Independent inner and outer needle valve type flexible fuel injector

Abstract

The invention relates to an independent inner and outer needle valve type flexible fuel injector which comprises an injector shell, internally and externally nested needle valve matching parts, an electromagnetic control valve assembly and a double-row injection hole structure, and a diesel oil high-pressure oil way and a low-carbon fuel high-pressure oil way are arranged in the injector shell; the electromagnetic control valve assembly is arranged in the upper portion of the ejector shell, independently controls diesel oil injection and is of a hydraulic balance valve structure. Needle valve matching parts nested inside and outside are installed at the bottom of the ejector shell and connected with the electromagnetic control valve assembly through a spring guide sleeve, a limiting block and a middle rod. A double-row spray hole structure is arranged at the bottom of the internally and externally nested needle valve matching part; the inerting valve set is connected to the low-carbon fuel high-pressure oil way and used for purging and inerting during fuel switching. By means of the nesting needle valve, the diesel oil lubrication seal, the independent control valve and the inerting design, efficient and stable dual-fuel injection is achieved, the problem of mixing in the prior art is solved, the service life of the injector is prolonged, and the dual-fuel injector is suitable for ship engines with alternative fuel such as methanol / ammonia.

Description

Technical Field

[0001] The present invention relates to the technical field of engine fuel injection, and is particularly applicable to a dual-fuel (diesel / methanol / ammonia) injection system for marine high-power medium-speed engines, realizing flexible fuel switching, independent control, and stable injection within a wide flow rate range. Background Art

[0002] With the increasingly stringent ship emission standards, the research on alternative energy sources for marine engines has become increasingly important. Low-carbon fuel methanol and zero-carbon fuel ammonia, as emerging fuels, can effectively reduce emissions, have relatively mature preparation technologies, clean and environmentally friendly refining processes, and broad market prospects. Relying on the structure of the original diesel injector to develop an alternative fuel-diesel dual-fuel injector is an important way for the new energy transformation of marine engines. However, due to the limited space in the cylinder head, the scheme of arranging one or more alternative fuel injectors with larger volumes beside the original diesel injector is hardly acceptable for the main engine layout. Therefore, a flexible fuel injection scheme that realizes the mode switching between diesel and alternative fuels with the same injector is urgently needed. However, the development of a flexible fuel injection device based on the transformation of a diesel injector faces the following technical difficulties:

[0003] The low-carbon fuel injection device requires a fuel injection method in which diesel and low-carbon fuels are independently injected and the injection timing is flexibly adjustable. Low-carbon fuels usually have the characteristics of high auto-ignition temperature and slow combustion speed. Therefore, the low-carbon fuel mode usually requires a traditional fuel with better combustibility, such as diesel, as the pilot fuel. At the same time, in the diesel mode, the injector also needs to have the characteristics of large-flow injection of diesel. This wide range of fuel quantity requirements poses a huge challenge to the design of the low-carbon fuel injector. In addition, while the low-carbon fuel injection device has both the functions of diesel and low-carbon fuel injection, it also needs to realize the functions of independent injection control and flexible injection timing adjustment of the two fuels. Undoubtedly, a new injector structure needs to be designed, which is very challenging in the design process of high-integration injectors.

[0004] During fuel mode switching, diesel and alternative fuels will be mixed, and the mixing ratio cannot be accurately determined. Moreover, during the mixing process, the conventional double-needle valve coupling structure has the problem of uneven mixing. The fuel component content during switching is complex, and the components injected per cycle are uneven and inconsistent, making it difficult to predict the combustion condition, with poor switching state stability and difficult engine speed regulation.

[0005] The characteristic of high saturated vapor pressure of low-carbon fuels leads to the need for an additional cooling oil circuit design inside the injector.

[0006] The above two alternative fuels have poor lubricity. The lubrication of the moving pairs of the fuel injection device needs to be considered emphatically to ensure the service life of the injection device.

[0007] The above two alternative fuels are toxic and corrosive, have a low flash point and an explosion risk, and leakage protection measures for the injection device need to be considered as a priority to ensure the safety of life and property at the device site.

[0008] Existing dual-fuel injectors (such as CN116398340A) use time-sharing control of inner and outer needle valves, but there are the following problems:

[0009] 1. Fuel mixing is likely to occur during fuel switching, resulting in unstable combustion;

[0010] 2. The lubricity of low-carbon fuels is poor, and the moving pairs are severely worn;

[0011] 3. Lack of efficient cooling and inerting design, there is a risk of leakage.

[0012] Therefore, it is particularly important to design a dual-fuel injector with high integration, a wide injection oil volume coverage range, flexible and independently adjustable pressure and timing for promoting the decarbonization process of the engine. The present invention solves the above problems through a nested needle valve, diesel lubrication seal, inerting valve group and double-row spray hole structure. Summary of the Invention

[0013] The present invention provides an independent inner and outer needle valve type flexible fuel injector, which can inject alternative fuels and diesel, and can adapt to different fuel injection volume requirements. Its beneficial effects include: 1) Flexible fuel, it can inject diesel or other new green fuels, and at the same time, the injector is a three-function integrated design for low-carbon fuel injection and diesel main ignition injection, meeting the high-integration layout requirements of medium- and high-speed engines; 2) The fuel switching process is uniform and stable, diesel and methanol can be injected simultaneously, and the injection control is independent; 3) During the operation of the engine, the injection device can adjust the injection volume, and at the same time, different fuel injection modes can be switched without disassembling the structure; 4) The methanol and diesel needle valves are designed in a nested manner, realizing the inner and outer ring layout of methanol spray holes and diesel spray holes, both located at the center of the combustion chamber and evenly distributed along the central axis, with uniform and efficient ignition, diesel main combustion and low-carbon fuel combustion; 5) The system oil circuit layout is simple and efficient. The diesel oil circuit not only serves as the fuel supply oil circuit for diesel injection, but also has the functions of circulating cooling, lubrication of moving pairs and sealing of low-carbon fuels in the low-carbon fuel mode.

[0014] To achieve the above object, the technical solution of the present invention is: an independent internal and external needle valve type flexible fuel injector, including an injector housing, a flow-limiting valve core, an inerting valve group, an internally and externally nested needle valve pair, an electromagnetic control valve assembly, and a double-row spray hole structure. A diesel high-pressure oil circuit and a low-carbon fuel high-pressure oil circuit are provided inside the injector housing; the flow-limiting valve core is arranged inside the upper end cover of the injector at the top of the injector housing, and the low-carbon fuel flow is regulated through a throttle hole; the electromagnetic control valve assembly is arranged inside the upper part of the injector housing to independently control diesel injection, adopting a hydraulic balance valve structure; the internally and externally nested needle valve pair is installed at the bottom of the injector housing and is connected to the electromagnetic control valve assembly through a spring guide sleeve, a limit block, and an intermediate rod; a double-row spray hole structure is provided at the bottom of the internally and externally nested needle valve pair; the inerting valve group is connected to the low-carbon fuel high-pressure oil circuit for purging and inerting during fuel switching.

[0015] Further, the internally and externally nested needle valve pair includes a needle valve body, an inner needle valve stem, and an outer needle valve stem. The inner needle valve stem is nested inside the outer needle valve stem, and the two move independently along the central axis.

[0016] Further, the inner needle valve stem and the outer needle valve stem cooperate with the needle valve body to respectively form a diesel oil sump and a low-carbon fuel sump.

[0017] Further, the diesel oil sump and the low-carbon fuel sump are isolated by an annular gap. Diesel seals and lubricates the low-carbon fuel needle valve pair through the annular gap; the high-pressure diesel in the diesel oil sump is continuously supplied in the low-carbon fuel mode for lubricating, sealing the low-carbon fuel needle valve pair, and cooling the inside of the injector.

[0018] Further, the opening of the outer needle valve stem is independently controlled by a boost control valve of an external low-carbon fuel boost pump to achieve independent timing adjustment of low-carbon fuel injection and diesel ignition injection.

[0019] Further, the double-row spray hole structure includes an upper row of spray holes and a lower row of spray holes, corresponding to low-carbon fuel and diesel injection respectively, and are evenly distributed along the central axis of the combustion chamber.

[0020] Further, the electromagnetic control valve assembly includes an armature, a control valve stem, and a cone valve seat. A return oil throttle hole is provided on the stem handle of the cone valve seat; a control chamber is provided inside the cone valve seat. Through the hydraulic balance design of the control chamber, the control valve stem is completely sealed without electromagnetic force and quickly relieves pressure under the action of electromagnetic force to drive the inner needle valve stem to open.

[0021] Further, in the diesel injection mode of the injector, after diesel enters the injector through the high-pressure diesel interface, one way enters the diesel oil sump of the needle valve pair through the diesel high-pressure oil circuit, and the other way enters the control chamber through the inlet throttle hole of the electromagnetic control valve assembly; when the inner needle valve stem in the needle valve pair opens, diesel enters the spray holes through the diesel high-pressure oil circuit for injection.

[0022] Furthermore, in the diesel ignition and low-carbon fuel mode, the high-pressure low-carbon fuel reaches the spool of the flow-limiting valve through the high-pressure low-carbon fuel interface, enters the flow-limiting valve cavity through the throttle hole on the spool of the flow-limiting valve, and enters the low-carbon fuel sump of the needle valve assembly through the high-pressure low-carbon fuel oil circuit, causing the outer needle valve stem to open and realizing low-carbon fuel injection.

[0023] Furthermore, when the injector is in the purging and inerting and fuel mode switching, high-pressure nitrogen is introduced into the high-pressure low-carbon fuel oil circuit through the inerting valve group to carry all the remaining low-pressure low-carbon fuel inside it away from the injector.

[0024] The injection device proposed by the present invention can produce the following several beneficial effects while achieving the expected functions:

[0025] 1) Adopting the internal and external needle valve design, and integrating the main injection and micro-injection of diesel fuel, stable injection can be realized within a wide flow range. The overall integration degree of the injector is high, reducing the number of fuel injectors required on the engine cylinder head and lowering the layout difficulty of the fuel injection system.

[0026] 2) The internal and external needle valves are independently controlled, enabling any injection timing combination of diesel and methanol, and the injection processes do not affect each other. Therefore, it can meet the fuel supply requirements of different combustion modes.

[0027] 3) The low-carbon fuel injection holes and diesel injection holes are both located at the center of the combustion chamber and are evenly distributed along the central axis. The ignition, diesel main combustion, and low-carbon fuel combustion are all evenly distributed and highly efficient.

[0028] 4) In the low-carbon fuel mode, high-pressure diesel can be used as the sealing and lubricating medium for the moving parts of the low-carbon fuel oil circuit. At the same time, when the inner needle injects the pilot fuel, the flow during the diesel injection process and the oil return of the control valve both have a certain cooling effect on the injector, reducing the risk of low-carbon fuel vaporization.

[0029] 5) The present invention realizes the efficient and stable injection of dual fuels through the nested needle valve, diesel lubrication and sealing, independent control valve, and inerting design, avoids the mixing problem of the prior art, extends the service life of the injector, and is applicable to marine engines using alternative fuels such as methanol / ammonia. Description of the Drawings

[0030] Figure 1 It is the overall structural schematic diagram of the independent internal and external needle valve type flexible fuel injector of the present invention;

[0031] Figure 2 It is the structural schematic diagram of the diesel injection electromagnetic control valve assembly;

[0032] Figure 3Partial enlarged view of the hydraulic principle of the balance valve structure;

[0033] Figure 4 Schematic diagram of the needle valve couple structure of an independent inner and outer needle valve type flexible fuel injector;

[0034] Figure 5 Detailed structure diagram of the needle valve body and nozzle and double-row centrally symmetric spray hole structure. Specific implementation manners

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] As Figure 1 shown in (a) and (b) of , the independent inner and outer needle valve type flexible fuel injector of the present invention includes components such as an injector upper end cover 001, a current-limiting valve core 002, a current-limiting valve spring 003, an inerting valve group 004, an injector housing 005, a nut 006, an electromagnetic control valve assembly 007, an intermediate rod 008, a limit block 009, a spring guide sleeve 010, a connecting nut 011, a needle valve couple 012, a needle valve spring 013, etc.

[0037] The top of the injector housing 005 is fixedly connected with the injector upper end cover 001, and the bottom is installed with the spring guide sleeve 010 and the needle valve couple 012 through the connecting nut 011. The injector upper end cover 001 is internally provided with a current-limiting valve core 002, and the throttle hole on the current-limiting valve core 002 communicates with the methanol fuel inlet of the injector upper end cover 001; inside the injector housing 005, a nut 006, an electromagnetic control valve assembly 007, an intermediate rod 008 and a limit block 009 are installed in sequence along the axis from top to bottom; a current-limiting valve spring 003 is arranged between the current-limiting valve core 002 and the nut 006; a needle valve spring 013 sleeved on the intermediate rod 008 is arranged between the intermediate rod 008 and the limit block 009, and a needle valve spring 013 sleeved on the limit block 009 is arranged between the limit block 009 and the needle valve couple 012. Inside the injector housing 005, there are a diesel high-pressure oil circuit and a low-carbon fuel high-pressure oil circuit; the diesel high-pressure oil circuit and the low-carbon fuel high-pressure oil circuit are respectively connected to the needle valve couple 012, and the diesel high-pressure oil circuit is connected to the high-pressure diesel interface, and the low-carbon fuel high-pressure oil circuit is connected to the high-pressure low-carbon fuel interface through the current-limiting valve cavity and the throttle hole on the current-limiting valve core 002, or is connected to the inerting valve group 004.

[0038] In the diesel injection mode, after the diesel enters the injector through the high-pressure diesel interface, one way enters the diesel oil sump 026 of the needle valve couple 012 through the diesel high-pressure oil circuit, and the other way enters the control cavity 025 through the oil inlet throttle hole 028 of the electromagnetic control valve assembly 007. When the inner needle valve stem 022 in the needle valve couple 012 is opened, the diesel enters the spray hole 031 through the diesel high-pressure oil circuit for spraying.

[0039] In the diesel ignition and low-carbon fuel mode, high-pressure low-carbon fuel reaches the throttle valve spool 002 through the high-pressure low-carbon fuel interface, enters the throttle valve cavity through the throttle hole on the throttle valve spool 002, and enters the low-carbon fuel sump 027 of the needle valve pair 012 through the high-pressure low-carbon fuel oil path, opening the outer needle valve stem 023 to achieve low-carbon fuel injection.

[0040] During purging and inerting and fuel mode switching, high-pressure nitrogen is introduced into the high-pressure low-carbon fuel oil path through the inerting valve group 004 to carry all the remaining low-pressure low-carbon fuel inside away from the injector.

[0041] As Figure 2 shown in (a) and (b) of Figure 3 shown, the electromagnetic control valve assembly 007 includes an electromagnet assembly 014, an armature 015, an adjusting shim 016, an armature seat 017, a control valve stem 018, a control valve spring 019, and a poppet valve seat 020; in addition, it also includes a control cavity 025 jointly constructed by the control valve group and the control valve stem, a fuel inlet throttle hole 028, and a fuel return throttle hole 029.

[0042] The top of the armature seat 017 is connected to the electromagnet assembly 014 through the armature 015. The control valve stem 018 is arranged inside the armature seat 017. The upper end of the control valve stem 018 is connected to the armature 015, and the lower end is connected to the poppet valve seat 020. A control valve spring 019 is also arranged between the control valve stem 018 and the poppet valve seat 020; a control cavity 025 is arranged inside the poppet valve seat 020. The control cavity 025 is communicated with the fuel inlet throttle hole 028, and a fuel return throttle hole 029 is arranged on the stem handle of the poppet valve seat 020.

[0043] As Figure 4 shown in Figure 5, the needle valve pair 012 includes parts such as a needle valve body 021, an inner needle valve stem 022, an outer needle valve stem 023, and a positioning pin 024. In addition, it also includes a diesel sump 026 and a low-carbon fuel sump 027 formed by the mating of the pair, an upper row of spray holes 030, and a lower row of spray holes 031.

[0044] The outer needle valve stem 023 is arranged inside the needle valve body 021, and the inner needle valve stem 022 is connected inside the outer needle valve stem 023; a diesel sump 026 is arranged between the middle part of the needle valve body 021 and the outer needle valve stem 023, a low-carbon fuel sump 027 is arranged between the bottom of the needle valve body 021 and the outer needle valve stem 023, and upper row of spray holes 030 and lower row of spray holes 031 are also arranged at the bottom.

[0045] The injection device proposed by the present invention can inject alternative fuels and diesel, and can adapt to different fuel injection quantity requirements. Its main functions and implementation methods are as follows:

[0046] 1) Diesel fuel injection function (i.e., diesel fuel is used as the main fuel for injection in the diesel mode)

[0047] 2) Diesel ignition and low-carbon fuel injection function (i.e., in the low-carbon fuel mode, diesel micro-injection for ignition and methanol fuel as the main fuel injection)

[0048] 3) Purge inerting and fuel mode switching function (i.e., switching from the low-carbon fuel mode to the diesel mode or from the diesel mode to the alternative fuel mode)

[0049] The implementation processes of the above three major functions are as follows:

[0050] Diesel fuel injection function:

[0051] 1) In the diesel injection mode, high-pressure diesel enters the injector through the high-pressure diesel interface, and fuel injection is controlled by the on-off of the electromagnetic control valve assembly 007. The specific working principle is as follows: After the diesel passes through the high-pressure diesel interface and enters the injector, one way passes through the high-pressure diesel oil path and enters the diesel oil sump 026 of the needle valve pair 012, and the other way enters the control chamber 025 through the control valve inlet throttle hole 028 (as Figure 2 shown). When the electromagnet 014 is not energized, the control valve stem 018 is pressed tightly on the cone valve seat 020 under the action of the spring force. The control valve structure is designed as a balanced valve structure using the principle of hydraulic balance. Even if the control chamber 025 is filled with high-pressure diesel, due to the principle of upper and lower hydraulic balance, the control valve stem is not subjected to the hydraulic pressure in the vertical direction. In this way, even a relatively small electromagnetic force can achieve complete sealing of the control valve. When the control chamber 025 is filled with high-pressure diesel, the intermediate rod 008 is subjected to the hydraulic pressure, so the inner needle valve stem 022 is pressed tightly on the seat surface of the needle valve body 021 under the action of the needle valve spring 013 and the hydraulic pressure of the intermediate rod 008, and the diesel is not injected. When the electromagnet is energized, the control valve stem 018 is lifted under the drive of the armature 015. The high-pressure diesel in the control chamber 025 flows out through the control valve return throttle hole 029 and returns to the low-pressure fuel tank through the control valve return oil path. Therefore, the pressure in the control chamber decreases, and the high-pressure diesel in the diesel oil sump 026 acts on the inner needle valve stem 022, and the hydraulic pressure overcomes the pre-tightening force of the needle valve spring 013, causing the inner needle valve stem 022 to open, and the diesel is injected through the inner ring diesel (lower) spray holes 031.

[0052] 2) Diesel ignition and low-carbon fuel injection function

[0053] In the diesel ignition and low-carbon fuel mode, high-pressure low-carbon fuel reaches the throttle valve spool 002 through the high-pressure low-carbon fuel interface ( Figure 1 the methanol inlet shown), enters the throttle valve chamber through the throttle hole on the throttle valve spool 002, and passes through the low-carbon fuel high-pressure oil path ( Figure 1It enters the low-carbon fuel oil storage tank 027 through the high-pressure methanol channel shown, and the hydraulic pressure acting on the outer needle valve stem 023 overcomes the pre-tightening force of the outer needle valve spring 013 to open the outer needle valve stem 023, realizing the injection of low-carbon fuel. The injection control of high-pressure low-carbon fuel is achieved by connecting and disconnecting the external high-pressure low-carbon fuel. This part of the function is realized by the boost control valve of the low-carbon fuel boost pump. In this mode, according to the required ignition injection timing, the pilot diesel can realize the injection of pilot fuel at any time through the same control principle as in the main diesel combustion mode, thus realizing the independent control of diesel ignition and low-carbon fuel injection, and they do not affect each other during the injection process.

[0054] 3) Purge inerting and fuel mode switching function

[0055] When the fuel mode needs to be switched from the low-carbon fuel mode to the diesel fuel injection mode, the external high-pressure low-carbon fuel stops being introduced, and high-pressure nitrogen is introduced into the high-pressure low-carbon fuel oil circuit through the inerting valve group 004 to carry away all the remaining low-pressure low-carbon fuel inside it from the injector, realizing the inerting of the low-carbon fuel oil circuit and preventing the remaining low-carbon fuel inside the injector from vaporizing under the high temperature of the engine, thus avoiding leakage.

[0056] 4) In the diesel mode, the injector is cooled by cooling water or cooling oil in the high-pressure low-carbon fuel oil circuit to prevent the injector from suffering structural damage due to thermal stress at high temperatures.

[0057] When the fuel mode needs to be switched from the diesel mode to the low-carbon fuel mode, the cooling medium in the methanol oil circuit is cut off, and high-pressure nitrogen is introduced into the high-pressure low-carbon fuel oil circuit through the inerting valve to carry away all the remaining cooling medium inside it from the injector, preventing the cooling medium from mixing with the low-carbon fuel and being sprayed into the cylinder, which affects the engine performance.

[0058] In the lubrication of the low-carbon fuel in this embodiment, since in the low-carbon fuel working mode, diesel is used as the pilot fuel and the diesel pressure is higher, the diesel in the diesel oil storage tank 026 seals and lubricates the clearance of the low-carbon fuel needle valve pair.

[0059] 5) Through the design of the inerting valve, it ensures that the fuel switching process is stable, reliable, and controllable, the fuel components sprayed into the cylinder are single, and there is no leakage risk for the low-carbon fuel.

[0060] (Note: The viscosities of low-carbon fuel methanol and zero-carbon fuel ammonia are lower than that of diesel, it is not easy to form an oil film, and the lubricity is poor; and they have a certain corrosive effect on some metals, which exacerbates wear. The injection device serves for the injection of engine gas fuel. As the engine runs, the moving parts in the injection device need to perform cyclic repetitive actions, and wear will affect the accuracy of the actions, thus affecting the injection performance and shortening the service life of the injection device. Therefore, establishing effective lubrication is very important for extending the service life of the injection device.

[0061] This is only one embodiment of the present invention and does not cover all the protected content. Simple deformations made based on the core structure of the present invention, such as the arrangement form of the needle valve couple that achieves the same function, and the form of fuel injection control, etc., are all within the protection scope of the present invention.

Claims

1. An independent inner and outer needle valve type flexible fuel injector, characterized in that: It includes an injector housing, a flow limiting valve core, an inerting valve group, an inner and outer nested needle valve pair, an electromagnetic control valve assembly, and a double-row spray hole structure. A diesel high-pressure oil circuit and a low-carbon fuel high-pressure oil circuit are arranged inside the injector housing; the flow limiting valve core is arranged in the injector upper end cover at the top of the injector housing, and the low-carbon fuel flow is adjusted through the throttle hole; the electromagnetic control valve assembly is arranged in the upper part of the injector housing, independently controls the diesel injection, and adopts a hydraulic balance valve structure; the inner and outer nested needle valve pair is installed at the bottom of the injector housing, and is connected to the electromagnetic control valve assembly through a spring guide sleeve, a limit block and an intermediate rod; a double-row spray hole structure is arranged at the bottom of the inner and outer nested needle valve pair; the inerting valve group is connected to the low-carbon fuel high-pressure oil circuit, which is used for purging and inerting during fuel switching.

2. The independent inner and outer needle valve type flexible fuel injector according to claim 1, characterized in that: The inner and outer nested needle valve pair comprises a needle valve body, an inner needle valve stem and an outer needle valve stem. The inner needle valve stem is nested in the outer needle valve stem, and the two move independently along the central axis.

3. The independent inner and outer needle valve type flexible fuel injector according to claim 2, characterized in that: The inner needle valve stem, the outer needle valve stem and the needle valve body cooperate to form a diesel oil tank and a low-carbon fuel oil tank respectively.

4. The independent inner and outer needle valve type flexible fuel injector according to claim 3, characterized in that: The diesel oil tank and the low-carbon fuel oil tank are separated by an annular gap, and the diesel seals and lubricates the low-carbon fuel needle valve pair through the annular gap; the high-pressure diesel in the diesel oil tank is continuously supplied in the low-carbon fuel mode, and is used for lubrication, sealing of the low-carbon fuel needle valve pair and internal cooling of the injector.

5. The independent inner and outer needle valve type flexible fuel injector according to claim 2, characterized in that: The opening of the outer needle valve stem is independently controlled by the boost control valve of the external low-carbon fuel boost pump, so that the timing of low-carbon fuel injection and diesel pilot injection can be independently adjusted.

6. The independent inner and outer needle valve type flexible fuel injector according to claim 1, characterized in that: The double-row spray hole structure includes an upper row of spray holes and a lower row of spray holes, which correspond to low-carbon fuel and diesel injection respectively and are evenly distributed along the central axis of the combustion chamber.

7. The independent inner and outer needle valve type flexible fuel injector according to claim 1, characterized in that: The electromagnetic control valve assembly includes an armature, a control valve stem and a cone valve seat. The stem handle of the cone valve seat is provided with an oil return throttling hole. A control chamber is provided in the cone valve seat. Through the hydraulic balance design of the control chamber, the control valve stem is completely sealed when there is no electromagnetic force, and the pressure is quickly released under the action of the electromagnetic force to drive the inner needle valve stem to open.

8. The independent inner and outer needle valve type flexible fuel injector according to claim 1, characterized in that: When the injector is in diesel injection mode, after the diesel enters the injector through the high-pressure diesel interface, it enters the diesel oil tank of the needle valve pair through the diesel high-pressure oil circuit one way, and enters the control chamber through the oil inlet throttle hole of the electromagnetic control valve assembly the other way; when the inner needle valve stem in the needle valve pair is opened, the diesel enters the spray hole through the diesel high-pressure oil circuit for injection.

9. The independent inner and outer needle valve type flexible fuel injector according to claim 1, characterized in that: When the injector is in the diesel ignition and low-carbon fuel mode, the high-pressure low-carbon fuel reaches the valve core of the flow limiting valve through the high-pressure low-carbon fuel interface, enters the flow limiting valve cavity through the throttle hole on the valve core of the flow limiting valve, and enters the low-carbon fuel oil tank of the needle valve pair through the low-carbon fuel high-pressure oil circuit, so that the outer needle valve stem is opened to realize the low-carbon fuel injection.

10. The independent inner and outer needle valve type flexible fuel injector according to claim 1, characterized in that: When the injector is purged and inerted and the fuel mode is switched, high-pressure nitrogen is introduced into the low-carbon fuel high-pressure oil circuit through the inerting valve group, and all the low-pressure low-carbon fuel remaining inside is taken away from the injector.

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