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Energy and the New Reality, Volume 1: Energy Efficiency and the Demand for Energy Services Chapter 5: Transportation Energy Use L. D. Danny Harvey harvey@geog.utoronto.ca.

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slide1

Energy and the New Reality, Volume 1:Energy Efficiency and the Demand for Energy ServicesChapter 5: Transportation Energy Use L. D. Danny Harveyharvey@geog.utoronto.ca

This material is intended for use in lectures, presentations and as handouts to students, and is provided in Powerpoint format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see www.earthscan.co.uk for contact details.

Publisher: Earthscan, UKHomepage: www.earthscan.co.uk/?tabid=101807

transportation energy use outline
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

technical options for cars light trucks
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)
issue with fuel cell vehicles
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
figure 5 1 proportion of different fuels used for world transportation
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)

figure 5 3a variation in world passenger km movement of people
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)

figure 5 3b variation in world tonne km movement of freight
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)

figure 5 4 historical variation in world passenger km transport by aircraft
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)

figure 5 6 historical variation in the number of cars per 1000 people
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)

figure 5 7 breakdown of total travel in usa
Figure 5.7 Breakdown of total travel in USA

Source: Gilbert and Pearl (2007, Transport Revolutions: Moving People and Freight Without Oil, Earthscan, London)

from table 5 1 energy intensities of different modes of travel within cities
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
from table 5 3 primary energy intensities of different modes of travel between cities
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
from table 5 4 the complete energy picture for transportation involves
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
some prominent results from table 5 4
Some prominent results from Table 5.4:
  • Vehicle+infrastructure embodied energy for urban light and heavy rail, interurban car and interurban rail is about ½ the direct+upstream 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)
figure 5 8 relationship between private transportation energy use and urban density
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)

slide19

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)

bicycling walking share in terms of number of trips taken in selected cities in 2001
Bicycling+walking 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%
importance of choice of car truck fuel use is given for city driving
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
figure 5 9a mix of vehicles purchased in the us in 1975
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)

figure 5 9b mix of vehicle purchased in the us in 2000
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)

figure 5 10 risks posed by different cars
Figure 5.10 Risks posed by different cars

Source: Ross and Wenzel (2002, An Analysis of Traffic Deaths by Vehicle Type and Model, ACEEE)

types of automobiles
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 air:fuel ratio)
  • Internal combustion engine (ICE) – refers to engines where combustion occurs in cylinders. Both SI and CI engines are ICEs
pollution controls
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 air:fuel 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.
however
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%
figure 5 11a fuel economy trend
Figure 5.11a Fuel Economy Trend

Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)

figure 5 11b car light truck fuel economy trend
Figure 5.11b Car/light truck fuel economy trend

Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)

figure 5 12a trends in automobile mass
Figure 5.12a Trends in automobile mass

Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)

figure 5 12b trends in automobile acceleration and top speed
Figure 5.12b Trends in automobile acceleration and top speed

Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)

figure 5 12c trends in engine power and power displacement
Figure 5.12c Trends in engine power and power/displacement

Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)

slide35

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)

options to improve the fuel economy of cars and light trucks part 1
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)
methods to improve engine thermal efficiency
Methods to improve engine thermal efficiency
  • Leaner fuel:air 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)
methods to improve engine mechanical efficiency
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%
increasing the transmission efficiency
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%
combining the savings from different steps
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
options to improve the fuel economy of cars and light trucks part 2
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
comparing figures 5 15 and 5 16
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 < 34.8+30.7)
  • Cross-check: the ratio of fuel inputs at the tops of the two figures is 1302/2882 = 0.452
alternative vehicle drive trains
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)
hybrid electric vehicles
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
other energy savings in hevs occur through
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
phevs
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
phevs continued
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
slide52
Figure 5.21 Gasoline savings with PHEVs as afunction of electric driving range for US driving patterns
figure 5 22 contributions to air conditioning energy requirements
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)

slide54
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)

slide55
Figure 5.24 Ratio of energy use by hybrid vehicles to energy use by conventional vehicles, with and without AC
fuel cell vehicles
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
slide57
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

attractions of hydrogen fcvs
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
options for onboard storage of h 2
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 gasoline+tank 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 gasoline+tank

- 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 gasoline+tank. More mining and processing of metals needed.

slide60
Table 5.18, mass and volume to store 3.9 kg of usable hydrogen or gasoline equivalent, sufficient for a 610 km driving range
figure 5 25 ballard 85 kw fuel cell for automotive applications
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)

figure 5 28 efficiency of fuel cell vs output
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)

slide65
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
problems
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
slide69

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)

slide70

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

slide71
Figure 5.33b Scenario for the growth in the fraction of new vehicles and of total vehicle stock as fuel cell vehicles
slide72
Figure 5.32b Cumulative Pt consumption for the 3 fleets,assuming 90% recycling of Pt from discarded vehicles
bottom line on pt constraint
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)
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

4 ways of using solar-energy to power cars
steps solar energy to battery
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%

steps solar energy to h 2 fuel cell
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%

steps solar energy to methanol to fuel cell methanol is another candidate as a fuel for fuel cells
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%

steps solar energy to ethanol used in an advanced ice
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%

conclusion
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%)
slide80

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.

inter city rail transport
Inter-City Rail Transport
  • French TGV (Train à grand vitesse)
  • German ICE (Inter-city express)
  • Japanese Shinkansen
recall
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 today’s high speed trains is ~ 0.08 to 0.15 MJ/person-km
slide86
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)

caveats
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
caveats continued
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
major types of aircraft
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)

slide92

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

slide93

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)

slide95

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
slide96

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

this is why turbofan aircraft were developed
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
slide98
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, 389–400, http://www.sciencedirect.com/science/journal/09696997)

figure 5 40b trend in lift drag ratio larger is better
Figure 5.40b Trend in lift/drag ratio (larger is better)

Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)

figure 5 40c trend in ratio of empty weight to maximum allowed take off weight smaller is better
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, 389–400, http://www.sciencedirect.com/science/journal/09696997)

observations from the previous figures
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
slide102

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

figure 5 40d aircraft energy intensity mj used per available seat km
Figure 5.40d Aircraft energy intensity (MJ used per available seat-km)

Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)

other factors affecting energy use per km travelled by air travel
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)
figure 5 41a ground efficiency for different aircraft and distances travelled
Figure 5.41a Ground efficiency for different aircraft and distances travelled

Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)

figure 5 41b airborne efficiency for different aircraft and travel distances
Figure 5.41b Airborne efficiency for different aircraft and travel distances

Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)

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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, 389–400, http://www.sciencedirect.com/science/journal/09696997)

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See Figure 5.37d again – note the difference between energy intensity while cruising (solid symbols) and overall flight energy intensity (open symbols)

prospects for the future
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
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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)

figure 5 45 variation freight energy intensity with capacity factor
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)

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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)
prospects for reducing road freight transport energy intensity continued
Prospects for reducing road freight transport energy intensity (continued )
  • Improved aerodynamics
  • Improved loading factor
  • Reduced speed
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Net result:A 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

locomotives for freight trains
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
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Figure 5.46 Locomotive energy flow with a diesel engine used to generate electricity that in turn drives an electric motor
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Figure 5.47 Locomotive energy flow using a fuel cell to generate electricity that in turn drives an electric motor
reducing the energy intensity of shipping
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)
reducing the need to transport freight
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
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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
impacts of e commerce
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
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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

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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, 480–492)

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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)
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Figure 5.29a Factors contributing to the reduction in the voltage of a PEM fuel cell compared to the theoretical maximum voltage
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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.

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Figure 5.30a Variation of voltage of a PEM cell with current density for operation at 50oC and at different pressures.
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Figure 5.30b Variation of voltage of a PEM cell with current density for operation at 70oC and at different pressures.