Performance analysis of TEGs applied in the EGR path of a heavy duty engine for a Transient Drive Cycle Thermo-electric Group Department of Aeronautical and Automotive Engineering Prof. Richard Stobart Dr. Guangyu Dong Dr. Jing li Ms. M. Anusha Wijewardane 24 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 works 2
Background Approximate energy balance for IC engines at maximum power; Brake power (%) Coolant (%) Oil (%) Exhaust (%) Incomplete combustion (%) SI Engines 25-28 17-26 3-10 34-45 2-5 CI Engines 34-38 16-35 2-6 22-35 1-2 Guzzella L., Sciarretta A. Vehicle Propulsion Systems Introduction to Modelling and Optimization, ISBN-13 978-3-540-25195-8 Pressure losses in exhaust after treatment system have to be considered for heavy duty diesel engine applications Potential for enhancement of ICE performance using advanced engine techniques such as; downsizing, VVT, advance fuel injection, advanced boosting and etc are extremely limited Enhanced BSFC and thermal efficiencies can be achieved by energy recovery from exhaust gas and coolant 3
Background cntd Average fuel economy improvements from energy recovery systems; Thermo-dynamic cycles - 6-8% 1 Turbo-machines - 5-7% 2 Thermo-electric - 3-5% 3 TEGs; Direct heat to electricity converters Solid state Durable 1. Sandra, H., Stobart, R.K, Adam, C. and Peter, C. Energy Recovery Systems for Engines. SAE Technical Paper, 2008-01-0309, 2008 2. Turbocharger Facts, BorgWarner Turbo Systems, Specialists in Advanced Turbocharger Technology, Switzerland, 2009 3. Stobart, R.K., Wijewardane, M. and Allen, C. The potential for thermoelectric devices in passenger vehicle applications, SAE Technical Paper, 2010-01-0833, 2010 4
Objectives Simplifying a 3-D TEG model into a 1-D TEG model Heat recovery from the TEG and performance analysis of a heavy duty engine for a transient drive cycle Development of a component-in-the-loop (CIL) tool to analyze the performance of a TEG instrumented in an engine in real-time 5
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; Q H Heat rate at sink; 6 = αit H + KA(T H T Q H = αitl + KA(TH TL) + Non-dimensional Thermoelectric Figure of merit Z L ) 0.5I = 0.5I 2 α np σ K 2 2 R R L L Conversion efficiency ϕ = ( ) ( + ) T T 1 ZTavg 1 h IR T h int c TE Couple 1+ ZT avg + T T c h
Thermo-electric generator (TEG) 3-D model 3-D modeling of the TEG was performed using Star- CCM+ 6.02.009 TEM properties were defined with respect to Heat flow across the TEG heat exchanger commercially available Hi-Z TEMs 1-D GT-Power model was developed and validated based on the results obtained by the 3-D steady state model 7 TEG used for 3-D modeling
Thermo-electric generator (TEG) 1-D model cntd... Engine Model A Caterpillar medium-duty offhighway engine is used build and validate of a 1-D engine model. Engine modified for experimental purposes with: high pressure loop EGR system variable geometry turbine Caterpillar diesel engine test bench (VGT) 8
Thermo-electric generator (TEG) 1-D model cntd... Engine Model Configuration parameters are all measured from the real engine or from the engine datasheet. 9 1-D Engine model in GT-power
Thermo-electric generator (TEG) 1-D model cntd... 1-D TEG model TE material characteristics Total Seebeck Coefficient (μv / K) 375 Internal Electric Resistance (Ohm) 0.15 Thermal Conductivity of TE material (W/mK) 2.40 Thermoelectric Material Cross Sectional Area (mm^2) 4225 Thermoelectric Material Height (mm) 4 1-D TEG model is positioned in the EGR path Energy recovery of the TEG was obtained for the NRTC cycle 10
NRTC drive cycle: Analysis of the operation condition of EGR path 800 NRTC Cycle run of C6.6 Diesel Engine 700 600 Torque (N.m) 500 400 300 200 100 0 0 500 1000 1500 2000 2500 Speed (r/min) Operation points under NRTC cycle NRTC 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 engines 11
NRTC drive cycle: Mass flow and Temperature Distribution EGR gas temperature window Torque (N.m) 800 700 600 500 400 300 200 100 0 NRTC Cycle run of C6.6 Diesel Engine Window of operating points 0 500 1000 1500 2000 2500 Speed (r/min) Exhaust Temperature (K) EGR gas mass flow (g/s) 850 800 750 700 650 600 550 500 450 400 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 Torque (N.m) Mass flow window 0 100 200 300 400 500 600 Torque (N.m) Zone 1 Zone 2 Zone 3 Zone 1 Zone 2 Zone 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 of 10-40 g/s. 12
NRTC drive cycle: Transient Performance Analysis of the engine Temperature and mass flow under NRTC cycle The control algorithm of the engine was constructed based on the look-up tables in the test engine ECU "Automatic Shut-Off When Steady-State" was off for the dynamic characteristics and the transient behaviour simulation 13
Results: Availability and Power Generation The availability represents the maximum amount of energy that can be recovered from the EGR flow During the NRTC, the maximum power is about 170 W and average of 60W is achieved, 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 requirement per drive cycle 14
Results: TEG induced pressure loss 5 4 Pressure drop (kpa) 3 2 1 The maximum pressure drop caused by current TEG system is about 4 kpa, this is less than 10% of the pressure drop in the EGR path. This indicates that the EGR amount will be only be slightly affected by the current TEG system. 15 0 0 200 400 600 800 1000 1200 Time (s) Back pressure developed by the TEG over the NRTC cycle
Development of Real-Time Simulation Tool Component in the loop simulation through GT-Power with NI VeriStand NI 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 model in GT-Power Generate the Real Time (RT).dat file and convert to executable code through Veristand Add the virtual TEG in the CIL system Real time simulation for TEG system performance analysis Diagram of CIL experiment 17
Conclusions (1) Based on a 1 dimensional engine model and TEG model built up in GT-power environment, the operating condition of EGR path under the NRTC cycle was analysed: The EGR temperature and mass flow rate were estimated There is almost a linear relationship between the EGR temperature and engine load. The range of EGR mass flow rate is mainly within the range of 10-40 g/s. The variation of temperature, mass flow and energy availability under NRTC cycle was simulated. 18
Conclusions (2) Using the control parameters in the test engine ECU as the reference, a control algorithm was developed to run the GTpower model in transient mode. The power regeneration can be calculated accordingly. The maximum power is about 170 W, and it will decreases nearly to zero when the EGR valve is closed. The pressure drop caused by current TEG system is about 4 kpa, less than 10% of the total pressure drop in EGR path. 19
Future Works Component in the loop simulation through GT-power coupling with NI Veristand has great potential for the analysis of TEG performance Permits parametric studies of TEG system Allows fast optimization cycles using physical models of TEG 20
Thank you!