Method for operating an internal combustion engine with the use of ammonia, internal combustion engine, and quick start device for an internal combustion engine of this type

Abstract

The invention relates to a method for operating an internal combustion engine with the use of ammonia as fuel, wherein ammonia is cracked by means of a cracker at least into a hydrogen / nitrogen mixture, and wherein, during starting of the internal combustion engine, first of all a gas comprising at least hydrogen is fed in from a starting store, in order to avoid a starting delay on account of the cracking of the ammonia, and subsequently the hydrogen / nitrogen mixture which is cracked at the cracker is fed to the internal combustion engine. The invention also relates to a quick start device and to an internal combustion engine for direct combustion of ammonia. The invention avoids the disadvantages of the prior art and, in the case of a combustion engine with ammonia as the sole fuel, ensures low-emission and direct starting (quick start) without relatively long preheating measures.

Description

[0001] Method for operating an internal combustion engine using ammonia, internal combustion engine and quick-start device for such an internal combustion engine

[0002] Field of the invention

[0003] The present invention relates to a method for operating an internal combustion engine using ammonia, an internal combustion engine and a quick-start device for such an internal combustion engine.

[0004] Background of the invention

[0005] Electromobility is reaching its capacity limits, especially in heavy-duty transport with long ranges. Ships, trains on non-electrified routes, heavy trucks, etc., in particular, are not suitable for everyday use in the foreseeable future when powered by electric batteries.

[0006] Hydrogen has the disadvantage of poor storage capacity and difficult handling by users.

[0007] Ammonia produced without CO2, so-called green ammonia, can also be used as a stream-based fuel and offers the advantage that it can be stored and transported cost-effectively in liquid form, does not require a carbon source and thus remains CO2-neutral and is available on an industrial scale.

[0008] When ammonia is burned under optimal conditions, only water and nitrogen are produced. A disadvantage compared to conventional fuels is the poor flammability and low flame speed of ammonia-air mixtures, which makes their use in heat engines difficult. To overcome this disadvantage, a small amount of hydrogen can be added to the ammonia, whereby the hydrogen acts as an igniter for the low-combustibility ammonia. Mixing ratios of 4:1 to approximately 10:1, based on the energy content, between ammonia and hydrogen are possible to obtain a combustible gas mixture for operating a heat engine. The combustion of pure ammonia is also possible, but results in losses in power and efficiency.

[0009] EP 3 859 138 A1 discloses a method for operating a diesel engine as a dual-fuel engine using two different fuels, with diesel or heavy fuel oil serving as the first fuel. A gaseous fuel consisting of a mixture of ammonia and hydrogen is used as the second fuel, with the gas mixture being ignited by injecting a small amount of diesel oil as ignition oil. However, such dual-fuel systems also require the refueling of two separate tank systems with different fuel types, which limits or prevents handling in some applications.

[0010] Hydrogen can be produced from ammonia itself, as disclosed, for example, in EP 3 028 990 A1. This means that only ammonia is used as a fuel. Hydrogen is produced using an energy-autonomous fission reactor that splits ammonia with high efficiency into the elements 2 NH3 => 3 H2 + N2. The resulting gas mixture contains 75% hydrogen and 25% nitrogen. This converts ammonia, which in practice is hardly usable as a fuel, into a highly flammable gas. The hydrogen thus obtained is added to the main stream of ammonia, and the gas mixture can be used as fuel in heat engines as usual. The residual nitrogen can undergo the combustion process as an inert gas.

[0011] When using a fuel system with only ammonia as

[0012] Fuel, additional measures are required, particularly when starting and operating a cold engine. In large engines or for ship propulsion, for example, upstream stationary cracking units for the (partial) splitting of NH3 into H2 and N2, as well as preheaters to operate the engine, are known. The crackers used in this case are heated externally, electrically or via burners. Alternatively, there are also concepts that use the exhaust gas temperature of the engine for heating. In mobile applications, for example in motor vehicles, there is also the requirement for quick start-up and low-emission engine warm-up. Long preheating phases are often not possible in these cases.

[0013] In particular, the first few seconds after the engine starts usually have a decisive influence on the engine's emissions.

[0014] Summary of the invention

[0015] It is therefore the object of the present invention to propose a method and a device which avoid the disadvantages of the aforementioned prior art and ensure a low-emission and direct start (quick start) without lengthy preheating measures in an internal combustion engine using ammonia as the sole fuel.

[0016] This object is achieved by a method for operating an internal combustion engine using ammonia as fuel with the features of claim 1, a quick-start device for an internal combustion engine for the direct combustion of ammonia with the features of claim 9, and an internal combustion engine for the direct combustion of ammonia with the features of claim 17. Advantageous developments and embodiments of the invention are specified in the dependent claims.

[0017] The method according to the invention for operating an internal combustion engine using ammonia as fuel, wherein ammonia is cracked into at least a hydrogen-nitrogen mixture by means of a cracker, initially comprises at least one gas containing hydrogen and nitrogen when the internal combustion engine is started, which gas is supplied from a start-up reservoir in order to avoid a start-up delay due to the cracking of the ammonia, and wherein the hydrogen-nitrogen mixture cracked in the cracker is then supplied to the internal combustion engine. In this case, the gas may, in addition to hydrogen and nitrogen, also optionally contain residual ammonia that was not fully converted in the cracker. The method according to the invention eliminates the need for additional fuels, and the internal combustion engine can be operated exclusively with ammonia.The method according to the invention avoids the disadvantages of the aforementioned prior art and ensures a low-emission and direct start (quick start) without lengthy preheating measures in an internal combustion engine using ammonia as the sole fuel.

[0018] An advantageous embodiment of the process according to the invention provides that any ammonia remaining after cracking is condensed out and returned to the cycle. The advantage of this condensation is that, downstream of the cracker, an H2 / N2 mixture that is up to 100% ammonia-free is present.

[0019] An advantageous embodiment of the process according to the invention provides for a high-pressure evaporator and a high-pressure cracker. The advantage here is that the compressed liquid ammonia present in the tank can now be passed through the high-pressure cracker in gaseous form, virtually maintaining the previously generated pressure level.

[0020] Another advantageous embodiment of the method according to the invention provides that, alternatively or in addition to the high-pressure evaporator and high-pressure cracker, a low-pressure evaporator and a low-pressure cracker are provided. This low-pressure path then has the function of splitting the ammonia for the majority of the required injection quantity for operating the internal combustion engine into a proportional amount of an H2 / N2 mixture based on the total amount of fuel located downstream in the cracker path.

[0021] A further advantageous embodiment of the method according to the invention provides that a portion of the hydrogen-nitrogen mixture produced in the cracker is stored in the starting accumulator. The other portion of the mixture is supplied to the engine via direct injection.

[0022] Yet another advantageous embodiment of the method according to the invention provides for liquid ammonia to be stored in at least one high-pressure ammonia tank. This allows not only a higher storage density but also compression of the ammonia to the required injection pressure in the liquid phase, thus achieving energy savings.

[0023] Yet another advantageous embodiment of the process according to the invention provides that the at least one cracker is heated via an exhaust gas heat exchanger and / or an electric heater. This enables the cracker to heat up quickly and with favorable energy consumption.

[0024] Yet another advantageous embodiment of the method according to the invention provides that the high-pressure ammonia tank has an additional internal ammonia tank. This ensures that, regardless of the fill level of the main tank, the ammonia pressure is sufficient to fill the starting reservoir.

[0025] Finally, a further advantageous embodiment of the method according to the invention provides for a high-pressure direct injection and / or a low-pressure fuel rail injection.

[0026] The quick-start device according to the invention for an internal combustion engine for the direct combustion of ammonia comprises a high-pressure ammonia tank, an evaporator, a cracker connected thereto, a fuel injection system of the internal combustion engine, and a starting accumulator. An advantageous embodiment of the quick-start device according to the invention provides that the starting accumulator has a pressure of 1 bar to 40 bar, preferably 3 bar to 20 bar. 3 bar represents the lower pressure when the starting accumulator is almost empty. The pressure of 20 bar is the upper pressure when the starting accumulator is full. In non-supercharged engines, the lower pressure could be reduced to as low as 1 bar. At a pressure of up to 40 bar, the condensation temperature could be increased to approximately 80°C, which might be advantageous for reliable condensation in the high-pressure cooler.

[0027] A further advantageous embodiment of the quick-start device according to the invention provides that the starting accumulator has a volume of 3 liters to 80 liters, preferably 5 liters to 50 liters, particularly preferably 10 to 30 liters. The size of the starting accumulator volume is determined not only by the maximum accumulator pressure, but also by the heating time of the cracker path(s) and the available installation space, and also depends on the size of the internal combustion engine.

[0028] Another advantageous embodiment of the quick-start device according to the invention provides that the starting reservoir is connected to a cracker. This cracker supplies a proportional amount of an H2 / N2 mixture to the starting reservoir.

[0029] Yet another advantageous embodiment of the quick-start device according to the invention provides for a two-way valve for filling, emptying, and closing the starting reservoir. A control valve is also conceivable for this purpose, enabling gradual opening, thus avoiding a sudden drop in pressure. The advantage of this also lies in the possibility of specifically applying the pressure behavior of the injection path when switching to the various operating modes of the internal combustion engine.

[0030] Yet another advantageous embodiment of the quick-start device according to the invention provides for an additional pump to fill the starter reservoir. By using such an additional pump, a starter reservoir could be filled and used even if the high-pressure cracker path were eliminated.

[0031] Yet another advantageous embodiment of the quick-start device according to the invention provides for a filling device for externally filling the starter reservoir. Externally filling the starter reservoir also allows for a comparatively simple retrofitting of the quick-start device into an internal combustion engine with an existing low-pressure system.

[0032] Yet another advantageous embodiment of the quick-start device according to the invention provides that the starter reservoir can be filled with a gas mixture comprising hydrogen and nitrogen and, when filled, at a pressure of 20 bar to 40 bar and / or a temperature of up to 80°C. This provides sufficient time to bring the cracker system(s) to operating temperature during low-emission engine operation.

[0033] Yet another advantageous embodiment of the quick-start device according to the invention provides that the fuel injection system is provided as a port injection.

[0034] Finally, a further advantageous embodiment of the quick-start device according to the invention provides that the fuel injection system is provided as a direct injection system.

[0035] The internal combustion engine according to the invention for the direct combustion of ammonia provides the quick start device according to the invention described above.

[0036] An advantageous embodiment of the internal combustion engine according to the invention provides for an exothermic heating device for a high-pressure cracker, wherein at least one line and nozzle are provided for supplying hydrogen generated by the cracker to an oxidation coating for catalytic heat generation. The high-pressure cracker can be a shell-and-tube heat exchanger.

[0037] A further advantageous embodiment of the internal combustion engine according to the invention provides for at least one electric heater in the area of ​​the high-pressure cracker, preferably in the exhaust gas bypass of the internal combustion engine (ICE). The electric heater can be provided in the exhaust gas stream or in the NH3 / H2 / N2 path.

[0038] A further advantageous embodiment of the internal combustion engine according to the invention provides that the operating temperature of the high-pressure cracker is greater than or equal to 600 °C.

[0039] A further advantageous embodiment of the internal combustion engine according to the invention provides for an electronic control device to control the cracker system. This can be configured, for example, as a cracker ECU.

[0040] A further advantageous embodiment of the internal combustion engine according to the invention provides for an air blower to flow gas, preferably air, through the cracker when the ICE is stationary, in order to enable appropriate heat transfer from the exothermic heating device into the cracker module. This allows a sufficient amount of H2 / N2 to be generated to refill the start / buffer storage.

[0041] A further advantageous embodiment of the method according to the invention provides that a step for automatically refilling the starter reservoir after a stop of the internal combustion engine (ICE) is provided, in which an air blower 30 flows through the cracker with gas, preferably air, when the ICE is stopped in order to enable a corresponding heat transport of the exothermic heating device into the cracker.A further advantageous embodiment of the method according to the invention provides that a step for heating the high-pressure cracker is provided after the engine has started, in which step, during the supply of the hydrogen-nitrogen mixture to the internal combustion engine (ICE) from the start-up storage, an electrical heater on the fuel side in the region of the high-pressure cracker enables a gas containing at least hydrogen to flow through the high-pressure cracker, which has an advantageous effect on the heat transfer and thus on the heating and thus on the speed at which the high-pressure cracker is ready for operation.

[0042] Short description of the characters

[0043] Further measures improving the invention are presented in more detail below together with the description of preferred embodiments of the invention with reference to the figures.

[0044] It shows

[0045] Figure 1 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and integration into the exhaust gas aftertreatment system as well as with component groupings of the two fuel paths according to a first embodiment;

[0046] Figure 2 shows a schematic representation of the internal combustion engine according to the invention with a quick-start device with integration into the exhaust gas aftertreatment according to the first embodiment;

[0047] Figure 3 shows a schematic representation of the internal combustion engine according to the invention with a quick-start device according to the first embodiment; Figure 4 shows an overview table of internal combustion engines according to the invention with a quick-start device, showing parameters of injection, temperature and pressure ranges, and switching positions of various valves according to the first embodiment;

[0048] Figure 5 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and a large high-pressure cracker and 3 bar / 20 bar injection DI according to a second embodiment;

[0049] Figure 6 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and a large high-pressure cracker and 3 bar injection PI according to embodiment 3a; an internal combustion engine according to the invention with a quick-start device and only one large high-pressure cracker and 3 bar injection DI according to embodiment 3b;

[0050] Figure 7 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and a large low-pressure cracker and compressor and 3 bar injection PI (embodiment 4a); only with a low-pressure cracker and compressor and 3 bar injection DI (embodiment 4b);

[0051] Figures 8a and 8b show a schematic representation of an internal combustion engine according to the invention with a quick-start device and a second fuel tank according to a fifth embodiment;

[0052] Figure 9 shows a further embodiment in which the two injection paths used in the invention are integrated into the cylinder head of an internal combustion engine (ICE);

[0053] Figure 10 shows a simplified schematic representation of a connection of an exothermic heating device to an extended high-pressure cracker (OHC cracker); Figure 11 shows a detailed representation of a high-pressure cracker 24 (OHC cracker) integrated into the exhaust system of the internal combustion engine (ICE) with an exothermic heating device;

[0054] Figure 12 shows a first embodiment of a high pressure cracker 24 (OHC cracker) with an exothermic heating device, referred to here as OHC1;

[0055] Figure 13 shows a first embodiment of a high pressure cracker 24 (OHC cracker) with exothermic heating device, referred to here as OHC2;

[0056] Figure 14 shows a first embodiment of a high pressure cracker 24 (OHC cracker) with exothermic heating device, referred to here as OHC3;

[0057] Figure 15 shows a first embodiment of a high pressure cracker 24 (OHC cracker) with exothermic heating device, referred to here as OHC4;

[0058] Figure 16 shows the cracker path integrated into the exhaust system of the internal combustion engine using the example of the OHC4 cracker with integrated start / buffer storage;

[0059] Figure 17 shows the connection of the system to a cracker ECU used to control the processes;

[0060] Figure 18 shows a section of the cracker path for the function of the start / buffer memory as an intermediate buffer;

[0061] Figure 19 shows the potential of the filling / supplementation areas of the start / buffer storage system in a characteristic map of an ICE using the example of a 4-cylinder naturally aspirated engine; Figure 20 shows a refilling process after switching off the ICE with the switching positions of the essential valves / actuators as shown in Figure 17.

[0062] Detailed description of the implementation examples

[0063] Embodiment 1

[0064] In a first embodiment according to Figure 1, the internal combustion engine according to the invention has a quick-start device with a connected starter reservoir 1. The starter reservoir 1 preferably has a volume of 5 to 50 liters and is shown in a design suitable for hydrogen storage. In order to achieve the lowest possible weight with high rigidity, fiber composite materials, for example made of carbon fibers, are preferably used.

[0065] In this exemplary embodiment, the start-up accumulator 1 is filled with a H2 / N2 mixture metered up to 100% via the high-pressure cracker path before the internal combustion engine is shut down while the engine is at operating temperature. A 2-way valve V-SS1 or a control valve is connected upstream of the start-up accumulator 1 for this purpose. The high-pressure cracker draws the ammonia from the high-pressure ammonia tank (>20 bar). The pressure in the high-pressure tank 2 is selected such that the ammonia in the high-pressure tank 2 is preferably in the liquid phase. High-pressure tank 2 optionally has an additional internal ammonia tank >20 bar 3. If the pressure in high-pressure tank 2 is lower than the pressure intended for start-up accumulator 1, the fuel pump is used to pressurize the internal ammonia tank >20 bar 3 with a portion of the fuel to the pressure level intended for the high-pressure cracker path. This pressure level is in the range of approximately 20 bar to 40 bar.As an alternative to the internal ammonia tank >20 bar 3, a pump package with a return line to the high-pressure ammonia tank 2 could also be provided. A high-pressure evaporator 8 is arranged downstream of the high-pressure tank 2. In the high-pressure evaporator 8, the liquid ammonia is converted into the gas phase by the addition of thermal energy, for example from the HP-C cooler downstream of the cracker 4, and is fed to the high-pressure cracker 4 as preferably superheated dry steam. The ammonia is at almost the same pressure at which the ammonia leaves the fuel tank 2 or the internal fuel tank 3. This pressure level is in the range of approximately 20 bar to 40 bar.

[0066] In the high-pressure cracker 4, the ammonia is split into its components H2 and N2 at high temperatures, as described above. Residual amounts of ammonia can also leave the high-pressure cracker 4. The high-pressure cracker 4 is preferably designed as a countercurrent gas / gas heat exchanger. This design allows high efficiencies to be achieved in a small installation space. In the present exemplary embodiment, the high-pressure cracker 4 is coated with nickel or cobalt, for example. A temperature level of greater than 600°C is selected, since the best cracker efficiencies are achieved with a nickel coating.

[0067] In the downstream high-pressure cooler (HP-C), the hydrogen-nitrogen-ammonia gas mixture is cooled below the ammonia's condensation temperature, and the liquefied ammonia is fed back into the upstream path. The now highly dosed H2 / N2 gas mixture is released via the fuel rail of high-pressure path 17 by direct injection. For this purpose, the 2-way valve upstream of fuel rail 17 is switched to the P-DI high-pressure regulator at approximately 20 bar.

[0068] At the same time, the starting storage 1 is filled with the H2 / N2 gas mixture until the starting storage is completely filled.

[0069] The injection of the H2 / N2 gas mixture via the injectors of the fuel rail 17 into the internal combustion engine takes place in the “engine operation warm” mode described above, as shown in Figure 4, as a pilot injection of a portion of the fuel required to operate the internal combustion engine during the compression phase and also serves as a catalytic converter afterheating injection during the exhaust phase of the internal combustion engine.

[0070] Injection management via the high-pressure cracker path achieves excellent ignition behavior of the H2 / N2 gas mixture in the internal combustion engine. In the illustrated embodiment, the internal combustion engine has an additional, so-called low-pressure cracker path in addition to the high-pressure cracker path described above.

[0071] The low-pressure cracker path is also connected to the ammonia high-pressure tank >20 bar 2 and, in addition to pressure regulators and other components, has a low-pressure evaporator ? downstream of the high-pressure tank 2, a low-pressure cracker 5 downstream of this, a low-pressure cooler downstream of this, and a fuel rail 14 with the port injection injectors.

[0072] The main fuel quantity of the internal combustion engine is then injected via this low-pressure cracker path shown. The low-pressure cracker 5 is preferably also designed as a countercurrent gas / gas heat exchanger. Since the requirements for the degree of cracking, and thus for the proportion of the H2 / N2 mixture in the total amount of fuel downstream of the cracker path, are lower for the main fuel quantity of the low-pressure cracker path than for the high-pressure cracker path, the low-pressure cracker 5 can be initially ready for operation at lower temperatures starting at approximately 450°C.

[0073] In the “engine stop” mode of the internal combustion engine according to Figure 4, the start accumulator 1 is closed via the upstream valve V-SS1.

[0074] In the subsequent "engine start" mode, the start accumulator 1 is now opened via the upstream valve V-SS1. This enables the injection of the gaseous, highly dosed H2 / N2 mixture via the fuel rail 17 of the high-pressure path by means of direct injection, primarily into the intake phase and temporarily also into the exhaust phase of the internal combustion engine.

[0075] For this purpose, the 2-way valve upstream of the fuel rail 17 is switched to the P-DI low-pressure regulator at approximately 3 bar to enable the starting reservoir 1 to be emptied to this pressure. This continues until the high-pressure cracker 4 has reached its operating temperature of greater than approximately 600°C. This duration depends on the internal combustion engine used and the overall packaging in the vehicle and will take less than 60 seconds.

[0076] If the downstream low-pressure cracker 5 has also reached a temperature of greater than approximately 450°C and thus a sufficient degree of splitting of ammonia into H2 / N2 components for the main fuel mixture is achieved, the following four states occur simultaneously or in short intervals:

[0077] 1 . The high-pressure cracker path is released by switching the 2-way valve V-HP1 to the start accumulator 1 and the fuel rail 17.

[0078] 2. The starting reservoir 1 is closed via the valve V-SS1.

[0079] 3. The pilot injection with switching to the pressure regulator P-DI-high is activated.

[0080] 4. The low-pressure cracker path is released by switching the valve V-LP1 of the fuel rail 14, so that a port injection of the main fuel quantity of the internal combustion engine takes place.

[0081] The internal combustion engine now operates in parallel again with both injection paths (14 and 17). The internal combustion engine is now in "engine warm operation" mode again (Fig. 4), whereby the start accumulator 1 can be repeatedly filled for the next new start-up process by opening the valve V-SS1 or by opening an alternative control valve. The high-pressure cracker is heated via a heat exchanger by integrating the high-pressure cracker 4 into the exhaust gas system of the internal combustion engine and via an electric heater 6 of the high-pressure cracker 4. For this purpose, the high-pressure cracker 4 is installed downstream of the oxidation catalyst 9 located near the engine.

[0082] If necessary, a connection to an exhaust gas bypass 10 is made here in order to focus the heating measures specifically on the cracker path and to prevent the downstream catalysts 11 and 12 from being permanently exposed to excessively high temperatures.

[0083] The low-pressure cracker 5 is located downstream of the high-pressure cracker 4 in the exhaust system. It is preferably also designed as a counterflow gas / gas heat exchanger.

[0084] The optional electric heater 6 serves to support the heating or preheating of the crackers 4; 5, especially when the starter reservoir is not sufficiently filled for an existing engine start.

[0085] Due to the higher levels of nitrogen oxide (NOX) in the exhaust gases caused by the use of ammonia as a fuel, special measures for exhaust gas purification can be taken. In the version shown here, the exhaust aftertreatment system includes several catalysts:

[0086] A close-coupled oxidation catalyst 9 serves not only to heat the cracker but also to oxidize any unburned ammonia. It is preferably coated with a platinum-palladium group to enable early catalyst activation.

[0087] A downstream SCR catalyst 11 reduces the nitrogen oxide NOx produced from the combustion process by adding small amounts of ammonia. The ammonia is added via residual amounts of unburned ammonia from the combustion process via the exhaust gas duct 13 and / or by adding adjusted amounts upstream of the SCR catalyst 11 from the high-pressure ammonia tank 2.

[0088] A downstream optional ammonia slip catalyst (ASC-Oxi) 12 ensures low-N2O oxidation in the event of ammonia slip from the SCR catalyst 11. It is also designed as an oxidation catalyst and has a coating spectrum that reduces the formation of N2O.

[0089] In version 1 shown here, evaporators 7, 8, crackers 4, 5, and the two coolers HP-C and LP-C are designed in component groups A, B, C and A+C. These component groups are enclosed in Figure 1 with a dashed line and marked with the letters A, B, C or A+C. The groupings A, B, C shown are designed, for example, by using common components, such as housings, each with a high-pressure and low-pressure connection. Or by combining several components in one component, such as A+C, with A (evaporator 7 and / or 8) and C (cooler LP-C and / or HP-C).

[0090] This can bring advantages in terms of installation space, costs and efficiency in the respective designs.

[0091] Figure 2 shows the schematic representation of the internal combustion engine according to the invention with quick start device with integration into the exhaust gas aftertreatment according to the first embodiment.

[0092] Figure 2 shows embodiment 1 as already shown in Figure 1, wherein the individual components evaporator 7, 8, cracker 4, 5, and the two coolers HP-C and LP-C are not designed in component groups and thus not in common components. This can bring advantages in specific installation conditions in the application / vehicle to be used, for example if components designed together result in excessive modifications to other existing components of the internal combustion engine due to their larger design. Figure 3 shows the schematic representation of the internal combustion engine according to the invention with a quick-start device according to the first embodiment, wherein the integration into the exhaust gas aftertreatment is not shown here.

[0093] Embodiment 2

[0094] Figure 5 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and a large high-pressure cracker 4 and 3 bar / 20 bar injection DI according to embodiment 2. In contrast to the first embodiment, this embodiment does not have a second low-pressure cracker path. In the second embodiment, the entire fuel quantity to be injected is injected via the high-pressure cracker path via the injectors of the fuel rail 17.

[0095] Embodiment 3a and 3b

[0096] Figure 6 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and a large high-pressure cracker 4 and 3 bar injection PI via the injectors of the fuel rail 17 according to embodiment 3a; an internal combustion engine according to the invention with a quick-start device and only one large high-pressure cracker 4 and 3 bar injection DI via the injectors of the fuel rail 17 according to embodiment 3b.

[0097] Embodiments 4a and 4b

[0098] Figure 7 shows a schematic representation of an internal combustion engine according to the invention with a quick-start device and a large low-pressure cracker 5 and compressor 15 and 3 bar injection PI via the injectors of the fuel rail 14 (embodiment 4a); with only a low-pressure cracker and compressor and 3 bar injection DI via the injectors of the fuel rail 14 (embodiment 4b);

[0099] Embodiment 5

[0100] Figures 8a and 8b show the schematic representation of an internal combustion engine according to the invention with a quick-start device and a second fuel tank 16 and compressor 15 according to embodiment 5. The injection of the fuel quantity with the quick-start device switched off takes place via a separate low-pressure cracker path with high-pressure tank 2, evaporator 7, low-pressure cracker 5, injectors of the fuel rail 14 as direct injection or as port injection.

[0101] Embodiment 6

[0102] Figure 9 shows a further embodiment in which the two injection paths used in the invention are integrated into the cylinder head of an internal combustion engine (ICE). Via the "NH3 path," with the ICE at operating temperature, the main NH3 fuel quantity is introduced into the engine via a port injection (port injector) at an injection pressure of approximately 3 bar. In this embodiment, the NH3 path is designed without a low-pressure cracker. Via the high-pressure cracker path, the H2 / N2 quantity generated by crackers 4; 24 is additionally introduced into the engine's combustion chamber as a supply sub-quantity at an injection pressure of approximately 20 bar by direct injection (direct injection injector 18).

[0103] During start-up and when warming up the ICE, the cracker is switched off and the ICE is supplied with the H2 / N2 mixture previously generated by the cracker from the start-up reservoir 21, at a reduced injection pressure of approximately 3 bar. No injection takes place via the "NH3 path" when the ICE is started; with increasing operating time, the NH3 quantity can then be increased via the port injector up to the maximum quantity required by the ICE. Depending on the respective operating mode, the H2 / N2 quantity is introduced during the intake phase of the engine as injection mode DI-SE1 or DI-SE2, as shown in Figure 4, and / or during the compression phase as DI-ZE or during the exhaust phase as injection mode DI-AE; sometimes also divided into several injection events to improve mixing in the combustion chamber.

[0104] Depending on the respective operating mode, this H2 / N2 quantity is supplied either by fuel extraction via the high-pressure cracker 4; 24 from the NH3 fuel tank 2, by extraction of the quantity from the start storage 1; 21, or by a combination of both.

[0105] The high-pressure cracker 4 is heated, among other things, by an oxidation catalyst 9 provided upstream in the exhaust system of the ICE (see, for example, Figure 1), and by an electric heater 6. Heating via the oxidation catalyst 9 is provided by a catalytic converter heating injection mode; hereinafter referred to as an exothermic heating device. In this heating mode, hydrogen-containing fuel, either from the start-up accumulator or directly generated after the high-pressure cracker, is introduced into the combustion chamber of the ICE by direct injection, primarily during the expansion phase of the ICE.

[0106] The exothermic heating device could be provided directly on or in the high-pressure cracker (Oxi Heat Cracker / OHC cracker).

[0107] Figure 10 shows a simplified schematic representation of the connection of an exothermic heating device to an extended high-pressure cracker (OHC cracker).

[0108] The OHC cracker 24, which is preferably located in an exhaust-side bypass 10 of the engine's exhaust system, now supplies not only the engine with an H2 / N2 mixture by means of direct injection 18, but also, to a greater extent, the exothermic heating device of the high-pressure cracker: The exothermic heating device of the OHC cracker is achieved by an additional line and injection of H2 / N2 directly into the cracker module, for example heating line 22 and H2 / N2 nozzle 28 in Fig. 10.

[0109] The H2 / N2 mixture fed to the OHC cracker for heating via heating line 22 is generated by the OHC cracker itself. A portion of the total amount produced by the OHC cracker, H2 / N2 out, is metered in again via the heating line using injection nozzle 28 and thus essentially returned to the OHC cracker. The H2 / N2 recirculation amount is on average in the range of 10% to 30% of the total amount of H2 / N2 produced. The return to the OHC cracker is preferably carried out by interposing the starter reservoir 21 from the starter reservoir, as shown in Figure 10.

[0110] Figure 11 shows a detailed view of an OHC cracker 24 integrated into the exhaust system of the internal combustion engine (ICE). In this example, it includes a shell-and-tube heat exchanger. Furthermore, the flow behavior of the engine exhaust and ammonia from the tank is shown. The exhaust flow through the cracker 24 is shown schematically as line 10.

[0111] A small oxidation catalyst 29, as shown in Figure 11, installed upstream of or integrated into the high-pressure cracker 24 in the cracker module, locally induces a strong exothermic reaction directly at the cracker upon H2 / N2 injection 28. In addition to the oxidation catalyst 29, or alternatively, the cracker is provided with an oxidation coating 31 on the outer reaction surfaces of the exhaust gas stream, as shown in Figure 14.

[0112] The exothermic heating device of this invention is therefore not an ammonia burner upstream of the cracker, but rather a temperature generation system through a catalytic reaction by supplying the hydrogen previously generated by the cracker to an oxidation coating, such as is currently used in oxidation catalysts for exhaust gas purification in the prior art. From the exhaust bypass 10 of the internal combustion engine, the engine exhaust gas enters the OHC cracker and flows through it with the most effective heat transfer possible to the fuel-carrying areas, here the pipes, as shown in Figure 11.

[0113] The ammonia fuel enters the OHC cracker on the side separated from the exhaust gas in a compressed and preferably gaseous state (NH3 in), is passed through the OHC cracker via the pipes and then exits the OHC cracker again, ideally as a highly dosed H2 / N2 gas mixture (H2 / N2 out).

[0114] The efficiency of the OHC cracker depends primarily on its design, the existing fuel pressure, the coating design, the current temperature, and the flow rates of the media. Depending on the efficiency of the OHC cracker, the mixture may still contain portions of unconverted NH3. For example, at 50% efficiency, a residual of 50% NH3 is present.

[0115] To achieve a high cracker efficiency, for example, greater than 70%, the OHC cracker's operating temperature is preferably set to greater than 600°C, depending on the coating of the fuel-carrying areas. In addition to nickel alloys, ruthenium or mixtures thereof can also be used to coat the fuel-carrying areas. This enables high efficiencies even at lower operating temperatures, given the pressure range of the OHC cracker set here, approximately 20 bar - 40 bar. The set temperature ranges can be approximately 100 to 200°C lower than without such a coating.

[0116] The OHC cracker has the advantage of an integrated, compact design of Mini-Oxikat 29 and Cracker 24, combined with short paths and low upstream heat capacities. The electric heat exchanger 6, shown in Figures 12 to 15, supports the system in reaching and regulating operating temperatures, for example, above 600 °C, to produce sufficient hydrogen.

[0117] In order to achieve the above-mentioned conditions during unsteady operation of the engine or during engine start-up, cracker designs with different configurations are provided, including the positioning of the electric heater 6.

[0118] Four different versions (OHC1 to OHC4) of the OHC cracker with electric heater are described below:

[0119] OHC1 crackers

[0120] Figure 12 shows a first embodiment of an exothermic heating device, referred to here as OHC1. A mini-oxygenator, as shown in Figure 11, is connected upstream of the cracker. An electric heater is connected upstream of this mini-oxygenator. Optionally, the cracker has an integrated air blower 30, which flows gas, preferably air, through the cracker even when the ICE is shut down. This also provides heating options that can occur when the internal combustion engine is shut down and thus even when there is no exhaust flow from the engine.

[0121] The upstream connection of the electric heater in the OHC1 variant is advantageous when the exothermic reaction is to be initiated with the internal combustion engine shut down and the mini-oxicate cooled down. This can be advantageous, for example, in the "automatic refilling with high-pressure cracker after the internal combustion engine is shut down" operating mode when the internal combustion engine is shut down for an extended period.

[0122] The description of the operating mode “automatic refilling with OHC after stopping the internal combustion engine” is given below with reference to Figure 20.

[0123] OHC2 Cracker The OHC2 cracker shown in Figure 13 according to a second embodiment has a structure comparable to the OHC1 cracker, but with an electric heater downstream of the mini-oxicate. The positioning of the electric heater close to the cracker in the second embodiment, OHC2, improves the dynamics of the heating behavior.

[0124] OHC3-C racker

[0125] The OHC3 cracker shown in Figure 14 according to a third embodiment has a structure comparable to the OHC1 cracker, but with an integrated exothermic heating device downstream of the electric heater 6. For this purpose, the fuel-carrying components of the OHC cracker, the tubes shown in Figure 14, are provided with an external, exhaust-side oxidation coating. This provides further advantages in terms of heat transfer as well as cost savings.

[0126] OHC4-C racker

[0127] Figure 15 shows an OHC4 cracker according to a fourth embodiment, in which an alternative or additional electric heater 6 is installed on the fuel side, in contrast to the OHC1-3 versions. In this case, the additional electric heater 6 is shown in the area where the fuel exits the OHC cracker. This fuel-side electric heater 6 is provided with a fuel-side coating to make the cracking process even more effective.

[0128] The OHC4 cracker provides advantages particularly in the “engine start and warm-up” operating mode of the internal combustion engine, as shown in Figure 4.

[0129] Figure 16 shows the cracker path integrated into the exhaust system of the internal combustion engine (section of the high-pressure cracker path 17 from Figure 9) using the example of the OHC4 cracker with the integrated start accumulator 21 and its essential hydraulic actuator devices, such as valves, throttles, and regulators. The OHC4 cracker shows the schematic flow behavior of the engine exhaust gas and the ammonia fuel media in Figure 16 with a dashed line.

[0130] The rapid start of the internal combustion engine is achieved by supplying the H2 / N2 mixture from the start accumulator used here via the start line now shown in Figure 16 by switching the valve 25. The injection of the H2 / N2 mixture into the combustion chambers of the internal combustion engine then takes place with the direct injection injectors 18 essentially during the intake phase with an injection pressure of at least 3 bar. In the present exemplary embodiment, by controlling the fuel-side electric heater 6 with an electrical power in the range of 2 kW to 8 kW when a temperature of the electric heater 6 of approximately 600 °C is reached, a cracking process of at least a small amount of NH3 into an H2 / N2 mixture can take place after a short time of approximately 5 - 30 seconds after the rapid start of the internal combustion engine.

[0131] This fuel-side electric heater is also known as a direct cracker and operates only temporarily, with electrical control when needed. The fuel flow through the OHC4 cracker, now enabled early after the rapid start of the internal combustion engine, enables particularly favorable heat transfer from the exhaust side to the fuel side of the cracker during the heat-up phase, thus resulting in a very effective, improved warm-up behavior. The fuel flow is not used to drive the internal combustion engine and is reduced to a level that results in a good compromise between the necessary electrical power and good heat-up behavior.

[0132] This flow can be regulated, for example, by using a throttle valve 27 shown in Figure 16 on the outlet side of the cracker (H2 / N2 out) or by reducing the volume flow upstream of the cracker inlet side (NH3 in). This cracked NH3 partial quantity is preferably fed as H2 / N2 to the start-up storage system via the filling line shown in Figure 16 and thus, during operation of the exothermic heating device, also increases the amount of H2 / N2 available in the start-up storage via the heating line. This results in an increase in the storage operation range. This is advantageous, among other things, for the dimensioning of the start-up storage system, which can be smaller and thus more space-saving.

[0133] Electronic control device for controlling the cracker system using different operating modes

[0134] Figure 17 shows the connection of the system to a control device or cracker ECU used to regulate the processes. This cracker ECU processes various sensor signals shown in Figure 17, such as pressure and temperature information, and thus calculates and adjusts the valve controls required for the system in various operating modes.

[0135] The sensor signals shown in Figure 17 represent the signals in a target application. By programming mathematical functions in the cracker ECU, efficiencies, for example of the exothermic heating device (TA2 / TA1) or efficiencies of the cracking process (TK2 / TK1), can be output. Model calculations are used that are based on other sensor signals in the development stage not shown here; for example, a resulting temperature within the cracker. This sensor signal data for the model calculation can be stored in a data memory connected to the cracker ECU.

[0136] Extended interaction of the OHC with the storage as start / buffer storage

[0137] Compared to the operating modes already shown in Figure 4, the extended exothermic heating device by means of H2 / N2 injection into the cracker module, as well as the now extended use of the storage as a buffer storage, result in two interactions between the OHC cracker 24 and the start-Z buffer storage 21 in particular: A) Filling / supplementing the start-Z buffer storage

[0138] B) Automatic refilling with OHC after stopping the ICE

[0139] A) Refilling / supplementing start buffer storage

[0140] Despite the improved dynamics in temperature adjustment with the OHC cracker and its exothermic heating system, the dynamic behavior of the ICE with regard to load-to-speed and the associated strongly fluctuating quantity requirements of the cracked fuel may not be fully covered by the OHC cracker. To achieve a high and defined cracker efficiency, it could, for example, be regulated within a small temperature window. The temperature window should preferably be between 650°C and +50°C. The H2 / N2 mass flow required by the ICE varies greatly over time depending on the ICE load point and the corresponding engine speed.

[0141] The H2 / N2 mass flow in the cracker is less dynamically adjustable and therefore may not always be able to meet the high dynamic requirements of the ICE with the correct quantity allocation. This results in H2 / N2 quantities produced by the OHC cracker that may be either too low or too high for optimal ICE operation. The start-up buffer storage now used acts as an intermediate buffer to ensure that the ICE is always supplied with the optimal amount of the H2 / N2 mixture:

[0142] If the ICE has a map-dependent low H2 / N2 injection requirement, the excess H2 / N2 produced by the OHC cracker can be fed to the start-Z buffer storage for storage filling via the filling line, as shown in Figure 16. If the ICE has a map-dependent high H2 / N2 injection requirement, the H2 / N2 produced insufficiently by the OHC cracker can be fed from the start-Z buffer storage via the supplementary line, as shown in Figure 16. Figure 18 shows a section of the cracker path for the function of the start- / buffer storage as an intermediate buffer, as well as an example of the valve circuits 23 and 26 for regulating an exemplary H2 / N2 quantity specified by the ICE.

[0143] Design of the OHC cracker with start / buffer storage

[0144] The goal in designing the OHC cracker is to achieve the most compact design possible, one that can be brought up to operating temperature as quickly as possible. Furthermore, the ammonia flow rate must be selected so that a sufficient admixture of H2 / N2 can be achieved by direct injection into the main fuel quantity introduced via the port injector for all engine operating points. Assuming that an admixture of 10% H2 (calorific value equivalent) appears sufficient to achieve good combustion behavior, a possible admixture of this 10% H2 at the nominal power point of the ICE would be a sensible way to dimension the cracker. Based on further optimization options for the ICE combustion process, a possible reduction of the maximum amount to less than 5% at the nominal power point also appears to be feasible.However, a sufficiently large reserve for filling the accumulator is necessary to ensure that the depleted start buffer accumulator can be quickly refilled after switching from the "cold start / warm-up phase" to "engine warm-up." This is necessary, on the one hand, to ensure continued starting from the accumulator, and, on the other hand, to be able to increase from the accumulator during engine warm-up with a high injection pressure of approximately 20 bar.

[0145] Figure 19 shows the potential of the fill-Z supplementary areas of the start-Z buffer storage system in a characteristic map of an ICE using the example of a 4-cylinder naturally aspirated engine with a maximum effective mean pressure of 10 bar and a maximum speed of 5000 rpm. The design point of the cracker was used to produce 10% H2 (calorific value equivalent) at the nominal power point of the ICE. With this design, large characteristic map areas with large H2 proportions, sometimes up to 100%, can be covered. These can then either be added to the engine during the intake phase by simple or timed injection (inmixing) or are available to the system for filling the start / buffer storage.

[0146] B) Automatic refilling with OHC after stopping the internal combustion engine

[0147] In the refill / supplement mode shown in A), the start / buffer reservoir is often not fully filled when the ICE is switched off. In addition, during short-distance operation, the start / buffer reservoir cannot be fully filled after being emptied in cold start / warm-up mode while the ICE is running. A subsequent cold start of the ICE requires the start / buffer reservoir to be constantly filled when the ICE is started. To ensure this, if the start / buffer reservoir is not fully filled, it is automatically refilled when the ICE is switched off. This automatic refilling function can be provided for all OHC crackers OHC1 to OHC4 and preferably starts immediately after the ICE is switched off, and thus when the OHC cracker and exhaust gas aftertreatment are still at least partially warmed up.

[0148] Figure 20 shows such a refilling process after shutting down the ICE with the switching positions of the key valves / actuators 22; 30; 27; 23, as shown in Figure 17. After shutting down the ICE and storing the fill level of the start / buffer storage, the H2 / N2 injector 28 and the integrated air blower 30 are activated. The air blower 30 has the function of flowing gas, preferably air, through the cracker while the ICE is stopped in order to achieve appropriate heat transfer from the exothermic heating device into the cracker. Depending on the fuel outlet temperature TK2, the throttle valve 27 on the outlet side of the cracker opens (H2 / N2 out); and the filling line is opened by switching valve 23 to position 2. The refilling process now begins until the storage is completely filled (here 20 bar storage pressure).The valves / actuators are then switched back as shown in Figure 20, and the start / buffer storage is filled and available for the next start-up process.

[0149] It is readily apparent to the person skilled in the art that, depending on the nature of the specific application, combinations of the embodiments shown can also be provided, provided that this is technically possible.

[0150] List of reference symbols

[0151] 1 startup memory

[0152] 2 ammonia high pressure tank

[0153] 3 Internal ammonia tank >20 bar

[0154] 4 high-pressure crackers

[0155] 5 low-pressure crackers

[0156] 6 electric heaters

[0157] 7 Low pressure evaporator

[0158] 8 high-pressure evaporators

[0159] 9 Oxi catalyst

[0160] 10 Bypass, temperature control NH3 cracker and SCR-ASC

[0161] 11 SCR

[0162] 12 ASC-Oxi

[0163] 13 Exhaust

[0164] 14 Fuelrail low-pressure cracker path

[0165] 15 Additional pump

[0166] 16 Second fuel tank

[0167] 17 Fuelrail High Pressure Cracker Path

[0168] 18 direct injection injector

[0169] 19 Spark plug

[0170] 20 cylinder head

[0171] 21 Start-ZBuffer memory

[0172] 22 heating cable

[0173] 23 Valve circuit filling line

[0174] 24 high-pressure crackers

[0175] 25 Valve circuit start line

[0176] 26 Valve circuit supplementary line

[0177] 27 Throttle valve

[0178] 28 H2 / N2 nozzle

[0179] 29 Mini-Oxikat

[0180] 30 air blowers

[0181] 31 Oxidation coating

[0182] 32 Cracker ECU

Claims

AMENDED CLAIMS received by the International Bureau on 09 December 2024 (09.12.2024) Patent claims 1. A method for operating an internal combustion engine using ammonia as fuel, wherein ammonia is cracked into at least a hydrogen-nitrogen mixture by means of a cracker, and wherein, upon starting the internal combustion engine, a gas comprising at least hydrogen is first supplied from a starter reservoir in order to avoid a start-up delay due to the cracking of the ammonia, and then the hydrogen-nitrogen mixture cracked at the cracker is supplied to the internal combustion engine, wherein the starter reservoir has a pressure of 3 bar to 40 bar, preferably 20 bar, and wherein a portion of the hydrogen-nitrogen mixture produced in the cracker is stored in the starter reservoir.

2. Process according to claim 1, wherein after the cracking by means of a cracker, any ammonia still present is condensed out and fed back into the cycle.

3. A process according to claim 1 or 2, wherein a high-pressure evaporator and a high-pressure cracker are provided.

4. The process according to claim 1 to 3, wherein a low-pressure evaporator and a low-pressure cracker are provided.

5. The method according to claim 1 to 4, wherein liquid ammonia is stored in at least one high-pressure ammonia tank.

6. The method according to claim 1 to 5, wherein the at least one cracker is heated via an exhaust gas heat exchanger and / or an electric heater.

7. The method according to claim 1 to 6, wherein a high-pressure direct injection and / or a low-pressure fuel rail injection is provided.

8. A quick-start device for an internal combustion engine for the direct combustion of ammonia, the device comprising a first ammonia reservoir, an evaporator, a cracker connected thereto, a fuel injection system of the internal combustion engine, and a starting reservoir, the starting reservoir having a pressure of 3 bar to 40 bar, preferably 20 bar, and the starting reservoir being connected to a cracker.

9. Quick start device according to claim 8, wherein the start accumulator has a volume of 3 liters to 80 liters, preferably 5 liters to 50 liters, particularly preferably 10 to 30 liters.

10. Quick start device according to claim 8 to 9, wherein an additional pump is provided for filling the start accumulator.

11. Quick start device according to claim 8 to 10, wherein the start accumulator can be filled with a gas mixture which comprises hydrogen and nitrogen and, when filled, can be filled at a pressure of 20 bar to 40 bar and a temperature of up to 80°C.

12. Quick start device according to claim 8 to 11, wherein the start memory is additionally provided as a buffer memory.

13. Quick start device according to claim 8 to 12, wherein the fuel injection system is provided as a direct injection.

14. Internal combustion engine for the direct combustion of ammonia with a quick-start device according to claims 8 to 13.

15. Internal combustion engine according to claim 14, wherein an exothermic heating device is provided for a high-pressure cracker, wherein at least one line and nozzle are provided for supplying hydrogen generated by means of the cracker to an oxidation coating for catalytic temperature generation.

16. The internal combustion engine of claim 15, wherein the high-pressure cracker comprises a shell-and-tube heat exchanger.

17. Internal combustion engine according to claim 15 or 16, wherein at least one electric heater is provided in the region of the high-pressure cracker, preferably in the exhaust gas bypass of the internal combustion engine (ICE).

18. Internal combustion engine according to claim 15, 16 or 17, wherein the operating temperature of the high-pressure cracker is greater than or equal to 600°C.

19. Internal combustion engine according to one of claims 14 to 18, wherein an electronic control device is provided for controlling the cracker system.

20. Internal combustion engine according to one of claims 14 to 19, wherein an air blower 30 is provided for flowing gas, preferably air, through the cracker when the ICE is stationary, in order to enable appropriate heat transport of the exothermic heating device into the cracker.

21. Method according to one of claims 1 to 7, wherein a step for automatically refilling the starter reservoir after a stop of the internal combustion engine (ICE) is provided, in which an air blower 30 flows through the cracker with gas, preferably air, when the ICE is stopped, in order to enable a corresponding heat transport of the exothermic heating device into the cracker.

22. Method according to one of claims 1 to 7 and 21, wherein a step for heating the high-pressure cracker after engine start is provided, in which during the supply of the hydrogen-nitrogen mixture into the internal combustion engine (ICE) from the start storage an electric heater on the fuel side in the area of the high-pressure cracker causes a gas containing at least hydrogen to flow through the high-pressure Cracker, which has a beneficial effect on heat transfer and thus on the heating and thus on the speed at which the high-pressure cracker reaches operational readiness.

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