METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE, SYSTEM FOR CARRYING OUT THE METHOD AND INTERNAL COMBUSTION ENGINE

Abstract

The present invention relates to a method of operating an internal combustion engine (2), comprising at least one combustion chamber (3) in which fuel is at least partially combusted with ambient air and an exhaust pipe (6) fluidly connected to an exhaust side (7b) of the at least one combustion chamber (3), wherein hydrogen is used as fuel for the internal combustion engine (2), wherein the internal combustion engine (2) also comprises at least one NOx storage catalyst (13), and exhaust gas discharged from the at least one combustion chamber (3) to the exhaust pipe (6) at least partially, preferably completely, flows through the at least one NOx storage catalyst (13), wherein a lean hydrogen-air mixture is combusted in the at least one combustion chamber (3) in a first operating state, and wherein the NOx storage catalyst (13) is regenerated in a second operating state. To facilitate operation of the internal combustion engine as a low-emission system, a rich hydrogen-air mixture is combusted in the at least one combustion chamber (3) in the second operating state.

Description

[Technical Field]

[0001] The present invention relates to a method for operating an internal combustion engine, a system for implementing the method, and an internal combustion engine. [Background technology]

[0002] From an emissions standpoint, hydrogen-powered internal combustion engines are known to be preferable, as carbon-containing exhaust products such as soot and carbon monoxide are eliminated in these engines.

[0003] Furthermore, German Patent Application No. 10 2016 107 466 A1 proposes selective catalytic reduction to reduce NOx components in the exhaust gas from a hydrogen-powered combustion engine. However, the reducing agent must be continuously supplied to the exhaust pipe. This requires a precise supply of reducing agent that requires continuous control, and in the event of a malfunction, NOx emissions may be released into the atmosphere.

[0004] JP 2006-057504 A describes a method for operating an internal combustion engine with hydrogen. A NOx storage catalyst, which stores nitrogen oxides produced during combustion, is located in the exhaust pipe of the internal combustion engine. To regenerate the NOx storage catalyst, fossil fuel is added to the combustion mixture.

[0005] Regeneration requires highly difficult control, and in addition, multiple types of fuel are involved in forming the combustion mixture, making the system and combustion complex. Summary of the Invention [Problem to be solved by the invention]

[0006] The basis of the present invention is therefore to operate an internal combustion engine as a zero / low emission system in a simple and robust way. [Means for solving the problem]

[0007] This problem is solved by a method for operating an internal combustion engine according to claim 1, 6 or 8.

[0008] According to a first aspect, there is provided a method for operating an internal combustion engine, the internal combustion engine comprising: at least one combustion chamber in which fuel is at least partially combusted with ambient air; and an exhaust pipe fluidly connected to an exhaust side of the at least one combustion chamber. Hydrogen is used as fuel for the internal combustion engine. The internal combustion engine also has at least one NOx storage catalyst, and exhaust gases discharged from the at least one combustion chamber into the exhaust pipe flow at least partially, preferably completely, through the at least one NOx storage catalyst. A lean air / hydrogen mixture is combusted in the at least one combustion chamber under a first operating condition. The NOx storage catalyst is regenerated under a second operating condition, and a rich air / hydrogen mixture is combusted in the at least one combustion chamber under the second operating condition.

[0009] According to a first aspect, an internal combustion engine includes at least one NOx storage catalyst through which emitted exhaust gas flows, whereby nitrogen oxide (NOx) emissions can be stored in the NOx storage catalyst, also referred to as an LNT catalyst, thereby eliminating the need for a continuous supply of reductant.

[0010] The first option utilizes the synergistic effect of using hydrogen as fuel in a combustion engine. A combustion engine operated in this way only produces nitrogen oxides as harmful combustion products thermally. Therefore, it is possible to dispense with other devices for exhaust gas aftertreatment. Therefore, there is space in the exhaust pipe for a suitably sized NOx storage catalyst.

[0011] Furthermore, the process conditions, such as combustion temperatures, of a hydrogen-powered combustion engine result in lower nitrogen oxide formation compared to, for example, a diesel engine, which means that nitrogen oxides can be reliably stored in the NOx catalyst for extended periods of time.

[0012] Further in the method, a lean air / hydrogen mixture is combusted in at least one combustion chamber under a first operating condition.

[0013] Burning a lean mixture can increase the efficiency of a combustion engine. At the same time, the combustion temperature can be lowered, which further inhibits the formation of nitrogen oxides, thereby allowing the NOx storage catalyst to store nitrogen oxides for a long period of time. In this process, the combustion of the lean mixture is preferably performed continuously, thus over multiple cycles of the combustion engine. A lean air / hydrogen mixture is a superstoichiometric mixture. Preferably, λ is set to be between 1 and 5; depending on the operating point, λ between 1.3 and 3.5 is particularly preferred.

[0014] In addition, the NOx storage catalyst is regenerated in the second operating state.

[0015] The nitrogen oxides stored in the NOx storage catalyst can be converted into atmospheric nitrogen and released into the atmosphere. The NOx storage catalyst can then absorb the nitrogen oxides again, thus preventing the continuous emission of harmful emissions.

[0016] According to the invention, in a second operating condition, a rich air / hydrogen mixture is combusted in at least one combustion chamber.

[0017] In the second operating mode, a substoichiometric air / hydrogen mixture can be supplied to the combustion chamber. λ is preferably set between 0.6 and 1.0, particularly preferably between 0.8 and 0.9. On the one hand, a rich air / hydrogen mixture can reduce, and preferably completely prevent, the formation of nitrogen oxides due to a lack of oxygen, and on the other hand, it can ensure that unburned hydrogen is supplied to the exhaust pipe as a reducing agent. This means that the NOx storage catalyst can be regenerated using excess hydrogen.

[0018] Rich mixtures can be established in appropriate circumstances due to the lower formation of nitrogen oxides and the associated long-term storage potential.

[0019] Preferably, the internal combustion engine also has an exhaust gas recirculation system which returns exhaust gases from the exhaust pipe to the combustion chamber.

[0020] This allows the inert components of the combustion products to be recirculated from the exhaust pipe back into the combustion chamber. These components no longer participate in the combustion and extract exothermic energy from the combustion process. This allows the process temperature to be lowered, which inhibits the formation of further nitrogen oxides. Preferably, the exhaust gas is recirculated as high-pressure exhaust gas, particularly from a position upstream of the turbine in the exhaust pipe. This ensures a sufficient recirculation rate.

[0021] According to yet another aspect, in a second operating condition, exhaust gases can be recirculated to the at least one combustion chamber via an exhaust gas recirculation device.

[0022] Therefore, in the second operating state for regeneration of the NOx storage catalyst, it is possible to reduce, preferably completely prevent, the formation of further nitrogen oxides and to ensure that the regeneration of the storage catalyst is carried out. Another positive effect is obtained, especially in conjunction with hydrogen, since the tendency of the less reactive mixture to pre-ignite, i.e., to ignite early, can be prevented.

[0023] Preferably, the second operating state is set during idling operation of the combustion engine.

[0024] In this way, it is possible to prevent the regeneration operation from affecting the behavior of the combustion engine-driven device, particularly in a vehicle equipped with a hydrogen-powered internal combustion engine. As mentioned above, the second operating state can therefore be implemented in appropriate situations, such as when the internal combustion engine is operating without performing a specific task, for example by being decoupled from at least one driving wheel of the vehicle, or, in other words, when the internal combustion engine is not under load, such as when stationary at a traffic light. This situation is quite likely to occur when the internal combustion engine is used in a vehicle, so that the vehicle's operation is not limited by the necessary regeneration phase of the catalyst. Furthermore, by throttling the air supply during idling, a high exhaust gas recirculation rate can be achieved. This is because the exhaust gas backpressure (upstream of a possible turbocharger turbine) is higher than the pressure in the intake manifold in this state. Therefore, the above-mentioned effects of exhaust gas recirculation can be reliably achieved in the regeneration mode.

[0025] According to a further aspect, the second operating state can be set in overrun operation of the internal combustion engine, which is characterized in particular by the power generated by the internal combustion engine being smaller than the drag force applied to the internal combustion engine, i.e., the internal combustion engine can be kept rotating from the output side.

[0026] In this case, too, overrun operation of the combustion engine is quite likely to occur during long-distance travel, so that vehicle operation is not limited by the regeneration phase required by the catalyst. Even though the air supply is throttled during idling mode, the amount of fuel supplied during overrun operation can be specifically set to burn a rich mixture. At the same time, ignition can be significantly delayed, thereby stabilizing combustion and thus reducing or preferably preventing the formation of further nitrogen oxides. Preferably, ignition occurs within a crankshaft angle range from a maximum of 40° before top dead center to the opening of the exhaust valve, in particular from a maximum of 40° before top dead center to a maximum of 360° after top dead center, more preferably from a maximum of 20° before top dead center to a maximum of 360° after top dead center, and even more preferably from the maximum angle corresponding to top dead center to a maximum of 360° after top dead center.

[0027] Rich mixtures and delayed ignition make it possible to increase the exhaust gas enthalpy, which ensures a sufficient temperature for catalyst regeneration. The power generated by the combustion engine during overrun operation is less than the applied drag force, and therefore overrun operation can be maintained. Combustion of rich mixtures in the overrun phase as a regeneration mode has the advantage that the transition from lean to rich mixture range can be made discontinuous, thus avoiding the need to go through the mixture range around λ equal to 1. In this range, the formation of nitrogen oxides is usually very high.

[0028] Preferably, the exhaust gas is at least temporarily recirculated during the transition between the first and second operating conditions.

[0029] Therefore, even when transitioning through a near-stoichiometric mixture, it is possible to reduce, and preferably completely prevent, the formation of nitrogen oxides.

[0030] According to a further aspect, which may be provided as an independent aspect or as an aspect dependent from the first aspect, there is provided a method of operating an internal combustion engine, wherein the internal combustion engine has at least one combustion chamber in which fuel is at least partially combusted with ambient air, and an exhaust pipe fluidly connected to an exhaust side of the at least one combustion chamber. Hydrogen is used as fuel for an internal combustion engine, which also has at least one NOx storage catalyst, and exhaust gas discharged from at least one combustion chamber into an exhaust pipe flows at least partially, preferably completely, through at least one NOx storage catalyst, wherein a lean air / hydrogen mixture is combusted in at least one combustion chamber in a first operating state, and wherein the NOx storage catalyst is regenerated in a second operating state, and wherein in the second operating state a reducing agent for reducing nitrogen oxides stored in the NOx storage catalyst is supplied as part of the exhaust gas to at least one combustion chamber or in the exhaust pipe downstream of the at least one combustion chamber and upstream of the NOx storage catalyst or to the NOx storage catalyst.

[0031] In this embodiment, only thermal nitrogen oxides are produced as harmful combustion products during the combustion of a lean air / hydrogen mixture, so it is possible to dispense with other exhaust gas aftertreatment devices, and there is therefore space in the exhaust pipe for a suitably sized NOx storage catalyst.

[0032] Furthermore, the process conditions, such as combustion temperatures, of hydrogen-powered internal combustion engines operating lean and / or with high exhaust gas recirculation rates result in lower nitrogen oxide formation compared to, for example, diesel engines, meaning that the NOx catalyst can reliably store nitrogen oxides for long periods of time.

[0033] Combustion of a lean mixture can increase the efficiency of a combustion engine. At the same time, the combustion temperature can be lowered, which further inhibits the formation of nitrogen oxides, thereby allowing the NOx storage catalyst to store nitrogen oxides for a long period of time. In this process, the combustion of the lean mixture is preferably performed continuously, thus over several cycles of the combustion engine. A lean air / hydrogen mixture is a superstoichiometric mixture. Preferably, λ is set to be between 1 and 5; λ between 1.3 and 3.5 is particularly preferred, depending on the operating point.

[0034] In addition, the NOx storage catalyst is regenerated in the second operating state.

[0035] The nitrogen oxides stored in the NOx storage catalyst can be converted into atmospheric nitrogen and released into the atmosphere. The NOx storage catalyst can then absorb the nitrogen oxides again, thus preventing the continuous emission of harmful emissions.

[0036] Furthermore, according to this embodiment, the reducing agent can be supplied directly to the exhaust pipe without having to be provided as exhaust gas from the combustion process. Therefore, the internal combustion engine can be continuously operated in the first operating state in which a lean air / hydrogen mixture is burned. In particular, a lean air / hydrogen mixture can be continuously burned. The first and second operating states are therefore not mutually exclusive and can coexist. Naturally, it is also possible to supply the reducing agent directly to the exhaust pipe in parallel with the combustion of a rich mixture, so that only the second operating state exists.

[0037] According to this embodiment, however, it is also possible to provide the reducing agent as part of the exhaust gas, particularly in internal combustion engines in which fuel is supplied directly to the combustion chamber, where the reducing agent can be supplied to the combustion chamber and then, after leaving the combustion chamber, to the exhaust pipe.

[0038] Preferably, a rotational or diffusive component is at least partially imparted to the supplied reducing agent stream.

[0039] This makes it possible to improve the mixing in the exhaust pipe, and also to ensure that the reducing agent flows evenly, thereby ensuring the regeneration of the storage catalyst.

[0040] Preferably, the reducing agent is hydrogen, particularly preferably from the same source as the hydrogen used as fuel, and in particular if the reducing agent is injected directly into the combustion chamber, it is possible to use the same supply equipment as that used to supply hydrogen to the combustion chamber.

[0041] This reduces the complexity of the system as all components can be hydrogen compatible, and additional storage devices such as reductant tanks are not required.

[0042] Preferably, the reducing agent is supplied to the combustion chamber after the combustion process is completed, more preferably during the exhaust stroke when the exhaust gases are expelled from the combustion chamber, thereby ensuring that the reducing agent is not combusted with oxygen from the air contained in the combustion chamber.

[0043] According to a further embodiment, the second operating state can be set at a saturation level of the NOx storage catalyst of more than 20% or less than 100%, preferably 70 to 90%, particularly preferably 80%. Known methods for measuring the saturation level can be used.

[0044] This means that the storage catalyst can utilize a large portion of its storage capacity. Due to the low nitrogen oxide formation in the first operating state, it is possible to prevent oversaturation during switching and therefore to switch very close to the storage capacity limit.

[0045] According to a further aspect, which may be provided as a further independent aspect or as an aspect dependent on the above aspect, there is provided a method of operating an internal combustion engine having at least one combustion chamber in which fuel is at least partially combusted with ambient air and an exhaust pipe fluidly connected to an exhaust side of the at least one combustion chamber, wherein hydrogen is used as a fuel for the internal combustion engine, the exhaust pipe having a plurality of exhaust pipe sections connected in parallel, at least two of the plurality of exhaust pipe sections each having at least one NOx storage catalyst through which at least a portion of exhaust gas discharged from the at least one combustion chamber into the exhaust pipe at least temporarily flows, and a flow rate through the at least one NOx storage catalyst is at least temporarily changed by a variable throttle device arranged in at least one of the exhaust pipe sections, preferably upstream of the at least one NOx storage catalyst.

[0046] The flow of exhaust gas can therefore be influenced depending on the remaining capacity of at least one NOx storage catalyst. If a NOx storage catalyst in the exhaust pipe is close to its capacity limit, the flow rate in this exhaust pipe can be reduced, while a larger amount can continue to flow through the parallel-connected NOx storage catalyst. This allows the NOx storage catalyst to be operated efficiently in the manner described above.

[0047] Preferably, the flow rates in a plurality of exhaust pipe sections each having at least one NOx storage catalyst are changed independently of one another.

[0048] For this purpose, it is possible to arrange variable throttle devices in at least one, preferably in several, exhaust pipe sections arranged in parallel with one another upstream of at least one NOx storage catalyst, and the variable throttle devices are independently controlled to adjust the amount of exhaust gas in each exhaust pipe section.

[0049] Therefore, it is possible to cause each of the NOx storage catalysts connected in parallel to react independently.

[0050] Furthermore, it is possible to reduce, preferably completely suppress, the flow rate in at least one of the exhaust pipe sections in order to regenerate at least one NOx storage catalyst.

[0051] For example, when an internal combustion engine is operated with a lean combustion mixture, nitrogen oxides continue to flow unthrottled through at least one exhaust pipe section having a NOx storage catalyst close to its capacity limit. By reducing the nitrogen oxides, it is therefore possible to prevent further large amounts of nitrogen oxides from being introduced into at least one exhaust pipe section during regeneration.

[0052] Preferably, a reducing agent for reducing nitrogen oxides stored in the NOx storage catalyst is supplied to at least one of a plurality of exhaust pipe sections connected in parallel with one another upstream of at least one NOx storage catalyst, particularly preferably to each exhaust pipe section, or to at least one NOx storage catalyst, and particularly preferably, the amount of reducing agent supplied is controlled individually for each exhaust pipe section.

[0053] This allows for increased efficiency of NOx storage and regeneration. The internal combustion engine can be continuously operated with a lean-burn mixture. In this manner, if only a single exhaust pipe is provided, a significant amount of reducing agent (hydrogen) must be added to compensate for the oxygen present for lean combustion. Only then can regeneration be performed in the absence of oxygen. In contrast, according to the above embodiment, the oxygen supply in at least one of the exhaust pipe sections can be reduced, for example, by a throttle device, so that a smaller amount of hydrogen is required, even when the internal combustion engine is continuously operated with a lean-burn mixture, compared to when only one exhaust pipe section is provided. Therefore, separate supply of reducing agent to each exhaust pipe section is particularly preferred when, for regeneration, the flow rate in each exhaust pipe section is reduced compared to a non-regenerative state, such as an unthrottled state.

[0054] According to a further embodiment, at least two of the exhaust pipe sections may be regenerated, at least temporarily, in an alternating manner.

[0055] For example, the greatest improvement in efficiency is achieved when two storage catalysts are connected in parallel and the internal combustion engine is operated at less than half of its maximum power. This is because in this case, the throttle device of the exhaust pipe section can be controlled to completely cut off the supply of exhaust gas to the exhaust pipe section in which at least one storage catalyst is regenerated, in order to regenerate at least one of the storage catalysts arranged therein. In parallel exhaust pipe sections, the throttle device is preferably controlled to be fully open. This means that regeneration alternates between the two exhaust pipe sections, with regeneration occurring in one exhaust pipe section and not in the other. Similarly, a change in flow rate, particularly a reduction, compared to a reference state, such as a non-regenerative state, can be alternated. Particularly preferably, each throttle device is alternately fully opened and closed during operation of the internal combustion engine at less than half of its maximum power, so that the respective flow rates are alternately completely suppressed and not reduced. Preferably, the flow rate is alternately reduced, particularly completely suppressed and not reduced, below "1 x rated power" minus "the reciprocal of the number of exhaust pipe sections arranged in parallel x rated power."

[0056] According to a further aspect, at least the parallel-connected storage catalysts, and preferably in each case the entire exhaust pipe section, can be configured to be able to completely store the nitrogen oxides produced at maximum power in all exhaust pipe sections in an unthrottled state and therefore when the flow rate is not reduced, in particular when the sum of the parallel-connected storage catalysts is configured according to a predetermined space velocity. The storage catalysts and the exhaust pipe sections are preferably of the same size.

[0057] However, it is also conceivable to configure at least the storage catalysts connected in parallel, preferably the entire respective exhaust pipe sections, so that the flow rate can be completely suppressed in at least one exhaust pipe section at rated power. This allows the flow rate to flow through the remaining exhaust pipe sections, in which the flow rate is not reduced and the storage catalyst is located, at rated power. Nitrogen oxides generated even at rated power are thus stored in the storage catalysts of the exhaust pipe sections where the flow rate is not reduced. In particular, the total of the remaining storage catalysts connected in parallel can be configured according to a predetermined space velocity. In the case of two parallel exhaust pipe sections, each of the exhaust pipe sections is preferably configured so that, at rated power, the nitrogen oxides generated are completely stored in at least one storage catalyst of the exhaust pipe section where the flow rate is not reduced. This allows the map range in which complete regeneration is possible to be extended.

[0058] Furthermore, the problem is solved by a control device configured to implement a method according to any of the previous aspects.

[0059] Such a control device allows the platform on which it is installed to operate as a low-emission system.

[0060] In addition to the control device, the present invention also relates to a program which, when executed on a computer connected to an internal combustion engine, performs the above-mentioned method. Likewise, the present invention relates to a computer-readable recording medium on which said program is executed.

[0061] The above problem is further solved by a system for carrying out the method according to any of the above aspects, wherein the system comprises: an internal combustion engine as defined in any of the above aspects; and a hydrogen storage device fluidly connected to the internal combustion engine.

[0062] Such a system constitutes a highly reliable zero / low emission system.

[0063] Preferably, the system further comprises a controller configured to carry out a method according to any of the above aspects.

[0064] The above effects can be reliably achieved through the interaction of the control device, the combustion engine and the storage device.

[0065] Preferably, in this system, the internal combustion engine also has at least one inlet device capable of supplying reducing agent to the combustion chamber or exhaust pipe, and preferably has at least one inlet device in each exhaust pipe section when multiple exhaust pipe sections are connected in parallel.

[0066] This allows the reductant to be fed to the exhaust pipe in a combustion engine either through the combustion chamber or bypassing the combustion chamber, so that a mixture switch from a lean to a rich mixture is not necessary.

[0067] Preferably, in the system, the internal combustion engine is further configured to impart, at least in part, a rotational or diffusive component to the flow of the reductant in the exhaust pipe, wherein the internal combustion engine preferably has a swirler or a profile that is inclined relative to the main flow direction.

[0068] This allows for improved mixing of the reductant in the exhaust pipe, thereby increasing the efficiency of the catalyst. A rotational component can be easily imparted by a swirler. The flow can be spread along the sloped profile by means of an inclined profile.

[0069] In particular, there is further provided an internal combustion engine for the above-described system, which may have any combination of structural features according to the present disclosure.

[0070] The above aspects will now be explained in more detail with reference to exemplary embodiments according to the drawings. [Brief explanation of the drawings]

[0071] [Figure 1]FIG. 1 shows a schematic representation of a system in which the above-described method can be implemented. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view of a modified example of an exhaust pipe for an internal combustion engine according to the present invention. [Figure 3] FIG. 3 shows a flow chart of a method for regenerating a NOx storage catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0072] The system 1 comprises an internal combustion engine 2 (engine), shown in Figure 1 in longitudinal section along the axis of a cylindrical combustion chamber 3 of the internal combustion engine 2. In addition to the combustion chamber 3, the internal combustion engine 2 has an intake manifold 5 and an exhaust pipe 6, which are fluidly connected to the combustion chamber via intake and exhaust ports 7a and 7b, respectively, which are opened and closed via valves.

[0073] As shown in Figure 1, a throttle valve 8 for regulating the amount of air and an injector 9 for injecting fuel into the intake manifold 5 may be arranged in the intake manifold 5. At the upper end, the combustion chamber 3 is closed by a cylinder head in which a spark plug 10 is arranged to ignite the air / fuel mixture entering the combustion chamber through the intake port 7a. At the lower end, the combustion chamber 3 is closed by a piston 11 rotatably connected to a crankshaft 12. Preferably, only hydrogen is used as fuel.

[0074] An outlet 7b, through which exhaust gases produced by combustion of the air / fuel mixture enter the exhaust pipe 6, is located on the opposite side of the axis to the inlet 7a.

[0075] A NOx storage catalyst (NSK) 13 is located downstream of the exhaust port 7b in the exhaust pipe 6. This NOx storage catalyst 13 is mainly composed of an aluminum oxide substrate to which, for example, CeO2 and Ba(OH)2 or BaCO3 are attached. For example, platinum and rhodium or palladium can be used as active components.

[0076] Upstream of the storage catalyst 13, the exhaust pipe has a branch 14. Branch 14a, in which the storage catalyst 13 is located, ends in the exhaust pipe terminal pipe, while another branch 14b is part of an exhaust gas recirculation system and opens into the intake manifold 5 at its downstream end relative to the branch. The exhaust gas recirculation system therefore recirculates high-pressure gas. The exhaust gas recirculation system can also be equipped with, for example, valves and sensors for monitoring the recirculated exhaust gas. At branch 14a, preferably upstream of the storage catalyst 13, a turbine can also be provided to drive an exhaust turbocharger.

[0077] The system 1 also includes a storage device 15 filled with hydrogen. The storage device 15 is fluidly connected to the intake manifold 5 via an injector 9, which is capable of injecting hydrogen into the intake manifold 5 upstream of the intake port 7a. The injector 9 is an example of a supply device for supplying fuel. The storage device 15 is further fluidly connected to the exhaust pipe upstream of the catalyst 13 via a line 16. The end portion 16a (injector) of the line 16 has a shape that widens toward the exhaust port 16a1 and is therefore angled with respect to the main flow direction of the line 16. The end portion 16a with the exhaust port 16a1 is a reducing agent inlet device within the meaning of the claims.

[0078] Furthermore, the system 1 has a control device 17, such as an ECU, that receives signals (shown in dashed lines) from numerous sensors located in the system 1 and then controls actuators and valves located in the system 1 via electrical signals (shown in dashed lines).

[0079] System 1 can be used to implement the method described above. When controller 17 receives a start signal to start internal combustion engine 2, injector 9 is activated to inject hydrogen fuel into the air in intake manifold 5 during the intake stroke. Combustion of the hydrogen / air mixture in combustion chamber 3, ignited by spark plug 10, powers crankshaft 12. Combustion products as exhaust gases enter exhaust pipe 6 through exhaust port 7b. The combustion products then flow through NOx storage catalyst 13.

[0080] The function of the storage catalyst 13 is as follows: in a first normal operating condition of the engine 2 (λ>1, burning a lean mixture), NO is oxidized by the excess oxygen at a noble metal such as platinum of the catalyst 13 to NO2 and is bound as nitrites, in particular nitrates, to storage components, preferably basic storage components such as Ba(OH)2 or BaCO3.

[0081] The engine 2 can be operated continuously in the first operating state. Burning a lean mixture can increase the efficiency of the engine 2. At the same time, the combustion temperature can be lowered, which inhibits the formation of nitrogen oxides and therefore allows the NOx storage catalyst 13 to store nitrogen oxides for a long period of time. The combustion of the lean mixture is preferably carried out continuously, thus over several cycles of the internal combustion engine. Preferably, λ is set to a value between 1 and 5; depending on the operating point, λ between 1.3 and 3.5 is particularly preferred.

[0082] If the control device 17 receives information that the engine 2 is idling, for example because the vehicle in which the system 1 is used is stopped at a traffic light, the control device 17 controls the throttle valve 8, thereby reducing the amount of air in the intake manifold 5. At the same time, the control device 17 activates the exhaust gas recirculation device, for example by opening a shut-off valve arranged in the branch 14b, thereby reducing the exhaust gas flow rate in the branch 14a. This reduces the amount of air to such an extent that a rich mixture is formed with the amount of fuel injected by the injector 9 for the same mixture heating value, thus establishing a second operating state during idling in which a rich air / hydrogen mixture (λ<1) is burned. At the same time, recirculated exhaust gas is supplied to the mixture. The air supply is preferably set so as to achieve a sub-stoichiometric mixture with at least the mixture heating value required for idling power.

[0083] On the one hand, a rich air / hydrogen mixture can reduce, or preferably completely prevent, the formation of nitrogen oxides due to the complete combustion of oxygen and hydrogen, and on the other hand, it is possible to reliably supply unburned hydrogen as a reducing agent to the exhaust pipe 6. This means that an excess amount of hydrogen can be used to regenerate the NOx storage catalyst 13. The recirculated exhaust gas returns inert components of the combustion products from the exhaust pipe 6 to the combustion chamber 3. These components no longer participate in the combustion process. This means that the process temperature can be lowered, thereby inhibiting the formation of further nitrogen oxides. This means that the storage catalyst can be reliably regenerated. For this reason, it is also preferable to at least temporarily recirculate the exhaust gas during the transition between the first and second operating states.

[0084] The second operating state is preferably set by the control device 17 until the catalyst 13 is fully regenerated.

[0085] As in idling operation, the control device can be set to the second operating state even during overrun operation of the engine 2. For example, if the control device 17 detects that an overrun mode is present, the control device 17 controls the injectors 9 so that a rich mixture is present, depending on the air supply that can be adjusted by the throttle valve 8. Furthermore, exhaust gas recirculation is activated as in idling operation.

[0086] One prerequisite for overrun operation is that the operator (e.g. the driver) is not requesting any torque from the combustion engine, i.e. the accelerator pedal is not depressed. To ensure zero torque despite the supply of fuel, the spark plug 10 is fired very late.

[0087] Preferably, ignition takes place within a crankshaft angle range from a maximum of 40° before top dead center to the opening of the exhaust valve, in particular from a maximum of 40° before top dead center to a maximum of 360° after top dead center, more preferably from a maximum of 20° before top dead center to a maximum of 360 after top dead center, and even more preferably from a maximum angle corresponding to maximum top dead center to a maximum of 360° after top dead center.

[0088] Preferably, the air supply in overrun operation is reduced compared to the operating mode (engine driven), for example by adjusting the throttle valve, which means that much less hydrogen needs to be supplied to form a rich mixture.

[0089] A rich mixture and delayed ignition can increase the exhaust gas enthalpy, thereby ensuring a sufficient temperature for the regeneration of the catalyst 13. The power generated by the internal combustion engine during overrun operation, which corresponds to the heat value of the rich mixture, is less than the drag force applied to the internal combustion engine. The advantage of burning a rich mixture in the overrun phase as a regeneration operation is that the transition from the lean to the rich mixture range can be made discontinuous, and therefore there is no need to go through the mixture range around λ equal to 1. In this range, the formation of nitrogen oxides is generally very high. If the mixture is continuously transitioned from the superstoichiometric range to the substoichiometric range, a mixture range with high nitrogen oxide formation can occur under certain circumstances during the transition to idle operation.

[0090] The above method is summarized in Figure 3. In step S1, system 1 continuously monitors the saturation NOx% of catalyst 13, where known methods can be used, for example by measurement, and / or the saturation can be modeled. If controller 17 determines that the saturation has reached a predetermined limit Th, for example above 20% or below 100%, preferably between 70 and 90%, then in step S2 regeneration is required and therefore a second operating state is indicated.

[0091] In step S3, it is checked whether idling (LL) or overrunning (SB) is expected within a predetermined time interval. For example, the route profile traveled by the vehicle equipped with the internal combustion engine or navigation data can be used. The predetermined time interval preferably depends on the limit value Th. If idling or overrunning is expected within a certain time interval, regeneration is performed in one of these two states in step S3a. If it is determined that idling or overrunning is not present or will not be present, for example, the shut-off valve in line 16 is opened and hydrogen is supplied from the hydrogen storage device 15 via the inlet device 16a directly to the exhaust pipe 6, bypassing the combustion chamber 3. In this way, regeneration of the catalyst 13 can be ensured even if conditions suitable for burning a rich mixture do not occur for an extended period of time. In particular, the catalyst 13 can be regenerated even at full load VL or TL.

[0092] If necessary, the line 16 and the inlet device 16a can be omitted. In this case, the control device 17 can issue a warning to the user (driver) of the internal combustion engine 2 that it is necessary to switch to idling operation, for example, when the saturation degree of the catalyst 13 is above 20% or below 100%, preferably 70 to 90%. In order to provide sufficient time to switch to overrun or idling operation, the limit value is preferably lower than when the inlet device is present.

[0093] However, the control device 17 can also be programmed not to set up combustion of a rich mixture with exhaust gas recirculation, either during overrun or idling. In this case, regeneration in the second operating state can be performed only via the line 16 and the inlet device 16a, where the reducing agent is supplied directly to the exhaust pipe 6. This means that the engine 2 can continue to operate in the first operating state (lean mixture) while the second operating state simultaneously exists. However, alternatively or additionally, it is also possible to supply the reducing agent as part of the exhaust gas, especially if the engine supplies fuel directly to the combustion chamber 3 via a supply device. In this case, the reducing agent can be supplied to the combustion chamber 3 and then to the exhaust pipe 6 after being discharged from the combustion chamber 3. The supply to the combustion chamber 3 preferably takes place after the combustion process is complete, i.e., when ignition by the spark plug is complete and the energy of the burned mixture does not allow the supplied reducing agent to be burned, especially during the exhaust stroke. In particular, the reducing agent is hydrogen, which can be supplied via the same supply device as the combustion hydrogen. In this case, lean mixtures can also be burned.

[0094] FIG. 2 shows a schematic longitudinal cross section of a modified exhaust pipe 106 of the engine.

[0095] As shown in FIG. 2, the exhaust pipe 106 differs from the exhaust pipe 6 described above in that it is divided into two exhaust pipe sections 106a and 106b connected in parallel, preferably downstream of the branch shown in FIG. 1. The exhaust pipe sections 106a and 106b have NOx storage catalysts 13a and 13b, respectively. Throttle valves (throttle devices described in the claims) 18a and 18b are provided upstream of the two catalysts 13a and 13b, respectively. Inlet devices 19a and 19b are further provided between the throttle valves 18a and 18b and the catalysts 13a and 13b, respectively, through which a reducing agent for regenerating the catalysts 13a and 13b can be supplied to the exhaust pipe sections 106a and 106b, respectively, bypassing at least one combustion chamber. In other words, the exhaust pipe sections 106a and 106b each have an inlet device 19a or 19b upstream of the catalysts 13a and 13b, respectively. Each of the inlet devices 19a and 19b preferably comprises an injector for injecting a reducing agent (hydrogen) into the exhaust pipe sections 106a and 106b.

[0096] The throttle valves 18a and 18b have variable throttle openings. The opening angle of each of the throttle valves 18a and 18b can be set individually, and therefore independently of the other throttle valves. This makes it possible to vary, in particular to individually adjust, the amount of exhaust gas flowing into each of the exhaust pipe sections 106a and 106b. Furthermore, the inlet devices (injectors) can be individually controlled, and reducing agent can be supplied separately to each of the exhaust pipe sections 106a and 106b. In particular, the amount (mass flow) of reducing agent supplied is individually controlled.

[0097] The above variant is advantageous in that the engine can be operated at an optimal operating point and does not require rich combustion to suppress oxygen and nitrogen oxide components in the exhaust gas. This variant also improves the efficiency of nitrogen oxide storage and regeneration. When one of the NOx storage catalysts 13a and 13b (e.g., 13a) in the parallel exhaust pipe section is near its capacity limit, e.g., above a predetermined limit value Th, the throttle device 18a in the exhaust pipe section where the storage catalyst 13a operating near its capacity limit is located can reduce, or preferably completely suppress, the flow rate of exhaust gas supplied to this exhaust pipe section, allowing the other NOx storage catalyst 13b in the other exhaust pipe section 106b to continue storing the exhaust gas. This configuration is particularly effective for regeneration. With only one storage catalyst, the internal combustion engine would have to operate rich for regeneration, or a significant amount of reducing agent would have to be separately supplied to the exhaust pipe, bypassing at least one combustion chamber. In the latter case, the internal combustion engine can still be operated lean, but a significant amount of reducing agent (hydrogen) must be supplied to compensate for the oxygen present for lean combustion. Only then can regeneration be carried out without oxygen. In contrast, in this embodiment, the oxygen supply in each exhaust pipe section 106a can be reduced by the throttle device 18a, which means that less hydrogen is needed compared to the case of only one exhaust pipe section as in the first embodiment.

[0098] Preferably, the storage catalysts 13a and 13b and the exhaust pipe sections 106a and 106b are of the same size. The parallel-connected storage catalysts 13a and 13b and the exhaust pipe sections 106a and 106b are configured together to be able to completely store the nitrogen oxides produced at maximum power when all the exhaust pipe sections are unthrottled and therefore the flow rate is not reduced. In other words, when the exhaust pipe sections 106a and 106b are fully open, all the exhaust gas produced at maximum power is purified of nitrogen oxides, possibly minus the amount of exhaust gas recirculation.

[0099] In this context, the greatest improvement in efficiency is achieved when two storage catalysts are connected in parallel and the combustion engine is operated at less than half of its maximum power. As a result, the flow rate can be alternately reduced, in particular completely suppressed, but not reduced below an applied power of "the reciprocal of the number of exhaust pipe sections arranged in parallel (2, reciprocal: 1 / 2) x rated power" minus "1 x rated power".

[0100] This is because in this case, the throttle device 18a of the exhaust pipe section 106a can be controlled to completely cut off the exhaust gas supply in this exhaust pipe section 106a when at least one of the storage catalysts 13a is being regenerated, for the regeneration of at least the storage catalyst 13a arranged therein. At the same time, the throttle device 18b in the parallel exhaust pipe section 106b is preferably controlled to be fully open. The respective flow rates are therefore alternately completely suppressed and not reduced.

[0101] Particularly preferably, the throttle devices 18a and 18b are alternately fully opened and closed during operation of the internal combustion engine when less than half of the maximum power is applied. The ECU 17 controls the throttle valves 18a and 18b and the inlet devices 19a and 19b.

[0102] However, it is also conceivable that at least the parallel storage catalysts, preferably the entire respective exhaust pipe sections, are configured to completely restrict the flow rate in at least one exhaust pipe section at rated power (maximum power). This allows the flow rate to flow through the remaining exhaust pipe sections, in which the flow rate is not reduced and in which the storage catalyst is located, at nominal power. This ensures that nitrogen oxides produced at nominal power are also stored in the storage catalyst of the exhaust pipe section where the flow rate is not reduced. In the case of two parallel exhaust pipe sections, each exhaust pipe section is preferably configured to completely store the nitrogen oxides produced at rated power in at least one storage catalyst of the exhaust pipe section where the flow rate is not reduced. This makes it possible to extend the map range in which complete regeneration is possible. The catalyst and exhaust gas train sections are therefore larger than if they were adapted to purify the entire amount of exhaust gas in an unthrottled state.

[0103] Downstream of the catalyst are provided nitrogen oxide sensors 21a and 21b, which detect the nitrogen oxide content in the treated exhaust gas and thus make it possible to determine whether the catalyst is completely saturated or malfunctioning. For example, if a nitrogen oxide content is detected downstream of the catalyst 13a, the control device 17 can control the throttle valve 18a to be completely closed. At the same time, the other throttle valve 18b is fully opened. The degree of saturation in the catalyst itself can be measured using known methods. The degree of saturation can also be modeled.

[0104] It is also possible to arrange at least one nitrogen oxide sensor upstream of the storage catalyst in each of the parallel exhaust pipe sections 106a and 106b, preferably upstream of the respective throttle valves and / or in the common exhaust pipe 106 upstream of the branch. In particular, the output of this at least one nitrogen oxide sensor can be used to control the parallel exhaust pipe sections.

[0105] The exhaust pipe sections, particularly the throttle valves and injectors, can therefore be controlled based on signals from at least one nitrogen oxide sensor upstream or downstream of the catalyst. The throttle valves 18a and 18b are preferably controlled so that when one catalyst 13a reaches a regeneration limit, such as 80% saturation, the other catalyst 13b has at least 20% saturation to its regeneration limit. In this way, it is possible to ensure that the other catalyst 13b has sufficient capacity for additional nitrogen oxides while the catalyst 13a is being regenerated.

[0106] In a variant, the number of exhaust pipe sections is not limited to two. It is also possible to provide three or more exhaust pipe sections. In addition, even if only one of the exhaust pipe sections upstream of the catalyst has a variable throttle device, the desired effect is already achieved, since the catalyst in question can be separated from further nitrogen oxides when it reaches its capacity limit and can be regenerated independently of the other parallel catalysts. Preferably, the parallel catalysts and / or exhaust pipe sections are each matched to a 1:1 size ratio in terms of storage capacity or cross-sectional area. This allows for a particularly high increase in efficiency.

[0107] Rich combustion mixtures can also be burned for regeneration.

[0108] Similarly, in the above embodiments, it is possible to provide multiple combustion chambers instead of one.

[0109] As already mentioned, the type of mixture formation is not important: it can occur inside or outside the combustion chamber.

[0110] Instead of an inclined profile at the end portion 16a of the line 16, it is also possible to provide a swirler with a screw flight along which the fluid is forced to flow. The main flow direction of the outlet 16a1 can also be inclined relative to the main flow direction of the exhaust pipe or pipe section. It is not necessary to provide an inclined profile. The inclined configuration imparts a rotational component to the flow.

[0111] It is preferred that the exhaust gases are recirculated upstream of the at least one storage catalyst; however, exhaust gas recirculation may also occur downstream of the at least one storage catalyst.

[0112] Unless the present disclosure teaches otherwise, "at least" also includes each entirety.

[0113] The above-described system 1 is preferably used and integrated into a motor vehicle. The engine 2 is preferably a converted conventional diesel engine, particularly preferably a diesel engine of a commercial vehicle such as a truck. The system further provides a hydrogen tank as fuel storage device 15 instead of a diesel tank. For the system 1 and the above-described method, preferably an internal combustion engine based on the diesel principle with a NOx storage catalyst is used, which is accordingly large and therefore ensures a long storage time for the hydrogen engine.

[0114] A further aspect of the invention therefore relates to a method for converting an existing diesel driveline, which can be implemented, for example, in a motor vehicle, in which the fuel storage device is replaced by a hydrogen storage device and the direct injection device is replaced by a spark plug. It is also conceivable to provide a supply device for supplying hydrogen to the combustion chamber, preferably to the cylinder head. If not available, a throttle valve can also be added. Furthermore, a control device is programmed to carry out the above method.

[0115] The present invention also relates to the use of an internal combustion engine used in a diesel driveline comprising at least one storage catalyst and / or at least one storage catalyst in the system and / or for the method described in the present disclosure. [Explanation of symbols]

[0116] 1 System 2. Internal combustion engine 3 Combustion chamber 5. Intake manifold 6,106 exhaust pipe 106a, 106b Exhaust pipe section 7a, 7b Intake and exhaust ports 8. Throttle valve 9 Injection device 10 Spark plugs 11 Piston 12 crankshaft 13, 13a, 13b NOx storage catalyst / NOx storage catalyst 14 Branch 14a, 14b Branch 15 Storage Device 16 lines 16a,19a,19b Inflow device 16a1 Outlet of end part (inlet device) 17 Control device 18a, 18b Throttle device / throttle valve 21a, 21b Nitrogen oxide sensor

Claims

1. A method for operating an internal combustion engine (2), comprising: at least one combustion chamber (3) in which fuel is at least partially combusted with ambient air; an exhaust pipe (6, 106) fluidly connected to the exhaust port side (7b) of the at least one combustion chamber (3); Hydrogen is used as fuel for the internal combustion engine (2), the internal combustion engine (2) has a NOx storage catalyst (13, 13a, 13b), and exhaust gas discharged from the at least one combustion chamber (3) to the exhaust pipe (6) flows at least partially, preferably completely, through the NOx storage catalyst (13, 13a, 13b); a lean air / hydrogen mixture is combusted in said at least one combustion chamber (3) in a first operating state; the NOx storage catalyst (13, 13a, 13b) is regenerated in a second operating state, a rich air / hydrogen mixture is combusted in said at least one combustion chamber (3) at said second operating condition; The second operating state is set to an idling operation of the internal combustion engine (2), and / or A method for operating an internal combustion engine (2), characterized in that the second operating state is set to an overrun operation of the internal combustion engine (2).

2. 2. The method for operating an internal combustion engine (2) according to claim 1, wherein the internal combustion engine (2) further comprises an exhaust gas recirculation device (14), and exhaust gas is returned from the exhaust pipe (6) to the combustion chamber (3) via the exhaust gas recirculation device (14).

3. 3. The method of claim 2, wherein in the second operating state, exhaust gases are recirculated to the at least one combustion chamber via the exhaust gas recirculation device.

4. A control device (17) configured to implement the method according to any one of claims 1 to 3.

5. A system (1) for carrying out the method according to any one of claims 1 to 3, comprising: An internal combustion engine (2) comprising: At least one combustion chamber (3) in which fuel can be at least partially combusted with ambient air; an exhaust pipe (6, 106) fluidly connected to the exhaust port side (7b) of the at least one combustion chamber (3); a NOx storage catalyst (13, 13a, 13b) through which exhaust gas discharged from the at least one combustion chamber (3) into the exhaust pipe (6) can at least partially, preferably completely, pass; an internal combustion engine (2) comprising: a storage device (15) for hydrogen fluidly connected to the internal combustion engine; A control device (17) according to claim 4, Preferably, the internal combustion engine (2) comprises at least one inlet device (16a) capable of supplying a reducing agent to the combustion chamber (3) or to the exhaust pipe (6), preferably at least one inlet device in each exhaust pipe section of a plurality of exhaust pipe sections connected in parallel, The inlet device (16a) is also preferably fluidly connected to the storage device (15) of hydrogen, system (1).

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