10th International Conference on Turbochargers and Turbocharging

404 Pages·2012·76.476 MB·English

by  Institution of Mechanical Engineers

10th International Conference on
Turbochargers and Turbocharging
Combustion Engines & Fuels Group Organising Committee
Dr Kian Banisoleiman Lloyd’s Register (Chairman)
Dr Roland Baar Technische Universität Berlin
Andrew Banks Ricardo
Steve Birnie BorgWarner
Dr Chris Brace University of Bath
Dr Geoff Capon Ford
Dr Ennio Codan ABB
Gavin Donkin Honeywell
Dr-Ing Dietmar Filsinger IHI Charging Systems Intl.
Pierre French Cummins Turbo Technologies
Dr Seiichi Ibaraki Mitsubishi Heavy Industries (MHI)
Per-Inge Larson Scania
Dr Ricardo Martinez-Botas Imperial College London
Takashi Otobe Honda R&D
Alexander Rippl MAN Diesel & Turbo
Prof Joerg Seume Hanover University
Dr Les Smith Jaguar Land Rover
Dr Mahmoud Tarabad Caterpillar
The Committee would like to thank the following supporters:
Gas Turbine Society of Japan (GTSJ) and SAE Japan
10th International Conference on
Turbochargers and Turbocharging
15–16 MAY 2012
SAVOY PLACE, LONDON
Conference Proceedings sponsored by:
Oxford Cambridge Philadelphia New Delhi
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HyBoost – An intelligently electrified
optimised downsized gasoline engine
concept

J King, M Heaney, E Bower, N Jackson, N Owen
Ricardo, UK
J Saward, A Fraser
Ford Motor Company, UK
G Morris, P Bloore
Controlled Power Technologies, UK
T Cheng, J Borges-Alejo, M Criddle
Valeo, France

ABSTRACT

The UK Technology Strategy Board (TSB) sponsored HyBoost project was a
collaborative research programme to develop an ultra efficient optimised gasoline
engine concept with “Intelligent Electrification”. The basis of the concept was use of
a highly downsized 1.0L boosted engine in conjunction with relatively low cost
synergistic ‘12+X’ Volt electrical management system and electrical supercharger
technologies to deliver better value CO reduction than a full hybrid vehicle. Project
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targets of 99 g/km CO as measured over the European Drive Cycle (EDC) in a
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standard 2011 Ford Focus whilst maintaining the same performance and driveability
attributes as a 2009 production 2.0L version of the car were achieved, and a
potential route through to <85 g/km CO identified. Ricardo was supported by a
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consortium consisting of Ford, Controlled Power Technologies, Valeo, the European
Advanced Lead Acid Battery Consortium, Imperial College London and the UK TSB.

1 INTRODUCTION

Mandation of road vehicle fuel economy is becoming a global phenomenon, with
legislation or binding agreements for substantial improvements coming into force in
Europe, the US, Canada, Australia, Japan and China. Passenger cars are a primary
focus of this legislation, with future targets calling typically for continuing
improvement of 3% per year as shown in Figure 1.

To put this change into context: in Europe, an average of 1.6% per year
improvement has been achieved over the last decade, driven by the now
superseded Voluntary Agreement. This is a world-leading pace of change, despite
missing the VA targets. Future legislation in the major markets now requires that
this pace of change must be doubled, for example in Europe a new car fleet
average tailpipe CO emission of 130g/km must be achieved, with phase-in from
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2012-18, with even tougher targets currently set for 2020.
____________________________________________
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© The author(s) and/or their employer(s), 2012
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E Canada-LDV
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ali China
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a Hollow dots and dotted lines: unannouncedproposal EU 2020: 95
Gr 90
2000 2005 2010 2015 2020 2025
[1] China's target reflects gasoline fleet scenario. If including other fuel types, the target will be lower.
[2] US and Canada light-duty vehiclesinclude light-commercial vehicles.

Figure 1: Future passenger car fuel economy targets & legislation
(Source: Passenger Vehicle Greenhouse Gas and Fuel
Economy Standards: A Global Update – ICCT)

The mass-market advancement of Hybrid vehicles still requires significant reduction
in product cost. Recent analysis by Ricardo (updating the 2003 DfT/DTI "Low
Carbon Roadmap") indicates that current Hybrid cars only offer marginal Total Cost
of Ownership savings unless these cost reductions are realised. This analysis also
continues to indicate that deploying low cost technologies across a large number of
vehicles remains more cost-effective than deploying costly technology to a few.

In the UK and Europe, the Diesel engine is currently established as the fuel-efficient
solution for the majority of passenger cars sold. However, its significant
incremental cost over a gasoline engine arising from the cost of precision fuel
injection and exhaust after-treatment devices forms a higher proportion of the
purchase price. Furthermore, rising demand for Diesel fuel rather than gasoline
impairs the efficiency of the refinery (meaning that CO savings on a "well to wheel"
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basis are becoming less attractive) and pushes up the price of Diesel fuel. The aim
of the HyBoost concept was to combine cost-effective hybridisation with synergistic
gasoline engine downsizing technologies to offer a CO /performance trade-off better
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than today’s more costly full hybrids and high efficiency Diesels.

2 HYBOOST CONCEPT

HyBoost targets were to deliver a C-segment model year 2011 (MY2011) Ford
Focus demonstrating a 30-40% reduction in CO emissions as measured over the
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EDC (to below 100 g/km) versus a baseline MY2009 2.0L Naturally Aspirated (NA)
gasoline engine version of the passenger car whilst maintaining the comparable
vehicle performance and driveability attributes. Figure 2 shows a simple scheme of
the concept with the 2.0L NA engine replaced with a downsized DI gasoline engine
equipped with a conventional fixed geometry turbocharger (FGT) delivering superior
steady state power and torque levels. A Front End Accessory Drive (FEAD) mounted
Belt Starter Generator (BSG) gave micro hybrid functionality of stop/start and more
efficient motoring and generation enabled through the higher voltage “12+X”
(typically between 18 – 27V) energy storage of an ultra capacitor system. Energy
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recovered during deceleration events could be deployed in a sophisticated boosting
system combining a 12+X electric supercharger “blowing through” the conventional
turbocharger and/or the BSG torque assist system, using the electrical energy
optimally to achieve good transient response or improved fuel consumption. The
component systems have previously been demonstrated individually at 12 volts,
but not brought together in this synergistic combination as a "12+X" system.

Figure 2: HyBoost concept scheme

The project also included exploration of electric turbocompounding (shown in the
scheme but not fitted to the HyBoost car) and a novel energy storage technology
for further enhancements to efficiency and cost respectively, but these items are
not covered in this paper.

3 RESULTS AND DISCUSSION

3.1 HyBoost engine and boost system
HyBoost uses a modified near production Ford 1.0L 3 cylinder turbo GDI EcoBoost
base engine. This gives 50% downsizing over the baseline engine. Figure 3 shows
the steady state torque curves of the two engines, and the superior performance of
the HyBoost engine can be clearly seen. The Ford 2.0L Duratec engine produces
peak power and torque levels of 107 kW at 6000 rpm and 185 Nm at 4000 rpm
respectively. This compares to the HyBoost (with no electric supercharger assist)
peak power and torque levels of 105 kW at 5500 rpm and 234 Nm at 2500 rpm
respectively, which were achieved through re-optimisation of the boosting system,
use of a new intake air path required to include the electric supercharger, and
fitment of a new high efficiency Valeo Water Charge Air Cooler (WCAC) system. The
WCAC system was specified with a very high (relative to engine size and
performance) heat rejection capability of between 16 – 18kW, and this was key to
enabling excellent charge cooling to mitigate knocking and maintain lambda 1
operation through to full load, resulting in excellent Brake Specific Fuel
Consumption (BSFC) across the entire operating map.

As the engine becomes more aggressively downsized several potential issues arise
with regards to perceived performance. Firstly, the main issue is turbocharger lag,
where the device itself takes time to build up boost pressure and the subsequent
transient torque curve does not meet the steady state torque curve. Secondly,
often there can be a big difference between the low engine speed “NA” torque
(typically 8 – 11 bar BMEP), where the FGT is not able to deliver any significant
boost pressure even during steady state conditions, and peak torque, which can be
as high at 34.5 bar BMEP in the case of HyBoost with a larger turbocharger fitted.
This also can give a perceived turbocharger lag feel during vehicle launch even if
the boosting system response is more than adequate. To counter these effects,
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Hyboost uses a Valeo 12+X 3.3 kW electric supercharger to mitigate turbocharger
lag in addition to enabling some degree of torque augmentation to the base engine,
and a CAD model of the device is shown on the engine in Figure 4.

280
260
240
220
m)200
N
e (
u
orq180
T
160
HyBoost Torque Curve no e/s
140
HyBoost Torque Curve with e/s
120 2.0L Duratec NA PFI
Potentialfill-in
from e/s HyBoost Torque Curve Large T/C no e/s
100
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
Engine Speed (rpm)
Figure 3: Ford 2.0L Duratec Vs HyBoost torque curves comparison

Figure 3 also shows the full load** torque curve of HyBoost with the electric
supercharger running from 1000 to 2000 rpm engine speed. The following key
benefits of the electric supercharger can be determined from the detailed analysis
performed on the HyBoost project:
 The electric supercharger provides additional boosting capability beyond
the FGT and thus enables significant steady state and transient torque
augmentation in the lower engine speed range. The FGT also behaves as a
pressure ratio multiplier of the electric supercharger boost so is effectively
an in-series, 2-stage compressor system. This gives the potential to
address the large step up seen between low and mid speed torque
 Figure 3 shows there is a thermodynamic multiplication of the electric
supercharger power through the engine. At 1000 rpm the torque rises
from 125 to 183 Nm with the electric supercharger assistance, which is
equivalent to a 6.1 kW increase in power at this speed (13.1 to 19.2 kW
respectively). At 1500 rpm the rise is from 185 to 239 Nm, which is an
8.48 kW increase, and both of these improvements were achieved with an
input of only 1.8 kW to the electric supercharger. This equates to a 47 and
29% increase in engine torque at those speeds respectively, and
transiently the proportional increase in engine torque could be even higher
dependant on the boost response without the electric supercharger
assistance
 As a function of the higher engine power achieved with the electric
supercharger assistance more energy is naturally released to the FGT
turbine, enhancing its run-up
 The air mass flow and pressure ratio provided by the electric supercharger
is essentially free if provided from stored recovered energy (although the
system can run in self-sustaining mode as long as the generator can
provide the required energy and the electric supercharger remains within
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temperature limits). This results in a lower Indicated Mean Effective
Pressure (IMEP) required to generate boost than it would be for a
conventional turbo or supercharged engine for the same Brake Mean
Effective Pressure (BMEP). With downsized gasoline engines IMEP levels
can be very high and it can be extremely challenging to operate the engine
at these levels without significantly compromised combustion (retarded
spark timing and high levels of fuel cooling to control Exhaust Gas
Temperature), that can then translates in to a degradation in “real world”
fuel economy

** Note that full load performance availability is dependent on available stored
energy

Figure 4: CAD Model of the HyBoost powertrain showing the Valeo
12+X electric supercharger and associated intake pipework

Application of the electric supercharger to mitigate turbocharger lag required only
relatively shorts bursts of usage, typically in the order or 1 to 3 seconds, with the
engine returning to conventional thermodynamic only (without electrical assist)
operation as soon as possible. Figure 5 shows some early test bed data taken on
prototype phase engine with a 12V electric supercharger fitted. Here a load step is
used at constant engine speed to evaluate the boost response with and without the
electric supercharger running. Following a pedal stamp to Wide Open Throttle
(WOT) from a minimum load condition the boost pressure rise is measured, and the
graph shows that the time to peak boost is halved with the electric supercharger
running for 2 seconds than without the electric supercharger running. This testing
was far from optimum but shows the benefit of the electric supercharger, and the
12+X electric supercharger proved to be capable of achieving maximum speed of
greater than 60,000 rpm in less than 200 ms and a maximum pressure ratio of 1.6
bar with high motor efficiency. Subsequent vehicle performance and driveability
attributes where maintained with the 50% engine downsizing as shown in table 1
later in the paper.

Finally from Figure 3 the torque curve from a revised larger turbocharger fitted to
the HyBoost engine is shown with application of a Valeo-supplied Low Pressure
cooled WOT Exhaust Gas Recirculation (LP WOT EGR) system. A peak power and
torque of 112 kW at 5500 rpm and 260 Nm at 3000 rpm respectively was achieved
despite the engine not being optimised for these high levels of specific output. The
detriment of the larger turbo can be seen below 2250 rpm where the engine torque
drops off considerably, however, in this case aggressive use of the electric
supercharger can be utilised to “fill in” the curve if necessary, as shown by the
large arrow. In HyBoost’s case, with a primary project focus on low CO , the main
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