A method for optimizing combustion in a natural gas engine with synergistic vortex

Abstract

The application discloses a natural gas engine combustion optimization method cooperating with vortex, and the method comprises the following steps: obtaining basic engine data; establishing a three-dimensional CFD simulation model of the basic engine coupled with detailed chemical kinetics; obtaining an in-cylinder vortex ratio and in-cylinder vortex motion expressed by a velocity vector through CFD calculation; combining in-cylinder flow characteristics to optimize the angle between the injection axis of the pilot fuel and the injection axis of the natural gas on the plane of the top view A ; optimizing the design; reconstructing a simulation model of the newly designed engine and performing CFD calculation, and comparing the combustion duration and engine thermal efficiency with the basic engine; repeating the above process to perform multiple optimization calculations to determine the optimal angle for realizing rapid diffusion combustion of the engine A . The application can make the injection range of the natural gas just in the high-temperature area provided after the combustion of the pilot fuel, so that the natural gas injected into the cylinder can be rapidly diffused and combusted, and the engine thermal efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of natural gas engine combustion technology, and specifically to a method for optimizing combustion in a micro-ignition high-pressure direct injection natural gas engine. Background Technology

[0002] Natural gas is a popular clean alternative fuel, characterized by low CO2 emissions and virtually no soot emissions when used in internal combustion engines. Therefore, natural gas engines can be used to replace diesel engines as a power source for vehicles to meet increasingly stringent carbon emission and harmful emission regulations. Under the background of energy conservation, emission reduction, and "dual carbon" (carbon diversification), future fuel consumption regulations for natural gas engines will be even stricter, making further improvements in the thermal efficiency of natural gas engines a major focus. Micro-ignition high-pressure direct-injection natural gas engines operating in dual-fuel configurations can achieve higher thermal efficiency. However, the main component of natural gas is methane, which has a higher ignition point than gasoline and diesel. This manifests as a longer combustion duration during combustion, which can easily lead to incomplete combustion during the combustion expansion process in natural gas engines. Poor combustion directly affects the engine's power, economy, and emissions.

[0003] Currently, methods to reduce the combustion duration of natural gas engines mainly include: high-turbulence technology, high-efficiency turbocharging technology, pre-combustion chamber technology, and injection parameter and strategy optimization techniques. For micro-ignition high-pressure direct injection natural gas engines, by changing the concentration distribution of natural gas injected into the cylinder, allowing more natural gas to be distributed in the high-temperature region, the combustion effect of the micro-ignition high-pressure direct injection natural gas engine can be effectively improved. However, the micro-airflow organization within the cylinder is complex and has a significant impact on the distribution of high-temperature regions, the concentration distribution of natural gas injected into the cylinder, and the combustion duration. Therefore, there is an urgent need for a method to better match the micro-airflow organization within the cylinder with the injection parameters and strategies of dual-fuel injectors to optimize the combustion effect of natural gas engines. For researchers, the biggest problem is that the flow and combustion within the engine cylinder are closed and invisible, making it difficult to visualize the flow characteristics within the cylinder, the distribution of high-temperature regions within the cylinder, and the concentration distribution of natural gas injected into the cylinder. Therefore, it is difficult for researchers to optimize the injection parameters and strategies of dual-fuel injectors. To solve this problem, CFD (Computational Fluid Dynamics) simulation coupled with detailed chemical dynamics has emerged. Currently, there is no proposed approach to designing injection parameters and strategies for dual-fuel injectors by using in-cylinder vortex motion obtained through collaborative CFD calculations to accelerate the combustion duration of micro-ignition high-pressure in-cylinder direct injection natural gas engines. Summary of the Invention

[0004] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a synergistic vortex natural gas engine combustion optimization method, which can realize rapid diffusion combustion in a micro-ignition high-pressure in-cylinder direct injection natural gas engine and improve engine thermal efficiency.

[0005] The technical solution adopted in this invention is:

[0006] A method for optimizing combustion in a natural gas engine using synergistic vortexes is characterized by: acquiring geometric data of the combustion system, fuel injection pulse width data, and bench test data of a base engine; establishing a three-dimensional CFD (Computational Fluid Dynamics) simulation model of the base engine coupled with detailed chemical dynamics, and obtaining the in-cylinder vortex ratio and in-cylinder vortex motion expressed as a velocity vector through CFD calculations; optimizing the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane by combining the obtained in-cylinder vortex ratio and in-cylinder vortex motion expressed as a velocity vector; reconstructing a three-dimensional CFD simulation model coupled with detailed chemical dynamics for the newly designed engine, calculating and comparing the combustion duration and engine thermal efficiency with the base engine; and determining the optimal angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane to achieve rapid diffusion combustion in the engine.

[0007] The combustion system geometry includes: a dual-fuel injector 1, a combustion chamber recess 2 machined into the piston crown, an intake manifold 3, two intake valves 4, an exhaust manifold 5, and two exhaust valves 6; wherein, the dual-fuel injector 1 consists of two concentric needle valves, which can simultaneously inject ignition fuel through the injection port 7 and natural gas through the injection port 8, and the combustion chamber recess 2 machined into the piston crown is... The shape of the intake duct 3 and the exhaust duct 5 is a spiral air passage.

[0008] The fuel injection pulse width data includes: ignition fuel injection pulse width d1, dual-fuel injection interval d2, and natural gas injection pulse width d3; the dual-fuel injector 1 injects a small amount of ignition fuel for ignition into the combustion chamber recess 2 machined in the piston top through the injection port in a high-pressure direct injection manner during the later stage of the compression stroke; the dual-fuel injector 1 injects a large amount of natural gas for power generation into the combustion chamber recess 2 machined in the piston top through the injection port in a high-pressure direct injection manner during the later stage of the compression stroke.

[0009] The bench test data is obtained through engine bench testing and includes: engine speed n, engine torque, engine thermal efficiency, intake manifold pressure and temperature, intake flow rate, cylinder pressure and heat release rate of each cylinder, and exhaust pressure and temperature of each cylinder.

[0010] The aforementioned three-dimensional CFD simulation model coupled with detailed chemical kinetics needs to include a turbulence model, a spray model, a detailed chemical kinetics solver, and the chemical reaction mechanism of the dual fuels of ignition fuel and natural gas. It needs to be verified for mesh independence and validated using measured data such as cylinder pressure and heat release rate obtained from bench tests.

[0011] The in-cylinder vortex motion refers to the organized airflow motion around the cylinder axis (defined as the Z-axis) formed during the intake process through the intake port 3, that is, the rotational motion of the air-fuel mixture around the Z-axis; the in-cylinder vortex ratio R is defined as the ratio of the angular velocity w of the air-fuel mixture around the Z-axis to the engine speed n.

[0012] The optimization design method is as follows: the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane is equal to the angle through which the mixture rotates within the ignition fuel injection pulse width d1 and the dual fuel injection interval d2; the angle through which the mixture rotates within the ignition fuel injection pulse width d1 and the dual fuel injection interval d2 is equal to the product of the angular velocity w of the mixture around the Z-axis and the sum of the ignition fuel injection pulse width d1 and the dual fuel injection interval d2; the angular velocity w of the mixture around the Z-axis is equal to the product of the in-cylinder swirl ratio R obtained by CFD calculation and the engine speed n.

[0013] The combustion duration is the time or crankshaft angle during the combustion of 10% to 90% of the air-fuel mixture; the engine thermal efficiency refers to the ratio of the engine cycle indicated work to the fuel heat consumed; the engine cycle indicated work is obtained by numerical integration of the cylinder pressure; the fuel heat consumed is equal to the heat of the injected ignition fuel plus the heat of the injected natural gas.

[0014] The evaluation criteria for achieving rapid diffusion combustion in an engine are the shortest combustion duration and the highest engine thermal efficiency.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] The flow and combustion within the engine cylinder are visible, as are the flow characteristics, the distribution of high-temperature regions within the cylinder, and the concentration distribution of the injected natural gas. The microscopic airflow organization within the cylinder, along with the injection parameters and strategies of the dual-fuel injector, can better coordinate to optimize the combustion effect of the natural gas engine. This invention allows the injection range of natural gas to be precisely within the high-temperature region provided by the combustion of the ignition fuel, thereby enabling the injected natural gas to diffuse and burn rapidly, thus improving engine thermal efficiency. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a diagram illustrating the implementation steps of the present invention.

[0019] Figure 2 This is a schematic diagram of the combustion system of the present invention.

[0020] Figure 3 This is a schematic diagram of the dual-fuel injection system of the present invention.

[0021] Figure 4 This is a schematic diagram of the fuel injection pulse width of the present invention.

[0022] Figure 5 This is a schematic diagram of the dual-fuel injector of the present invention injecting ignition fuel into the cylinder.

[0023] Figure 6 This is a schematic diagram of the dual-fuel injector of the present invention injecting natural gas into the cylinder.

[0024] Figure 7 This is a schematic diagram of the ignition fuel injection axis and the natural gas injection axis of the present invention on a top view plane.

[0025] Figure 8 This is a diagram showing the in-cylinder vortex motion results of the engine obtained by CFD calculation according to the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] A method for optimizing combustion in a natural gas engine using cooperative vortex flow; see the detailed implementation process below. Figure 1 The specific steps are as follows:

[0029] Step one involves acquiring the combustion system geometry data, fuel injection pulse width data, and bench test data of the basic engine through measurement and testing.

[0030] Combination Figure 2 The combustion system geometry includes: a dual-fuel injector 1, a combustion chamber recess 2 machined into the piston top, an intake manifold 3, an intake valve 4, an exhaust manifold 5, and an exhaust valve 6. The dual-fuel injector 1 consists of two concentric needle valves, see [reference needed]. Figure 3 It can simultaneously inject ignition fuel through injection hole 7 and natural gas through jet hole 8; the combustion chamber recess 2 machined inside the piston top is... Shape; intake port 3 and exhaust port 5 are spiral intake ports, and the spiral intake port is used to generate in-cylinder vortex motion; there are two intake valves 4 and two exhaust valves 6.

[0031] Combination Figure 4 The fuel injection pulse width data includes the ignition fuel injection pulse width d1, the dual-fuel injection interval d2, and the natural gas injection pulse width d3. Wherein, t0 is the ignition fuel injection start time, t1 is the ignition fuel injection end time, t2 is the natural gas injection start time, and t3 is the natural gas injection end time; the time interval between t0 and t1 is the ignition fuel injection pulse width d1, the time interval between t2 and t3 is the natural gas injection pulse width d3, and the time interval between t1 and t2 is defined as the dual-fuel injection interval d2. The range of d1 is 8°CA~15°CA, the range of d2 is 1°CA~3°CA, and the range of d3 is 20°CA~40°CA.

[0032] Under the control of the fuel injection pulse width, the operating mode of the dual fuel injector 1 is as follows:

[0033] First, during the later stages of the compression stroke, the dual-fuel injector 1 injects a small amount of ignition fuel into the combustion chamber recess 2 machined in the piston crown via a high-pressure direct injection through the injection port in a manner corresponding to the set ignition fuel injection pulse width d1. (See [link to other documentation]). Figure 5 The number of injection holes ranges from 7 to 9, and the hole diameter ranges from 0.1 to 0.2 mm; the ignition fuel is a highly reactive fuel (high cetane number fuel, such as diesel), and the injection pressure is above 32 MPa; the angle B1 formed by the axis of the injection hole and the axis of the dual fuel injector 1 ranges from 70° to 75°.

[0034] Subsequently, the ignition fuel injected into the cylinder is compressed and spontaneously combusted, providing a sufficiently high temperature to initiate the combustion of the natural gas. At this time, the dual-fuel injector 1 injects a large amount of natural gas for work into the combustion chamber recess 2 machined within the piston crown through the injection port in a high-pressure direct injection manner within a set natural gas injection pulse width d3. See [link to other documentation]. Figure 6The number of jet orifices ranges from 7 to 9, and the orifice diameter ranges from 0.5 to 0.7 mm; the natural gas injection pressure is above 30 MPa; the angle B2 formed by the axis of the jet orifice and the axis of the dual-fuel injector 1 ranges from 70° to 75°.

[0035] The heat of the injected ignition fuel accounts for 5% of the total heat of the fuel consumed, and the heat of the injected natural gas accounts for 95% of the total heat of the fuel consumed. The total heat of the fuel consumed is equal to the heat of the injected ignition fuel plus the heat of the injected natural gas.

[0036] The bench test data, obtained through engine bench testing, includes: engine speed n, engine torque, engine thermal efficiency, intake manifold pressure and temperature, intake flow rate, cylinder pressure and heat release rate of each cylinder, and exhaust pressure and temperature of each cylinder. The bench test conditions are the engine's external characteristic conditions (full-load speed characteristic test); the performance pressure limit during the test is 180 bar to 200 bar. The measured data, such as cylinder pressure and heat release rate, obtained through bench testing provide a reliable basis for the calibration of the simulation model.

[0037] Step 2: Based on the acquired combustion system geometric data, fuel injection pulse width data, and bench test data, establish a three-dimensional CFD simulation model of the basic engine with coupled detailed chemical dynamics, and obtain the in-cylinder flow characteristics and combustion characteristics results through CFD calculations.

[0038] The process of constructing the three-dimensional CFD simulation model coupled with detailed chemical kinetics is as follows:

[0039] First, a geometric model is established based on the acquired combustion system geometric data;

[0040] Next, accurately set the boundary conditions and initial conditions;

[0041] Next, the physicochemical model is set up, using turbulence and spray models to simulate in-cylinder gas flow and fuel injection events. Simultaneously, a detailed chemical kinetics solver and a dual-fuel chemical reaction mechanism for igniting fuel and natural gas are used to simulate in-cylinder combustion events.

[0042] Next, mesh independence verification was performed to select an appropriate mesh size. Considering both computational accuracy and computation time, a mesh size of 2mm was chosen.

[0043] Finally, the calculated results were compared with the experimental results to ensure consistency, thereby verifying the effectiveness of the constructed three-dimensional CFD simulation model coupled with detailed chemical kinetics. The in-cylinder flow and combustion characteristics results include two-dimensional data such as in-cylinder swirl ratio, cylinder pressure, and heat release rate, as well as three-dimensional data such as swirl motion and temperature distribution expressed as velocity vectors. The constructed three-dimensional CFD simulation model coupled with detailed chemical kinetics was calibrated and verified based on the cylinder pressure and heat release rate obtained from bench tests.

[0044] Step 3: Combining the obtained in-cylinder swirl ratio and the calculation results of in-cylinder flow characteristics such as swirl motion expressed as a velocity vector, the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane is optimized. See [link to relevant documentation]. Figure 7 .

[0045] Combination Figure 8 The in-cylinder swirl motion refers to the organized airflow motion around the cylinder axis (defined as the Z-axis) formed during the intake process through the intake manifold 3, i.e., the rotational motion of the air-fuel mixture around the Z-axis; the in-cylinder swirl ratio R is defined as the ratio of the angular velocity ω of the air-fuel mixture around the Z-axis to the engine speed n. The range of the in-cylinder swirl ratio R obtained by CFD calculation is 1~2.

[0046] The calculation results of the in-cylinder vortex motion are obtained by using the velocity vector on the top view slice (e.g., Figure 8 The arrow shown in the image represents the in-cylinder vortex motion calculation result, which is the counterclockwise rotational motion of the air-fuel mixture around the Z-axis; the angular velocity ω of the air-fuel mixture around the Z-axis is defined as the velocity of the air-fuel mixture per unit time. The angle through which the inside rotates .

[0047] The method for optimizing the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane is as follows:

[0048] The angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane is equal to the angle through which the mixture rotates within the ignition fuel injection pulse width d1 and the dual fuel injection interval d2;

[0049] The angle through which the mixture rotates within the ignition fuel injection pulse width d1 and the dual fuel injection interval d2 is equal to the product of the angular velocity w of the mixture about the Z-axis and the sum of the ignition fuel injection pulse width d1 and the dual fuel injection interval d2.

[0050] The angular velocity of the mixed gas about the Z-axis It equals the in-cylinder swirl ratio R obtained through CFD calculation and the engine speed. The product of.

[0051] The principle of optimized design is to ensure that the natural gas injection range is precisely within the high-temperature region provided by the combustion of the ignition fuel. This allows the injected natural gas to diffuse and burn rapidly, thereby improving engine thermal efficiency. Therefore, the natural gas engine performs optimally when the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane is equal to the angle through which the mixture rotates within the ignition fuel injection pulse width d1 and the dual-fuel injection interval d2.

[0052] Step four: After optimizing the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane, a three-dimensional CFD simulation model coupled with detailed chemical dynamics is reconstructed for the newly designed engine, and the calculation results are compared with those of the basic engine.

[0053] The corresponding calculation results mainly include combustion duration and engine thermal efficiency. The combustion duration is the time or crankshaft angle during which 10% to 90% of the air-fuel mixture burns. This time or crankshaft angle is obtained through the burned mass fraction curve. The burned mass fraction is obtained by cumulative integration and normalization of the heat release rate. The engine thermal efficiency refers to the ratio of the engine cycle indicated work to the consumed fuel heat. The engine cycle indicated work is obtained by numerical integration of the cylinder pressure.

[0054] Step 5: Determine the angle A between the optimal ignition fuel injection axis and the natural gas injection axis on the top view plane to achieve rapid diffusion combustion in the engine.

[0055] By comparing the corresponding calculation results, the angle A between the designed ignition fuel injection axis and the natural gas injection axis on the top view plane is the optimal angle when the combustion duration is shortest and the engine thermal efficiency is maximum. The optimal range of the angle A between the ignition fuel injection axis and the natural gas injection axis on the top view plane is 5°~15°.

[0056] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0057] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for optimizing combustion in a natural gas engine using synergistic vortex flow, characterized in that, Includes the following steps: Step 1: Obtain the combustion system geometry data, fuel injection pulse width data, and bench test data of the basic engine. The combustion system geometry data includes: dual fuel injectors, combustion chamber recess, intake manifold, two intake valves, exhaust manifold, and two exhaust valves. The fuel injection pulse width data includes: ignition fuel injection pulse width, dual fuel injection interval, and natural gas injection pulse width. The bench test data is obtained through engine bench testing and includes: engine speed, engine torque, engine thermal efficiency, intake manifold pressure and temperature, intake flow rate, cylinder pressure and heat release rate of each cylinder, and exhaust pressure and temperature of each cylinder. Step 2: Based on the basic engine data obtained in Step 1, establish a three-dimensional CFD simulation model of the basic engine with coupled detailed chemical dynamics, perform mesh generation and define model boundary parameters, and calculate the in-cylinder swirl ratio and in-cylinder swirl motion expressed as velocity vector through the three-dimensional CFD simulation model. Step 3: Based on the calculation results obtained in Step 2, perform in-cylinder flow characteristic analysis of the engine, and optimize the angle between the ignition fuel injection axis and the natural gas injection axis on the top view plane in combination with the in-cylinder flow characteristics. The optimization design method is as follows: The angle between the ignition fuel injection axis and the natural gas injection axis on the top view plane is equal to the angle through which the mixture rotates within the ignition fuel injection pulse width and the dual fuel injection interval; The angle through which the mixture rotates within the ignition fuel injection pulse width and the dual fuel injection interval is equal to the product of the rotational angular velocity of the mixture about the cylinder axis and the sum of the ignition fuel injection pulse width and the dual fuel injection interval. The rotational angular velocity of the mixed gas around the cylinder axis is equal to the product of the in-cylinder vortex ratio calculated by the three-dimensional CFD simulation model and the engine speed. Step 4: Reconstruct a three-dimensional CFD simulation model of the newly designed engine coupled with detailed chemical dynamics and perform calculations to obtain simulation results of combustion duration and engine thermal efficiency, and compare them with the basic engine. Step 5: Repeat steps 2 through 4 to determine the optimal angle for achieving rapid diffusion combustion in the engine.

2. The method for optimizing combustion in a natural gas engine using a cooperative vortex according to claim 1, characterized in that, The dual-fuel injector consists of two concentric needle valves, which can simultaneously inject ignition fuel through the injection port and natural gas through the jet port. The combustion chamber recess is ω-shaped, and the intake and exhaust ports are spiral air passages.

3. The method for optimizing combustion in a natural gas engine using a cooperative vortex according to claim 1, characterized in that, The dual-fuel injector injects ignition fuel for ignition into the combustion chamber recess machined in the piston crown via a high-pressure direct injection method through an injection port during the later stage of the compression stroke; the dual-fuel injector injects natural gas for power generation into the combustion chamber recess machined in the piston crown via a high-pressure direct injection method through an injection port.

4. The method for optimizing combustion in a natural gas engine using a cooperative vortex according to claim 1, characterized in that, The three-dimensional CFD simulation model includes a turbulence model, a spray model, a detailed chemical kinetics solver, and a dual-fuel chemical reaction mechanism for ignition fuel and natural gas. The mesh independence of the three-dimensional CFD simulation model is verified. The three-dimensional CFD simulation model is verified by measured data of cylinder pressure and heat release rate obtained from bench tests.

5. The method for optimizing combustion in a natural gas engine using a cooperative vortex according to claim 1, characterized in that, The cylinder axis is defined as the Z-axis, and the in-cylinder vortex motion is the organized airflow motion around the Z-axis formed during the intake process through the intake port, that is, the rotational motion of the air-fuel mixture around the Z-axis; the in-cylinder vortex ratio is defined as the ratio of the rotational angular velocity of the air-fuel mixture around the Z-axis to the engine speed.

6. The method for optimizing combustion in a natural gas engine using a cooperative vortex according to claim 1, characterized in that, The combustion duration is the time or crankshaft angle during the combustion of 10% to 90% of the air-fuel mixture; the engine thermal efficiency refers to the ratio of the engine cycle indicated work to the fuel heat consumed, the engine cycle indicated work is obtained by numerical integration of the cylinder pressure, and the fuel heat consumed is equal to the heat of the injected ignition fuel plus the heat of the injected natural gas.

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