Method for operating an internal combustion engine, a system for carrying out the method and an internal combustion engine

Abstract

The invention relates to a method for operating an internal combustion engine (2), wherein the internal combustion engine (2) comprises at least one combustion chamber (3) in which a fuel is at least partially burned with ambient air, an exhaust tract (6) that is fluidically coupled to an outlet 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 has at least one NOx storage catalyst (13) and an exhaust gas discharged from the at least one combustion chamber (3) into the exhaust tract (6) at least partially, preferably entirely, flows through the at least one NOx storage catalyst (13), wherein a lean hydrogen-air mixture is burned in the at least one combustion chamber (3) in a first operating state, wherein the NOx storage catalyst (13) is regenerated in a second operating state. In order to easily operate the internal combustion engine as a low-emissions system, a rich hydrogen-air mixture is burned in the at least one combustion chamber (3) in the second operating state.

Description

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

[0002] It is well known that hydrogen-powered internal combustion engines offer advantages in terms of emissions. These engines eliminate carbon-containing emissions such as soot and carbon monoxide.

[0003] Furthermore, DE10 2016 107 466 A1 proposes a selective catalytic reduction process for reducing NOx components in exhaust gases from hydrogen-powered combustion engines. However, this requires a continuous supply of a reducing agent to the exhaust system. This requires a finely controlled dosing of the reducing agent, which could result in NOx emissions being released into the atmosphere if the reducing agent fails.

[0004] JP 2006 057504 discloses a method in which an internal combustion engine is powered by hydrogen. A nitrogen oxide storage catalyst is located in the exhaust system of the internal combustion engine, which stores nitrogen oxides produced during combustion. To regenerate the nitrogen oxide storage catalyst, fossil fuel is added to the combustion mixture.

[0005] US 2004 / 055 281 A1 and EP 1 754 874 A1 each disclose a method according to the preamble of claim 1.

[0006] Regeneration requires complex control, and several fuels are involved in the formation of the combustion mixture, which complicates the system and combustion.

[0007] The object of this invention is therefore to operate an internal combustion engine in a simple and robust manner as a zero / lowest emission system.

[0008] This object is achieved by a method for operating an internal combustion engine according to claim 1.

[0009] According to a first aspect, a method for operating an internal combustion engine is provided, wherein the internal combustion engine comprises: at least one combustion chamber in which a fuel is at least partially combusted with ambient air; an exhaust system that is fluidly coupled to an outlet side of the at least one combustion chamber. Hydrogen is used as fuel for the internal combustion engine. The internal combustion engine further comprises at least one nitrogen oxide storage catalyst, and an exhaust gas discharged from the at least one combustion chamber into the exhaust system flows at least partially, preferably completely, through the at least one nitrogen oxide storage catalyst. In a first operating state, a lean air / hydrogen mixture is combusted in the at least one combustion chamber.In a second operating state, the nitrogen oxide storage catalyst is regenerated, wherein in the second operating state a rich air / hydrogen mixture is burned in the at least one combustion chamber.

[0010] According to the first aspect, the internal combustion engine has at least one nitrogen oxide storage catalyst through which the discharged exhaust gas flows. This allows nitrogen oxide (NOx) emissions to be stored in said nitrogen oxide storage catalyst, also referred to as an LNT catalyst. Therefore, the continuous supply of reducing agents is unnecessary.

[0011] The first aspect utilizes synergy effects that arise from using hydrogen as fuel for the internal combustion engine. Internal combustion engines operated in this way only produce thermal nitrogen oxides as harmful combustion products. Other exhaust gas aftertreatment systems are therefore unnecessary. Accordingly, space is available in the exhaust system for an appropriately sized nitrogen oxide storage catalyst.

[0012] Furthermore, the process conditions, such as the combustion temperature, of a hydrogen-powered internal combustion engine result in lower nitrogen oxide formation compared to, for example, diesel engines. This allows nitrogen oxides to be reliably stored in the nitrogen oxide catalyst over a long period of time.

[0013] Furthermore, in the method, a lean air / hydrogen mixture is burned in the at least one combustion chamber in a first operating state.

[0014] Combustion of a lean mixture can increase the efficiency of the internal combustion engine. At the same time, combustion temperatures can be reduced, which further inhibits the formation of nitrogen oxides and thus allows the nitrogen oxide storage catalyst to store nitrogen oxides over a long period of time. The lean mixture is preferably burned continuously, i.e., over a large number of internal combustion engine cycles. A lean air / hydrogen mixture is a superstoichiometric mixture. A λ of greater than or equal to 1 and less than or equal to 5 is preferably set; depending on the operating point, a λ of greater than or equal to 1.3 and less than or equal to 3.5 is particularly preferred.

[0015] In addition, the nitrogen oxide storage catalyst is regenerated in a second operating state.

[0016] The nitrogen oxide stored in the nitrogen oxide storage catalyst can be converted into atmospheric nitrogen and released into the environment. The storage catalyst can then absorb new nitrogen oxides. This continuously prevents the release of pollutant emissions.

[0017] According to the invention, in the second operating state, a rich air / hydrogen mixture is burned in the at least one combustion chamber.

[0018] In the second operating state, a substoichiometric air / hydrogen mixture can be supplied to the combustion chamber. A λ of greater than or equal to 0.6 and less than or equal to 1.0, particularly preferably greater than or equal to 0.8 and less than or equal to 0.9, is preferably set. A rich air / hydrogen mixture can, on the one hand, reduce the formation of nitrogen oxide due to a lack of oxygen, preferably completely prevent it, and, on the other hand, ensure that unburned hydrogen is supplied to the exhaust system as a reducing agent. This allows the excess hydrogen to be used to regenerate the nitrogen oxide storage catalyst.

[0019] The rich mixture can be adjusted in appropriate situations due to the low nitrogen oxide formation and the associated long storage period.

[0020] Preferably, the internal combustion engine further comprises an exhaust gas recirculation device which recirculates exhaust gas from the exhaust system into the combustion chamber.

[0021] This allows inert components of the combustion product to be recirculated from the exhaust system to the combustion chamber. These components no longer participate in combustion and extract exothermic energy from the combustion process. This allows the process temperature to be reduced, inhibiting the formation of further nitrogen oxide. Preferably, the exhaust gas is recirculated as high-pressure exhaust gas, particularly from a position upstream of a turbine in the exhaust system. This ensures a sufficient recirculation quantity.

[0022] According to yet another aspect, in the second operating state, exhaust gas can be recirculated into the at least one combustion chamber via the exhaust gas recirculation device.

[0023] Thus, in the second operating state for regenerating the nitrogen oxide storage catalyst, the formation of further nitrogen oxide can be reduced, preferably completely prevented, and the regeneration of the storage catalyst can be carried out reliably. A further advantageous effect occurs particularly in conjunction with hydrogen, since the less reactive mixture can prevent a tendency to pre-ignition, i.e., premature ignition.

[0024] According to the invention, the second operating state can be set in an idling operation of the internal combustion engine.

[0025] In this way, effects of regeneration operation on the behavior of the device driven by the internal combustion engine can be prevented. In particular, in motor vehicles with a hydrogen-powered internal combustion engine, effects on driving behavior can be prevented. As already mentioned, the second operating state can be implemented in appropriate situations, such as when stopped at a traffic light, i.e., in particular when the internal combustion engine is operated without performing its predetermined work, for example, by being disconnected from at least one drive wheel of a vehicle, or in other words, when there is no load on the internal combustion engine. Since such situations occur with sufficient probability when the internal combustion engine is used in a motor vehicle, the operation of the motor vehicle is not limited by necessary regeneration phases of the catalytic converter.Furthermore, by throttling the air flow at idle, high rates of exhaust gas recirculation can be achieved. This is because the exhaust backpressure (upstream of the turbine of a possible turbocharger) is greater than the pressure in the intake manifold in this state. Thus, the above-mentioned effects of exhaust gas recirculation can be reliably achieved in regeneration mode.

[0026] According to the invention, the second operating state can also be set during overrun of the internal combustion engine. Overrun is characterized in particular by the fact that the power generated by the internal combustion engine is less than the drag power applied to the internal combustion engine. In other words, the internal combustion engine can be kept rotating from the output side.

[0027] In this case, too, the operation of a motor vehicle is not limited by necessary regeneration phases of the catalytic converter, since the overrun of the internal combustion engine also occurs with sufficient probability during long journeys. While the amount of air supplied is throttled during idle operation, the amount of fuel supplied can be specifically adjusted during overrun operation to ensure a rich mixture is burned. At the same time, ignition can be delayed very late, which stabilizes combustion and thus reduces, or preferably prevents, the formation of further nitrogen oxides.Preferably, the ignition takes place in a range of a maximum of 40° before the top dead center of a crankshaft angle until the opening of an exhaust valve, in particular in an angular range of a crankshaft of a maximum of 40° before to a maximum of 360° after the top dead center, further preferably from a maximum of 20° before to a maximum of 360° after the top dead center, again preferably from a maximum of an angle corresponding to a top dead center to a maximum of 360° after the top dead center.

[0028] The rich mixture and the delayed ignition allow the exhaust gas enthalpy to be increased, which ensures a sufficient temperature for catalyst regeneration. The power generated by the internal combustion engine during overrun is lower than the applied drag power so that overrun can be maintained. Combusting a rich mixture as regeneration mode during the overrun phase has the advantage that the transition from the lean to the rich mixture range can occur discontinuously, thus eliminating the need to pass through a mixture range around λ equal to 1. In this range, the formation of nitrogen oxides is generally very high.

[0029] Preferably, exhaust gas is recirculated at least temporarily during a transition between the first operating state and the second operating state.

[0030] Thus, even in a case where a mixture close to the stoichiometric ratio is passed through during the transition, the formation of nitrogen oxides can be reduced, preferably completely prevented.

[0031] According to yet another aspect disclosed herein, but not per se according to the invention, which can be provided as an aspect dependent on the first aspect, a method for operating an internal combustion engine is provided, wherein the internal combustion engine has at least one combustion chamber in which a fuel is at least partially combusted with ambient air, and an exhaust system which is coupled in a fluid-communicating manner to an outlet side of the at least one combustion chamber.Hydrogen is used as fuel for the internal combustion engine, wherein the internal combustion engine further comprises at least one nitrogen oxide storage catalyst and an exhaust gas discharged from the at least one combustion chamber into the exhaust system flows at least partially, preferably completely, through the at least one nitrogen oxide storage catalyst, wherein in a first operating state a lean air / hydrogen mixture is combusted in the at least one combustion chamber, wherein in a second operating state the nitrogen oxide storage catalyst is regenerated, wherein in the second operating state a reducing agent for reducing the nitrogen oxides stored in the nitrogen oxide storage catalyst is supplied as part of the exhaust gas into the at least one combustion chamber, or downstream of the at least one combustion chamber upstream of the nitrogen oxide storage catalyst or into the nitrogen oxide storage catalyst into the exhaust system.

[0032] According to this aspect, the combustion of the lean air / hydrogen mixture also produces only thermal nitrogen oxides as harmful combustion products. Other exhaust aftertreatment systems are therefore unnecessary. Accordingly, there is space in the exhaust system for an appropriately dimensioned nitrogen oxide storage catalyst.

[0033] Furthermore, the process conditions, such as the combustion temperature of a lean-burn and / or high-efficiency hydrogen-powered internal combustion engine, result in lower nitrogen oxide formation compared to, for example, diesel engines. This allows nitrogen oxides to be reliably stored in the nitrogen oxide catalyst over a long period of time.

[0034] Combustion of a lean mixture can increase the efficiency of the internal combustion engine. At the same time, combustion temperatures can be reduced, which further inhibits the formation of nitrogen oxides and thus allows the nitrogen oxide storage catalyst to store nitrogen oxides over a long period of time. The lean mixture is preferably burned continuously, i.e., over a large number of internal combustion engine cycles. A lean air / hydrogen mixture is a superstoichiometric mixture. A λ of greater than or equal to 1 and less than or equal to 5 is preferably set; depending on the operating point, a λ of greater than or equal to 1.3 and less than or equal to 3.5 is particularly preferred.

[0035] In addition, the nitrogen oxide storage catalyst is regenerated in a second operating state.

[0036] The nitrogen oxide stored in the nitrogen oxide storage catalyst can be converted into atmospheric nitrogen and released into the environment. The storage catalyst can then absorb new nitrogen oxides. This continuously prevents the release of pollutant emissions.

[0037] Furthermore, according to this aspect, the reducing agent can be supplied directly to the exhaust system without having to be provided as exhaust gas from combustion. Thus, the internal combustion engine can continue to be operated in the first operating state of combustion of a lean air / hydrogen mixture. In particular, a lean air / hydrogen mixture can continue to be combusted. The first and second operating states are therefore not mutually exclusive, but can also exist alongside one another. Of course, the direct supply of a reducing agent to the exhaust system can also occur alongside the combustion of a rich mixture, so that only the second operating state then exists.

[0038] According to this aspect, it is also possible, particularly in internal combustion engines that feed the fuel directly into the combustion chamber, to provide the reducing agent as part of the exhaust gas. The reducing agent can be fed into the combustion chamber and then, after being discharged from the combustion chamber, fed into the exhaust system.

[0039] Preferably, a rotary or divergent component is imparted to the flow of the supplied reducing agent at least in sections.

[0040] This allows the mixing in the exhaust system to be increased and the storage catalyst to be reliably regenerated because the reducing agent flows through it evenly.

[0041] The reducing agent is preferably hydrogen and particularly preferably originates from the same source as the hydrogen used as fuel. In particular, if the reducing agent is injected directly into the combustion chamber, the same supply device used to supply the hydrogen to the combustion chamber can be used.

[0042] This reduces the complexity of the system, as all components can be designed for hydrogen. Furthermore, additional storage devices such as a tank for the reducing agent are no longer required.

[0043] Preferably, the reducing agent is supplied to the combustion chamber after completion of a combustion process, and further preferably during an exhaust stroke in which the exhaust gas is discharged from the combustion chamber. This ensures that the reducing agent is not combusted with the oxygen in the air contained in the combustion chamber.

[0044] According to a further aspect, the second operating state can be set at a saturation level of the nitrogen oxide storage catalyst of greater than 20% or less than 100%, preferably 70-90%, particularly preferably 80%. Known methods for determining the saturation level can be used.

[0045] This allows the storage catalyst to be used across a large portion of its storage capacity. The low nitrogen oxide formation in the initial operating state prevents oversaturation during switching, allowing the switchover to occur very close to the storage capacity limit.

[0046] According to yet another aspect disclosed herein, but not per se according to the invention, which can be provided as an aspect dependent on the above aspects, a method for operating an internal combustion engine is provided, wherein the internal combustion engine has at least one combustion chamber in which a fuel is at least partially combusted with ambient air, and an exhaust system which is fluidly coupled to an outlet side of the at least one combustion chamber, wherein hydrogen is used as fuel for the internal combustion engine.The exhaust system has a plurality of exhaust system sections connected in parallel, wherein at least two of the plurality of exhaust system sections each have at least one nitrogen oxide storage catalyst through which at least a portion of an exhaust gas discharged from the at least one combustion chamber into the exhaust system flows at least temporarily, wherein at least temporarily the flow rate through the at least one nitrogen oxide storage catalyst in at least one of the exhaust system sections is changed, preferably by a variable throttle device arranged upstream of the at least one nitrogen oxide storage catalyst.

[0047] Thus, the flow of the exhaust gas can be influenced depending on the residual capacity of at least one nitrogen oxide storage catalyst. If the nitrogen oxide storage catalyst in an exhaust system is close to its capacity limit, the flow rate in this exhaust system can be reduced, while larger amounts can continue to flow through nitrogen oxide storage catalysts connected in parallel. This also allows the nitrogen oxide storage catalyst to be operated efficiently, as in the above aspects.

[0048] Preferably, the flow rate is changed independently of one another in a plurality of exhaust system sections, each of which has the at least one nitrogen oxide storage catalyst.

[0049] For this purpose, a variable throttle device can be arranged at least in one, preferably in a plurality of, the plurality of exhaust line sections arranged parallel to one another upstream of the at least one nitrogen oxide storage catalyst, which is individually controlled to regulate the amount of exhaust gas in the respective exhaust line section.

[0050] This means that each nitrogen oxide storage catalyst connected in parallel can react independently.

[0051] Furthermore, in order to regenerate the at least one nitrogen oxide storage catalyst, the flow rate in at least one of the exhaust system sections can be reduced, preferably completely suppressed.

[0052] For example, if the internal combustion engine is operated with a lean combustion mixture, nitrogen oxides would continue to flow through at least one exhaust system section with the nitrogen oxide storage catalyst in an unthrottled state, near the capacity limit. This reduction can thus suppress a further significant supply of nitrogen oxides in at least one of the exhaust system sections during regeneration.

[0053] Preferably, a reducing agent for reducing the nitrogen oxides stored in the nitrogen oxide storage catalyst is supplied upstream of the at least one nitrogen oxide storage catalyst or into the at least one nitrogen oxide storage catalyst at least in one, particularly preferably in each, of the plurality of exhaust gas line sections connected in parallel, and particularly preferably the amount of reducing agent supplied is individually controlled for each exhaust gas line section.

[0054] This increases the efficiency of nitrogen oxide storage and regeneration. The internal combustion engine can continue to operate with a lean combustion mixture. If only a single exhaust system is provided in this process, a considerable amount of reducing agent (hydrogen) must be supplied to compensate for the oxygen present due to the lean combustion. Only then can regeneration take place in the absence of oxygen. In contrast, the above aspect allows the oxygen supply in the at least one exhaust system section in question to be reduced, for example by the throttle device, whereby a smaller amount of hydrogen is required compared to the case in which only one exhaust system section is provided, even if the internal combustion engine continues to operate with a lean combustion mixture.The separate supply of reducing agent to the respective exhaust line section is therefore particularly advantageous if, for regeneration purposes, the flow rate in the respective exhaust line section is reduced compared to a non-regeneration state such as the unthrottled state.

[0055] According to a further aspect, regeneration can be carried out alternately at least in two of the exhaust system sections.

[0056] For example, the greatest increase in efficiency is achieved in the case of two storage catalytic converters connected in parallel when the internal combustion engine is operated at a maximum of half its maximum power. In this case, the throttle device of an exhaust system section can be controlled, at least for the regeneration of the storage catalytic converter arranged therein, in such a way that it completely blocks the exhaust gas supply in this exhaust system section, at least one of whose storage catalytic converters is to be regenerated. In this case, the throttle device in the parallel exhaust system section is preferably controlled so that it is fully open. Thus, regeneration takes place alternately in two of the exhaust system sections, with regeneration occurring in one exhaust system section and not in the other. Likewise, the change in the flow rate compared to a reference state, such as the non-regeneration state, in particular the reduction, can take place alternately.Particularly preferably, the respective throttle devices are alternately fully opened and closed during operation of the internal combustion engine up to half of the maximum power, i.e., the respective flow rates are alternately completely suppressed and not reduced. Preferably, the flow rates are alternately reduced, in particular completely suppressed, and not reduced, up to one times the rated power minus the reciprocal of the number of parallel exhaust system sections times the rated power.

[0057] According to a further aspect, at least the storage catalysts connected in parallel, preferably the entire exhaust system sections, can be configured such that the nitrogen oxides generated at maximum power can be completely stored in the unthrottled state of all exhaust system sections, i.e., when the flow rate is not reduced. In particular, the sum of all storage catalysts connected in parallel is configured according to a predetermined space velocity. Preferably, the storage catalysts and exhaust system sections are dimensioned identically.

[0058] However, it is also conceivable to configure at least the storage catalysts connected in parallel, preferably the entire respective exhaust system section, such that the flow rate can be completely suppressed at least in one exhaust system section at rated power. The flow rate can then flow at rated power through the remaining exhaust system sections, in which the flow rate is not reduced, and the storage catalysts arranged therein. This ensures that nitrogen oxide generated even at rated power is stored in the storage catalysts of the non-reduced exhaust system sections. In particular, the sum of the remaining storage catalysts connected in parallel can be configured according to the specified space velocity.In the case of two parallel exhaust system sections, each of the exhaust system sections is preferably configured such that, at rated power, the nitrogen oxides generated are completely stored in the at least one storage catalyst of the exhaust system section in which the flow rate is not reduced. Thus, the map range in which complete regeneration is possible can be expanded.

[0059] Furthermore, the object is achieved by a control device which is configured to carry out the method according to one of the preceding aspects.

[0060] Such a control device allows a platform in which it is installed to be operated as a low-emission system.

[0061] In addition to the control device, this invention also relates to a program that, when executed on a computer coupled to an internal combustion engine, carries out the above method. This invention also relates to a computer-readable storage medium on which said program is stored.

[0062] Furthermore, the above object is achieved by a system for carrying out a method according to one of the above aspects, wherein the system comprises: an internal combustion engine as defined according to one of the above aspects; and a storage device for hydrogen which is fluidly coupled to the internal combustion engine.

[0063] Such a system represents a reliable zero / low emission system.

[0064] Furthermore, the system further comprises a control device which is configured to carry out the method according to one of the above aspects.

[0065] Through the interaction of the control device, the internal combustion engine and the storage device, the above effects can be reliably realized.

[0066] Preferably, in the system, the internal combustion engine further comprises at least one inflow device via which the reducing agent can be supplied into the combustion chamber or into the exhaust system, preferably at least one inflow device for each exhaust system section in the case of a plurality of exhaust system sections connected in parallel.

[0067] This means that in the internal combustion engine, the reducing agent can be fed into the exhaust system via the combustion chamber or bypassing the combustion chamber, so that a mixture switch from a lean mixture to a rich mixture is not necessary.

[0068] Preferably, in the system, the internal combustion engine is further configured to impart a rotary or divergent component to the flow of the reducing agent in the exhaust gas line, at least in sections, wherein the internal combustion engine preferably has a spiral device or a profile inclined relative to a main flow direction.

[0069] This allows for improved mixing of the reducing agent in the exhaust system, increasing the efficiency of the catalyst. The spiral device makes it easy to impose the rotational component. By adjusting the profile, the flow can be made divergent along this profile.

[0070] Furthermore, an internal combustion engine for the system just described is provided, which in particular can have any combination of the structural features of this disclosure.

[0071] The above aspects will now be explained in more detail using exemplary embodiments according to the figures.

[0072] Fig. 1 shows a schematic of a system with which the method explained above can be carried out.

[0073] Fig. 2 shows a schematic longitudinal sectional view of a modification of an exhaust system of an internal combustion engine not according to the invention as such.

[0074] Fig. 3 shows a flow chart for a process for regenerating a nitrogen oxide storage catalyst.

[0075] The system 1 has an internal combustion engine 2 (motor) which Fig. 1 in a longitudinal sectional view along an 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 pipe 5 and an exhaust line 6, each of which is fluidly connected to the combustion chamber via an inlet and outlet 7a and 7b, which are opened and closed by valves.

[0076] In the intake pipe 5, as shown in the Fig. 1 As shown, a throttle valve 8 for regulating the air flow and an injection device 9 for injecting fuel into the intake manifold 5 are located. At an 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 inlet 7a. At the lower end, the combustion chamber 3 is closed by a piston 11, which is rotatably coupled to a crankshaft 12. Hydrogen is preferably used exclusively as the fuel.

[0077] With respect to the axis, opposite the inlet 7a is the outlet 7b, through which the exhaust gas produced by combustion of the air / fuel mixture flows into the exhaust system 6.

[0078] A NOx storage catalyst (NSC) 13 is located in the exhaust system 6 downstream of the outlet 7b. This NOx storage catalyst 13 consists essentially of an aluminum oxide support on which CeO2 and Ba(OH)2 or BaCO3 are applied. Platinum, rhodium, or even palladium can serve as active components, for example.

[0079] Upstream of the storage catalyst 13, the exhaust system has a branch 14. Branch 14a, in which the storage catalyst 13 is located, ends in a tailpipe of the exhaust system, while the other branch 14b is part of an exhaust gas recirculation device and opens into the intake pipe 5 at the downstream end relative to the branch. The exhaust gas recirculation device thus recirculates high-pressure gas. The exhaust gas recirculation device can further contain, for example, valves and sensors for monitoring the recirculated exhaust gas. A turbine driving an exhaust gas turbocharger can also be provided in branch 14a, preferably upstream of the storage catalyst 13.

[0080] The system 1 further comprises a storage device 15 filled with hydrogen. The storage device 15 is coupled to the intake pipe 5 in a fluid-communicating manner via the injection device 9, wherein the injection device 9 can inject the hydrogen into the intake pipe 5 upstream of the inlet 7a. The injection device 9 is an example of a supply device for supplying the fuel. Furthermore, the storage device 15 is coupled to the exhaust system upstream of the catalyst 13 in a fluid-communicating manner via a line 16. An end section 16a (injector) of the line 16 is designed in a divergent shape toward the outlet 16a1, thus representing a profile inclined with respect to a main flow direction of the line 16. The end section 16a with the outlet 16a1 is an inflow device for the reducing agent within the meaning of the claims.

[0081] Furthermore, the system 1 comprises a control device 17, such as an ECU. The control device 17 receives signals (shown in dashed lines) from numerous sensors arranged in the system 1 and, in turn, controls actuators and valves arranged in the system 1 via electrical signals (shown in dashed lines).

[0082] The method described above can be carried out with system 1. If the control device 17 receives a start signal to start the internal combustion engine 2, the injection device 9 is activated to inject the hydrogen fuel into the air in the intake manifold 5 during the intake stroke. The combustion of the hydrogen / air mixture in the combustion chamber 3, ignited by the spark plug 10, delivers power to the crankshaft 12. The combustion product enters the exhaust system 6 as exhaust gas through the outlet 7b. There, it flows through the NOx storage catalyst 13.

[0083] The function of the storage catalyst 13 is as follows. In a regular first operating state of the engine 2 (λ>1, combustion of a lean mixture), NO is oxidized by the precious metals, such as platinum, of the catalyst 9 by means of the excess oxygen to form NO2. This NO2 is bound to storage components, preferably basic storage components such as Ba(OH)2 or BaCO3, as nitrite and, above all, nitrate.

[0084] The engine 2 can be operated continuously in the first operating state. Combustion of a lean mixture can increase the efficiency of the engine 2. At the same time, combustion temperatures can be reduced, which inhibits the formation of nitrogen oxides and thus allows the nitrogen oxide storage catalyst 13 to store nitrogen oxides over a long period of time. The lean mixture is preferably burned continuously, i.e., over a large number of cycles of the internal combustion engine. Preferably, a λ of greater than or equal to 1 and less than or equal to 5 is set; depending on the operating point, a λ of greater than or equal to 1.3 and less than or equal to 3.5 is particularly preferred.

[0085] If the control device 17 now receives the information that the engine 2 is operating in idling mode, for example because the motor vehicle in which the system 1 is used is stopped at a traffic light, the control device 17 controls the throttle valve 8 and thus reduces the amount of air in the intake pipe 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 branch 14b and reducing the flow rate of the exhaust gas in branch 14a. Thus, in idling mode, a second operating state is set in which a rich air / hydrogen mixture (λ<1) is burned, since the amount of air is reduced to such an extent that a rich mixture is established with the amount of fuel injected by the injection device 9 at the same mixture calorific value. At the same time, recirculated exhaust gas is fed to the mixture.The air supply is preferably adjusted so that a substoichiometric mixture with the mixture heating value required at least for idle power is achieved.

[0086] A rich air / hydrogen mixture can, on the one hand, reduce, preferably completely prevent, the formation of nitrogen oxide due to the complete combustion of oxygen with hydrogen. On the other hand, it can ensure that unburned hydrogen is supplied to the exhaust system 6 as a reducing agent. This allows the excess hydrogen to be used to regenerate the nitrogen oxide storage catalyst 13. The recirculated exhaust gas returns inert components of the combustion product from the exhaust system 6 to the combustion chamber 3. These components no longer participate in combustion. This allows the process temperature to be reduced, which inhibits the formation of further nitrogen oxide. This allows the regeneration of the storage catalyst to be carried out reliably.For this reason, it is also advantageous if exhaust gas is recirculated at least temporarily during a transition between the first operating state and the second operating state.

[0087] Preferably, the second operating state is set by the control device 17 until the catalyst 13 is completely regenerated.

[0088] In a similar manner to idle operation, the control device can also set the second operating state during overrun of the engine 2. If, for example, the control device 17 determines that overrun is present, the control device 17 controls the injection device 9 such that a rich mixture is present in accordance with the supplied air quantity, which can be regulated by the throttle valve 8. Furthermore, the exhaust gas recirculation is activated in a similar manner to idle operation.

[0089] A prerequisite for overrun operation is that the operator (e.g., a driver) does not request any torque from the internal combustion engine, i.e., the accelerator pedal is not depressed. To ensure zero torque despite fuel supply, spark plug 10 is activated at a very late point in time.

[0090] Preferably, the ignition takes place in a range of a maximum of 40° before the top dead center of a crankshaft angle until the opening of an exhaust valve, in particular in an angular range of a crankshaft of a maximum of 40° before to a maximum of 360° after the top dead center, further preferably from a maximum of 20° before to a maximum of 360° after the top dead center, again preferably from a maximum of an angle corresponding to a top dead center to a maximum of 360° after the top dead center.

[0091] Preferably, the air supply during overrun is reduced compared to a working mode (driven by the internal combustion engine), for example, by opening the throttle valve. This means that only a very small amount of hydrogen needs to be supplied to create a rich mixture.

[0092] The rich mixture and the late ignition allow the exhaust gas enthalpy to be increased, which ensures a temperature sufficient for regeneration of the catalytic converter 13. The power generated by the internal combustion engine during overrun mode, corresponding to the rich mixture calorific value, is less than the drag power applied to the internal combustion engine. Carrying out combustion of a rich mixture as regeneration mode during the overrun phase has the advantage that the transition from the lean to the rich mixture range can be discontinuous and thus a mixture range around λ equal to 1 does not have to be passed through. In this range, the formation of nitrogen oxides is generally very high. During the transition to idling mode, it may under certain circumstances occur that a mixture range with high nitrogen oxide formation is passed through if the mixture is continuously transferred from the superstoichiometric to the substoichiometric range.

[0093] The procedure described above is carried out with the help of Fig. 3 summarized. In a step S1, system 1 continuously monitors the NOx saturation level of the catalyst 13. Known methods, for example, can be used by measuring and / or modeling the saturation level. If control device 17 determines that the saturation level has reached a predetermined limit value Th, for example, greater than 20% or less than 100%, preferably 70-90%, regeneration is requested in step S2, i.e., the second operating state is specified.

[0094] In a step S3, a check is carried out to determine whether idling operation LL or overrun operation SB can be expected within a predetermined time interval. For example, reference can be made to the route profile on which a motor vehicle with an internal combustion engine is traveling, or to navigation data. The predetermined time interval preferably depends on the limit value Th. If idling or overrun operation can be expected within the predetermined time interval, regeneration is carried out in one of the two states in a step S3a. If it is determined that idling or overrun operation is not or will not be present, a shut-off valve in line 16 is released, for example, and hydrogen from the hydrogen storage device 15 is fed directly into the exhaust system 6 via the inflow device 16a, bypassing the combustion chamber 3.Thus, regeneration of catalyst 13 can be ensured even if an appropriate condition for rich combustion does not occur over a long period of time. In particular, catalyst 13 can be regenerated at full load (VL or TL).

[0095] If necessary, line 16 and inflow device 16a can also be omitted. Then, for example, when the saturation level of the catalyst 13 is greater than 20% or less than 100%, preferably 70-90%, the control device 17 can issue a warning to the user of the internal combustion engine 2 (driver) that they should switch to idle mode. The limit value is preferably lower than when the inflow device is present, in order to provide sufficient time to switch to overrun or idle mode.

[0096] Likewise, the control device 17, not according to the invention as such, can also be programmed such that it does not adjust the combustion of a rich mixture with exhaust gas recirculation either during overrun or idling operation. In this case, regeneration in the second operating state can take place solely via the line 16 and the inflow device 16a, with a reducing agent being fed directly into the exhaust system 6. The engine 2 can thus continue to be operated in the first operating state (lean mixture) while the second operating state exists simultaneously. Alternatively or additionally, it is also possible, particularly if the fuel in the engine is fed directly into the combustion chamber 3 via a feed device, to provide the reducing agent as part of the exhaust gas. The reducing agent can be fed into the combustion chamber 3 and then, after being discharged from the combustion chamber 3, fed to the exhaust system 6.The supply to the combustion chamber 3 preferably occurs after the completion of a combustion process, i.e., when ignition by the spark plug is complete, and the energy of the combusted mixture does not allow combustion of the reducing agent supplied, particularly during the exhaust stroke. In particular, the reducing agent is hydrogen and can be supplied via the same supply device as the combusted hydrogen. In this case, too, a lean mixture can be combusted.

[0097] In Fig. 2 a schematic longitudinal sectional view of a modification of an exhaust system 106 of the engine, which is not in itself according to the invention, is shown.

[0098] As in Fig. 2 As shown, the exhaust line 106 differs from the above exhaust line 6 in that it is divided into two exhaust line sections 106a and 106b, preferably downstream of the Fig. 1shown branching, which are connected in parallel to one another, for example. Both the exhaust line section 106a and the exhaust line section 106b each have a nitrogen oxide storage catalyst 13a and 13b. Throttle valves (throttle devices within the meaning of the claims) 18a and 18b are located upstream of the two catalysts 13a and 13b. Between the throttle valves 18a and 18b and the catalysts 13a and 13b, an inflow device 19a or 19b is also provided, via which a reducing agent for regenerating the catalysts 13a and 13b can be supplied to the respective exhaust line section 106a and 106b, whereby at least one combustion chamber is bypassed. In other words, each exhaust system section 106a and 106b has an inflow device 19a and 19b upstream of the catalysts 13a and 13b. Each inflow device 19a and 19b preferably comprises an injector.The injector injects the reducing agent (hydrogen) into the exhaust line section 106a and 106b.

[0099] The throttle valves 18a and 18b are designed to be variable in terms of their degree of throttling. The opening angle of each throttle valve 18a and 18b can be adjusted individually, i.e., independently of the other throttle valve. Thus, the amount of exhaust gas flowing into the respective exhaust line section 106a and 106b can be varied, in particular, individually regulated. Likewise, the inflow devices (injectors) can be individually controlled, so that reducing agent can be supplied separately to each exhaust line section 106a and 106b. In particular, the supplied amount (mass flow) of reducing agent is individually controlled.

[0100] The advantage of the above modification is that the engine can be operated at the optimal operating point and does not have to perform rich combustion to avoid oxygen and nitrogen oxide components in the exhaust gas. According to the above modification, the efficiency of nitrogen oxide storage and regeneration can be increased. If one (e.g. 13a) of the nitrogen oxide storage catalysts 13a and 13b in the parallel exhaust system sections is close to its capacity limit, for example above the predetermined limit value Th, exhaust gas can still be stored in the other nitrogen oxide storage catalyst 13b in the other exhaust system section 106b by the throttle device 18a of the exhaust system section in which the storage catalyst 13a is located, which is operating close to its capacity limit, reducing the supplied flow rate for this exhaust system section, preferably by completely suppressing it.This configuration proves particularly effective during regeneration. With only one storage catalyst, either the internal combustion engine must be operated rich for regeneration, or a significant amount of reducing agent must be separately introduced into the exhaust system, bypassing at least one combustion chamber. With the latter method, the internal combustion engine can continue to operate lean, but a significant amount of reducing agent (hydrogen) must be introduced to compensate for the oxygen present due to lean combustion. Only then can regeneration take place in the absence of oxygen.In contrast, the present embodiment allows the oxygen supply in the relevant exhaust gas section 106a to be reduced by the throttle device 18a, whereby a smaller amount of hydrogen is required compared to only one exhaust gas section as in the first embodiment.

[0101] Preferably, the storage catalysts 13a and 13b and the exhaust system sections 106a and 106b are identically dimensioned. The parallel-connected storage catalysts 13a and 13b and the exhaust system sections 106a and 106b are configured in such a way that the nitrogen oxides produced at maximum power can be completely stored when all exhaust system sections are unthrottled, i.e., when the flow rate is not reduced. In other words, the entire exhaust gas produced at maximum power, possibly minus an exhaust gas recirculation amount, is purified of nitrogen oxide when the exhaust system sections 106a and 106b are fully open.

[0102] The greatest efficiency increase is achieved with two storage catalysts connected in parallel when the internal combustion engine is operated at a maximum of half its maximum power. Consequently, the flow rates are alternately reduced, specifically completely suppressed, and not reduced at an applied power of up to one times the rated power minus the reciprocal of the number of exhaust system sections arranged in parallel (two, reciprocal: 1 / 2) times the rated power.

[0103] In this case, the throttle device 18a of an exhaust system section can be controlled, at least for the purpose of regenerating the storage catalyst 13a arranged therein, such that it completely blocks the exhaust gas supply in this exhaust system section 106a, whose at least one storage catalyst 13a is to be regenerated. In the parallel exhaust system section 106b, the throttle device 18b is preferably controlled such that it is fully open. The respective flow rates are thus alternately completely suppressed and not reduced.

[0104] Particularly preferably, the respective throttle devices 18a and 18b are alternately fully opened and closed during operation of the internal combustion engine at an applied power of up to half of the maximum power. The ECU 17 controls the throttle valves 18a and 18b, as well as the intake devices 19a and 19b.

[0105] However, it is also conceivable to configure at least the storage catalysts arranged in parallel, preferably the entire respective exhaust system section, in such a way that the flow rate can be completely suppressed at least in one exhaust system section at rated power (maximum power). The flow rate can then flow through the remaining exhaust system sections, in which the flow rate is not reduced, and the storage catalysts arranged therein at rated power. This ensures that nitrogen oxide generated is stored in the storage catalysts of the non-reduced exhaust system sections, even at rated power.With two parallel exhaust system sections, each of the exhaust system sections is preferably configured so that, at rated power, the resulting nitrogen oxides can be completely stored in the at least one storage catalyst of the exhaust system section, where the flow rate is not reduced. This allows the engine map range in which complete regeneration is possible to be expanded. The catalysts and exhaust system sections are thus oversized compared to the case where they are collectively designed so that the entire exhaust gas volume can be purified in the unthrottled state.

[0106] Downstream of the catalysts are nitrogen oxide sensors 21a and 21b, which detect the nitrogen oxide content in the aftertreated exhaust gas and can thus determine complete saturation or a malfunction of the catalysts. For example, if a nitrogen oxide content is detected downstream of the catalyst 13a, the control device 17 can control the throttle valve 18a so that it is completely closed. At the same time, the other throttle valve 18b is completely opened. The saturation level in the catalysts themselves can be measured using known methods. The saturation level can also be modeled.

[0107] It is also possible to arrange at least one nitrogen oxide sensor upstream of the storage catalysts. This can be done in each of the parallel exhaust system sections 106a and 106b, preferably upstream of the respective throttle valve, and / or in the common exhaust system 106 upstream of the split. In particular, an output of this at least one nitrogen oxide sensor can be used to control the parallel exhaust system sections.

[0108] The exhaust system sections, in particular throttle valves and injectors, can thus be controlled based on a signal from at least one nitrogen oxide sensor upstream or downstream of the catalysts. It is preferred that the throttle valves 18a and 18b be controlled such that when the regeneration limit, for example, of 80% saturation level in one catalyst 13a, is reached, the other catalyst 13b has a saturation level difference of at least 20% from its regeneration limit. In this way, it can be ensured that when the catalyst 13a is regenerated, the other catalyst 13b has sufficient capacity for additional nitrogen oxide.

[0109] In this modification, the number of exhaust system sections is not limited to two. Rather, more than two exhaust system sections can be provided. Furthermore, advantageous effects are achieved even if only one of the exhaust system sections upstream of the catalytic converter has a variable throttle device. This allows the respective catalytic converter to be kept free of further nitrogen oxide when its capacity limit is reached and to be regenerated independently of the other parallel catalytic converters. Preferably, the parallel catalytic converters and / or the exhaust system sections are designed with a 1:1 storage volume or cross-sectional area ratio. This allows for a particularly significant increase in efficiency.

[0110] A rich combustion mixture can also be burned for regeneration.

[0111] Likewise, in the above embodiments, a plurality of combustion chambers can be provided instead of one combustion chamber.

[0112] As already mentioned, the type of mixture formation is irrelevant. This can occur inside or outside the combustion chamber.

[0113] Instead of the inclined profile in the end section 16a of the line 16, a spiral device with helical flights can also be provided, 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 line or exhaust line section. In this case, an inclined profile does not need to be provided. The inclined arrangement imparts a rotational component to the flow.

[0114] It is advantageous if the exhaust gas is recirculated upstream of the at least one storage catalyst, but the exhaust gas recirculation can also take place downstream of the at least one storage catalyst.

[0115] Unless the present disclosure teaches otherwise, "at least" also includes the respective entirety.

[0116] The above system 1 is preferably used in a motor vehicle and is embedded therein. The engine 2 is preferably a converted conventional diesel engine, particularly preferably a diesel engine of a commercial vehicle such as a truck. Furthermore, instead of a diesel tank, a hydrogen tank is provided in the system as the fuel storage device 15. For the system 1 and the above method, an internal combustion engine based on the diesel principle is preferably used, including a nitrogen oxide storage catalyst. The catalyst is correspondingly large and thus ensures long storage times for the hydrogen engine.

[0117] A further aspect of this disclosure is thus directed to a conversion method for an existing diesel-powered system, which can be implemented, for example, in a motor vehicle, wherein 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 the hydrogen into the combustion chamber, preferably on the cylinder head. If not present, a throttle valve can also be added. Furthermore, the control device is programmed to execute the above method.

[0118] The disclosure also relates to a use of an internal combustion engine used in a diesel-powered system, which is provided with at least one storage catalyst, and / or the at least one storage catalyst in a system described in this disclosure and / or for a method described in this system. List of reference symbols

[0119] 1System 2Internal combustion engine 3Combustion chamber 5Intake pipe 6, 106Exhaust system 106a, 106bExhaust system sections 7a, 7bInlet, outlet 8Throttle valve 9Injection device 10Spark plug 11Piston 12Crankshaft 13, 13a, 13bNitrogen oxide storage catalyst 14Branch 14a, 14bBranch 15Storage device 16Line 16a, 19a, 19bInlet device 16a1Outlet of the end section (of the inlet device) 17Control device 18a, 18bThrottle device 21a, 21bNitrogen oxide sensor

Claims

1. Method for operating an internal combustion engine (2), wherein the internal combustion engine (2) comprises: at least one combustion chamber (3) in which a fuel is at least partially burned with ambient air, an exhaust tract (6, 106) that is coupled to an outlet side (7b) of the at least one combustion chamber (3) in a fluid communicating manner, wherein hydrogen is used as fuel for the internal combustion engine (2), wherein the internal combustion engine (2) also has at least one NOx storage catalyst (13, 13a, 13b) and an exhaust gas discharged from the at least one combustion chamber (3) into the exhaust tract (6) at least partially, preferably entirely, flows through the at least one NOx storage catalyst (13, 13a, 13b), wherein a lean air / hydrogen mixture is burned in the at least one combustion chamber (3) in a first operating state, wherein the NOx storage catalyst (13, 13a, 13b) is regenerated in a second operating state, and a rich air / hydrogen mixture is burned in the at least one combustion chamber (3) in the second operating state characterized in that the second operating state is set in an idling operation of the internal combustion engine (2) and / or the second operating state is set in an overrun operation of the internal combustion engine (2).

2. 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), via which exhaust gas is returned from the exhaust tract (6) to the combustion chamber (3).

3. Method for operating an internal combustion engine (2) according to claim 2, wherein, in the second operating state, exhaust gas is recirculated into the at least one combustion chamber (3) via the exhaust gas recirculation device (14).

4. Control device (17) configured to carry out a method according to one of the preceding claims.

5. System (1) for carrying out a method according to one of claims 1 to 3, comprising: an internal combustion engine (2), wherein the internal combustion engine (2) comprises: at least one combustion chamber (3) in which a fuel is at least partially burnable with ambient air, an exhaust tract (6, 106) which is coupled to an outlet side (7b) of the at least one combustion chamber (3) in a fluid communicating manner, and also at least one NOx storage catalyst (13, 13a, 13b), wherein an exhaust gas discharged from the at least one combustion chamber (3) into the exhaust tract (6) can at least partially, preferably entirely, flow through the at least one NOx storage catalyst (13, 13a, 13b); and a storage device (15) for hydrogen, which is coupled to the internal combustion engine in a fluid communicating manner, and the control device (17) according to claim 4, and wherein preferably the internal combustion engine (2) also has at least one inflow device (16a) via which a reduction agent can be fed into the combustion chamber (3) or into the exhaust tract (6), preferably at least one inflow device for each exhaust tract section of a plurality of exhaust tract sections connected in parallel, respectively, wherein the inflow device (16a) is also preferably coupled to the storage device (15) for hydrogen in a fluid communicating manner.

6. Program configured to carry out a method according to at least one of the claims 1 to 3, when it is executed on a control device (4) according to claim 4 coupled to an internal combustion engine (2).

7. Storage medium, on which the program according to claim 6 is stored.

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