HERGOTT Julien & MOISY Alexandre 26-10 - 2015 EHRS modelling with GT-Suite European GT Conference 2015
Reduce CO2 by more than 50% in Europe, USA and China between 2005 and 2025 Average CO2 emissions from new passenger cars g/km 200 180 160 140 120 100 80 60 160 190 180 136 180 160 130 2005 2010 2015 2020 2025 Mid term Longer term 125 115 95 Long term 95? 89? 68-75? Time (year) USA CHN EUR Strong short-term and long-term pressure on CO 2 will create demand for fuel-saving technologies
While about one third of the fuel s energy is lost as heat through exhaust gas support the thermal system : Heat to Heat Fuel Power Friction reduction engine & gearbox Exhaust Heat Recovery Manifold (EHRM) Cabin heating in cold weather Mechanical Power Cooling heat Exhaust heat Exhaust Heat Recovery System (EHRS) generate on-board electricity: Heat to Power Seebeck effect Thermo-Electric Generation (TEG) Rankine cycle Exhaust Heat Power Generation (EHPG) Recovering Exhaust Heat to... * indicative values
Why EHRS improves fuel economy on an FHEV? On Hybrid vehicles, typical strategies will trigger Combustion engine start on : Wheel power demand Coolant temperature Typically 50 to 60 C Typical FHEV ICE Strategy Battery State of Charge 4
By improving engine warm-up on FHEVs, EHRS enables earlier and more frequently the pure Electric mode, thus improves significantly the fuel economy. Inputs WITHOUT EHRS Inputs WITH EHRS EV mode EV mode EV mode EV mode EV mode 70 70 Coolant temperature C 60 50 40 30 20 Coolant temperature C 60 50 40 30 20 10 10 0 0 200 400 600 800 0 0 200 400 600 800 EHRS allows Coolant loop to reach temperature threshold quicker Combustion engine running time is decreased Fuel mass consumed is lowered 5
How to estimate EHRS Benefits on customer vehicles? Evaluate EHRS Design Performance Estimate Impact on vehicle Requirement Measured on Component bench Predicted using CFD Measured on roller bench on prototype Problem Complex Expensive Not flexible Solution Build 1D Model of EHRS component for EHRS Performance prediction Build 1D model of EHRS environnent on vehicle for Impact prediction 6
Overview of System model Inputs Input Engine Exhaust EHRS Outputs Driving conditions Coolant Temperature ICE Trigger strategy Combustion heat Cooling Recovered heat Ambient conditions Cabin Engine running duty cycle Heating demand Cabin heat EHRS Configuration Ambient losses Ambient Fuel economy Simplified thermal model to assess EHRS impact on vehicle thermal behavior and fuel economy 7
Generating Engine outputs by using 1D Engine model 1D Engine Model with Cylinder Twall Solver allows to use Vehicle Inputs to estimate Combustion to Cooling heat transfer Engine Fuel efficiency Exhaust Enthalpy Engine - Input Engine Model Output Vehicle data (SCx, Mass, Gear ratio) Speed vs. Time (NEDC, FTP, Steady ) Hybrid strategy Heat rejected Power Air Mass flow Fuel Mass flow Exhaust Enthalpy 1D Engine model can be used Directly into the System Model as FRM Engine model To feed EngineState model with Heat, Fuel & Enthalpy Maps
Generating Engine outputs by using Customer data 1D Engine Model generates engine Outputs based on Vehicle data but Requires time to be built Not suitable for quick system evaluation (evaluation for customer) Bench data Analysis : engine outputs based on 0D Engine model Drawbacks Based on test data Not predictive Advantages Estimates EHRS Impact with customer data Uses widely available data Principle Calculation of Fuel to Heat efficiency & Calibration of Ambient Losses from bench transient profiles Data Analysis Engine Mass flow Coolant Temperature Material Masses Coolant Volume Ambient Temperature 9 Combustion Heat transfer Ambient Losses transfer
Cooling system Cooling Model Data Measured data Fluid & Components masses Pipes geometry Bench Data Radiator Heat power CAD estimated data Fluid mass distribution Heat transfer Area Cooling Model Ambient Losses TWall Solver on each pipe + Engine Case HT Area Cabin Model Cabin Volume Cabin ambient losses Engine Model Combustion Heat Rejection Engine Speed Pump flow 1D Cooling model is the key of Vehicle Model : translates EHRS design to understandable values From EHRS Gas To Coolant heat transfer to Coolant temperature improved heating Fuel economy through earlier combustion engine shut-off Cabin Comfort with higher increase in cabin temperature profile
EHRS 1D model Component Overview EHRS = liquid / gas heat exchanger Counter-flow Shell / Tube heat exchanger Integrated bypass to avoid engine coolant overheating when coolant reach control temperature Heat Recovery mode Bypass mode Coolant outlet Gas inlet Coolant inlet Bypass valve Gas outlet Bypass valve is closed Exhaust gases enters tubes and are cooled down by the engine coolant in the shell Bypass valve is opened Exhaust gases do not enter exchanger 11
EHRS 1D model Component Overview FECT build up complete exchanger specifications Type of tubes Corrugated Internal fins Number of tubes wax vacuum electric Bypass actuator type Wax actuator (opens when wax melts) Vacuum actuator (use vacuum network of engine) Electric actuator (use electrical command) For this study, we will use Finned tubes + vaccum actuator Title - Place - Date 12
EHRS 1D Model Thermal / mass balance Q U tttt Steady thermal balance Q cccc,ii Q bbbb Q cccc,ooo Q BB,ii : Inlet bypass heat losses Q BB,ooo : Outlet bypass heat losses Q cccc,ii : Inlet cone heat losses Q cccc,ooo : outlet cone heat losses Q U tttt : U-turn heat losses Q bbbb : Exchanger body heat losses Q ggg = Q cccc + ΣQ Steady mass balance llllll m eee m hx m llll m eee : exhaust inlet mass flow m HH : effective exchanger mass flow m llll : gas leakage through bypass m hh = m eee m llllll Q BB,ii Q BB,ooo The more accurate the assumptions, the easiest the calibration process 13
EHRS 1D model Way to model heat exchanger within GT Master/Slave Built-in template + Easy to build with experimental data + Scaling capability - Heat transfer maps include all losses - Out of range behavior? - No internal finned tube template Detailed Primitive flow & thermal components + Complete thermal balance + Better bypass modelling (can include leak) + Could be used for acoustic modeling - Require more time to build - Require CAD data Detailed model is well adapted for our application 14
EHRS 1D model Detailed model Detail model discretize heat exchanger using primitive template Flow pipes: gas and coolant path Thermal masses: wall / fins Thermal connections: convection / conduction / radiation FlowSplits: cones / fluid distribution Example of discretized exchanger A custom PipeFin template was created to avoid a (very) long model building task Simplified 1D thermal layout 1x gas + fin element Custom PipeFin template 15
EHRS 1D model Complete Layout External losses Exchanger Coolant flow Inlet cone Outlet cone Gas flow Bypass Thanks to user compounds, model map looks quite simple 16
EHRS 1D model Calibration workflow 3D to 1D geometry simplification Heat transfer area Hydraulic diameter CFD Calibration Gas and coolant HTM calibration Gas and coolant pressure drop calibration Synthetic gas bench Valve leakages calibration : gas pressure drop matching Engine bench: Driving cycle Transient / global validation 17
Experimental vs simulation NEDC: Temperature HEAT RECOVERY MODE BYPASS MODE High mass flow = low ΔT better consider heat rate Detailed model better predict gas temperature, especially in bypass mode 18
Experimental vs simulation NEDC: Heat rate Gas heat rate Detailed model better predict coolant and gas heat rate Detailed model can predict some «parasitic losses» (heat transfer into coolant when bypassed) Detailed model is more reliable in out of range mode 19 Coolant heat rate Experimental 1000 W 515 W Detailed 938 W 593 W Hx Master/Slave 657 W 647 W
System Model outputs & Results EHRS Heating Power Quicker Coolant heating Lower ICE Request Faster Cabin Heating Lower Fuel consumption Cabin Heating is improved with noticeable reduced time to reach target temperature Electric Load of Auxilliary heaters could be decreased : SOC savings Fuel Consumption is decreased by up to 8% on cold conditions In line with OEM claims & experimental test resuls 20
Conclusion A method has been developed to build a Transient 1D EHRS model under GT suite It can be used for various purpose Using customer input, predict how much heat can be extracted It can be embedded in a vehicle model to perform system model Comparison can be made with other exchanger model to compare performances This model can generate maps to feed an HxSlave model to perform scaling studies Simulation plateform is valuable to Simulate any powertrain and thermal management strategies Simulate any exhaust configuration and EHRS architectures Estimate benefits of our component on customer systems Title - Place - Date 21
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