Urea injection system for marine diesel engine onboard SCR and marine diesel engine

Abstract

The invention discloses a urea injection system for a marine diesel engine with an onboard SCR and a marine diesel engine, and belongs to the technical field of energy conservation and emission reduction of diesel engines. The urea injection system comprises a urea spray gun, a urea supply branch, a compressed gas supply branch and a controller, wherein the urea supply branch comprises a urea supply pipeline, and the compressed gas supply branch comprises a gas pipeline. By arranging a pressure measuring element and a pressure regulating element on both the urea supply pipeline and the gas pipeline, the pressure in the urea supply pipeline and the gas pipeline can be regulated. And by arranging a flow regulating element and a flow measuring element on both the urea supply pipeline and the gas pipeline, the pressure in the urea supply pipeline and the gas pipeline can be regulated. The urea injection system for a marine diesel engine with an onboard SCR not only has a simple structure and low cost, but also can accurately control the pressure and flow of the urea supply branch and the compressed gas supply branch, thereby improving the stability of the urea spray gun in spraying urea solution.

Description

Technical Field

[0001] The invention relates to the technical field of diesel engine energy saving and emission reduction, and in particular to a urea injection system of an SCR mounted on a marine diesel engine and a marine diesel engine. Background Art

[0002] Marine diesel engines are the main energy source for ships. During operation, they emit a large amount of exhaust gas, which contains various harmful pollutants, such as NO x For NO x , the International Convention for the Prevention of Pollution from Ships on NO x Emissions have a clear standard of Tier 3. In order to meet the Tier 3 emission standard, it is necessary to install an SCR system on the marine diesel engine to reduce NO x emissions.

[0003] At present, the SCR system mainly decomposes ammonia gas by injecting urea under high temperature and high pressure, and uses ammonia gas and NO x The reaction is carried out under the action of a catalyst to reduce NO x Urea injection is an important part of the SCR system. The existing urea injection system is not only complex and costly, but also needs to improve the stability of injection.

[0004] How to simplify the injection system and improve the stability of injection is a technical problem that needs to be solved urgently. Summary of the invention

[0005] One object of the present invention is to provide a urea injection system for an onboard SCR of a marine diesel engine, which has a simple structure, low cost and high stability;

[0006] Another object of the present invention is to provide a marine diesel engine, NO x Less pollutant emissions, energy saving and environmental protection.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] A urea injection system for an onboard SCR of a marine diesel engine, comprising:

[0009] A urea spray gun, wherein the urea spray gun is provided with a urea inlet and a compressed gas inlet;

[0010] a urea supply branch, the urea supply branch comprising a urea supply pipeline and a urea pump, a first pressure measuring element, a first pressure regulating element, a first flow regulating element and a first flow measuring element arranged on the urea supply pipeline, one end of the urea supply pipeline being communicable with a urea source, and the other end being communicable with the urea inlet, the first pressure measuring element being used to measure the pressure of the urea supply pipeline, the first pressure regulating element being used to regulate the pressure of the urea supply pipeline, the first flow measuring element being used to measure the flow of the urea supply pipeline, and the first flow regulating element being used to regulate the flow of the urea supply pipeline;

[0011] A compressed gas supply branch, the compressed gas supply branch comprising a gas pipeline and a second pressure measuring element, a second pressure regulating element, a second flow regulating element and a second flow measuring element arranged on the gas pipeline, one end of the gas pipeline being able to communicate with a compressed gas source, and the other end being communicated with the compressed gas inlet, the second pressure measuring element being used to measure the pressure of the gas pipeline, the second pressure regulating element being used to regulate the pressure of the gas pipeline, the second flow measuring element being used to measure the flow of the gas pipeline, and the second flow regulating element being used to regulate the flow of the gas pipeline;

[0012] A controller is communicatively connected with the first pressure measuring element, the first pressure regulating element, the first flow regulating element, the first flow measuring element, the second pressure measuring element, the second pressure regulating element, the second flow regulating element and the second flow measuring element.

[0013] Preferably, the urea injection system of the marine diesel engine onboard SCR further comprises:

[0014] The urea reflux branch comprises a urea reflux pipeline, one end of which is connected to the urea supply pipeline.

[0015] Preferably, the first pressure regulating element is a first pressure control valve, and the first pressure control valve is arranged on the urea return pipeline.

[0016] Preferably, the urea injection system of the marine diesel engine onboard SCR further comprises:

[0017] An electromagnetic stop valve is arranged on the urea supply pipeline and is located on a side of the first flow measurement element close to the urea pump.

[0018] Preferably, the urea injection system of the marine diesel engine onboard SCR further comprises:

[0019] An air filter is located on the gas pipeline.

[0020] Preferably, the second pressure regulating element includes a second pressure control valve, and the second pressure measuring element includes an air pressure sensor, which can obtain the pressure signal in the gas pipeline and transmit it to the controller, and the controller is configured to control the second pressure control valve according to the pressure signal.

[0021] Preferably, the second pressure regulating element further includes a manual pressure reducing valve, and the second pressure measuring element further includes a pressure gauge, and the pressure gauge is arranged on a side of the manual pressure reducing valve close to the compressed gas inlet.

[0022] Preferably, the urea injection system of the marine diesel engine onboard SCR further comprises:

[0023] A cleaning branch, wherein the cleaning branch comprises a cleaning pipeline, one end of the cleaning pipeline is connected to the urea supply pipeline, and the other end of the cleaning pipeline is connected to the gas pipeline.

[0024] Preferably, a one-way valve and a third pressure control valve are provided on the cleaning branch.

[0025] A marine diesel engine comprises the above-mentioned marine diesel engine onboard SCR urea injection system.

[0026] Beneficial effects of the present invention:

[0027] The present invention provides a urea injection system for an onboard SCR of a marine diesel engine, the urea injection system comprising a urea spray gun, a urea supply branch, a compressed gas supply branch and a controller, the urea supply branch comprising a urea supply pipeline, and the compressed gas supply branch comprising a gas pipeline. The urea injection system can transmit the pressure signal detected by the pressure measuring element to the controller by arranging a pressure measuring element and a pressure regulating element on both the urea supply pipeline and the gas pipeline, and control the pressure regulating element by the controller, thereby regulating the pressure in the urea supply pipeline and the gas pipeline. And by arranging a flow regulating element and a flow measuring element on both the urea supply pipeline and the gas pipeline, the flow signal detected by the flow measuring element can be transmitted to the controller, and control the flow regulating element by the controller, thereby regulating the pressure in the urea supply pipeline and the gas pipeline. The urea injection system for an onboard SCR of a marine diesel engine is not only simple in structure and low in cost, but also can accurately control the pressure and flow in the urea supply branch and the compressed gas supply branch, thereby improving the stability of the urea spray gun when spraying urea. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1It is a schematic diagram of the urea injection system of the marine diesel engine-mounted SCR provided by the present invention.

[0029] In the figure:

[0030] 100, urea supply pipeline; 200, gas pipeline; 300, urea return pipeline; 400, cleaning pipeline;

[0031] 1. Urea pump; 2. First pressure control valve; 3. First pressure sensor; 4. Solenoid stop valve; 5. First flow meter; 6. First flow control valve; 7. One-way valve; 8. Third pressure control valve; 9. Second pressure sensor; 10. Air filter; 11. Manual pressure reducing valve; 12. Pressure gauge; 13. Second flow meter; 14. Second pressure control valve; 15. Air pressure sensor; 16. Urea spray gun. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] This embodiment provides a urea injection system for a marine diesel engine with an SCR (hereinafter referred to as a urea injection system). The urea injection system can be used to reduce NO in the exhaust gas emitted by the marine diesel engine. xcontent, thereby reducing harmful pollutants in the exhaust gas, which is conducive to energy conservation and environmental protection. Figure 1 As shown, the urea injection system includes a urea spray gun 16, a urea supply branch, a compressed gas supply branch and a controller.

[0036] The urea spray gun 16 is provided with a urea inlet and a compressed gas inlet. The urea inlet is used to inject urea solution into the urea spray gun 16, and the compressed gas inlet is used to inject compressed gas into the urea spray gun 16. In this embodiment, the compressed gas is compressed air. The urea spray gun 16 is used to mix the urea solution with the compressed gas, and spray the urea solution at a certain pressure into a high-temperature and high-pressure environment under the action of the compressed gas. The urea solution can decompose ammonia under high temperature and high pressure, and the ammonia can react with NO in the exhaust gas emitted by the marine diesel engine. x A chemical reaction occurs, converting NO x The urea spray gun 16 is used as a urea spray gun. The specific structure of the urea spray gun 16 is a prior art and will not be described in detail here.

[0037] The urea supply branch is mainly used to stably input the urea solution into the urea spray gun 16. Figure 1 As shown, the urea supply branch includes a urea supply pipeline 100, one end of which is connected to a urea source (not shown in the figure), the urea source is used to contain a urea solution, and the other end of the urea supply pipeline 100 is connected to a urea inlet of a urea spray gun 16. A urea pump 1 is provided on the urea supply pipeline 100, and the urea pump 1 is used to pump the urea solution from the urea source into the urea supply pipeline 100.

[0038] The urea supply pipeline 100 is also provided with a first pressure measuring element and a first pressure regulating element. Both the first pressure measuring element and the first pressure regulating element are connected to the controller by communication. The connection method may be a wireless connection, such as a Bluetooth connection, a wifi connection, etc. In the present embodiment, the first pressure measuring element includes a first pressure sensor 3 and a second pressure sensor 9. The first pressure sensor 3 is located upstream of the urea supply pipeline 100, i.e., close to the urea pump 1, and the second pressure sensor 9 is located downstream of the urea supply pipeline 100, i.e., close to the urea inlet. The first pressure sensor 3 and the second pressure sensor 9 are both used to measure the pressure of the urea supply pipeline 100 and transmit the detected pressure signal to the controller. The controller can control the first pressure regulating element and other related components according to the received pressure signal, so that the first pressure regulating element can regulate the pressure of the urea supply pipeline 100 in real time. In the present embodiment, the first pressure regulating element is a first pressure control valve 2, and the first pressure control valve 2 is a solenoid valve, which is not only easy to purchase, low in cost, but also easy to control. By arranging the first pressure measuring element and the first pressure regulating element on the urea supply pipeline 100 , the pressure in the urea supply pipeline 100 can be regulated in real time, which is beneficial to improving the transmission stability of the urea solution input into the urea spray gun 16 .

[0039] like Figure 1 As shown, the urea supply pipeline 100 is also provided with a first flow control element and a first flow measurement element, and the first flow control element and the first flow measurement element are both connected to the controller in communication, and the connection method can be a wireless connection, such as Bluetooth, wifi connection, etc. In this embodiment, the first flow measurement element is a first flow meter 5, and the first flow meter 5 is used to measure the flow of the urea supply pipeline 100, and transmit the obtained flow signal to the controller, and the controller controls the first flow control element according to the obtained flow signal, so as to perform real-time control on the flow in the urea supply pipeline 100. In this embodiment, the first flow meter 5 is a Coriolis flow meter. The first flow control element includes a first flow control valve 6, and the first flow control valve 6 is a solenoid valve, which is not only easy to purchase, low in cost, but also easy to control. By arranging the first flow control element and the first flow measurement element on the urea supply pipeline 100, the flow in the urea supply pipeline 100 can be controlled in real time, which is conducive to improving the transmission stability of the urea solution input into the urea spray gun 16.

[0040] Optionally, in this embodiment, along the transmission direction of the urea solution in the urea supply pipeline 100, the urea pump 1, the first pressure control valve 2, the first pressure sensor 3, the first flow meter 5, the first flow control valve 6, and the second pressure sensor 9 are sequentially arranged on the urea supply pipeline 100.

[0041] Alternatively, if Figure 1As shown, the urea injection system further includes a urea reflux branch, the urea reflux branch includes a urea reflux pipeline 300, and one end of the urea reflux pipeline 300 is connected to the urea supply pipeline 100. In this embodiment, the first pressure control valve 2 is arranged on the urea reflux pipeline 300, and the connection point between the urea reflux pipeline 300 and the urea supply pipeline 100 is located between the urea pump 1 and the first pressure sensor 3. When the first pressure sensor 3 detects that the pressure in the urea supply pipeline 100 is greater than the preset value, the controller controls the first pressure control valve 2 to adjust the flow in the urea reflux pipeline 300, so as to achieve the purpose of maintaining the flow in the urea supply pipeline 100 at the preset value.

[0042] However, since the first pressure control valve 2 has a certain response time for regulating the pressure in the urea reflux pipeline 300, in order to protect the first flowmeter 5 and prevent the first flowmeter 5 from being damaged when the pressure in the urea supply pipeline 100 is too high, an electromagnetic stop valve 4 is further provided upstream of the first flowmeter 5, that is, between the first flowmeter 5 and the first pressure sensor 3. The electromagnetic stop valve 4 can achieve the purpose of cutting off the flow of urea solution in the urea supply pipeline 100. When the pressure in the urea supply pipeline 100 is too high, the electromagnetic stop valve 4 can be closed to protect the first flowmeter 5 and prevent the first flowmeter 5 from being damaged.

[0043] The compressed gas supply branch is used to input compressed gas into the urea spray gun 16 to provide power for the urea solution to be sprayed out from the urea spray gun 16. Figure 1 As shown, the compressed gas supply branch includes a gas pipeline 200, one end of the gas pipeline 200 is connected to the compressed gas source (not shown in the figure), and the other end is connected to the compressed gas inlet. The gas pipeline 200 is provided with a second pressure measuring element and a second pressure regulating element, and the second pressure measuring element and the second pressure regulating element are both communicatively connected to the controller, and the connection method can be a wireless connection, such as Bluetooth, wifi connection, etc.

[0044] In this embodiment, the second pressure regulating element includes a manual pressure reducing valve 11 and a second pressure control valve 14, which are arranged in sequence on the gas pipeline 200 along the inflow direction of the compressed gas. The second pressure measuring element includes a pressure gauge 12 and an air pressure sensor 15, the pressure gauge 12 is arranged on the side of the manual pressure reducing valve 11 close to the compressed gas inlet, and the air pressure sensor 15 is arranged on the side of the second pressure control valve 14 close to the compressed gas inlet. The air pressure sensor 15 is used to measure the pressure of the gas pipeline 200 and transmit the detected pressure signal to the controller, and the controller can control the second pressure control valve 14 according to the received pressure signal, so that the second pressure control valve 14 can regulate the pressure in the gas pipeline 200 in real time. In this embodiment, the second pressure control valve 14 is an electromagnetic valve, which is not only easy to purchase, low in cost, but also easy to control. The manual pressure reducing valve 11 is manually controlled, and the pressure in the gas pipeline 200 can be manually reduced by it, and the pressure gauge 12 is used to measure the pressure of the compressed air after decompression. By providing a second pressure measuring element and a second pressure regulating element on the gas pipeline 200, the pressure of the compressed gas in the gas pipeline 200 can be regulated in real time, which is conducive to achieving stable transmission of compressed air.

[0045] like Figure 1 As shown, the gas pipeline 200 is provided with a second flow control element and a second flow measurement element, and the second flow control element and the second flow measurement element are both connected to the controller in communication, and the connection method can be a wireless connection, such as Bluetooth, wifi connection, etc. In this embodiment, the second flow measurement element is a second flow meter 13, and the second flow meter 13 is used to measure the flow of the gas pipeline 200, and transmit the obtained flow signal to the controller, and the controller controls the second flow control element according to the obtained flow signal, so as to achieve real-time control of the flow of the gas pipeline 200. In this embodiment, the second flow meter 13 is a Coriolis flow meter. The second flow control element is a second flow control valve, and the second flow control valve is an electromagnetic valve, which is not only easy to purchase, low in cost, but also easy to control. By arranging the second flow control element and the second flow measurement element on the gas pipeline 200, the flow in the gas pipeline 200 can be controlled in real time, which is conducive to the stable transmission of compressed gas.

[0046] In this embodiment, if Figure 1 As shown, the manual pressure reducing valve 11, the pressure gauge 12, the second flow meter 13, the second pressure control valve 14 and the air pressure sensor 15 are arranged in sequence on the gas pipeline 200 along the input direction of the compressed air. Optionally, an air filter 10 is further provided upstream of the manual pressure reducing valve 11, and the air filter 10 can filter the compressed air to remove condensed water in the compressed air, thereby realizing the single-phase input of the compressed gas.

[0047] In this embodiment, the controller is connected to the urea pump 1, the first pressure control valve 2, the first pressure sensor 3, the electromagnetic stop valve 4, the first flow meter 5, the first flow control valve 6, the second pressure sensor 9, the second flow meter 13, the second pressure control valve 14, and the air pressure sensor 15. The controller can be a centralized or distributed controller, for example, the controller can be a single chip microcomputer, or it can be composed of multiple distributed single chip microcomputers, and the control program can be run in the single chip microcomputer to control the urea pump 1, the first pressure control valve 2, the first pressure sensor 3, the electromagnetic stop valve 4, the first flow meter 5, the first flow control valve 6, the second pressure sensor 9, the second flow meter 13, the second pressure control valve 14, and the air pressure sensor 15 to realize their functions.

[0048] Optionally, in order to facilitate self-cleaning, the urea injection system also includes a cleaning branch. Figure 1 As shown, the cleaning branch includes a cleaning pipeline 400, one end of which is connected to the urea supply pipeline 100, and the other end is connected to the gas pipeline 200. Specifically, the connection point between the cleaning pipeline 400 and the urea supply pipeline 100 is located at the pressure gauge 12, and the connection point between the cleaning pipeline 400 and the gas pipeline 200 is located at the second pressure sensor 9. A one-way valve 7 and a third pressure control valve 8 are provided on the cleaning branch. The one-way valve 7 is used to prevent the urea solution from flowing back into the gas pipeline 200. The third pressure control valve 8 is connected to the controller in communication, and the controller controls the third pressure control valve 8 according to the pressure signal fed back by the second pressure sensor 9, so that the pressure in the cleaning pipeline 400 reaches the preset value of the cleaning pressure.

[0049] The urea injection system includes two states: urea injection state and cleaning state:

[0050] When the urea injection system is in the urea injection state:

[0051] For the urea supply branch: the urea solution flows from the urea source through the urea pump 1 into the urea supply pipeline 100, and the first pressure sensor 3 feeds back the measured pressure signal to the controller, and the controller controls the first pressure control valve 2 to adjust the flow in the urea reflux branch to adjust the pressure in the urea supply pipeline 100 to within the preset value. Since the adjustment of this pressure requires a certain response time, when the pressure in the urea supply branch is too large, the controller can protect the first flow meter 5 by closing the electromagnetic stop valve 4. Thereafter, the first flow meter 5 feeds back the measured flow signal to the controller, and the controller controls the first flow control valve 6 according to the flow signal to make the flow in the urea supply pipeline 100 reach the preset value, and finally makes the urea solution in the urea supply pipeline 100 flow into the urea spray gun 16 at an accurate flow rate. The second pressure sensor 9 can feed back the measured pressure signal to the controller, and the controller can dynamically adjust the pressure in the gas pipeline 200 according to the pressure signal to be consistent with the pressure in the urea supply pipeline 100 as much as possible, which is conducive to reducing the fluctuation of the urea spray gun 16 during injection and ensuring the stability of the injection process.

[0052] For compressed air: compressed air flows in from the inlet of the air filter 10, and the condensed water therein is removed by the air filter 10. Subsequently, the excessive air pressure in the compressed air is reduced by controlling the manual pressure reducing valve 11, and the pressure gauge 12 is used to measure the pressure of the compressed air after pressure reduction to ensure that the pressure value of the compressed air is within the preset value. The second flow meter 13 feeds back the measured flow signal to the controller, and the controller uses the second pressure control valve 14 to control the pressure in the gas pipeline 200 according to the received flow signal. Subsequently, the pressure in the gas pipeline 200 is fed back to the controller through the air pressure sensor 15, and the controller adjusts the second pressure control valve 14 according to the obtained pressure signal and flow signal, so that the pressure in the gas pipeline 200 is basically consistent with the pressure downstream of the urea supply pipeline 100, thereby ensuring the stability of the injection. During this process, the third pressure control valve 8 is closed to isolate the gas pipeline 200 from the urea supply pipeline 100.

[0053] When the urea injection system is in the cleaning state:

[0054] The controller controls the urea pump 1 to stop supplying the urea solution, and controls the first flow control valve 6 to close and the third pressure control valve 8 to open. At this time, the compressed air flows through the gas pipeline 200 and then enters the cleaning pipeline 400, and then flows into the downstream of the urea supply pipeline 100 to clean the urea solution remaining in the urea supply pipeline 100. The one-way valve 7 on the cleaning pipeline 400 is used to prevent the urea solution from flowing back into the gas pipeline 200.

[0055] In this process, although precise control is not required, the stability of air flow must be ensured to prevent excessive pressure and flow from damaging the components on each branch. The process is similar to that in the urea injection state. The compressed air flows through the air filter 10 to remove the condensed water in the compressed air; then, the excessive air pressure can be reduced by controlling the manual pressure reducing valve 11. The pressure gauge 12 is used to measure the pressure of the compressed air after decompression. The second flow meter 13 feeds back the measured flow signal to the controller. Then, the pressure in the gas pipeline 200 is fed back to the controller through the air pressure sensor 15. The controller adjusts the second pressure control valve 14 according to the obtained pressure signal, so that the pressure of the gas pipeline 200 reaches the set value of the cleaning pressure. At the same time, in the cleaning branch, the controller controls the third pressure control valve 8 to adjust the pressure in the cleaning pipeline 400 to the preset value of the cleaning pressure according to the signal fed back by the second pressure sensor 9.

[0056] This embodiment also provides a marine diesel engine, which includes the above-mentioned marine diesel engine airborne SCR urea injection system. By using the marine diesel engine airborne SCR urea injection system, NO in the marine diesel engine exhaust can be reduced to a great extent. x The emission of pollutants is conducive to energy conservation and environmental protection.

[0057] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A urea injection system for an onboard SCR of a marine diesel engine, characterized in that: include: A urea spray gun (16), wherein the urea spray gun (16) is provided with a urea inlet and a compressed gas inlet; A urea supply branch, the urea supply branch comprising a urea supply pipeline (100) and a urea pump (1) arranged on the urea supply pipeline (100), a first pressure measuring element, a first pressure regulating element, a first flow regulating element and a first flow measuring element, one end of the urea supply pipeline (100) being able to communicate with a urea source, and the other end being communicated with the urea inlet, the first pressure measuring element being used to measure the pressure of the urea supply pipeline (100), the first pressure regulating element being used to regulate the pressure of the urea supply pipeline (100), the first flow measuring element being used to measure the flow of the urea supply pipeline (100), and the first flow regulating element being used to regulate the flow of the urea supply pipeline (100); A compressed gas supply branch, the compressed gas supply branch comprising a gas pipeline (200) and a second pressure measuring element, a second pressure regulating element, a second flow regulating element and a second flow measuring element arranged on the gas pipeline (200), one end of the gas pipeline (200) being able to communicate with a compressed gas source, and the other end being connected with the compressed gas inlet, the second pressure measuring element being used to measure the pressure of the gas pipeline (200), the second pressure regulating element being used to regulate the pressure of the gas pipeline (200), the second flow measuring element being used to measure the flow of the gas pipeline (200), and the second flow regulating element being used to regulate the flow of the gas pipeline (200); a cleaning branch, the cleaning branch comprising a cleaning pipeline (400), one end of the cleaning pipeline (400) being connected to the urea supply pipeline (100), and the other end of the cleaning pipeline (400) being connected to the gas pipeline (200), and the connection point between the cleaning pipeline (400) and the urea supply pipeline (100) being located at the second pressure sensor (9); a controller, the controller being communicatively connected with the first pressure measuring element, the first pressure regulating element, the first flow regulating element, the first flow measuring element, the second pressure measuring element, the second pressure regulating element, the second flow regulating element and the second flow measuring element; The first pressure measuring element comprises a first pressure sensor (3) and a second pressure sensor (9), wherein the first pressure sensor (3) is located upstream of the urea supply pipeline (100) and is arranged close to the urea pump (1), and the second pressure sensor (9) is located downstream of the urea supply pipeline (100) and is arranged close to the urea inlet; When the urea injection system is in a urea injection state, the second pressure sensor (9) in the urea supply branch can feed back a measured pressure signal to the controller, and the controller dynamically adjusts the pressure in the gas pipeline (200) to be consistent with the pressure in the urea supply pipeline (100) based on the pressure signal.

2. The urea injection system for marine diesel engine-mounted SCR according to claim 1, characterized in that: Also includes: A urea reflux branch, the urea reflux branch comprising a urea reflux pipeline (300), one end of the urea reflux pipeline (300) being in communication with the urea supply pipeline (100).

3. The urea injection system for marine diesel engine-mounted SCR according to claim 2, characterized in that: The first pressure regulating element is a first pressure control valve (2), and the first pressure control valve (2) is arranged on the urea return pipeline (300).

4. The urea injection system for marine diesel engine-mounted SCR according to claim 1, characterized in that: Also includes: An electromagnetic stop valve (4), the electromagnetic stop valve (4) being arranged on the urea supply pipeline (100) and located on a side of the first flow measurement element close to the urea pump (1).

5. The urea injection system for marine diesel engine-mounted SCR according to claim 1, characterized in that: Also includes: An air filter (10), wherein the air filter (10) is located on the gas pipeline (200).

6. The urea injection system for marine diesel engine-mounted SCR according to claim 1, characterized in that: The second pressure regulating element comprises a second pressure control valve (14), and the second pressure measuring element comprises an air pressure sensor (15). The air pressure sensor (15) is capable of acquiring a pressure signal in the gas pipeline (200) and transmitting the pressure signal to the controller. The controller is configured to control the second pressure control valve (14) according to the pressure signal.

7. The urea injection system for marine diesel engine-mounted SCR according to claim 6, characterized in that: The second pressure regulating element further comprises a manual pressure reducing valve (11), and the second pressure measuring element further comprises a pressure gauge (12), wherein the pressure gauge (12) is arranged on a side of the manual pressure reducing valve (11) close to the compressed gas inlet.

8. The urea injection system for the marine diesel engine onboard SCR according to claim 7, characterized in that: The cleaning branch line is provided with a one-way valve (7) and a third pressure control valve (8).

9. A marine diesel engine, characterized in that: A urea injection system for an onboard SCR of a marine diesel engine comprising the method described in any one of claims 1 to 8.

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