Since the start of the jet age, aviation has improved fuel efficiency by some
70% through enhancements in airframe design, engine technology, airline
operations, airspace and airport capacity as well as rising load factors. More
than half of this improvement has come from advances in engine technology.
Just in the past two years (2004-2005) fuel efficiency has progressed close
to 5%, to the extent that IATA's efficiency goal of 10% fuel improvements
between 2000 and 2010 was reached before the end of 2006.
Modern aircraft achieve fuel efficiencies of 3.5 litres per 100 passenger-km
or 67 passenger-mile per US gallon. The next generation of aircraft (A380 &
B787) target less than 3 litres per 100 passenger-km or 78 passenger-mile per US
gallon, which exceeds the efficiency of any modern compact car on the
market.
Jet fuel
Aviation consumes 2% of all fossil fuels burnt. This represents 12% of the
fuel consumption of the entire transportation sector, to be compared with 80%
dedicated to road transport.
The most common fuel is a kerosene/paraffin oil-based fuel classified as
JET A-1, which is produced to an internationally standardised set of
specifications.
- In 2005, the total Jet A-1 fuel consumption represented 55 billion US
Gallons or 208 billion litres. This corresponds to an average fuel consumption
per flight hour of 970 US gallons or 3 metric tonnes.
- Each tonne of fuel burnt in the air or on the ground produced 3.16 tonnes of
CO2. Therefore, 55 billion US gallons of jet-fuel represent 540 million tonnes
of carbon dioxide.
The development of alternatives
While the dependency of the aviation sector on fossil fuels is expected to
continue for the foreseeable future, concerns about rising fuel costs, energy
supply, security and aviation emissions have called for a fresh look at the use
of alternative fuels.
The potential for alternative fuel use in aviation is not a new concept.
Early jet engines were developed using hydrogen, but the very strict technical
requirements for aircraft to use a fuel with high energy content per weight and
volume led to the adoption of kerosene as the standard aviation fuel.
- In the late 1970s, synthetic aviation fuels were developed for military use
from shale oil, tar sands and coal liquids but programmes to further develop
these fuels were abandoned as synthetic fuels were not cost-effective.
- In the early 1980s, Brazil developed PROSENE, an alternative combustible
lipofuel (vegetable oil) used as an alternative to aviation kerosene. However,
this programme was also stopped in favour of national biodiesel and biokerosene.
- The embargo to end apartheid in South Africa led to the adoption of
semi-synthetic aviation fuel, SASOL, a blend of petroleum derived and synthetic
kerosene. A blend of 50% synthetic fuel and 50% crude oil fuel has been tested
and approved for aviation. This semi-synthetic fuel is used by South African
Airways and is fully satisfactory. Use of fully synthetic jet fuel is being
tested and approval deemed imminent.
The dramatic rise in fuel prices in recent years and months has caused
intense concern within the air transport industry. Moreover, the discovery of
new crude oil resources has become a rarity although global demand for air
transport is on the increase. Faced with these challenges, ATAG and other
stakeholders have started to press governments, industry and research
institutions to reassess the whole situation. For example, at the 2nd Aviation
& Environment Summit held in Geneva on 25-26 April 2006 (www.environment.aero) ATAG
responded by organising a Roundtable debate on alternative fuels, which
generated considerable interest. For further information, contact info@environment.aero
Alternative fuel options
There are a number of alternative fuel options for aviation. The main two
criteria for optimum fuel efficiency are:
- Aircraft need to be lightweight and have low drag (as well as efficient
engines and wings)
- Aircraft fuel needs to have a high energy content per unit volume and
weight
Synthetic liquid fuels: Synthetic fuel or synfuel is any
liquid fuel obtained from coal, natural gas or biomass. It can sometimes refer
to fuels derived from other solids such as oil shale, tar sand, waste plastics
or from the fermentation of biomatter.
The leading company in the commercialization of synthetic fuel is Sasol, a
company based in South Africa. Sasol currently operates the world's only
commercial coal-to-liquids facility at Secunda, with a capacity of 150,000
barrels a day. Other companies that have developed coal- or gas-to-liquids
processes (at the pilot plant or commercial stage) include Sasol, Shell, Exxon,
Statoil, Rentech, and Syntroleum.
Bio-jet fuel: jet fuels made from converted agricultural oil
crops like soya.
Ethanol fuel: can be combined with gasoline in any
concentration up to pure ethanol (E100). Ethanol is, by far, mostly used to
power cars, but it may be used to power other vehicles, like farm tractors and
perhaps in the future, airplanes.
Hydrogen: The use of hydrogen in aviation is expected to
start with fuel cell applications for the replacement of Auxilliary Power Units
(APUs), ram air turbine (RAT) and distributed power units. These applications
will generate large fuel savings on the ground, lower noise and lower NOx.
Benefits of alternative fuels
A limited oil supply could make synthetic or biofuel essential in the
long-term.
Synthetic liquid fuel is nearly identical to kerosene. It is
limited in use today, but could be environmentally promising. Immediate benefits
will include a very "clean" burn, meaning less coking up of the engine and
reduced maintenance costs. They have no sulfur and no or limited aromatic
components. Such fuels are also expected to produce less particulate matter.
However, they produce equivalent levels of CO2 to petroleum kerosene, and
possibly more depending on the energy, which is used for their production. In
addition, the new fuels are chemically compatible with all fuel system
materials, such as seals and joints and aircraft airframes. They can also make
use of existing distribution systems*.
Bio-jet
fuel appears as a mid-term option, but may be affected by limited
production capacity. However, it will require considerable land resources, which
may generate other environmental and social costs. The synthetic or biojet-fuels
of the future will have to behave like jet fuel and meet all current
specifications, allowing engine architecture to develop along established lines.
Ethanol is not a good option for long-haul aircraft
(ethanol fuelled aircraft will require much larger wings and engines reducing
its fuel efficiency) but may be relevant to regional short-haul and general
aviation.
Hydrogen may be a very long-term option for aircraft engine
sdependent on technological developments and potentially prohibitive
infrastructure investment (e.g. airports will have to be converted).
Since air transport is a relatively "compact" industry, it would be logical
for the air transport industry to be one of the first sectors within the
transport industry to take the lead by using alternative fuels. However, the
challenge is that aviation's demand may not be sufficient to justify the
important investments required. Hence the idea to consider the role of airports
in supplying alternative fuels not only to aircraft and ground airport
activities, but also to the local communities around airports.
This sustainable approach deserves to be further explored, as well as many
other aspects concerning the use of alternative fuels not only for aviation
application, but also for use in many other sectors.
ATAG is inviting all interested readers to provide their
views on this new issue, whose importance will be growing over time.
Interesting websites for further information on fuel consumption and
alternative fuels:
· The potential for renewable energy sources in
Aviation, Imperial College London: www.iccept.ic.ac.uk
· http://www.chevronglobalaviation.com/ga/ga_operational.asp
· IATA
Fuel Action Campaign: www.iata.org
· Institut Français du
Pétrole and Biofuels: www.ifp.fr
*From Airlines International Issue 04 Oct/Nov 2006, "Fuel for thought"
article