Waste Heat Recuperation for Passenger Vehicles · 2017-11-17 · Radioisotope Thermoelectric Generators (RTG’s) for deep space probes. Radioisotope provides thermal energy RTG’s

Waste Heat Recuperation for Passenger Vehicles

Jim Salvador

[email protected]

Outline

• Brief Introduction to Thermoelectric Technology.

• Thermoelectric Generator System Basics.

• Future Research and Development Needs.

This report was prepared as an account of work sponsored by an agency of the

United States Government. Neither the United States Government nor any

agency thereof, nor any of their employees, make any warranty, express or

implied, or assumes any legal liability or responsibility for the accuracy,

completeness, or usefulness of any information, apparatus, product, or process

disclosed, or represents that its use would not infringe privately owned rights.

Reference herein to any specific commercial product, process, or service by

trade name, trademark, manufacturer, or otherwise does not necessarily

constitute or imply its endorsement, recommendation, or favoring by the United

States Government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United States

Government or any agency thereof.

Disclaimer

SupportU.S. Department of Energy Grant # DE-FC26-04NT 42278 and DE-EEE0005432

John Fairbanks and Gurpreet Singh (DOE), Carl Maronde (NETL)

U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle

Technologies, as part of the Propulsion Materials Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC

nm mm mm m

log(Length scale)

Engineering

Materials

Science

Chemistry

Physics

Competency

Electronic

Microstructural

0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045 0.0050

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1406

1269

1131

994.1

856.8

719.5

582.2

444.9

307.6

170.3

Lp [m]

Wout

PbTe/TAGS85

Continuum

Atomistic

Waste Heat Recovery by Thermoelectrics• Thermoelectric materials make use of the Seebeck effect to generate a voltage from a

temperature difference.

• The voltage is then used to drive an external load.

• The electricity generated by the device can be used to supplement the alternator to

reduce its torque load on the engine, charge batteries, or be used for propulsion.

• High quality heat, like that found in the exhaust gas stream, is ideal for generating

large temperature difference for higher power densities.

𝑃𝑜𝑢𝑡 = 𝑉𝑜𝑐2

𝑅𝐿𝑜𝑎𝑑(𝑅𝑖𝑛𝑡 + 𝑅𝑙𝑜𝑎𝑑)

2

𝑉𝑂𝐶 = 𝑆Δ𝑇

z𝑇 =𝑆2

𝜌∙𝜅𝑇

Materials Level Performance Metrics

System Level Metrics

TE Applications

Radioisotope Thermoelectric Generators (RTG’s) for deep space probes. Radioisotope

provides thermal energy

RTG’s are used when solar flux is insufficient to supply onboard power requirements or when

sustained power.

Illustration of SNAP-19 RTG with n and p-type PbTe.

• TEGs go after waste exhaust heat, which is a sizeable portion of the energy flow through an ICE.

• TEGs can operate continuously EGHR systems often harvest heat only during warm up to improve engine and transmission performance.

• TEG’s go after an energy stream that is typically a total loss.

TEG System Basics (Your Power Source).

Operating Temperatures

Location is everything for TEG Performance

Effect of TEG Location on Power Output

Average Power:

Cat Out = 136 W

Flex = 94 W

Mid Muffler = 78.5 W

Full Size Truck 5.3 L V-8 Average Power:

Cat Out = 136 W

Flex = 94 W

Mid Muffler = 78.5 W

Effect of TEG Location on Power Output

Full Size Truck 5.3 L V-8

TEG Design (Integrated System Approach)

TEG Design (Integrated System Approach)

TEG Design and Packaging Location

TEG Design and Packaging Location

Power Management

The voltage of a TEG is a function of:

1) Seebeck Coefficient

2) The Junction Temperatures

3) The number of TE elements connected in series

Maximum power is extracted from the TEG at near half the open circuit voltage.

The voltage needs to be regulated to the voltage of the Vehicle.

This generally requires some type of DC-DC converter (Boost/Buck).

Battery Voltage

Expected On-cycle Fuel Economy Benefits• TEGs provide two FE improvement functions

1) Faster Powertrain warmup.

2) Supplemental electrical power to offset the alternator.

• Electrical power is generated after 2/3 of the energy of

combustion is lost and the alternator is not terribly efficient.

• Vehicle modeling and testing find that if all the electrical loads

can be met by the TEG the FE can be improved by about ½

MPG (250 to 350 W electrical load for FST).

• The relationship between the % power supplied by the TEG and

the expected FE benefit is linear.

• Further there is another 0.1-0.2 MPG from active warm up.

Off Cycle Credits

• EPA has 1.5 gCO2/mile credit for cars and 3.2 for light

trucks for active warm up of engines.

• There are additional 1.5 gCO2/mile credit for cars and 3.2

for light trucks for active transmission warm-up. This

requires an additional heat exchanger dedicated to the

Transmission

• There is a thermoelectric specific off-cycle credit equal to

0.7g CO2/mile for each 100 W of “rated electrical power”

• Rated electrical power is taken as the simple average of the

power output over the 5 cycles.

Challenging Characteristics of TEGs

• A TEG adds weight and cost

– OEM’s spend a bulk of their resources stripping these out of vehicles

and now we want to add it back in.

• A TEG is not customer facing

– If it works the way its supposed to the customer will never know that it’s

there.

• Does not benefit FE in all driving conditions.

– US DOT finds ~50% of all miles driven in the US are at higher speeds

on rural / urban interstates and highways.

• Packaging and Competing Space

– Smaller cars, where a TEG could arguable have a larger impact in FE,

are challenging to fit a TEG into and the radiator capacity are an issue.

R&D Needs

• There are still no materials commercially available that are well

suited to TEG applications.

• Cost effective DC-DC converter technology is still needed.

• TEGs at the current level of development are well suited to

larger vehicle.

• Reduction in TEG size and weight is still needed to make

these more broadly applicable to smaller cars.

Summary• TEGs have the same benefits of EGHR systems while providing recuperated

electrical energy under a variety of drive cycles.

• TEGs can provide a 0.5 MPG improvement on FTP cycle.

• There are three potential off-cycle credits available to TEGs.

• New approaches to TE generator designs are quickly reducing cost weight and

size of generator systems.

• Improvements in TE material performance is still needed to make TE’s more

competitive with more mature forms of waste heat recovery.

Acknowledgements

Collaborators/Subcontractors:

Marlow Industries: Jeff Sharp and Alan Thompson

Oak Ridge National Laboratory: Hsin Wang and Andy Wereszczak

University of Washington: Jihui Yang

Future Tech: Francis Stabler

Dana, Inc: Edward Gerges, John Burgers and Matthew Birkett

Eberspaecher: Lakshmikanth Meda and Martin Romzek

Molycorp: David Brown and David Miller

NASA JPL: Jean-Pierre Fleurial and Terry Hendricks

Brookhaven National Laboratory: Qiang Li

University of Michigan: Jeff Sakamoto

Delphi: Scott Brandenburg, Ray Fairchild and David Ihms

Purdue University: Xianfan Xu,