Cooling System Library. Version September 2004

Transcription

1 Cooling System Library Version September 2004

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3 Copyright IMAGINE S.A AMESim is the registered trademark of IMAGINE S.A. AMESet is the registered trademark of IMAGINE S.A. ADAMS is a registered United States trademark of Mechanical Dynamics, Incorporated. ADAMS/Solver and ADAMS/View are trademarks of Mechanical Dynamics, Incorporated. MATLAB and SIMULINK are registered trademarks of the Math Works, Inc. Netscape and Netscape Navigator are registered trademarks of Netscape Communications Corporation in the United States and other countries. Netscape s logos and Netscape product and service names are also trademarks of Netscape Communications Corporation, which may be registered in other countries. PostScript is a trademark of Adobe Systems Inc. UNIX is a registered trademark in the United States and other countries exclusively licensed by X / Open Company Ltd. Windows, Windows NT, Windows 2000 and Windows XP are registered trademarks of the Microsoft Corporation. X windows is a trademark of the Massachusetts Institute of Technology. All other product names are trademarks or registered trademarks of their respective companies.

4 TABLE OF CONTENTS 1. Introduction Getting started with the Cooling System Library The cooling system data components The cooling system specific components Hydraulic calculations Thermal calculations Engine component Heater core component Oil coolant heat exchanger component EGR heat exchanger component Radiator component Interpretation and analysis of the simple cooling system simulation results Highlighting important phenomena Influence of the heater component Influence of the fan operating Influence of the condenser component Influence of the immersion heaters component Influence of the EGR heat exchanger Influence of the oil/coolant heat exchanger Use of some specific components Using the thermostat with hysteresis effects Influence of the mission profile Description of Cooling system submodels Mission profile icon Vehicle icon Expansion tank icons Engine with EGR signal port icon Simple engine icon Simple radiator icon Simple radiator icon with shutters control Complex radiator icon Complex radiator icon with shutters control Modeling a cooling system: important rules...54 APPENDIX...1 September 2004 Table of Contents 1/1

5 1. Introduction Using the Cooling System Library The cooling system has a great influence on the design of an engine, it is indispensable because metallurgical constraints imply that the engine is limited to a maximum operating temperature level. However, from a thermodynamic point of view, cooling the engine tends to reduce the ratio of power over fuel consumption, which is not desirable. For this reason, the aim of the engine cooling system is to provide during cold start or low ambient temperature conditions, an increase in temperature of the coolant, the oil and the engine metal masses. Under uphill and full load conditions, it must provide sufficient cooling of the oil and the engine metal masses. By improving these aspects, it is possible to achieve an optimum compromise between important engine requirements (low fuel consumption, extended engine life and reduced gas emissions) and high performance. In order to design and validate innovative solutions and as a response to the increasing demands for engine cooling system efficiency, the AMESim Cooling System Library has been developed. This library comprises a set of specific application components fully compatible with AMESim Thermal-hydraulic and Thermal Libraries. By connecting together components from these three libraries, it is possible to study the thermal transient and steady-state behavior of the engine cooling system and to investigate several features: - the sizing of influential components (heater core, radiator and fan, thermostat ), - the influence of the thermostat technology (oscillations, thermal effects) - cavitation at the pump inlet, - the response of the system for given engine operating points or standard mission profiles (evolution of flow rates and temperatures in the system ), - the effect of a brutal stop (temperature peaks, coolant flow rates in the expansion tank), - the pump and thermostat control, - the influence of the heater core, the EGR and oil/coolant heat exchangers and the immersion heaters (position, thermal impact ) - the time needed for the engine to reach its operating temperature after a cold start by modeling in detail all the engine internal thermal exchanges. In this manual, examples of cooling system models are presented. It begins with a minimal model of an engine cooling circuit which will be used to introduce the concepts of this library. Then, this system will be gradually modified so as to end up with a complete cooling system taking into account most of the influential components. These examples illustrate the possibilities of the AMESim Cooling System Library. However, it is assumed that the reader is familiar with the use of AMESim, AMESim Thermal Library and AMESim Thermal-hydraulic library. If not, we suggest that you read the manuals of AMESim, AMESim Thermal Library and AMESim Thermal-hydraulic library before attempting the examples below. September 2004 Using the Cooling System Library 1/56

6 2. Getting started with the Cooling System Library To get started using the components in the Cooling System library, consider the given simple typical structure of a cooling system shown in Figure 1: thermostat expansion tank heater component engine pump radiator Figure 1: Engine cooling system structure This is a typical cooling system structure. It is obvious that this structure will differ depending on the engine types and the different car manufacturers cooling systems topologies. This example will give insights in the modeling of a wide variety of cooling system structures. Modeling and simulating an engine cooling system permits the calculation of the flow rate distribution in the different branches of the system as well as the coolant pressure and temperature in each component. This is the purpose of this simple example. To model the simple structure shown in Figure 1, select the thermal, thermal-hydraulic and cooling system library category icons shown in Figure 2 : Figure 2: Thermal, Thermal-Hydraulic and Cooling System library category icons This will produce the popups shown in figures 3, 4 and Figure 3 : Components of the Thermal library September 2004 Using the Cooling System Library 2/56

7 Figure 4 : Components of the Thermal hydraulic library used (two categories among three) September 2004 Using the Cooling System Library 3/56

8 Figure 5 : Components of thecooling system library September 2004 Using the Cooling System Library 4/56

9 Figure 6: model of a simplified cooling system First look at the components available in these libraries. Display the titles of each component by moving the pointer over the icons. When this is done, build the model of the cooling system shown in Figure 6. This model comprises twenty four elements from the thermal, thermal-hydraulic, cooling system and signal libraries. Each one is referenced by a number. Fill in the parameters of these components as described in the table below leaving the others at their default values. If you have difficulty finding a component, refer to its number in Figure 6 corresponding to the numbers in Figure 3, Figure 4 and Figure 5. Submodel name and type 1 CSMP1 mission profile 2 CSED0 ambient conditions 3 CSES0 vehicle data 4 TFFD1 thermalhydraulic properties 5 UD00 signal source 6 UD00 signal source 7 CSHC0 heater core 8 TF206 thermalhydraulic T- junction 9 TFPC1 thermalhydraulic adiabatic pipe Belongs to category Cooling system Cooling system Cooling system Thermal-Hydraulic Signal, control and observers Signal, control and observers Cooling system Thermal-Hydraulic Thermal-Hydraulic Principal simulation parameters Velocity at start of stage 1 = 45 km/h Velocity at end of stage 1 = 45 km/h Gearbox ratio start of stage 1 = 2 Gearbox ratio end of stage 1 = 2 Road inclination percentage at stage1 = 6 % Default parameters Default parameters Filename for fluid characteristic data = $AME/libthh/data/coolant.data Default parameters Default parameters Default parameters Default parameters Default parameters September 2004 Using the Cooling System Library 5/56

10 Submodel name and type Belongs to category Principal simulation parameters 10 CSCP1 centrifugal Cooling system Default parameters pump 11 CSEN00 engine Cooling system Filename for heat exchanged =f (engine speed, power developed by shaft):./data/peng1.data previously generated 12 UD00 signal Signal, control and Default parameters source observers 13 TFN02 thermalhydraulic Thermal-Hydraulic Default parameters node 14 UD00 signal Signal, control and Default parameters source observers 15 CSTH1 thermostat Cooling system Default parameters 16 TFTS1 thermalhydraulic Thermal-Hydraulic Default parameters temperature sensor 17 TRIG0 trigger Signal, control and observers Low input threshold value = 82 High input threshold value = TF223 thermalhydraulic Thermal-Hydraulic Default parameters restriction 19 TFAC0 thermalhydraulic Thermal-Hydraulic Default parameters accumulator 20 THHF0 zero heat Thermal Default parameters flow source 21 CSRA22 radiator Cooling system Default parameters 22 CSVT0 air Cooling system Default parameters velocity and ambient temperature source 23 GA00 gain Signal, control and observers Value of gain = 1/3.6 = CSDATA characteristic data of the system Cooling system Index for data observed = 3 At this stage, it is important to highlight the fact that most of the cooling system components are characterized hydraulically or thermally using data tables. In order to avoid spending time generating these data tables, the cooling system library is provided with existing data files. These files are located in the directory $AME/libcs/data. Before running the simulation, copy the $AME/libcs/data directory and its content in your working directory. September 2004 Using the Cooling System Library 6/56

11 Then, create the text file peng1.data as follows and save it in the data directory : Detail of the data file peng1.data Finally, run a simulation with the final time 300 seconds, the communication interval 1 second and the tolerance 1e-07. Note that the default value for the tolerance (1e-05) is not used for Cooling System models because in some particular cases, it may lead to slow runs. Plot a few graphs to get an idea of how the temperature evolves in various parts of the cooling system. We will examine the results of the simulation in more detail in section 2.3 but first we will describe certain important submodels. September 2004 Using the Cooling System Library 7/56

12 2.1. The cooling system data components There are some components with no ports which are used to define the operating point of the system. We have the following four icons : With these icons are associated data submodels in which are defined the control variables of the cooling system. These control variables are the car velocity, the gearbox ratio, the slope of the road, the ambient conditions and the vehicle characteristic data (total mass, aerodynamic trail, tire pressure ). They are used to compute global variables which define the operating point of the engine (rotary speed, torque, power developed by shaft, percentage of wide-opened throttle ). These variables are used by the other components of the model. Let us consider now the function of the submodels associated with icons 1, 2, 3 and 4. The submodels associated with this icon are used to define the car velocity, the gearbox ratio and the slope of the road for user-defined duty cycles. From this data is computed the car acceleration. The submodel associated with this icon is used to define the ambient conditions (temperature and pressure) for user-defined duty cycles. The submodels associated with this icon are used to define the vehicle characteristic data such as the engine idling rotary speed, the car total mass, the aerodynamic trail, the tire pressure, the transmission efficiency and other data which are used to compute the operating point of the engine. The global variables computed in this component are the engine speed, the power at the wheel rim and the engine torque. The submodel associated with this icon is used to define globally the thermal-hydraulic properties of the liquid which is used for the simulation. These properties are the density, the viscosity, the specific heat, the thermal conductivity, the specific enthalpy and these are varying with temperature and pressure. September 2004 Using the Cooling System Library 8/56

13 2.2. The cooling system specific components These are the major components of the cooling system models such as the engine, radiator, thermostat, etc. They have thermal-hydraulic, thermal and signal ports. There are four variables exchanged at thermal-hydraulic ports : Temperature T [degc] Enthalpy flow rate dmh [W] Pressure p [bara] Mass flow rate dm [kg/s] There are two variables exchanged at thermal ports : Temperature T [degc] Heat flow rate dh [W] Consider the engine icon below, there are two thermal-hydraulic ports (2 and 4) and two signal ports (1 and 3) on which a number of variables are exchanged. With this icon, several submodels are associated. In the example, the icon is associated with submodel CSEN00. T2 signal 3 p2 dm dmh T4 p4 dm dmh signal 1 Figure 7: Engine component variables exchanged at ports Ports 2 and 4 are thermal-hydraulic ports. At these ports the variables pressure, temperature, mass flow rate and enthalpy flow rates are computed. Port 4 is the coolant inlet and port 2 is the coolant outlet. The equations used to compute all these variables are described in the thermal-hydraulic manual. In this component, as in most of the specific cooling system components, hydraulic and the thermal calculations have to be taken into consideration Hydraulic calculations In the specific components of the cooling system library, the user has two ways to characterize the pressure drops in the components: - supply an equivalent area for the component - supply a data table or an expression for the volumetric flow rate as a function of the pressure drop in the component The components concerned are the engine, the heater core, the immersion heaters, the EGR heat exchanger, the radiator and the oil/coolant heat exchanger. September 2004 Using the Cooling System Library 9/56

14 Thermal calculations In the specific components of the cooling system library, the power absorbed or given to the coolant is calculated using experimental data tables belonging to the car manufacturer. This experimental data are specific to each component. In what follows is a summary of the list of data tables needed to characterize the heat exchanged with the coolant in the different components Engine component In this component, there are two ways to compute the heat provided by the engine to the coolant: - supply a data table giving the heat exchanged between the engine and the coolant as a function of the engine rotary speed and the power developed by shaft (which are global variables computed by vehicle characteristic data submodels CSES0 or CSES1) - supply a data table giving the heat exchanged between the engine and the coolant as a function of the engine rotary speed and the percentage of wide-opened throttle (which are global variables computed by vehicle characteristic data submodel CSES2) Heater core component To compute the heat exchanged between the air flowing through the heater core and the coolant, the user must: - supply a data table giving the power evacuated from the coolant as a function of the coolant volumetric flow rate and the air mass flow rate. This table contains data measured for a given experimental temperature difference corresponding to the difference between the air temperature at the heater core inlet and the coolant temperature at the heater core inlet Oil coolant heat exchanger component To compute the heat exchanged between the oil flowing through the heat exchanger and the coolant, the user must : - supply a data table giving the heat exchanged between the oil and the coolant as a function of the oil volumetric flow rate and the coolant volumetric flow rate. This table contains data measured for a given experimental temperature difference corresponding to the difference between the oil temperature at the heat exchanger inlet and the coolant temperature at the heat exchanger inlet EGR heat exchanger component To compute the heat exchanged between the gas flowing through the EGR heat exchanger and the coolant, the user must : - supply a data table giving the heat exchanged between the gas and the coolant as a function of the mean effective pressure and the engine rotary speed. September 2004 Using the Cooling System Library 10/56

15 Radiator component To compute the power evacuated from the coolant in the radiator, the user has two possibilities: - supply a data table giving the heat evacuated from the coolant as a function of the coolant volumetric flow rate and the air pressure drop through the radiator. This table contains data measured for a given experimental temperature difference corresponding to the difference between the coolant temperature at the radiator inlet and the air temperature at the radiator inlet. - supply a data table giving the heat evacuated from the coolant as a function of the coolant volumetric flow rate and the air velocity through the radiator. This table contains data measured for a given experimental temperature difference corresponding to the difference between the coolant temperature at the radiator inlet and the air temperature at the radiator inlet. A detailed description of all the submodels, their parameter settings and usage is given directly in AMESim by clicking on the description button in each submodel Interpretation and analysis of the simple cooling system simulation results This first simple example permits the study of the cooling system behavior for a given operating point of the engine (car velocity = 45 km/h, gearbox ratio = 2, road inclination = 6%). The initial temperature in the circuit is T ini = 20degC. The main point of interest in this case is to study how the temperature varies in each component and how the flow rates are distributed in the different branches of the system. What we expect from such a system is to regulate the coolant temperature around a suitable value (approximately 90 degc) and to reach an equilibrium state materialized by the energy balance between the heat given by the engine and the heat evacuated in the heater core and in the radiator. Of course, this energy balance is strongly influenced by the operating of the thermostat and the possible operating of the fan. In this first example, no air is allowed to flow through heater core. It only has an influence on the flow rate distribution in the system. To highlight these phenomena, plot first the temperature of the coolant at the engine outlet and the thermostat fractional area as a function of time as shown on Figure 8: September 2004 Using the Cooling System Library 11/56

16 Figure 8: Coolant temperature at engine outlet and thermostat fractional area In Figure 8, three important phenomena can be observed: - From time t = 0 sec to 80 sec, the thermostat is closed because its opening temperature is set to 88.5 degc in submodel CSTH1. Meanwhile, the engine provides heat to the coolant and as a result the coolant temperature increases. As the thermostat is closed, the coolant only flows into the warm loop which is the loop constituted by the pump, the engine and the heater core (see Figure 9). - At time t = 80 sec, the wax temperature is equal to the thermostat opening temperature. As a result, the thermostat starts to open and the coolant begins to flow into the cold loop constituted by the pump, the engine, the thermostat and the radiator (see Figure 9). This opening of the thermostat leads to the mixing of the hot coolant flowing into the warm loop and the cold coolant which was in the cold loop. - From time t = 80 sec to 140 sec, it is possible to observe temperature oscillations which are due to the consecutive closing and opening of the thermostat trying to reach an equilibrium opening. These oscillations are damped and the coolant reaches a steady-state temperature of 89 degc. Warm loop Cold loop Figure 9: Definition of the Cold and the Warm loops September 2004 Using the Cooling System Library 12/56

17 Then plot the evolution of the volumetric flow rates in the engine, the heater core and the radiator as a function of time as shown in Figure 10 : Figure 10: Volumetric flow rates in the different branches In Figure 10, the volumetric flow rates in the different branches are dictated by the thermostat opening and closing. From 0 to 80 sec, the coolant only flows into the warm loop, that is to say in the engine and the heater core. During this period, the volumetric flow rate which is the same in the heater core and the engine increases slightly due to the variations of the coolant thermal-hydraulic properties with respect to temperature. At time t = 80 sec, the thermostat opens and the coolant starts to flow into the radiator branch. At the same time, the flow rate into the engine increases. This is due to the fact that the hydraulic resistance of the whole system is modified and as a result the pump has to supply the radiator branch as well. When the thermostat oscillations are totally damped, the volumetric flow rates in each branch reach their steady-state values. Now plot on the same graph the evolution of the coolant temperature at the engine outlet and at the radiator outlet as shown in Figure 11. September 2004 Using the Cooling System Library 13/56

18 Figure 11: Coolant temperatures at radiator and engine outlets The coolant temperature at the radiator outlet reaches a steady-state value of 30 degc which does not require the operating of the fan. We will show later in this manual that under certain heavy conditions, the fan has to operate in order to maintain sufficient cooling. The fan is switched on when the thermostat is fully opened to evacuate additional power from the coolant in the radiator and to avoid critical temperatures in the system. In the present case, the thermostat is not fully opened but the power evacuated from the coolant in the radiator is sufficient to maintain a suitable temperature in the system. The thermostat submodel used in this example is a simple one. To understand the way it behaves, plot its fractional area evolution against the wax temperature as shown in Figure 12. As you can see in that X-Y plot, the fractional area oscillates along a slope with respect to the variations of the wax temperature. Figure 12: Thermostat fractional area September 2004 Using the Cooling System Library 14/56

19 Then display its parameter popup as shown in Figure 13. Figure 13: Thermostat submodel parameters In the thermostat submodel, a convective exchange is taken into account between the coolant flowing along the wax and the wax. As a result the temperature of the wax increases with the temperature of the coolant. When the wax temperature reaches the initial temperature parameter, the thermostat starts to open. If the wax temperature reaches the final temperature parameter, the thermostat will be fully opened and in this case, the cross-sectional area of the thermostat will be equal to the cross-sectional area at maximum opening parameter. Therefore, the fractional area displayed in simulation mode is defined by: f T T T T A wax ini = (1) area max fin ini where f area is the fractional area, T wax is the current wax temperature, T ini is the initial temperature parameter, T fin is the final temperature parameter and A max is the crosssectional area at maximum opening. Plot now the evolution of the wax and the coolant temperatures at the thermostat inlet as a function of time as well as the fractional area as a function of time as shown in Figure 14 and Figure 15. September 2004 Using the Cooling System Library 15/56

20 Figure 14: Wax and coolant temperatures evolution In the thermostat submodel, the temperature of the wax is a state variable and is computed from its derivative with respect to time as follows: d T dt wax = h.a m.c p ( T cool T wax ) (2) Where h is the convective exchange coefficient, A is the exchange area, m is the mass of wax and c p is the wax specific heat at constant pressure. From this equation, it is easy to understand that the wax temperature will increase with the coolant temperature but with a time constant. This time constant is a function of the convective exchange coefficient and the heat capacitance of the wax. This dynamic phenomenon is clearly shown on Figure 14. Figure 15: Thermostat fractional area evolution September 2004 Using the Cooling System Library 16/56

21 This thermostat submodel is simple in that the opening and the closing follow the same law and no hysteresis is taken into consideration. There are other thermostat submodels in the cooling system library which do take into account hysteresis effects and different laws for the opening and the closing of the thermostat. The use of such thermostats will be described later in this manual. The figures plotted for this example are the most interesting ones. They give a brief overview of the phenomena involved in this simple example. Do not hesitate to plot other variables such as the power exchanged in each component, the control variables so as to get familiar with sign conventions and variables computed in each components. Next we will progressively increase the complexity of the structure of this example so as to highlight other interesting phenomena : - influence of the heater core, - influence of the fan operating, - influence of the condenser, - influence of the immersion heaters, - influence of the EGR heat exchanger, - influence of the oil/coolant heat exchanger, - influence of the mission profile, - influence of the thermostat with hysteresis effects, - influence of the power absorbed by auxiliaries on the heat exchanged between the engine and the coolant. Do not forget to save the system with a different name each time a new phenomenon is observed or a component added. Work through the following examples constructing the systems and plotting the graphs. September 2004 Using the Cooling System Library 17/56

22 3. Highlighting important phenomena 3.1. Influence of the heater component To show the influence of the heater core on the system, we will focus on the coolant temperature at the engine outlet. Run a simulation with the initial system and save the evolution of the coolant temperature at the engine outlet with respect to time. The operating of the heater core will be determined by the parameters supplied in components 5 and 6. Initially, the parameters in these two components are set to zero. Component 5 is used to control or impose the air mass flow rate flowing through the heater core and component 6 is used to determine the temperature of the air coming into the heater core. Change the parameters of component 5 and 6 as shown in the table below and run a simulation keeping the same simulation parameters as used in the first example. Submodel name and type Belongs to category New simulation parameters 5 UD00 signal source Signal, control and observers Output at start of stage1 = 300 Output at end of stage1 = UD00 signal source Signal, control and observers Output at start of stage1 = 20 Output at end of stage1 = 20 By changing these parameters, we get a 300 kg/hr air mass flow rate in the heater component and a constant air temperature of 20 degc which implies that the heater core is operating. Finally, plot the curve of the coolant temperature evolution at the engine outlet and compare it with the one saved for the system without heater core operating as shown in Figure 16. Engine outlet temperature [degc] Figure 16: Influence of the heater core operating In Figure 16, the operation of the heater core causes a delay in the coolant temperature increase at the engine outlet. This is obviously due to the heat evacuated from the coolant by the air flowing through the heater core. September 2004 Using the Cooling System Library 18/56

23 3.2. Influence of the fan operating Before looking at the influence of the fan, go back to the configuration of the simple system with heater core switched off. As previously stated, under certain load conditions, the fan has to be switched on in order to evacuate additional heat from the coolant. In this section, we will take into account the slope of the road and the influence of the radiator grille which tends to modify the air velocity flowing through the radiator. By doing this, we will increase the heat provided by the engine to the coolant and show the operating of the fan. To do this, modify the parameters of components 1, 21 and 23 as shown in the table below. Submodel name and type Belongs to category New simulation parameters 1 CSMP1 mission profile Cooling system Velocity at start of stage 1 = 45 km/h Velocity at end of stage 1 = 45 km/h Gearbox ratio start of stage 1 = 2 Gearbox ratio end of stage 1 = 2 Road inclination percentage at stage1 = 10 % 21 CSRA22 radiator Cooling system Expression for air velocity increase due to fan operating = 0.4*x 23 GA00 gain Signal, control and observers Gain = 1/(3.6*7) Now run a simulation with final time 600 seconds and plot the evolution of the coolant temperature at the engine and the radiator outlets and the output from component 17 as shown in Figure 17. The output of component 17 represents the state of operation of the fan. Finally, plot the evolution of the thermostat fractional area and the fan operating state with respect to time as shown in Figure 18. September 2004 Using the Cooling System Library 19/56

24 Figure 17: Evolution of coolant temperatures and fan operating state What we observe is that the fan starts to operate at time = 270 sec. This results in a decrease of the coolant temperature in the system. At the same time the fractional area of the thermostat is maximum and is equal to 1, that is to say that the thermostat is fully opened and that the heat exchanged in the radiator is not sufficient to maintain a certain level of temperature at the radiator outlet. That is why the fan starts to operate. This results in an additional air velocity in the radiator leading to an increase in the power evacuated in the radiator and consequently to a decrease of the coolant temperature at the radiator outlet. Figure 18: Thermostat fractional area and fan operating state At this stage, it is important to explain briefly what happens in the radiator branch. For this purpose, look carefully at Figure 19. September 2004 Using the Cooling System Library 20/56

25 Figure 19: Radiator and fan system In some cooling systems, there is a probe which is used to measure the temperature of the coolant at the radiator outlet and to control, if necessary, the operating of the fan. This probe is modeled here by the combination of component 16 and component 17. Component 16 is a temperature sensor which measures the temperature of the coolant at the radiator outlet. This information is transmitted to component 17. At this stage, look at the parameters of component 17 as shown in Figure 20: Figure 20: Parameters of component 17 Component 17 is a trigger signal submodel which is used to control the operating state of the fan. In this cooling system model, it behaves as follows: if the temperature measured by component 16 reaches 92 degc, the output from component 17 will be equal to 1, so the fan will be switched on and the coolant temperature measured by component 16 will decrease. Then if the measured temperature decreases to under 82 degc, the fan will be switched off by component 17 whose output will then be equal to zero. How is the action of the fan taken into account by the radiator component? To understand this, display the parameter popup of the radiator (component 21) as shown in Figure 21. For more details on the radiator index parameter, please refer to paragraph 5.9. September 2004 Using the Cooling System Library 21/56

26 Figure 21: Radiator submodel parameters In the radiator component, the heat exchanged between the air and the coolant is computed from an experimental data table which gives the heat exchanged as a function of the air velocity and the coolant flow rate. Notice that there is also an experimental temperature difference parameter which is used to compute the real heat exchanged between the air and the coolant in the radiator. Thus, the data are measured for a given experimental temperature difference between the coolant temperature at the radiator inlet and the air temperature at the radiator inlet. During a simulation this temperature difference is never equal to the experimental one and therefore, the real heat exchanged is computed as follows: H H T T real real = exp (3) exp This experimental temperature parameter is also used in the heater core component and in the oil/coolant heat exchanger component. When the fan is switched on, an additional air velocity has to be taken into account to compute the real heat exchanged in the radiator. This air velocity increase is computed from the operating state of the fan (x) using the expression 0.4*x. To check this, plot the output signal from the component 17 and the variable additional air velocity due to fan operating from the component 21 with respect to time as shown in Figure 22: September 2004 Using the Cooling System Library 22/56

27 Figure 22: Air velocity increase due to fan operating Note: In the cooling system library, there are several radiator icons and several submodels associated with each icon. In some of them, the heat exchanged between the coolant and the air flowing through the radiator can also be characterized as a function of the coolant volumetric flow rate and the air pressure drop through the radiator. In this case, the fan operating induces an additional pressure drop in the component which is a function of the input signal on the fan port. For more information, please refer to the documentation of these submodels directly either directly in the AMESim submodel description or in the HTML documentation Influence of the condenser component In the cooling system library, you can find a condenser compressor component whose icon is shown in Figure 23. Figure 23: Compressor and condenser component In most recent cooling systems, a condenser can be found just ahead of the radiator. This component is part of the air-conditioning system of the vehicle. The operating of this condenser is controlled by the compressor. This component has a double influence on the cooling system: - the fact that the condenser is located just ahead of the radiator implies that the air temperature flowing through the radiator is modified because power is evacuated from the condenser which tends to warm the air, September 2004 Using the Cooling System Library 23/56

28 - to make the compressor work, the power developed by shaft has to be increased. As a result, the operating point of the engine is modified which consequently influences the heat exchanged between the engine and the coolant. By inserting the component shown in Figure 23 on the sketch of the initial simple cooling system model, you have the possibility to model the double influence mentioned before. To do this, update the initial cooling system as shown in Figure 24. Figure 24: Cooling system with condenser and compressor The modification consists in inserting the condenser-compressor component 26 between the radiator and the air velocity source, in connecting component 25 to the condensercompressor system and in connecting the compressor-condenser system to the engine component. When this is done, fill in the parameters of components 25 and 26 as shown in the table below: Submodel name and type Belongs to category New simulation parameters 25 UD00 signal source Signal, control and observers Output at start of stage 1 = 0 Output at end of stage 1 = 0 Duration of stage 1 = 150 sec Output at start of stage 2 = 1 Output at end of stage 2 = 1 26 CSCO10 condenser and compressor Cooling system Duration of stage 2 = 150 sec Default parameters Then run a simulation for 300 seconds, still with a communication interval of 1second and a tolerance of 1e-07. Component 25 is used to control the operating of the compressor. If the signal is equal to 0, the compressor is not operating. If the signal is equal to 1, the compressor is operating. To highlight the influence of the condenser on the air temperature flowing through the radiator, plot the temperature of the air at the condenser outlet and the signal output of component 25 as shown in Figure 25. September 2004 Using the Cooling System Library 24/56

29 Figure 25: Condenser influence on the air temperature At time t =150 sec, the compressor is switched on, implying the operating of the airconditioning circuit. As a result the condenser evacuates power into the ambient air and consequently, the air is warmed at the condenser outlet and flows through the radiator with a temperature of 21.2 degc. Notice that on the system shown in Figure 24, the condenser-compressor system is linked to the engine component by a signal port. This link is used to pass the power absorbed by the operating of the compressor to the engine. This absorbed power is then taken into account in the computation of the power developed by the shaft. When the compressor is operating, the power developed by the engine shaft has to be increased so as to maintain the initial car velocity which in this case is equal to 45 km/h. Another consequence is that, as the heat exchanged between the engine and the coolant is a function of the power developed by the shaft, it will inevitably be modified as well. To illustrate this, plot the power developed by the shaft and the heat exchanged between the engine and the coolant in the engine component as shown in Figure 26: September 2004 Using the Cooling System Library 25/56

30 Figure 26: Power developed by the shaft and heat exchanged At time = 150 sec, the compressor starts to operate, requiring a power of 1000 W. This additional power is then delivered by the engine shaft which modifies instantly the level of heat exchanged between the engine and the coolant. To understand the way the power absorbed by the compressor is computed, display the parameter popup of the condenser-compressor component as shown in Figure 27: Figure 27: Condenser-compressor parameter popup The condenser power parameter corresponds to the power released in the ambient air (P cond ). This power is used to compute the temperature of the air at the condenser outlet. The power absorbed by the compressor (P comp ) to make the condenser operate which is the power transmitted to the engine component and is computed as follows: P comp P cond = (4) 1 + COP The COP coefficient characterizes the performance of the system. Other auxiliaries and power consuming components can be taken into account such as the immersion heaters. This is illustrated in the following section. September 2004 Using the Cooling System Library 26/56

31 3.4. Influence of the immersion heaters component In the cooling system library, the user can find an immersion heater component whose icon is shown in Figure 28 below. Figure 28: Immersion heaters icon In some cooling system configurations, immersion heaters can be found. These components are often required in countries where the ambient temperatures are very low. For very low temperature operating conditions, the immersion heaters are used in the warm loop of the system to decrease the time needed for the coolant to reach its steadystate temperature in the system and at the same time, to warm more rapidly the inside of the vehicle by means of the heater core. The use of this component is now described. Update the system shown in Figure 24 by inserting the immersion heaters component in the system as shown in Figure 29. Figure 29: Cooling system with immersion heaters component The modification consists in inserting components 27, 28 and 29 as shown in Figure 29. The immersion heater component (27) is inserted in the heater core branch. Component 28 will be used to control the operating of the immersion heaters and component 29 is a summing junction from the signal category. This last component is linked to the compressor and to the immersion heaters component. This is used to sum the power absorbed by the auxiliaries (immersion heaters and compressor) and to pass this information to the engine component. In this case, the power developed by shaft will be modified due to not only the compressor but also the immersion heaters. As a result, the heat exchanged between the engine and the coolant will change as well. When the sketch is updated, fill in the parameters of components 27, 28 and 29 as described in the table below. September 2004 Using the Cooling System Library 27/56

32 Submodel name and type Belongs to category New simulation parameters 27 UD00 signal source Signal, control and observers Output at start of stage 1 = 1 Output at end of stage 1 = 1 Duration of stage 1 = 100 sec 28 CSIH1 immersion Cooling system Default parameters heaters 29 JUN3P summing junction Signal, control and observers Default parameters Then run a simulation for 300 seconds, still with a communication interval of 1 second and a tolerance of 1e-07. Component 28 is used to control the operating of the immersion heaters. As previously said, these often operate in cold start conditions. The parameters given in component 27 imply that the immersion heaters operate for 100 sec, at the start of the simulation and then switch off. Of course, in this case their operating state is arbitrarily controlled but it can easily be driven using the same method as for the radiator fan whose operating state is a function of the coolant temperature at the radiator outlet. To highlight the influence of the immersion heaters, compare the temperature of the coolant at the engine outlet with immersion heaters on and off by running two consecutive simulations: one with the parameters given in the table above and one by keeping the operating state of the immersion heaters to zero during the overall simulation. Plot the temperature evolution in the two cases as shown in Figure 30. In addition, switch off the condenser operating during the whole two simulations. Figure 30: Influence of the immersion heaters on the system The immersion heaters are switched on from the beginning of the simulation. This results in a faster increase in the coolant temperature and has an influence on the time needed to reach the steady-state temperature at the engine outlet. Reset the operating of the compressor as in the previous example and plot the power developed by the shaft in the engine and the heat exchanged between the engine and the coolant as a function of time as shown in Figure 31 below : September 2004 Using the Cooling System Library 28/56

33 Figure 31: Influence of the auxiliaries on the power developed by shaft and the heat exchanged between the engine and the coolant Three steps are taken into account during this simulation: - between time t = 0 to t = 100 sec, the immersion heaters are operating. To do so, they require a power of 1200 W. This power is then delivered additionally by the engine shaft. The consequence is a higher level of heat exchanged between the engine and the coolant. - At time t = 100 sec, the immersion heaters are switched off. Therefore, the power developed by shaft decreases of 1200 W, and the heat exchanged is modified consequently. - At time t = 150 sec, the compressor starts to operate and we observe the same phenomena as in the previous example. At this stage, it is helpful to have a look at the parameters of the immersion heaters component. Display the immersion heater component parameter popup as shown in Figure 32. Figure 32: Immersion heaters component parameters September 2004 Using the Cooling System Library 29/56

34 The equivalent area parameter is used to compute the volumetric flow rate in the component using Bernoulli s formula described below: Q v = A equiv 2 (5) p ρ Where A equiv is the equivalent area of the component, p is the pressure drop in the component and ρ is the density of the liquid. To compute the heat exchanged between the immersion heaters and the coolant and the power absorbed by the immersion heaters, the following parameters are used: - number of immersion heaters (n heat), - electric power needed for each immersion heater (p elec ), - global electric efficiency of the alternator used to make the immersion heaters work (g eff), - time constant (tau). The heat exchanged between the immersion heaters and the coolant is computed as follows: H n exch = heat p elec (6) The time constant tau is then used to take into account the time needed for the immersion heaters to warm up. The power absorbed by the immersion heaters is transmitted to the engine and is computed as follows: P H g abs = exch (7) eff As seen in this example, the operating of the compressor and the immersion heaters strongly influences the heat exchanged between the coolant and the engine. Another component of the cooling system library influences this heat exchanged. This is the EGR heat exchanger which special influence is studied in detail below. September 2004 Using the Cooling System Library 30/56

35 3.5. Influence of the EGR heat exchanger In the cooling system library, the user can find an EGR heat exchanger component whose icon is shown in Figure 33 below. Figure 33: EGR heat exchanger icon With current pollutant rejection standards, cars are sometimes equipped with an exhaust gas recirculation heat exchanger. This component has an impact on the cooling system in that: - it influences the coolant flow rate distribution in the system, - it is the location of a heat transfer between the coolant and the exhaust gas redirected to the combustion chamber, - its operating state tends to modify the thermal operating of the engine, that is to say, when the EGR heat exchanger is operating, hot gas is injected into the combustion chamber and as a result, the heat transferred from the engine to the coolant is increased. To show the influence of such a submodel, update the system shown in Figure 30 by inserting components 30, 31, 32 and 33 on the sketch, as shown in Figure 34 : Figure 34: Influence of the EGR heat exchanger on the system In some cooling system configurations, this component is located on a special branch found between the heater core and the engine. Remember that this is a general example and that the location of this component as well as the others depends on the car manufacturers technologies. The update consists in inserting components 30, 31, 32 and 33 and in connecting the EGR heat exchanger to the engine component. September 2004 Using the Cooling System Library 31/56

36 When this is done, set the parameters of the new components as shown in the table below: Submodel name and type Belongs to category New simulation parameters 30 TFN02 thermal-hydraulic Thermal-hydraulic Default parameters node 31 CSEG0 EGR heat Cooling system Default parameters exchanger 32 TFN01 thermal-hydraulic Thermal-hydraulic Default parameters node 33 TF223 thermal-hydraulic restriction Thermal-hydraulic Cross-sectional area = 600 mm 2 Then compare the evolution of the coolant temperature at the engine outlet with EGR operating and with EGR not operating as shown in Figure 35. Figure 35: Influence of the EGR heat exchanger on the coolant temperature at the engine outlet Obviously, the EGR operation implies a faster increase in the coolant temperature. As previously said, this is the result of the heat transfer from the hot gas going back to the combustion chamber to the coolant, and to the fact that the heat exchanged with the engine is increased. To understand what is happening, display the EGR heat exchanger parameter popup as shown in Figure 36: September 2004 Using the Cooling System Library 32/56

37 Figure 36: EGR heat exchanger parameter popup The equivalent area is used to compute the coolant volumetric flow rate in the EGR heat exchanger using Bernoulli s formula described in previous equation (5). In the EGR heat exchanger, the heat exchanged between the coolant and the hot gas is computed from the following parameters: - the effective mean pressure gain (k), - the maximum effective mean pressure (P max ), - the maximum engine rotary speed (ω max ), - the engine capacity (V), - a data table giving the heat exchanged as a function of the effective mean pressure and the engine speed. The effective mean pressure (P) is computed as follows: T P k V = (8) Where T is the engine torque. This is a global variable computed in the data components and retrieved in the EGR heat exchanger. Then, the heat exchanged between the hot gas and the coolant flowing into the component is computed from the effective mean pressure and the engine rotary speed which is also a global variable computed by the data components. Something important to say is that the exhaust gas recirculation happens under certain conditions which are taken into account in the EGR heat exchanger component. These conditions are controlling the EGR operating: EGR is operating if: Effective mean pressure < maximum effective mean pressure parameter and Engine rotary speed < maximum engine rotary speed parameter September 2004 Using the Cooling System Library 33/56