Exhaust system for a hydrogen combustion engine and method for operating an exhaust system of a hydrogen combustion engine

Abstract

Exhaust system (100) for a hydrogen combustion engine (10) designed to be operated with hydrogen gas as fuel, wherein the hydrogen gas is burned with air in at least one combustion chamber, wherein the exhaust system (100) comprises: - an exhaust pipe (102) for directing the exhaust gas flowing out of at least one combustion chamber, - a first catalyst device (110) arranged in the exhaust pipe (102) downstream of at least one combustion chamber, which is designed to at least partially treat the exhaust gas, - a second catalyst device (120) arranged in the exhaust pipe (102) downstream of the at least one combustion chamber and upstream of the first catalyst device (110), which is designed to at least partially treat the exhaust gas, and - a hydrogen gas injection device (170) arranged upstream of the second catalyst device (120), which is configured to inject hydrogen gas so that the injected hydrogen gas reacts with the oxygen present in the second catalyst device (120) to heat the exhaust gas, and - a bypass line (104) designed to direct the exhaust gas past the second catalyst device (120) to the first catalyst device (110).

Description

[0001] The present invention relates to an exhaust system for a hydrogen combustion engine and a method for operating an exhaust system of a hydrogen combustion engine, in particular an exhaust system for a hydrogen combustion engine with a device for rapidly heating the catalyst device and a corresponding method for this purpose.

[0002] Hydrogen combustion engines are becoming increasingly important due to ever stricter emissions regulations, particularly regarding carbon oxide emissions. In a hydrogen combustion engine, the high temperatures and the nitrogen present in the air can also produce nitrogen oxides in the exhaust gas. These can be treated with a catalyst, such as one based on the principle of selective catalytic reduction (SCR), in combination with hydrogen gas to significantly reduce nitrogen oxide emissions. In contrast, it is known that in fossil fuel combustion engines, a catalyst, such as one based on SCR, must be heated to a predetermined operating temperature to ensure efficient conversion of the nitrogen oxides.For this purpose, it is known to combine a conventional catalyst substrate with an electrically heated disk that can heat the catalyst substrate to the predetermined temperature.

[0003] Furthermore, an exhaust gas purification system for a hydrogen engine is known from DE 10 2007 021 827 A1. The exhaust gas purification system disclosed therein comprises a hydrogen storage tank for storing hydrogen under high pressure, a hydrogen engine for burning hydrogen supplied from the hydrogen storage tank, and a catalyst. The exhaust gas purification system is capable of introducing hydrogen gas into the exhaust pipe during operation of the hydrogen engine. The system also includes an upstream exhaust gas sensor, which is arranged in the exhaust pipe upstream of the catalyst for detecting the exhaust gas element, and an exhaust-side hydrogen gas injection device, which is configured upstream of the upstream exhaust gas sensor for injecting hydrogen gas into the exhaust pipe.

[0004] DE 103 47 133 A1 relates to a system and a method for effective NOx and particulate matter control in a diesel or other internal combustion lean-burn engine. The system comprises a urea-based SCR catalyst with an oxidation catalyst connected upstream of it and a particulate filter connected downstream of the SCR catalyst. The method for particulate filter regeneration teaches the control of operating conditions to bring the particulate filter temperature into a range at which an exothermic reaction occurs between hydrocarbons and oxygen. Once this is achieved, additional hydrocarbons are injected into the exhaust gas entering the particulate filter, where they combust and the resulting exothermic reaction regenerates the filter.

[0005] DE 10 2005 037 959 A1 relates to a device for the aftertreatment of exhaust gases exiting an internal combustion engine. The device has an exhaust pipe in which an oxidation catalyst for the oxidation of nitrogen oxides is arranged. A bypass pipe branches off from the exhaust pipe upstream of the oxidation catalyst in the direction of exhaust gas flow and opens back into the exhaust pipe downstream of the oxidation catalyst. The amount of exhaust gas flowing through the oxidation catalyst and the bypass pipe is adjustable by means of a flow distribution device.

[0006] The present invention is based, at least in part, on the objective of providing an exhaust system for a hydrogen combustion engine and a method for operating an exhaust system of a hydrogen combustion engine, in each case to heat the catalyst device arranged in the exhaust system to its operating temperature as early and quickly as possible.

[0007] This problem is solved by an exhaust system for a hydrogen combustion engine according to independent claim 1 and a method for operating an exhaust system of a hydrogen combustion engine with the features according to independent claim 10. Preferred and advantageous embodiments are specified in the dependent claims.

[0008] The present invention is essentially based on the idea of ​​heating a (main) catalyst device, in particular an SCR catalyst device, of an exhaust system for a hydrogen combustion engine to its predetermined operating temperature by providing an additional catalyst device upstream of the (main) catalyst device and a hydrogen gas injection device configured to inject hydrogen gas upstream of the additional catalyst device, so that the injected hydrogen gas can react with the oxygen present in the additional catalyst device to heat the exhaust gas. The exhaust gas thus heated can then be used by the (main) catalyst device to preheat it in order to heat it to the predetermined operating temperature as early and as quickly as possible.

[0009] Consequently, according to a first aspect, an exhaust system for a hydrogen combustion engine is disclosed, which is configured to be operated with hydrogen gas as fuel. The hydrogen gas is combusted with air in at least one combustion chamber. The exhaust system according to the invention comprises an exhaust pipe for directing the exhaust gas flowing out of the at least one combustion chamber, a first catalyst device arranged in the exhaust pipe downstream of the at least one combustion chamber, which is configured to at least partially treat the exhaust gas, a second catalyst device arranged in the exhaust pipe downstream of the at least one combustion chamber and upstream of the first catalyst device, which is configured to at least partially treat the exhaust gas, and a hydrogen gas injection device arranged upstream of the second catalyst device, which is configured toTo inject hydrogen gas so that the injected hydrogen gas reacts with the oxygen present in the second catalyst device to heat the exhaust gas and, as it flows through the exhaust pipe and through the first catalyst device, heats it to a predetermined operating temperature.

[0010] The invention takes advantage of the fact that in the second catalyst device, the hydrogen gas injected upstream can react with the oxygen it contains, generating exothermic energy, which simultaneously heats the exhaust gas flowing through it significantly. This significantly heated exhaust gas can then heat the first catalyst device, located downstream of the second catalyst device in the exhaust pipe, to its predetermined operating temperature much more quickly. This can lead to the first (main) catalyst device reaching its efficient normal operating temperature sooner, thus reducing the pollutant emissions of the hydrogen combustion engine.

[0011] Preferably, the first catalyst device is a so-called SCR catalyst device, which is based on the principle of selective catalytic reduction with hydrogen gas. In this process, the injected hydrogen gas reacts with the nitrogen oxides in the exhaust gas to form water and nitrogen.

[0012] Furthermore, it is preferred that the second catalyst device is an oxidation catalyst device. In this device, the injected hydrogen gas can readily combine with the oxygen present in the oxidation catalyst device through catalytic action, releasing heat energy. This released heat energy warms the exhaust gas, which in turn can heat the first catalyst device more quickly.

[0013] According to the invention, the exhaust system has a bypass line designed to direct the exhaust gas past the second catalyst device and directly to the first catalyst device. The bypass line is arranged such that it bypasses the section of the exhaust system in which the second catalyst device is located and directs the exhaust gas past it, allowing it to flow directly through the first catalyst device.

[0014] Preferably, a control valve is located at least partially in the bypass line, which is configured to direct the exhaust gas flow either through the second catalyst device or through the bypass line. Preferably, the control valve is a 3 / 2-way valve.

[0015] In a further preferred embodiment, the exhaust system according to the invention also includes a further hydrogen gas injection device, which is configured to inject hydrogen gas into the exhaust pipe at a position upstream of the first catalyst device and downstream of the second catalyst device. In particular, the hydrogen gas injected by means of the at least one further hydrogen gas injection device serves as a reducing agent for the reduction taking place in the first catalyst device.

[0016] In a further advantageous embodiment of the exhaust system according to the invention, the hydrogen gas injection device is configured to inject hydrogen into the at least one combustion chamber during a working phase and / or during an exhaust phase of the hydrogen combustion engine. In particular, the main injection device for the hydrogen gas can be used to introduce unburned hydrogen gas into the exhaust line so that, as already mentioned, it can react with the oxygen present in the second catalyst device to heat the exhaust gas.

[0017] According to a further aspect of the present invention, a hydrogen engine is disclosed which has at least one combustion chamber and an exhaust stream arranged downstream of the at least one combustion chamber according to the invention.

[0018] According to a further aspect of the present invention, a method for operating an exhaust system of a hydrogen combustion engine is disclosed, which is designed to be operated with hydrogen gas as fuel. The hydrogen gas is combusted with air in at least one combustion chamber.The exhaust system comprises an exhaust pipe for directing the exhaust gas flowing from the at least one combustion chamber, a first catalyst device arranged in the exhaust pipe downstream of the at least one combustion chamber, which is designed to at least partially treat the exhaust gas, a second catalyst device arranged in the exhaust pipe downstream of the at least one combustion chamber and upstream of the first catalyst device, which is designed to at least partially treat the exhaust gas, and a hydrogen gas injection device arranged upstream of the second catalyst device, which is designed to inject hydrogen gas.The method according to the invention comprises injecting hydrogen gas by means of the hydrogen gas injection device so that the injected hydrogen gas can react with the oxygen present in the second catalyst device to heat the exhaust gas, heating the first catalyst device by means of flows of the exhaust gas heated in the second catalyst device through it, and stopping the injection of hydrogen gas when the temperature of the first catalyst device has reached a predetermined operating temperature.

[0019] The additional hydrogen gas is injected into the exhaust pipe until the first catalyst unit reaches its predetermined operating temperature. After that, the exhaust system switches to normal operation.

[0020] According to the invention, the exhaust system further comprises a bypass line configured to direct the exhaust gas past the second catalyst device to the first catalyst device, and a control valve arranged at least partially in the bypass line, which is configured to direct the exhaust gas flow either through the second exhaust catalyst device or through the bypass line. In particular, hydrogen gas is injected when the control valve closes the bypass line and the exhaust gas, together with the injected hydrogen gas, can consequently flow through the second catalyst device.

[0021] In a further preferred embodiment, the method according to the invention also includes the injection of additional hydrogen gas into the exhaust gas line at a position upstream of the first catalyst device and downstream of the second catalyst device when the temperature of the first catalyst device has reached the predetermined operating temperature. The additional injection of hydrogen gas is thus used as a reducing agent for the first catalyst device, which is in particular an SCR catalyst device, during normal operation of the exhaust system.

[0022] In an alternative embodiment, the method according to the invention further comprises the injection of additional hydrogen gas into the at least one combustion chamber during a working phase and / or during an exhaust phase of the hydrogen combustion engine when the temperature of the first catalyst device has reached the predetermined operating temperature. In particular, this allows unburned hydrogen gas to enter the exhaust line and be used there as a reducing agent in the first catalyst device.

[0023] Preferably, the predetermined operating temperature of the first catalyst device is approximately 100 °C.

[0024] In a further preferred embodiment, the method according to the invention further comprises a determination of whether the hydrogen combustion engine has been started, wherein hydrogen gas is injected to heat the first catalyst device when a successful start of the hydrogen combustion engine has been determined.

[0025] Further features and functions of the present invention will become apparent to the person skilled in the art by carrying out the present teaching and by looking at the accompanying drawings, in which: Fig. Figure 1 shows a schematic view of an exemplary hydrogen combustion engine with an exhaust system according to the invention, Fig. Figure 2 shows a schematic view of an exemplary hydrogen combustion engine with a further exhaust system according to the invention, and Fig. Figure 3 shows an exemplary flowchart of a method according to the invention for operating an exhaust system of a hydrogen combustion engine.

[0026] Elements of the same construction or function are provided with the same reference symbols across all figures.

[0027] The Fig. Figure 1 shows a schematic view of an exemplary hydrogen combustion engine 10 with an exhaust system 100 according to the invention. The hydrogen combustion engine 10 is operated with hydrogen gas as fuel and is known in principle from the prior art. In particular, a hydrogen gas-air mixture is combusted in at least one combustion chamber (not explicitly shown) of the hydrogen combustion engine 10, and the resulting exhaust gas is released to the environment via the exhaust system 100 according to the invention. The hydrogen combustion engine 10 is, in particular, a four-stroke engine with the phases intake, compression, power, and exhaust.

[0028] The exhaust system 100 comprises an exhaust line 102, which is fluidly connected to the at least one combustion chamber (not explicitly shown) of the internal combustion engine 10 and is designed to convey the exhaust gas flowing out of the at least one combustion chamber. The exhaust system 100 further comprises a first catalyst device 110 arranged in the exhaust line 102 downstream of the at least one combustion chamber, which is designed to at least partially treat the exhaust gas. The first catalyst device 110 is preferably an SCR catalyst device based on the principle of selective catalytic reduction with hydrogen gas.

[0029] The exhaust system 100 further comprises a second catalyst device 120 arranged in the exhaust pipe 102 downstream of the at least one combustion chamber and upstream of the first catalyst device 110, which is designed to at least partially treat the exhaust gas. The second catalyst device 120 is preferably an oxidation catalyst device.

[0030] The exhaust system 100 further comprises a sensor device 130, which is arranged downstream of the first catalyst device 110 and is configured to measure the exhaust gas with regard to its components. Preferably, the sensor device 130 is a nitrogen oxide sensor configured to detect any nitrogen oxides present in the exhaust gas. The sensor device 130 can, for example, be configured as a nitrogen oxide sensor with an additionally integrated mixed potential electrode or sensor and be based on the electrochemical principle. Preferably, the sensor device 130 can detect the nitrogen oxide concentration and hydrogen concentration present in the exhaust gas.

[0031] Optionally, a further sensor device 140 can be provided, which can be arranged downstream of the at least one combustion chamber and upstream of the second catalyst device 120 in the exhaust gas line 102 and is configured to detect components in the exhaust gas. Preferably, the further sensor device 140 is also a nitrogen oxide sensor configured to detect nitrogen oxides present in the exhaust gas.

[0032] Furthermore, the exhaust system exhibits 100 of the Fig. 1. A hydrogen gas injection device 150 is described, which is configured to inject hydrogen gas into the exhaust line 102 at a position downstream of the second catalyst device 120 and upstream of the first catalyst device 110. The hydrogen gas injected by means of the hydrogen gas injection device 150 can, in particular, be used as a reducing agent for the first catalyst device 110.

[0033] The exhaust system 100 of the Fig. 1 can further comprise a hydrogen gas injection device 170 arranged upstream of the second catalyst device 120 and downstream of the at least one combustion chamber, which is designed to inject hydrogen gas as a reducing agent into the exhaust gas line 102.

[0034] The first sensor device 130, the second sensor device 140, the hydrogen gas injection device 150, and the hydrogen gas injection device 170 are each connected to a control device 160, which is configured to receive the respective signals and also to control signals for controlling the hydrogen gas injection by means of the hydrogen gas injection devices 150 and 170. The sensor device 140 is provided for controlling the amount of hydrogen gas to be injected by means of the hydrogen gas injection device 170.

[0035] The Fig. Figure 2 shows a further embodiment of an exhaust system 100 according to the invention for a hydrogen combustion engine 10. The exhaust system 100 of the Fig. 2 differs from the exhaust system of the Fig. 1. The design includes an additional bypass line 104, which directs the exhaust gas exiting from at least one combustion chamber of the hydrogen combustion engine 10 around the second catalyst device 120 to the first catalyst device 110. For controlling the exhaust gas flow, a control valve 106 is provided upstream of the second catalyst device 120, which is at least partially located in the bypass line 104. The control valve 106 is thus located in the upstream opening of the bypass line 104 into the exhaust gas line 102 and is preferably a 3 / 2-way valve, allowing the exhaust gas to be directed either through the bypass 104 or through the second catalyst device 120. The control valve 106 is connected to the control device 160 for control purposes.

[0036] Furthermore, the exhaust system differs by 100%. Fig. 2 of the exhaust system 100 of the Fig. 1 in that the hydrogen gas injection device 150 in the design according to Fig. 2 is not present. The hydrogen gas, which serves as a reducing agent for the first catalyst device 110, can be taken from the hydrogen gas injection device that constitutes the main hydrogen gas injection device for at least one combustion chamber of the hydrogen combustion engine 10. It is, of course, self-evident to those skilled in the art that even in the embodiment according to Fig. 2 the hydrogen gas injection device 150 can be arranged, which in turn can be arranged downstream of the second catalyst device 120 and upstream of the first catalyst device 110.

[0037] Referring to the Fig. Figure 3 is an exemplary flowchart of a method according to the invention for operating the exhaust system according to the invention. Fig. 1 described.

[0038] The procedure according to Fig. The process starts at step 200 and then proceeds to step 210, where it is determined whether the hydrogen combustion engine 10 has been started. The procedure remains at step 210 until a start of the hydrogen combustion engine 10 has been detected.

[0039] If, in step 210, it is determined that the hydrogen combustion engine has started, the process proceeds to step 220, in which hydrogen gas is injected into the exhaust line 102 by means of the hydrogen gas injection device 170. The hydrogen gas injected by the hydrogen gas injection device 170 can react with the oxygen present in the second catalyst device 120 and generate exothermic energy, which significantly increases the temperature of the exhaust gas. The heated exhaust gas then flows on to the first catalyst device 110, where it can then transfer the heat to it in order to at least partially heat the first catalyst device 110.

[0040] In a subsequent step 230, it is determined whether the first catalyst device 110 has reached its operating temperature. If step 230 reveals that the operating temperature of the first catalyst device 110 has not yet been reached, the process returns to step 220 and hydrogen gas continues to be injected via the hydrogen gas injection device 170.

[0041] When, in step 230, it is determined that the predetermined operating temperature, for example approximately 100 °C, of ​​the first catalyst device 110 has been reached, the process proceeds to step 240, in which the injection of the hydrogen gas intended for heating by means of the further hydrogen gas injection device 170 is stopped and the exhaust system 100 is switched to normal operation. During normal operation, hydrogen gas is then injected by means of the hydrogen gas injection device 150, which serves as a reducing agent for the first catalyst device 110. The process then ends in step 250.

[0042] In step 220, as an alternative to injecting hydrogen gas using the hydrogen gas injection device 170, the hydrogen gas intended for heating the exhaust gas in the second catalyst device can also originate from a main hydrogen gas injection device, which is injected during a working phase and / or exhaust phase of the hydrogen combustion engine 10 and can flow unburned into the exhaust stream 100.

[0043] With further reference to the Fig. 2. The heating of the first catalyst device 110 by means of additionally injected hydrogen gas can also be achieved by controlling the control valve 106 during the heating phase of the first catalyst device 110 in such a way that the exhaust gas flows through the second catalyst device 120 and thus does not pass through the bypass 104. Consequently, the hydrogen gas can react with the oxygen present in the second catalyst device 110 and, as already described, significantly heat the exhaust gas before it flows into the first catalyst device 100.

[0044] As soon as step 230 of the Fig.3. Once it is determined that the predetermined operating temperature of the first catalyst device 110 has been reached, the control valve 106 switches to a position in which the exhaust gas passes through the bypass 104 and no longer through the second catalyst device 120. At the same time, the injection of the hydrogen gas intended for heating the first catalyst device 110 (either by means of the hydrogen gas injection device 170 or via the main hydrogen gas injection device of the hydrogen combustion engine) is stopped, and the process then proceeds to step 240, in which the exhaust gas stream is switched to normal operation for aftertreatment of the exhaust gas.

[0045] The measure of catalyst heating by oxidation of hydrogen gas with oxygen in the oxidation catalyst can also be enhanced with other heating measures such as ignition timing delay and / or increasing the idle speed after starting (e.g. above 1500 rpm), whereby the other measures can continue until the catalyst device reaches its operating temperature of approximately 100°C.

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