The Lotus Range Extender Engine

J.W.G. Turner, D. Blake, J. Moore, P. Burke, R.J. Pearson, R. Patel, D.W. Blundell, R. B. Chandrashekar, L. Matteucci,

P. Barker, and C.A. Card

Paper Number 2010Paper Number 2010--0101--22082208

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Project Partners – Limo Green

The Lotus Range Extender Engine is being designed as part of the “Limo Green” projectyTo demonstrate a luxury saloon with a series hybrid drive train and charge-sustaining CO2 emissions of less than 120 g/km

This project is led by Jaguar Cars LtdyWho are conducting the vehicle packaging workyProject partners include MIRA and Caparo Vehicle Technologies

Limo Green is part-funded by the UK government’s Technology Strategy Board as part of its Low Carbon Vehicles Integrated Delivery Platform

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How the Original Idea Came About…

Current engines in series hybrid applications are largely adaptations of existing architecturesy… But an engine can be more efficient if designed to operate within a heavily constrained speed and load regime

We believed that the specific requirements of the automotive market called for a solution decided upon from an automotive standpointyIt should 1) be light, 2) have good NVH and 3) be efficient enough

InverterDriveUnit

HV Battery

IC Engine Motor

Starter Generator

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Concept Definition Phase

Initial vehicle modelling concentrated on achieving a charge-sustaining level-ground Vmax of 80 mph / 137 km/hyThis would require an engine power of approximately 38 kW (with an electrical generator output of 35 kW)

Reciprocating (2- or 4-stroke), rotary, gas turbine and fuel cell engines were all considered, but 4-stroke reciprocating was chosen in order to offer a near-term solutionEngine modelling investigated two main options: I2 and I3 yEngine speed was to be kept to ~3500 rpm for NVH and frictionyWith currently-attainable BMEP on 95 RON ULG, this meant 1.2 l

There was little between an I2 and I3 when the final decision was made, assuming both had a primary balanceryIn the end an I3 was chosen because it permitted removal of the balance shaft for some applications

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Basic Engine SpecificationGeneral 1.2 litre 3-cylinder with 2 valves per cylinder, SOHC

Construction Monoblock with Integrated Exhaust ManifoldBalance shaft (deletable)

Bore and Stroke 75.0 mm x 90.0 mm

Compression ratio 10:1 (protected for higher values)

Maximum power 38 kW (51 bhp) at 3500 rpm

Peak torque 107 Nm at 2500 rpm (11.2 bar BMEP)

Maximum Engine Speed 3500 rpm (protection for 4000 rpm)

Fuel System Port fuel injection, Lotus EMS

Fuel 95 RON ULG / ethanol / methanol

Dry weight 60 kg / 56 kg (with/without balance shaft)

The monoblock architecture of the engine aims to investigate further improvements in terms of cost and massyWhich should also be immediately applicable to diesel engines

The engine will operate at λ = 1 everywhere

Very undersquare

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Monoblock (1)

The monoblock integrates cylinder block and head together, together with an integrated exhaust manifold (IEM)yWe have designed 4 engines with monoblock construction and 7 with IEMs

The resulting casting is complex, but overall the approach minimises BOM and assembly costs, engine mass and size, and improves emissions, cooling and warm-upyApproximately 17 components are removed by the monoblock and 22 are removed by the IEM

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Monoblock (2)

Port design was conducted together with in-cylinder CFDyPort flow box used for physical comparative testingyMonoblock permitted more port-shape flexibility through absence of bolt pillars

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2-valve optimised combustion chamberyModified bath tub with ‘slant squish’

Nickel-ceramic bore plating and honing process for optimised friction benefitsCooling jacket designed to minimise wetted area of cylinderyFor best thermal efficiencyyWith cooling system CFD analysis

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Crankcase AssemblyBedplate with cast-in iron bearing housing insertsyMain bearings through-bolted into monoblock

Full attachment of generator to crankcase assembly at rear flange to reduce localised stressesyNo monoblock changes to fit a different generator

Since it contains no water, there is some potential to adopt magnesium in this assembly

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Cranktrain (1)

All cranktrain dimensions have been optimised for low friction and massMain and big end bearings are the same diameter – 38 mmyNo bearing overlap

Crankshaft mass is 7 kgConnecting rod is piston guided for minimum frictiony3.36 L/R

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Cranktrain (2)

Piston have a CR of 10:1y11:1 pistons for development testingyPiston bowl volume change only (negligible effect on mass)

Piston mass is 176 gEngine has a primary couple balancer shaft in oil panyDriven by a gear on the rear crank webyRolling element bearings for low frictionyCounterweights shielded for minimum windageyPossibility to delete for some applications

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Valvetrain and Cam DriveValvetrain system optimised for performance, cost and friction ySOHC, belt-driven format selectedyPushrod no advantage in single-bank engines

Concept Valvetrain software used to define optimised springs and cam geometryy5mm valve stems, graded mechanical tappetsy31mm inlet and 26mm exhaust diameters

No cam phasingyUnnecessary due to defined operating area and start-up procedure

Off-the-shelf tensioner and idleryTensioner mounted on oil pump, idler mounted on dedicated bracket from front engine mount bosses

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Catalyst and EMS

Catalyst bolts straight to monoblockyHeat shielding/cooling ducts to be optimised for vehicle installation

Utilises off-the-shelf brick with 1.0 litre volumeyVehicle-based tests conducted for starting strategy and catalyst loading

T6e EMS used with electronic throttleyWith flex-fuel strategies for ethanol and methanol operationyVehicle-mounted

Wiring loom is on intake side of engine (except for O2 sensors)

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Ignition and Fuelling Systems

The ignition and fuelling system are incorporated into a single assemblyCoils are minimum-size off-the-shelf unitsySignificant opportunity to reduce coil size and integrate fuel rail and coil housing into a single component in future

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Engine SectionsRemoval of head bolts and IEM provide very compact

upper architecture

Shielded balance shaft

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Finished Engine

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Engine 001 Installation on Test Bed

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Preliminary Full-Load Results (BIPO)

0

20

40

60

80

100

120

1750 2000 2250 2500 2750 3000 3250 3500 3750

Engine Speed / [rpm]

Cor

rect

ed T

orqu

e / [

Nm

] and

Pow

er /

[kW

]

230

235

240

245

250

255

260

Obs

erve

d B

SFC

/ [g

/kW

h]

Torque Power BSFC

Increasingly knock-limited

MBT

FMEP ~ 0.6 barηmech. = 90-92%

Operation at λ = 1 on 95 RON ULG with 10:1 CR

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Preliminary Full-Load BSFC v Power (BIPO)

220

225

230

235

240

245

250

255

15 20 25 30 35 40

Brake Power / [kW]

BSF

C /

[g/k

Wh]

28

30

32

34

36

38

40

42

Bra

ke T

herm

al E

ffici

ency

/ [%

]

BSFC Brake Thermal Efficiency

There is scope to improve this due tothe increasingly knock-limited nature

as engine speed is reduced –we have seen <240 g/kWh in testing

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BSFC from Several Engines (BIPO)

220

240

260

280

300

320

340

360

380

5 10 15 20 25 30 35 40

Brake Power / [kW]

BSF

C /

[g/k

Wh] Possibility of <290 g/kWh at 10 kW

Possibility of <240 g/kWhFrom 18-38 kW

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Electrical Power and SFC

245

250

255

260

265

270

275

280

15 20 25 30 35 40

Electrical Power / [kW]

Elec

tric

al S

FC /

[g/k

Wh]

26

28

30

32

34

36

38

40

Elec

tric

al T

herm

al E

ffici

ency

/ [%

]

UQM Elec. SFC UQM Elec. Therm. Eff.

With UQM Powerphase 75 generator,as used in the Limo Green project

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Installation in Evora 414E Demonstrator

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Conclusions

A bespoke Range Extender engine for plug-in series hybrid vehicles (PHEVs) has been designedyIt has all the attributes necessary for use in the automotive market because it has been designed using automotive processes

The engine has been designed to mass, size and efficiency targets which were determined from our previous work in engineering series hybrid vehiclesIt adopts some unusual architectural solutions which in turn have been permitted by its constrained operating rangeyBut which are also especially applicable to diesel engines

Performance and fuel economy are as good as the wide-range-4-stroke PFI normyDue to an academically-led approach to the combustion systemyMapping is expected to show improvements at low power outputs

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