal) combustion mode. During this default combustion mode, only the previous main H2 injection is used, and the secondary H2 injection is not used. The default combustion mode in S50 generally corresponds to a four-stroke cycle.

[0106] It should be noted that the SCR catalyst 40 , the ASC 50 , and the particulate filter 60 may be housed in separate containers or canisters.

[0107] It should be understood that the present invention is not limited to the embodiments described above and shown in the accompanying drawings; rather, those skilled in the art will recognize that many changes and modifications may be made within the scope of the appended claims. For example, EATS may be used to clean the exhaust of engines other than hydrogen combustion engines, such as in a dual fuel engine system (where one of the engines is a hydrogen combustion engine). For example, EATS of the present invention may be used to clean exhaust, such as by converting NOx emissions from the exhaust of an internal combustion engine based on H2 (hydrogen) or a mixture of H2 and natural gas.

[0108] In addition, by studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and effect variations to the disclosed embodiments in practicing the claimed inventive concepts. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A method for controlling operation of a hydrogen combustion engine system (10) of a vehicle (1), the hydrogen combustion engine system (10) comprising a hydrogen combustion engine (15, 15') and an exhaust gas aftertreatment system (EATS) (20) configured to reduce emissions of engine exhaust, the EATS (20) comprising a selective catalytic reduction (SCR) catalyst (40) and an ammonia slip catalyst (ASC) (50) arranged downstream of the SCR catalyst (40), wherein the method comprises: - determining (S10) the temperature of the SCR catalyst (40); - determining (S20) the temperature of the ASC (50); as well as In response to determining that the temperature of the SCR catalyst (40) is below a predetermined SCR temperature threshold and the temperature of the ASC (50) is below a predetermined ASC temperature threshold, operating (S30) the hydrogen combustion engine (15, 15') in an H2 exhaust excess mode defined by an amount of unburned H2 in the engine exhaust being at least 0.2 mol%, and using (S40) the unburned H2 in the engine exhaust as a reductant for NOx conversion in the ASC (50).

2. The method of claim 1, wherein the H2 exhaust excess mode comprises operating (S31) the hydrogen combustion engine (15) by injecting H2 into engine cylinders (310) during an exhaust stroke.

3. A method according to any one of the preceding claims, wherein the H2 exhaust excess mode is defined by an amount of unburned H2 in the engine exhaust being at least 0.5 mol%.

4. The method according to any one of the preceding claims, wherein the H2 exhaust excess mode comprises operating (S32) the hydrogen combustion engine (15, 15') by injecting H2 into the engine cylinder (310) during a compression stroke to achieve a target lambda.

5. The method according to any one of the preceding claims, wherein the H2 exhaust excess mode comprises operating (S33) the hydrogen combustion engine (15, 15') by injecting (404a) water into the engine cylinder (310) during an intake stroke.

6. The method according to any one of the preceding claims, further comprising: - delivering (S36) the unburned H2 from the engine outlet (17) of the hydrogen combustion engine (15, 15') to the ASC (50) such that the mole fraction of H2 in the exhaust gas reaching the ASC (50) is at least 80% of the mole fraction of H2 at the engine outlet (17).

7. The method according to any one of the preceding claims, wherein the ASC (50) is a monolithic catalyst comprising an oxidation catalyst and a metal zeolite coating, and the method comprises: - converting (S40a) ammonia into NOx in the ASC (50) using the oxidation catalyst; as well as - using the metal zeolite to convert (S40b) NOx into N2 in the ASC (50).

8. Method according to any of the preceding claims, wherein the method is performed during a cold start of the hydrogen combustion engine (15, 15').

9. A hydrogen combustion engine system (10) for a vehicle (1), the hydrogen combustion engine system (10) comprising a hydrogen combustion engine (15, 15') and an exhaust gas aftertreatment system EATS (20) configured to reduce emissions of engine exhaust, the EATS (20) comprising a selective catalytic reduction (SCR) catalyst (40) and an ammonia slip catalyst (ASC) (50) arranged downstream of the SCR catalyst (40), wherein the hydrogen combustion engine system (10) comprises a control unit (18), the control unit being configured to: - determining the temperature of the SCR catalyst (40); - determining the temperature of the ASC (50); - In response to determining that the temperature of the SCR catalyst (40) is below a predetermined SCR temperature threshold and the temperature of the ASC (50) is below a predetermined ASC temperature threshold, commanding the hydrogen combustion engine (15, 15') to operate in an H2 exhaust excess mode defined by an amount of unburned H2 in the engine exhaust being at least 0.2 mol% to use the unburned H2 in the engine exhaust as a reductant for NOx conversion in the ASC (50).

10. The hydrogen combustion engine system (10) of claim 9, wherein the EATS (20) is free of any oxidation catalyst disposed downstream of the exhaust inlet (22) of the EATS (20) and upstream of the ASC (50).

11. A vehicle (1) comprising a hydrogen combustion engine system (10) according to any one of claims 9 to 10.

12. A computer program comprising program code means comprising instructions for causing a hydrogen combustion engine system (10) according to any one of claims 9 to 10 to perform the steps of the method according to any one of claims 1 to 8 when the program is run on a computer.

13. A computer-readable medium carrying a computer program, the computer program comprising program code means, the program code means comprising instructions for causing a hydrogen combustion engine system (10) according to any one of claims 9 to 10 to execute the steps of a method according to any one of claims 1 to 8 when the computer program is run on a computer.

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