A SIMULATION STUDY OF COOLING SYSTEM FOR HEAVY DUTY DIESEL ENGINE

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1 A SIMULATION STUDY OF COOLING SYSTEM FOR HEAVY DUTY DIESEL ENGINE Pranita Asul 1, Vino Kotebavi 1, Sanjeev Beekar 2, an Ashwini Mishra 2 1 Department of Mechanical Engineering, Amrita School of Engineering, Bengaluru, Amrita Vishwa Viyapeetham, Inia 2 Cummins Inia Office Campus, Balewai, Pune, Maharashtra , Inia Abstract. The main function of the cooling system is to control the temperature of the engine components an improve the performance of an engine. To know the flow an temperature istribution in the jacket cooling system for 6 cyliner iesel engine is analyze using 1 imensional metho by using GT-Suite 1D simulation software package. The present work employs 1D simulation of water jacket in GT-ISE to perform a comprehensive stuy of mass-flow an thermal istribution over the inlet of the cooling package of a selecte engine in several steay state operating points. The results show, that the suggeste preictive metho successfully captures the thermal effect of recirculation while reucing the necessity for calibration one by prototype testing. Keywors. GT-Suite, 1 Dimensional, Calibration, water-jacket. 1 INTRODUCTION The role of engine cooling system is to take away heat fast enough to keep the engine material temperature well below its melting point an increase the urability of engine [1]. Complexity of cooling system of a vehicle increases with the avancement of technology. Cooling system of an internal combustion engine involves a complex geometry of cooling jacket. Engine specification along with engine block shape an operating range etermine the cooling jacket layout. A cooling jacket is not only intene to carry away heat from engine, but also helps to accomplish the optimal operating temperature at the earliest. It is very ifficult to analyze the complete behavior of water jacket experimentally an theoretically, ue to complex geometries an flow paths [2]. Vehicle thermal management system ha fairly remaine constant from last few years. In this fiel primary targets are to achieve quick engine warm-up, avoiance of overheating or over cooling an temperature maintenance. However recently, the nee of improve efficiency ha riven higher eman. Also, the engine is esire to operate with less parasitic losses [3]. In actual practice, almost all parts of cooling circuit take part in heat transfer, in other phenomenon which influences the efficiency of cooling system. For example, pressure rop influence the flui flow rate, which etermine the convective heat transfer coefficient. Therefore, there are many physical phenomenon one coul moel in orer to capture the behavior of the system as thoroughly as possible [4]. The main objective of the present research is to prove the feasibility of a cooling system moel evelope in GT-Suite. GT-Suite is one-imensional simulation software which plays major role to reuce the lea time as well as overall cost. Flow moel use in GT-Suite base to solve the basic equations of thermoynamics an flui mechanics (generally, the Navier-Stokes equations). The Navier-Stokes equation is the continuity equation an law of conservation of momentum an energy equation. These equations are solve for each element of iscretise moel separately, either using explicit or implicit schemes [5]. Cooling system with special kin of water jacket is simulate. Due to the complexity of the cooling system it is ifficult to achieve the simulation results close to bench test [6]. Total temperature rise through water jacket has been measure an results were compare with test ata. However, one imensional cooling system thermal flui analysis enables the stuy of entire cooling system control an also optimization of piping but it oes not provie etaile flui flow analysis insie water jacket [7]. Coolant circuit consists of numerous components, an 1D thermal flui simulation is applie to stuy the temperature behavior of the coolant. For both normal an severe riving conitions automotive esigners shoul esign a robust engine cooling system [8]. However, the interaction of the all vehicle components can be very complex, such that, in many cases it is very * Corresponing author: k_vino@blr.amrita.eu; asul.pranita@gmail.com The Authors, publishe by EDP Sciences. This is an open access article istribute uner the terms of the Creative Commons Attribution License 4.0 (

2 ifficult to preict how a new thermal management component may interact with entire vehicle power train, especially in terms of fuel economy an emission control. The challenge is to evelop simulation moels that can help to optimize the vehicle thermal management strategy in effort to fin out a proper cost/benefit ratio for new components an control strategy [9]. Prior to the oing any engine water jacket moifications, the coolant flow characteristics such as pressure rop, water jacket wall temperature an velocity must be ientifie an fixe carefully [11]. Internal combustion engines are also classifie accoring to cooling system, air coole engines an water coole engines. In later system water is use as a heat transfer meium which is preferre over air because of its higher specific heat capacity, ensity an thermal conuctivity. It allows water to transfer heat to greater istance compare to less volumetric flow an reuce temperature ifference [12]. Aequate temperature management strategies will be beneficial to achieve high NOx conversion level in after treatment system. Splitcooling system an other thermal management measures have potential to reuce CO 2 an increase exhaust temperature uring col start simultaneously [13]. 2 METHDOLOGY In this paper one-imensional moel of cooling system for iesel engine has been evelope in GT-Suite software. The performance preiction through any tool requires so, require input parameters fe to the tool. However, care shoul be taken with input ata to get preiction near to test ata. Figure 1 illustrates the methoology followe to evelop preictive moel. Inputs require To evelop 1 D moel main requisites are: 1) CAD moel of an engine 2) Performance etails of components 3) Thermostat hysteresis curve 4) Bounary conition ata Fig. 1. Methoology aopte to evelop 1 D simulation network CAD moel of an engine hea an block importe in to the Spaceclaim software to extract cooling jacket. Spaceclaim is the pre-processing tool of GT-Suite. Which is use to efine the flow area of coolant. Then flow path of coolant through engine hea an block has been extracte [figure 2] an converte it in to the flow splits. Whole core spit ivie in to six ifferent flow spilt each one for one cyliner an one inlet to the water jacket an outlet from the water jacket to the thermostat shown in figure 2. Heat transfer coefficient (HTC) taken from the 3D CFD (Computational Flui Dynamics) moel an temperature bounary conitions are taken from the engine performance moel which was evelope in GT-Power. So again, the accuracy of the complete cooling system moel results is epen on the accuracy of engine performance (GT-Power) moel an the 3D CFD HTC results. 2

3 Thermostat Inlet Pump Fig. 2. Extracte core of an engine water jacket 2.1. Simulation metho an Cooling Circuit theory GT-Suite is base on one-imensional tool which represents the flow an heat transfer in piping an other components of a cooling system. Several researchers have use GT-Suite to simulate engine cooling system, lube system etc. [14, 15]. This tool allows moeling the integration of all heat management activities arising in engine an vehicle evelopment. Also, it provies flexibility to moel for avance concepts an has built in vehicle/engine simulation calculation of thermal loas uner ifferent conitions or uner any riving cycle. Because of these avantages GT-Suite provies powerful moel builing facility an reuces user efforts. Implicit solver is use to solve the Navier-Stokes equation for flow splits to escribe how the temperature, pressure an ensity of a moving flui are relate. For the heat transfer calculation Colburn analogy is use. Always it's not possible to get satisfactory results by Reynols analogy. Thus, Colburn empirically moifie Reynol s analogy which is given by equation, introuces the j-factor. use to valiate the analytical results are Limiting Ambient Temperature (LAT) an Coolant out temperature. LAT is efine as the maximum allowable ambient temperature to which the vehicle cooling system can work without failure. For the preiction of a stanar cooling system performance of an engine at least two circuits has to be consiere. Primary circuit through which heat is taken away from the engine thermal masses to the coolant through convective heat transfer an secon is the cooling moule in the vehicle where heat is rejecte to the air passing over raiator. Cooling circuit analysis inclues, water pump, water jacket, thermostat, raiator an fan. Heat transfer from oil to coolant in oil cooler system has moelle using single flow split, where heat rate input from oil to coolant is given as single value of input which has obtaine from the etaile analysis of oil cooler. This extraction of heat from oïl increases coolant temperature but it oes not affect much on coolant working as that of it is much effective for oil to release heat to coolant which helps to retain oil properties by maintaining oil temperature in limit. CAC has moelle in the same way as that of oil cooler. Moelling of the cooling components has an avantage of optimizing each component iniviually irrespective to whole complex system. A simplifie iagram of the cooling circuit is represente in Figure 3. (2.3.a) Where, f is the friction factor ( ) ( ) (2.3.b) The focus of the stuy is to evelop a cooling system moel with close loop incluing unerhoo components to preict performance of the cooling system an valiate the results with test ata. This work will reuce the number of tests thereby saving cost, time an efforts involve. The most important parameters Fig. 3. Scheme of the cooling circuit A wax thermostat has been use, in which opening of thermostat is temperature boune. If the coolant temperature is below 82 C, coolant flows through bypass valve an again circulates to the engine block through pump. To accommoate bypass connection, there are two interepenent thermostat valves namely, 1) Master thermostat an 2) Slave thermostat. The master 3

4 thermostat valve is connecte to the raiator an slave thermostat valve by passes the coolant to the pump without flowing through the raiator. To compare test ata arrangement has been one to keep thermostat in fully open conition irrespective of the coolant temperature. Fan has been moelle with rive ratio of 1.1 an it is engage at any flow conition to valiate the results with test ata. The steay state analysis has been performe for engine cooling system an methoology valiate experimentally. The eviation between the test results an analytical results foun reasonable. 2.2 Engine Testing The objective of engine testing was to valiate simulation tool which has been evelope for cooling system performance preiction an also to test the behavior of cooling system of an engine in worst case conitions. The combination of two ifferent conitions such as rate spee an peak torque were use in testing to unerstan the effect of performance parameters on components on the en results. The etails of combination of testing parameters an components are mentione in Table 1. Vehicle level testing has been performe to test the behavior of cooling system at worst operating conitions; engine teste at rate spee an peak torque conitions. Thermostat has been kept at fully open conition an fan at fully engage conition with engine irrespective of the coolant temperature. Table 1. Combination use for cooling trials Spee Torque Engine 180 hp 180 hp Make Cummins Cummins Thickness Raiator Fin Pitch (fpi) Core Size 785 X X 48 mm 785 X X 48 mm Pulley ratio Fan Blae Diameter (mm) The parameters of interest uring testing are engine water inlet temperature, engine water outlet temperature before raiator or top tank temperature an ambient temperature to calculate LAT. (1) = Ambient temperature 3 RESULTS AND DISCUSSION The moel is prepare to solve the steay state conition. The simulation results were compare with test results. It is inferre that, the simulation allows quick calculation an iminutive amount of time to complete the simulation. The calculations can be accelerate with appropriate selection of the initial conitions (temperature of particular parts, system pressure). In our simulation, we focuse on unfavorable cases where, unerhoo cooling circuit is expose to the highest loa. Table 2 represents the comparison between simulation an test results. There is aroun +/-2% eviation in results. The present moel is over preicting the coolant out temperature for rate spee as well as for torque conition. Such results may be owe to the assumption of constant temperature of thermal masses expose to combustion gases for one engine spee as well as it has consiere that heat transfer coefficient is same over all range of temperature. Consiering the equation (2), the heat transfer coefficient is also epens on the thermos physical properties as well as on the geometrical properties, namely hyraulic iameter an velocity. ( ) (2) Apart from this also, have to consier the sensitivity error of the sensors an man-mae. Table 2. Comparison of test an simulation results Sr. N o. 1 Paramete rs Ambient Temperat ure 4 LAT Limit Test conition Torq Spee ue Simulation Spee Torq ue 21~ UCL < LCL spee> Torque> 41 All the values are expresse in Degree ( C) Where, LAT is limiting ambient temperature = Reference temperature of coolant TTT= Top tank temperature 4

5 4 CONCLUSIONS In the present paper a steay state analysis has been performe for six cyliner iesel engine cooling system using GT-Suite 1D simulation software package. The result illustrates that, the maximum eviation between simulation an test result is nearly +/-2%. The accuracy of the propose metho is epen on the accuracy of the components characteristic in the cooling system as well as on the operating point of a components. It also inferre that, operating point for pump an fan is falling within characteristics ata points. Conclusively, this kin of simulation reuces the require time compare to the 3D CFD simulation, as well as efforts an cost require for testing, the accuracy of the results are also in acceptable range. So, such stuies will be helpful to reuce analysis time an overall cost. Further, this moel can be moifie to take in account some more components such as conenser, cabin-heater etc. which can affect the cooling system. In future, this moel can be couple with engine moel an the effect of cooling system, on performance parameters like bsfc (brake specific fuel consumption), bmep (brake mean effective pressure), gmep (gross mean effective pressure) an torque of an engine can be observe with running moel in uty cycle which will help in unerstaning the behavior of an engine cooling system as well as engine performance in transient way. Furthermore, GT-Suite is capable of builing complete virtual moel of a complete vehicle, from cooling system components, transmission system, accessories an tire. Acknowlegements Authors are immensely grateful to Cummins Inia Pvt. Lt. for proviing necessary facilities to carry out the present research work. We also wish to acknowlege the valuable guiance an encouragement from the Director, Hea of the Department of Mechanical Engineering an teachers, Amrita school of engineering, Bangalore, uring the work. Acronyms GT- Gamma Technology GT-ISE GT- Integrate Simulation Environment 1D- One Dimensional HTC- Heat Transfer Coefficient LAT- Limiting Ambient Temperature UCL- Upper Cooling Limit LCL- Lower Cooling Limit BSFC- Brake Specific Fuel Consumption BMEP- Brake Mean Effective Pressure GMEP - Gross Mean Effective Pressure References 1. Umekar, Manvenra M., an D. Govinaraj., No SAE Technical Paper, (2011). 2. Mulemane, Aitya, an Ravinra Soman, No SAE Technical Paper, (2007). 3. Shutty, John, Wolfgang Wenzel, Michael Becker, Stephen Bohan, an Glenn Kowalske, No SAE Technical Paper, (2013). 4. Minovski, Blago B., an Lennart Lofahl, No SAE Technical Paper, (2014). 5. Bolehovský, Onřej, an Jan Novotný, Journal of Mile European Construction an Design of Cars 13, no. 3 (2015): Soujanya, C., an V. Sunaram., No SAE Technical Paper, (2015). 7. Nessim, Walee, F. Zhang, Zhao Changlu, an Zhu Zhenxia, In International Conference on Mechanical Engineering an Material Science (MEMS 2012), Shanghai, Dec, pp (2012). 8. Masjuki, H. H, Engineering e-transaction (ISSN ) 7, no. 2, pp (2012) 9. Keller, Philip, Wolfgang Wenzel, Michael Becker, an Josh Roby, No SAE Technical Paper, (2010). 10. Kotebavi, V., Shetty, D an Sahu, D, Pollution Research Volume 35, Issue 1, Pages (2016) 11. Qasemian, Ali, an Ali Keshavarz, Tehnički vjesnik 23.1: pp (2016) 12. Umekar, Manvenra M., an D. Govinaraj, No SAE Technical Paper, (2011). 13. Honarar, Sharareh, et al., No SAE Technical Paper, (2011). 14. Mayer, A., et al. Engine intake throttling for active regeneration of iesel particle filters. No SAE Technical Paper, Seier, Geral, et al., No SAE Technical Paper, (2001). FPI- Fins per inch 5