Future of Engines

7/30/2019 Future of Engines

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Future efficiency of theinternal combustion engine

Nick Collings

Cambridge University EngineeringDepartment


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Motivation and scope

What are the concerns? CO2 emissions

Fuel economy

Oil price/scarcity Noxious emissions

Vehicle intrusivity

What are the alternatives? Work from home

Public transport (what sort?)

More efficient conventional vehicles Different vehicle concepts

Hybrid ( + plug-in)

All electric Fuel cell

?


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In its mid-term review of the 2001 Transport

White Paper, the EU Commission commented:

.city dwellers directly experience the

negative effects of their own mobility, andmay be open to innovative solutions forcreating sustainable mobility.


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Whats wrong with current

vehicles?They are too big and heavy

Their are too many of them, with too fewpeople on-board.

Their average speed is low (esp. in theurban environment)

There is little/no opprobrium attached to

usage last and possibly least

They are not very efficient.


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A few preliminary observations

As a rule of thumb:- emissions are

proportional to (fossil) fuel consumptionTrue statement for CO2 and H2O

More complex for noxious emissions

depends on driving patterns + regulation level. Sulphur dioxide more complex due to

substitution.

Reducing noxious emissions increasesCO2 emissions.


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A modern gasoline engine


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The classic 4 stroke engine cycle


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Gasoline Engine Cycle Plotted on Cylinder

pressure vs Cylinder volume axes.

Full thrott le Part thrott le

Cylinder volumeCylinder volume

Cylin

derpressure

Cylin

derpressu

re

The ratio of air: fuel in a gasoline engine has to be close tochemically correct so power change is via changes in the airand fuel (i.e. dropping the inlet mixture pressure).

Diesel engines run without throttling because the fuel (which isinjected directly into the cylinder) burns spontaneously so powerchange is possible with only fuel quantity changes.


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Just after the spark

The flame will only propagate reliably if the air fuelmixture is close to stoichiometric

G li E i P f Ch t i ti


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torq

ue

Engine speed1000 2000 50003000 4000

maximum torque wide open throttle

Top gear

torque road

load

Gasoline Engine Performance Characteristics

G li E i P f Ch t i ti


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torq

ue

Engine speed1000 2000 50003000 4000

constant power

curvesmaximum torque

wide open throttle

Top gear

torque road

load

Torque

reserve




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torq

ue

Engine speed1000 2000 50003000 4000

constant power


wide open throttle

Constant specificfuel consumption

curves

Top gear

torque road

load

Most efficient

operating point

Torque

reserve

0.25

0.3

0.35

0.4

0.5

0.6




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torq

ue

Engine speed1000 2000 50003000 4000

constant power


wide open throttle


curves (kg/kWhr)

Top gear

torque road

load

Most efficient

operating point

Torque

reserve

0.25

0.3

0.35

0.4

0.5

0.6

Highly thrott led

High

frictionallo

sses



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T i


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To summarise

The losses increase at Low torque

High revs

(and high speed!)

So, how to we reduce/prevent operation in

these conditions? Smaller engines (+ turbo charging)

Downsizing

Energy storage and Boost methods (onedoes not accelerate for ever.)

Gearing (CVT)


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Hydrogen fuelled engines

Burn hydrogen

No CO2

Negligible noxious emissionsBut

Where does the H2come from?

Efficiency similar to current gasoline vehicles

H2 storage issues


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Hydrogen fuel cell vehicles

Use hydrogen to generate electricity using

a fuel Cell No CO2

Negligible noxious emissions

But

Where does the H2come from?

Efficiency little better than current gasolinevehicles

H2

storage issues


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Hydrogen in action
http://www.fuel-cell-bus-club.com/index.php?module=pagesetter&func=viewpub&tid=1&pid=51http://www.fuel-cell-bus-club.com/index.php?module=pagesetter&func=viewpub&tid=1&pid=46


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T i l f l ll ffi i


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Typical fuel cell efficiency

% of maximum power


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Hybrid vehicles

What is a hybrid?Typically a vehicle with an IC engine and an

electrical drive system combined.

Why do they have better fuel economy?

The flexibility engendered by the additional

hardware allows for better matching of theengine to the driving condition.



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torq

ue

Engine speed1000 2000 50003000 4000

constant power

curvesmaximum torque wide open throttle


curves (kg/kWhr)

Top gear

torque road

load

Most efficient

operating point

Torque

reserve

0.25

0.3

0.35

0.4

0.5

0.6

Highly thrott led

High

frictionallo

sses

g


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Conventional transmission system


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The Differential

(The fastest car in the world)
http://www.modernracer.com/member/memberfeatures/carcutaways/bugattiveyroninsides1.jpghttp://www.modernracer.com/member/memberfeatures/carcutaways/bugattiveyroninsides1.jpg


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28

Mechanical Path

Electrical PathSeries Hybrid System (SHS)

Generator Motor/Generator

Battery

Inverter

Wheel

Wheel

Engine

Main CharacteristicsMain Characteristics

Motor delivers all power

Engine drives generator


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29

Mechanical Path

Parallel Hybrid System (PHS)

Transmission Motor/

Generator

Wheel

Wheel

Engine

Electrical PathMain CharacteristicsMain Characteristics

Engine supplies main power

Motor assists

Inverter

Battery


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30

Toyota Hybrid System (THS)

Power Split

Device

Motor/

Generator

Wheel

Wheel

Engine

Electrical PathMain CharacteristicsMain Characteristics

Motor/Generator

Two Power PathsController BalancesEngine Load

Mechanical PathBattery

Inverter


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Planetary ring gear
http://en.wikipedia.org/wiki/Image:Epicyclic_gear_ratios.pnghttp://en.wikipedia.org/wiki/Image:Pencil_sharpener_mechanism.jpg


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32

Toyota Hybrid System PowertrainToyota Hybrid System Powertrain

ReductionGear

GeneratorMotor

Drive Shaft

Planetarygear

Engine


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33

THS Cutaway


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34

Battery Comparison THS RAV4-EV

Type Nickel Metal-Hydride

Voltage(V) 288(240 cells) 288(24 modules of 10 cells)Energy

(kW-hr)1.8 29

Specific Energy

(W-hr/kg) 45 64Power

(kW)21 126

Specific Power

(W/kg) 525 280Weight

(kg)40 450


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SOCSOC

Time

Overdischarging AreaOverdischarging Area

Upper LimitUpper Limit

Lower Limit

Target SOCTarget SOC

Actual SOCActual SOC

Overcharging AreaOvercharging Area

State of Charge Control


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36

Operational modes

Vehicle Speed

Engine & MotorEngine & Motor

Battery EnergyBattery Energy

MotorMotor

Full Throttle Acceleration

Moderate Acceleration

Road Load Max. Speed at Cruising

Max. Speed


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37

Energy Flow at Light LoadEnergy Flow at Light LoadBattery (EV drive)(EV drive)


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38

Energy Flow at Medium LoadEnergy Flow at Medium Load

(HEV drive)(HEV drive)


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39

Energy Flow at High LoadEnergy Flow at High Load(HEV drive +(HEV drive +

battery assist)battery assist)

Battery

A few comments


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A few comments

Strangely, at motorway cruise conditions,the Prius appears to have a negative fuel

economy benefit. Extra cost ICE + power electrical system

Battery life?

Other energy storage methods:- Flywheels

Hydraulic accumulators Super capacitors


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Lets look at batteries

Why?

In principle they offer more freedom ofmovement

(compared with trains, trams etc)

Pollution free (?)

CO2 free (?)

Why arent we all driving battery powered vehicles?

i


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Battery Comparisons

Energy density of various materials


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Material Watt-hr/litre Watt-hr/kg

Fission of U-235 4.7 x 1012 2.5 x1010

Diesel Fuel 10,700 12,700

Heating Oil 10,400 12,800

Gasoline 9,700 12,200

LNG (-160C) 7,216 12,100

Propane 6,600 13,900

Ethanol 6,100 7,850

Liquid H2 2,600 39,000150 Bar H2 405 39,000

STP Propane 26 13,900

STP NG 11 12,100

STP H2 3 39,000

Li-Ion Battery 200 150

NiMH Battery 280 100

Lead-Acid Battery 40 25

gy y

Batteries for transport are being


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Batteries for transport are being

looked at for applications such as:-

Improved Prius-like vehicles Plug in Hybrids (Biggish battery + IC

engine)With a hope that for many journeys, the IC engine

will not operate at all.

All-electric vehicles

Nothing new in all-battery


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Nothing new in all battery

vehicles

N t ll till d


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Not all are still around.

Some are appearing in increasing
http://upload.wikimedia.org/wikipedia/commons/2/22/SinclairC5.jpg


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Some are appearing in increasing

numbers..

Pl I H b id


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Plug In Hybrids

Use a bigger battery than in the Prius

Charge intelligently Cheaply (gridsupport)?

No trip length limit (c.f. battery only)

Near future? GM VOLT


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Near future? - GM VOLT

DETROIT (Reuters) - General Motors

Corp's plug-in Chevy Volt and otherelectric vehicles have generatedwidespread consumer fervour for cleaner,

less fuel-dependent cars, but the highbattery cost means it will be years before

those cars are affordable to mostAmericans.

Progress with Li ion batteries


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Progress with Li-ion batteries

Pl i H b id b tt k


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Plug-in Hybrid battery packcharacteristics

B tt l t i hi l b tt


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Battery electric vehicle batterypack specs.

So whats the future of


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personal transport? My guess:-

Incremental movement towards more nuclearpower + renewables.

Transport in cities becomes more electrified.

Owning/using a personal vehicle becomesmore and more expensive in real terms.
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Future of Engines