Method for operating an ammonia combustion engine, ammonia combustion engine and mobile or stationary installation

Abstract

In a method for operating an ammonia combustion engine (12) with a combustion chamber (16) and an injection device (26) in flow communication with the combustion chamber (16), by which ammonia can be metered into the combustion chamber (16), ammonia is metered into the combustion chamber (16) such that an exhaust gas stream generated by the ammonia combustion engine (12) has a predetermined molar ratio of ammonia to nitrogen oxides, regardless of the current operating point of the ammonia combustion engine (12). Furthermore, an ammonia combustion engine (12) and a mobile or stationary system with such an ammonia combustion engine are described.

Description

[0001] The invention relates to a method for operating an ammonia combustion engine, an ammonia combustion engine and a mobile or stationary system comprising an ammonia combustion engine.

[0002] Ammonia combustion engines are internal combustion engines that use ammonia as fuel and represent an alternative to "conventional" combustion engines that use hydrocarbons such as natural gas, gasoline, or diesel. The use of ammonia combustion engines is particularly desirable when hydrocarbons from fossil sources are at least partially replaced by ammonia, which has a lower CO₂ footprint. This is advantageous even if fuels other than ammonia are still used for ignition or combustion. Furthermore, many ammonia combustion engines are multi-fuel capable, meaning they can continue to run on other fuels in addition to ammonia.

[0003] However, ammonia combustion engines produce exhaust streams that differ fundamentally from those of a conventional combustion engine. The problem here is that, depending on the operating point, design, and tuning of the ammonia combustion engine, the exhaust stream can contain an excess of either nitrogen oxides (NOx) or ammonia (NH3). This places high demands on downstream exhaust aftertreatment systems, as they must be designed for both situations, resulting in high complexity and cost for the exhaust aftertreatment of ammonia combustion engines.

[0004] DE 11 2011 01487 T5 discloses an ammonia-burning internal combustion engine with a downstream exhaust gas purification catalyst for removing ammonia and NOx from an exhaust gas stream. Furthermore, an inlet gas control system is provided which adjusts the control parameters of the internal combustion engine depending on the ratio of ammonia to nitrogen oxides in the exhaust gas flowing into the exhaust gas purification catalyst, such that the ammonia-nitrogen oxide ratio becomes a target ratio corresponding to a full purification ratio, at which ammonia and nitrogen oxides are completely removed in the exhaust gas purification catalyst.

[0005] The object of the invention is to provide a way to reduce the complexity and / or the cost of the exhaust aftertreatment of an exhaust stream generated in an ammonia combustion engine.

[0006] The object of the invention is achieved by a method for operating an ammonia combustion engine with a combustion chamber and an injection device in flow communication with the combustion chamber, by which ammonia can be metered into the combustion chamber, wherein ammonia is metered into the combustion chamber such that an exhaust gas stream generated by the ammonia combustion engine has a predetermined molar ratio of ammonia to nitrogen oxides, regardless of the current operating point of the ammonia combustion engine. The method comprises the following steps: a) Determining the current operating point of the ammonia combustion engine, b) Determining an expected molar ratio of ammonia to nitrogen oxides in the generated exhaust gas stream at the current operating point, c) Comparing the expected molar ratio with the predetermined molar ratio, and d) Adjusting the amount of ammonia metered into the combustion chamber via the injection device if the expected molar ratio deviates from the predetermined molar ratio by more than a threshold value.

[0007] The "operating point" of an ammonia combustion engine refers to a specific point on the engine's performance map. Accordingly, the current operating point is the point on the engine's performance map that exists at the present moment. The current operating point thus also reflects the combustion conditions within the ammonia combustion engine.

[0008] Here and in the following, the term "molar ratio" refers to the molar ratio of ammonia to nitrogen oxides, unless otherwise stated.

[0009] The invention is based on the fundamental idea of ​​actively controlling or adjusting the molar ratio in the generated exhaust gas stream in such a way that a predetermined and therefore sufficiently known molar ratio of ammonia to nitrogen oxides is always produced in the exhaust gas stream. In this way, an exhaust aftertreatment system downstream of the ammonia combustion engine only needs to be adjusted or aligned to the predetermined molar ratio, thereby minimizing the complexity and design, and thus the costs, of the exhaust aftertreatment system.

[0010] The predetermined molar ratio of ammonia to nitrogen oxides refers specifically to the molar ratio of ammonia to nitrogen oxides in the exhaust gas stream at an outlet of the ammonia combustion engine, for example, at the end of a discharge line of the ammonia combustion engine that is in flow communication with the combustion chamber. In other words, the predetermined molar ratio is specifically the molar ratio of ammonia to nitrogen oxides that the exhaust gas stream generated by the ammonia combustion engine exhibits before treatment by an exhaust aftertreatment system downstream of the ammonia combustion engine.

[0011] However, it is also possible that the predetermined molar ratio of ammonia to nitrogen oxides is the molar ratio of ammonia to nitrogen oxides that the exhaust gas stream exhibits before it is treated in an actively controlled component of the exhaust aftertreatment system downstream of the ammonia combustion engine. Thus, passively operating components of the exhaust aftertreatment system may have already treated the exhaust gas stream.

[0012] In one variant, the predetermined molar ratio of ammonia to nitrogen oxides (R) lies in the range of R:1 to 1.1×R:1, where R denotes a target NOₓ reduction rate. In other words, the predetermined molar ratio is at most 1.1 times the target NOₓ reduction rate. For example, if the target NOₓ reduction rate is 80%, the predetermined molar ratio can range from 0.8:1 to 0.88:1. The target NOₓ reduction rate R can correspondingly be less than 100%, for example, in the range of 80% to less than 100%.

[0013] In another variant, the predetermined molar ratio of ammonia to nitrogen oxides is 1:1 or higher. Specifically, the predetermined molar ratio is in the range of 1:1 to 1.5:1.

[0014] In this variant, an excess of ammonia is selected compared to the nitrogen oxide content in the exhaust stream, or at least an equilibrium is reached between ammonia and the nitrogen oxides to be reduced. In other words, a so-called "ammonia slip" can be deliberately utilized. It has been shown that particularly advantageous operating points of ammonia combustion engines can be achieved when ammonia slip in the exhaust stream is accepted.

[0015] A further advantage of ammonia slip in the exhaust gas stream is that it eliminates the need for additional dosing systems in a downstream exhaust aftertreatment system to add ammonia to the exhaust gas stream, or at least minimizes the dosing range of the exhaust aftertreatment system. Such dosing systems are necessary when there is an excess of nitrogen oxides in the exhaust gas stream, in order to convert them to nitrogen and water. This allows for a further reduction in the complexity, cost, and space requirements of the exhaust aftertreatment system, as either a dosing system can be completely eliminated or at least more cost-effective dosing systems with smaller dosing ranges and / or simpler components can be used.

[0016] Furthermore, it is possible to choose a predetermined molar ratio that is optimized for the breakdown of nitrous oxide, since nitrous oxide (N2O) is also present in the exhaust gas stream in addition to ammonia and nitrogen oxides.

[0017] Nitrous oxide is a byproduct produced at at least some operating points of an ammonia combustion engine, with a global warming potential that, over a 100-year time horizon, is more than 250 times that of carbon dioxide. Therefore, it is crucial that nitrous oxide contained in the exhaust stream is reliably converted from the exhaust gas stream in the exhaust aftertreatment system.

[0018] For this purpose, the predetermined molar ratio can be selected such that, while not optimized for ammonia and nitrogen oxide aftertreatment, it is optimized for removing nitrous oxide from the exhaust stream. This can be achieved by adjusting the ammonia to nitrogen oxide molar ratio in the exhaust stream to suit an N₂O decomposition catalyst located in the exhaust aftertreatment system, ensuring that the N₂O decomposition catalyst achieves an optimized conversion rate and selectivity.

[0019] The threshold is specifically set such that if there is a deviation of more than 5% between the expected molar ratio and the predetermined molar ratio, the dosed amount of ammonia is adjusted.

[0020] Steps a) to d) can be performed in a control unit of the ammonia combustion engine, wherein the threshold value is stored in the control unit.

[0021] Preferably, steps a) to d) are repeated continuously so that any excessive deviations from the predetermined molar ratio can be detected promptly and compensated for with minimal time delay.

[0022] In this context, "continuously repeated" means that the time between two repetitions of the respective procedural steps is limited to the time absolutely necessary for carrying out the subsequent procedural steps.

[0023] The expected molar ratio is determined in particular on the basis of a data set stored in a control unit of the ammonia combustion engine, wherein the data set is based at least on operational information on the behavior of the ammonia combustion engine.

[0024] The operating information relating to the behavior of the ammonia combustion engine (also referred to as engine operating parameters) may include at least one of the following: amount of ammonia metered into the combustion chamber per unit of time, total amount of ammonia metered into the combustion chamber in a combustion cycle, temporal distribution of the amount of ammonia metered into the combustion chamber, charge air pressure, temperature, relative humidity, air-fuel ratio, and ignition pressure.

[0025] The stored data set thus represents a "mapping" of the behavior of the ammonia combustion engine. The more comprehensive the stored data set, the more accurately the expected molar ratio can be determined based on the data set.

[0026] In particular, the expected molar ratio can be determined entirely passively using the stored data set; that is, no additional actively measured parameters need to be included in the calculation of the expected molar ratio. This is especially advantageous if the behavior of the ammonia combustion engine is sufficiently known at all relevant operating points and can be described with sufficient accuracy using the operating information stored in the data set.

[0027] Alternatively or additionally, the ammonia combustion engine can be equipped with at least one sensor that samples the generated exhaust gas stream, with the expected molar ratio being determined based on the sensor measurement data generated during sampling. In this way, a particularly precise statement regarding the expected molar ratio of ammonia to nitrogen oxides can be obtained by actively monitoring the composition of the generated exhaust gas stream. In particular, the ammonia dosage into the combustion chamber of the exhaust aftertreatment system can be adjusted in a closed-loop process based on the generated sensor measurement data.

[0028] It is also possible to use a combination of the operational information contained in the stored data set and sensor measurement data generated by at least one sensor to determine the expected molar ratio of ammonia to nitrogen oxides.

[0029] Furthermore, the control unit can have a machine learning module configured to adapt at least one piece of operating information based on the sensor measurement data generated by at least one sensor. In this way, deviations detected during the operation of the ammonia combustion engine can be taken into account, ensuring that the expected molar ratio of ammonia to nitrogen oxides can be reliably and precisely determined at all times.

[0030] The at least one sensor can be located at a point in the exhaust gas stream where the predetermined molar ratio of ammonia to nitrogen oxides must be present, as well as at a point that merely allows a conclusion to be drawn about the actual molar ratio of ammonia to nitrogen oxides at another point in the exhaust gas stream where the predetermined molar ratio of ammonia to nitrogen oxides must be present.

[0031] For example, it is possible that at least one of the sensors is located in an exhaust aftertreatment system associated with the ammonia combustion engine.

[0032] In one variant, the amount of ammonia dosed into the combustion chamber is selected via charging and / or purging of the combustion chamber, in particular via valve overlap of the ammonia combustion engine.

[0033] Valve overlap can be determined via the opening behavior. a) an inlet valve or several inlet valves and an exhaust valve or several exhaust valves of the combustion chamber of the ammonia combustion engine, b) via an inlet port or several inlet ports and an exhaust port or several exhaust ports of the combustion chamber of the ammonia combustion engine, c) a combination of one or more inlet ports and one or more exhaust valves of the combustion chamber of the ammonia combustion engine, or d) a combination of one or more inlet valves and one or more exhaust ports The parameters can be specified or varied. It is also possible to additionally use exhaust gas recirculation (EGR).

[0034] In another variant, the injection system is a direct injection system and ammonia is metered into the combustion chamber using a modified injection method.

[0035] A modified injection can be achieved through a longer duration of the main injection, multiple injections, or an additional post-injection.

[0036] If ammonia is additionally metered into the combustion chamber via post-injection, the timing of the post-injection is chosen so that at least the total amount of ammonia metered in the post-injection is no longer used in the current stroke or combustion cycle of the ammonia combustion engine. This means that the post-injection occurs at a point when the main combustion of fuel in the current stroke or combustion cycle of the ammonia combustion engine is completely or almost complete. Thus, the ammonia metered via post-injection no longer functions, at least partially, as fuel, but rather as a chemical for optimizing or simplifying the exhaust aftertreatment of the exhaust gas stream generated in the combustion chamber. Analogous post-injection methods are well known, for example, from diesel engines.

[0037] The fuel in the combustion chamber is ignited primarily by means of a pilot jet. This eliminates the need for alternative ignition devices, such as a spark plug, while simultaneously ensuring reliable ignition and a defined combustion profile. Furthermore, the use of a pilot jet allows for even more precise control of the ammonia metering into the combustion chamber and the predetermined molar ratio present in the generated exhaust gas stream at the current operating point.

[0038] The object is further solved according to the invention by an ammonia combustion engine with a combustion chamber and an injection device in flow communication with the combustion chamber, with which ammonia can be metered into the combustion chamber, wherein the ammonia combustion engine is configured to carry out the method as described above.

[0039] The features and properties of the method according to the invention apply accordingly to the ammonia combustion engine according to the invention and vice versa.

[0040] The problem is further solved according to the invention by a mobile or stationary system comprising an ammonia combustion engine as described above and an exhaust aftertreatment system in flow communication with the ammonia combustion engine for treating the exhaust gas stream generated by the ammonia combustion engine.

[0041] The mobile installation can be a vehicle, such as a land vehicle or a watercraft, for example, a ship. The land vehicle can be road- or rail-bound. However, it is also possible that it is not a road- or rail-bound vehicle, for example, a vehicle used in forestry, agriculture, or mining.

[0042] The stationary system can be a power plant for electricity, heat, and / or cooling production. It is also possible that the stationary system is a compression system, a pump, or a system for the stationary direct drive of mechanical processes.

[0043] Further features and characteristics of the invention will become apparent from the following description of an exemplary embodiment, which is not to be understood in a limiting sense, as well as from the drawings. These show: Fig. 1 a vehicle according to the invention with an ammonia combustion engine according to the invention, and Fig. 2 a schematic representation of the ammonia combustion engine according to the invention, equipped to carry out a method according to the invention for operating the ammonia combustion engine.

[0044] In Fig. 1 A mobile or stationary system 10 according to the invention is shown, which in the embodiment shown is a vehicle, specifically a watercraft, namely a cargo ship.

[0045] The mobile or stationary system 10 according to the invention can, in principle, also be another watercraft or a land vehicle, for example, a road-bound vehicle or a rail-bound vehicle. It is also possible that the mobile or stationary system 10 according to the invention is a power plant.

[0046] The vehicle is powered by an ammonia combustion engine 12, that is, an engine that uses ammonia (NH3) as fuel and reacts it with oxygen (O2). Oxygen is present in the ambient air of the ammonia combustion engine 12, which can be used directly for the combustion of ammonia.

[0047] The exhaust gas stream produced during this combustion process may contain unreacted ammonia and nitrogen oxides (NOx) in addition to the desired conversion products nitrogen (N2) and water (H2O), which must be removed from the exhaust gas stream before it is released into the environment.

[0048] The generated exhaust gas stream is therefore treated with an exhaust gas aftertreatment system 14 assigned to the ammonia combustion engine 12.

[0049] Fig. 2 shows further details of the ammonia combustion engine 12 according to the invention and the exhaust aftertreatment system 14.

[0050] The ammonia combustion engine 12 has a cylinder 15 which has a combustion chamber 16 and includes a piston 18 which is movably arranged within the cylinder 15 and is connected to a crankshaft (not shown).

[0051] Fresh air can be supplied to the combustion chamber 16 via an air supply line 20 and an air inlet valve 22, starting from an air supply 24. Thus, the air supply 24 is in flow communication with the combustion chamber 16.

[0052] Ammonia can be metered into the combustion chamber 16 by means of an injection device 26, wherein the injection device 26 comprises an injection nozzle 28 and an injection control unit 30, which are in flow communication with each other.

[0053] The injection control unit 30 is supplied via an ammonia supply line 32 by means of a pump 34 from a tank 36 in which ammonia is stored.

[0054] In the illustrated embodiment, this is a direct injection system in which air and ammonia are metered directly into the combustion chamber 16. It is understood that alternative configurations of the ammonia combustion engine 12 can also be used. For example, an upstream mixing chamber can be provided in which ammonia and air are mixed to form an ammonia-air mixture, and this ammonia-air mixture is then metered into the combustion chamber 16.

[0055] It is also possible to provide a configuration of the ammonia combustion engine 12 in which the ammonia-air mixture present in the combustion chamber 16 is ignited by means of a pilot jet.

[0056] The exhaust gas generated within the combustion chamber 16 is directed as an exhaust stream via an exhaust valve 38 into a discharge line 40 of the ammonia combustion engine 12 and from there to the exhaust aftertreatment system 14, as shown in Fig. 2 indicated by an arrow P.

[0057] The exhaust aftertreatment system 14 has a first catalyst unit 42, a second catalyst unit 44 and a third catalyst unit 46, which are arranged in the aforementioned order in the direction of the exhaust gas flow.

[0058] The type and function of the catalyst units 42, 44 and 46 is geared towards the expected chemical composition of the exhaust gas stream in order to convert nitrogen oxides and ammonia contained in the exhaust gas stream to nitrogen and water.

[0059] For example, the first catalyst unit 42 is a first SCR catalyst, the second catalyst unit 44 is an oxidation catalyst for the reduction of ammonia, and the third catalyst unit 46 is a second SCR catalyst.

[0060] The exhaust aftertreatment system 14 may also include a different number of and / or other types of catalyst units, for example an additional N2O decomposition catalyst that converts nitrous oxide (N2O) contained in the exhaust stream into nitrogen and oxygen.

[0061] The ammonia combustion engine 12 further comprises a control unit 48, which is designed to control the injection control unit 30 and thus to regulate the amount of ammonia injected into the combustion chamber 16.

[0062] The control unit 48 includes a storage module 50 in which operating information on the behavior of the ammonia combustion engine 12 is stored.

[0063] In addition, the control unit 48 has a machine learning module 52, the function of which will be discussed later.

[0064] The control unit 48 is connected to sensors 54, 56 and 58 via signal transmission, with sensor 54 being assigned to the ammonia combustion engine 12, namely the discharge line 40, and sensors 56 and 58 being assigned to the exhaust aftertreatment system 14.

[0065] The sensor 56 is located upstream of the first catalyst unit 42, and the sensor 58 is located between the first catalyst unit 42 and the second catalyst unit 44, as viewed along the direction of the exhaust gas flow.

[0066] Sensors 54, 56 and 58 sample the exhaust gas stream, and the molar ratio of ammonia to nitrogen oxides in the exhaust gas stream at the location of the respective sensor 54, 56 and 58 can be deduced from the sensor measurement data obtained from sensors 54, 56 and 58.

[0067] In the following, a method according to the invention for operating the ammonia combustion engine 12 is explained.

[0068] As previously described, ammonia is reacted with air as fuel within the combustion chamber 16. The chemical composition of the exhaust gas produced during the reaction, and thus the chemical composition of the exhaust gas stream discharged via the discharge line 40, generally depends on the current operating point of the ammonia combustion engine 12, for example, on the currently prevailing load conditions.

[0069] According to the invention, the metering of ammonia via the injection device 26 is carried out in such a way that the molar ratio of ammonia to nitrogen oxides in the exhaust gas stream corresponds to a predetermined molar ratio of ammonia to nitrogen oxides.

[0070] Preferably, the predetermined molar ratio of ammonia to nitrogen oxides is 1:1 or higher, and is particularly in the range of 1:1 to 1.5:1, so that an equimolar ratio between ammonia and nitrogen oxides or an excess of ammonia is always present. It is also possible to aim for a significant excess of ammonia by setting the predetermined molar ratio of ammonia to nitrogen oxides to 2:1 or higher, for example, in the range of 2:1 to 10:1.

[0071] In another embodiment, the predetermined molar ratio of ammonia to nitrogen oxides (R) is in the range of R:1 to 1.1×R:1, where R denotes a desired NOₓ reduction rate. For example, if the desired NOₓ reduction rate is 80%, the predetermined molar ratio can be in the range of 0.8:1 to 0.88:1.

[0072] In yet another embodiment, the predetermined molar ratio is selected such that an N2O decomposition catalyst used in the exhaust aftertreatment system 14 achieves an optimized conversion rate and selectivity.

[0073] According to the invention, the exhaust aftertreatment system 14 can thus be designed in such a way that only exhaust gas flows with the predetermined molar ratio of ammonia to nitrogen oxides have to be handled.

[0074] To ensure that the predetermined molar ratio of ammonia to nitrogen oxides is present in the exhaust gas stream at all times, the following sequence of steps can be carried out.

[0075] First, the current operating point of the ammonia combustion engine 12 is determined, that is, the point in the characteristic map of the ammonia combustion engine 12 that reflects the currently prevailing load conditions.

[0076] Subsequently, an expected molar ratio of ammonia to nitrogen is determined in the exhaust gas stream generated at the current operating point.

[0077] The expected molar ratio of ammonia to nitrogen oxides can be determined using the data set stored in storage module 50. For this purpose, the data set is based on at least one piece of operating information regarding the behavior of the ammonia combustion engine.

[0078] The operating information may include one or more of the following: amount of ammonia dosed into the combustion chamber per unit of time, total amount of ammonia dosed into the combustion chamber in a combustion cycle, temporal distribution of the amount of ammonia dosed into the combustion chamber, charge air pressure, temperature, relative humidity, air-fuel ratio, and ignition pressure.

[0079] In other words, based on empirical data on the behavior of the ammonia combustion engine 12, its behavior at the current operating point can be estimated and, based on this, the dosage of ammonia into the combustion chamber 16 can be adjusted so that the exhaust gas flow has the required predetermined molar ratio of ammonia to nitrogen.

[0080] In the embodiment shown, the control unit 48 can additionally access the sensor measurement data collected by the sensors 54, 56 and 58.

[0081] In this context, sensor 54 provides information on the composition of the exhaust gas flow immediately after it has left the combustion chamber 16.

[0082] The sensor 56 makes it possible to determine the composition of the exhaust gas flow at the beginning of the exhaust gas aftertreatment system 14, i.e. before the exhaust gas flow has been treated by one of the catalyst units 42, 44 and 46.

[0083] The sensor 58 provides information on the composition of the exhaust gas flow after the exhaust gas flow has already passed through the first catalyst unit 42.

[0084] Based on the sensor measurement data of sensors 54, 56 and 58, it is therefore possible to estimate the actual value of the molar ratio of ammonia to nitrogen oxides in the exhaust gas stream at the installation location of the respective sensor 54, 56 and 58, which can be used as the expected molar ratio.

[0085] However, it is also possible that the expected molar ratio of ammonia to nitrogen oxides at another location within the discharge line 40 and / or the exhaust aftertreatment system 14 is determined solely on the basis of the sensor measurement data in the control unit 48.

[0086] Fundamentally, the expected molar ratio of ammonia to nitrogen can also be determined solely based on the data set or solely based on the collected sensor measurements. Furthermore, fewer or more sensors may be used than in [reference to specific example]. Fig. 2 depicted.

[0087] In the embodiment shown, the control unit 48 can update the operating information contained in the data set using the machine learning module 52, based on the sensor measurement data obtained from the sensors 54, 56 and 58, so that operating information can be provided at any time that optimally describes the real behavior of the ammonia combustion engine 12.

[0088] The determined expected molar ratio of ammonia to nitrogen oxides is then compared with the predetermined molar ratio of ammonia to nitrogen oxides.

[0089] If the expected molar ratio deviates from the predetermined molar ratio by more than a threshold value, the amount of ammonia metered into the combustion chamber 16 via the injection device 26 is adjusted so that the predetermined molar ratio of ammonia to nitrogen oxides is restored.

[0090] For example, if necessary, an ammonia post-injection is carried out into the combustion chamber 16 via the injection nozzle 28 in order to increase the proportion of ammonia in the exhaust gas stream.

[0091] The process steps described above can be repeated continuously in order to react at any time to changes in the current molar ratio of ammonia to nitrogen oxides and thus to ensure with particular reliability that the predetermined molar ratio of ammonia to nitrogen oxides is achieved.

[0092] The method according to the invention makes it possible to generate a controlled composition of the exhaust gas stream at any time and thus minimize the complexity and operating costs of the exhaust gas aftertreatment system 14 without having to accept disadvantages in the quality of the exhaust gas aftertreatment.

Claims

1. A method of operating an ammonia combustion engine (12) comprising a combustion chamber (16) and an injection device (26) which is in fluid communication with the combustion chamber (16) and which can be used to meter ammonia into the combustion chamber (16), wherein ammonia is metered into the combustion chamber (16) such that an exhaust gas stream generated by the ammonia combustion engine (12) has a predetermined molar ratio of ammonia to nitrogen oxides independently of the current operating point of the ammonia combustion engine (12), and wherein the method comprises the following steps: (a) determining the current operating point of the ammonia combustion engine (12); (b) determining an expected molar ratio of ammonia to nitrogen oxides in the generated exhaust gas stream at the current operating point; (c) comparing the expected molar ratio with the predetermined molar ratio; and (d) adjusting the quantity of ammonia metered into the combustion chamber (16) via the injection device (26), characterized in that the adjusting is performed if the expected molar ratio deviates from the predetermined molar ratio by more than a threshold value.

2. The method according to claim 1, wherein the predetermined molar ratio of ammonia to nitrogen oxides (R) is in the range of from R:1 to 1.1×R:1, wherein R denotes a provided NOx reduction rate or is 1:1 or higher, in particular in the range of from 1:1 to 1.5:1.

3. The method according to claim 1 or 2, wherein steps (a) to (d) are repeated continuously.

4. The method according to any of the preceding claims, wherein the expected molar ratio is determined on the basis of a data set stored in a control unit (48) of the ammonia combustion engine (12), wherein the data set is based on at least one piece of operating information on the behavior of the ammonia combustion engine (12).

5. The method according to any of the preceding claims, wherein the ammonia combustion engine (12) has at least one sensor (54, 56, 58) which samples the exhaust gas stream generated, and wherein the expected molar ratio is determined on the basis of the sensor measurement data generated by the sensor (54, 56, 58) during sampling.

6. The method according to any of the preceding claims, wherein the amount of ammonia metered into the combustion chamber (16) is selected by means of forced induction and / or purging of the combustion chamber (16).

7. The method according to any of the preceding claims, wherein the injection device (26) is a direct injection device, and ammonia is metered into the combustion chamber (16) in a modified injection, wherein the modified injection is realized, in particular, over a longer duration of the main injection, a multiple injection or an additional post-injection.

8. An ammonia combustion engine (12) comprising a combustion chamber (16) and an injection device (26) which is in fluid communication with the combustion chamber (16) and which can be used to meter ammonia into the combustion chamber (16), wherein the ammonia combustion engine (12) is configured to carry out the method according to any of the preceding claims.

9. A mobile or stationary system (10) comprising an ammonia combustion engine (12) according to claim 8 and an exhaust gas aftertreatment system (14) which is in fluid communication with the ammonia combustion engine (12), for treating the exhaust gas stream generated by the ammonia combustion engine (12).

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