This paper presents several case studies carried out by students of the IFP School "Engines & Energy" and "Powertrain Engineering" Masters Degree program on the potential use of a direct injection two-stroke engine for three different combinations of range extenders and electric vehicles.

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Small Gasoline Direct Fuel Injection Two-Stroke Engines for
Range Extender Applications
Pierre Duret1
, Stéphane Venturi2
, Prakash Dewangan1
1: IFP School, Rueil-Malmaison, France
2: IFP Energies Nouvelles, Rueil-Malmaison, France
Abstract: The main purpose of this paper will be to
discuss various possibilities of using a small gasoline
direct injected two-stroke engine as a range
extender (REX) for electric vehicles (EV).
For such REX applications, the main requested
specifications are: low noise and vibrations (NVH),
compactness, lightweight, minimum production cost
and efficiency. It is considered that meeting the
emissions standards will be in any case compulsory.
Considering these specifications, this paper explores
how the gasoline DI 2-stroke engine, thanks to its
advantages resulting from its double combustion
cycle frequency, can be a good candidate compared
to other possible engine technologies. We will
illustrate that through three examples of range
extender applications based on DI 2-stroke engines:
• a small displacement 2-cylinder scooter based
engine as a safety device for an EV city car.
• a modified 2-cylinder snowmobile engine as a
REX (series hybrid) for a small multi-usage
lightweight electric car,
• a 3-cylinder marine outboard engine as REX for
a multi-usage high performance EV sport car,
Various design and simulation studies have been
performed with these three configurations and will be
presented. The results will show that emissions
standards can be met when gasoline direct injection
and ultra-low NOx Controlled Auto-Ignition (CAI) are
combined together with an oxidation catalyst for
aftertreatment. Beside the achievement of the Euro 6
NOx target, remarkably low level of average CO2
emissions can be achieved with impressively
increased vehicle range (compared to the pure EV
range) with only a few litres of gasoline.
Keywords: Two-stroke engines, direct injection, CAI
Controlled Auto-Ignition, range extender, electric
vehicle
1. Introduction
Electric vehicles (EV) can be seen as a way to
mitigate the GHG emissions according to the
solution used for the production of the required
electricity. Nevertheless, it is generally considered
that, due to its drawbacks mainly linked to the
electric energy storage system (heavy, bulky and
expensive battery), the purely electric vehicle will be
limited in short-medium term for some specific
applications. Even if significant progresses can be
expected in the battery technology, during the
transition, the solution to increase the chance of
acceptance of EV by the public in a large scale could
be to keep a limited pure EV range (with therefore
minimum battery cost) corresponding to most of the
urban usages and to equip the vehicle with a
lightweight range extender. This range extender
could allow to multiply by several times the pure EV
range without sacrifying the global CO2 emissions.
It is interesting to remind ourselves that Citröen
presented in 1998 at the Paris Auto Show an electric
vehicle (based on a Saxo Citröen model) and
equipped with a small direct injected gasoline 2-
stroke engine as range extender. This innovative
vehicle (vehicle mass 1050 kg; max speed 120
km/h) was presented with a pure EV range of 80 km
and an extended range up to 340 km. The auxiliary
power unit used was a prototype DI 2-stroke engine
technology, 2 cylinder opposite 200 cc, delivering a
power of 6,5 kW and directly coupled with a starter
generator. The auxiliary power unit (thermal engine
+ starter generator) was remarkably packaged with
overall dimensions of vol. 30x30x25 cm & a mass of
20 kg. With such small size, it was possible to
implement this auxiliary unit under the rear seat of
the Saxo car. A schematic view of the whole
powertrain of the car is presented in Figure 1.
Figure 1: The Citroën Saxo Dynavolt: an electric
vehicle concept presented in 1998 with a small DI 2-
stroke engine as range extender [1]
But this very interesting project was not further
investigated after the 1998 Paris Auto Show for two
main reasons: firstly, it was not the right period for
electric vehicles (too much in advance) and 2-stroke
gasoline DI technology was not yet mature.
In parallel, during the last decades the DI 2-stroke
technology has been further developed outside
automotive and successfully applied in production for
marine outboards and 2-3 wheelers engines [2-4].

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Taking into account these two considerations
(results achieved in the 90's with a DI 2-stroke with a
non-mature technology & more recent availability of
well proven DI 2-stroke technology outside
automotive) it seems natural to wonder if for the
range extender application, a small DI 2-stroke
engine could be a relevant candidate for such
application [5,6].
For this purpose, three different case studies of
range extender versus vehicle applications
undertaken by several teams of IFP School students
are examined in this paper and their potential results
presented.
2. EV city car with 15 kW range extender
The first project presented in this paper is a small
displacement 2-cylinder scooter based engine that
could be designed and optimized as a safety device
for a typical EV city car.
2.1 Requested specifications for the thermal engine
For this project, we chose to study a 2-cylinder 250
cc DI 2-stroke that could be based on the use of
existing 125 cc Honda Pantheon 2-stroke engine
production components (piston, rod, CAI-AR
valve,…). The reason of the choice of this engine is
that it is already designed to operate in Controlled
Auto-Ignition (CAI) also named Activated Radicals
(AR) combustion [7-12].
The other following specifications were fixed at the
beginning of the project:
• maximum power of 15 kW at moderate engine
speed for noise control
• Range extender engine operating point in CAI
for NOx & PM control
• Euro 6 emissions standards
• Minimum packaging in 160 liters: the idea was to
try to integrate all the REX components (engine
with intake, exhaust, fuel circuit, cooling system,
generator, fuel tank,…) into a kind of box that
could be considered as a REX kit or module.
The choice of a packaging within 160 liters was
chosen in reference to a Wankel based
benchmark [13]
2.2 Engine architecture for REX application
Several possible 2-cylinder designs were
considered:
• In-line, combustion phasing @ 180 deg
• In-line, combustion phasing @ 0 deg
• In-line, combustion phasing @ 90 deg
• V2 90°
• Opposed cylinders (boxer)
• Opposed pistons
Figure 2: illustration of the opposed piston
configuration
Each 2-cylinder engine configuration has then been
rated according to the most important selection
criteria considered for a range extender application
[6,14]:
• NVH / balancing: with balancing shaft for in-line
configurations
• NVH / torque fluctuation: combustion frequency
and phasing
• Packaging / volume: intake & exhaust systems,
accessories,…
• Packaging / weight: engine, exhaust system,
balancing shaft,…
• Cost: complexity of manufacturing of the engine
and components (exhaust system, balancing
shaft, belts & accessories,…)
• Efficiency: scavenging process, exhaust
tuning,…
The results of this rating are summarized in the
Table 1. From this analysis, the Opposed pistons
configuration seems the most promising followed by
the 2-cylinder in-line with combustion phasing every
180 deg. CA.
Table 1: comparison of various engine architecture
versus REX application criteria
2.3 Energy management optimization
The purpose of this sub-section is to study the
optimum energy management strategy for the range
extender application. The main tasks undertaken are
as follows:
• to determine the optimized REX operating point
necessary to undertake the NEDC with
maintained battery SOC, taking into account
efficiency of the whole chain from the requested
power at the wheels to the corresponding power
of the REX thermal engine;

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• to estimate (based on the extensive IFP
experimental DI CAI 2-stroke engine data base
build during the last 25 years of experience [15-
18]) the pollutant emissions level in comparison
with Euro 6 legislation and the fuel consumption
and corresponding EV range extension.
This energy management optimisation has been
simulated with 4 examples of vehicle application.
The weight and estimated SCx of the 4 selected
vehicles are shown in the Table 2.
Table 2: example of vehicle applications studied
We considered a range extender giving a maximum
power output of 15 kW (which is a quite reasonable
power for a 250 cc 2-stroke engine that can be
achieved at a moderate engine speed of about
4500-5000 rpm for minimum REX noise). Taking into
account the various efficiencies from the REX
crankshaft to the wheels, we can estimate that it
should correspond to a power at the wheels of about
11,33 kW. From this value and taking into account
the vehicle characteristics in Table 2, it is possible to
estimate the top speed of each vehicle in REX mode
and for different road slopes. The results are
summarized in the Table 3 here below.
Table 3: maximum vehicle top speed in REX mode
with 0, 2 and 4% of slope
The type of REX considered in this study are more
like a safety device allowing to be able to continue to
drive only when the battery charge becomes too low.
Therefore, since it will be an exceptional mode of
operation, it is possible to accept some reduced
vehicle performance.
During REX operating mode, it was then chosen to
limit the vehicle speed to a maximum of 90 km/h for
all the 4 vehicles. In such case the NEDC Cycle
used for the emissions calculation is also limited to
90 km/h as shown in Figure 3.
It is then possible to calculate the average power at
the REX crankshaft that is necessary for each
vehicle to perform this revised NEDC cycle. This
calculation includes the various efficiencies and also
the regenerative braking during deceleration. In such
case, if the REX engine runs during the whole NEDC
at the same average power of the Table 4, it will
allow to maintain the same battery state of charge
between the beginning and the end of the cycle.
Figure 3: revised NEDC driving cycle with 90 km/h
top speed
Table 4: average power of the REX for maintained
battery state of charge during the revised NEDC
This required average power can be achieved at
different engine speeds. The choice of the engine
speed results from a trade-off between NOx
emissions which decrease when the engine speed
increases (because the engine load decreases) and
the engine noise which increases when the speed
increases. In fact the optimum operating point
corresponds to the minimum engine speed for Euro
6 NOx emissions. 4000 rpm seems in this case a
good compromise. At this engine speed, from our DI
CAI 2-stroke data base, the REX should be able to
meet Euro 6 NOx limit up to a power of 2,97 kW
(corresponding to 1,78 bar BMEP) without DeNOx.
This power is slightly above the power required for
the 4 vehicles.
If we now look to the other pollutant emissions (see
Table 5), we see that without aftertreatment, the CO
level should be just above the Euro 6 limit and the
HC level about 6 times above. From previous
experience, we can be confident that, with such raw
CO and HC emissions levels, Euro 6 limits can be
achieved with an appropriate oxidation catalyst
design (location, dimensions, cells density, precious
metal formulation) and an appropriate fast oxi-cat
lighting strategy.
Table 5: estimated emissions of the REX
(2,97 kW @ 4000 rpm)

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2.4 In-vehicle integration
The following Table 6 summarizes the main
performance results achieved with this case study of
a 15 kW range extender for EV city car.
Table 6: summary of the simulated main
performance results of the 15 kW REX
Finally, about the initial 160 litres packaging target, a
CATIA predesign study has been undertaken based
on the choice of the opposite pistons engine
configuration.
Figure 4: CATIA pre-design study of the REX
packaging in a 160 liters volume
The Figure 4 shows that all the following
components of the complete range extender “kit” can
be incorporated in such a volume:
• DI/CAI 250cc 2-stroke with intake & exhaust
• generator and its coupling with the engine
• cooling system with radiator and fan
• DC/DC convertor
• fuel tank (10 liters)
3. Lightweight urban sport plug-in hybrid
3.1 Vehicle specifications (Segula Hagora project):
In this second case study of range extender
application, the selected vehicle is a urban sport
plug-in hybrid vehicle concept developed by Segula
and named the Hagora project. Its main
specifications are:
• Lightweight 3-seat mid-size vehicle
• Plug-in hybrid
• 25 km full electric range
• Acceleration: 0-100 km/h < 10s
• Top speed: 185 km/h
• Average fuel consumption target: 2 l/100 km [19]
Figure 5 : the Segula Hagora vehicle project
3.2 Thermal engine specifications
In this study, the thermal engine will develop about
30-35 kW at moderate engine speed. Its main
specifications are as follows:
• based on a modified 2-cylinder snowmobile
production ROTAX 600 HO engine
• high power / weight ratio
• longest stroke available engine
• already equipped with direct injection (E-Tec)
• modified for high torque at low speed and limited
maximum speed
• Euro 6 emissions capability (exhaust valve for
ultra low NOx CAI)
Figure 6: the production ROTAX 600 HO engine
The following Table 7 show the new targets for
reduced power & speed of the modified engine in
order to achieve Euro 6 emissions limits.
Table 7: new performance targets
of the modified engine

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3.3 GT Power modeling of modified configuration
versus performance targets
During this project, GT Power has been first
calibrated on the production engine. In a second
step, it has been used to select the best transfer and
exhaust ports timings for the new engine
performance targets. The results are summarized in
the Table 8.
Table 8: compared port timings & exhaust tuning
speed between production versus modified engine
The motivations for such engine modifications were:
• to reduce the maximum engine speed
• to increase the low speed torque
• to decrease the raw emissions (HC)
• to improve the ability to CAI combustion
in order to finally reach the efficiency & emissions of
IFP experimental DI CAI 2-stroke data base (see
Figure 7) .
Figure 7: Iso-BSFC map used
for DI CAI 2-stroke engine
3.4 Selected Plug-in Hybrid architecture
In this project, a specific innovative plug-in hybrid
architecture has been chosen as illustrated in Figure
8. This particular architecture allows a lot of
possibility in terms of the optimization of the energy
management of the whole powertrain. In a first step
of this study, the possibility to use the DI 2-stroke
engine in the hybrid mode has been investigated.
Figure 8: selected hybrid architecture
3.5 Simulink energy management optimization –
Hybrid strategy
An online Equivalent Consumption Minimization
Strategy (ECMS) in Simulink for energy optimization
has been firstly studied. The following Figures 9 & 10
show the selected engine operating points resulting
from this minimum NOx optimisation strategy on
NEDC cycle under charge sustaining constraints.
Figure 10: DI 2-stroke engine operating points along
the iso-NOx emissions map in hybrid mode
Figure 9: DI 2-stroke engine operating points along
the iso-BSFC map in hybrid mode

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In the Figures 11 here above, it is possible to see as
a function of the time corresponding to the NEDC
cycle:
• the vehicle speed in km/h along the NEDC
• the instantaneous DI 2-stroke engine torque
• the instantaneous electric motor torque
• the evolution of the battery SOC during the cycle
It can be observed from Figure 10 that the strategy
succeeds to place most of the operating points at
low NOx regions however being on-line optimization
it suffers some full load operations as can be seen in
the red circle on Figures 10 and 11. These high load-
high NOx points could be avoided in an offline
optimization which would be less relevant for real
application.
Table 9: fuel consumption and emissions results
for the “hybrid strategy”
The global efficiency and emissions results
presented in the Table 9 show that with this
optimized hybrid mode strategy:
• very good fuel consumption can be achieved
• unfortunately NOx emissions are too high, about
4 times the Euro 6 level, which then cannot be
achievable without DeNOx. This can be easily
understandable when looking to the Figure 10
which shows several operating points above the
low load ultra-low NOX CAI region
• CO & HC emissions remain compatible to be
decreased by an oxidation catalyst.
3.5 Simulink energy management optimization –
Range extender strategy
Therefore after this first step showing that a DI 2-
stroke engine is not adapted for an hybrid strategy
without DeNOx, in a second step the range extender
strategy is now investigated. Here are the main
characteristics of this “range extender” strategy:
• the CVT is tuned for lowest NOx emissions
• the DI 2-stroke supplies constant power all the
time
o with an average power allowing to cover
the NEDC cycle with ICE only
o with a low load working point in CAI for
ultra-low NOx (Figure 13) even if BSFC
is not the best (Figure 12)
• the battery is used as a buffer
• the E-motor is also used as a generator when
the ICE power is superior to the vehicle demand
• the system is globally charge sustaining
o the batteries slowly charged during
urban part of NEDC (Figures 14)
o there is a battery depletion during the
extra-urban part of NEDC (Figures 14)
Figure 12: DI 2-stroke operating points along the iso-
BSFC map in range extender mode
Figure 11: optimized hybrid mode strategy for best
fuel consumption versus NOx trade-off

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Figure13: DI 2-stroke operating points along the iso-
NOx emissions map in range extender mode
Figure 14: optimized range extender mode strategy
for minimum NOx emissions
Table 10: fuel consumption and emissions results
for the “range extender” strategy
The results achieved with this “range extender”
strategy are very interesting. They show again that a
DI 2-stroke engine when it is used as a range
extender has the potential to reach the Euro 6 NOx
emissions limit without aftertreatment, and with
significant margin in this example. The fuel
consumption is obviously slightly increased
compared to the efficiency optimized “hybrid
strategy” but the average fuel consumption still
remains below the 2 l/100 km target. In addition, CO
and HC remain at a level compatible for their
conversion by an oxidation catalyst.
4. Multi-usage high performance luxury electric
sport car
4.1 Electric vehicle specifications (Exagon Furtive)
In the third and last case study of range extender
application in this paper, we will describe briefly
another project of using a modified marine outboard
DI 2-stroke engine as range extender of a high
performance multi usage luxury electric sport car.
The vehicle chosen for this study is the Exagon
Furtive (Figure 15).
Figure 15 : the Exagon Furtive luxury EV sport car
Its main specifications are :
• Weight: 1950 kg
• SCx: 0,81 m2
• Electric motors: 250 kW
• Electric range:
o 300 km on NEDC
o 197 km @ 130 km/h
4.2 Enhanced specifications with Range extender
The targets of the project are to study a range
extender application that could enhance the vehicle
specifications as follows:
• Maximum vehicle speed in REX mode: 140 km/h
• + 300 km range on NEDC
• + 247 km range @ 130 km/h
• with 30 l fuel tank
0.2
0.2
0.4
0.4
0.6
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0.8
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23
4
5 6
7
7
7
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Engine RPM
EngineTorque[N.m]
NOx emission (g/kWh)
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
10
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60

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4.3 Choice of the engine architecture adapted for
REX application
One of the major target of this project was to use an
existing “on the shelf” engine as a range extender to
minimize the development cost of a new engine. In
this study, we investigated the possibility of using a
DI 2-stroke engine based on a production marine
outboard engine. Its main specifications are in the
Table 11 and Figure 16 here after.
Table 11: main specifications of the marine outboard
DI 2-stroke engine investigated as range extender
Figure 16: the 3-cilinder Selva
marine outboard DI 2-stroke [3]
The required engine modifications and adaptations
for this range extender applications are limited to
what is strictly necessary:
• no change of the thermodynamics/scavenging
characteristics
• use of existing production DI system (IAPAC
compressed air assisted fuel injection)
• implementation of exhaust throttling valves for
CAI combustion
• new exhaust system to be designed including
oxidation catalyst.
4.4 Energy management optimization for minimum
NOx in range extender mode
Similarly to the two previous case studies, we will
keep the main energy management optimization
with:
• a single operating point in CAI combustion for
ultra-low NOx
• the same battery SOC at the beginning and at
the end of the NEDC cycle
Table 12: selected REX operating point and NOx
emissions compliance
The results in Table 12 show that here again, the
Euro 6 NOx emissions limit can be met without
DeNOx after treatment and with regulated vehicle
CO2 emissions of 18 g/km.
5. Conclusions
From the results presented in this paper, we have
been able to draw the following conclusions:
• To be able to propose electric vehicles equipped
with a range extender will help to develop the EV
customer acceptance
• Small engine technologies are well adapted for
such application and will therefore bring their
contribution for future Sustainable Mobility
• Among those technologies, the DI 2-stroke
engine represents a relevant candidate thanks to
its advantages of lightweight, compactness,
double cycle frequency and NVH, cost and
efficiency
• One of the major challenge of the use of DI 2-
stroke engines for automotive range extender
application is the NOx & PM emissions issue
• Energy management optimization of 3 examples
of DI 2-stroke REX / EV combination shows
that, when combined with part load Controlled
Auto Ignition, Euro 6 NOx emissions can be
achieved without DeNOx aftertreatment.
6. Acknowledgement
The authors would like to particularly thank the
following contributors to this work:
IFP School students project teams:
• Alexandre BORIE, Thomas BRICHARD,
Thomas CREMILLEUX, Samuel QUESADA
• Félix GALLIENNE, Sébastien LEMOINE, Adrian
MIGUEL SANCHEZ
• Ivo LANIAR, Thomas LE BIHAN, Quentin
PIRAUD
• Estelle GRILLIERES, Vijaykannan MOHAN,
Vincent ROVERE, Michel SANCHO
The support from industry
• Lorenzo SERRAO – DANA
• Benoit BAGUR – Exagon Motors
• Pascal GIRARD – Segula Technologies

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[19] Journal officiel de l'Union européenne – Règlement
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8. Contact
Pierre DURET: pierre.duret@ifpen.fr