Study on Effects of Diesel Engine Cooling System Parameters on Water Temperature

JOURNAL OF CHINA ORDNANCEStudy on Effects of Diesel Engine CoolingSystem Parameters on Water TemperatureLUO Qing-guo(骆清国)' ,FENG Jian-tao( 冯建涛)2 ,LIU Guo-fu(刘国夫) ,CUI Yong(桂勇)'(1. Department of Mechanical Engineering, Academy of Amored Force Engineering, Bijing 100,0 China;2. Department of Vehieular Engineering, Amored Force Technology Insitute , Changchun 130117, Jilin, China)Abstract: A simulation model for a certain diesel engine coing system is set up by using CT-C0OL The backwaler tem-perature response in diferent operating conditions is simulated numerically. The eleets of single or multiple system parame-ters on the water tenperature are analyzed. The results show that, changing dfferet single parameters, the time taken forthe steady backwater temperature is diferent, but relatively short; and if multiple parameters are changed, the time will belonger. Referred to the thermal balance test, the simulation resuls are validated and provide a basis for the inelligent con-trol of the cooling system.Key Words: power machinery engineering; diesel engine ; cooling system; transient response ; simulationCLC Number: TK424Document Code: AArticle ID: 1673 002X( 2011 )03 0129-06vide a basis for intelligent control.Introduction1 Simulation Modeling for Diesel En-Diesel engine cooling system has been developedgine Cooling Systemto intelligent cooling system with the engine power in-crease'. The military vehicle engines are high power,1.1 Principle of Cooling Systemand their operating conditions are complex. The cool-The engine cooling system uses high and low tem-ing water temperature can not be controlled easily. Itsperature dual-circulation loop technology. Major com-control is a closed loop with nonlinear, time-varyingponents include diesel body, water pump, oil exchang-and large time lag'l，etc. Therefore, the coolant tem-er, high temperature exchanger, low temperature ex-perature overshoot and the slow adjustment processchanger, air cooler, expansion tank and correspondingarise easily, if its time-varying and large delay charac-pipes, as shown in Fig. 1. The high and low tempera-teristics are not considered accurately in the coolingture loops share the water pump'control strategies3. It has been a difficult problem forair 一rxpansion tankdevelopment of control strategy. To master the influ-waler pumpences of the system parameters on the coolant tempera-ture is significance to develop wonderful control sys-low temperature exchanger- oil exchangertems and ensure the engine run always in the best tem-air cooler ][ dise] engine )perature range.{ high lrmperature exchanger ]In this paper, a simulation model for the dieselengine cooling system is established by using GT-Fig. 1 Principle of cooling systemCOOL，and the cooling water temperatures in differentThe pump forces the cooling water to enter the oiloperation conditions are simulated numerically to pro- heat exchanger, and the cooling water passed the ex-中国煤化工Biography LUO Qing-guo( 1965 - ), male, professor, E-mail: luoqingguozgy@ yahoo.Received 2011-06-20CHCNM HG一129一JOURNAL OF CHINA ORDNANCE, 2011, Vol.7, No. 3changer is divided in two parts. One of them enters in-m'; p is the pressure in Pa; h is the heat transfer coef-to the body, head and then high temperature exchang-ficient in W/(m2.K); A. is the heat transfer area iner; another into the air cooler through the low tempera-m2; Tnud is the fluid temperature in K; T.an is the wallture exchanger, and mixes with the high temperaturetemperature in K; A is the flow cross-sectional area incirculating cooling water after cooling the charged air,m'; u is the boundary flow velocity in m/s; Cq is theand finally enters into the water pump to circulate' .surface friction coefficient; C, is the pressure loss coef-1.2 Mathematical Model of Pipeline Flowficient; D is the pipe's equivalent diameter in m.The flow model involves the simultaneous solution1.3 Simulation Model of Cooling Systemof the continuity, momentum and energy equations'5).According to the principle of cooling system, aThese equations can be solved in one dimension. Itsimulation model can be set up by using CT-COOL, asmeans that all quantities are averages across the flowshown in Fig. 2.direction. The primary solution variables are massengine slalusflow, density and total internal energy. The wholepipeline system is divided into many control volumes,highlemperalureand each pipe is divided into one or more volumes.These volumes are connected by boundaries. The sca-diesel engine中lar variables, such as the density, total internal ener-gy, pressure, temperature and total enthalpy, are as-. oil exchanger'water pumpsumed to be uniform in each volume and are calculatedat the center of the volume. The vector variables, suchas the mass flux, velocity and mass fraction fluxes, arecalculated in each boundary. The basic equations in-air coolerlow temperature总课喬肃clude the continuity ，enthalpy and momentum equa-exchangertions'5] .Fig.2 Simulation model of cooling systemContinuity equation :The high and low temperature exchangers heatdmtransfer coefficients can be calculated by using Nusselt=2in.(1)boundariesnumber"lEnthalpy equation:Nu = aRe'Pr' ,(4)d(pHV)=. E (mH)+v业 - h,(.m...).andJtboundarie(2)Mu=(告). Re=(凹),=(")Momentum equation :where L is the reference length in m; k is the fuid'sdi =dtthermal conductivity in W/(m.K); μ is the fuid's dy-namic viscosity in Pa.s; v is the fluid velocity in m/s;dpA+ E (mu)-4c,ml!sC,(号11)c, is the fluid's heat capacity in J/(kg. K).dx"he constant a and b can be determined by the(3heat exchanger experiments. The high and low temper-where m is the volume mass in kg; m is the boundaryature heat exchangers are plate types. Their main pa-mass flux in kg/s; ρ is the density in kg/m'; H is theramete中国煤化工Tab.2, respectively. .a= 1: temperature heat ex-total enthalpy in J/kg and H=e+上; e is the total in-JYH.CNMH G the low tmpratureternal energy per unit mass in J/kg; V is the volume inheat exchanger.-130-LUO Qing-guo, et al. / Study on Efects of Diesel Engine Cooling System Parameters on Water TemperatureTab.1 Parameters of high temperature radiator366itemparameterdimension L mmxD mmx H mm650x1 008x1169364-number of plate6:now rale qv. /(m'.h~')64兰362-plate spacing d/ mm3.十experimental data360-. simulation dataheat transfer area S/m20.22Tab.2 Parameters of low temperature radiator00 1000 1200 1400 1600180020002200n/(r . min-)dimension L mmxD mmxH mm340 x215 x 580Fig.4 Cooling water temperaturenumber of plale40-how rale qn/(m'.h-')14.4210-+ experimental data幽simulation dala2. s80一0.031客15020)2 Analyses for Simulation Results0-2.1 Verification for Simulation ModelThe thermal balance for the engine cooling system800 1000 1200 1400 16001800 2000 2200n/(r.min ")is tested in a test bench, as shown in Fig. 3. The ex-Fig.5 Thermal loss in low temperature radiatorperiment ambient parameters are 89. 1 kPa in pressure ,25 C in temperature, 40% in humidity, and external11.25circulating cooling water is used instead of cooling fan.10.00 tIn the experiment， the steady state engine parametersare measured only, and the transient state parametersare not measured for limited experiment conditions.7.50+ experimental dlata一simulation dala6.25 t00 1000 1200 1400 1600 1800 2000 2200n/{r . min')Fig.6 Pump flow rateture change when the diesel engine runs from a stablecondition to another. In order to ensure the previousoperation is steady, the simulation time is set longerFig.3 Test benchwhen the simulation under variable operation condi-The simulation and experiment results are com-tions. Changed the operation conditions and the colingpared，as shown in Fig.4-6. It can be seen that theysystem parameters at 3 000s, the efects of the enginecoincide with each other, and the simulation model isspeed, torque and external circulating water flow rateverified.on the outlet中国煤化Ianalyzed. Now,2.2 Analyses for Response of Cooling Systemthe transientYHC N M H Gsystem are dis-This paper only analyzes the water outlet tempera-cussed in four ditterent cases.JOURNAL OF CHINA ORDNANCE, 2011, Vol.7, No.31) The engine speed is 2 200 r/min. Change en-circulating water in the low temperature exchanger.gine torque from 458. 1 N.m to 1 726. 7 N.m at 3 000s,When the water flow increases, h●A increases first,as shown in Fig. 7.and then decreases, from 5 247.0 W/K at 3 000s to1 8006331.8 W/K at3 008 s and then to 6 240.0 W/K at .3865 s. The reason is the increases of water flow rate1 500and heat transfer coefficient and the decrease of the官1200water's dynamic viscosity with temperature". The heatdissipation capacity of the low temperature exchanger is900enhanced after the external circulating water flow in-600creases, and it makes the engine outlet water tempera-ture gradually deerease the low temperature exchanger's300 1380 2760 4140 5520 6900water temperature also fall, and the dynamic viscosityof water increase. According to Eq. (4), the transferFig.7 Torque vs. timecoefficient decreases.Fig. 10 shows that the oulet wa-The effect of torque on water temperature is shownin Fig.8. At 1 306 s, the engine reaches a stable con-ter temperature changes from 375.8 K at 3 000s to .dition of 2 200 r/min in speed and 458.1 N.m in369.9 K at 3865s, and it lasts 865 s.6 500torque. After increase of torque， the coolant takesmore heat quantity from the engine body. The water6 000temperature gradually increases from 337.2 K at 3 000 sto 375.8 K at 4 057 s. That is, the process lasts1 057 s, and the cooling system can reach a new steady弓5000-stateof2200r/mininspeedand1726.7N.mintorque. .38040001380 2760 4140 5520 6900360operating conditionFig.9 Effects of fow rate of external circulating water340onh.A of low temperature exchanger's external兰circulating watersteady state of first20-/380- -00360-2805 1380 2760 4140 5520 6 900Fig.8 Effects of torque on water temperature202) The engine speed is 2 200 r/min， and itstorque 1 726. 7 N.m. Change the low temperature ex-ternal eireulating water flow from 1 L/s to 1.28 L/s at2803 000 s.Fig. 10 Effects of low temperature external circulatingAs the flow increases, the flow rates of the inter-water flow on cooling water temperaturenal and external circulating water in the low tempera-ture exchanger increase and heat transfer coefficient:[H中国煤化工18 N.m. Change thechanges. Fig. 9 shows h.A, i. e. heat transfer coeffi-engineCN M H G200 r/ min at 3000s.cient multiplied by heat transfer area, of the external .The water pump is a mechanical pump connectedLUO Qing-guo, et al. 1 Sudy on Effects of Diesel Engine Cooling System Parameters on Water Temperaturewith the diesel engine crankshaft. The pump speed375changes in a certain gear ratio, and in turn the pumpflow rate changes， when the engine speed changes.345-Fig. 11 shows that the pump flow rate changes from兰330-9.051 L/sat 3000sto11.262 L/sat 3865s. Fig. 12shows that h.A of the internal cireulating water in the310low temperature exchanger changes with the pump flow300rom 10310 W/K at 3000s to 12964.7 W/K at 4211 s.13802760414055206900It make the heat capacity of the exchanger enhance. Inaddition, due to the engine speed increases, the heatFig. 13 Effects of engine speed on coolingcoolant removed by the coolant from engine increases.water temperatureBy these two effects， the outlet water temperature.3971.4 W/K at3000s to 5 247.0 W/K at 4 340 s.changes, as shown in Fig. 13, from 360.2K at 3000 sh.A of the internal circulating water in the low temper-to 371.4 K at4211 s, and it lasts 1 211 s.ature exchanger changes from 11 105.8 W/K at3 000 s12.0-to 13 335.0 W/K at 4 340 s，as shown in Fig. 15.Fig. 16 shows that the outlet water temperature changesfrom 370.5 K at 3000s to375.8 K at 4340s, and it。10.4 rlasts 1 340 s..6-5 500.8k4 500.13802760414055206900t/王4000Fig.11 Efects of engine speed on pump flow rate3 50013 50030001380 27604140 5520 6 90012 000/sFig.14 Effects of multiple parameters on h.A of exter-10 500nal circulating water in low temperature ex.9 000changer7 5006000513802760414055206 900￥10500Fig.12 Effects of engine speed on h.A of internal circu-lating water in low temperature exchanger90004) Change the engine speed from 1 800 rpm to2 200 rpm，the engine torque from 1 717.9 N.m to1 726. 8 N.m, and the external eirculating water flow中国煤化工from0. 722 L/sto 1 L/s, at 3 000s.Fig. 15ters on h.A of inter-Fig. 14 shows that h.A of the external circulating.YHC.N.M.H.G%ow temperature exwater in the low temperature exchanger changes from- 133JOURNAL OF CHINA ORDNANCE, 2011, Vol.7, No. 3torque changes only, it will take 1 057 s to reach a380steady state. If the engine speed changes only, it will360take 1 211 s to reach a steady state. And, if the condi-340tions and the water flow all change，the cooling systemwill need 1 340s to reach a steady state. It is the lon-320gest time to reach a steady state3003) In study on intelligent control systems, thmechanical water pump can be replaced with an elec-28051380 2760 4140 5520 6900tronically controlled pump which can not be affected byththe engine speed. In development of control strategies,Fig. 16 Effects of multiple parameters on coolingto make the outlet water temperature reach a steadywater temperaturestate quickly, the external eirculating water flow shouldIt can be seen that, if the external cireulating wa-be adjusted first according to engine operation condi-ter flow rate changes only，the system takes the shortesttions, then the water pump speed should be controlledtime to reach a steady state. The reason is， in thisaccording to the water temperature.case, the affected main parameter is the external cool-ing water flow rate in the low temperature exchanger. ItReferencesmakes the heat transfer coefficient of low temperature[1] HAN Shu, CAI Feng, LUO Qing-guo, et al. Researchexchanger change. And， the other parameters of theand development of cooling system in armored vehicle en-cooling system are less affected; the outlet water tem-gine [J]. Inter Combustion Engines, 2007, (5):5-8.perature reaches a steady state quickly. While the en-( in Chinese)gine speed changes, the cooling water flow rate chan-[2] DONG Chang-chun. The research for the network PIDges because the water pump is connected with thecontrol of the main engine cooling water temperature con-trol system[ D]. Shanghai: Shanghai M aritime Universi-diesel engine crankshaft. The outlet water temperaturety, 2005. (in Chinese)reaches a steady state slowly. If the engine operation[3WU Gui-tao, SUN Pei-ting. 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