Combustion chamber structure of marine diesel engine for improving thermal efficiency and reducing nitrogen oxide emission

Abstract

Aiming at the technical problems that methanol fuel is difficult to ignite reliably in compression ignition engine, combustion efficiency is low and emission control is difficult, the application provides a combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emission of marine diesel engine, mainly including cylinder head, cylinder, piston, diesel oil injector, methanol injector and piston pit arranged on the top of the piston. The application can ignite methanol with a small amount of diesel oil; meanwhile, a combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emission is designed to inhibit the generation of thermal type NO X The application can realize high-efficiency and clean combustion of methanol / diesel double direct injection engine, the thermal efficiency of which can be obviously improved compared with traditional diesel engine, the combustion duration is shortened, the nitrogen oxide emission reduction effect is obvious, and the application provides a practical engineering solution for low-carbon transformation of ships.

Description

Technical Field

[0001] This invention belongs to the field of marine engine technology, specifically relating to a combustion chamber structure for marine diesel engines that improves thermal efficiency and reduces nitrogen oxide emissions. Background Technology

[0002] With the advancement of global carbon peaking and carbon neutrality goals and the increasingly stringent greenhouse gas emission reduction requirements for ships from the International Maritime Organization, the development of clean and efficient marine propulsion technologies has become an urgent need for the sustainable development of the shipping industry. Methanol, as a clean alternative fuel, has advantages such as a simple molecular structure, absence of C / C bonds, low carbon emissions, and excellent anti-knock properties. Furthermore, it can be produced from various sources, including coal, natural gas, biomass, and renewable electricity. Green methanol also possesses excellent carbon cycle characteristics.

[0003] However, the direct application of methanol in compression ignition engines still faces several technical challenges: methanol has an extremely low cetane number and an auto-ignition temperature as high as 470 °C, while diesel's auto-ignition temperature is only 260 °C, making it difficult for methanol to achieve reliable ignition in traditional compression ignition engines; methanol has a low calorific value of only 20.1 MJ / kg, about 45% of that of diesel, resulting in reduced engine range; methanol has a high latent heat of vaporization, which may cause the in-cylinder mixture to become too cold, further inhibiting the ignition process. These defects make it difficult to use methanol directly as a single fuel for traditional marine diesel engines.

[0004] To address the aforementioned issues, methanol / diesel dual-fuel technology has gradually developed. Currently, dual-fuel injection mainly falls into two categories: port injection and direct injection. Port injection is relatively simple, but it suffers from problems such as uneven air-fuel mixture, methanol wall wetting, and backfire risk, limiting the improvement of methanol substitution rates. While direct injection technology has higher system complexity, it enables more precise fuel control and better combustion performance. Methanol / diesel dual direct injection technology employs two completely independent fuel supply systems, enabling sequential injection of two fuels and providing greater flexibility for precise combustion process control.

[0005] The combustion chamber structure directly determines the fuel atomization quality, mixture formation characteristics, and flame propagation patterns. Current technologies for optimizing marine diesel engine combustion chambers primarily focus on traditional ω-shaped or shallow-bowl structures, lacking systematic research on key parameters such as aspect ratio and compression ratio, making it difficult to simultaneously achieve high thermal efficiency and low NOx emissions. X Emissions. Therefore, it is necessary to develop a method that can improve thermal efficiency and significantly reduce NO emissions. X The structure of the combustion chamber for emissions control is of great significance for the green upgrading of marine diesel engines. Summary of the Invention

[0006] This invention aims to provide a combustion chamber structure for marine diesel engines that improves thermal efficiency and reduces nitrogen oxide emissions, thereby solving the problem that existing marine diesel engine combustion chambers cannot simultaneously achieve high thermal efficiency and low NOx emissions. X Technical issues related to emissions.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A combustion chamber structure for a marine diesel engine to improve thermal efficiency and reduce nitrogen oxide emissions includes a cylinder head, a cylinder, a piston, a diesel injector, a methanol injector, and a piston recess located on the top of the piston, wherein: Both the diesel injector and the methanol injector are mounted on the cylinder head and extend into the combustion chamber. The diesel injector is used to inject diesel fuel before the top dead center of the compression stroke, and the methanol injector is used to inject methanol fuel after the diesel fuel injection. The piston recess has a diameter-to-depth ratio of 2.5-6.3, and the engine has a compression ratio of 11.9-16.9.

[0008] Preferably, the cross-sectional profile of the combustion chamber recess is constricted, consisting of a recess bottom, recess sidewalls, and recess top. The recess sidewalls and recess bottom are connected by an arc transition, and the ratio of the radius of the transition arc to the maximum diameter of the recess is 0.10-0.25.

[0009] Preferably, the top edge of the combustion chamber recess is provided with an extrusion platform, which occupies 15%-30% of the piston top surface area.

[0010] Preferably, the injection timing of the diesel injector is 7.0° crankshaft angle before the top dead center of the compression stroke, and the injection duration is 3.5° crankshaft angle; the injection timing of the methanol injector is 5.5° crankshaft angle before the top dead center of the compression stroke, and the injection duration is 19.5° crankshaft angle.

[0011] Preferably, the diesel injector has 7 nozzles with an included angle of 145° and an injection pressure of 15-20 MPa; the methanol injector has 12 nozzles with an included angle of 145° and an injection pressure of 35-45 MPa.

[0012] Preferably, the engine has an intake pressure of 209 kPa and an intake temperature of 308 K.

[0013] Preferably, the engine has a swirl ratio of 1.1, an exhaust valve opening angle of 110-120 °CA ATDC, and an intake valve closing angle of 580-595 °CA ATDC.

[0014] An optimization of combustion chamber geometry parameters for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines using the aforementioned apparatus is performed using either method A or method B: Method A: By proportionally changing the diameter and depth of the piston recess, while keeping the compression ratio constant, a series of combustion chamber structures with different piston recess diameter-to-depth ratios are generated. The piston recess diameter-to-depth ratio is selected from 2.5-6.3, and the compression ratio is fixed at 14.0. In step 3, in method A, computational fluid dynamics numerical simulation technology is used to simulate the combustion process under various diameter-to-depth ratios, and to calculate the cylinder pressure, heat release rate, peak heat release rate, combustion phase parameters, and indicated thermal efficiency. In step 3, in method A, the indicated thermal efficiency is above 48.74%, and the combustion duration is above 25.01 °CA ATDC. In step 3, in method A, the calculation time is set to -360 °CA ATDC to 180 °CA ATDC, where 0 °CA ATDC is the compression top dead center.

[0015] Method B: Based on the combustion chamber structure with a piston recess diameter-to-depth ratio of 4.3, the compression ratio is adjusted by changing the piston recess depth to generate a series of combustion chamber structures with different compression ratios, with compression ratio values ​​selected from 11.9 to 16.9; In step 3, in method B, computational fluid dynamics numerical simulation technology is used to simulate the combustion process at various compression ratios and calculate the cylinder pressure, heat release rate, peak heat release rate, combustion phase parameters and indicated thermal efficiency. In step 3, in method B, the indicated thermal efficiency is above 49.45%, the combustion duration is above 25.01 °CA ATDC, and the HC emission is above 0.001 ppm. In step 3, in method B, since the diameter of the piston recess remains constant, the diameter-to-depth ratio changes monotonically with the diameter-to-depth ratio when the depth is changed.

[0016] Compared with the prior art, the combustion chamber structure of a marine diesel engine provided by the present invention, which improves thermal efficiency and reduces nitrogen oxide emissions, has the following beneficial effects: (1) Only 5% diesel fuel can ignite 95% methanol, effectively solving the technical problem that methanol is difficult to compress and ignite. The methanol substitution rate is as high as 95%, giving full play to the environmental advantages of clean combustion of methanol. (2) Using the technical solution of the present invention, the indicated thermal efficiency can reach up to 53.12%, which is about 10 percentage points higher than that of traditional diesel engines; the peak heat release rate is increased by 39.51%, the combustion duration is shortened by 47%, and nitrogen oxide emissions are reduced by 42.5%. (3) Focusing on the characteristics of large cylinder diameter in marine engines, and taking into account special issues such as long spray penetration distance, extended flame propagation path, and high wall heat load, a special combustion chamber design strategy for marine applications has been formed, filling the gap in the research on combustion chamber structure optimization of large-bore dual direct injection engines for marine applications. Attached Figure Description

[0017] Figure 1 This is a structural diagram of a combustion chamber for a marine diesel engine designed to improve thermal efficiency and reduce nitrogen oxide emissions. Detailed Implementation Example 1

[0018] This embodiment provides a combustion chamber structure for a marine diesel engine to improve thermal efficiency and reduce nitrogen oxide emissions. Both diesel and methanol injectors are mounted on the cylinder head and extend into the combustion chamber. The diesel injector injects diesel fuel before top dead center of the compression stroke, and the methanol injector injects methanol fuel after diesel fuel injection. The process includes three steps: changing the bore-to-depth ratio, setting engine parameters, and sequential dual-fuel injection. Specifically, the steps are as follows: By proportionally changing the diameter and depth of the piston recess, a combustion chamber structure that improves thermal efficiency and reduces nitrogen oxide emissions is generated. At this time, the diameter-to-depth ratio of the combustion chamber structure is 4.3, and the compression ratio is 14.

[0019] The specific parameters of the dual direct injection engine are as follows: single-cylinder displacement 12.425L, cylinder bore 215mm, stroke 320mm, compression ratio 14, swirl ratio 1.1, exhaust valve opening angle 116°CA ATDC, intake valve opening angle 589°CA ATDC. Intake pressure is 209kPa, and intake temperature is 308K.

[0020] The process of achieving dual-fuel sequential injection on engine structures with different diameter-to-depth ratios is as follows: 7.0°CA before top dead center of compression, 5% by mass of diesel fuel is injected into the cylinder through a high-pressure injector, where it rapidly ignites under the high temperature of compression, forming a stable premixed flame; 5.5°CA before top dead center of compression, 95% by mass of methanol is injected into the cylinder in the form of a high-pressure jet, where the methanol spray interacts with the diesel premixed flame, is rapidly ignited, and undergoes diffusion combustion.

[0021] Using this embodiment, the indicated thermal efficiency reaches 52.21%, and the peak heat release rate can reach 1997.84 J / °CA, NO X Emissions were reduced by 42.5%. Example 2

[0022] This embodiment provides a combustion chamber structure for a marine diesel engine to improve thermal efficiency and reduce nitrogen oxide emissions. Both diesel and methanol injectors are mounted on the cylinder head and extend into the combustion chamber. The diesel injector injects diesel fuel before top dead center of the compression stroke, and the methanol injector injects methanol fuel after diesel fuel injection. The process includes three steps: changing the compression ratio, setting engine parameters, and sequential dual-fuel injection. Specifically, the steps are as follows: By adjusting the compression ratio by changing the depth of the recess, a combustion chamber structure that improves thermal efficiency and reduces nitrogen oxide emissions is generated. At this time, the diameter-to-depth ratio of the combustion chamber structure is 6.2, and the compression ratio is 16.9.

[0023] The specific parameters of the dual direct injection engine are as follows: single-cylinder displacement 12.425L, cylinder bore 215mm, stroke 320mm, compression ratio 14, swirl ratio 1.1, exhaust valve opening angle 116°CA ATDC, intake valve opening angle 589°CA ATDC. Intake pressure is 209kPa, and intake temperature is 308K.

[0024] The process of achieving dual-fuel sequential injection on engine structures with different diameter-to-depth ratios is as follows: 7.0°CA before top dead center of compression, 5% by mass of diesel fuel is injected into the cylinder through a high-pressure injector, where it rapidly ignites under the high temperature of compression, forming a stable premixed flame; 5.5°CA before top dead center of compression, 95% by mass of methanol is injected into the cylinder in the form of a high-pressure jet, where the methanol spray interacts with the diesel premixed flame, is rapidly ignited, and undergoes diffusion combustion.

[0025] Using this embodiment, the indicated thermal efficiency reaches 53.12%, and the peak heat release rate can reach 2002.48 J / °CA, NO X Emissions were reduced by 28.3%.

Claims

1. A combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in a marine diesel engine, comprising a cylinder head, a cylinder, a piston, a diesel injector, a methanol injector, and a combustion chamber recess disposed on the top of the piston, characterized in that, Both the diesel injector and the methanol injector are mounted on the cylinder head and extend into the combustion chamber. The diesel injector is used to inject diesel fuel before the top dead center of the compression stroke, and the methanol injector is used to inject methanol fuel after the diesel fuel injection. The diameter-to-depth ratio of the combustion chamber recess is 2.5-6.3, and the compression ratio of the engine is 11.9-16.

9. The diameter-to-depth ratio is defined as the ratio of the maximum diameter of the combustion chamber recess to the depth of the recess. The cross-sectional profile of the combustion chamber recess is a constricted type.

2. The combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines according to claim 1, characterized in that, An extrusion platform is provided at the top edge of the combustion chamber recess, and the extrusion platform occupies 15%-30% of the piston top surface area.

3. The combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines according to claim 1, characterized in that, The injection timing of the diesel injector is 7.0° crankshaft rotation before top dead center of compression, and the injection timing of the methanol injector is 5.5° crankshaft rotation before top dead center of compression.

4. The combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines according to claim 1, characterized in that, The engine has a swirl ratio of 1.1, an exhaust valve opening angle of 110-120 °CA ATDC, and an intake valve closing angle of 580-595 °CA ATDC.

5. The combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines according to claim 1, characterized in that, The diesel injector has 7 nozzles with an included angle of 145° and an injection pressure of 15-20 MPa; the methanol injector has 12 nozzles with an included angle of 145° and an injection pressure of 35-45 MPa.

6. The combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines according to claim 1, characterized in that, The engine has an intake pressure of 200-220 kPa and an intake temperature of 300-320 K.

7. The combustion chamber structure for improving thermal efficiency and reducing nitrogen oxide emissions in marine diesel engines according to claim 1, characterized in that, The methanol injection mass accounts for 95% of the total fuel injection mass, and the diesel injection mass accounts for 5% of the total fuel injection mass.

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