Method for operating an internal combustion engine with a mixture of ammonia and dimethyl ether, and internal combustion engine therefor

Abstract

The present invention relates to a method for operating an internal combustion engine with a mixture of ammonia and dimethyl ether, comprising the steps of: injecting or blowing the liquefied or gaseous mixture into a combustion chamber, igniting the injected or blown-in mixture in the combustion chamber, and using the expansion of the ignited mixture for driving the internal combustion engine, preferably also comprising the step, prior to the injection or blowing step; liquefying the mixture by generating an overpressure, preferably an overpressure of at least 5 bar, preferably of 8 bar, and particularly preferably of 9 bar and an overpressure of at most 20 bar, preferably of 15 bar, and particularly preferably of 10 bar.

Description

[0001] The present invention relates to a method for operating an internal combustion engine with a mixture of ammonia and dimethyl ether, and to an internal combustion engine for this purpose.

[0002] For environmental reasons, there is a strong push to operate internal combustion engines with CO2-neutral fuels, ideally produced from renewable energy sources or whose production completely eliminates the need for a carbon source. Typically, in addition to hydrogen and other synthetic fuels (for example, methanol or OME, i.e., oxymethylene ether), ammonia is a possible candidate.

[0003] The problem with using ammonia as a primary fuel for an internal combustion engine is that it is not self-igniting, meaning it requires an initial ignition in every operating cycle of the internal combustion engine.

[0004] According to the state of the art, it is therefore common to provide a dual-fuel combustion system in which two separate injection systems first perform a self-igniting pre-injection and subsequently a main injection with the non-self-igniting fuel, so that ignition of the self-igniting pre-injection leads to ignition of the main injection.

[0005] For example, it may be possible to have several injectors per cylinder, one of which injects the self-igniting fluid and another the non-ignitable fluid into the combustion chamber. Alternatively, the initial ignition of the main injection may be achieved via a spark plug, although this is a wear part that entails corresponding maintenance.

[0006] From the disclosure RYU KYUNGHYUN ET AL: "Performance characteristics of compression-ignition engine using high concentration of ammonia mixed with dimethyl ether" APPLIED ENERGY, ELSEVIER SCIENCE PUBLISHERS, GB, Vol. 113, 24 August 2013 (2013-08-24), XP028762967, a method according to the preamble of claim 1 is known.

[0007] CN 1 970 699 A also discloses a method according to the preamble of claim 1.

[0008] The objective of the present invention is to overcome or partially mitigate the above disadvantages, which is achieved with a method that incorporates all the steps of claim 1 or an internal combustion engine with the features of claim 10.

[0009] According to the inventive method, it is provided that an internal combustion engine is operated with a mixture of or containing ammonia and dimethyl ether, wherein the following steps are further provided in the method: Introducing, in particular injecting or blowing the liquefied or gaseous mixture into a combustion chamber, igniting the mixture introduced into the combustion chamber, and utilizing the expansion of the ignited mixture to drive the internal combustion engine, preferably further comprising the step prior to the step of introducing it into the combustion chamber; liquefying the mixture by generating an overpressure, preferably by an overpressure of at least 5 bar, more preferably 8 bar, and particularly preferably 9 bar and an overpressure of at most 60 bar, more preferably at most 20 bar, and particularly preferably at most 10 bar.

[0010] The mixture of ammonia and dimethyl ether (abbreviated DME) forms an azeotropic mixture, in which the vapor phase and the liquid state have the same composition. Its behavior is therefore similar to that of a pure substance; however, in this mixture of ammonia and dimethyl ether, the ignition temperature is advantageously lower compared to pure ammonia, and the lower flammability limit in air is also reduced.

[0011] According to the invention, it can therefore also be provided that the mixture for operating the internal combustion engine is an azeotropic mixture comprising or consisting of ammonia and dimethyl ether.

[0012] According to the invention, it can further be provided that the mixture consists of or comprises 55-65%, preferably 60%, ammonia and 35-45%, preferably 40%, dimethyl ether, and is preferably R-723.

[0013] The designation "R-723" is the typical term used in technical jargon for a mixture of ammonia and dimethyl ether in a 60:40 ratio. It should be noted that this designation does not correspond to the official nomenclature according to ISO 817, as the official listing of this mixture in DIN EN 378 is still pending due to the associated complex registration and assignment of an R-number.

[0014] The use of an azeotropic mixture (containing ammonia) significantly improves the characteristic combustion properties of ammonia. This can be seen in the example of R-723, where the ignition temperature increases from 630 °C to 440 °C and the lower flammability limit in air decreases from 15% to 6%.

[0015] The method may also provide for a spark plug to ignite the mixture introduced (e.g., injected or blown into) in the combustion chamber.

[0016] Even though the inclusion of a spark plug represents another component subject to wear, its use in gasoline engines is well-established and reliably ensures the ignition of a non-self-igniting fuel.

[0017] According to the invention, it is provided that, in order to ignite the injected mixture in the combustion chamber, a pre-injection with a self-igniting fuel takes place beforehand, so that ignition of the pre-injection leads to ignition of the subsequently injected mixture, wherein the self-igniting fuel preferably contains or consists of diesel and / or dimethyl ether.

[0018] To eliminate the need for a spark plug, the main injection, consisting of non-self-igniting fuel, can be ignited by means of a pre-injection according to the inventive method. In this process, a self-igniting fuel is introduced into the combustion chamber prior to the main injection and is then ignited by compression or other influences. A non-self-igniting fuel (main injection) introduced only shortly after the pre-injection is then also ignited by the ignition of the pre-injection.

[0019] A particular advantage is that dimethyl ether can be used as a pre-injection, since with a cetane number greater than 55 it has an ignitability in the range of diesel (cetane number greater than 51) and therefore - similar to diesel - can only be ignited by compression in a combustion chamber.

[0020] A particular advantage here is that the fuel for the pre-injection (DME) is a component of the fuel for the main injection, so that providing different fuel types is not strictly necessary, since dimethyl ether can be separated from the ammonia-dimethyl ether mixture. Storing and refueling a vehicle with two different fuels is therefore unnecessary, as the appropriate fuel for pre-injection can be obtained from the mixture.

[0021] According to the invention, it is also provided that the pre-injection is carried out with dimethyl ether, which has been separated from the liquefied mixture of ammonia and dimethyl ether, wherein preferably the pre-injection is introduced into the combustion chamber via the same feed as the mixture, but before it.

[0022] It may also be provided that the pre-injection takes place via a separate injector or via the same injector as the main injection. If, in addition, an identical supply to the combustion chamber is used, one of the two supply lines typically provided in the prior art for the different injection processes (pre-injection and main injection) is eliminated.

[0023] However, for easier handling of the timing, a separate injector and injector line may also be provided.

[0024] Furthermore, according to the present invention, it can be provided that the liquefied mixture is brought to an injection pressure of more than 500 bar, preferably more than 700 bar and preferably more than 900 bar, before being injected into a combustion chamber.

[0025] It is clear to the expert that, depending on the chosen state of matter of the azeotropic mixture and the chosen combustion process concept, the pressure ranges applicable to the injection system according to the state of the art can be applied.

[0026] According to a further advantageous modification of the present invention, it can be provided that an exhaust gas produced after ignition of the injected mixture in the combustion chamber is subjected to exhaust gas aftertreatment in which ammonia is used, which has preferably been separated from the liquefied mixture of ammonia and dimethyl ether.

[0027] Exhaust gas aftertreatment plays a crucial role in minimizing pollutants produced during combustion. In selective catalytic reduction (SCR) systems, for example, there is a small urea tank from which urea is converted into ammonia via thermolysis and hydrolysis. According to the invention, if a mixture of ammonia and dimethyl ether is used, the urea tank required for effective exhaust gas purification can be omitted after separating these two components, since ammonia is already present in the mixture due to the separation of the dimethyl ether.

[0028] Furthermore, according to the invention, it can also be provided that, after ignition of the injected mixture, nitrous oxide is separated from the exhaust gas and, if necessary, returned to the combustion chamber via a gas storage tank.

[0029] Since the combustion of ammonia produces nitrous oxide (N₂O), also known as laughing gas, a catalyst or a specially designed separator unit can be used to extract the nitrous oxide from the exhaust gas and introduce it into a gas storage tank. Providing a gas storage tank is only advantageous if a sufficient quantity of nitrous oxide is produced. If this is not the case, it can also be beneficial to neutralize the nitrous oxide produced using a neutralization unit.

[0030] If a temporary increase in the power output of an internal combustion engine is required, nitrous oxide can be injected into the combustion chamber, resulting in a power boost. Such nitrous oxide injection is particularly well-known in motorsports, where it is used for short-term power enhancements of internal combustion engines.

[0031] The invention further relates to an internal combustion engine for carrying out a method according to one of the previously discussed variants.

[0032] The internal combustion engine according to the invention for operation with a mixture of ammonia and dimethyl ether comprises a fuel tank for receiving the mixture in liquid form at an overpressure, preferably at an overpressure of at least 5 bar, more preferably 8 bar, and particularly preferably 9 bar and at an overpressure of at most 20 bar, more preferably 15 bar, and particularly preferably 10 bar, and a fuel supply line that connects the fuel tank to a combustion chamber of the internal combustion engine and serves to introduce the mixture located in the fuel tank into the combustion chamber, and is characterized by a separation unit connected to the fuel tank for separating the components of the mixture into pure ammonia and pure dimethyl ether.

[0033] As explained above in connection with the inventive method, the individual components of the ammonia-dimethyl ether mixture in their pure form can be advantageous and also eliminate the need for holding and refilling specific tanks for alternative substances (e.g. urea for SCR catalysis or a second fuel for pre-injection).

[0034] The separation unit can separate the two components of the mixture using a membrane, preferably in a gaseous state. Therefore, the separation unit can be designed to separate the components of the mixture using a separating membrane. A pressure reducer can be provided for converting the mixture into a gaseous state.

[0035] Alternatively or additionally, it can be provided that the separation of the two components can also be successfully carried out if the fuel is in a liquid state. In this case, the principle of reverse osmosis is used, so that converting the liquid fuel into a gaseous form is not necessary.

[0036] It can therefore be provided that the separation unit separates the components of the mixture using reverse osmosis, whereby the mixture can be in a liquid state.

[0037] Furthermore, according to an optional modification of the present invention, the internal combustion engine may also be provided with a storage unit for dimethyl ether, which is fed by the separation unit and has an output line connected to the fuel line, wherein the amount of dimethyl ether to be introduced into the fuel line is preferably controllable via a feed valve.

[0038] Alternatively, it can also be provided that a separate line is provided from the storage tank for dimethyl ether to supply it to the combustion chamber.

[0039] This ensures that a sufficient quantity of dimethyl ether can always be kept on hand, which can be used as a self-igniting fuel for pre-injection.

[0040] Alternatively or additionally, the internal combustion engine may be provided with an ammonia storage tank which is fed by the separation unit and has an output line connected to a catalyst, in particular an SCR catalyst, wherein the catalyst serves to clean exhaust gas emitted from the combustion chamber, preferably with regard to NO x emissions.

[0041] The storage of ammonia can be used for selective catalytic reduction in the catalyst. The addition of a further substance besides the fuel itself is no longer necessary, since ammonia can be generated from the mixture. Therefore, in the internal combustion engine according to the invention, a further filling port is not required, nor is the separate filling of such an additive (urea, commonly known as, among others, urea).The following must be observed when operating such an internal combustion engine (AdBlue): According to a further optional modification of the present invention, it can be provided that the internal combustion engine is equipped with a separator unit which is arranged in an exhaust gas line of the internal combustion engine and is designed to cut off any nitrous oxide produced during the combustion of the mixture, wherein preferably a gas intermediate storage unit is provided to temporarily store the separated nitrous oxide and return it to the combustion chamber when required.

[0042] When ammonia or the azeotropic mixture of ammonia and dimethyl ether is burned, nitrous oxide is produced, which can be separated from the exhaust gas and, if necessary, recycled back into the combustion chamber to increase the power output of the internal combustion engine.

[0043] According to an advantageous embodiment of the present invention, the internal combustion engine may further be provided with a control unit designed to first inject the dimethyl ether obtained via the separation unit in order to carry out a combustion process in the combustion chamber, in order to form a self-igniting pre-injection with the aid of which ignition of the subsequently injected mixture (ammonia, DME and possibly air) takes place.

[0044] The present invention also relates to the use of a mixture of ammonia and dimethyl ether as fuel in an internal combustion engine. The mixture may consist of 55-65%, preferably 60%, ammonia and 35-45%, preferably 40%, dimethyl ether, and preferably R-723.

[0045] Further features, details, and advantages of the invention will become apparent from the following description of the figures. These show: Fig. 1: a schematic diagram of an internal combustion engine according to the invention.

[0046] Fig. 1Figure 1 shows a schematic diagram of an internal combustion engine 1 according to the invention. The fuel tank 2 is filled with a mixture of ammonia and dimethyl ether, which is introduced into at least one combustion chamber 4 via a fuel supply line 3. In the combustion chamber 4, the non-self-igniting mixture is then ignited and used to drive a piston. The combusted mixture is subsequently discharged from the combustion chamber 4 via an exhaust line 13, so that the combustion chamber 4 is available for the reintroduction of the ammonia-dimethyl ether mixture. It is clear to those skilled in the art that, for example, a spark plug can be provided to ignite the mixture in the combustion chamber 4, or that a self-igniting mixture can be ignited beforehand by means of compression of the piston, so that a subsequently introduced non-self-igniting mixture (in this case, ammonia and dimethyl ether) can be ignited by the ignition of the self-igniting mixture.

[0047] Furthermore, a separation unit 5 is connected to the fuel tank 2. This unit is designed to separate the individual components of the mixture contained in the fuel tank 2 so that they can be used for advantageous tasks related to the internal combustion engine 1. The separation unit 5 thus separates the individual components ammonia and dimethyl ether and feeds them to their respective storage tanks 6 and 9.

[0048] The storage tank 6 for dimethyl ether has an outlet line 7 connected to the fuel supply line 3, making it possible to introduce pure dimethyl ether into the combustion chamber 4. Since pure dimethyl ether is self-igniting, it can first be introduced into the combustion chamber 4, so that a subsequently introduced mixture from the fuel tank 2 is ignited by the pure dimethyl ether (e.g., by compression). Therefore, separate refueling of the internal combustion engine with its own self-igniting fuel is not necessary, thus reducing the operating requirements of the engine.

[0049] For example, the storage tank for dimethyl ether 6 can be connected to the fuel supply line 3 via a supply valve 8, so that the combustion chamber 4 is filled with pure dimethyl ether at desired times.

[0050] Downstream of the supply valve 8, components known to those skilled in the art for filtering and pressurizing a fluid to be introduced into the combustion chamber 4 can be arranged. The fluid to be introduced into the combustion chamber 4 can first pass through a pre-filter 15 before being pressurized to an intermediate pressure level by a first feed pump 16. Typically, it then passes through a further filter 17 before being pressurized to the final pressure level by a high-pressure pump 18. A fluid connection also runs from the high-pressure pump 18 back to the fuel tank 2, so that any leakage occurring at the high-pressure pump 18 can be routed back.Alternatively or additionally, if fuel under high pressure (ammonia-dimethyl ether mixture or pure dimethyl ether) is available but not needed in combustion chamber 4, it is simply returned to fuel tank 2.

[0051] Starting from the separation unit 5, there is also a storage unit 9 for ammonia, which has an output line 11 that leads to a unit for exhaust gas aftertreatment 10, 12.

[0052] In the exhaust pipe 13, downstream of the combustion chamber 4, an exhaust aftertreatment unit is provided, for example in the form of a catalyst 10, which is designed to filter pollutants from the exhaust stream. The exhaust aftertreatment unit can perform selective catalytic reduction to reduce NOx pollutants.

[0053] It is known to those skilled in the art that such selective catalytic reduction requires ammonia, which in conventional applications is obtained from urea through thermolysis and hydrolysis. Therefore, the user is required to ensure that this urea (brand name: e.g., AdBlue) is refilled after a certain time interval to continue the selective catalytic reduction process. For this purpose, a further, smaller opening is typically provided near the fuel tank filler neck, through which the urea can be filled into a separate tank.

[0054] According to the present invention, the provision of a separate opening area for the supply of urea or of a means required for selective catalytic reduction can be omitted, since the ammonia required for this can be generated directly from the fuel mixture.

[0055] Furthermore, one can recognize in Fig. 1A return line leads from the exhaust aftertreatment unit 10, 12 to the combustion chamber 4 and includes a tank 14 for nitrous oxide (N₂O). The exhaust aftertreatment unit can further include a separator unit 12, which filters the nitrous oxide contained in the exhaust gas from the exhaust stream and introduces it into the nitrous oxide tank 14. From there, it can be injected directly into the combustion chamber 4 as needed, thus increasing the power output of the internal combustion engine. The operating principle of nitrous oxide injection is known from motorsport, although there the nitrous oxide to be injected is not taken from the exhaust stream but is stored separately in independent tanks. Reference symbol list:

[0056] 1 Internal combustion engine 2 Fuel tank 3 Fuel supply line 4 Combustion chamber 5 Separation unit 6 Dimethyl ether storage 7 Outlet line 8 Supply valve 9 Ammonia storage 10 Catalyst 11 Outlet line 12 Separator unit 13 Exhaust line 14 Gas storage tank 15 Pre-filter 16 Pre-supply pump 17 Filter 18 High-pressure pump

Claims

1. Method for operating an internal combustion engine (1) with a mixture consisting of or containing ammonia and dimethyl ether, said method comprising the steps of: introducing, in particular injecting or blowing, the liquefied or gaseous mixture into a combustion chamber (4), igniting the mixture introduced into the combustion chamber (4), and using the expansion of the ignited mixture for driving the internal combustion engine (1), characterised in that for igniting the introduced mixture in the combustion chamber (4), a pre-injection with a self-igniting fuel takes place in advance, such that an inflammation of the pre-injection leads to an ignition of the mixture subsequently injected in, wherein the pre-injection takes place with dimethyl ether that has been separated out from the liquified or gaseous mixture of ammonia and dimethyl ether.

2. Method according to claim 1, wherein the mixture is an azeotropic mixture, and / or consists of or comprises 55-65 %, preferably 60 %, ammonia, and 35-45 %, preferably 40%, dimethyl ether, and more preferably consists of a mixture of ammonia and dimethyl ether in a ratio of 60:40.

3. Method according to either of the preceding claims, wherein for igniting the injected-in or blown-in mixture in the combustion chamber (4), a spark plug is provided, which ignites the mixture.

4. Method according to any of the preceding claims, wherein the self-igniting fuel contains or consists of dimethyl ether or diesel and dimethyl ether.

5. Method according to the preceding claim 4, wherein the pre-injection is introduced into the combustion chamber via the identical feed as the mixture, but temporally before said mixture.

6. Method according to any of the preceding claims, wherein prior to injection into a combustion chamber (4) the liquified or gaseous mixture is brought to an injection pressure of more than 500 bar, preferably more than 700 bar, and more preferably more than 900 bar.

7. Method according to any of the preceding claims, wherein an exhaust gas resulting after an ignition of the introduced mixture in the combustion chamber (4) undergoes exhaust gas post-treatment, in which ammonia is used.

8. Method according to the preceding claim 7, wherein the ammonia used in the exhaust gas post-treatment has been separated from the liquified or gaseous mixture of ammonia and dimethyl ether.

9. Method according to any of the preceding claims, further comprising the step: before the step of introduction into the combustion chamber (4); of liquifying the mixture by generating an excess pressure, preferably by an excess pressure of at least 5 bar, more preferably 8 bar, and particularly preferably 9 bar, and an excess pressure of at most 60 bar, more preferably at most 20 bar, and particularly preferably at most 10 bar.

10. Internal combustion engine (1) for operating with a mixture consisting of or containing ammonia and dimethyl ether, comprising: a fuel tank (2) for receiving the mixture in liquid or gaseous state at an excess pressure, preferably at an excess pressure of at least 5 bar, more preferably 8 bar, and particularly preferably 9 bar, and an excess pressure of at most 60 bar, more preferably at most 20 bar, and particularly preferably 10 bar, and a fuel feed line (3) which connects the fuel tank (2) to a combustion chamber (4) of the internal combustion engine (1) and serves for introducing the mixture locate din the fuel tank (2) into the combustion chamber (4), characterised by a separation unit (5) connected to the fuel tank (2), for separating the components of the mixture into pure ammonia and pure dimethyl ether.

11. Internal combustion engine (1) according to the preceding claim 10, further comprising a reservoir (6) for dimethyl ether, which is supplied from the separation unit (5) and comprises an output line (7) connected to the fuel feed line (3).

12. Internal combustion engine (1) according to either of the preceding claims 10 or 11, wherein the amount of dimethyl ether to be fed into the fuel feed line (3) can be controlled via a feed valve (8).

13. Internal combustion engine (1) according to any of the preceding claims 10, 11 or 12, further comprising a reservoir (9) for ammonia, which is supplied from the separation unit (5) and comprises an output line (11) connected to a catalyst (10), in particular an SCR catalyst, wherein the catalyst (10) serves for cleaning an exhaust gas emitted from the combustion chamber (4), preferably with respect to the NOx emissions.

14. Internal combustion engine (1) according to any of the preceding claims 10-13, developed with the features of claim 11, further comprising a control unit which is configured, for carrying out a combustion process in the combustion chamber (4), to firstly inject in the dimethyl ether obtained via the separation unit (5), in order to form a self-ignitable pre-injection therewith, with the aid of which an inflammation of the subsequently injected mixture takes place.

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