EHRS modelling with GT-Suite European GT Conference 2015

HERGOTT Julien & MOISY Alexandre 26 - 10 - 2015

Reduce CO2 by more than 50% in Europe, USA and China between 2005 and 2025

Strong short-term and long-term pressure on CO2 will create demand for fuel-saving technologies

Average CO2 emissions from new passenger cars

USA

CHN

EUR

Time (year)

2005 2025 Long term

g/km

80

180

100 120

140

60

160

2020 Longer term

68-75 ?

95 ? 89 ?

200

2015 Mid term

2010

160

190 180

136

160

180

130 125

95

115

… While about one third of the fuel’s energy is lost as heat through exhaust gas

* indicative values

… support the thermal system : Heat to Heat

… generate on-board electricity: Heat to Power

Cooling heat

Cabin heating in cold weather Friction reduction engine & gearbox

Exhaust Heat Recovery Manifold (EHRM)

Exhaust Heat Recovery System (EHRS)

Thermo-Electric Generation (TEG)

Exhaust Heat Power Generation (EHPG)

Seebeck effect Rankine cycle

Recovering Exhaust Heat to ...

Mechanical Pow

er

Fuel Power

Exhaust heat

Why EHRS improves fuel economy on an FHEV?

4

On Hybrid vehicles, typical strategies will trigger Combustion engine start on :

Typical FHEV

ICE Strategy

Battery State of Charge

Wheel power demand

Coolant temperature

Typically 50 to 60°C

Inputs

Inputs

5

By improving engine warm-up on FHEVs, EHRS enables earlier and more frequently the pure Electric mode, thus improves significantly the fuel economy.

0

10

20

30

40

50

60

70

0 200 400 600 8000

10

20

30

40

50

60

70

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

EV mode EV mode EV mode EV mode EV mode

WITHOUT EHRS WITH EHRS

Coo

lant

tem

pera

ture

°C

Coo

lant

tem

pera

ture

°C

How to estimate EHRS Benefits on customer vehicles ?

6

Requirement

• Evaluate EHRS Design Performance

⇒Measured on Component bench ⇒Predicted using CFD

• Estimate Impact on vehicle

⇒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

Outputs

Coolant Temperature

Fuel economy

Engine running duty cycle

Overview of System model

7

Exhaust

Cooling Recovered heat

Combustion heat

Ambient losses

EHRS

Cabin heat

Ambient

Cabin

Engine

Simplified thermal model to assess EHRS impact on vehicle thermal behavior and fuel economy

Inputs

• Driving conditions

• ICE Trigger strategy

• Ambient conditions

• Heating demand

• EHRS Configuration

Input Output

• Vehicle data (SCx, Mass, Gear ratio)

• Speed vs. Time (NEDC, FTP, Steady…) • Hybrid strategy

Generating Engine outputs by using 1D Engine model

Engine - Input • Heat rejected Power

• Air Mass flow • Fuel Mass flow

• Exhaust Enthalpy

Output Engine Model

1D Engine model can be used

⇨ Directly into the System Model as FRM Engine model

⇨ To feed EngineState model with Heat, Fuel & Enthalpy Maps

1D Engine Model with Cylinder Twall Solver allows to use Vehicle Inputs to estimate ⇨ Combustion to Cooling heat transfer ⇨ Engine Fuel efficiency ⇨ Exhaust Enthalpy

Generating Engine outputs by using Customer data

9

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

Material Masses

Coolant Volume

Ambient Temperature

Data Analysis

Engine Mass flow

Coolant Temperature

Combustion Heat transfer

Ambient Losses transfer

• Measured data Fluid & Components masses Pipes geometry • Bench Data Radiator Heat power • CAD estimated data Fluid mass distribution Heat transfer Area

Cooling Model Data

• Combustion Heat Rejection • Engine Speed – Pump flow

Engine Model

• Cabin Volume • Cabin ambient losses

Cooling system

Ambient Losses TWall Solver on each pipe + Engine Case HT Area

Cabin Model Cooling Model

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 = liquid / gas heat exchanger Counter-flow Shell / Tube heat exchanger

Integrated bypass to avoid engine coolant overheating when coolant reach control temperature

EHRS 1D model Component Overview

11

• 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

Gas inlet

Gas outlet

Coolant inlet

Coolant outlet

Bypass valve

Heat Recovery mode Bypass mode

FECT build up complete exchanger specifications Type of tubes

Corrugated Internal fins

Number of tubes Bypass actuator type

Wax actuator (opens when wax melts) Vacuum actuator (use vacuum network of engine) Electric actuator (use electrical command)

EHRS 1D model Component Overview

Title - Place - Date 12

vacuum wax electric

For this study, we will use Finned tubes + vaccum actuator

EHRS 1D Model Thermal / mass balance

13

The more accurate the assumptions, the easiest the calibration process

Steady thermal balance • �̇�𝐵𝐵,𝑖𝑖 : Inlet bypass heat losses • �̇�𝐵𝐵,𝑜𝑜𝑜 : Outlet bypass heat losses • �̇�𝑐𝑜𝑖𝑐,𝑖𝑖 : Inlet cone heat losses • �̇�𝑐𝑜𝑖𝑐,𝑜𝑜𝑜 : outlet cone heat losses • �̇�𝑈−𝑜𝑜𝑡𝑖 : U-turn heat losses • �̇�𝑏𝑜𝑏𝑏 : Exchanger body heat losses

�̇�𝒈𝒈𝒈 = �̇�𝒄𝒄𝒄𝒄 + 𝚺�̇�𝒄𝒄𝒈𝒈𝒍𝒈 Steady mass balance • �̇�𝑐𝑒𝑒 : exhaust inlet mass flow • �̇�𝐻𝑒 : effective exchanger mass flow • �̇�𝑙𝑐𝑙𝑙 : gas leakage through bypass

�̇�𝒉𝒉 = �̇�𝒍𝒉𝒉 − �̇�𝒄𝒄𝒈𝒈𝒍𝒈

�̇�𝑈−𝑜𝑜𝑡𝑖

�̇�𝑐𝑜𝑖𝑐,𝑜𝑜𝑜 �̇�𝑐𝑜𝑖𝑐,𝑖𝑖

�̇�𝐵𝐵,𝑖𝑖 �̇�𝐵𝐵,𝑜𝑜𝑜

�̇�𝑏𝑜𝑏𝑏

�̇�𝑐𝑒𝑒

�̇�𝑒𝑒

�̇�𝑙𝑐𝑙𝑙

EHRS 1D model Way to model heat exchanger within GT

14

Master/Slave Built-in template

Detailed Primitive flow & thermal components

+ Easy to build with experimental data + Scaling capability

+ Complete thermal balance + Better bypass modelling (can include leak) + Could be used for acoustic modeling

- Heat transfer maps include all losses - Out of range behavior ? - No internal finned tube template

- Require more time to build - Require CAD data

Detailed model is well adapted for our application

EHRS 1D model Detailed model

15

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

A custom PipeFin template was created to avoid a (very) long model building task

Custom PipeFin template

Simplified 1D thermal layout 1x gas + fin element

Example of discretized exchanger

EHRS 1D model Complete Layout

16

Thanks to user compounds, model map looks quite simple

Bypass

External losses

Exchanger

Inlet cone Outlet cone

Gas flow

Coolant flow

EHRS 1D model Calibration workflow

17

3D to 1D geometry simplification • Heat transfer area • Hydraulic diameter

Engine bench: Driving cycle • Transient / global validation

Synthetic gas bench • Valve leakages calibration : gas pressure drop matching

CFD Calibration • Gas and coolant HTM calibration • Gas and coolant pressure drop calibration

Experimental vs simulation NEDC: Temperature

18

Detailed model better predict gas temperature, especially in bypass mode

HEAT RECOVERY MODE BYPASS MODE

High mass flow = low Δ𝑇 better consider heat rate

Experimental vs simulation NEDC: Heat rate

19

• 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

Gas heat rate Coolant heat rate Experimental 1000 W 515 W Detailed 938 W 593 W Hx Master/Slave 657 W 647 W

20

System Model outputs & Results

Quicker Coolant heating

Lower ICE Request

Faster Cabin Heating

EHRS Heating Power

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

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

Conclusion

Title - Place - Date 21

THANK YOU FOR YOUR ATTENTION !!