Modeling and Simulation of the thermal management

2022-08-06
  • Detail

Modeling and Simulation of vehicle thermal management system

the film produced by ecovio is superior to the traditional product management system. In a broad sense, it includes the comprehensive management and optimization of all on-board heat source systems. At this stage, the main research object usually takes the cooling system as the core, and comprehensively considers the interaction between the oil cooler of the lubrication system, the condenser and intercooler of the air conditioning system and the cooling system, The study of engine cold start characteristics and the analysis of flow and heat transfer in engine compartment are the primary issues of vehicle thermal management

a typical vehicle cooling system (see Figure 1), including: cooling water pump, engine, oil cooler, thermostat, radiator, heater, etc. the electrical interference of the instrument is often random and symmetrical with the expansion water tank and other components

Figure 1 typical vehicle cooling system structure

through modeling and Simulation of the system, the following physical phenomena must be considered:

1 Flow, pressure and temperature distribution of each branch of the system

2. Operating characteristics of thermostat

3. System dynamic process temperature fluctuation

4. Heat exchange conditions at various parts of the system

vehicle cooling system

amesim provides professional libraries such as heat reservoir, heat fluid reservoir and cooling system library for the vehicle cooling system, covering all components required for cooling system modeling. The simulation model of the cooling system can be quickly established by dragging and dropping the mouse

Figure 2 AMESim vehicle cooling system model

Figure 2 shows the vehicle cooling system model established by using AMESim. The parameters required for the model are as follows:

1 Pipe structure of actual system

2. Type of coolant used

3. Geometric dimensions of each section of cooling water pipe

4. Pump characteristic curve

5. Flow resistance characteristics of all components of the system (radiator, oil cooler, water jacket, etc.)

6. Radiator performance map

by setting the external boundary conditions of the system (atmospheric pressure, atmospheric temperature, etc.) and the initial conditions of the system, given the simulation cycle, AMESim can automatically select the optimal integration algorithm and step size to quickly complete the system transient calculation. See Figure 3 for typical simulation results of AMESim vehicle cooling system

Figure 3 AMESim vehicle cooling system simulation results

it can be seen from Figure 3 that AMESim modeling and simulation can be used to calculate the flow and flow resistance of each branch of the system, evaluate the overall performance of the system, select the size of key components and design control strategies. Based on AMESim cooling system solution, engineers can study the impact of new components and new structures on system efficiency and performance, including:

1 The influence of new electronic water pump and electronic thermostat is analyzed

2. Maximum operating temperature of the analyzer

3. Analyze the influence of new components, new layout structure and pipeline size

4. Analyze the effect of higher water tank pressure on cavitation

engine thermal model

the above cooling system model can not accurately calculate the engine cold start process, because the above model does not consider the energy stored in the engine block and the heat exchange process inside the engine block. Therefore, it is necessary to establish a more detailed engine block thermal model and fully consider the heat exchange process inside the engine block. Firstly, a typical engine block structure is considered. In order to establish the heat dissipation model of the engine block, the properties of thermal fluid (lubricating oil, coolant, air and combustion exhaust), solid heat capacity (aluminum, cast iron) and the heat transfer between these heat capacities (conduction, convection and radiation) must be considered. The engine block (see Figure 4) is discretized into the following heat capacity structures (the least heat capacity point discretization method can be further refined): oil pan, crankcase, crankshaft, connecting rod, piston, cylinder block outer wall, cylinder, cylinder head and camshaft

Figure 4 basic structure of engine block thermal model

after the engine block is discretized, the heat transfer phenomenon between various parts after discretization must be correctly considered, including:

1 Heat conduction between discrete mass points (cylinder block, cylinder head, piston, etc.)

2. Convective heat transfer between coolant and mass points in the engine block, between lubricating oil and mass points, and between gas and mass points

3. Friction heat generation and combustion heat generation in combustion chamber

Figure 5 shows the discrete engine block thermal model. The discrete engine block thermal model takes into account the heat exchange among solids, liquids and gases in each part of the engine block. Therefore, the model can fully consider the engine cold start process and give the temperature information of various points inside the engine block to avoid local overheating

Figure 5 AMESim body thermal model

engine compartment thermal model

in the relatively small space of the vehicle engine compartment, the engine, radiator, air conditioning condenser, oil cooler, intercooler and EGR cooler are arranged in a complex way. Each subsystem in the vehicle affects and interferes with each other in the vehicle thermal ring, and its flow and heat transfer process is very complex. AMESim provides engineers with a heat (heat exchanger assembly tool) library to solve the complex flow and heat transfer in the engine compartment

the purpose of developing heat library is to specially solve the flow and heat transfer problems in narrow spaces such as automobile engine compartment, and assist engineers to complete corresponding tasks at different stages of product development, so as to make the design and spatial layout of engine compartment a success. Using the heat library, engineers can study the influence of different spatial layout relationships in the engine compartment, and accurately evaluate the thermal state of each subsystem in the vehicle test cycle to ensure that all systems in the vehicle are kept within the normal range

the heat library shown in Figure 6 provides 3D design and analysis capabilities for the engine compartment. Through the heat library, engineers can set the three-dimensional space of the engine compartment, and automatically calculate their mutual influence according to the relative position of each component and the flow channel structure, taking full account of the influence of the imbalance of flow and heat transfer in the engine compartment

Figure 6 3D design and analysis capability of heat library

the relative position and geometric size of radiator, oil cooler, air conditioning condenser and other components are the primary factors affecting the flow and heat transfer inside the engine compartment. The overlap between radiators causes great imbalance in the cooling air duct, and great changes in the flow field and temperature field everywhere

as shown in figure 7-a, assuming that part 1 is an air conditioning condenser, Part 2 is an oil cooler, and Part 3 is a radiator, the three parts are arranged in parallel at the front of the engine compartment, and the wind direction is the x-axis direction. According to the position relationship and size of the three parts, the cooling air duct can be divided into four areas as shown in figure 7-b. the flow and heat transfer status in each area are different, even in the same area, The surface heat distribution of the radiator is also very uneven due to the different forms of the internal flow channel. The heat library provides engineers with a complete and easy-to-use tool to fully consider the impact of these factors, making the flow and heat transfer analysis and structural optimization design of the engine compartment simple and feasible, and the final results meet the overall design requirements

Figure 7 spatial position relationship of engine compartment

in AMESim component parameter table, it is easy to set the spatial coordinates and geometric dimensions of each component according to the actual layout relationship of engine compartment, including the spatial coordinates x, y, Z of components and the length, width and thickness of dimension parameters

amesim can automatically complete the grid division of the flow channel according to the position relationship and geometric size of each component. AMESim automatically completes the division of grids (see Figure 8), and considers the imbalance of flow and heat transfer in different grid areas

figure 8 automatic grid division

in addition to the spatial location, the flow pattern inside the radiator will also produce imbalance between flow and heat transfer, such as I-shaped, U-shaped and serpentine flow channels inside the radiator. At present, the park consists of fluorine mining, anhydrous hydrogen fluoride, 3-chloromethane, 4-fluoroethylene, 6-fluoropropylene and poly-4-fluoroethylene channels, which will have an impact on the heat exchange results. AMESim has taken this into full consideration, Figure 9 shows the calculation results of the U-shaped channel. It can be seen that the temperature of the coolant decreases gradually along the flow direction, but the temperature of the radiator surface is uneven. The temperature at the inlet is higher, while the temperature at the outlet on the same side is lower

Figure 9 temperature distribution of U-shaped channel

the flow structure can be easily set in AMESim, including the number of channels, inlet position and the number of pipes in each channel (see Figure 10)

Figure 10 setting of internal flow channel of radiator

in addition to the imbalance of mutual flow and heat transfer between radiators, there is often a large imbalance in the inlet boundary of cooling air in the engine compartment. The front end of the engine compartment is usually equipped with an air inlet grille. The front end of the high-speed running car is turbulent flow. After the disturbance of the grille, the flow is usually more uneven, as shown in the CFD calculation results shown in Figure 11 (provided by Renault automobile company)

Figure 11 CFD calculation results of engine compartment windward boundary

in AMESim, arbitrary CFD data can be used as boundary conditions, such as fluent, star CD, fire and other software. Taking the setting of windward boundary conditions as an example, the CFD boundary data are discretized along the X and Y axes on the windward surface, and the data value of this point is input in the grid corresponding to the corresponding (x, y) coordinates. Different values are set between the grids, This can truly set the boundary conditions that gaoxiaobing, a lithium battery analyst at engine engineering, believes the flow in the cabin. Figure 12 shows the velocity boundary field generated by the axisymmetric double fans. In AMESim, there are two kinds of boundary conditions for users to set: velocity boundary and pressure boundary. The velocity boundary is suitable for the compact layout such as the engine compartment, and the velocity field is easy to determine; The pressure boundary is suitable for the form with large distance

Figure 12 velocity boundary mode

as shown in Figure 13, the results of simulation calculation using the heat Library of AMESim show that the temperature distribution on the surface of the radiator is uneven. The temperature in region 4 (where the three radiators coincide) is the highest, the temperature in regions 2 and 3 (where the two radiators coincide) is low, and the temperature in region 1 is the lowest. Even in region 1, the temperature is not completely consistent due to different flow forms in the radiator

Figure 13 example results

amesim's heat library provides engineers with a complete and easy-to-use tool. Taking full account of the effects of these factors, it makes the flow and heat transfer analysis and structural optimization design of the engine compartment simple and feasible, and the final results meet the overall design requirements

model validation

the above AMESim vehicle thermal management solutions have been widely used in the world's major automobile manufacturers and parts suppliers to study the impact of temperature changes during vehicle cold start and the layout of engine compartment on engine fuel consumption, emissions and other indicators. At the same time, they can be used to study the new thermal management system structure and control strategy. Different manufacturers have conducted a large number of test comparisons on AMESim simulation results. Figure 14 shows the comparison of simulation and test results under the same engine working condition. The data are from Toyota Motor Company

Fig. 14 comparison between simulation and test at single operating point

in order to verify the model more accurately, in addition to comparing the data at single operating point, we should also compare the data under cyclic conditions. Figure 15 shows the test comparison of the same AMESim model under European cycle test conditions

Figure 15 comparison between simulation and test under European cycle test conditions

once the accuracy of the model is fully proved, it can be

Copyright © 2011 JIN SHI