Performance analysis of TEGs applied in the EGR path of a heavy ...

Performance analysis of TEGs applied in theEGR path of a heavy duty engine for aTransient Drive CycleThermo-electric GroupDepartment of Aeronautical and Automotive EngineeringProf. Richard StobartDr. Guangyu DongDr. Jing liMs. M. Anusha Wijewardane24 th October 2011 – GT-Suite Conference

Outline• Background• Objectives• Introduction to 1-D TEG modeling equations• C6.6 engine and thermo-electric generator (TEG) 1-D model• NRTC drive cycle• Results• Development of a Real-Time (RT) Simulation Tool• Conclusions• Future works2

Background• Approximate energy balance for IC engines at maximum power;Brake power(%)Coolant (%) Oil (%) Exhaust (%) Incompletecombustion (%)SI Engines 25-28 17-26 3-10 34-45 2-5CI Engines 34-38 16-35 2-6 22-35 1-2Guzzella L., Sciarretta A. Vehicle Propulsion Systems – Introduction to Modelling and Optimization, ISBN-13 978-3-540-25195-8Pressure losses in exhaust after treatment system have to be considered forheavy duty diesel engine applications• Potential for enhancement of ICE performance using advanced enginetechniques such as; downsizing, VVT, advance fuel injection, advancedboosting and etc are extremely limited• Enhanced BSFC and thermal efficiencies can be achieved by energyrecovery from exhaust gas and coolant3

Background cntd…Average fuel economy improvementsfrom energy recovery systems;• Thermo-dynamic cycles - 6-8% 1• Turbo-machines - 5-7% 2• Thermo-electric - 3-5% 3TEGs;• Direct heat to electricity converters• Solid state• Durable1. Sandra, H., Stobart, R.K, Adam, C. and Peter, C. Energy Recovery Systems for Engines. SAE Technical Paper, 2008-01-0309,20082. Turbocharger Facts, BorgWarner Turbo Systems, Specialists in Advanced Turbocharger Technology, Switzerland, 20093. Stobart, R.K., Wijewardane, M. and Allen, C. The potential for thermoelectric devices in passenger vehicle applications, SAETechnical Paper, 2010-01-0833, 20104

Objectives• Simplifying a 3-D TEG model into a 1-D TEG model• Heat recovery from the TEG and performance analysis of aheavy duty engine for a transient drive cycle• Development of a component-in-the-loop (CIL) tool to analyzethe performance of a TEG instrumented in an engine in real-time5

Introduction to 1-D TEG modeling equations• Voltage across the external load;V total = VSeebeck- Vresist;VSeebeck= αnp(TH- TL);Vresist=• Power generated by a TE-couple;P total = IVtotal• Heat rate at source;QH• Heat rate at sink;6=αITH+KA(TH− TQ H = αITL+ KA(TH− TL)+Non-dimensionalThermoelectricFigure of meritZL) − 0.5I=0.5I2α npσK22RRLLConversionefficiencyϕ =( ) ( + − )T − T 1 ZTavg1hIRThintc⎛⎜⎝TE Couple1+ZTavg+TTch⎞⎟⎠

Thermo-electric generator (TEG) 3-D model• 3-D modeling of the TEGwas performed using Star-CCM+ 6.02.009• TEM properties weredefined with respect toHeat flow across the TEG heat exchangercommercially available Hi-ZTEMs• 1-D GT-Power model wasdeveloped and validatedbased on the resultsobtained by the 3-D steadystate model7TEG used for 3-D modeling

Thermo-electric generator (TEG) 1-D model cntd... Engine ModelA Caterpillar medium-duty offhighwayengine is used buildand validate of a 1-D enginemodel.Engine modified forexperimental purposes with:‣ high pressure loop EGRsystem‣ variable geometry turbineCaterpillar diesel engine test bench(VGT)8

Thermo-electric generator (TEG) 1-D model cntd... Engine ModelConfiguration parameters are all measured from the real engine or from the enginedatasheet.91-D Engine model in GT-power

Thermo-electric generator (TEG) 1-D model cntd...1-D TEG model TE material characteristicsTotal SeebeckCoefficient (μV / K) 375Internal ElectricResistance (Ohm) 0.15Thermal Conductivity ofTE material (W/mK) 2.40Thermoelectric MaterialCross Sectional Area(mm^2) 4225Thermoelectric MaterialHeight (mm) 4‣ 1-D TEG model is positioned in the EGR path‣ Energy recovery of the TEG was obtained for the NRTC cycle10

NRTC drive cycle: Analysis of the operation condition of EGR path800NRTC Cycle run of C6.6 Diesel Engine700600Torque (N.m)50040030020010000 500 1000 1500 2000 2500Speed (r/min)Operation points under NRTC cycleNRTC is a transient driving cycle‣ Developed by the US EPA in cooperation with the EU authorities‣ For mobile non-road diesel engines‣ Used for emission certification/type approval of non-road engines11

NRTC drive cycle: Mass flow and Temperature DistributionEGR gas temperature windowTorque (N.m)8007006005004003002001000NRTC Cycle run of C6.6 Diesel EngineWindow of operating points0 500 1000 1500 2000 2500Speed (r/min)Exhaust Temperature (K)EGR gas mass flow (g/s)8508007507006506005505004504007060504030201000 100 200 300 400 500 600Torque (N.m)Mass flow window0 100 200 300 400 500 600Torque (N.m)Zone 1Zone 2Zone 3Zone 1Zone 2Zone 3• An approximately linear relationship between the EGR temperature and engine load.• The figure of EGR mass flow rate shows that the range is mainly within the range of10-40 g/s.12

NRTC drive cycle: Transient Performance Analysis of the engineTemperature and mass flow under NRTC cycle• The control algorithm of the engine was constructed based on the look-up tables inthe test engine ECU• "Automatic Shut-Off When Steady-State" was off for the dynamic characteristics andthe transient behaviour simulation13

Results: Availability and Power Generation• The availability represents the maximum amount of energy that can be recoveredfrom the EGR flow• During the NRTC, the maximum power is about 170 W and average of 60W isachieved, but will decrease dramatically when the EGR valve getting closed• 8TEM-TEG installed in the EGR path is able to save, 0.06% of total fuel requirementper drive cycle14

Results: TEG induced pressure loss54Pressure drop (kPa)321• The maximum pressure drop caused by current TEG system is about 4 kPa, this isless than 10% of the pressure drop in the EGR path.• This indicates that the EGR amount will be only be slightly affected by the currentTEG system.1500 200 400 600 800 1000 1200Time (s)Back pressure developed by the TEG over the NRTC cycle

Development of Real-Time Simulation ToolComponent in the loop simulation through GT-Power with NI VeriStandNI VeriStand is a software environment for real-time testing applications.• Helps configure a multicore-ready real-time engine to execute• Run the TEG model in real time and predict the energy recovery process.• Reduce the experimental cost and accelerate the TEG system optimization.16

Development of Real-Time Simulation Tool• Create TEG 1-D modelin GT-Power• Generate the Real Time(RT) .dat file andconvert to executablecode through Veristand• Add the virtual TEG inthe CIL system• Real time simulation forTEG systemperformance analysisDiagram of CIL experiment17

Conclusions (1)Based on a 1 dimensional engine model and TEG model built upin GT-power environment, the operating condition of EGR pathunder the NRTC cycle was analysed:‣ The EGR temperature and mass flow rate were estimated‣ There is almost a linear relationship between the EGRtemperature and engine load.‣ The range of EGR mass flow rate is mainly within the rangeof 10-40 g/s.‣ The variation of temperature, mass flow and energyavailability under NRTC cycle was simulated.18

Conclusions (2)‣ Using the control parameters in the test engine ECU as thereference, a control algorithm was developed to run the GTpowermodel in transient mode.‣ The power regeneration can be calculated accordingly. Themaximum power is about 170 W, and it will decreases nearlyto zero when the EGR valve is closed.‣ The pressure drop caused by current TEG system is about 4kPa, less than 10% of the total pressure drop in EGR path.19

Future Works‣ Component in the loop simulation through GT-power couplingwith NI Veristand has great potential for the analysis of TEGperformance‣ Permits parametric studies of TEG system‣ Allows fast optimization cycles using physical models of TEG20

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