Stirling machine as auxiliary power unit for range

extender hybrid electric vehicles

Sylvie BEGOT, Steve DJETEL,

François LANZETTA– Femto st

Wissam BOU NADER – Groupe PSA

30/01/2019

Context and short term solutions

2

Problematic arises for post 2025 due to more stringent

reglementation regarding CO2 emissions

95g CO2/km

80g CO2/km

59g CO2/km

130g CO2/km

-37,5%

Powertrain & EMSEnergetic demands

ICE efficiency

aerodynamic

Rolling

resistancce

weight

Thermal

energetic needs

Auxiliaries

consumption

CO2 emission

≈

fuel consumption

CAFE = Corporate Average Fuel Economy / ICE=Internal Combustion engine / EMS = Energy Management Strategy

Internal Combustion Engine (ICE) powertrains main problematics

3

ICE multi-fuel compatibility

!Confort thermal energetic needs

Stirling

Gas-Turbine

Combined cycle

Split cycle

Solid combution E-fuel Hydrogen Bio-fuel

ICE Max efficiency

On the other hand… ongoing development of Battery Electric Vehicles (BEV)

4

Tesla

Renault Zoe

Citroën C0Benefit of Zero Vehicle Emission

(Tank to wheel emissions !!!)

5

AC

DC

Battery

Vehicle Controller

Driver performance request

APU Controller

SOC

Brake

Hydraulic brake

command

Traction/brake

recovery command

Wheel

>100kW.h

(500km)

(≈600kg)

• Large battery capacities for long autonomy range: Additional weight

However, BEVs present many drawbacks

Ele

ctri

c M

oto

r

• Thermal confort such as heating is not free compared to thermal based powertrains

• CO2 emission (well to wheel analysis) depends on the electricity production

• Geopolitical problematic for European automotive manufacturers

• Cost for the customer

BEV = Battery Electric Vehicle

6

Po

wer

trai

n a

nd

ener

gy

cost

(€

)

(15

.00

0km

/ye

ar/

10

yea

rs)

Tax

Other Energy

Electrical Energy

Engine / APU

Battery

E-motor

Reductor

ICE FCVBEVREX

SHEV

AC

DC

Battery

Vehicle Controller

APU Controller

Ele

ctri

c M

oto

r

Brake

Hydraulic brake

command

Traction/brake

recovery command

Wheel

≈10kW.h

(50km)

(≈150kg)

Ele

ctri

c G

ener

ato

r

Energy

Converter

Auxiliary Power Unit (APU)

BEV = Battery Electric Vehicle, FCV = Fuel Cell Vehicle, REX = Range Extender Vehicle,

SHEV = Series Hybrid Electric Vehicle, ZEV = Zero Emission Vehilce

SOC

Different energy converters with

different thermodynamic

configurations can be envisaged

Driver performance request

Range Extender powertrain seems to be a comprimise

>100kW.h

(500km)

(≈600kg)

• ZEV mode compared to ICE

• Low emission compared to ICE

• Cost compared to BEV and FCV

• Vehicle weight compared to BEV

• Fun to drive (such as BEV)

State of the art – Energy converters for automotive application

7

TA

TEG

PEM Fuel CellICE StirlingRankine

EricssonECGT

Mature technology for

automotive applications

Mature technology for non-

automotive applicationsNon-mature technology

Split Cycle

Gas Turbine

Internal Combustion Electro ChemicalExternal Combustion

CCGT = Combined cycle Gas Turbine

TA = Thermoacoustic

TEG = Thermoelectric Generator

ECGT=External Combustion Gas-Turbine

PEM = Proton Exchange Membrane

SOFC = Solid Oxide Fuel Cell

SOFCCCGT

Conventional Non Conventional

8

Early development of Stirling machine for automotive applications

Ford Torino Chevrolet Celebrity Opel Kadet

Automotive intrinstic benefits: Multi-fuel capability, good thermal efficiency, high

torque at low speed, silent operation, low vibration.

Many reasons hindered their deployments: Leakage, controllability, Investment

costs, and particularly the simplicity and price of the ICE at that time

9

Today with CO2 and emissions topics, Stirling for automotive applications gain interest

• Development of Series Hybrid Electric Vehicles (SHEV) :

o efficiently operation under all driving cycle

o quasi-stable operating state: reduce control complexity

• External combustion machine - Emission reduction through:

o Choice of fuel and continuous combustion

• Development of magnetic coupling systems:

o Complete sealing to avoid working fluid leakages

• Material advancement to reach higher temperature and pressure:

o Higher thermodynamic cycle efficiency and higher power density

10

AC

DC

AC

DC

Battery

Driver performance request

APU Controller

Ele

ctri

c

Gen

erat

or

Ele

ctri

c

Mo

tor

SOC

Brake

Hydraulic brake

command

AP

U O

N/O

FF

Traction/brake

recovery command

Wheel

Auxiliary Power Unit (APU)

Stirling

machine

Vehicle Criteria: fuel consumption

Requirements: Acceleration, Max speed, gradability

Constraints: Weight, Size, Frontal surface

Target of this work

Cabine

heatingAuxiliariesAC

WLTC cycle

Vehicle Controller

0

20

40

60

80

100

120

140

0

1000

2000

3000

4000

Vel

oci

ty (

km

/h)

Ener

get

ic n

eeds

Po

wer

(W)

Time (s)

Cogeneration machine for

automotive applications

11

Stirling cycle - Theory

Ideal Stirling Cycle

• 2 isothermal transformations

• Expansion 3-4

• Compression 1-2

• 2 isochoric transfromations

• Heating 2-3

• Cooling 4-1

Robert Stirling (1816) Hot air engine

Stirling engines

• External heat supply

• Closed cycle

• Regenerative engine

P

V

2

3

4

1

QH

2 QL

1

3 4

QR

QR

TH

TL

T

S

QR

P

V

2

3

4

1

Mechanical configuration : Beta

• One cylinder with 2 pistons

• Work piston : compression and

expansion

• Displacer piston : no work done,

moves the gas from the expansion

space to the compression space

Beta

Configuration

Cycle moteur Cycle frigorifique

Proto Femto 300 W

Designed prototype characteristics

Engine characteristics

Beta type Single cylinder

Working gas Nitrogen

Pressure 60 x 105 Pa

Power 12 kW

Generator 3 phase

Power piston diameter 10-1 m

Compression swept

volume

4.5 x 10-4 m3

Hot temperature 937 K

Cold temperature 337 K

Efficiency (target) 39 %

Frequency 35 Hz

PV Diagram from isothermal

analysis (Schmidt)

First tests :

• engine is driven by an electric drive

asynchronous engine

Inverter

• Reduced pressure 15 bar instead of 60

bar

• Reversed cycle : heat pump or

refrigerating cycle

Designed prototype characteristics

1

2

3

4

5

6

1: hot exchanger, 2: cold exchanger,

3: gas burner, 4: torquemeter,

5: electrical engine,

6: power electronics converter.

Results: pressure, torque, rotational speed for a few cycles

Results: as a refrigerating machine

-30°C dans le volume de détente

Vehicle model including an APU with ICE or Stirling engine

Vehicle specifications

Vehicle mass (+ driver) 1210 kg

Wheel friction coefficient 0.0106

Air density 1.205 kg/m3

Wheel radius 0.307 m

Auxiliaries consumption 750 W

Battery max. power 78 kW

Battery capacity [5, 10, 20] kWh

Battery mass[188, 259, 356]

kg

Battery state of charge [0.4, 0.6, 0.8, 1]

Stirling system 12 kW

Stirling efficiency 39 %

ICE power 97 kW

ICE max. efficiency 36 %

Vehicle specifications

Generator max. power 12 kW

Generator max.

efficiency95 %

Motor max. power 80 kW

Motor max. efficiency 93 %

Transmission ratio 5.4

Transmission efficiency 97 %

Fuel heating value 42.5 MJ/kg

Energy converters operation

• for both Stirling and ICE on plug-In SHEVs

powertrains

• three repeated WLTP

• 10kWh battery capacity

• Stirling engine operates at a lower power

and more continuously than ICE

Model results

Model results

Battery and fuel energy trade-off

for the plug-in configuration on one to

five-repeated WLTP, under the three

investigated battery capacities.

Powertrain efficiency of the

plug-in configuration, on one to

five-repeated WLTP, under the

three investigated battery

capacities.a

Fuel consumption results between

Stirling-system and ICE of the plug-in

on one to five-repeated WLTP, under

the three investigated battery

capacities.

• Alternative automobile powertrains are needed

• Series Hybrid Vehicles including a Stirling engine as APU is a good candidate

• Powertrain efficiencies and fuel consumption present good performances when

compared to a conventional ICE APU

• A 10 kW Stirling engine prototype has been developed and is currently under tests

Conclusion