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FINAL MANUSCRIPT Page 1 of 22 SIAT26.doc – MDA / GBB – 28/06/01
2001-01-0010
Advanced Electronic Fuel Injection Systems –
An Emissions Solution for both 2- and 4-stroke
Small Vehicle Engines
Mark Archer, Greg Bell
Synerject Systems Integration, Balcatta, Australia
ABSTRACT
This paper describes two advanced electronic fuel
injection systems for small vehicles which have recently
become commercially available. Both systems have been
designed and developed by the authors’ organisation.
One of the two systems (‘aSDI’) has been
designed and developed for 2-stroke engines and the other
(‘SePI’) for 4-stroke engines. Both systems are intended
for application on small vehicles fitted with small 1 – 2
cylinder gasoline engines of displacement 50 – 250 cm3
per cylinder. Typical examples of such small vehicles
are: ATV’s (All Terrain Vehicles), auto-rickshaws,
motorcycles, motorscooters and mopeds1.
Fuel consumption and emissions results from
both systems are presented, and in both cases it is
shown that engine-out exhaust emissions meet current
and future limits in Europe, India and Taiwan, without the
need for exhaust after-treatment. It is also shown that
both systems offer significant fuel savings relative to
otherwise-equivalent, carburetted baseline vehicles.
Other important benefits of these systems which
are discussed in this paper are improved cold start and
improved driveability.
The paper also includes a short overview of the
performance and cost implications of both systems
relative to alternative emissions control methods.
1 For reasons of convenience, these types of vehicles will
be referred to collectively as ‘small vehicles’ in this paper.
1. INTRODUCTION
During the last 30 years or so, reductions in
tailpipe exhaust emissions of more than 90% have been
demanded of, and achieved by the automobile industry
[1], with one of the most important enabling technologies
being low-cost, series-production EFI (Electronic Fuel
Injection).
Relative to carburetted fuel systems, the main
mechanisms by which EFI has helped to reduce exhaust
emissions are as follows:
1) Reduced wall wetting.
2) Improved fuel atomisation.
3) Greater flexibility in A/F (Air/Fuel ratio) control, which
in turn has facilitated:
• Improved warm - and cold-start emissions.
• Reduced transient emissions.
• Increased lean A/F operation.
• High conversion-efficiency exhaust after-
treatment.
4) Improved unit-to-unit repeatability.
In addition to reduced exhaust emissions, EFI
has also introduced other benefits such as reduced brake-
specific fuel consumption, increased full-load output and
improved driveability [2].
As a result of this reduction in automobile
exhaust emissions, it is now often smaller vehicles such
as auto-rickshaws, motorcycles, motorscooters and
mopeds which are becoming responsible for an
increasingly significant proportion of the HC (unburnt
hydrocarbons) and CO (carbon monoxide) exhaust
FINAL MANUSCRIPT Page 2 of 22 SIAT26.doc – MDA / GBB – 28/06/01
emissions burden in some urban environments. In the EU
for example, two- and three-wheeled motor vehicles are
currently believed to be responsible for around 5 – 10% of
overall HC and CO emissions, and it is anticipated that
this proportion will increase to 15 – 20% by the year 2020
[3].
In some large Asian cities, the situation is
already more serious; the high popularity of motorcycles
in Taiwan for example, means that they are currently
believed to be responsible for approximately 30% of overall
HC and 40% of overall CO emissions [4].
Increased attention is therefore now being paid to
reducing exhaust emissions from small vehicles, and one
obvious means of achieving such a reduction is to apply
EFI technology from the automotive sector.
When considering the small vehicle market
relative to the automobile market however, one key
difference immediately becomes apparent; namely: cost.
This ‘cost’ issue manifests itself in two very important
ways as follows:
1) In the small vehicle market, the maximum allowable
piece cost of an emissions reduction system, is
smaller than in the automobile market (by
approximately one order of magnitude).
2) The incremental investment cost of a new technology
which will be tolerated by the small vehicle industry is
also much smaller than in the automobile industry.
The need for cost-effective emissions solutions in
the small vehicle industry is therefore widely recognised,
and, as outlined in the following section, a number of
alternative low-cost strategies are currently being pursued.
The strategy detailed in this paper involves the
application of advanced electronic injection systems:
Direct-Injected (DI) in the case of 2-stroke engines and
Port-Injected (PI) in the case of 4-stroke engines.
Although higher in piece cost than some alternative
systems, we believe that such systems offer a better
overall cost / benefit balance (i.e. when piece cost,
production cost, operational, reliability, environmental, and
other issues are all taken into account).
The aims of this paper are therefore:
1) To provide a brief description of the Synerject 2-stroke
and 4-stroke fuel injection systems.
2) To present test results and other information which
help give a better understanding of the overall cost /
benefit balance offered by both systems.
The 2-stroke system described in this paper
became available to the public for the first time in June
2000 on the Aprilia ‘DITECH’ SR 50 motorscooter (Figure
1) and will soon appear on a number of other small vehicle
models produced by a variety of manufacturers worldwide.
Public response to the Aprilia DITECH SR50
motorscooter has been very positive with most significant
operating benefits being [5]:
• ‘Real world’ fuel consumption benefit of 40%.
• Negligible exhaust smoke emissions.
• Improved cold-start.
• Improved driveability.
• Oil consumption reduced by more than 50%.
• Oil ‘top-up’ service interval increased to 4,000 km.
Figure 1 - Aprilia DITECH SR50 motorscooter
The 4-stroke system described in this paper is
due to be released to the public in 2001.
2. ALTERNATIVE EMISSIONS REDUCTION
METHODS FOR SMALL VEHICLES
This section includes a brief description of the
main emissions reduction methods currently being used
and/or considered for use by the small vehicle industry.
The advantages and disadvantages associated with these
various emissions reduction methods are summarised in
Table 1 and Table 2. These methods are as follows:
FINAL MANUSCRIPT Page 3 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Table 1 – Comparison of different emissions control systems for small vehicle 2-stroke engines
Attribute
System
Fuel consumption
& CO2 emissions
CO emissions
HC + NOx emissions
Emissions durability
(catalyst aging / misfire)
Specific torque & power
(Acceleration)
Cold start
Driveability
Maintenance
(Oil / oil filter servicing)
Incremental piece cost *
– relative
Incremental investment cost
* – relative
Key
2-stroke carburettor
(Baseline): ( = ) ( = )
( = ) ( = ) ( = ) ( = ) ( = ) ( = ) 0.0 0.0 66 Much worse
Oxidation catalyst:
= 3 3 6 6 = = = 0.3 0.5 6 Worse
Replace with
4-stroke:
3 6 3 3 66 = 3 6 1.0 2.0 = Equal
2-stroke electronic
injection (‘aSDI’):
33 3 3 3 = 3 33 3 1.0 1.0 3 Better
‘aSDI’ + oxidation
catalyst:
33 33
33 3 = 3 33 3 1.3 1.5 33 Much better
* Indicative cost increment only for 10,000 units per annum – actual costs vary significantly from market to market
Data sources: [3], [5], [6] & [7] plus internal cost estimates
Table 2 - Comparison of different emissions control systems for small vehicle 4-stroke engines
Attribute
System
Fuel consumption
& CO2 emissions
CO emissions
HC + NOx emissions
Emissions durability
(cat. aging / tampering)
Specific torque & power
(Acceleration)
Cold start
Driveability
Maintenance
(SAI valve inspect/clean)
Incremental piece cost *
– relative
Incremental investment cost
* – relative
Key
4-stroke carburettor
(Baseline): ( = ) ( = )
( = ) ( = ) ( = ) ( = ) ( = ) ( = ) 0.0 0.0 66 Much worse
SAI (Secondary Air
Injection): = 3 3 6 = = = 6 0.5 1.0 6 Worse
SAI + oxidation
catalyst: = 33
33 6 = = = 6 0.8 1.5 = Equal
4-stroke electronic
injection (‘SePI’):
3 3 3 3 3 3 3 = 1.0 1.0 3 Better
‘SePI’ + Three-Way
Catalyst (TWC):
3 33
33 3 3 3 3 = 1.3 1.5 33 Much better
* Indicative cost increment only for 10,000 units per annum – actual costs vary significantly from market to market
Data sources: [3] & [6] plus internal cost estimates
FINAL MANUSCRIPT Page 4 of 22 SIAT26.doc – MDA / GBB – 28/06/01
2.1 SUBSTITUTE CARBURETTED 4-STROKE
ENGINES FOR CARBURETTED 2-STROKE
ENGINES.
Relative to carburetted 2-stroke engines, the main benefits
offered by carburetted 4-stroke engines are:
• Misfire-free operation.
• Reduced fuel consumption and CO2 emissions.
• Reduced HC emissions.
• Improved driveability
However, this is a relatively high piece and
investment cost strategy, which is sometimes driven more
by the ‘clean’ image of 4-strokes relative to 2-strokes,
rather than an objective consideration of state-of-the-art 2-
stroke and 4-stroke engine performance per se.
While this ‘substitution’ strategy successfully
eliminates the high levels of HC, smoke and odour
emissions typically associated with carburetted 2-stroke
engines, the engine-out CO and NOx (Nitrogen Oxide)
emissions are usually higher, and because of the
difference in specific output between 2-stroke and 4-stroke
engines, a larger, heavier and more expensive ‘substitute’
4-stroke engine is normally required to maintain an
equivalent level of performance.
2.2 FIT EXHAUST AFTER-TREATMENT
CATALYSTS.
Because small vehicles are only responsible for a
relatively low proportion of overall NOx emissions
(estimated to be less than 3% [3] [4]), oxidation-only
catalysts are usually fitted to small vehicle engines. In
the case of 4-stroke engines, these catalysts are used
principally to control CO emissions, while in the case of 2-
stroke engines they are used to treat both HC and CO
emissions. The main advantage of this strategy, is that it
is one of the cheaper means of achieving compliance with
current emissions legislation, if the base engine is a
carburetted 2-stroke [3] [6].
Although attractive from the perspective of low
piece and investment cost therefore, catalysts offer no
reduction in fuel consumption or CO2 emissions, and are
susceptible to deterioration, particularly on carburetted 2-
strokes due to the large quantity of unburnt fuel and oil in
the exhaust [8].
Catalyst fitment also increases exhaust
temperature and back-pressure, and, particularly in the
case of 2-stroke engines, peak power output can be
significantly reduced as a result. In the absence of
periodic emissions testing, the effectiveness of this
strategy can also be reduced by tampering (e.g.
intentional modification and/or removal).
The anticipated, widespread introduction of
emissions durability requirements and/or ‘cold-start’
emissions testing will make small vehicle catalyst
durability and ‘light-off’ more important issues than is
currently the case.
2.3 SECONDARY AIR INJECTION (SAI).
This technique is now being increasingly applied
to small vehicle 4-stroke engines as a means to reduce
CO, and to a lesser extent, HC. Usually a ‘passive’ reed
valve system is used; i.e. negative pressure pulses in the
exhaust system are used to draw fresh, filtered air into the
exhaust stream, immediately downstream of the exhaust
valve. The main advantage of this strategy, is that it is
one of the cheaper ways of achieving compliance with
current emissions legislation if the base engine is a
carburetted 4-stroke [3] [6].
Potential problems with such systems include
backfiring [6] and carboning of the reed valve. To ensure
continued system function, periodic inspection and/or
cleaning of the reed valve(s) is usually recommended (for
motorcycles: typically every 5,000 – 6,000 km).
‘Passive’ SAI is not well suited to carburetted 2-
stroke engine applications, due to the following reasons:
• 2-stroke engines rely on negative exhaust pressure
pulsations to help scavenge the combustion chamber.
If these pulsations are instead used to draw fresh air
into the exhaust stream, cylinder scavenging (and
thus engine performance) can be compromised.
• On a carburetted 2-stroke engine, unburnt HC are
generated mostly as a result of the intake charge
‘short-circuiting’ to the exhaust port during
scavenging. By definition however, this ‘short-
circuited’ charge will contain both unburnt HC and
unburnt air. As a result, adding extra air to such a
mixture achieves little in it’s own right.
• In the case of ‘combined’ SAI / oxidation catalyst
systems, passive SAI can result in excessive catalyst
temperature with reduced catalyst and muffler
durability as a result [9].
2.4 APPLY ADVANCED ELECTRONIC FUEL
INJECTION SYSTEMS.
This is the strategy advocated by Synerject for
both 2-stroke and 4-stroke engines, and the one which will
be detailed in the remainder of this paper. Although
higher in piece cost than either oxidation catalysts or SAI
systems (refer Table 1 and Table 2), by offering
significantly reduced fuel consumption and increased
riding pleasure in addition to very low engine-out exhaust
emissions, we believe that such systems offer the best of
all worlds to both manufacturer and end user on an overall
cost / benefit basis.
FINAL MANUSCRIPT Page 5 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Of course, certain combinations of the various
methods described above can also be implemented. For
example, both 2-stroke and 4-stroke electronic injection
systems have been successfully combined with exhaust
catalysts, and in the medium term it is anticipated that
such systems will become ‘standard’ as emissions
requirements become more stringent [7]. ‘Combined’ fuel
injection / catalyst and SAI / catalyst systems have
therefore also been included in Table 1 and Table 2, for
comparison purposes.
Note that catalyst fitment has much less effect on
the performance of a DI 2-stroke engine relative to a
carburetted 2-stroke engine; because DI produces far less
engine-out HC and CO emissions, and catalyst
temperature / back-pressure are considerably reduced as
a result.
On small vehicle 4-stroke engines, electronic
injection systems can be combined with an Exhaust Gas
Oxygen (EGO) sensor and Three-Way Catalyst (TWC) to
facilitate simultaneous treatment of HC, CO and NOx
emissions as is currently done in the automobile industry.
3. OVERVIEW – 2-STROKE VS. 4-STROKE SYSTEMS
The 2-stroke and 4-stroke electronic injection
systems presented in this paper are similar in many
respects. Both are intended for fitment to 1 – 2 cylinder
gasoline engines of 50 – 250 cm3 swept volume, and
consequently share many of the same components.
However, the two systems also differ in a number of
important respects, the most significant difference being
that the 2-stroke system is a DI (Direct Injection) system,
whereas the 4-stroke system is a PI (Port Injection)
system.
Table 3, Table 4 and Table 5 list the key
components of both systems and schematic diagrams of
both systems are shown on Figure 2 and Figure 3.
Of course, DI can be applied to gasoline 4-stroke
engines also; since 1996 four major auto manufacturers
have released engines of this type to the market, and
many others have indicated that they are developing
engines of this type for near-term market release [10].
The main driver for this change is the reduced fuel
consumption available (typically 10 – 20% better than an
otherwise-equivalent PI 4-stroke engine), in conjunction
with low engine-out NOx [11] [12] . In light of this
development, a logical question is: “Why not apply DI to
small vehicle 4-stroke engines also ?”
Table 3 - Engine management sub-system - key
components
Component ‘aSDI’
2-stroke
system
‘SePI’
4-stroke
system
ECU 3 3
Integrated throttle body /
Throttle Position Sensor
(TPS)
3 3
IAV (Idle Air Valve) 3
Electronic Ignition – High
Energy Inductive (HEI)
coil
3 3
Engine crank sensor 3 3
Engine temperature
sensor
3 3
Vehicle speed sensor Optional Optional
Ambient air pressure
sensor Optional Optional
Immobiliser Optional Optional
Electronic oil pump Optional
‘CO potentiometer’ * Optional Optional
* This function can be carried out by means of a
diagnostic / service tool if required.
(Refer section: ‘Diagnostics and Servicing’ below).
Table 4 - Fuel sub-system - key components
Component ‘aSDI’
2-stroke
system
‘SePI’
4-stroke
system
Fuel injector 3 3
Fuel pump 3 3
Fuel regulator 3 3
Fuel filter 3 3
Air injector 3
Air compressor 3
Air/fuel rail 3
CVP valve Optional Optional
Table 5 - Combustion sub-system - key components
Component ‘aSDI’
2-stroke
system
‘SePI’
4-stroke
system
Modified cylinder head 3
Long-projection spark
plug
3
Modified piston Optional
FINAL MANUSCRIPT Page 6 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Figure 2 - System schematic - 'aSDI' 2-stroke electronic injection
Figure 3 - System schematic - 'SePI' 4-stroke electronic injection
FINAL MANUSCRIPT Page 7 of 22 SIAT26.doc – MDA / GBB – 28/06/01
FINAL MANUSCRIPT Page 8 of 22 SIAT26.doc – MDA / GBB – 28/06/01
In fact, a development of this type does seem
likely in the medium term, as small vehicle fuel
consumption and exhaust emissions continue to assume
still greater importance. In the current small vehicle
market environment however, demand for DI 4-stroke
engines is tempered relative to the automobile market by
the following factors:
1) Increased emphasis on system low cost.
As discussed in the ‘Introduction’ section above.
2) Component availability.
To fully exploit the combined emissions / fuel
consumption benefits offered by DI relative to PI on a
4-stroke engine, the in-cylinder gas/fuel ratio should
be lean, but not unthrottled. On a passenger car
engine, this ‘controlled enleanment’ is readily
achieved by means of an ETB (Electronic Throttle
Body) and/or EGR (Exhaust Gas Recirculation).
Although not yet widely available in the small vehicle
industry, such components are standard fitment on
many modern automobiles, and in relative terms, DI 4-
stroke application is cheaper and easier as a result.
3) Low demand for reduced engine-out NOx.
Small vehicle emissions legislation in many countries
has been written with the aim of encouraging more
widespread use of 4-stroke engines at the expense of
(carburetted) 2-stroke engines. Because 4-stroke
engines generally produce more NOx than 2-stroke
engines, the emissions legislation ‘push’ towards low
NOx in the small vehicle market is currently weaker
than in the passenger car market, and so there is
little demand to exploit the reduced engine-out NOx
emissions available with DI 4-stroke engines as a
result.
The above arguments explain why PI is currently
preferred to DI for small vehicle 4-stroke engines; so why
not use the same system on small vehicle 2-stroke
engines also?
The short answer to this question is: “cost /
benefit”; on a 2-stroke engine, the cost / benefit offered by
DI is much more favourable than that offered by PI as a
result of the much larger fuel consumption and emissions
benefits available. The main reason for this difference is
that, relative to a carburettor, DI is able to drastically
reduce 2-stroke charge losses during scavenging (to the
point where engine-out HC emissions are on-par with a 4-
stroke engine of similar displacement), whereas PI can
only offer a limited improvement (relative to a carburettor)
in this respect.
Because of the fundamentally different cylinder
charge processes of 2-stroke versus 4-stroke engines, DI-
2-stroke fuel systems are also simpler and cheaper than
their 4-stroke counterparts. As demonstrated by the test
results presented in this paper for example, large
improvements in fuel consumption, HC and CO can be
achieved without electronic gasflow control components
(such as ETB’s and/or EGR).
The main benefits offered by PI on a 2-stroke
engine are: reduced fuel consumption (typically by around
10%), improved cold start and improved warm-up;
however, these benefits are available with DI to an even
greater extent.
Because of improved combustion stability, DI 2-
stroke NOx emissions are often higher than those from an
otherwise equivalent carburetted (or PI) engine, however,
the NOx emissions from 2-stroke engine are low in any
case, and even on a DI 2-stroke engine, engine-out NOx
emissions are typically:
• Less than the NOx emissions produced by a
carburetted 4-stroke engine of similar displacement.
• Up to an order of magnitude smaller than HC
emissions in massflow terms.
• Well within current and expected legislated limits (see
below).
4. SYSTEM DESCRIPTION – 2-STROKE SYSTEM
(‘aSDI’)
A schematic diagram of the DI 2-stroke system,
known as ‘aSDI’ (air-assisted Synerject Direct Injection),
is shown on Figure 2 above. This system is based on the
well-known, air-assisted, direct-injection Orbital
Combustion Process (OCP), which was first released to
the general public in 1996 [13] [14], and has since been
applied to a number of engines in a variety of markets
worldwide.
Key features of OCP are:
• The use of low-pressure compressed air (as opposed
to high fuel pressure) to achieve fuel atomisation.
• The ability to generate an in-cylinder air/fuel ‘cloud’
consisting of very fine droplets.
• High tolerance to in-cylinder ‘residuals’ (i.e. retained
exhaust gas), by virtue of the injected air.
• Separation of fuel metering and in-cylinder injection
functions; these are performed by the fuel injector and
‘air injector’ respectively (refer Figure 4). This ‘division
of responsibilities’ facilitates a number of important
performance benefits including: increased fuel cloud
shaping flexibility, greater deposit immunity and
reduced system cost.
FINAL MANUSCRIPT Page 9 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Figure 4 - OCP fuel and air injectors – typical
arrangement
In order to further reduce system cost however,
the ‘aSDI’ system has been significantly simplified relative
to the OCP systems currently used on other series-
production 2-stroke applications [13]. Key changes in
this respect are:
1) The ‘aSDI’ air compressor is run directly off an
eccentric on the crankshaft (Figure 5); other
applications on larger engines typically use a belt- or
gear-driven compressor.
Figure 5 – ‘Direct acting’ compressor drive
2) The ‘aSDI’ compressed air system does not include
an air pressure regulator.
3) Key system-specific components such as the ECU
and fuel pump have been re-designed and developed
to suit the reduced size, cost and complexity
requirements of the small vehicle market.
4) The complete ‘aSDI’ system has been designed to
minimise electric current consumption,
commensurate with the limited electrical power
generation capacity available on most small vehicles.
Note that ‘aSDI’ also differs in a number of
important respects from the OCP-based motorscooter
system previously presented in [15]. Whereas the earlier
system used a FMP (Fuel Metering Pump) for fuel delivery
and metering, ‘aSDI’ now uses a more conventional
automotive fuel delivery system with electric fuel pump,
(re-calibrated) automotive fuel regulator and (re-calibrated)
automotive fuel injector. This change was implemented
due to the following reasons:
• Improved response to step changes in driver demand.
• Reduced development and investment costs.
• Increased customer confidence.
• Reduced commercial risk.
Two key components which were required to
enable this change were:
1) The fuel injector.
2) The fuel pump.
These components, along with some of the other
system-specific components used by ‘aSDI’ are described
in greater detail below.
5. SYSTEM DESCRIPTION – 4-STROKE SYSTEM
(‘SePI’)
A schematic diagram of the ‘SePI’ (Synerject
electronic Port Injection) PI 4-stroke system is shown on
Figure 3.
Relative to contemporary automobile PI systems,
the ‘SePI’ system offers both reduced cost and reduced
functionality, in accordance with the demands of the small
vehicle market.
Key differences between ‘SePI’ and a
contemporary automotive PI system are as follows:
• ‘SePI’ has been designed and developed specifically
for application to small vehicle 1 – 2 cylinder gasoline
engines. Unnecessary automotive functionality (e.g.
extra inputs and drivers such as those required for
additional cylinders, EGR, electronic throttle control
and/or transmission control) have not been included.
Air compressor
Crank web
Crankshaft
Piston
Machined
eccentric
Air
injector
Fuel
injector
Fuel
Compressed air
Direct-injected,
pre-mixed charge
Air/fuel rail
FINAL MANUSCRIPT Page 10 of 22 SIAT26.doc – MDA / GBB – 28/06/01
• The same, low-cost ECU is used as is used for
‘aSDI’.
• Like ‘aSDI’, ‘SePI’ also uses a low-cost, low-flow,
high-efficiency electrical fuel pump.
• Like ‘aSDI’, care has been taken to minimise
electrical current consumption of the overall ‘SePI’
system.
The result is a 4-stroke PI system that can be
implemented with reduced investment cost, but still offers
the performance necessary to meet current and future
customer and legislative demands in the small vehicle
market.
6. COST REDUCTION STRATEGIES
With both ‘aSDI’ and ‘SePI’ systems, piece and
investment costs have been minimised by means of the
following strategies:
• The functionality of both systems has been reduced
to meet only the requirements of the small vehicle
target market.
• Modifications to the base vehicle have been
minimised.
• Unnecessary differences between applications have
been eliminated wherever possible (e.g. ‘aSDI’ and
‘SePI’ share many common components and control
strategies).
• High-volume, off-the-shelf components have been
used where possible (e.g. temperature, pressure,
crankangle and throttle position sensors; ‘aSDI’ oil
pump).
• Re-calibrated automotive components have been used
in preference to ‘clean sheet’ designs where
practicable (e.g. IAV, fuel injectors and regulators).
• Where necessary (e.g. ECU and fuel pump), the most
cost-effective solution has been to design a new
system-specific component, tailored to suit the
requirements of the small vehicle market, rather than
attempting to modify existing automotive components.
• All necessary system components (both system-
specific and non-system-specific) are sourced and/or
manufactured in high volume by ‘Synerject’, an Orbital
Engine Corporation / Siemens Automotive joint
venture company, established for this purpose in
1997.
7. KEY SYSTEM-SPECIFIC COMPONENTS
7.1 ENGINE CONTROL UNIT (ECU)
Figure 6 - ECU external appearance
Both ‘aSDI’ 2-stroke and ‘SePI’ 4-stroke systems
are controlled by an ECU developed specifically for small
vehicle applications. Relative to a depopulated automotive
ECU, this unit offers reduced size, cost and electrical
power consumption. Key ECU requirements are
summarised in Table 6.
Table 6 – ECU size, weight & performance
Attribute Re quirement
CPU 8 bit / 8 MHz
Mask ROM (kB) 32
RAM (kB) 1.0
EEPROM (kB) 2.5
Connector 22 pin
Length 150
Width 100
Size (mm)
Height 20
Mass (g) ~ 300
7.2 FUEL INJECTORS
Both ‘aSDI’ and ‘SePI’ systems use re-calibrated
‘Siemens’ automotive fuel injectors (refer Table 7 for a list
of key requirements).
FINAL MANUSCRIPT Page 11 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Table 7 – Fuel injector requirements
Requirement Attribute ‘aSDI’
2-stroke
system
‘SePI’
4-stroke
system
Normal differential
pressure (Bar) 2.5
< 7.5 kW
engines 0.7 Typical
flow rate
(g/sec) 7.5 – 15 kW
engines 1.5
Voltage – nominal (V) 14
Voltage – range (V) 8 – 18
Injector type Side-feed
(Siemens
‘Deka 2’)
Top-feed
(Siemens
‘Deka 1D’)
Mounting position Air/fuel rail Inlet
manifold
In the case of ‘aSDI’, both the fuel injector and
fuel regulator are mounted on the air/fuel rail, which also
holds the ‘air injector’ (see below) to the cylinder head –
refer Figure 7.
In the case of SePI, the fuel injector is mounted
to the inlet manifold, and is aimed at the back of the inlet
valve(s) in accordance normal PI design practice – refer
Figure 8.
Figure 7 – Mounting of 'aSDI' fuel injector and fuel
regulator to air/fuel rail (which also holds air injector
to cylinder head)
Figure 8 - Mounting of 'SePI' fuel injector to inlet
manifold
7.3 FUEL PUMP
Although the fuel pump requirements of the 2-
stroke and 4-stroke systems are not identical, a low-cost,
high energy -efficiency fuel pump is critical for both
systems.
The fuel pump requirements of both systems differ
mainly in the pressure required for injection (refer Table 8
below). This difference arises from the fact that on ‘aSDI’,
metered fuel is delivered into the back of the air injector,
which contains compressed air held at a nominal pressure
of 5.0 Bar (gauge); in the case of ‘SePI’ the pressure
downstream of the fuel injector is inlet manifold pressure
(i.e. typically –0.7 to 0.0 Bar (gauge)).
Prior to designing the fuel pump described below,
a thorough analysis was undertaken to determine:
• What type of pump(s) best suited the above
requirements.
• What off-the-shelf fuel pump(s) were best able to meet
the above requirements.
The main conclusions of this study were as
follows:
1) The pump should be electrically rather than
mechanically driven.
Two key disadvantages of mechanically-driven pumps
are:
Cylinder head
Spark
plug
Fuel
regulator
Air/fuel
rail
Fuel injector
Air
injector
connector
Inlet
manifold
Fuel
injector
Fuel
injector
‘cup’
FINAL MANUSCRIPT Page 12 of 22 SIAT26.doc – MDA / GBB – 28/06/01
• A mechanical pump has an additional sealing
requirement at the engine / fuel pump drive
interface. Because leaking fuel is hazardous,
both from the perspectives of flammability and
load control, this seal is a ‘critical’ design
element.
• Prime and hence start times are longer with a
mechanical pump.
Table 8 – Required fuel pump performance
Requirement Attribute ‘aSDI’
2-stroke
system
‘SePI’
4-stroke
system
Delivery pressure –
gauge (Bar) 7.5 2.5
< 7.5 kW
engines 7 Delivered
fuelflow
(l/h) 7.5 – 15 kW
engines 15
Voltage – nominal (V) 14
Voltage – range (V) 8 – 18
< 7.5 kW
engines 0.7 Maximum
current
draw (A) 7.5 – 15 kW
engines 2.0
Mounting position In-line
OR
In-tank
2) Turbine-style pumps were found to be capable of
meeting the 2.5 Bar ‘SePI’ fuel pressure requirement,
but were unable to meet the 7.5 Bar ‘aSDI’ fuel
pressure requirement.
3) A piston-style pump offers the best energy efficiency
and is the preferred way of meeting the ‘aSDI’ 7.5 Bar
fuel pressure requirement as well as the 2.5 Bar fuel
pressure requirement on small / ‘low-output’ (< 7.5
kW) engines.
4) Other pump styles such as roller cell or gerotor were
found to be too expensive and/or susceptible to
manufacturing tolerance variations.
Figure 9 shows the external appearance of the ‘in-line’
version of the piston-style pump designed and developed
by Synerject in response to the results of this study (an
‘in-tank’ version has also been designed).
This pump is a fully-sealed, self-priming
electrically-driven piston-pump. The electric motor
operates ‘fully flooded’ but is subjected to only tank (i.e.
atmospheric) pressure. The pumping chamber and outlet
housing are the only parts of this pump that see full
delivery pressure.
Figure 9 - External appearance of 'Synerject' piston-
style fuel pump for 'aSDI’ and 'SePI'
Depending upon customer preference, a cheaper,
in-tank, turbine-style pump can be used to supply fuel to
‘high-output’ (> 7.5 kW) ‘SePI’ engines. However turbine-
style pumps are not recommended for small / low-output
‘SePI’ engines, due to the relatively high current draw /
low energy efficiency associated with this style of pump.
Table 9 below summarises the suitability of piston-style
versus turbine-style fuel pumps for various ‘aSDI’ and
‘SePI’ applications.
Table 9 – Comparison – Piston-style versus turbine -
style fuel pumps
Attribute Piston-style
pump Turbine-
style pump
Lower cost 3
Lower current draw 3
< 7.5 kW
engines
3 6 *
Suitability
– ‘aSDI’
(2-stroke) 7.5 – 15 kW
engines
3 6 *
< 7.5 kW
engines
3 **
Suitability
– ‘SePI’
(4-stroke) 7.5 – 15 kW
engines
3 3
In-line 3 Not available
Mounting In-tank 3 3
* Turbine pump unable to supply fuel at 7.5 Bar.
** Current draw > 1.0 A
FINAL MANUSCRIPT Page 13 of 22 SIAT26.doc – MDA / GBB – 28/06/01
7.4 FUEL REGULATOR
The fuel regulator used for both ‘aSDI’ and ‘SePI’
systems is a high-volume Siemens ‘Euro’ automotive
regulator recalibrated so as to maintain a differential
pressure of 2.5 Bar under reduced (small engine) fuel flow
conditions.
7.5 AIR INJECTOR (‘aSDI’ SYSTEM ONLY)
The air injector is a solenoid-actuated, outwardly-
opening poppet valve, designed and developed specifically
for the purpose of injecting precise quantities of fuel and
air directly into the cylinder in the form of a finely
atomised air / fuel ‘cloud’. The air injector is often
considered to be the ‘heart’ of the ‘aSDI’ system
controlling, as it does, both the shape and timing of this
‘cloud’. As mentioned previously, the fuel that passes
through the air injector is both metered and delivered into
the top of the air injector by a separate, PI-type
automotive fuel injector.
Figure 10 - External appearance of air injector
Table 10 - Key 'air injector' requirements
Attribute Requirement
Differential pressure
(Bar) -50 to +5.0
Operating engine speed
range (RPM) 0 – 12,000
Voltage – nominal (V) 14
Voltage – range (V) 8 – 18
Solenoid
diameter 20
‘Leg’
diameter 10
Size (mm)
Overall
Height 50 (typical) *
Mass (g) ~ 100
* Leg length can be altered to suit application
The external appearance of a typical air injector is
as shown in Figure 10, and some key requirements of the
air injector are listed in Table 10 above.
7.6 AIR COMPRESSOR (‘aSDI’ SYSTEM ONLY)
Compressed air for the ‘aSDI’ system is supplied
by a small, 3 cm3 swept-volume, piston-compressor which
is mounted to the crankcase and driven off an eccentric
machined into one of the crankshaft webs (Figure 5). A
cross-section of the compressor is shown on Figure 11.
Fresh, filtered air from the engine crankcase is
drawn into the compressor via ports in the compressor
cylinder wall. This air is then compressed and delivered
to the air/fuel rail via a disc valve in the head of the
compressor. Unlike a conventional piston compressor,
this design requires no belt, pulley, compressor con-rod /
crankshaft, inlet valve, inlet hose and/or inlet air filter. By
eliminating unnecessary components in this way, this
design offers an exceptionally simple, elegant and low-
cost means of supplying compressed air to the air/fuel
rail.
Figure 11 - 'aSDI' air compressor
8. VEHICLE FUEL CONSUMPTION AND EMISSIONS
Before considering actual vehicle test data, a brief
review of international small vehicle emissions legislation
may help to put the test results subsequently presented
in better context.
8.1 INTERNATIONAL EMISSIONS LEGISLATION
‘FAMILIES’ (DRIVECYCLES)
Although there are more than 15 small vehicle
emissions standards currently in use world-wide [1], the
three most widely-applied emissions legislation ‘families’
are those based on the ECE 40, ECE 47 and IDC
drivecycles, because they apply to the largest number of
small vehicles produced annually – refer Table 11. This
table shows that 18.1 million motorcycles and
motorscooters (approximately 90% of the total number
produced annually), must be designed to pass an
emissions test carried out over one of these three
Piston Compressed
air out
Disc valve
Roller follower
Solenoid
‘Leg’
FINAL MANUSCRIPT Page 14 of 22 SIAT26.doc – MDA / GBB – 28/06/01
drivecycles, and it is therefore results from these ‘top
three’ drivecycles which are presented in this paper.
Table 11 – Motorcycle / motorscooter emissions
legislation ‘families’ (drivecycles)
Market
volume
(x106)*
Drivecycle / ‘family’ Country /
region
ECE
40 ECE
47 IDC Others
China: 11.0 3**
India: 3.6 3
Europe:
(> 50 cm3
engines)
1.5 3
Europe:
(≤50 cm3
engines)
1.2 3
Japan: 0.9 3
Taiwan: 0.8 3***
South
America:
0.7 3
USA: 0.4 3
* Based on sales of motorcycles and motorscooters
worldwide in 1999; source: Chambre Syndicale Nationale
du Motocycle (CSNM).
** Chinese standards are still being defined, but are
expected to be similar to the European ‘ECE 40’
standards.
*** Although the ‘warm-up’ phase of the Taiwanese CNS
11386 drivecycle is different to that of the ECE 40
drivecycle, the ‘bagged’ portion of both drivecycles is
identical, and the two tests will be treated as being
equivalent for the purposes of this paper.
8.2 VEHICLE TEST RESULTS
So as to provide a broad overview of the fuel
consumption and emissions performance which can be
achieved with both the ‘aSDI’ 2-stroke and ‘SePI’ 4-stroke
fuel systems, results from 10 test combinations involving
three different vehicle models tested over the ‘top three’
small vehicle drivecycles will be presented as outlined in
Table 12 below.
All three vehicle models tested (i.e. ‘Small 2S’,
‘Large 2S’ and ‘Large 4S’) were contemporary-model,
high-performance, ‘sports’ motorscooters fitted with:
• 1-cylinder gasoline engines of specific output > 50
kW/litre.
• CVT’s (Continuously Variable Transmissions) which
automatically adjust engine speed relative to
roadspeed. In each case, the CVT used on the
‘aSDI’- or ‘SePI’-equipped vehicle was unaltered from
that fitted to the baseline carburetted vehicle.
Table 12 – Vehicle test results presented - overview
Vehicle Drivecycle
Model Fuel system ECE 40 ECE 47
IDC
Carburettor
(baseline) 3
‘aSDI’
(‘Euro I’) 3
‘Small 2S’
(≤ 50 cm3
2-stroke)
‘aSDI’
(‘Devel.’) 3
Carburettor
(baseline)
3
‘aSDI’
(‘Euro I’)
3 3
‘Large 2S’
(150-200
cm3
2-stroke)
‘aSDI’
(‘Devel.’)
Carburettor
(baseline)
3 3
‘SePI’
(‘Euro I’)
‘Large 4S’
(150-200
cm3
4-stroke)
‘SePI’
(‘Devel.’)
3 3
Differences between the ‘Euro I’- and
‘Development’-specification ‘Small 2S’ ‘aSDI’ systems
tested (refer Table 12) were as follows:
• The ‘development’ system used a direct-injector with
modified nozzle geometry.
• The geometry of the piston crown was modified on the
‘development’ engine for improved spray containment.
• Port timing was revised on the ‘development’ engine
to improve scavenging.
• The ‘development’ ECU calibration was re-optimised
to suit these hardware changes.
The fuel consumption and emissions results from
all tests, along with relevant current and future emissions
limits, are presented on a drivecycle basis in Table 13 to
Table 15 below. In each case:
FINAL MANUSCRIPT Page 15 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Table 13 – Tailpipe emissions (uncatalysed) and fuel consumption – ECE 40 drivecycle
Vehicle Tailpipe emissions – measured Fuel consumption – measured
(g/km) (l/100km) (km/l) Model Fuel system HC
(g/km) CO
(g/km) NOx
(g/km) HC+NOx
(g/km) Absolute Relative
Carburettor
(baseline): 8.5 10.9 0.04 8.5 33.4 - 4.43 22.6
1.06 1.47 0.09 1.16 19.6 -41% 2.58 38.7
‘Large 2S’
(150-200
cm3
2-stroke) ‘aSDI’
(Euro I
system): 1.76 * 1.82 * 0.06 * 1.82 * 20.4 * -39% * 2.70 * 37.0 *
Carburettor
(baseline): 0.85 11.1 0.17 1.02 24.6 - 3.33 30.0 ‘Large 4S’
(150-200
cm3
4-stroke) ‘SePI’
(Devel.
system):
0.50 1.34 0.25 0.72 20.5 -17% 2.79 35.9
Vehicle type approval Tailpipe emissions limits
Category
(Region) Year HC
(g/km) CO
(g/km) NOx
(g/km) HC+NOx
(g/km)
1998: - < 3.5 - < 2.0
2S - < 7.0 ** - < 1.0 **
Motor-
cycle
(Taiwan) 2003**: 4S - < 7.0 ** - < 2.0 **
2S < 4.0 < 8.0 < 0.1 ( < 4.1 ) 1999:
(Euro I) 4S < 3.0 < 13.0 < 0.3 ( < 3.3 ) > 50 cm3
2-wheeler
(Europe) 2003:
(Euro II) *** < 1.2 *** < 5.5 *** < 0.3 *** ( < 1.5 )
***
* Re-calibrated for improved compliance with ‘Euro I’ 0.1 g/km NOx limit for 2-stroke vehicles.
** Cold-start emissions limits – cannot be directly compared to hot-start results presented.
*** Expected limits only – refer [3].
• All tests were carried out at ‘stabilised’ low mileage
(typically around 500 km).
• Engine-out emissions are quoted in all cases (i.e. no
exhaust after-treatment catalysts were fitted).
• Each result quoted has been averaged from 2- or 3-off
repeat tests.
Important conclusions, drawn from the data
presented in Table 13 to Table 15, are as follows:
1) For each vehicle/drivecycle combination tested, it was
possible to meet current emissions limits in Europe,
India and Taiwan, without requiring exhaust after-
treatment.
2) The ‘Large 2S’ and ‘Large 4S’ engines were also able
to meet future emissions standards in Europe and
India without requiring exhaust after-treatment.
3) The ‘Development’ version of the ‘Small 2S’ engine
was able to meet future European emissions
standards without requiring exhaust after-treatment.
4) Relative to the baseline carburetted 2-stroke engines,
the ‘aSDI’ engines demonstrated a fuel consumption
saving of up to 50%.
5) Relative to the baseline carburetted 4-stroke engine,
the ‘SePI’ engine demonstrated a fuel consumption
saving of up to 20%.
8.3 EXPECTED FUTURE TRENDS IN
INTERNATIONAL EMISSIONS LEGISLATION
Aside from on-going reductions in drivecycle
emissions limits (as reflected by the current and expected
emissions limits presented in Table 13 to Table 15), other
anticipated trends in international small vehicle emissions
legislation are as follows:
FINAL MANUSCRIPT Page 16 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Table 14 – Tailpipe emissions (uncatalysed) and fuel consumption – ECE 47 drivecycle
Vehicle Tailpipe emissions – measured Fuel consumption – measured
(g/km) (km/l) Model Fuel system HC
(g/km) CO
(g/km) NOx
(g/km) HC+NOx
(g/km) Absolute Relative (l/100km)
Carburettor
(baseline): 7.2 19.1 0.1 7.3 25.8 - 3.46 28.9
‘aSDI’
(Euro I
system):
1.80 2.47 0.25 2.06 14.9 -42% 1.97 50.8
‘Small 2S’
(≤ 50 cm3
2-stroke)
‘aSDI’
(Devel.
system):
0.48 0.75 0.45 0.92 11.8 -54% 1.55 64.7
Vehicle type approval Tailpipe emissions limits
Category
(Region) Year HC
(g/km) CO
(g/km) NOx
(g/km) HC+NOx
(g/km)
1999:
(Euro I) - < 6.0 - < 3.0 ≤ 50 cm3
2-wheeler
(Europe) 2002:
(Euro II) - < 1.0 - < 1.2
Table 15 – Tailpipe emissions (uncatalysed) and fuel consumption – IDC drivecycle
Vehicle Tailpipe emissions – measured Fuel consumption – measured
(g/km) (l/100km) (km/l) Model Fuel system HC
(g/km) CO
(g/km) NOx
(g/km) HC+NOx
(g/km) Absolute Relative
‘Large 2S’
(150-200
cm3
2-stroke)
‘aSDI’
(Euro I
system):
1.09 1.22 0.08 1.17 17.9 ( N/A ) * 2.37 42.2
Carburettor
(baseline): 0.90 9.59 0.10 1.00 22.9 - 3.13 32.0 ‘Large 4S’
(150-200
cm3
4-stroke) ‘SePI’
(Devel.
system):
0.56 1.21 0.22 0.78 18.3 -20% 2.50 40.0
Vehicle type approval Tailpipe emissions limits
Category
(Region) Year HC
(g/km) CO
(g/km) NOx
(g/km) HC+NOx
(g/km)
2000:
[COPA] ** - < 2.0
[+20%] **
- < 2.0
[+20%] **
2003 ***: - < 1.5 *** - < 1.5 ***
2-wheeler
(India)
2005 ***: - < 1.0 *** - < 1.0 ***
* Baseline carburettor vehicle not tested over IDC (anticipated fuel consumption benefit ≅ 40%).
** [COPA] = ‘Conformity of Production Allowance’ (relative to ‘Type Approval’ emissions limit); no COPA after 2003.
*** Expected limits only – Future Indian emissions limits have not yet been finalised.
FINAL MANUSCRIPT Page 17 of 22 SIAT26.doc – MDA / GBB – 28/06/01
1) Increased specification of ‘cold-start’ emissions
testing:
In the USA, motorcycles are currently tested using
the same (FTP 75) ‘cold-start’ drivecycle as
passenger cars [1], and Taiwan plans to introduce a
‘cold-start’ version of the (ECE 40-based) CNS 11386
drivecycle in 2003 [16]. In Europe, research is
currently underway aimed at developing a new, more
representative, small vehicle emissions test drivecycle
by 2002 which may also be of the ‘cold-start’ type and
which will be used for certification from 2006 onwards
[3].
2) New / more stringent emissions durability
requirements:
In Taiwan and Thailand, it is already the case that
small vehicles must meet specified emissions limits
at 15,000 and 12,000 km respectively; it is anticipated
that similar requirements will soon be introduced into
Europe, India and China.
3) Increased implementation of evaporative emissions
requirements:
California has had an evaporative emissions
requirement for motorcycles since 1978 [17], and
Taiwan since 1988 [4]; motorcycles of greater than
150 cm3 swept volume which are sold into the Thai
market must also meet an evaporative emissions
requirement from 2001 onwards [18], and similar
legislation in other countries / regions may be
introduced in the near-to-medium term.
Synerject’s ‘aSDI’ and ‘SePI’ small vehicle fuel
injection systems are well placed to meet these
anticipated developments by virtue of the following
features:
1) Large reductions in engine-out emissions.
(As demonstrated by Table 13 to Table 15).
2) Reduced unit-to-unit performance variation.
Although unit-to-unit exhaust emissions scatter is
affected by many factors other than the fuel system
(e.g: engine compression ratio; squish; inlet / exhaust
timing; etc.), based on accumulated experience in the
automobile industry, it is well known that fuel-injected
vehicles typically exhibit less unit-to-unit emissions
variation than carburetted vehicles, particularly when
an oxidising catalyst is used to control exhaust
emissions [19].
3) Proven emissions durability.
Figure 12 and Figure 13 show the results from a
15,000 km emissions durability test on a ‘Small 2S’,
‘aSDI’-equipped, Euro I vehicle. As can be seen from
these figures, the emissions performance remained
stable. This correlates well with the high level of
emissions durability previously demonstrated on other
versions of the OCP air-assisted DI system [14] [20] .
Figure 12 – HC+NOx emissions durability
– 'Small 2S' Euro I vehicle
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
015,000
Distance travelled (km)
HC + NOx (g/km)
aSDI
Euro I limit
Figure 13 – CO emissions durability
– 'Small 2S' Euro I vehicle
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
015,000
Distance travelled (km)
CO (g/km)
aSDI
Euro I limit
4) (Optional) electronically-controlled CVP valve:
A CVP (Canister Vapour Purge) valve has been
allowed for in the ECU design. Currently, a simple
and cheap ‘On/Off’ driver is considered sufficient for
this purpose; this can be upgraded to a PWM (Pulse
Width Modulated) driver if more stringent requirements
in this area are introduced.
5) (Optional) catalyst fitment:
Both ‘aSDI’ and ‘SePI’ systems can be combined with
an exhaust after-treatment catalyst if required,
thereby further reducing tailpipe HC and CO by 50%
or more.
FINAL MANUSCRIPT Page 18 of 22 SIAT26.doc – MDA / GBB – 28/06/01
9. VEHICLE DRIVEABILITY
Relative to carburetted fuel systems, both ‘aSDI’
and ‘SePI’ systems offer significantly improved vehicle
driveability as a result of the following engine performance
benefits:
1) Better combustion stability and better vehicle-to-
vehicle performance repeatability, due to precise
control of A/F, ignition and injection timing.
2) Fast, reliable cold start. Both systems are capable of
good, repeatable starts at all ambient temperatures in
the range: -10°C to 40°C. Otherwise-equivalent
carburetted vehicles have longer and/or less
repeatable crank-to-run times (particularly when the
ambient temperature is below 10°C), and may
subsequently stall or ‘race’.
3) Automatic optimisation of all parameters as engine
warms up. The ECU compensates for engine
temperature differences automatically, and engine
response is not affected. Manual ‘choke’ actuation is
not required.
4) Automatic compensation for changes in air inlet
pressure due to altitude and/or partial inlet air filter
blockage (with optional ambient air pressure sensor).
Because of its good combustion stability and
(optional) electronic oiling system, ‘aSDI’ also reduces the
amount of visible smoke and odour emitted by 2-stroke
engines down to near-imperceptible levels.
As a result of the above benefits, significantly
improved vehicle driving behaviour is perceived by the
average operator.
Using the driveability rating system specified in
Table 16 for example, the results from back-to-back
driveability tests carried out with carburetted and fuel-
injected ‘Small 2S’ and ‘Large 4S’ vehicles are as shown
in Table 17 and Table 18 below.
Based on these results, it can be seen that the
average operator is likely to perceive a clear driveability
benefit when ‘SePI’ is fitted (i.e. relative to an otherwise-
equivalent baseline carburetted engine), and that this
driveability difference is even greater in the case of ‘aSDI’.
Table 16 - Vehicle driveability rating system
Rating * Description
10 Exceptional
(No undesirable elements)
9 No deficiencies
(Traces of undesirable elements)
8 No significant deficiencies
(Deficiencies only under special operating
conditions)
7 Minor deficiencies
(One or more hard-to-detect deficiencies)
6 Obvious, but not objectionable, problems
(One or more noticeable deficiencies)
5 Marginal
(One or more obvious deficiencies –
customer complaint likely)
4 Disturbing
(One or more obvious deficiencies –
customer seeks corrective action)
3 Lack of confidence
(One or more obvious deficiencies –
customer looses confidence in the ability
of the vehicle to perform reliably)
2 Unreliable
(Vehicle function is unreliable)
1 Unpredictable
(Vehicle function is unpredictable)
* A driveability rating difference of more than 0.5
represents a significant difference, as perceived by the
average operator
Note that the only area in which the ‘aSDI’ and
‘SePI’ vehicles were not judged to be superior than the
baseline carburetted vehicles was in terms of roll-on
throttle response (refer Table 17 and Table 18). In this
category, the good response of the baseline carburetted
vehicles is a reflection of rich jetting, commonly used on
small vehicles to avoid ‘hesitation’ during transient throttle
operation. The ‘aSDI’ and ‘SePI’ vehicles were also
calibrated to accelerate without hesitation, however unlike
the baseline carburetted vehicles, excess fuel has also
been eliminated wherever possible in the interests of
optimum fuel consumption and reduced engine-out
exhaust emissions. This driveability difference therefore
reflects the greater flexibility available when trading off
exhaust emissions against throttle response with ‘aSDI’
and/or ‘SePI’, rather than a response limitation of the
‘aSDI’ and/or ‘SePI’ systems per se.
FINAL MANUSCRIPT Page 19 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Table 17 - Vehicle driveability test results –
‘Small 2S’ (≤ 50 cm3 2-stroke vehicle)
Test Carburetted
vehicle ‘aSDI’
vehicle
Cold start: 5.0 7.0
Hot start: 7.0 7.0
Warm-up: 6.5 7.5
Idle: 5.5 7.0
Roll-on throttle response: 7.5 7.0
Low-speed cruise:
(10 km/h) 5.5 8.0
High-speed cruise:
(40 km/h) 7.5 7.5
Maximum acceleration: 7.5 7.5
Overrun: 5.0 8.0
Average rating: 6.33 7.39
Table 18 - Vehicle driveability test results –
‘Large 4S’ (150 – 200 cm3 4-stroke vehicle)
Test Carburetted
vehicle ‘SePI’
vehicle
Cold start: 5.5 7.0
Hot start: 7.0 7.5
Warm-up: 6.5 7.5
Idle: 7.0 7.5
Roll-on throttle response: 7.5 7.0
Low-speed cruise:
(10 km/h) 7.0 8.0
High-speed cruise:
(60 km/h) 7.5 7.5
Maximum acceleration: 7.5 7.5
Overrun: 7.0 8.0
Average rating: 6.95 7.50
10. DIAGNOSTICS AND SERVICING
To make the servicing of ‘aSDI’ and ‘SePI’
vehicles as fast and simple as possible, all ECU’s come
complete with a comprehensive, on-board, diagnostic
software package. The aims of this software package are
to:
• Provide service personnel with easy access to
necessary information.
• Provide service personnel with a simple means of
carrying out common tests as required for the
purpose of problem diagnosis and/or regular servicing.
• Help make the transition from carburetted to ‘aSDI’-
and/or ‘SePI’-equipped vehicles as smooth and easy
as possible.
Depending on customer preference, two different
means are available for accessing this information as
follows:
1) Diagnostic/service information can be displayed via
MIL (Malfunction Indication Lamp) flashing codes.
2) Diagnostic/service information can be displayed by
means of a suitable tool which communicates with
the ECU using the ‘Keyword 2000’ communications
protocol.
To facilitate option 2) above in cases where the
customer does not have an existing tool, Orbital Engine
Co. has developed a low-cost, hand-held
diagnostic/service tool known as ‘Pocket Dash’.
Key features of ‘Pocket Dash’ are as follows:
1) Small, hand-held, low-cost electronic display.
2) Easy-to-understand, graphic display format.
3) Display text available in various languages to suit
different geographical markets.
4) Ability to display various operating parameters such
as engine RPM, ignition angle, injection angle, etc. for
servicing purposes.
5) Ability to undertake tests commonly required for
diagnostic purposes; e.g. operate temperature gauge
or MIL (Malfunction Indication Lamp); generate spark
at spark plug; etc.
6) Ability to display any faults which are stored within
the ECU.
7) Ability to adjust a limited number of factory presets
(e.g. ‘SePI’ idle A/F) within a ‘safe’ range for the
purpose of continued vehicle compliance with local
emissions standards. (This feature eliminates the
need to fit a ‘CO potentiometer’ to the vehicle).
8) Ability to download software upgrades (if required).
11. FUTURE DEVELOPMENTS
The main aim of this paper so far has been to
describe the current status of Synerject’s ‘aSDI’ 2-stroke
and ‘SePI’ 4-stroke small vehicle systems. Looking
forward, planned future developments are as follows:
1) On-going work to ensure compliance with future
emissions standards.
FINAL MANUSCRIPT Page 20 of 22 SIAT26.doc – MDA / GBB – 28/06/01
2) Piece cost reductions through improved economies of
scale.
3) Piece cost reductions through localisation.
4) System cost reductions through improved integration
of the ‘aSDI’ and ‘SePI’ systems into the base engine
design.
Under category 2), our intent is to broaden the
range of application of ‘aSDI’ and ‘SePI’ to include not just
gasoline-powered small vehicles, but also:
• Other small engines such as small outboard engines
and those used on electrical generators and heavy-
duty gardening equipment.
• Alternative fuels such as CNG (Compressed Natural
Gas) and LPG (Liquid Petroleum Gas).
CONCLUSIONS
The main conclusions arising from the information
presented in this paper are as follows:
1) Significant reductions in small vehicle fuel
consumption and emissions are available, through
application of the recently introduced DI ‘aSDI’
system to 2-stroke engines, and PI ‘SePI’ system to
4-stroke engines.
2) By applying these systems to contemporary-market
2- and 4-stroke vehicles, current emissions limits
were met in Europe, India and Taiwan, without
requiring exhaust after-treatment. In most cases,
future emissions limits were also met, again without
requiring exhaust after-treatment.
3) Relative to otherwise-equivalent carburetted 2-stroke
engines, ‘aSDI’ demonstrated a fuel consumption
saving of around 40% while simultaneously meeting
current emissions limits.
4) Relative to otherwise-equivalent carburetted 4-stroke
engines, ‘SePI’ demonstrated a fuel consumption
saving of around 20% while simultaneously meeting
current emissions limits.
5) Relative to otherwise-equivalent carburetted vehicles,
‘aSDI’- and ‘SePI’-equipped vehicles exhibit
significantly improved driveability.
6) While high-volume, low-cost automotive components
are used wherever possible, ‘aSDI’ and ‘SePI’ are
more than simple ‘adaptations’ of passenger-car fuel
systems. Rather, both systems have been carefully
designed ‘from the ground up’ and developed to meet
the cost and performance requirements of small
vehicles world-wide. In some cases (e.g. ECU and
fuel pump), new system-specific components have
been developed for this purpose.
7) Through careful analysis and understanding of future
trends in small vehicle markets world-wide (in
particular: trends in international exhaust emissions
standards), both ‘aSDI’ and ‘SePI’ have been
designed and developed to be ‘future proof’.
By combining low cost and high performance in
this way, we at Synerject believe that our ‘aSDI’ and
‘SePI’ systems truly offer an optimum ‘emissions solution’
for small, gasoline-fuelled vehicles world-wide, irrespective
of whether a 2-stroke or 4-stroke base engine is preferred.
DEFINITIONS, ACRONYMS, ABBREVIATIONS
Below is a short description of acronyms, abbreviations
and other words with special definitions which have been
used in this paper.
Word / Abbreviation Meaning
A/F Air / Fuel Ratio
‘aSDI’ air-assisted Synerject
Direct Injection
‘Bagged’ (phase of
drivecycle) Phase of drivecycle during
which exhaust emissions
sampling is carried out.
CNS Chinese National Standard
CO Carbon monOxide
‘Cold start’ (emissions test) Vehicle emissions test
which requires that vehicle
is started ‘cold’ and that
exhaust emissions
sampling commences
simultaneously with engine
starting.
COP(A) Conformity of Production
(Allowance)
CO Potentiometer A potentiometer which can
be used by service
personnel to adjust idle A/F
for the purpose of ensuring
continued compliance with
legislated CO limits.
CVP Canister Vapour Purge
CVT Continuously Variable
Transmission
Development / Devel.
(system) Development phase
(system)
DI Direct Injection
ECU Engine Control Unit
EFI Electronic Fuel Injection
EGR Exhaust Gas Recirculation
ETB Electronic Throttle Body
HC unburnt HydroCarbons
FINAL MANUSCRIPT Page 21 of 22 SIAT26.doc – MDA / GBB – 28/06/01
Word / Abbreviation Meaning
HEI (ignition system) High Energy Inductive
(ignition system)
IAV Idle Air Valve
(catalyst) ‘Light-off’ Temperature at which the
chemical conversion
efficiency of an exhaust
catalyst rises above 50%.
MIL Malfunction Indication Lamp
N/A Not Available
NOx Nitrogen Oxides
OCP Orbital Combustion
Process
PI Port Injection
SAI Secondary Air Injection
‘SePI’ Synerject electronic Port
Injection
‘Small vehicles’ auto-rickshaws,
motorcycles,
motorscooters, etc.
TA Type Approval
T-AP (sensor) Temperature - Absolute
Pressure (sensor)
TPS Throttle Position Sensor
TWC Three-Way Catalyst
(i.e. oxidises HC / CO &
reduces NOx
simultaneously)
‘Warm-up’ (drivecycle
phase) Phase of drivecycle which
is used to warm the engine
up to normal operating
temperature prior to
commencement of exhaust
emissions sampling.
REFERENCES
[1] CONCAWE, “Motor Vehicle Emission
Regulations and Fuel Specifications – Part 2 –
Detailed Information and Historic Review (1970 –
1999)”, 2000.
[2] Norbye J., “Automotive Fuel Injection Systems –
A Technical Guide”, ISBN 0 85429 347 7, 1985.
[3] Commission of the European Communities,
“Proposal for a Directive of the European
Parliament and of the Council Amending Directive
97/24/EC on Certain Components and
Characteristics of Two or Three-Wheeled Motor
Vehicles”, 2000/0136 (COD), 2000.
[4] Environmental Protection Administration (EPA) of
the Government of the Republic of China, “Current
Situation of Motorcycles Pollution Control in
Republic of China”, 1996.
[5] Aprilia S.P.A., “DITECH, Direct Injection
Technology”, Press release, May 2000.
[6] ACEM Pollution working group, “The motorcycle
industry in Europe, ACEM Pollution Research
Program on Motorcycles”, 1998.
[7] Nuti M., “Emissions from Two-Stroke Engines”,
ISBN 0-7680-0215-X, 1998.
[8] McDowell A. et al, “Catalyst Deactivation on a
Two-Stroke Engine”, SAE paper 982015.
[9] Caponi D. and Nuti M., “Appraisal of Secondary
Air Injection for Emission Reduction in Small 2T
SI Engines”, SAE paper 2000-01-0899.
[10] Conference proceedings: “21. Internationales
Wiener Motorensymposium, 4.-5. Mai 2000 (21st
International Vienna Engine Symposium, 4.-5.
May 2000)”, ISBN 3-18-342012-0, 2000.
[11] Houston R. and Cathcart G., “Combustion and
Emissions Characteristics of Orbital’s
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Automotive Direct Injected 4-Stroke Engines”,
SAE paper 980153.
[12] Eichlseder E. et al, “Chancen und Risken von
Ottomotoren mit Direkteinspritzung (Potential and
Risks of Gasoline Direct Injection Engines for
Future Passenger Car Drivelines)”, MTZ 61, No. 3,
2000.
[13] Worth D. et al, “Design Considerations for the
Application of Air-Assisted Direct In-Cylinder
Injection Systems”, SAE paper 972074.
[14] Shawcross D. et al, “A Five-Million Kilometre,
100-Vehicle Fleet Trial, of an Air-Assist Direct
Fuel Injected, Automotive 2-Stroke Engine”, SAE
paper 2000-01-0898.
[15] Bell G. and Finucci C., “Exhaust Emissions
Sensitivities with Direct Injection on a 50cc
Scooter”, SAE paper 970365.
[16] Communication with Environmental Protection
Administration (EPA) of the Government of the
Republic of China, 1998.
[17] State of California Air Resources Board (CARB),
“Hearing Notice and Staff Report – Proposed
Amendments to the California On-Road
Motorcycle Regulation”, 1998.
[18] Walsh M., “Motor Vehicle Standards and
Regulations around the World”,
mpwalsh@igc.apc.org, 1999.
FINAL MANUSCRIPT Page 22 of 22 SIAT26.doc – MDA / GBB – 28/06/01
[19] Klingenberg H., et al, “Exhaust Emission
Compliance and Testing Procedures based on
Averaging”, Second Symposium on Indian
Automotive Technology (SIAT), Volume 1, 1987.
[20] Houston R. et al, “Development of a Durable
Emissions Control System for an Automotive
Two-Stroke Engine”, SAE paper 960361.
CONTACT DETAILS
Greg Bell
Synerject Systems Integration
1 Whipple Street
Balcatta, 6021
AUSTRALIA
Telephone: + 61 (0)8 9441 2311
Facsimile: + 61 (0)8 9441 2309
Email: gbell@orbeng.com.au
