DE102021119723A1 - Method of operating an internal combustion engine with a mixture of ammonia and dimethyl ether and internal combustion engine therefor - Google Patents

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: injecting or blowing the liquefied or gaseous mixture into a combustion chamber, igniting the injected or injected mixture in the combustion chamber, and using the expansion the ignited mixture for driving the internal combustion engine, preferably further comprising the step before the step of injecting or blowing into the combustion chamber; Liquefaction of the mixture by generating an overpressure, preferably an overpressure of at least 5 bar, preferably 8 bar, and particularly preferably 9 bar and an overpressure of at most 20 bar, preferably 15 bar, and particularly preferably 10 bar.

Description

The present invention relates to a method for operating an internal combustion engine with a mixture of ammonia and dimethyl ether and an internal combustion engine therefor.

For reasons of environmental protection, there is a very strong desire to be able to operate internal combustion engines with CO ₂ -neutral fuels, which can best be produced from renewable energies or in the production of which a carbon source can be completely dispensed with. In addition to hydrogen and other synthetic fuels (e.g. methanol or OME, i.e. oxymethylene ether), ammonia is typically an option.

The problem with the use of ammonia as the primary fuel for an internal combustion engine is that it cannot self-ignite, ie it requires an initial ignition in each operating cycle of the internal combustion engine.

According to the prior art, it is therefore customary to provide dual-fuel combustion in which two separate injection systems first carry out a self-ignitable pre-injection and then a main injection with the non-self-ignitable fuel, so that the self-ignitable fuel is ignited Pilot injection leads to an ignition of the main injection.

For example, it can be provided that several injectors are provided for each cylinder, one of which injects the self-igniting fluid and another the non-igniting fluid into the combustion chamber. As an alternative to this, provision can be made for the initial ignition of the main injection to take place via a spark plug, although such a plug represents a wearing part that entails a corresponding maintenance effort.

It is the object of the present invention to overcome or partially mitigate the above disadvantages, which is achieved with a method having all the steps of claim 1 or an internal combustion engine having the features of claim 10.

• Einführen, insbesondere Einspritzen bzw. Einblasen des verflüssigten oder gasförmigen Gemisches in einen Brennraum,
• Entzünden des in dem Brennraum eingeführten Gemisches, und
• Nutzen der Expansion des entzündeten Gemisches zum Antrieb der Brennkraftmaschine, vorzugsweise ferner umfassend den Schritt
• vor dem Schritt des Einführens in den Brennraum; Verflüssigen des Gemisches durch Erzeugen eines Überdrucks, vorzugsweise durch einen Überdruck von mindestens 5 bar, bevorzugterweise 8 bar, und besonders bevorzugterweise 9 bar und einem Überdruck von höchstens 60 bar, bevorzugterweise höchstens 20 bar, und besonders bevorzugterweise höchstens 10 bar.

According to the method according to the invention, it is provided to operate an internal combustion engine with a mixture of or containing ammonia and dimethyl ether, with the following steps also being 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 power the internal combustion engine, preferably further comprising the step of
• prior to the introducing step into the combustion chamber; Liquefaction of the mixture by generating an overpressure, preferably an overpressure of at least 5 bar, preferably 8 bar and particularly preferably 9 bar and an overpressure of at most 60 bar, preferably at most 20 bar and particularly preferably at most 10 bar.

The use of the ammonia-dimethyl ether mixture, which is known from the prior art but has not received any attention as an alternative fuel, is regarded as a significant difference from the prior art. The use of the claimed mixture is limited to refrigeration applications, since the advantages that can be achieved with it have not been recognized.

The mixture of ammonia and dimethyl ether (also abbreviated: DME) forms a so-called azeotropic mixture in which the vapor phase and the liquid state have the same composition. The behavior is thus similar to that of a pure substance, although the ignition temperature in the present mixture of ammonia and dimethyl ether is advantageously lower than that of pure ammonia and the lower ignition limit of air is also reduced.

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

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.

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

The use of an azeotropic mixture (comprising ammonia) improves the cha characteristic combustion properties of ammonia in a considerable way. This can be seen in the example of R-723, in which the ignition temperature increases from 630 °C to 440 °C and the lower ignition limit of air falls from 15% to 6%.

According to the method, provision can also be made for a spark plug, which ignites the mixture, to ignite the introduced (eg injected or blown in) mixture in the combustion chamber.

Even if the provision of a spark plug is another component that is subject to wear, its use in petrol engines has been tried and tested and reliably ensures that fuel that is not self-igniting is ignited.

Alternatively or additionally, the invention can provide for a pre-injection with a self-igniting fuel to ignite the injected mixture in the combustion chamber, so that ignition of the pre-injection leads to ignition of the subsequently injected mixture, with the self-igniting fuel preferably being diesel and / or dimethyl ether contains or consists of it.

In order to make the use or provision of a spark plug obsolete, the main injection, which consists of the non-self-ignitable fuel, can be ignited with the aid of a pre-injection according to the method according to the invention. In this case, before the main injection, a self-ignitable fuel is introduced into the combustion chamber, which is then ignited due to compression or other influences. A non-self-igniting fuel (main injection) introduced only shortly after the introduction of the pilot injection is then also ignited due to the ignition of the pilot injection.

It is particularly advantageous that dimethyl ether can be used as a pre-injection, as this, with a cetane number greater than 55, 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 .

It is particularly advantageous here that the fuel for the pre-injection (DME) is part of the fuel for the main injection, so that the provision of different fuel types is not absolutely necessary, since dimethyl ether can be separated from the ammonia-dimethyl ether mixture. It is not necessary to keep and refuel a vehicle with two different fuels, since the appropriate fuel for the pre-injection can be obtained from the mixture.

According to an optional modification of the invention, it can therefore be provided that the pre-injection takes place with dimethyl ether, which has been separated from the liquefied mixture of ammonia and dimethyl ether, with preferably the pre-injection via the identical supply as the mixture, but before this, in the Combustion chamber is introduced.

Provision can also be made for the pre-injection to take place via a separate injector or via the same injector as the main injection

If one also uses an identical feed into the combustion chamber, one of the two feed lines typically provided in the prior art for the different injection processes (pilot injection and main injection) is omitted.

However, to make the timing easier to manage, a separate injector and a separate injector line can also be provided.

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 more preferably more than 900 bar before being injected into a combustion chamber.

It is clear to the person skilled in the art that the pressure ranges applicable according to the prior art for the injection system can be used depending on the selected aggregate state of the azeotropic mixture and the selected combustion process concept.

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

The after-treatment of exhaust gas makes a significant contribution to minimizing the pollutants produced during the combustion process. In a selective catalytic reduction, e.g. so-called SCR catalysts, there is a small urea tank from which urea is converted into ammonia with the help of thermolysis and hydrolysis. Is now used according to the invention mixture of ammonia and dimethyl ether, after separating these two components, the urea tank required for effective exhaust gas purification can also be dispensed with, since ammonia is already present in the mixture due to the separation of dimethyl ether.

In addition, it can also be provided according to the invention that, after the injected mixture has been ignited, dinitrogen monoxide is separated from the exhaust gas and, if necessary, fed back into the combustion chamber via an intermediate gas store.

Since nitrous oxide (N ₂ O), so-called nitrous oxide, is produced when ammonia is burned, nitrous oxide can be extracted from the exhaust gas with the help of a catalyst or a separator unit specially designed for it and introduced into an intermediate gas storage facility. The provision of an intermediate gas store is only advantageous if a sufficient quantity of dinitrogen monoxide accumulates. If this is not the case, it can also be advantageous to use a neutralization unit to neutralize the nitrous oxide that occurs.

If the power of the internal combustion engine is to be increased for a short time, the nitrous oxide can then be fed into the combustion chamber, resulting in an increase in power. Such a nitrous oxide injection, which is used for short-term power boosts of the internal combustion engine, is known in particular from racing.

The invention also relates to an internal combustion engine for carrying out a method according to one of the variants discussed above.

The internal combustion engine according to the invention for operation with a mixture of ammonia and dimethyl ether comprises a fuel tank for holding the mixture in the liquid state at an overpressure, preferably at an overpressure of at least 5 bar, preferably 8 bar, and particularly preferably 9 bar and an overpressure of at most 20 bar, 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 in the fuel tank into the combustion chamber, and is characterized by a connected to the fuel tank Separation unit for separating the components of the mixture into pure ammonia and pure dimethyl ether.

As explained above in connection with the method according to the invention, the individual components of the ammonia-dimethyl ether mixture can be advantageous in their pure form and also the provision and refilling of specific tanks for alternative substances (e.g. urea for SCR catalysis or second fuel for a pre-injection) superfluous.

The separation unit can use a membrane to separate the two components of the mixture from one another, with the mixture preferably being in a gaseous state for this purpose. Provision can therefore be made for the separation unit to separate the components of the mixture using a separating membrane. A pressure reducer can be provided for the conversion into the gaseous state.

Alternatively or additionally, it can be provided that the separation of the two components can also be carried out successfully when the fuel is in a liquid state. The principle of reverse osmosis is then used here, so that it is not necessary to convert the liquid fuel into the gaseous form.

Provision can therefore be made for the separation unit to separate the components of the mixture using reverse osmosis, in which case the mixture can be in the liquid state.

In addition, according to an optional modification of the present invention, it can be provided that the internal combustion engine is also provided with a store for dimethyl ether, which is fed by the separation unit and has an outlet line connected to the fuel line, with the quantity of to be introduced dimethyl ether is adjustable.

Alternatively, it can also be provided that a separate line is provided from the store for dimethyl ether for supply to the combustion chamber.

In this way, a sufficient quantity of dimethyl ether can always be kept available, which can be used as a self-igniting fuel for a pre-injection.

Alternatively or additionally, it can be provided that the internal combustion engine is also provided with an accumulator for ammonia, which is fed by the separation unit and has an outlet line connected to a catalytic converter, in particular an SCR catalytic converter, with the catalytic converter serving to to clean emitted exhaust gas, preferably in terms of NO _x emissions.

The storage of ammonia can be used for a selective catalytic reduction in the catalyst. It is no longer necessary to supply another substance in addition to the fuel itself, since ammonia can be generated from the mixture. In the internal combustion engine according to the invention, an additional filling opening is therefore not required, and no separate filling of such an additive (urea, commercial designation including AddBlue) has to be taken into account when operating such an internal combustion engine

According to a further optional modification of the present invention, it can be provided that the internal combustion engine is provided with a separator unit which is arranged in an exhaust gas line of the internal combustion engine and is designed to cut off nitrous oxide occurring during the combustion of the mixture, with a gas intermediate storage preferably being provided to temporarily store the separated nitrous oxide and return it to the combustion chamber if required.

The combustion of ammonia or the azeotropic mixture of ammonia and dimethyl ether produces nitrous oxide, which can be separated from the exhaust gas and, if necessary, returned to the combustion chamber in order to increase the power of the internal combustion engine.

According to an advantageous variant of the present invention, it can be provided that the internal combustion engine is also provided with a control unit which is 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 thereby carry out a self-igniting pre-injection form, with the help of which the subsequently injected mixture (ammonia, DME and possibly air) is ignited.

The present invention also relates to the use of a mixture of ammonia and dimethyl ether as a fuel in an internal combustion engine. It can be provided that the mixture consists of 55-65%, preferably 60%, ammonia and 35-45%, preferably 40%, dimethyl ether and preferably consists of R-723.

• 1: eine Prinzipskizze einer erfindungsgemäßen Brennkraftmaschine.

Further features, details and advantages of the invention can be seen from the following description of the figures. It shows:

• 1 : a schematic diagram of an internal combustion engine according to the invention.

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 . The non-self-ignitable mixture is then ignited in the combustion chamber 4 and used to drive a piston. The combusted mixture is then discharged from the combustion chamber 4 via an exhaust pipe 13, so that the combustion chamber 4 is available for the ammonia-dimethyl ether mixture to be fed in again. It is clear to the person skilled in the art that a spark plug, for example, can be provided for ignition in the combustion chamber 4, or that a self-igniting mixture can be ignited beforehand by means of a compression of the piston, so that a subsequently introduced non-self-igniting mixture (in this case Ammonia and dimethyl ether) can be ignited by igniting the self-igniting mixture.

A separation unit 5 is also connected to the fuel tank 2 and 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 associated with the internal combustion engine 1 . The separation unit 5 thus separates the individual components ammonia and dimethyl ether and feeds them to a respective storage device 6, 9.

The reservoir 6 for dimethyl ether has an outlet line 7 connected to the fuel supply line 3 so that it is also possible to introduce pure dimethyl ether into the combustion chamber 4 . Since pure dimethyl ether is self-igniting, the self-igniting dimethyl ether can first be introduced into a combustion chamber 4 in this way, so that a subsequently introduced mixture from the fuel tank 2 is ignited due to ignition of the pure dimethyl ether (e.g. caused by compression). . The separate refueling of the internal combustion engine with its own self-ignitable fuel is therefore not necessary, so that the operating effort of the internal combustion engine is reduced.

For example, it can be provided that the reservoir for dimethyl ether 6 is 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 the desired times.

Downstream of the supply valve 8, the components known to those skilled in the art for filtering and pressurizing in the combustion space 4 fluid to be introduced may be arranged. The fluid to be introduced into the combustion chamber 4 can first run through a pre-filter 15 before it is brought to an intermediate pressure level by a first feed pump 16 . It is then typically passed through a further filter 17 before the fluid to be introduced into the combustion chamber 4 is brought to the final pressure level by means of a high-pressure pump 18 . There is also a fluid connection from the high-pressure pump 18 back to the fuel tank 2, so that a leakage occurring at the high-pressure pump 18 can be fed back. Alternatively or additionally, however, it is also possible that when highly pressurized fuel (ammonia-dimethyl ether mixture or pure dimethyl ether) is available but not needed in combustion chamber 4 , it is simply fed back into fuel tank 2 .

Starting from the separation unit 5 there is also a store 9 for ammonia, which has an outlet line 11 which leads to a unit for exhaust gas aftertreatment 10, 12.

An exhaust gas aftertreatment unit is provided in the exhaust gas line 13 downstream of the combustion chamber 4, for example in the form of a catalytic converter 10, which is designed to filter out pollutants from the exhaust gas flow. The exhaust aftertreatment unit can carry out a selective catalytic reduction in order to reduce NOx pollutants.

Those skilled in the art know that such a selective catalytic reduction requires ammonia, which in conventional applications is obtained from urea by thermal and hydrolysis. The user is prompted to ensure that this urea (brand name: e.g. AddBlue) is also refilled after a certain time interval in order to be able to continue operating the selective catalytic reduction. For this purpose, a further, smaller opening area is typically provided in the area of the fuel tank opening, via which the urea can be filled into a separate tank.

According to the present invention, there is no need to provide a separate opening area for feeding in urea or an agent required for the selective catalytic reduction, since the ammonia required for this can be generated directly from the fuel mixture.

In addition, one recognizes in 1 a recirculation line directed from the exhaust gas aftertreatment unit 10, 12 to the combustion chamber 4, which has a tank 14 for nitrous oxide (N ₂ O). Specifically, the exhaust gas aftertreatment unit can further comprise a separator unit 12 which filters out the nitrous oxide contained in the exhaust gas from the exhaust gas flow and introduces it into the tank 14 for nitrous oxide. From there it can then be introduced directly into the combustion chamber 4, if required, so that the power of the internal combustion engine can be increased. The operating principle of nitrous oxide injection is known from racing, although the nitrous oxide to be injected does not come from the exhaust gas flow, but is kept in separate tanks.

Reference List

1

internal combustion engine

2

fuel tank

3

fuel supply line

4

combustion chamber

5

separation unit

6

Storage for dimethyl ether

7

output line

8th

supply valve

9

storage for ammonia

10

catalyst

11

output line

12

separator unit

13

exhaust pipe

14

intermediate gas storage

15

pre-filter

16

pre-feed pump

17

filter

18

high pressure pump

Claims (15)

Method for operating an internal combustion engine (1) with a mixture of or containing ammonia and dimethyl ether, comprising the steps: 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). mixture, and utilizing the expansion of the ignited mixture to drive the internal combustion engine (1), preferably further comprising the step preceding the step of introducing it into the combustion chamber (4); Liquefaction of the mixture by generating an overpressure, preferably an overpressure of at least 5 bar, preferably 8 bar, and particularly preferably 9 bar and an overpressure of at most 60 bar, preferably tertially at most 20 bar, and particularly preferably at most 10 bar. procedure after claim 1 wherein the mixture is an azeotropic mixture and/or consists of 55-65%, preferably 60%, ammonia and 35-45%, preferably 40%, dimethyl ether and preferably consists of R-723. Method according to one of the preceding claims, a spark plug which ignites the mixture being provided in the combustion chamber (4) in order to ignite the injected or blown-in mixture. Method according to one of the preceding claims, wherein a pre-injection with a self-igniting fuel takes place beforehand to ignite the mixture introduced in the combustion chamber (4), so that ignition of the pre-injection leads to ignition of the subsequently injected mixture, the self-igniting fuel preferably being diesel and/or Contains or consists of dimethyl ether. Procedure after the previous one claim 4 , wherein the pre-injection takes place with dimethyl ether, which has been separated from the liquefied or gaseous mixture of ammonia and dimethyl ether, with the pre-injection preferably being introduced into the combustion chamber via the identical supply as the mixture, but before this. Method according to one of the preceding claims, in which the liquefied 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 before being injected into a combustion chamber (4). Method according to one of the preceding claims, in which an exhaust gas produced after igniting the introduced mixture in the combustion chamber (4) is subjected to exhaust gas aftertreatment using ammonia which has preferably been separated from the liquefied or gaseous mixture of ammonia and dimethyl ether. Method according to one of the preceding claims, in which, after the mixture introduced has been ignited, dinitrogen monoxide is separated from the exhaust gas and, if required, is returned to the combustion chamber (4) via an intermediate gas store. Internal combustion engine (1) for carrying out a method according to any one of the preceding claims. Internal combustion engine (1) for operation with a mixture of or containing ammonia and dimethyl ether, preferably after claim 9 , comprising: a fuel tank (2) for receiving the mixture in liquid or gaseous state at an overpressure, preferably at an overpressure of at least 5 bar, preferably 8 bar, and particularly preferably 9 bar and an overpressure of at most 60 bar, preferably 20 bar , and particularly preferably 10 bar, and a fuel supply line (3), which connects the fuel tank (2) to a combustion chamber (4) of the internal combustion engine (1) and serves to feed the mixture in the fuel tank (2) into the combustion chamber (4 ) to introduce, characterized by a fuel tank (2) connected to the separation unit (5) for separating the components of the mixture into pure ammonia and pure dimethyl ether. Internal combustion engine (1) according to the preceding one claim 10 , furthermore with a reservoir (6) for dimethyl ether, which is fed by the separation unit (5) and has an outlet line (7) connected to the fuel supply line (3), wherein the quantity of dimethyl ether fed into the fuel supply line (3 ) to be introduced dimethyl ether is adjustable. Internal combustion engine (1) according to any one of the preceding Claims 10 or 11 , furthermore with a store (9) for ammonia, which is fed by the separation unit (5) and has an outlet line (11) connected to a catalytic converter (10), in particular an SCR catalytic converter, the catalytic converter (10) serving to to clean an exhaust gas emitted from the combustion chamber (4), preferably with regard to the NO _x emissions. Internal combustion engine (1) according to any one of the preceding Claims 10 - 12 , further having a separator unit (12) which is arranged in an exhaust pipe (13) of the internal combustion engine (1) and is designed to cut off nitrous oxide produced during the combustion of the mixture, with an intermediate gas storage device (14) preferably being provided to collect the separated To temporarily store nitrous oxide and, if necessary, to return it to the combustion chamber (4). Internal combustion engine (1) according to any one of the preceding Claims 10 - 13 , trained with the characteristics of Claim 11 , further with a control unit which is designed to carry out a combustion process in the combustion chamber (4) to first inject the dimethyl ether obtained via the separation unit (5) in order to create a self-igniting pre-injection which is used to ignite the subsequently injected mixture. Use of a mixture of ammonia and dimethyl ether, preferably developed with the features of claim 2 , as fuel in an internal combustion engine (1).

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