Energy and the New Reality, Volume 1: Energy Efficiency and the Demand for Energy Services Chapter 5: Transportation Energy Use L. D. Danny Harvey [e-mail]

1
Energy and the New Reality, Volume 1Energy
Efficiency and the Demand for Energy Services
Chapter 5 Transportation Energy Use L. D.
Danny Harveyharvey_at_geog.utoronto.ca
Publisher Earthscan, UKHomepage
www.earthscan.co.uk/?tabid101807

• This material is intended for use in lectures,
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  customization for the individual needs of course
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2
Transportation Energy Use, Outline

• Trends in movement of people and goods
• Energy use by different modes of transport
• Role of urban form and infrastructure
• Role of vehicle choice today
• Technical options for reducing energy use in
• - Cars and light trucks
• - Inter-city rail and buses
• - Passenger aircraft
• - Freight transport

3
Technical options for cars light trucks

• Downsizing
• Drive-train efficiency (thermal, mechanical,
  transmission)
• Reduced loads (requiring the engine to do less
  work)
• Hybrid electric vehicles (HEVs)
• Plug-in hybrid electric vehicles (FCVs)
• Fuel cell vehicles (FCVs)

4
Issue with fuel cell vehicles

• Cost and performance of fuel cells
• Constraints on supply of precious-metal catalysts
• Difficulties with on-board processing of
  hydrocarbon fuels
• Difficulties with on-board storage of hydrogen
  and development of H2 supply infrastructure

5
Figure 5.1 Proportion of different fuels usedfor
world transportation
Source Gilbert and Pearl (2007, Transport
Revolutions Moving People and Freight Without
Oil, Earthscan, London)
6
Figure 5.2a Breakdown of transportation energy
use in OECD countries in 2005
7
Figure 5.2b Break down of transportation energy
usein non-OECD countries in 2005
8
Figure 5.3a Variation in world passenger-km
movement of people
Source Gilbert and Pearl (2007, Transport
Revolutions Moving People and Freight Without
Oil, Earthscan, London)
9
Figure 5.3b Variation in world tonne-km movement
of freight
Source Gilbert and Pearl (2007, Transport
Revolutions Moving People and Freight Without
Oil, Earthscan, London)
10
Figure 5.4 Historical variation in world
passenger-km transport by aircraft
Source Gilbert and Pearl (2007, Transport
Revolutions Moving People and Freight Without
Oil, Earthscan, London)
11
Figure 5.5 Growth in the number of passenger and
commercial vehicles worldwide
12
Figure 5.6 Historical variation in the number of
cars per 1000 people
Source Gilbert and Pearl (2007, Transport
Revolutions Moving People and Freight Without
Oil, Earthscan, London)
13
Figure 5.7 Breakdown of total travel in USA
Source Gilbert and Pearl (2007, Transport
Revolutions Moving People and Freight Without
Oil, Earthscan, London)
14
From Table 5.1, energy intensities of different
modes of travel within cities

• Gas guzzling car (20 litres/100 km), one person
  
• 6.5 MJ/person-km (7.8 MJ/p-km primary
  energy)
• Energy efficient car (8 litres/100 km), 4
  persons
• 0.65 MJ/person-km (0.78 MJ/p-km primary
  energy)
• Diesel bus, typical US loading 1-2 MJ/person-km
• Light rail 0.8 MJ/person-km of electricity, 2
  MJ/person-km primary energy
• Heavy rail 0.4 MJ/person-km electricity, 1.0
  MJ/person-km primary energy
• Walking 0.13 MJ/person-km food energy
• Bicycling 0.1 MJ/person-km food energy

15
From Table 5.3, primary-energy intensities of
different modes of travel between cities

• Gas guzzling car (12 litres/100 km, 4 people)
• 1.16 MJ/person-km
• Fuel efficient car (6 litres/100 km, 4 people)
• 0.58 MJ/person-km
• Intercity bus 0.28 MJ/person-km
• Diesel train 0.2-0.5 MJ/person-km
• High speed electric train 0.2-0.4 MJ/person-km
• Air 0.6-1.5 MJ/person-km

16
From Table 5.4 The complete energy picture for
transportation involves

• On-site fuel or electricity use
• Upstream energy use in producing and supplying
  the fuel or electricity (this and on-site energy
  give primary energy use for the operation of the
  vehicle, which is what is given in the preceding
  two slides)
• The energy used to make the vehicle (embodied
  energy), averaged over the total distance
  travelled during the lifetime of the vehicle
• The energy used to make and maintain the
  infrastructure for the vehicles (roads, rail
  lines, airports), averaged over the total
  distance travelled during the lifetime of the
  vehicle

17
Some prominent results from Table 5.4

• Vehicleinfrastructure embodied energy for urban
  light and heavy rail, interurban car and
  interurban rail is about ½ the directupstream
  operating energy use
• Embodied energy for short air travel (trips of
  390 km) exceeds the operating energy
• For international air travel (average distance of
  7500 km), the aircraft embodied energy is
  important (about 40 of the operating energy)

18
Figure 5.8 Relationship between private
transportationenergy use and urban density
Source Newman and Kenworthy (1999,
Sustainability and Cities Overcoming Automobile
Dependence, Island Press, Washington)
19
Compact urban form with different land uses
(residential, retail, offices, schools and
daycare centres, medical) intermixed reduces
transportation energy requirements by

• Reducing the distances that need to be travelled
• Making is more practical and economical to serve
  the reduced travel demand with high-quality
  (i.e., rail-based) public transit
• Increasing the viability of walking and bicycling

Once people start using transit, there is a
further reduction in travel demand (in the
distances travelled) because people start
planning their trips to be more efficient (i.e.,
combining errands in one trip)
20
Bicyclingwalking share (in terms of number of
trips taken) in selected cities in 2001

• Amsterdam, 52
• Copenhagen, 39
• Hong Kong, 38 (another 46 by public transit)
• Sao Paulo, 37
• Berlin, 36
• New York, 9
• Atlanta, 0

21
Importance of Choice of Car/Truck (fuel use is
given for city driving)

• Pickup truck, 16 to 26 litres/100 km
• SUV, 8 to 26 litres/100 km
• Minivan, 11 to 21 litres/100 km
• Large car, 11 to 26 litres/ 100 km
• Mid-size car, 9 to 24 liters/100 km
• Subcompact car, 8 to 21 litres/100 km
• Subcompact hybrid, 6 litres/100 km
• 2-seater, 7 to 29 liters/100 km

22
Figure 5.9a Mix of vehicles purchased in the US
in 1975
Source Friedman et al (2001, Drilling in
Detroit Tapping Automaker Ingenuity to Build
Safe and Efficient Automobile, Union of Concerned
Scientists)
23
Figure 5.9b Mix of vehicle purchased in the US in
2000
Source Friedman et al (2001, Drilling in
Detroit Tapping Automaker Ingenuity to Build
Safe and Efficient Automobile, Union of Concerned
Scientists)
24
Figure 5.10 Risks posed by different cars
Source Ross and Wenzel (2002, An Analysis of
Traffic Deaths by Vehicle Type and Model, ACEEE)
25
Types of automobiles

• Spark ignition (SI) runs on gasoline, with
  power output reduced by reducing the flow of fuel
  and throttling (partially blocking) the airflow,
  causing a major loss of efficiency at part load
  (which is the typical driving condition)
• Compression ignition (CI) runs on diesel fuel,
  which is ignited by compression without the need
  for spark plugs. More efficient than SI engines
  due to absence of throttling, high compression
  ratio and lean fuel mixture (high airfuel ratio)
• Internal combustion engine (ICE) refers to
  engines where combustion occurs in cylinders.
  Both SI and CI engines are ICEs

26
Pollution controls

• SI engines use 3-way catalytic converters to
  oxidize (add oxygen to) CO and hydrocarbons in
  the exhaust while reducing (removing oxygen from)
  NOx
• This requires a stoichiometric airfuel ratio
• Until recently, 3-way catalytic converters could
  not reduce NOx in diesel exhaust because of the
  excess oxygen
• Recent advances that entail the use of ammonia
  have solved this problem
• Much stricter (and comparable) emission standards
  can be expected for both gasoline and diesel
  vehicles in the future.

27
However ....

• Stricter pollution controls require ultra-low S
  concentrations in the fuel ( 10 ppm, vs 10-250
  today in gasoline and 10-500 ppm today in diesel
  fuel)
• Achieving the very low S content in fuels
  increases refinery energy use by about 1.5, and
  the stricter pollution controls for diesel trucks
  (at least) would increase fuel use by 4-10

28
Figure 5.11a Fuel Economy Trend
Source Zachariadis, T. (2006, Energy Policy 34,
17731785, http//www.sciencedirect.com/science/jo
urnal/03014215)
29
Figure 5.11b Car/light truck fuel economy trend
Source Zachariadis, T. (2006, Energy Policy 34,
17731785, http//www.sciencedirect.com/science/jo
urnal/03014215)
30
Figure 5.12a Trends in automobile mass
Source Zachariadis, T. (2006, Energy Policy 34,
17731785, http//www.sciencedirect.com/science/jo
urnal/03014215)
31
Figure 5.12b Trends in automobile acceleration
and top speed
Source Zachariadis, T. (2006, Energy Policy 34,
17731785, http//www.sciencedirect.com/science/jo
urnal/03014215)
32
Figure 5.12c Trends in engine power and
power/displacement
Source Zachariadis, T. (2006, Energy Policy 34,
17731785, http//www.sciencedirect.com/science/jo
urnal/03014215)
33
Figure 5.13 Auto Loads vs. Speed
34
Figure 5.14 Fuel Use vs Speed
35
Figs 5.15-5.16 Energy flow in a typical present
day car (8.9 litres/100 km, 26.4 mpg) (left) and
advanced vehicle (4.0 litres/100 km, 58.4 mpg)
(right)
36
Options to Improve the Fuel Economy of Cars and
Light Trucks, Part 1

• Improve engine thermal efficiency (fraction of
  fuel energy supplied to the pistons, through
  combustion)
• Improve engine mechanical efficiency (fraction of
  piston energy transferred to the drive shaft)
• Improve the transmission efficiency (fraction of
  drive shaft energy transferred to the wheels)

37
Methods to improve engine thermal efficiency

• Leaner fuelair mixture (but worsens NOx
  emissions)
• Variable compression ratio (currently fixed)
  saves 10-15 if combined with supercharged
  downsized engine
• Direct injection gasoline fuel sprayed directly
  into cylinders at high pressure saves 4-6
• Variable stroke (switch between 2-stroke
  operation during acceleration and 4-stroke
  operation at high speeds) saves 25
• Resultant fuel use would be 0.85 x 0.95 x 0.75
  0.60, a savings of 40 (best case)

38
Methods to improve engine mechanical efficiency

• Aggressive transmission management running at
  optimal gear ratio at all times, which makes the
  engine operate at the torque-rpm combination that
  maximizes the engine efficiency for any given
  driving condition.
• Smaller engines (most of the time the engine
  operates at a small fraction of its peak power).
  10 smaller saves 6.6 in fuel because the engine
  on average will operate more efficiently
• Variable valve control instead of throttling of
  air flow in gasoline engines saves up to 10
• Reduced friction through better lubricants and
  other measures 1-5 savings
• Automatic idle-off when stopped saves 1-2

39
Increasing the transmission efficiency

• As noted above, the way in which the transmission
  is operated affects the engine mechanical
  efficiency
• The transmission itself is another source of
  energy loss, which can be reduced
• Typical transmission efficiencies today
• - automatic, 70-80
• - manual, 94
• Future automatic 88 with continuously variable
  transmission
• Energy use if we go from 70 to 88 is multiplied
  by 70/88 0.795, a savings of about 20

40
Combining the savings from different steps

• Certainly do not add the savings, because the
  savings from each successive step applies only to
  the remaining energy use, not to the original
  energy use
• Instead, multiply the individual factors
  representing the reduction in fuel use in each
  step
• Thus, if improved engine thermal efficiency,
  engine mechanical efficiency and improved
  transmission efficiency save 40, 10 and 20,
  respectively, then multiply 0.6 x 0.9 x 0.8 to
  get the overall fuel requirement
• In the above example, this would be 0.432 a
  savings of 56.8
• The factor of 0.432 would be multiplied by a
  further factor to represent the effect of reduced
  loads, giving an even larger potential savings

41
Options to Improve the Fuel Economy of Cars and
Light Trucks, Part 2

• Reduced tire rolling resistance through
  higher-pressure tires
• Reduced aerodynamic resistance through changes in
  car shape
• Reduced vehicle weight (affects energy use during
  acceleration and when climbing hills)
• Reduced vehicle accessory loads

42
Comparing Figures 5.15 and 5.16

• The energy flow to the wheels increases from
  14.8 to 22.7 of the fuel input
• Thus, for the same energy flow, we need only
  14.8/22.7 0.652 as much fuel (a savings of
  34.8)
• The loads on the wheels (due to reduced rolling
  and aerodynamic resistance and reduced vehicle
  weight) drop from 429.9 kJ/km to 298.0 kJ/km, so
  the fuel requirement from this alone would be
  multiplied by 298.0/429.9 0.693 (a savings of
  30.7)
• The overall fuel requirement is multiplied by
  0.652 x 0.693 0.452 (a savings of 54.8, which
  is lt 34.830.7)
• Cross-check the ratio of fuel inputs at the tops
  of the two figures is 1302/2882 0.452

43
Alternative vehicle drive trains

• Hybrid gasoline-electric or diesel-electric
  vehicles (HEVs)
• Plug-in hybrid electric vehicles (PHEVs)
• All-electric or battery electric vehicles (BEVs)
• Fuel cell vehicles (FCVs)

44
Hybrid electric vehicles

• Use the engine to supply average power
  requirements and to recharge a battery, with the
  battery used to meet peak requirements
  (acceleration, hill climbing)
• This allows downsizing of the engine, thereby
  reducing friction losses
• It also allows the engine to operate closer to
  the torque-rpm combination that maximizes its
  mechanical efficiency

45
Other energy savings in HEVs occur through

• Regenerative braking using vehicle kinetic
  energy to recharge the battery
• Elimination of idling when stopped
• Shifting power steering and other accessories to
  more efficient electric operation
• However, the Toyota Prius is not much more
  fuel-efficient than a 1993 Honda Civic because
  the technology has largely gone into giving
  better acceleration rather than improving fuel
  economy

46
Figure 5.17 Gasoline-battery hybrid vehicle
(parallel drive-train option)
47
PHEVs

• The idea here is to recharge the battery from the
  AC power grid (i.e., by plugging it in when
  parked) and using the battery until the battery
  energy drops, then switching to the gasoline (or
  diesel) engine
• This requires batteries with greater storage
  capacity than in HEVs, giving 40-60 km driving
  range on the battery
• Since most trips are shorter than this, a large
  portion of total distance travelled could be
  shifted to electricity in this way

48
PHEVs (continued)

• The key issues are the cost of the battery, the
  mass of the battery (cars with heavier batteries
  will need more energy for acceleration and
  climbing hills), the amount of energy stored
  (usually represent in Wh), which determines the
  driving range, and the peak power output from the
  battery (W), which determines how fast the
  vehicle can accelerate
• The key battery performance parameters are thus
  specific energy, Wh/kg, and specific power, W/kg

49
Figure 5.18 Specific power and specific energy
of different batteries
50
Figure 5.19 Battery cost vs battery powerenergy
ratio
60
51
Figure 5.20 kWh-fuel trade off
52
Figure 5.21 Gasoline savings with PHEVs as
afunction of electric driving range for US
driving patterns
53
Figure 5.22 Contributions to air conditioning
energy requirements
Source Kromer and Heywood (2007, Electric
Powertrains Opportunities and Challenges in the
U.S. Light-Duty Vehicle Fleet, Laboratory for
Energy and the Environment, MIT)
54
Figure 5.23 AC and non-AC energy Use (with AC
energy use given as a percentage of the driving
energy use)
Source Kromer and Heywood (2007, Electric
Powertrains Opportunities and Challenges in the
U.S. Light-Duty Vehicle Fleet, Laboratory for
Energy and the Environment, MIT)
55
Figure 5.24 Ratio of energy use by hybrid
vehicles to energy use by conventional vehicles,
with and without AC
56
Fuel Cell Vehicles

• A fuel cell is an electrochemical device that
  produces electricity, water and heat
• It requires a hydrogen-rich fuel
• There had been some effort to develop systems to
  convert gasoline on-board into a hydrogen-rich
  fuel that in turn would be fed to the fuel cell,
  but these efforts have largely been abandoned

57

• Instead, pure hydrogen fuel would be stored on
  board the vehicle
• The major issues are
• - How to store the hydrogen
• - How to build up a hydrogen-distribution
  infrastructure
• - What energy sources would be used to make
  hydrogen
• - Cost of fuel cells and of hydrogen fuel

58
Attractions of hydrogen FCVs

• Zero pollution emissions
• Much lower noise
• The hydrogen could be produced by electrolysis
  (splitting) of water using electricity supplied
  from renewable wind, solar or hydro sources of
  energy
• Thus, zero greenhouse gas emissions and
  sustainable energy supply

59
Options for Onboard Storage of H2

• As a gas compressed to 700 atm pressure
• over 3 times the volume and 1.4 times the
  weight of gasolinetank in a gasoline-powered
  vehicle with the same driving range
• - energy equiv to 10 that of the stored
  hydrogen would be needed for compression
• As liquid hydrogen, at 20 K ( -253ºC)
• just over 2 times the volume but half the
  weight of the gasolinetank
• - energy equiv to 1/3 that of the stored
  hydrogen would be needed for liquefaction
  (possibly reduced to 20 in the future)
• As a metal hydride
• almost 4 times the weight but only 80 of
  the volume of gasolinetank. More mining and
  processing of metals needed.

60
Table 5.18, mass and volume to store 3.9 kg of
usable hydrogen or gasoline equivalent,
sufficient for a 610 km driving range
61
Figure 5.25 Ballard 85-kW fuel cell for
automotive applications
Source Little (2000, Cost Analysis of Fuel Cell
System for Transportation, Baseline System Cost
Estimate, Task 1 and 2 Final Report to Department
of Energy, Cambridge)
62
Figure 5.26 Ballard 85-kW fuel cell
Source www.ballard.com
63
Figure 5.27 Fuel cell-battery hybrid vehicle
64
Figure 5.28 Efficiency of fuel cell vs output
Box 5.1, at the end of this file, contains
Figures 5.29 and 5.30
Source Kromer and Heywood (2007, Electric
Powertrains Opportunities and Challenges in the
U.S. Light-Duty Vehicle Fleet, Laboratory for
Energy and the Environment, MIT)
65
Thus,

• A hydrogen FCV would operate at a typical
  efficiency of 60, which is about three times
  the efficiency of a typical ICE (internal
  combustion engine) vehicle today
• This in turn reduces the amount of energy (as H2)
  that needs to be stored on the vehicle for a
  given driving range by a factor of 3
• This in turn is critical because any system of
  onboard hydrogen storage will be bulky and/or
  heavy in relation to the amount of energy stored
• The high efficiency also greatly reduces the
  amount of wind or solar power that would need to
  be installed in order to produce enough hydrogen
  to replace petroleum for transportation

66
Problems

• Fuel cells suitable for use in cars need to be
  able to operate at low temperature (120ºC)
• Low-temperature fuel cells require precious-metal
  catalysts (Pt and ruthenium) in order to operate
  (these catalysts are also needed in 3-way
  catalytic converters, but would not be needed for
  such in H2 FCVs)
• Supplies of Pt are quite limited the
  availability of Pt could be a significant
  constraint on the long-term viability of H2 FCVs
• Hydrogen could instead be used in ICEs (with much
  less pollution), but with only a 10-20
  efficiency gain so the problem of being able to
  store enough H2 onboard in order to get a
  reasonable driving range would arise

67
Figure 5.31 Distribution of Exploitable Pt
Resources
68
Box 5.3 Constructing a scenario for Pt demand
69
Figure 5.32a Pt Scenario for future automobile
fleets of 1, 2 or 5 billion (compared to about
700 million passenger vehicles and 100 million
commercial vehicles today)
70
Figure 5.33a Scenario for the growth in vehicle
production rate and vehicle population used for
the 5-billion-vehicle case in the previous slide
71
Figure 5.33b Scenario for the growth in the
fraction of new vehicles and of total vehicle
stock as fuel cell vehicles
72
Figure 5.32b Cumulative Pt consumption for the 3
fleets,assuming 90 recycling of Pt from
discarded vehicles
73
Bottom-line on Pt constraint

• A vehicle fleet reaching 5 billion (which would
  result from a human population of 10 billion with
  European levels of car ownership) and consisting
  entirely of FCVs would have a cumulative Pt
  demand by 2100 equal to the upper limit of the
  estimated amount of Pt that could be mined
• This leaves no room for other uses of Pt (such as
  in jewelry and electronics)

74
4 ways of using solar-energy to power cars

• Using solar electricity to charge batteries
• Using solar electricity to make H2 for use in a
  fuel cell
• Using solar energy to grow biomass that is
  converted to methanol and used in a fuel cell
• Using solar energy to grow biomass that is
  converted into ethanol and used in an ICE

75
Steps, solar energy to battery

• PV modules, 15 efficiency
• DC to AC conversion, 85
• Transmission, 96 (say)
• Battery charging, 95
• Drive train, 87
• Overall sunlight to wheels energy transfer
  10.1

76
Steps, solar energy to H2 Fuel cell

• PV modules, 15 efficiency
• PV to electrolyzer coupling, 85
• Production of hydrogen and compression to 30 atm,
  80
• Transmission 1000 km at 30 atm pressure, 98
• Compression from 30 to 700 atm pressure, 90
• Fuel cell, 50
• Drive train, 87
• Overall sunlight to wheels energy transfer
  3.9

77
Steps, solar energy to methanol to fuel cell
(methanol is another candidate as a fuel for
fuel cells)

• Photosynthesis, 1 efficiency
• Biomass to methanol, 67
• Transport, 98 (say)
• Fuel cell, 45 (less than using H2)
• Drive train, 87
• Overall sunlight to wheels energy transfer
  0.26

78
Steps, solar energy to ethanol, used in an
advanced ICE

• Photosynthesis, 1 efficiency
• Biomass to ethanol, 67
• Transport, 98 (say)
• ICE, 20
• Drive train, 87
• Overall sunlight to wheels energy transfer
  0.11

79
Conclusion

• Direct use of renewably-based electricity to
  recharge batteries makes far better use of the
  renewable electricity than using it to make H2 to
  for use in a fuel cell (extra steps mean extra
  losses)
• The land area required to convert sunlight to H2
  and drive a given distance is 20 times less
  than growing biomass to make methanol for use in
  a fuel cell, or 40 times less than growing
  biomass to make ethanol
• This is because the efficiency of PV modules (15
  or more) is vastly greater than the efficiency
  of photosynthesis ( 1)

80
Thus, the best bet seems to move to plug-in
hybrid vehicles that are recharged with solar- or
wind-generated electricity, with maybe a small
amount of hydrogen as a range extender in order
to eventually get completely off of fossil
fuelsLiquid biofuels would be a distant second
best as a range extender, but might be needed if
problems with H2 cannot be resolvedSwapping the
battery for a freshly charged battery every 100
km might be another solutionIn any case, the
underlying vehicle should be as efficient as
possible to minimize the electricity and/or
hydrogen or biofuel requirements.
81
Figure 5.34 Fuel-efficient cars
82
Figure 5.35 Drive-train cost components (NPVnet
present value)
83
Figure 5.36 Lifecycle costs for alternative
vehicles
84
Inter-City Rail Transport

• French TGV (Train à grand vitesse)
• German ICE (Inter-city express)
• Japanese Shinkansen

85
Recall

• Energy use to move people by cars is 2.5
  MJ/person km with 1 person per car, and projected
  to be 1 MJ/person-km with advanced future
  vehicles ( 0.25 MJ/person-km if you pack 4
  people into the car)
• The energy required in todays high speed trains
  is 0.08 to 0.15 MJ/person-km

86
Figure 5.37 Energy intensity for successive
generations of the German Intercity Express (ICE)
high-speed trains
Source Kemp (2007, T618 Traction Energy
Metrics, Lancaster University, Lancaster,
www.rssb.co.uk)
87
Figure 5.38 Shinkansen energy use
88
Caveats

• The savings are not quite as large as they appear
  to be, because high speed trains use electricity
  which will typically be generated at an
  efficiency of only 35-40
• So, divide the (electrical) energy use by the
  train by (0.35 to 0.4 times the transmission and
  transformer efficiencies) to get fuel use at the
  powerplant that generates the electricity
• Compare this with the amount of crude oil needed
  to produce the gasoline energy that is saved when
  people switch to trains. This will be the saved
  gasoline divided by the efficiency in making
  gasoline from oil, about 0.85

89
Caveats (continued)

• The energy requirements for high speed trains
  increase rapidly with increasing speed beyond
  about 300 km per hour
• The absolute time savings over a given distance
  gets smaller and smaller for each additional
  increment of speed
• Faster trains increase total transportation
  demand so some of the passengers on the train
  are people who would not have travelled at all
• Thus, careful market analysis is required to
  determine if the introduction of high-speed
  trains really does save energy

90
Aircraft Energy Use
91
Major types of aircraft

• Turbojet
• Turbo fan (popularly called jets)
• Turbo prop

All three have, as their core, a gas turbine (the
gas turbines now used to generate electricity
using natural gas were derived from aircraft
turbines developed for the military)
92
In a true jet, all of the air thrown behind the
aircraft passes through the turbine, where
combustion of fuel occurs. This is found only in
military fighter jets
93
In commercial jet aircraft, most of the air
thrown behind the jet bypasses the turbine, as it
is accelerated by a big fan attached to the
turbine (this is what you see when you look at a
the engine of a commercial jet)
94
A third option is for the turbine to drive a
propeller that is in front of the turbine
95
The performance of an aircraft is represented by
the specific air range, which is the distance
that can be travelled per MJ of fuel energy used.
It depends on 3 factors

• The amount of thrust produced by the engines per
  kg of fuel used
• The aircraft drag for a given velocity
• The aircraft weight

96
The thrust generated by the engine is equal to
the product of mass x velocity of the air thrown
behind the engineDoubling the mass of air
thrown and cutting its speed in half gives the
same thrust, but much less kinetic energy (which
varies with v2) needs to be added in this
caseThus, the engine needs to do less work
while producing the same thrust
97
This is why turbofan aircraft were developed

• The larger the bypass ratio, the greater the
  amount of air that is thrown behind the engine,
  but the less it needs to be accelerated
• This tends to make the engine more effective
• However, this requires a larger engine casing,
  which increases the drag and weight
• Thus, there is an optimal bypass ratio, which is
  where we are now not much further improvement
  can be expected

98
Figure 5.40a Trends in thrust specific fuel
consumption (fuel consumption per unit of thrust
generated smaller is better)
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
99
Figure 5.40b Trend in lift/drag ratio (larger is
better)
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
100
Figure 5.40c Trend in ratio of empty weight to
maximum allowed take-off weight (smaller is
better).
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
101
Observations from the previous figures

• The big improvement has been in thrust specific
  fuel consumption (TSFC) decreasing by about 50
  for long-haul aircraft from 1959 to 1998,
  achieved in part through development of engines
  with larger bypass ratios
• Turboprop aircraft have about 20 smaller TSFC
  than turbofan aircraft
• No trend in lift/drag ratio improvements in
  overall aerodynamics have offset the impact of
  fatter engines with larger bypass ratios
• A slight upward trend in ratio of empty to full
  weight related in part of extra in-flight
  entertainment systems

102
The energy requirement per passenger-km under
cruising conditions is equal to the reciprocal of
the (specific air range x seating capacity). It
is shown by the coloured (solid) symbols in the
next figure
103
Figure 5.40d Aircraft energy intensity (MJ used
per available seat-km)
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
104
Other factors affecting energy use per km
travelled by air travel

• Distance the most energy-intensive part of the
  flight is the takeoff. On longer flights, this
  energy use is spread over more kms, reducing the
  average energy use per km
• The airborne efficiency related to distance
  flown (and thus flying time) to the shortest
  distance between the starting and ending points
• The ground efficiency the ratio of flying hours
  to total hours (including taxiing)

105
Figure 5.41a Ground efficiency for different
aircraft and distances travelled
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
106
Figure 5.41b Airborne efficiency for different
aircraft and travel distances
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
107
Figure 5.42 Energy intensity averaged over the
entire flight (including taxiing, waiting to take
off, circling before landing)
Source Babikian et al (2002, Journal of Air
Transport Management 8, 389400,
http//www.sciencedirect.com/science/journal/09696
997)
108
See Figure 5.37d again note the difference
between energy intensity while cruising (solid
symbols) and overall flight energy intensity
(open symbols)
109
Prospects for the future

• Weight reductions through increasing use of
  C-fibre composite materials
• 10-25 further improvement in engine efficiency
• Overall reduction in fleet average energy use per
  passenger-km of 20-25 from 1995 to 2030 seems to
  be quite feasible
• Shifting from turbofan (jet) to the latest
  turboprop aircraft for distances up to 1000 km
  also reduces energy use
• The most efficient aircraft will still be many
  times as energy intensive as high-speed trains

110
Freight Transport
111
Figure 5.43 Freight transport modes
112
Figure 5.44 Variation of freight energy intensity
with distance transported, and difference
between modes of transport
Source Skolsvik et al (2000b, Study of
Greenhouse Gas Emissions from Ships, Appendices,
International Marine Organization, London)
113
Figure 5.45 Variation freight energy intensity
with capacity factor
Source Skolsvik et al (2000b, Study of
Greenhouse Gas Emissions from Ships, Appendices,
International Marine Organization, London)
114
Prospects for reducing road freight transport
energy intensity (that, reducing energy use per
tonne-km of transport)

• Improved diesel engine thermal efficiency (from
  45 to 55)
• Hybrid diesel-electric trucks 25-45 savings
  for delivery vehicles in urban settings
• Elimination of idling in heavy trucks (averages
  about 2400 hours/year) through use of auxiliary
  power units such as fuel cells for air
  conditioning and other loads (high-temp fuel
  cells, not requiring Pt catalysts, could be used)

115
Prospects for reducing road freight transport
energy intensity (continued )

• Improved aerodynamics
• Improved loading factor
• Reduced speed

116
Net resultA 50 or better reduction in the
energy intensity of freight transport by new
trucks is achievable over the next two decades.
More time would be required to see this
improvement over the entire fleet of trucks
117
Locomotives for Freight Trains

• Ideal candidate for early application of fuel
  cells (on-board fuel storage and start-up time
  are not an issue)
• Upfront costs less important than for passenger
  vehicles because fuel cost savings over a 20-30
  year lifespan are important

118
Figure 5.46 Locomotive energy flow with a diesel
engine used to generate electricity that in turn
drives an electric motor
119
Figure 5.47 Locomotive energy flow using a fuel
cell to generate electricity that in turn drives
an electric motor
120
Reducing the energy intensity of shipping

• The International Maritime Organization has
  identified measures that could be phased in and
  which would reduce shipping energy intensity by
  37 over 20 years and by 45 over 30 years
• Small wind turbines on a vertical axis (Flettner
  rotors) fitted to ships and connected to
  propellers could potentially reduce the remaining
  energy requirement by 30-40 (already used by the
  German wind turbine manufacture Enercon on the
  barges used to transport its offshore wind
  turbines to where they are installed)

121
Reducing the need to transport freight

• The previous discussion has focused on the energy
  intensity of freight transport the energy used
  to transport a given amount of freight a given
  distance
• Globalization and free trade deals have caused
  global freight movement to increase much faster
  than the growth of the global economy

122

• This growth has depended on cheap fuel and
  unequal wages, worker benefits, and health,
  safety and environmental standards in different
  countries (and, in some cases, artificial
  exchange rates)
• With the inevitable increase in fuel costs and a
  reduction in the differences between countries,
  the trend toward ever greater trade may very well
  be reversed, thereby contributing to reduced
  freight transportation energy use
• Conscious effort by consumers to buy
  locally-produced products can also contribute to
  this

123
Impacts of e-commerce

• Allows greater transport distances and greater
  delivery frequencies (tending to increase energy
  use), but can also be used to improve the
  distribution system
• Can result in greater use of packaging
• Can result in reduced warehouse building area by
  facilitating just-in-time delivery, thereby
  reducing warehouse energy use
• Can permit electronic grocery shopping and home
  delivery services

124
To maximize the energy savings from e-shopping
and home delivery, a re-organization of the
relationship between suppliers, distribution and
collection centres, and retailers would need to
occur. This might happen spontaneously from the
need for improved logistics
125
Figure 5.48 Flow of goods from producers to
consumers at present (left) and as might occur
with an energy-efficient e-commerce arrangement
Source Bratt and Persson (2001, European Council
for an Energy Efficient Economy, 2001 Summer
Proceedings 3, 480492)
126
Box 5.1 Efficiency of a fuel cellThe
efficiency of a fuel cell is equal to the product
of three efficiencies

• The reversible efficiency
• The voltage efficiency (high operating voltage
  gives a larger voltage efficiency)
• The Faradic efficiency (almost always 1.0)

127
Figure 5.29a Factors contributing to the
reduction in the voltage of a PEM fuel cell
compared to the theoretical maximum voltage
128
Figure 5.29b Variation of the efficiency and
power density of a PEM fuel cell with current
density. A smaller current density means that a
larger and hence more expensive fuel cell is
needed for a given power.
129
Figure 5.30a Variation of voltage of a PEM cell
with current density for operation at 50oC and at
different pressures.
130
Figure 5.30b Variation of voltage of a PEM cell
with current density for operation at 70oC and at
different pressures.