A diesel flushing system and flushing method after a methanol dual-fuel engine bench test

Abstract

The present invention provides a diesel flushing system after a bench test of a methanol dual-fuel engine is completed, comprising a first shut-off valve, a second shut-off valve, a pressure reducing valve and a connecting pipe, wherein the first shut-off valve is used to be installed in a connecting pipe between a methanol low-pressure supply pump unit and a methanol high-pressure pump unit used in a bench test of a methanol dual-fuel engine, the second shut-off valve and the pressure reducing valve are both installed in a connecting pipe, the connecting pipe is used to be placed between a bench diesel supply unit and a methanol high-pressure pump unit used in a bench test of a methanol dual-fuel engine and respectively connect the two, and the second shut-off valve is used to connect the methanol high-pressure pump unit through a pressure reducing valve. A related flushing method is also provided. The diesel flushing system after a bench test of a methanol dual-fuel engine of the present invention can completely remove the methanol remaining in the methanol dual-fuel engine and in the methanol pipeline after the bench test is completed, ensuring that the removal of the methanol dual-fuel engine will not affect safety and personnel health.

Description

Technical Field

[0001] The present invention relates to the technical field of engine bench test, more specifically, to the technical field of methanol dual-fuel engine bench test, and in particular to a diesel flushing system and a flushing method after the methanol dual-fuel engine bench test is completed. Background Art

[0002] Engine bench testing refers to the testing and evaluation of various performance parameters of the engine on a specially designed test bench before the engine leaves the factory. This test method can simulate various states of the engine in actual work, such as the running state at different speeds and loads, so as to have a more comprehensive understanding of the engine's performance and potential problems.

[0003] See also Figure 1 As shown, the methanol dual-fuel engine bench test mainly adopts a methanol dual-fuel engine, a methanol storage tank, a methanol low-pressure supply pump unit, a methanol high-pressure pump unit, a bench diesel supply unit, a nitrogen purge inlet pipe 2, a nitrogen purge outlet pipe 3 and a methanol collecting box. The methanol storage tank is connected to the methanol high-pressure pump unit through a methanol low-pressure supply pump unit pipeline. The methanol high-pressure pump unit and the bench diesel supply unit are both connected to the methanol dual-fuel engine through pipelines. A methanol discharge valve 1 is provided in the methanol dual-fuel engine. The methanol discharge valve 1 pipeline is connected to the methanol collecting box. The nitrogen purge inlet pipe 2 is connected to the connecting pipeline between the methanol high-pressure pump unit and the methanol dual-fuel engine. The nitrogen purge outlet pipe 3 is connected to the connecting pipeline between the methanol discharge valve 1 and the methanol collecting box. The methanol low-pressure supply pump unit is used to transfer methanol from the methanol The methanol storage tank supplies the methanol high-pressure pump unit with a stable pressure of 5 bar; the methanol high-pressure pump unit is used to increase the 5 bar methanol from the methanol low-pressure supply pump unit to 600 bar and supply it to the methanol dual-fuel engine for combustion; since the methanol dual-fuel engine requires diesel as a pilot oil when the methanol mode works normally, a bench diesel supply unit is required to supply 7-8 bar diesel to the methanol dual-fuel engine; the methanol unloading valve 1 is used to unload the methanol in the methanol dual-fuel engine and the methanol pipeline into the methanol collection box; the nitrogen purge inlet pipe 2 and the nitrogen purge outlet pipe 3 are used to purge the methanol in the methanol dual-fuel engine and the methanol pipeline into the methanol collection box; the methanol collection box (500L) is used to collect the methanol after unloading and purging in the methanol dual-fuel engine and the methanol pipeline.

[0004] When the methanol dual-fuel engine is running in normal methanol mode: the bench diesel supply unit supplies diesel at 7 bar to the methanol dual-fuel engine as a pilot oil, and the methanol in the methanol storage tank is supplied to the methanol high-pressure pump unit through the methanol low-pressure supply pump unit (adjusting the pressure to 5 bar). The methanol high-pressure pump unit boosts the methanol to 600 bar and then supplies it to the methanol pipeline of the methanol dual-fuel engine for combustion. When the methanol dual-fuel engine switches from methanol mode to diesel mode: the methanol high-pressure pump unit stops running, the methanol discharge valve 1 opens, and the methanol in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank, the nitrogen purge inlet pipe 2 and the nitrogen purge outlet pipe 3 are opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine runs with diesel.

[0005] When the methanol dual-fuel engine is undergoing bench testing, due to the engine's operating design, after the methanol mode is completed, a certain amount of methanol will remain in the methanol dual-fuel engine and the methanol pipeline. Due to the properties of methanol (volatile, flammable, and toxic to the human body), when the methanol dual-fuel engine is dismantled and leaves the test room, a certain amount of methanol will leak to the outside, which will affect safety and personnel health.

[0006] Therefore, when the bench test of the methanol dual-fuel engine is completed, the methanol mode of the methanol dual-fuel engine is switched to the diesel mode, the methanol high-pressure pump unit stops running, the methanol unloading valve 1 is opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is unloaded into the methanol collection tank, the nitrogen purge inlet pipe 2 and the nitrogen purge outlet pipe 3 are opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is purged into the methanol collection tank, and the methanol dual-fuel engine runs with diesel.

[0007] However, when ending the methanol dual-fuel engine bench test in this way, the methanol is not completely removed. Some methanol still remains in the methanol dual-fuel engine and the methanol pipeline. During dismantling, methanol will still leak to the outside, which will still affect safety and personnel health.

[0008] Therefore, it is hoped to provide a flushing system after the bench test of a methanol dual-fuel engine is completed, which can completely remove the residual methanol in the methanol dual-fuel engine and the methanol pipeline after the bench test is completed, ensuring that the dismantling of the methanol dual-fuel engine will not affect safety and personnel health. Summary of the invention

[0009] In order to overcome the shortcomings of the above-mentioned prior art, one object of the present invention is to provide a diesel flushing system after the bench test of a methanol dual-fuel engine is completed, which can completely remove the residual methanol in the methanol dual-fuel engine and the methanol pipeline after the bench test is completed, ensuring that the dismantling of the methanol dual-fuel engine will not affect the safety and health of personnel, and is suitable for large-scale promotion and application.

[0010] Another object of the present invention is to provide a diesel flushing method after the bench test of a methanol dual-fuel engine is completed, which can completely remove the residual methanol in the methanol dual-fuel engine and the methanol pipeline after the bench test is completed, ensuring that the dismantling of the methanol dual-fuel engine will not affect the safety and health of personnel, and is suitable for large-scale promotion and application.

[0011] To achieve the above objectives, in a first aspect of the present invention, a diesel flushing system after a methanol dual-fuel engine bench test is provided, which is characterized in that it includes a first shut-off valve, a second shut-off valve, a pressure reducing valve and a connecting pipe, wherein:

[0012] The first cut-off valve is used to be installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit used in the methanol dual-fuel engine bench test. The second cut-off valve and the pressure reducing valve are both installed in the connecting pipeline. The connecting pipeline is used to be placed between the bench diesel supply unit and the methanol high-pressure pump unit used in the methanol dual-fuel engine bench test and to connect the bench diesel supply unit and the methanol high-pressure pump unit by pipelines respectively. The second cut-off valve is used to connect the methanol high-pressure pump unit by pipeline through the pressure reducing valve.

[0013] Preferably, both the first shut-off valve and the second shut-off valve are electrically controlled pneumatic valves.

[0014] Preferably, the pressure reducing valve is a mechanical self-supporting pressure reducing valve.

[0015] Preferably, the diesel flushing system after the methanol dual-fuel engine bench test also includes a first check valve and a second check valve, wherein the first check valve is used to be installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit, and the second check valve is installed in the connecting pipeline.

[0016] More preferably, the first shut-off valve is used for pipeline connection to the methanol high-pressure pump unit through the first check valve.

[0017] More preferably, the second check valve is connected to the pressure reducing valve through the second cut-off valve pipeline.

[0018] In a second aspect of the present invention, a diesel flushing method after the above-mentioned methanol dual-fuel engine bench test is provided, which is characterized in that the diesel flushing system after the above-mentioned methanol dual-fuel engine bench test is adopted, and the diesel flushing method after the above-mentioned methanol dual-fuel engine bench test is completed comprises the following steps:

[0019] (1) installing the first shut-off valve in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit, placing the connecting pipeline between the bench diesel supply unit and the methanol high-pressure pump unit and connecting the bench diesel supply unit and the methanol high-pressure pump unit with pipelines respectively;

[0020] (2) When the methanol dual-fuel engine is in normal methanol mode: the second shut-off valve, the pressure reducing valve, the methanol discharge valve, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe of the methanol dual-fuel engine used in the bench test of the methanol dual-fuel engine are closed, the first shut-off valve is opened, diesel is supplied to the methanol dual-fuel engine as a pilot oil through the bench diesel supply unit, the methanol in the methanol storage tank is supplied to the methanol high-pressure pump unit through the methanol low-pressure supply pump unit, and the methanol is pressurized by the methanol high-pressure pump unit and supplied to the methanol pipeline of the methanol dual-fuel engine for combustion;

[0021] (3) When the methanol dual-fuel engine switches from methanol mode to diesel mode: the methanol high-pressure pump unit is stopped, the first shut-off valve is closed, the methanol discharge valve is opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank used in the bench test of the methanol dual-fuel engine, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe are opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine is operated with diesel;

[0022] (4) Washing the methanol pipeline with diesel: close the methanol discharge valve, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe, open the second shut-off valve and the pressure reducing valve, operate the methanol high-pressure pump unit, supply diesel to the pressure reducing valve through the bench diesel supply unit, supply it to the methanol high-pressure pump unit after reducing the pressure through the pressure reducing valve, and supply the diesel to the methanol dual-fuel engine methanol pipeline for combustion after boosting the diesel through the methanol high-pressure pump unit;

[0023] (5) After the preset combustion time, the methanol dual-fuel engine is switched to the diesel mode, the methanol high-pressure pump unit is stopped, the second shut-off valve and the pressure reducing valve are closed, the methanol discharge valve is opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe are opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine is stopped.

[0024] Preferably, in step (2), diesel is supplied to the methanol dual-fuel engine at 8 bar as ignition oil through the bench diesel supply unit, methanol in the methanol storage tank is supplied to the methanol high-pressure pump unit at 5 bar through the methanol low-pressure supply pump unit, and methanol is pressurized by the methanol high-pressure pump unit and supplied to the methanol dual-fuel engine methanol pipeline at 600 bar for combustion.

[0025] Preferably, in step (4), diesel is supplied to the pressure reducing valve at 8 bar through the bench diesel supply unit, and is supplied to the methanol high-pressure pump unit at 5 bar after being reduced in pressure by the pressure reducing valve, and the diesel is pressurized by the methanol high-pressure pump unit and is supplied to the methanol dual-fuel engine methanol pipeline at 600 bar for combustion.

[0026] Preferably, in step (5), the preset time is 10 minutes.

[0027] The beneficial effects of the present invention are:

[0028] 1. The diesel flushing system after the bench test of the methanol dual-fuel engine of the present invention comprises a first shut-off valve, a second shut-off valve, a pressure reducing valve and a connecting pipe. The first shut-off valve is used to be installed in the connecting pipe between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit used in the bench test of the methanol dual-fuel engine. The second shut-off valve and the pressure reducing valve are both installed in the connecting pipe. The connecting pipe is used to be placed between the bench diesel supply unit and the methanol high-pressure pump unit used in the bench test of the methanol dual-fuel engine and to connect the bench diesel supply unit and the methanol high-pressure pump unit with pipelines respectively. The second shut-off valve is used to connect the methanol high-pressure pump unit with the pipeline through the pressure reducing valve. Therefore, it can completely remove the methanol remaining in the methanol dual-fuel engine and the methanol pipeline after the bench test, ensuring that the methanol dual-fuel engine will not affect safety and personnel health when it is dismantled, and is suitable for large-scale promotion and application.

[0029] 2. The diesel flushing method after the bench test of the methanol dual-fuel engine of the present invention is to use diesel to wash the methanol pipeline after the methanol mode is switched to the diesel mode: the methanol discharge valve, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe are closed, the second cut-off valve and the pressure reducing valve are opened, the methanol high-pressure pump unit is operated, the diesel is supplied to the pressure reducing valve through the bench diesel supply unit, and the pressure is reduced by the pressure reducing valve and then supplied to the methanol high-pressure pump unit, and the diesel is boosted by the methanol high-pressure pump unit and then supplied to the methanol pipeline of the methanol dual-fuel engine for combustion; after the preset combustion time, the methanol dual-fuel engine is switched to the diesel mode, and the methanol is The alcohol high-pressure pump unit stops running, the second shut-off valve and the pressure reducing valve are closed, the methanol unloading valve is opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is unloaded into the methanol collecting tank, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe are opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is purged into the methanol collecting tank, and the methanol dual-fuel engine is shut down. Therefore, it is possible to completely remove the residual methanol in the methanol dual-fuel engine and the methanol pipeline after the bench test is completed, ensuring that the dismantling of the methanol dual-fuel engine will not affect safety and personnel health, and is suitable for large-scale promotion and application.

[0030] These and other objects, features and advantages of the present invention will be more fully reflected in the following detailed description and claims, and may be achieved by the means, devices and combinations thereof particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the connection structure of multiple devices used in the methanol dual-fuel engine bench test.

[0032] Figure 2 A specific embodiment of the diesel flushing system after the methanol dual-fuel engine bench test of the present invention is combined with Figure 1 The diagram shows the structure of multiple equipment connections used in the methanol dual-fuel engine bench test.

[0033] (Explanation of symbols)

[0034] 1 methanol discharge valve; 2 nitrogen purge inlet pipe; 3 nitrogen purge outlet pipe; 4 first shut-off valve; 5 second shut-off valve; 6 connecting pipeline; 7 first check valve; 8 second check valve. DETAILED DESCRIPTION

[0035] In order to completely remove the residual methanol in the methanol dual-fuel engine and the methanol pipeline after the bench test is completed, and to ensure that the dismantling of the methanol dual-fuel engine will not affect the safety and health of personnel, the inventors, through in-depth and extensive research, have proposed a diesel flushing system and flushing method after the bench test of the methanol dual-fuel engine is completed.

[0036] See also Figure 2 As shown, in a specific embodiment of the present invention, the diesel flushing system after the methanol dual-fuel engine bench test of the present invention includes a first cut-off valve 4, a second cut-off valve 5, a pressure reducing valve and a connecting pipe 6, wherein:

[0037] The first cut-off valve 4 is used to be installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit used in the methanol dual-fuel engine bench test. The second cut-off valve 5 and the pressure reducing valve are both installed in the connecting pipeline 6. The connecting pipeline 6 is used to be placed between the bench diesel supply unit and the methanol high-pressure pump unit used in the methanol dual-fuel engine bench test and to connect the bench diesel supply unit and the methanol high-pressure pump unit by pipelines respectively. The second cut-off valve 5 is used to connect the methanol high-pressure pump unit by pipeline through the pressure reducing valve.

[0038] The pressure reducing valve may be any suitable pressure reducing valve. In a specific embodiment of the present invention, the pressure reducing valve is a mechanical self-supporting pressure reducing valve. The pressure regulating range of the mechanical self-supporting pressure reducing valve may be, for example, 6-8 bar before the valve and 4-5 bar after the valve.

[0039] The first cut-off valve 4 and the second cut-off valve 5 can be any suitable cut-off valves. In a specific embodiment of the present invention, the first cut-off valve 4 and the second cut-off valve 5 are both electrically controlled pneumatic valves. With the above arrangement, the corresponding pipelines can be opened and closed remotely.

[0040] After the methanol dual-fuel engine bench test, the diesel flushing system may also include any other suitable components, see Figure 2 As shown, in a specific embodiment of the present invention, the diesel flushing system after the methanol dual-fuel engine bench test also includes a first check valve 7 and a second check valve 8. The first check valve 7 is used to be installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit, and the second check valve 8 is installed in the connecting pipe 6.

[0041] The first check valve 7 can be installed upstream or downstream of the first shut-off valve 4, see Figure 2 As shown, in a specific embodiment of the present invention, the first shut-off valve 4 is used for pipeline connection to the methanol high-pressure pump unit through the first check valve 7.

[0042] The second check valve 8 can be installed upstream of the second shut-off valve 5, between the second shut-off valve 5 and the pressure reducing valve, or downstream of the pressure reducing valve. Figure 2 As shown, in a specific embodiment of the present invention, the second check valve 8 is connected to the pressure reducing valve through the second cut-off valve 5 pipeline.

[0043] The diesel flushing method after the methanol dual-fuel engine bench test of the present invention is briefly described as follows:

[0044] (1) Please see Figure 2 As shown, the first shut-off valve 4 is installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit, and the connecting pipeline 6 is placed between the bench diesel supply unit and the methanol high-pressure pump unit and the bench diesel supply unit and the methanol high-pressure pump unit are connected by pipelines respectively;

[0045] (2) When the methanol dual-fuel engine is operating in normal methanol mode (50% load): the second shut-off valve 5, the pressure reducing valve, and the methanol discharge valve 1, the nitrogen purge inlet pipe 2, and the nitrogen purge outlet pipe 3 of the methanol dual-fuel engine used in the bench test of the methanol dual-fuel engine are closed, and the first shut-off valve 4 is opened, and diesel is supplied to the methanol dual-fuel engine at 8 bar as a pilot oil through the bench diesel supply unit, and the methanol in the methanol storage tank is supplied to the methanol high-pressure pump unit at 5 bar through the methanol low-pressure supply pump unit, and the methanol is pressurized by the methanol high-pressure pump unit and supplied to the methanol dual-fuel engine methanol pipeline at 600 bar for combustion;

[0046] (3) When the methanol dual-fuel engine switches from methanol mode to diesel mode (50% load): the methanol high-pressure pump unit is stopped, the first shut-off valve 4 is closed, the methanol discharge valve 1 is opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank used in the bench test of the methanol dual-fuel engine, the nitrogen purge inlet pipe 2 and the nitrogen purge outlet pipe 3 are opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine is operated with diesel;

[0047] (4) Washing the methanol pipeline with diesel (50% load): close the methanol discharge valve 1, the nitrogen purge inlet pipe 2 and the nitrogen purge outlet pipe 3, open the second shut-off valve 5 and the pressure reducing valve, operate the methanol high-pressure pump unit, supply diesel to the pressure reducing valve at 8 bar through the bench diesel supply unit, supply it to the methanol high-pressure pump unit at 5 bar after being reduced in pressure by the pressure reducing valve, and supply it to the methanol dual-fuel engine methanol pipeline at 600 bar after boosting the diesel through the methanol high-pressure pump unit for combustion (since the calorific value of methanol is half that of diesel, the operator can manually adjust the parameters of the methanol dual-fuel engine to ensure the normal operation of the methanol dual-fuel engine);

[0048] (5) After a preset combustion time, for example, 10 minutes, the methanol dual-fuel engine is switched to the diesel mode, the methanol high-pressure pump unit is stopped, the second shut-off valve 5 and the pressure reducing valve are closed, the methanol discharge valve 1 is opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank, the nitrogen purge inlet pipe 2 and the nitrogen purge outlet pipe 3 are opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine is stopped.

[0049] In this way, the residual liquid in the methanol dual-fuel engine and the external methanol pipeline is completely replaced by diesel, which will not cause harm to the environment and personnel.

[0050] Therefore, the present invention proposes a diesel flushing system after the bench test of a methanol dual-fuel engine is completed, which is used for processing residual methanol in the methanol dual-fuel engine and the methanol pipeline during the bench test of the methanol dual-fuel engine. The diesel flushing system after the bench test of the methanol dual-fuel engine is adopted, by adding a control valve between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit and adding a pipeline and related valves from the bench diesel supply unit to the methanol high-pressure pump unit, so that the methanol dual-fuel engine burns diesel instead of methanol in the methanol mode, ensuring that there is no methanol in the methanol dual-fuel engine and the methanol pipeline, and then unloading and purging the methanol dual-fuel engine and the methanol pipeline, so that after shutdown, the methanol dual-fuel engine and the methanol pipeline are full of diesel, and the safety of personnel and the environment is guaranteed when disassembling and assembling the methanol dual-fuel engine.

[0051] In summary, the diesel flushing system and flushing method of the present invention can completely remove the residual methanol in the methanol dual-fuel engine and the methanol pipeline after the bench test, ensuring that the dismantling of the methanol dual-fuel engine will not affect the safety and health of personnel, and is suitable for large-scale promotion and application.

[0052] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it is apparent that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the description should be regarded as illustrative rather than restrictive.

Claims

1. A diesel flushing system after a methanol dual-fuel engine bench test, characterized in that: It includes a first shut-off valve, a second shut-off valve, a pressure reducing valve and a connecting pipeline, wherein: The first cut-off valve is used to be installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit used in the methanol dual-fuel engine bench test. The second cut-off valve and the pressure reducing valve are both installed in the connecting pipeline. The connecting pipeline is used to be placed between the bench diesel supply unit and the methanol high-pressure pump unit used in the methanol dual-fuel engine bench test and to connect the bench diesel supply unit and the methanol high-pressure pump unit by pipelines respectively. The second cut-off valve is used to connect the methanol high-pressure pump unit by pipeline through the pressure reducing valve.

2. The diesel flushing system after the methanol dual-fuel engine bench test according to claim 1 is characterized in that: The first cut-off valve and the second cut-off valve are both electrically controlled pneumatic valves.

3. The diesel flushing system after the methanol dual-fuel engine bench test according to claim 1 is characterized in that: The pressure reducing valve is a mechanical self-supporting pressure reducing valve.

4. The diesel flushing system after the methanol dual-fuel engine bench test according to claim 1 is characterized in that: The diesel flushing system after the methanol dual-fuel engine bench test also includes a first check valve and a second check valve. The first check valve is used to be installed in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit, and the second check valve is installed in the connecting pipeline.

5. The diesel flushing system after the methanol dual-fuel engine bench test according to claim 4 is characterized in that: The first shut-off valve is used for pipeline connection to the methanol high-pressure pump unit through the first check valve.

6. The diesel flushing system after the methanol dual-fuel engine bench test according to claim 4 is characterized in that: The second check valve is connected to the pressure reducing valve through the second cut-off valve pipeline.

7. A diesel flushing method after a methanol dual-fuel engine bench test, characterized in that: The diesel flushing system after the methanol dual-fuel engine bench test according to claim 1 is used, and the diesel flushing method after the methanol dual-fuel engine bench test is completed comprises the following steps: (1) installing the first shut-off valve in the connecting pipeline between the methanol low-pressure supply pump unit and the methanol high-pressure pump unit, placing the connecting pipeline between the bench diesel supply unit and the methanol high-pressure pump unit and connecting the bench diesel supply unit and the methanol high-pressure pump unit with pipelines respectively; (2) When the methanol dual-fuel engine is in normal methanol mode: the second shut-off valve, the pressure reducing valve, the methanol discharge valve, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe of the methanol dual-fuel engine used in the bench test of the methanol dual-fuel engine are closed, the first shut-off valve is opened, diesel is supplied to the methanol dual-fuel engine as a pilot oil through the bench diesel supply unit, the methanol in the methanol storage tank is supplied to the methanol high-pressure pump unit through the methanol low-pressure supply pump unit, and the methanol is pressurized by the methanol high-pressure pump unit and supplied to the methanol pipeline of the methanol dual-fuel engine for combustion; (3) When the methanol dual-fuel engine switches from methanol mode to diesel mode: the methanol high-pressure pump unit is stopped, the first shut-off valve is closed, the methanol discharge valve is opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank used in the bench test of the methanol dual-fuel engine, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe are opened, and the methanol in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine is operated with diesel; (4) Washing the methanol pipeline with diesel: close the methanol discharge valve, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe, open the second shut-off valve and the pressure reducing valve, operate the methanol high-pressure pump unit, supply diesel to the pressure reducing valve through the bench diesel supply unit, supply it to the methanol high-pressure pump unit after reducing the pressure through the pressure reducing valve, and supply the diesel to the methanol dual-fuel engine methanol pipeline for combustion after boosting the diesel through the methanol high-pressure pump unit; (5) After the preset combustion time, the methanol dual-fuel engine is switched to the diesel mode, the methanol high-pressure pump unit is stopped, the second shut-off valve and the pressure reducing valve are closed, the methanol discharge valve is opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is discharged to the methanol collection tank, the nitrogen purge inlet pipe and the nitrogen purge outlet pipe are opened, the diesel in the methanol dual-fuel engine and the methanol pipeline is purged to the methanol collection tank, and the methanol dual-fuel engine is stopped.

8. The flushing method according to claim 7, characterized in that: In the step (2), diesel is supplied to the methanol dual-fuel engine at 8 bar as ignition oil through the bench diesel supply unit, methanol in the methanol storage tank is supplied to the methanol high-pressure pump unit at 5 bar through the methanol low-pressure supply pump unit, and methanol is pressurized by the methanol high-pressure pump unit and supplied to the methanol dual-fuel engine methanol pipeline for combustion at 600 bar.

9. The flushing method according to claim 7, characterized in that: In step (4), diesel is supplied to the pressure reducing valve at 8 bar through the bench diesel supply unit, and is supplied to the methanol high-pressure pump unit at 5 bar after being reduced in pressure by the pressure reducing valve. The diesel is pressurized by the methanol high-pressure pump unit and is supplied to the methanol dual-fuel engine methanol pipeline at 600 bar for combustion.

10. The flushing method according to claim 7, characterized in that: In step (5), the preset time is 10 minutes.

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