Memorandum submitted by the Society of
British Aerospace Industries
1.1 SBAC is the UK's national trade association
representing companies supplying civil air transport, aerospace
defence, homeland security and space markets. SBAC encompasses
the British Airports Group and UKspace. Together with its regional
partners, SBAC represents over 2,600 companies across the UK supply
chain, assisting them in developing new business globally, facilitating
innovation and competitiveness and providing regulatory services
in technical standards and accreditation.
1.2 The development of new technology drives
competitiveness in the aerospace sector and SBAC members are amongst
the highest UK investors in research and development. Last year
aerospace companies invested £2.5 billion in R&D.
1.3 To help inform the committee's inquiry
on biofuels SBAC has set out in this submission some of the research
that is underway in industry. It also identifies the requirements
of any fuel used in aircraft and progress that has been made on
different fuel types and some of the inherent limitations that
some biofuels have from an aviation perspective.
2. AVIATION FUEL
REQUIREMENTS
2.1 Ground-based transport fuel systems
have one key requirement, to provide an uninterrupted fuel supply
to the combustor for a small range of conditions (ground temperatures,
pressures, acceleration rates, etc). As a result, meeting the
specification requirements for such fuels is relatively straight-forward.
2.2 Aviation fuel systems, on the other
hand, must be able to operate over a much wider range of conditions
(from hot day take-off to high altitude temperatures and pressures)
and power settings whilst satisfying multiple requirements. Aviation
fuels must provide:
— an uninterrupted fuel supply to the
combustor and reheat systems;
— a source of hydraulic power for actuators;
and
— a heat sink for the oil system and
electrical generating systems of the engines.
2.3 In order to fulfil these requirements
and ensure safe and efficient engine operation, any fuel proposed
for aviation must have the following characteristics:
— High energy content—to minimise
fuel burn, operating costs and CO2 emissions.
— Low freeze point—to ensure
fuel does not freeze at altitude.
— Excellent thermal stability—to
provide required heat sink capability.
— Low flash point—to ensure safety
of handling.
— Good storage stability—to ensure
quality of the fuel is maintained with time.
— Good combustion properties.
2.4 To date, the only fuel that has been
shown to fulfil all of these criteria, at a reasonable cost is
Jet A (Kerosene). As a result Jet A has been utilised almost exclusively
by the aviation industry throughout the world for many years.
2.5 Significant research and development
effort into uncovering alternative fuels for aviation has been
conducted. However, finding a fuel that is able to fulfil all
of the specification requirements that can be produced in the
required quantities, sustainably and with minimal changes to existing
infrastructure is extremely challenging.
3.1 There is no obvious biofuel for use
in aviation. Some of the research shows promising characteristics,
but where some fuels bring an advantage in one area they have
a disadvantage in another. In assessing whether a particular fuel
is a suitable alternative to Jet A, from an environmental perspective,
the following considerations must be borne in mind.
3.2 The combustion process in an aero engine
produces some emissions. Some of these affect local air quality,
others affect the global atmosphere. Considerable uncertainty
remains about the exact environmental impacts of many emission
types, however it is widely acknowledged that the three main contributors
to climate change are carbon dioxide (CO2), nitrous oxides (NOx)
and water vapour (H2O), which in certain conditions can form contrails
and cirrus clouds.
3.3 The relationship between fuel type and
the production of emissions is outlined below:
— CO2—The amount of CO2 produced
is directly related to fuel burn and thus using a fuel with a
different energy density to Jet A will affect the CO2 emissions
produced by the engine.
— NOx—NOx formation is not directly
dependent on fuel burn; it is a function of temperature, pressure
and time. It is not likely to be affected by fuel choice.
— Contrails/cirrus—The mechanisms
responsible for contrail and cirrus cloud formation are not well
understood and it is not therefore clear exactly how fuel choice
will affect contrail and cirrus cloud formation. However a relationship
clearly exists between the amount of water vapour produced and
the resulting number of contrails/cirrus clouds so that a fuel
that produces more water vapour (eg hydrogen) will lead to an
increase in contrails/cirrus.
3.4 Fuel choice will also influence the
production of smoke, particulates and oxides of sulphur (SOx),
all of which affect local air quality and the global atmosphere.
4. ALTERNATIVE
AVIATION FUELS
4.1 Fuels derived from fossil resources
(coal, natural gas, oil) and from biomass (any organic material)
are being investigated within industry and academic institutions
as alternative aviation fuels. However only biofuels (fuels made
from biomass) that are generally recognised to have some future
potential are discussed in this submission.
4.2 Biofuels currently being researched
within the UK that will be discussed in this submission are:
— Fatty Acid Methyl Esters (FAMEs)
— Synthetic kerosene produced from
biomass (BTL)
— Hydrogenated plant/vegetable oils
5. FATTY ACID
METHYL ESTERS
(FAME'S)
5.1 FAMEs are produced through the extraction
and esterification of oil from oilseed crops such as rape, sunflowers,
soybeans and corn, and plants such as palm and algae. The resultant
fuel has several properties that make it undesirable for use in
aviation: high freeze point, low thermal stability, lower energy
density than Jet A and vulnerability to oxidation/microbial attack
in storage. Some of these undesirable properties can be reduced
through additional processing and the inclusion of additives,
however FAMEs suitability for use in aero engines is still limited
to low proportions (predicted to be around 20-30% FAME in FAME/JetA
blends). Even when used in these quantities, it has not yet been
demonstrated that the fuel will not freeze at altitude.
5.2 FAMEs are a good alternative from an
emissions perspective. FAME production is more energy intensive
than the production of bio-diesel for land-based transport, but
its energy usage and emissions are still less than those associated
with the production of kerosene. However, sustainability is problematic
for FAMEs. Limited excess farmland means that producing sufficient
FAMEs to supply the world's aviation industry, using conventional
oilseed crops as the feedstock, would require the displacement
of human food production and/or increased deforestation. Given
the limited amount of cultivatable land, the fact that more energy
is required to produce FAMEs than to produce biodiesel for land-based
transport and the undesirable properties that make FAMEs challenging
to use as aviation fuel, many argue that dedicating available
land to produce biodiesel for land-based transport rather than
aircraft is the most effective use of resource.
5.3 One potential feedstock that may avoid
the problem of land usage, however, is algae. Algae, with its
high yield rates and ability to grow on non-cultivatable land,
offers promise as a sustainable feedstock for FAMEs. The development
of algae as a potential feedstock is still in its infancy.
6. SYNTHETIC
KEROSENE PRODUCED
FROM BIOMASS
(BTL)
6.1 Synthetic kerosene can be produced from
a number of feed stocks (coal, gas, biomass) using the Fischer-Tropsch
process. The process begins with the gasification of the feedstock
to produce a carbon monoxide and hydrogen mix, which then goes
through a catalyzed chemical reaction to produce liquid hydrocarbons.
The properties of the synthetic kerosene produced are independent
of the feedstock used and are similar to or better than those
of Jet A fuel. Improved properties like increased energy density,
excellent thermal stability and low temperature performance could
result in improved engine performance and life.
6.2 Synthetic kerosene has close to zero
sulphur content and aromatics which means that its emissions will
not include SOx and will have reduced smoke. Improvements in fuel
properties will allow the engine to run at increased temperatures,
leading to reduced fuel burn and CO2 emissions. In addition, if
biomass is used as the feedstock and also used to power the fuel
production process, the CO2 emissions associated with the production
of this fuel alternative, are minimal.
6.3 However the production of BTL is not
without challenges. Producing the amount of feedstock (woodchips,
straw, switch grass, etc) required to satisfy the aviation industry's
fuel needs and converting it to fuel, without excessive use of
long distance transport is one significant challenge associated
with this alternative. The high cost of the BTL processing plants
is also a potential deterrent to embracing this technology.
7. HYDROGENATED
PLANT/VEGETABLE
OILS
7.1 Hydrogenated plant and vegetable oils
are in early stages of development. Hydrogenation consists of
a series of chemical reactions in which unsaturated compounds
(eg plant oils) are converted into saturated compounds (eg hydrocarbons)
through the addition of hydrogen. The exact composition of the
resulting fuel is dependent on the feed stock, however it is believed
that kerosene, with properties similar to synthetic kerosene,
will be produced. The production process uses conventional technology
and is not expensive. The challenges associated with this alternative
include finding a feedstock with the appropriate chemical structure
that has the availability and affordability to make it a sustainable
fuel choice.
8. BIO-HYDROGEN
8.1 There are many ways to produce hydrogen.
Two preferred methods, in terms of environmental impact, are biomass
gasification and electrolysis of water. In gasification, biomass
is reacted at high temperatures with a controlled amount of oxygen
to produce carbon monoxide and hydrogen. In electrolysis, water
is decomposed into oxygen and hydrogen by application of an electric
current.
8.2 Hydrogen has very different properties
and requirements to Jet A fuel. One of the major differences is
its energy density; hydrogen has a much higher energy density
by mass than kerosene but a much lower density by volume. Increased
energy density by mass, allows the engine thrust rating and size
to be reduced, however reduced energy density by volume requires
an increase in fuel tank size and consequently increases weight
and drag. Accommodating these changes would require a complete
redesign of aircraft and engine systems. The resulting aircraft/engine
design is likely to have an increased fuel burn on short-haul
flights but reduced fuel burn on long-haul flights. Specific requirements
for the storage and handling of pressurized/liquefied hydrogen
also necessitates a complete redesign of ground handling systems
and storage facilities.
8.3 A hydrogen- fuelled engine will produce
no CO2 emissions; its CO2 impact will be limited to the emissions
produced during its production process. However, a hydrogen fuelled
engine will produce significantly more water vapour than an engine
utilising Jet A fuel, which is likely to increase contrails and
cirrus cloud formation.
9. CURRENT WORK
ON BIOFUELS
9.1 Biofuels are currently being evaluated
by a number of aerospace and aviation companies (eg engine and
aircraft manufacturers, airlines), academic institutions and fuel
companies within the U.K. Despite this significant research effort,
much of the technology is not yet mature and there is a lack of
consensus on which alternatives are the most promising and whether
the technical and logistical challenges associated with biofuels
can be overcome.
9.2 Over the years there have been a number
of strong advocates of biofuels for aviation. Currently AirNewZealand,
Boeing and Rolls-Royce are conducting fuel trials, with a full
evaluation due to take place in the second half of 2008 using
a biofuel mix blended with kerosene. The fuel will be used on
an AirNewZealand owned Boeing 747-400, and shall power one of
the four Rolls Royce RB211-524 engines, with the remainder using
kerosene. Virgin Atlantic, in partnership with Boeing and General
Electric is also planning a similar experiment for 2008.
9.3 Shell Aviation is focused on developing
hydrogenated vegetable/plant oils and BTL. A Shell-Choren BTL
plant is planned to commence operation in Germany in 2008. A 50/50
blend of synthetic kerosene (produced from coal) and Jet A fuel
has been approved by regulatory bodies for use and is currently
being put into aircraft landing/departing/refuelling in Johannesburg.
Extensive work is being undertaken by industry groups to get approval
for 100% synthetic kerosene fuel. This will pave the way for synthetic
fuel derived from biomass to be utilised in the future, provided
production and cost issues can be overcome.
10. CONCLUDING
REMARKS
10.1 Biofuels remain an area of research
and interest to the aviation industry. The technical and logistical
challenges associated with the use of biofuels in aviation prevent
its wide-spread use in the near term. FAMEs, BTL and hydrogenated
vegetable/plant oils could be feasible alternatives in the medium
term, the results of the Virgin FAME-powered flight test and the
opening of the Shell-Choren BTL plant in 2008 will help to provide
an indication of the feasibility of these two alternatives. The
extensive system redesign associated with the use of hydrogen
mean that it is an alternative only in the long term.
2 October 2007
| 
