A diesel engine cold start operating condition rotating speed prediction method based on a non-uniform temperature field
By acquiring data on the non-uniform temperature field distribution during the cold start of a diesel engine, calculating the viscosity and thermal deformation of the lubricating oil, and constructing a component resistance torque model, the problem of deviation in the cold start speed prediction of diesel engines was solved, and high-precision speed prediction and control optimization were achieved in extreme low-temperature environments.
Patent Information
- Application Number
- CN202610505516.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-16
- Publication Date
- 2026-07-14
AI Technical Summary
Existing methods for predicting the cold start speed of diesel engines are based on the assumption of a uniform temperature field, which cannot accurately reflect the actual resistance variation. This results in a large deviation between the predicted results and the actual speed, and thus cannot provide accurate guidance for start-up control.
By combining multiphysics field coupling simulation and bench experiments, non-uniform temperature field distribution data of diesel engine cold start process is obtained, dynamic oil viscosity of lubricating oil and thermal deformation of components are calculated, a starting resistance torque model of sub-components is constructed, and the model is substituted into the dynamic equation of diesel engine starting system for speed prediction.
It significantly improves the accuracy of predicting diesel engine starting performance under extreme low temperature conditions, provides a reliable basis for optimizing starting control strategies and preheating system design, and solves the prediction deviation problem caused by the assumption of a uniform temperature field in traditional methods.
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Figure CN122389707A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of diesel engine control, and in particular to a method for predicting the engine speed during cold start of a diesel engine based on a non-uniform temperature field. Background Technology
[0002] Diesel engines, as power devices with high thermal efficiency and reliability, are widely used in transportation, construction machinery, national defense equipment, and many other fields. Cold start performance is one of the key indicators for evaluating the overall performance of a diesel engine, directly affecting the starting response speed, operational safety, and service life of equipment. Especially in extreme low-temperature environments such as high-latitude regions and frigid seasons, diesel engines face multiple challenges during cold starts, including increased lubricating oil viscosity, increased frictional resistance of moving parts, and poor fuel atomization. This can easily lead to starting difficulties, large speed fluctuations, or even starting failures, affecting operational efficiency and potentially causing mechanical failures. Therefore, achieving accurate prediction of diesel engine speed during cold starts, providing data support for optimizing starting control strategies and designing preheating systems, has become a core technological requirement for improving the adaptability of diesel engines to extreme environments.
[0003] The variation of diesel engine cold start speed directly depends on the dynamic balance between the starting system's power and the engine's resistance torque. Accurate calculation of the cold start resistance torque is a core prerequisite for speed prediction. Existing technologies for predicting diesel engine cold start resistance torque often rely on the idealized assumption of a "uniform temperature field." This assumes that during cold start preheating and the initial starting phase, the temperature distribution of key diesel engine components (such as cylinder liners, pistons, piston rings, and crankshaft main bearings) is uniform, and that the lubricating oil temperature remains synchronized with the component temperatures. Based on this assumption, previous researchers typically established a resistance torque calculation model by setting a single ambient temperature or average component temperature, combined with empirical formulas to calculate the lubricating oil viscosity and component friction coefficients.
[0004] However, in actual diesel engine cold starts, the assumption of a "uniform temperature field" deviates significantly from engineering realities, leading to obvious limitations in existing prediction methods. On one hand, the materials, structures, and thermal conductivity characteristics of key diesel engine components vary considerably. During the preheating stage, the temperature distribution exhibits significant non-uniformity due to the influence of the preheating device's heating range, the component's own heat capacity, and heat dissipation conditions. For example, the cylinder liner's inner wall has a higher temperature due to contact with the preheating medium, while the outer wall temperature is lower; the piston top, being close to the combustion chamber, experiences a faster temperature rise due to radiant heat, while the skirt temperature lags behind. On the other hand, the lubricating oil's temperature distribution is also uneven in the initial cold start phase. The temperature of the lubricating oil film in contact with components changes locally due to component temperature, while the main body temperature of the lubricating oil in the oil pan remains relatively low. This non-uniform temperature field distribution directly leads to differences in the thermal deformation of various components and causes the lubricating oil viscosity to exhibit spatially uneven distribution, resulting in deviations in the calculation of frictional resistance torque for each friction pair. As the ambient temperature decreases, the deviation between the resistance torque under the assumption of a uniform temperature field and the non-uniform temperature field becomes increasingly larger.
[0005] The combination of these factors makes the drag torque model based on the assumption of a uniform temperature field unable to accurately reflect the actual drag variation, ultimately resulting in a large deviation between the predicted cold start speed and the actual speed, failing to provide precise guidance for start-up control. For example, if the predicted speed is higher than the actual speed, it may lead to insufficient preheating and increased wear on moving parts; if the predicted speed is lower than the actual speed, it may cause overheating, increasing start-up costs and energy consumption.
[0006] Therefore, breaking through the limitations of the traditional assumption of a uniform temperature field and establishing an accurate drag torque model and rotational speed prediction method based on the actual temperature distribution has become the key to solving the current technical bottleneck. Summary of the Invention
[0007] The purpose of this invention is to provide a method for predicting the engine speed under cold start conditions of diesel engines based on a non-uniform temperature field. This method overcomes the idealized assumption of uniform temperature in traditional methods, significantly improves the accuracy of predicting the starting performance of diesel engines under extreme low temperature conditions, and provides a reliable basis for optimizing starting control strategies and designing preheating systems.
[0008] To achieve the above objectives, this invention provides a method for predicting the engine speed during cold start based on a non-uniform temperature field, comprising the following steps: Step 1: Obtain the non-uniform temperature field distribution data of key components of the diesel engine during the cold start preheating process by combining multiphysics field coupled simulation and bench test. Step 2: Based on the non-uniform temperature field distribution data, calculate the dynamic viscosity of the lubricating oil and the thermal deformation of the components under the influence of temperature. Step 3: Integrate the dynamic viscosity of the lubricating oil, the thermal deformation of the components, and the structural parameters of the components to construct a starting resistance torque model for each component; Step 4: Obtain the total frictional resistance torque through the component starting resistance torque model, substitute the total frictional resistance torque into the dynamic equation of the diesel engine starting system for solution, and obtain the speed change curve with time during cold start, so as to realize the dynamic prediction of cold start speed. Based on the prediction results, optimize the preheating time and starting cost.
[0009] Preferably, in step 1, the key components include cylinder liners, pistons, piston rings, crankshaft main bearings, and connecting rod bearings.
[0010] Preferably, in step 1, a multiphysics coupled simulation and bench test are combined to establish a multiphysics coupled model of the solid and fluid domains of the diesel engine, simulating the heat conduction, heat convection and heat radiation characteristics of the cold start preheating process under extreme low temperature conditions, and outputting temperature field cloud map data of each component; at the same time, high-precision temperature sensors are arranged at different locations of key components to collect temperature data in real time; the Kalman filter algorithm is used to fuse and correct the simulation data and experimental data to form non-uniform temperature field distribution data with high spatial resolution and complete time series.
[0011] Preferably, the relevant equations for fusing simulation data and experimental data and updating the filter using the Kalman filter algorithm are as follows: 1) Equations of state: ; 2) Observation equation: ; 3) Predicting covariance: ; 4) Kalman gain: ; 5) State update equation: ; 6) Covariance update equation: ; in, for Temperature state vector at any given time; A This is the state transition matrix; B For control matrix; For control input; For process noise (Gaussian white noise, variance Q); H represents the observed values; H is the observation matrix; The observation noise is Gaussian white noise with variance R. It is the covariance matrix; It is an identity matrix.
[0012] Preferably, in the calculation of the dynamic viscosity of the lubricating oil in step 2, the lubricating oil viscosity calculation formula is modified based on the local temperature value of the components for the lubricating oil film in contact with each key component, so as to obtain the dynamic viscosity data of the lubricating oil in different regions.
[0013] Preferably, the formula for calculating the dynamic viscosity of lubricating oil is: ; in, The dynamic viscosity of the lubricating oil at temperature T; Viscosity at reference temperature; The activation energy of lubricating oil; This is the universal gas constant; This represents the actual temperature of the component.
[0014] Preferably, in step 2, the calculation of component thermal deformation is based on the thermal expansion coefficient of each component material and the local temperature gradient, and a thermal deformation calculation model is established to output the thermal deformation data of each part.
[0015] Preferably, the formula for calculating the thermal deformation of the component is: ; in, This refers to the thermal deformation of the component. This is the initial length of the component; The coefficient of linear expansion of the material; This is the second-order correction factor for thermal expansion; The initial ambient temperature.
[0016] Preferably, in step 3, the starting resistance torque of the sub-components includes the piston assembly resistance torque and the crankcase assembly resistance torque; the piston assembly resistance torque includes the piston ring fluid lubrication friction torque, the piston ring mixed lubrication friction torque, the piston skirt friction torque, and the valve assembly friction torque; the crankcase assembly resistance torque includes the friction torque of the accessories and unloaded bearings and the friction torque of the loaded bearings.
[0017] Preferably, the piston ring fluid lubrication friction torque The calculation formula is: ; in, It depends on the shape of the piston rings and can be adjusted based on test results; The dynamic viscosity of the lubricating oil; Piston speed; For contact pressure; D is the cylinder pressure; D is the cylinder diameter. To determine the equivalent number of oil rings, The number of oil rings, This refers to the number of air rings; This refers to the piston ring width; The transformation ratio is the ratio of the piston's instantaneous velocity to the crank's linear velocity. Where is the crank radius; The coefficients are constants. Piston ring mixed lubrication friction torque The calculation formula is: ; Among them, among them, This refers to the crankshaft rotation angle; The constant coefficient reflects the influence of the boundary friction coefficient on the mixed friction of the piston rings; Piston skirt friction torque The calculation formula is: ; in, This is a constant coefficient that reflects the effect of oil film thickness variation caused by piston tilt on piston skirt friction, and can be adjusted based on experiments; The thickness of the oil film; This refers to the length of the piston skirt. Valve assembly friction torque The calculation formula is as follows: ; in, This is a constant coefficient, depending on the type of valve assembly. This refers to the friction of the valve assembly and the number of valves. This refers to the spring preload. Angular velocity; Frictional torque of accessories and unloaded bearings The calculation formula is: ; in, The coefficients are constants. Frictional torque of loaded bearing The calculation formula is: ; in, These are constant coefficients.
[0018] Preferably, in step 4, the formula for calculating the total frictional resistance torque is: ; Substituting the total frictional resistance torque into the dynamic equation of the diesel engine starting system, the change of crankshaft speed with time during cold start is solved, expressed as: ; ; in, The equivalent rotational inertia of the starting system; for Crankshaft angular velocity at any given moment; This is to provide the output torque for the starter motor; This refers to the total resistance torque of the diesel engine. This refers to the cylinder compression resistance torque. This refers to the air resistance torque of the intake and exhaust pumps. Other minor resistance torques, such as sealing resistance, gear churning losses, and other minute loads.
[0019] Therefore, the diesel engine cold start speed prediction method based on a non-uniform temperature field of the present invention has the following beneficial effects: (1) The method protected by this invention breaks through the assumption of uniform temperature field. It obtains non-uniform temperature field distribution data of key components of diesel engine through simulation and experiment, which fits the temperature state of the actual cold start preheating process. Based on the non-uniform temperature field, the viscosity of lubricating oil and thermal deformation of each component are calculated, and an accurate component starting resistance torque model reflecting the actual thermal state is established. The accurate resistance torque model is substituted into the dynamic equation of the starting system, which significantly improves the accuracy of speed prediction under extreme low temperature environment, and provides a reliable basis for optimizing the starting control strategy and designing the preheating system.
[0020] (2) Based on the actual temperature distribution of key components during the cold start of a diesel engine, this invention improves the prediction accuracy through a closed-loop technical path of “data acquisition-parameter calculation-model construction-speed prediction”.
[0021] (3) This method effectively solves the prediction bias problem of traditional methods by acquiring non-uniform temperature fields through multi-source data fusion, accurate modeling of components and dynamic correction algorithm. It can provide accurate data support for the optimization of diesel engine cold start control strategy and the design of preheating system parameters, and is especially suitable for diesel engine application scenarios in extreme low temperature environments.
[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0023] Figure 1 This is an overall architecture diagram of the diesel engine cold start speed prediction method based on a non-uniform temperature field according to an embodiment of the present invention; Figure 2 This is a schematic diagram of uniform temperature field data acquisition and fusion according to an embodiment of the present invention; Figure 3 This is a temperature field cloud map obtained from the multiphysics coupling model in an embodiment of the present invention; Figure 4 A comparison diagram of the drag torque between the non-uniform temperature field of the embodiment and the uniform temperature field of the comparative example under different ambient temperatures; Figure 5 The speed curve predicted by the diesel engine cold start condition speed prediction method under non-uniform temperature field according to an embodiment of the present invention. Detailed Implementation
[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.
[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.
[0026] This invention relates to a method for predicting the engine speed during cold start of a diesel engine based on a non-uniform temperature field, comprising the following steps: Step 1: Obtain the non-uniform temperature field distribution data of key components of the diesel engine during cold start preheating by combining multiphysics field coupling simulation and bench experiments; among which, key components include cylinder liners, pistons, piston rings, crankshaft main bearings, and connecting rod bearings.
[0027] Specifically, a multiphysics coupled simulation and bench test were used to establish a multiphysics coupled model of the solid and fluid domains of the diesel engine. This model simulates the heat conduction, heat convection, and heat radiation characteristics of the cold start preheating process under extreme low temperature conditions, and outputs temperature field cloud map data for each component. At the same time, high-precision temperature sensors were placed at different locations of key components to collect temperature data in real time. The Kalman filter algorithm was used to fuse and correct the simulation data and experimental data to form non-uniform temperature field distribution data with high spatial resolution and complete time series, ensuring the consistency of temperature distribution data with engineering reality.
[0028] Step 2: Based on the non-uniform temperature field distribution data, calculate the dynamic viscosity of the lubricating oil and the thermal deformation of each component under the influence of temperature; for the lubricating oil film in contact with each key component, modify the lubricating oil viscosity calculation formula by combining the local temperature value of the component to obtain the dynamic viscosity data of the lubricating oil in different regions; the dynamic viscosity calculation formula of the lubricating oil is: ; in, The dynamic viscosity of the lubricating oil at temperature T; Viscosity at reference temperature; The activation energy of lubricating oil; This is the universal gas constant; This represents the actual temperature of the component.
[0029] Simultaneously, based on the thermal expansion coefficients of each component material and the local temperature gradient, a thermal deformation calculation model is established, outputting thermal deformation data for different parts. The formula for calculating the thermal deformation of a component is: ; in, This refers to the thermal deformation of the component. This is the initial length of the component; The coefficient of linear expansion of the material; This is the second-order correction factor for thermal expansion; The initial ambient temperature.
[0030] Step 3: Integrate the dynamic viscosity of the lubricating oil, the thermal deformation of the components, and the structural parameters of the components to construct a starting resistance torque model for each component. The starting resistance torque of each component includes the piston assembly resistance torque and the crankcase assembly resistance torque. The piston assembly resistance torque includes the piston ring fluid lubrication friction torque, the piston ring mixed lubrication friction torque, the piston skirt friction torque, and the valve assembly friction torque. The crankcase assembly resistance torque includes the friction torque of accessories and unloaded bearings as well as the friction torque of loaded bearings.
[0031] Piston ring fluid lubrication friction torque The calculation formula is: ; in, It depends on the shape of the piston rings and can be adjusted based on test results; The dynamic viscosity of the lubricating oil; Piston speed; For contact pressure; D is the cylinder pressure; D is the cylinder diameter. To determine the equivalent number of oil rings, The number of oil rings, This refers to the number of air rings; This refers to the piston ring width; The transformation ratio is the ratio of the piston's instantaneous velocity to the crankshaft's linear velocity. Where is the crank radius.
[0032] Piston ring mixed lubrication friction torque The calculation formula is: ; in, This demonstrates the influence of the boundary friction coefficient on the mixed friction of piston rings. This refers to the crankshaft rotation angle.
[0033] Piston skirt friction torque The calculation formula is: ; in, This demonstrates the effect of oil film thickness variation caused by piston tilt on piston skirt friction, which can be adjusted based on experiments; The thickness of the oil film; This refers to the length of the piston skirt.
[0034] Valve assembly friction torque The calculation formula is as follows: ; in, Depending on the type of valve assembly, This refers to the friction of the valve assembly and the number of valves. This is the spring preload. ω is the angular velocity.
[0035] Frictional torque of accessories and unloaded bearings The calculation formula is: .
[0036] Frictional torque of loaded bearing The calculation formula is: ; In the above content, - These are all constant coefficients for each friction torque model.
[0037] Step 4: Obtain the total frictional resistance torque using the component starting resistance torque model. The formula for calculating the total frictional resistance torque is: .
[0038] Substituting the total frictional resistance torque into the dynamic equation of the diesel engine starting system and solving it, the crankshaft speed variation curve during cold start is obtained, enabling dynamic prediction of the cold start speed. Based on this prediction result, the preheating time and starting cost are optimized. This is expressed as: ; ; in, The equivalent rotational inertia of the starting system; for Crankshaft angular velocity at any given moment; This is to provide the output torque for the starter motor; This refers to the total resistance torque of the diesel engine. This refers to the cylinder compression resistance torque. This refers to the air resistance torque of the intake and exhaust pumps. Other minor resistance torques, such as sealing resistance, gear churning losses, and other minute loads.
[0039] Example This embodiment uses the above method, taking a certain type of 8-cylinder diesel engine as the application object, to verify the speed prediction method under cold start conditions in an extremely cold environment of -43℃, and applies the speed prediction method to the prediction of optimal preheating time. This system and method are also applicable to other types of diesel engines and different low-temperature environments.
[0040] See Figure 1 This method for predicting the engine speed under cold start conditions in a diesel engine based on a non-uniform temperature field begins with inputting the initial cold start preheating time. First, multi-physics coupled simulation calculations are performed using the initial preheating time as input to establish a temperature field database for key components of the diesel engine. Then, based on this temperature field database, a resistance torque model under a non-uniform temperature field is constructed to obtain the operating resistance torque under different preheating times. Simultaneously, the operating dynamic torque is obtained based on the characteristics of the motor drive torque. This operating dynamic torque, along with the operating resistance torque under different preheating times, is input into the dynamic resistance torque coupled model to calculate the engine starting speed. Figure 5 As shown, the speed prediction is now complete.
[0041] The results of the above speed prediction are applied to the determination of the optimal preheating time for cold start requirements. A specific example is as follows: Based on the existing thermodynamic state prediction model and the in-cylinder thermodynamic conditions, the critical speed for spray ignition is calculated. The starting speed calculated using the method protected by this invention is compared with the critical speed. If the starting speed is less than the critical speed, the preheating time is updated and the entire process of multiphysics coupling simulation, temperature field database construction, resistance torque modeling, and starting speed calculation is re-executed. If the starting speed is greater than or equal to the critical speed, the in-cylinder ignition stage is entered. After in-cylinder ignition, the engine speed increases, resulting in a larger operating resistance torque. At the same time, the power torque is recalculated. In the verification cycle continuous ignition module, it is determined whether the power torque is continuously greater than the resistance torque. If the power torque cannot be continuously greater than the resistance torque, the preheating time is updated and the entire process is re-executed. If the power torque is continuously greater than the resistance torque, the diesel engine is determined to have successfully started cold, and the optimal preheating time that meets the cold start requirements is finally output.
[0042] In this embodiment, the method for constructing the database of non-uniform temperature field distribution includes parallel implementation of simulation modeling and experimental calibration paths, such as... Figure 2 As shown. The simulation modeling path is based on the ANSYS Workbench platform to establish a multiphysics coupling model. Thermo-solid coupling simulation is performed using the Transient Structural module. After setting specific ambient temperature and preheating time boundary conditions, temperature field contour map data of key components are calculated and output. The contour map is shown in the example below. Figure 3 As shown.
[0043] Meanwhile, the experimental calibration path uses sensing units such as K-type thermocouples arranged on the inner / outer walls of the cylinder liner, fiber optic temperature sensors on the piston top and skirt, and contact temperature sensors at the crankshaft main bearing to collect physical measured temperature data in real time via the NI cDAQ-9178 data acquisition card.
[0044] The simulation and experimental data obtained from the two paths are finally merged and corrected and complemented through a data fusion processing step based on the Kalman filter algorithm to eliminate model errors and measurement noise, thereby generating a high-confidence non-uniform temperature field database, providing a reliable data foundation for subsequent precise thermal management and control optimization.
[0045] The next step is to calculate key parameters. Based on the above non-uniform temperature field data, the dynamic viscosity of the lubricating oil and the thermal deformation of the components affected by local temperature are calculated in parallel for each component. Then, a precise resistance torque model is constructed, the calculated parameters are integrated, a starting resistance torque model for each component is established, and a more accurate total friction resistance torque is obtained by superimposing the models.
[0046] The total frictional resistance torque model is substituted into the dynamic equation of the diesel engine starting system for solution, and the starting speed curve is predicted.
[0047] Based on the prediction results, the preheating time and start-up control parameters are optimized to achieve the lowest start-up cost and the optimal preheating time through closed-loop optimization.
[0048] Comparative Example This comparative example assumes a uniform temperature field, assuming that during cold start preheating and the initial start-up phase, the temperature distribution of key components of the diesel engine (such as cylinder liners, pistons, piston rings, crankshaft main bearings, etc.) is uniform and consistent, and that the lubricating oil temperature remains synchronized with the component temperatures. By setting a single ambient temperature or average component temperature, and combining empirical formulas to calculate the lubricating oil viscosity and component friction coefficients, a resistance torque calculation model is established. The total frictional resistance torque model is then substituted into the dynamic equations of the diesel engine starting system for solution, predicting the starting speed curve.
[0049] like Figure 4 As shown, the drag torque obtained by different methods under different ambient temperatures in the embodiment and the comparative example is compared. It can be seen that: the embodiment establishes a more accurate component starting drag torque model that reflects the actual thermal state by accurately capturing the temperature distribution characteristics of the components and the correlation law of the parameters, thus achieving high-precision prediction of the cold start speed; while the drag torque model in the comparative example based on the assumption of a uniform temperature field cannot accurately reflect the actual drag change law, which ultimately leads to a large deviation between the predicted cold start speed and the actual speed, and cannot provide accurate guidance for starting control.
[0050] Therefore, this invention provides a diesel engine cold start speed prediction method based on a non-uniform temperature field. By acquiring a non-uniform temperature field through multi-source data fusion, accurate modeling of components, and dynamic correction algorithms, it effectively solves the problems in traditional diesel engine cold start speed prediction technology, which suffers from large deviations in resistance torque calculation and low speed prediction accuracy due to reliance on the assumption of a uniform temperature field, thus failing to provide a reliable basis for start-up control. It can provide accurate data support for optimizing diesel engine cold start control strategies and designing preheating system parameters, and is especially suitable for diesel engine application scenarios in extreme low-temperature environments.
[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.
Claims
1. A method for predicting the engine speed during cold start of a diesel engine based on a non-uniform temperature field, characterized in that, Includes the following steps: Step 1: Obtain the non-uniform temperature field distribution data of key components of the diesel engine during the cold start preheating process by combining multiphysics field coupled simulation and bench test. Step 2: Based on the non-uniform temperature field distribution data, calculate the dynamic oil viscosity of the lubricating oil and the thermal deformation of the components under the influence of temperature. Step 3: Integrate the dynamic viscosity of the lubricating oil, the thermal deformation of the components, and the structural parameters of the components to construct a starting resistance torque model for each component; Step 4: Obtain the total frictional resistance torque through the component starting resistance torque model, substitute the total frictional resistance torque into the dynamic equation of the diesel engine starting system for solution, and obtain the speed change curve with time during cold start, so as to realize the dynamic prediction of cold start speed.
2. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 1, characterized in that: In step 1, key components include cylinder liners, pistons, piston rings, crankshaft main bearings, and connecting rod bearings.
3. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 2, characterized in that: In step 1, a multiphysics coupled simulation and bench test were combined to establish a multiphysics coupled model of the solid and fluid domains of the diesel engine. This model simulates the heat conduction, heat convection and heat radiation characteristics of the cold start preheating process under extreme low temperature conditions, and outputs temperature field cloud map data of each component. At the same time, high-precision temperature sensors were arranged at different locations of key components to collect temperature data in real time. The Kalman filter algorithm was used to fuse and correct the simulation data and experimental data to form non-uniform temperature field distribution data with high spatial resolution and complete time series.
4. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 3, characterized in that: In step 2, the dynamic viscosity calculation of the lubricating oil is performed. The lubricating oil viscosity calculation formula is modified based on the local temperature value of the components and the lubricating oil film in contact with each key component to obtain the dynamic viscosity data of the lubricating oil in different regions.
5. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 4, characterized in that: The formula for calculating the dynamic viscosity of lubricating oil is: ； in, The dynamic viscosity of the lubricating oil at temperature T; Viscosity at reference temperature; The activation energy of lubricating oil; This is the universal gas constant; This represents the actual temperature of the component.
6. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 5, characterized in that: In step 2, the calculation of component thermal deformation is carried out by establishing a thermal deformation calculation model based on the thermal expansion coefficient of each component material and the local temperature gradient, and outputting the thermal deformation data of each part.
7. The method for predicting the engine speed during cold start based on a non-uniform temperature field for a diesel engine according to claim 6, characterized in that, The formula for calculating the thermal deformation of a component is: ； in, This refers to the thermal deformation of the component. This is the initial length of the component; The coefficient of linear expansion of the material; This is the second-order correction factor for thermal expansion; The initial ambient temperature.
8. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 7, characterized in that: In step 3, the starting resistance torque of the sub-components includes the piston assembly resistance torque and the crankcase assembly resistance torque; the piston assembly resistance torque includes the piston ring fluid lubrication friction torque, the piston ring mixed lubrication friction torque, the piston skirt friction torque, and the valve assembly friction torque; the crankcase assembly resistance torque includes the friction torque of accessories and unloaded bearings and the friction torque of loaded bearings.
9. The method for predicting the engine speed during cold start based on a non-uniform temperature field for a diesel engine according to claim 8, characterized in that: Piston ring fluid lubrication friction torque The calculation formula is: ； in, The dynamic viscosity of the lubricating oil; Piston speed; For contact pressure; D is the cylinder pressure; D is the cylinder diameter. To determine the equivalent number of oil rings, The number of oil rings, This refers to the number of air rings; This refers to the piston ring width; The transformation ratio; Where is the crank radius; The coefficients are constants. Piston ring mixed lubrication friction torque The calculation formula is: ； in, This refers to the crankshaft rotation angle; The coefficients are constants. Piston skirt friction torque The calculation formula is: ； in, The thickness of the oil film; This refers to the length of the piston skirt. A constant coefficient; valve assembly friction torque The calculation formula is as follows: ； in, This refers to the friction of the valve assembly and the number of valves. This refers to the spring preload. Angular velocity; The coefficients are constants. Frictional torque of accessories and unloaded bearings The calculation formula is: ； in, The coefficients are constants. Frictional torque of loaded bearing The calculation formula is: ； in, These are constant coefficients.
10. The method for predicting the engine speed under cold start conditions of a diesel engine based on a non-uniform temperature field according to claim 9, characterized in that: In step 4, the formula for calculating the total frictional resistance torque is: ； Substituting the total frictional resistance torque into the dynamic equation of the diesel engine starting system, the change of crankshaft speed with time during cold start is solved, expressed as: ； ； in, The equivalent rotational inertia of the starting system; for Crankshaft angular velocity at any given moment; This is to provide the output torque for the starter motor; This represents the total resistance torque of the diesel engine. This refers to the cylinder compression resistance torque; This refers to the air resistance torque of the intake and exhaust pumps. For other secondary resistance torques.