Thermoelectric Conversion of Waste Heat to Electricity in an IC Engine Powered Vehicle

Principal Investigator: Harold Schock

Prepared by:Harold Schock, Eldon Case, Jonathan D’Angelo, Andrew Hartsig, Tim Hogan,

Mercouri Kanatzidis, James Novak, Fang Peng, Fei Ren,Tom Shih, Jeff Sakamoto, Todd Sheridan, Ed Timm

08/15/2007

Supported By: Acknowledgement: ONR support US Department of Energy under MURI Program Energy Efficiency Renewable Energy (EERE) Mihal Gross, Project Monitor John Fairbanks and Samuel Taylor, Contract Monitors

IOWA STATE

UNIVERSITY

Implementation of a Thermoelectric Generator with a Cummins ISX Over-the-Road Powerplant

Engine-TEG Simulation and Experimental Verification

MSU / Cummins

• Complete engine system- f(x,t)

• Temperatures and heat flux

• EGR energy

• Energy in exhaust (T, P, m)

• Turbine work, inlet/outlet temperatures

3D CFD Analysis

Iowa State / MSU

• Couple and Module Issues Convection and radiation between

legs with and without insulation Current distribution, Joule heating,

Heat fluxes

• Electrical energy production

• Unsteady heat transfer analysis to and from modules (3D, pulsatile, comp.)

TEG Design and Construction

MSU/JPL

• Generator design • TEG materials selection • Mechanical and TE material propertycharacterization including Weibullanalysis • FEA analysis • Leg and module fabrication methods

6 Cyl. Engine Test Data

Cummins

P2 - Single cylinder +TEG Demo

MSU

Systems for Utilizationof Electrical Power Recovered

MSU

• Design of electrical energy conditioning and utilization system

• Control system design and construction

• Inverter, Belt Integrated Starter-Generator Selection

Goals and ObjectivesGoals and Objectives� Using a TEG, provide a 10% improvement in fuel

economy by converting waste heat to electricity used by the OTR truck

� Evaluate currently available thermoelectric materials to determine optimum material selection and segmentation geometry for this application

� Develop TEG fabrication protocol for module and system demonstration

� Determine heat exchanger requirements needed for building TEGs of reasonable length

� Determine power electronic/control requirements � Determine if Phase 2 results make an engine demo

in Phase 3 reasonable

Important BarriersImportant Barriers• Design of heat exchanger is a major challenge with heat

transfer coefficients needed which are 5x higher than withoutenhanced heat transfer modes

• Reliable thermoelectric module fabrication methods need to be developed for the new high efficiency TE materials

• Material strength and thermoelectiric properties must meet lifecycle performance criteria

• Powder processing methods are being refined to provideincreased strength while maintaining thermoelectric propertiesof ingot forms of the material

• ZT for the temperature ranges (700K) for last material areabout 1.5 and need to be closer to 3.0 to reach the efficiencygoals requested by DOE

Accomplishment to dateAccomplishment to date� Systems for ingot synthesis and leg preparation demonstrated

� March 07, 100 ton hot press operational at MSU (up to a 10 cm puck) � Tube furnaces and leg cutting equipment operational (500 grams/batch) � Segmented legs demonstrated by Sakamoto at JPL (now at MSU)

� Segmented leg - module fabrication methods being developed� Sakamoto at JPL demonstrated segmented p-leg with 14.5% efficiency � Hogan group fabricated and tested numerous LAST/LASTT modules � Diffusion bonding of stainless steel to LAST and BiTe demonstrated

� Power electronic module isolation methods designed andbeing tested at MSU

� Transport measurements conducted by MSU have beenverified by Northwestern, JPL, Iowa State and the generalliterature

� Sublimation issues appear to be under control with aerogelcoatings developed by Sakamoto at JPL and Fortifax at MSU

� Analytical studies performed for various operation modes andconditions � Geometries for high efficiency heat transfer rates evaluated � Efficiency improvements for various operational modes for the Cummins

ISX engine evaluated for various geometries

Problems of Traditional Connection Methods

Parallel connection Series connection

¾ Different output characteristics of TEG modules cause problems when connect them with traditional methods;

¾ One TEG module can become the load of another and waste power;

¾ Can not guarantee maximum power output from each TEG module;

¾ Single failed module can cause power output interruption .

Power Electronics for TE Generation

Developing power electronic circuit as an interface between TEG module and load with the features of:

¾ Load matching; ¾ Power conditioning; ¾ Maximum power point tracking; ¾ Failed TEG module bypassing.

Power Electronics Solution

A power electronic circuit is designed for each TEG module and features functions of:

¾Maximum power point tracking;

¾ Bypassing failed module;

PECircuit 2

PECircuit 2

PECircuit 2

PECircuit 2

To Achieve High Power Output

RLV0

I0

Vn

Rn

V1

R1

V0nMn

M1

PE Circuit n

PE Circuit 1

V01

Vn

Rn

V1

R1

V0n

Mn

M1

PE Circuit n

PE Circuit 1

V01

¾ High power output can be achieved by series-parallel connection of TEG modules;

¾ Power electronic circuits guarantee each TEG module output its maximum power;

¾ Failed modules will not effect the operation of other modules.

TEG module and Heat Exchanger Heatsink

TEG modules

TEG module from Tellurex®

Heat elements

AssemblyOutput characteristics (Tellurex®)

¾ A heat exchanger capable of 100 W electrical power output has been fabricated and Tested.

Our test results

Test Setup & Condition

Set 1: Without PE Circuit Set 2: With PE Circuit

¾ Set 1 is directly connected to a 50 W light bulb; ¾ Set 2 is connected to a 50 W light bulb via the power electronic circuit.

Demo and Test Results of the PE Circuit for Maximum Power Point Tracking

TEG output electric power vs ∆T

0

5

10

15

20

25

30

35

40

45

50

30 50 70 90 110 130

ΔT=T (Hot)−T (Cold) (degree C)

TEG

Out

put P

ower

(W)

W/O PE circuit With PE circuit

¾ The PE circuit can extract the maximum electrical power from the TE modules and feed any electric loads regardless of TE module’s heat flux and load impedance/conditions.

W/O PE circuit

with PE circuit TEG maximum power

Device level efficiency projections:Skutterudite+heritage materials

CeFe3.5Co0.5Sb12 p-leg n-leg

700C

100C

CoSb3

TAGS LAST or PbTe

Option 1: LAST for cold stage of n-leg (525C interface) = 14.80% efficiency

Option 2: PbTe for cold stage of n-leg (438C interface) = ~12.4% efficiency

Option 3: PbTe for cold stage of n-leg (525C interface + TAGS at 500C) = 13.0% efficiency

SOA: Heritage TAGS & PbTe 450C-100C = 8% efficiency

Device details & power outputOption 3: PbTe for cold stage of n-leg (525C interface + TAGS at 500C) = 13.0% efficiency

CeFe3.5Co0.5Sb12 p-leg n-leg

700C

100C

CoSb3

TAGS PbTe

•0.5cm long legs 0.5cm2 each leg

•1 gram (total) for each couple

•2.2 mOhm per couple

•0.127 mV at peak load

•41 amps

•5.2W output

•Assumes 40W/cm2

•200 couples in series at 25V (6” by 6” footprint including gaps) = 1040W

MSU53 Power Output Validation @ JPLMSU53 Power Output Validation

0 10 20 30 40 50 60 70 80 90

100

Pote

ntia

l (m

V)

2.74 mΩ

2.93 mΩ

3.03 mΩ 800700 500C600 635C500400300

Pow

er (m

W)

700C

700C

200 100 0 -100 -200

0 5 10 15 20 25 30

Current (Amps)

•Resistance is within ~1% of predicted value

•14.57% conversion efficiency!

Cummins ISX 6 cylinder diesel engine

Σ

Induction Intercooler

EGR CoolerTEG-1

Thermal Power Split Hybrid – OptionsUsing the electric power recovered from waste heat

X % of exhaust to EGR, (100-X) % of exhaust to turbine.

Additional energy recovery opportunity

ηINV= 0.96 ηBIMG=0.93

Cool Exhaust Out ηmi= 0.89

Pm=249+TEG@ 100%, TEG@ 62%

I E

Wheels FD

Trans.

C

T

Induction Air

EGR

EGR Mixer

ESS, Batt + Ultra-Cap

Th , qh

Pe @62% = Y kW Pe @ 100%= Z kW

Pow

er E

lect

30 -

50 k

VA

WP

Engine Coolant

Air

Exhaust

Coolant Pump

Rad

iato

r

B-I

MG

Excess Electrical Power

T/C or clutch

Powered Ancillaries

TEG-2

Single TEG with exploded view of a module

ISX Engine Operating Conditions for ESC Duty Cycle Modes

cold

Issues: hot

Heat Exchanger (HX) • How to fully utilize the hot &

cold

cold temperature sources as efficiently and compactly as possible.

Heat Transfer in the TE Couple • TE cavity: inert gas/insulation • TE legs RC TH

Durability and Life • thermal stress

considerations

J J

x RC TC

J J

HX: Heat Transfer Enhancement

Goal: ¾ high heat transfer rate ¾ low pressure drop

How to get high heat-transfer rate?

¾ ribs ¾ Dimples ¾ vortex

generators ¾ hybrid

(combinations of ribs, dimples, …)with rib

no rib

Guiding Principle for HT Enhancement

¾ Increase streamwise vorticity / recirculating flow to increases surface heat transfer

Why?Brings hotter & higher momentum fluid in the “core” to the surface.

¾ Interrupting the streamwise recirculating flow periodically is needed (i.e., restart boundary layer).

¾ Induce unsteadiness as another mechanism to restart boundary layer.

New Concept hwith rib / hno rib

TEG for Waste Heat from IC Engines

T2 T2' T3 T3' Outlet 6-1 731 727 524 342

Midpoint 6-1 781 777 546 338 Inlet 6-1 831 826 567 334

Outlet EGR Cooler 495 493 408 331 Midpoint EGR Cooler 636 633 474 331

Inlet EGR Cooler 834 829 568 334

TEG Configuration

Inlet Midpoint Outlet

1

2

2’

3

3’

radial

axial

Heat flux

Outer wall

Inner wall

Temperature

n p n pn p… …

1 Cylinder per TEG MP Module EfficiencyM

odul

e Ef

ficie

ncy

(%)

(LAST, BiTe (470K) ), T2` = 644K, T3` = 338K

9.2 J = -26.3 (A/cm2)p max

9 J = 20.4 (A/cm2)n max

An/Ap = 1.29 8.8 η = 9.1%max

8.6

8.4

8.2

8

7.8 -45 -40 -35 -30 -25 -20 -15 -10

J (A/cm2)p

An = 0.793 (cm) An = 0.861 (cm) An = 0.946 (cm) An = 1.032 (cm) An = 1.117 (cm) An = 1.202 (cm) An = 1.288 (cm) An = 1.373 (cm) An = 1.459 (cm) An = 1.544 (cm) An = 1.629 (cm)

Fuel economy of ISX Engine Operating at Cruise (B62 Point) – Phase I Work

TEG Placed at Head in Exhaust Port

% Imp. In BSFC * = QTEG ⋅ NTEG ⋅ηTEG ⋅ηBISG ⋅η INV

BHP ⋅0.746

1 Cylinder into 1 TEG (6TEGs) = 31.9(6)(0.091)(0.96)(0.93) = 6.2% 334.6 ⋅0.746

3 Cylinders into 1 TEG (2 TEGs) = 50.2(2)(0.11)(0.96)(0.93) = 4.0% 334.6 ⋅0.746

6 Cylinders into 1 TEG (1TEG) = 64.5(1)(0.123)(0.96)(0.93) = 2.8% 334.6 ⋅ 0.746

Note: This does not include improvement in BSFC by utilizing an ISG which has an efficiency 2x that of current alternators or the higher TEG efficiencies at higher load operation

WAVE Diagram of ISX Engine Layout: Secondary TEG attached to Turbo Exhaust

TEG located in EGR Circuit

VGT Turbocharger

Intercooler

Intake

Exhaust

EGR Flow

EGR Valve Additional TEG

added after Turbine

Note: Both TEG lengths have been increased from 150cm to 200cm from Phase I studies

Animation of Temperature Gradients

TEG in EGR Circuit

Additional TEG added

after Turbine

BSFC % Improvement: Single TEG EGR Cooler and Dual TEG

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

A-25 A-100 B-62 B-100 C-100

Operating Point

% Im

prov

emen

t

Dual TEG: EGR Cooler & After Turbine Single EGR Cooler TEG

Collaborations/InteractionsCollaborations/Interactions

• MSU, JPL, Tellurex, Northwestern, Iowa State and Cummins Team continue to partner in this effort

• Office of Naval Research sponsored effort has provided the basis for new material exploration and assisted in module fabrication developments

• Oak Ridge DOE (High Temperature Materials Laboratory) has provided significant assistance in material property characterization

Publications/PatentPublications/Patent• Characterization of dry milled LAST (Lead-Antimony-Silver-Tellurium)

thermoelectric material, Pilchak, A., Ren, F., Case, E., Timm, E. and Schock, H., submitted to Philosophical Magazine, Spring 07

• Nanostructured Thermoelectric Materials and High Efficiency PowerGeneration Modules, Hogan, T., Downey, A., Short, J. et al., prepared spring07

• The Young’s modulus and Poisson’s ratio of lead-telluride basedthermoelectric materials as a function of temperature, Ren, F., Case, E., Timm, E., Schock, H., Lara-Cuzio, E., Trejo, R., Lin, C.H.,Kanatzidis, M., submitted to International Journal of Applied Ceramics Technology, Spring, 07

• Hardness as a function of composition for n-type LAST thermoelectric materials, F. Ren, E.D. Case, E.J. Timm, and H.J. Schock, Journal of Alloysand Compounds, (2007) doi:10.1016/jallcom.2007.01.086

• Young’s modulus as a function of composition of n-type lead-antimony-silver-telluride (LAST) thermoelectric materials, F. Ren, E.D. Case, E.J. Timm, and H.J. Schock, submitted to Philosophical Magazine, Spring 07

• Weibull analysis of the biaxial fracture strength of a cast p-type LAST-Tthermoelectric material, F. Ren, E.D. Case, E.J. Timm, M.D. Jacobs and H.J. Schock, Philosophical Magazine Letters, Vol. 86, No. 10, Oct. 2006, 673-682

Plans for the Rest of the YearPlans for the Rest of the Year

� July ~ Aug, 2007: Modules being fabricated, segmented concepts testing and powder processing method development ongoing

� Aug ~ Dec. 2007 Evaluation of new TE systems and stoichiometries � Sept ~ Dec. 2007 Demonstrate power electronics for 100 watt TEG � Aug ~ Nov, 2007: High efficiency module construction and performance

testing � Sept ~ Nov, 2007: Design of heat exchanger and numerical simulation of

expected system performance � Dec, 2007: Preparing quarterly project report

SummarySummary• Systems for material synthesis, powder processing, hot pressing,

leg and module fabrication are operational at MSU • Facility in place to produce materials required for a 40 watt

module in one week …thus new concepts can be evaluated inabout one week

• Thermoelectric performance testing of legs and modules at MSUis in agreement with others doing similar measurements

• Power conditioning electronics for maximum power tracking andfault mitigation are being tested

• Improved head exchanger designs are critical to success of TEeffort for waste heat recovery

• Using TEG technology, a 5% improvement in bsfc for and OTR truck is a reasonable 5 year goal …10% improvement possiblewith new TE materials

leg

5mm

MSU53: Metallized (end-end) Segmented pSKD+TAGS

•Test set up for validating power output of pSKD/TAGS segmented leg

Res

ista

nce

( μΩ

)2000

MSU 53 Contact Resistance Measurement 1800

NOTE: 4A with 89% efficiency 1600

pSKD1400

0.538mΩ cm-1200 metallization measured 4200 1000 4100

800 0.797mΩ cm-measured

600 TAGS 400

Con

tact

Res

ista

nce

(mic

ro O

hms/

cm2) 4000

3900

3800 ~170 μΩ/cm2 3700

3600

3500

3400

200

0

3300

3200 3700 3900 4100 4300 4500 4700 4900 5100 5300 5500

Distance (microns)

0 2000 4000 6000 8000

Distance (μm) •Contact resistance measured using new 100nm step scanning probe

•Measured resistivity of TAGS & pSKD within +/- 2% of published data

•Contact resistance at segmented interface is low and can be reduced by reducing thickness of metallurgical bond

uncoated uncoated aerogel coated aerogel coated

Goal = 2 x 10-6

TAGS Sublimation at 535C

1.00E-06

1.00E-05

1.00E-04

0 100 200 300 400 500 600 700 800 time (hours)

Subl

im at

ion

rate

(g/c

m2 h)

�Aerogel suppressed sublimation by a factor of 10 and is approaching the 10years of operation goal at 535C