LCVTP
The Development and Demonstration
of APU Technology
Date :
21 February 2012
Nick Powell
Chief Engineer
Ricardo
Contents

What is an APU

Requirements specification

Potential technology solutions

Implications for engine design and operation

Base engine research for APU application

Generator design, build and test

After treatment studies

Integration in Technology Demonstrator vehicle
2
An auxiliary power unit provides an onboard
electricity source for an electric vehicle
A range extended electric vehicle (RE-EV)
receives energy from two sources:
On board auxiliary power unit (APU)
>
Electricity grid
LCVTP studied the requirements and optimum
design for an auxiliary power unit (APU)
consisting of an integrated internal combustion
engine and generator
APU
>

Electricity Grid

Illustration of energy flow in a RE-EV
3
An APU extends the range of an electric vehicle
and can allow a reduction in battery size

An APU provides the following key benefits:
>
Extends the autonomous range of an electric vehicle
>
Allows rapid refuelling, using existing liquid fuel infrastructure (assuming APU operates on
gasoline or diesel) and hence overcomes ‘range anxiety’
>
Potential to downsize the battery, compared to a pure battery electric vehicle, and thus reduce
the vehicle cost, weight and embedded CO2
>
Allows flexibility in vehicle architecture and engine operating strategy, due to absence of
mechanical connection between APU and wheels
>
Provides freedom to operate the engine and generator at optimum efficiency conditions
APU
A system requirement for a combined engine and generator to enable continued driving once EV
battery has depleted below lower threshold State of Charge (SOC)
4
However, the series hybrid architecture of a RE-EV
leads to inherent inefficiencies due to energy
conversions
* Charging efficiency not
relevant when operating
as pure series-HEV
Series hybrid vehicle; typical BSFC @ steady cruise = 331g/kW.h
230
g/kW.h
90%
95%
95%*
95%
90%
Conventional vehicle; typical BSFC @ steady cruise = 315g/kW.h
A series hybrid does not have
an efficiency benefit in charge
sustaining mode, so efficiency
of every system in the
powertrain must be optimised
to maintain competitive edge
300
g/kW.h
95%
5
Current European regulation applies a weighted
average to the calculation of PHEV CO2 emissions
Determination of PHEV weighted results (Regulation 101, Annex 9)
 The weighted values of CO2 shall be calculated as below:
>
M = (De x M1 + Dav x M2) / (De + Dav)
M1 = CO2 in g/km with a fully charged electrical energy/power storage device (Condition A
SOC-depleting)
M2 = CO2 in g/km with an electrical energy/power storage device in minimum state of charge
(Condition B SOC-sustaining)
De = Electric range
Dav = 25km (assumed average distance between opportunities to recharge the battery)
>
Example: Vehicle has test-results as follows:

Condition A (SOC-depleting) CO2




•
Condition B (SOC-sustaining) CO2
Electric-range
Weighted CO2 = (40 * 0 + 25 * 150) / (40 + 25)
= 0 g/km (test can be
completed in EV-mode)
= 150 g/km
= 40km
= 57 g/km
The same method is used to for the weighted values of fuel-consumption and electric energy
consumption
>
Note: No account is taken of CO2 used to generate the grid-supplied electricity
>
The electric energy consumption is reported separately, in Wh/km, and has no associated CO2
Toxic emissions must complied with Condition B
Source : UNECE Regulation 101 and 83
6
Total journey WTW CO2 emissions is a function
of architecture, duty cycle and APU efficiency
160 km
100 km
310 km
460 km
105 km
135 km

A RE-EV has lower
well-to-wheel (WTW)
emissions, than other
vehicle architectures,
up to certain journey
length

This journey length is
a function of the
architecture, duty cycle
and APU efficiency
Cycle
EV range (km)
NEDC
86.4
ArtUrb
62
ArtRd
104.7
ArtMw
55.2
Source : Ricardo analysis
7
The power requirement of an APU is largely
determined by the sustained vehicle functionality

The APU power requirement is determined by the vehicle functionality required when the battery SOC
has reached a specified SOC threshold

These may be a combination of short duration and sustained duration requirements
>
Occasional short duration events may be accommodated by allowing the battery SOC to go
below the normal minimum limit, and/or by a peak power output of the APU
Sustained power requirements are
more relevant to APU sizing.
These may be calculated as
follows:


The average power required
to complete the required
vehicle mixed duty cycle (this
may be derived from a
vehicle simulation model
such as Ricardo V-Sim)
The power required to
maintain high speed cruising,
and/or up hill gradient
condition
100
Example
90
SOC
Upper threshold
Lower theshold
80
70
SOC (%)
>
60
APU start-up
50
APU shut-down
40
30
20
10
0
0
10
Distance
travelled30
(km)
20
40
50
8
An APU can be sized between an emergency
power source and a full utility series hybrid

The power requirements specification for an APU will differ depending upon the sustained vehicle
functionality required
Typical APU power requirements for different levels of vehicle functionality
Vehicle Functionality
Power [kW]
Emergency, limp home, APU (Maximum 60km/hr, minimum
ancillaries)
<10
Majority of conventional vehicle functionality (sustained
120kph cruise + electric air conditioning)
30-50
Full
series
hybrid
functionality
compromised by depleted battery)
(Functionality
not
>90
9
The suitability of technologies have been
assessed against key APU attributes
Different weighting factors have
been derived for different APU
power requirements
10
An initial Pugh matrix assessment identified
gasoline piston engines as well suited to APU
power source in the short and medium term
WS5.7 APU Technology Ranking
35kW
<10kW
Increased η gasoline (+ Atkinson / Miller) ICE
Conventional diesel ICE - with or without HCCI
Low cost conventional ICE - gasoline
Air engine
Free piston with linear generator
~90kW
~35kW
Rotary - Wankel
Split cycle - Scuderi
<10kW
Fuel cell
Reciprocating external combustion (e.g. Stirling cycle)
Steam turbine
Gas turbine with heat recovery
Gas turbine
150
200
250
300
350
400
450
500
550
Weighted assessment
More appropriate technology
This analysis has shown that conventional gasoline engine architectures, optimised for
APU duty cycles, are well suited as an APU power source in the short to medium term
11
In the short to medium term 30-50kW is likely to
most common APU power

It is anticipated that in the short to medium term, customers will expect most of the functionality
of a conventional vehicle under APU operation, at least to be able to cruise at motorway speed
conditions
>
Therefore in the short to medium term (up to 2020) a 30-50kW APU is likely to be the most
typical APU to provide acceptable functionality under sustained cruising conditions
>
Most of the LCVTP research has been focused on a 30-50kW APU
12
A RE-EV architecture presents unconventional
constraints on the engine operating strategy

An APU will typically operate between lower and upper thresholds of battery SOC

The engine operating strategy in a RE-EV differs from a conventional vehicle
>
Conventional vehicles do not permit operation at peak efficiency for sustained periods
because the engine is normally sized to the peak vehicle power requirements. The engine
therefore operates at low load, speed and efficiency under most typical driving conditions
>
The APU engine can be sized and operated at conditions of peak efficiency subject to NVH,
emissions and durability constraints, because the electric powertrain provides for peak vehicle
power requirements
>
Driveability does not need to be considered for an APU, so there is no requirement for rapid
transient response
>
The APU is not under direct driver control, so the possibility of driver induced overspeed is
eliminated
>
As well as efficiency other factors will influence the operating strategy, including:

Subjective NVH (a function of vehicle speed)

Allowable battery charge rates

Toxic emissions, including catalyst light-off

Possible driver or electronic-horizon input (e.g. in mountainous regions)
13
Example of typical APU operating map
22
6
2
36
35
33
3
30 1
4
Conventional vehicle
low efficiency
operating region on
legislated drive cycles
32
33
3
4
35
34
34
12
31
BMEP [bar]
Low load,
efficiency
15
8
300
33 80
34
30
40
33
20
60
High speed,
poor efficiency
2
&3 NVH
1
30 3 0
31
30
2 820
26
24
22
10
20
15
30
50
40 8
2
2360
20
24
20
22
To improve
NVH and
reduce friction,
high speed
operation is
avoided
15
0
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
Engine Speed [rev/min]
Engine
changes to
improve high
load, low speed
efficiency
desirable
70
3
32
28 10
26
poor
24
22
20
50
31
14
31
70
60
16
8
50
34
5
3
36
1032
Engine started at higher
than normal speed
33
18
10
31
2035
– Durability
32
33
20
– NVH
– Emissions
Example only
40
Single operating
point calibration is
possible but may not
be advisable due to
consideration of
Specific Power kW/l
Thermal Efficiency %
The APU operating cycle presents different design freedoms on the engine design
14
A RE-EV requires high levels of refinement from
the APU

The powertrain of an electrified vehicle does not yield sound quality which is considered to be
desirable hence it is subdued to a level which is considered to be acceptable

In a RE-EV, the operation of the APU is not expected to be within the direct control of the driver

Low levels of masking noise, and ‘unexpected APU operation’ mean the required levels of
acoustic refinement of the APU are very high
Interior cruising noise powertrain contribution
Green = ICE powertrain
Blue = e-drive powertrain
Source: SAE2011-01-1724
LMS Intl & Nippon Steel Corp.
15
LCVTP studied two engines to inform future APU
design
Tata Nano 2 cylinder

•
•
•
To study optimisation of base engine for
APU operation through modelling and
testing
>
Engine breathing
>
Atkinson cycle
>
Aftertreatment
Fiat Twinair
•
•
To provide hardware for application in
GTV vehicle
To build an APU with a bespoke LCVTP
integrated generator
To study the design changes required to optimise an engine for APU application so as to inform the
design of future APU engines
Demonstration of base engine modifications for APU operation
To provide an APU for R- GTV vehicle and to further understanding of a small (2 cylinder) APU based
on off-the-shelf engine
16
At least 6% fuel consumption improvement
demonstrated by Atkinson cycle


A Tata Nano engine was modified, based on results of performance simulation
>
To optimise the breathing for lower maximum speed operation of an APU application
>
To demonstrate the efficiency benefits of Atkinson cycle operation
At least a 6% fuel efficiency improvement was demonstrated through this work
17
To validate the APU integration options two
generator and coupling solutions were studied


Two motor/generator and coupling options were developed in hardware, connected to the TwinAir
engine, to inform future APU design
>
An EVO Electric 140 motor/generator was coupled via a compliant rubber coupling
>
A bespoke generator directly bolted to the crankshaft
The engine has been calibrated for APU operation on the test bed at MIRA
Coupling image source: Centa
18
A bespoke generator was designed to validate a
compact APU concept and an e-drive toolset

A bespoke generator was designed and built to validate the APU concept and to validate an e-drive
toolset, developed on LCVTP

Bespoke starter/generator coupled to volume production 2
cylinder gasoline engine

>
Permanent magnet machine, 55kW peak @
4000rev/min
>
Outer rotor, radial flux for high torque density
>
Liquid cooled
>
Integrated design directly coupled to crankshaft for
compactness
>
Scaleable concept
>
Operating strategy optimised for APU application
>
One of many concepts evaluated and selected for
learning opportunities
Fitted to GTV (Generic Technology Validator) technology
demonstration platform vehicle
19
Manufacturing of the bespoke starter-generator
Activities
•
•
Review design for assembly suitability
•
•
Procure machined parts & materials
•
•
Bench (static) tests
Review design for compatibility with
assembly tools & test facilities
Wind stator, resin-impregnate winding
& assemble machine
Dynamometer test
20
Manufacturing of the bespoke starter-generator
Design Reviews & Procurement
•
Machine was intended to be a
“Build-To-Print” design
•
Important to ensure machine can
actually be assembled!
•
Need to understand key characteristics
in order for procurement to proceed
smoothly
•
Need to ensure mechanical & other
interfaces are adapted to (for example)
dynamometer
21
Manufacturing of the bespoke starter-generator
Stator & Stator Wind
•
Laser-cut laminations – bonded to form
stack
•
•
•
Hand-wound (random-wound)
•
Trickle impregnation process replicated in
accordance with resin manufacturer’s
recommendations
•
Multiple K-type thermocouples
incorporated in stator winding to monitor
temperatures (insulation problems)
•
Tested to 2.7kV
Class H insulation (rated for 180 deg C)
Preliminary wind undertaken to assess
slot fill
22
Manufacturing of the bespoke starter-generator
Assembly
•
Machine assembly straightforward –
minor problems experienced consistent
with prototype build status of machine
•
Machine rotor is not supported by own
bearings – requires adaptor for dyno test
and has set screws to support rotor
when machine is separated from engine
or dyno adaptor.
23
Testing of the bespoke starter-generator
Test Status
•
•
Machine testing currently in progress
Zytek test inverter used
24
APU after treatment requirements were studied
by catalyst by-pass testing and simulation

Optimum fuel economy requires an APU
engine to be operated either at best BSFC
points or switched off

Understanding and optimisation of the CAT
light-off strategy is therefore important for
an APU application

This is especially important as for REEV
the UN ECE Reg. 83 requires toxic
emissions compliance under all SOC
conditions (including charge sustaining)

A catalyst by-pass system has been set up
on a engine test bench at MIRA to study cat
light-off behaviour

Continuation of previous Coventry
University studies; Benjamin, S. F. &
Roberts, C. A. Catalyst warm-up to light-off
by pulsating engine exhaust: twodimensional studies. Int. J. Eng. Res. 2003,
5, 257-280
25
Engine testing has shown NOx emissions as a
potential issue for APUs

Region of optimum BSFC (lower CO2 emissions) coincides with high NOx levels

Catalyst flow optimisation was performed and is reported separately
1000
1
0.9
Power/max power
1.0076
0.8
Power
1.0266
0.6
1.0456
0.5
1.0837
0.4
0.3
1.0266
1.0076
0.7
Inlet manifold pressure [mbar]
BSFC/best BSFC
1.1407
1.2167
1.3308
0.2
1.5209
1.9011
2.6616
0.1
1500
2000
2500
3000
Engine speed [rpm]
3.4221
3500
900
5.26
4.67
4.08
4.08
4.67
5.26
3.49
800
2.9
700
600
2.31
1.72
500
400
1500
Brake-specific NOx emissions[g/kWh]
1.13
2000
2500
3000
Engine speed [rpm]
3500
26
However, it is shown that Euro 5 emissions can
be achieved with existing size of close coupled
catalyst

Catalyst bypass emissions measurements were also carried out on the Twin Air engine at APU
operating conditions

It was shown that toxic emissions can be achieved close to or below Euro 5 legislated levels, with
the existing engine close coupled catalyst

However, further work is recommended to confirm this for further applications
13
12
11
Total CO emissions [g]
10
9
High power demand
Euro 5
limit
Steady state
Cold start
8
7
6
5
4
3
Euro 5
limit
2
Euro 5
limit
1
0
CO
THC
NOx
27
Multiple packaging solutions were studied


Packaging solutions were developed for the selected APU
hardware installed in the LCVTP GTV vehicle based on a
Land Rover Freelander 2

Ricardo WAVE analysis was used to optimise the
exhaust design

Multi-body dynamic system analysis was used to
study mounting solutions
The design allows installation of either the EVO Electric
140 or the bespoke LCVTP generator solutions
28
The GTV vehicle was initially developed as an
electric vehicle
EVO AF230 Drive Motor
Power: 108kW nom / 325kW peak
Torque: 240Nm nom / 480Nm peak
Reinhart DM100 Inverter
(2 units per drive motor)
Eberspächer PTC Heater 6kW &
Hella Brake Vacuum Pump
Installed in Freelander
TRW 12V Rack-Drive ePAS
Installed in Freelander
A123 22kWh Battery Pack &
Brusa 3.3kW Charger
Installed in Freelander
Ricardo 1.5kW DC:DC Converter
Mounted on Cooling Plate with Bespoke Enclosure
(3 units per vehicle)
29
The GTV was successfully demonstrated as an
electric vehicle…..

Launch

Damp conditions
•
•
•
Steady state
60mph drive past
Rough tarmac
30
… before being modified to be a RE-EV
Ricardo Single
Speed
Gearbox
Rinehart Inverter
Stack (only one
shown)
EVO AF230
Traction Motor
Fiat Twin Air
APU
31
Key Learning and Conclusions

LCVTP has provided a clearer understanding of the following :
>
The requirements specification for an APU
>
The current state of the art of APU technologies
>
The issues associated with generator integration
>
The benefits of Atkinson or Miller cycle, and other base engine modifications
>
The issues associated with toxic emissions and potential solutions
>
The overall CO2 impact of the RE-EV architecture
>
Approaches to APU testing
>
The challenges involved in creating an APU from a volume production 2 cylinder engine
>
The performance of an APU in a RE-EV
32
Acknowledgements
This work stream is part of the Low Carbon Vehicle Technology Project (LCVTP) which
comprises a combined financial investment worth £19 million by Advantage West
Midlands and the European Regional Development Fund, with further contributions from
the project’s industrial partners Ricardo, Jaguar Land Rover, Tata Motors, MIRA, and
Zytek Automotive, who are joined in the research by Warwick Manufacturing Group and
Coventry University
The authors wish to thank their many colleagues for contribution to this work.
Source xxx
33