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Transport fuel in the future - Batteries and Hydrogen fuel cells.
With oil reserves only sufficient for possibly 30 years practical alternatives are now being developed and will shortly be introduced.
Transport fuel will be obtained mainly via electricity and hydrogen (both secondary fuel sources). Bio fuels will also play a part. Cars and other road transport will be fueled by batteries supported by a rapid recharging and/or changeover - refueling infrastructure. Later on hydrogen will also be used as a fuel to supply fuel cells which generate electricity (see hydrogen page). Rail will be electric mostly. Battery and Hydrogen cars and buses are available now but expensive and waiting for incentives to encourage a change from high to low or zero carbon emissions.
Battery powered cars with battery charge and battery changeover infrastructure in a few years.
A revolution is imminent to widely extend the use of battery cars powered by Lithium-ion batteries, giving a range up to 300 km (200m), rechargeable via the mains.
See page on choice of Cars, electric, hybrid, fuel cell, bio, efficiencies
Trains - electric and diesel replaced coal in trains and in the future, Maglevs.
From the outset, coal was the fuel used for steam engines but train travel has for many years lent itself to electrification enabling power to be drawn from the more efficient electrical grid systems. Diesel electric first replaced steam on main lines and diesel locos on branch lines.
In the future very fast intercity trains, say up to 300 mph or 500 km per hour, may take the form of the train suspended magnetically on a cushion of air and propelled by linear induction motors (electrical power), so eliminating friction, an example being the Maglev project. These could replace intercity flights, although the 'rail network' will be expensive. Japan plan to extend the maglev line for a Tokyo - Osaka service and the Chinese plan two intercity lines .
To reduce power for a future intercity train it could run in a tunnel falling 1 to 3% per 10 km -a depth of up to 180 m - and rising to the next station, using the stored kinetic energy (rather as on U/G trains.) The train would be supported on PM magnetic levitation to reduce friction and would have battery assistance recharged by wind and no external power source. The tunnels would be 2 way with many interconnecting passages to enable low resistance to air flow. (ref 172)
Comparison of CO2 emissions for travel 2007 (Ref 237)
Aircraft, high level emission problem as well as the CO2 problem.
Air travel cost is low between major cities and countries while private jets are attractive for the very wealthy.
Boeing have said that it is unlikely that fuel cells would ever provide primary power for large passenger aircraft, while demonstrating that it is possible for very light aircraft. Thus the future for all but small aircraft would lie with reducing CO2 by economy and use of bio fuels.
In addition to the contribution to CO2 emissions it has been suggested that the emissions of aircraft at high level cause a haze around the globe which, unlike emissions at low level (due to cars, heating, power stations etc) do not disperse, and therefore cause an additional and serious greenhouse effect (ref 153). As aircraft emissions include water, ozone, Nitrous oxide and CO2, the carbon footprint is equivalent to 2 to 3 times the emissions from CO2 only.(ref 9.)
Developments in air transport to reduce CO2 emissions.
Basics taken from ref 9 (p269) indicate that a plane (flying below the speed of sound) has an optimum speed; for a Boeing 747 this is 540 mph. Fuel use increases if it flies slower than the optimum speed. The transport cost (in fuel) does not depend on the size of a plane nor its weight (total weight) but on effect, shape, drag and is given in general as 0.4 kw hr/ton-km. The range of a plane also does not depend on size nor mass and is given as 4000 km, generally (Range and fuel cost hold true for all sizes of air transport be it a large plane or even a bird.)
To reduce CO2 emissions possibilities are:-
1) Bio fuels which must meet standards of freeze point, flash point and net heat of combustion could be the long term solution. Isobutalol may be the answer; it doesn't absorb water and it can be made from sugar etc.
Jatropa bushes produce oil rich seeds that grow well in soils and conditions not generally suitable for arable farming, but considerable space is needed.
2) Hydrogen as a direct fuel. Hydrogen burns with the oxygen in the air at low altitudes. Above 25 km the intakes move to cut off air and stored oxygen is used. See the Sabre engine (by Reaction Engines developed for the Skylon pilotless spaceplane). Possible use by 2020.
3) Reduce surface friction. A future design plan to increase efficiency is a giant flying wing where the drag due to air friction is reduced on the wing surface by millions of tiny holes that suck in air; and the use of lighter materials such as Carbon Fibre instead of Aluminum based materials. These planes may come into service after 2025 and could reduce fuel use to 33%.
4) Open rotor. Engine development may also improve efficiency by 30% by developing an 'open rotor' design; (ref 152.) The fan of an open rotor configuration is at the front of the engine and without a cowling enclosing it. Open rotors could come in by 2020. More on open rotor engines.
5) GFT fan geared down. An alternative GFT design enables the fan of a turbo jet to be geared down to the more efficient lower speed while the turbine driven by high temperature gas expansion runs at the higher speed. This arrangement should save 15% fuel burn up.
6) Fuel cell for intercity? An EU funded project is to develop intercity aircraft using fuel cell technology for the propulsion system and hydrogen storage (ref155.) Low noise levels are an added advantage to low emissions and could therefore allow take off and land at night.
Rolls Royce suggest that overall efficiency could be improved by 50% of which 20-25% could be due to airframe improvements, 15 to 20% due to engine design and 5 to 10% due to operational refinements.
Ships
The shipping industry burns 4.5% of the fuel used in the world (1.2 bn tonnes CO2 per year - 0.33 bn tonnes carbon), twice that of air travel. Ships produce more SO2 than all cars and lorries in the world and 27 % of the worlds NO2.
Coal / steam replaced sail in the 1800's and now diesel or gas turbine drives. Very large vessels, submarines, ice breakers, cargo and tankers use nuclear reactors for power which avoid or minimize CO2 emission. Fast passenger liners could in the future be nuclear powered.
