Alternative Fuels—An Airbus Perspective

By Helen Osmaston.

One of the most interesting and undeniably critical challenges facing the aviation industry in the face of today’s economic and environmental concerns is the question of how our aircraft will be fuelled in years to come. These challenges present themselves not only in terms of the development of those alternative technologies, but also in the degree of cooperation required between all areas of the industry in order to make meaningful in-roads in an acceptable timeframe.

During a recent visit to Australia, Sebastien Remy, the head of Alternative Fuels Research Programmes for Airbus, highlighted the importance of cross-industry collaboration in the development of alternative jet fuels for commercial aviation. He points out that Airbus is partaking in a number of working groups and initiatives to progress the issue of alternative fuels.

One of these initiatives is CAAFI (Commercial Alternative Aviation Fuels Initiative) a consortium made up of government agencies, airlines, manufacturers, airports, research establishments, and current and prospective fuel suppliers. Their remit is to provide a forum to share and collect data, along with motivating and directing research on alternative fuels for aviation. The consortium is comprised of four working groups: Fuel Certification and Qualification, Research and Development, Environmental Impact, and Economics and Business Cases.

The International Air Transport Association (IATA) is also working with a number of stakeholders and recently published the IATA 2008 Report on Alternative Fuels, which is a comprehensive read for anyone wishing to research the subject further.

On the subject of collaboration, Mr Remy explained that Airbus believes it is important for the company to do its part to help the aviation community. He said it is in Airbus’s—as well as everyone else’s—interests to cooperate and create synergies, wherever possible, in order to avoid duplicating activities and effort.

However, this essential sharing of data also poses challenges in terms of protecting the intellectual property rights of small businesses that might be involved in only some aspects of alternative fuel development. Possibly, the answer to this lies in consolidating the small companies and forming consortia. According to Mr Remy, Airbus is encouraging this and in the consortium of partners it is trying to assemble, it aims to cover the whole supply chain.

Such consortia (or “viable sequences of partners”) are also essential if complete and realistic life-cycle assessments (sometimes known as “well-to-wake” assessments) are to be carried out.

An overview of the alternatives

There is now little doubt that with the unpredictability of oil prices and deepening environmental concerns, the aviation industry needs to reduce its dependence on fossil based fuels. That being the case, what are the alternatives?

There is cross-industry consensus that in the short to medium term, any alternative fuel should be a ‘drop-in’ fuel. Airbus defines this as: “An alternative fuel that is interchangeable and intermixable, and which does not require any changes to the engine or the airframe, or the distribution and storage infrastructure.”

Without discounting the possibility that others may emerge in future, Mr Remy said that there are currently two types of workable alternatives: synthetic fuels and hydrogenated vegetable oils, both of which are potentially viable options.

The synthetic fuels under consideration include “coal to liquid” (CTL), “gas to liquid” (GTL) and “biomass to liquid” (BTL). These are produced by gasification and a process known as Fischer-Tropsch (FT) synthesis, widely used during South Africa’s apartheid era to meet the country’s energy needs while sanctions existed. FT synthesis is a highly energy intensive process and, in the case of CTL, the resulting fuel has a carbon footprint higher than current petroleum based fuel (the carbon footprint of GTL is approximately the same, while BTL has only around half the carbon footprint of petroleum-based fuel).

While this makes BTL an attractive prospect, there are some advantages of using GTL. For example, the GTL technology is tried and tested, and the resulting fuel has the same characteristics as BTL, making it a good precursor to future biojet fuels. GTL also has less particulate matter than current jet fuel. Particulates contribute to local air pollution and some scientific experts believe (albeit with a high degree of uncertainty) that particulate matter encourages contrails to develop into cirrus cloud, something that could potentially be a major contributor to climate change, according to the IPCC (Intergovernmental Panel on Climate Change).

The second type of fuel to show promise as a viable alternative is hydrogenated vegetable oil. The process of producing the oil is less energy intensive than the FT method. The biomass from which the oil and BTL feedstocks are sourced, broadly speaking, falls into two groups: first- and second-generation. First-generation alternatives are controversial as they compete for land and water used for food crops. Second-generation ones, which Airbus supports, are defined as renewable and sustainable whilst not competing with food crops or water resources. Examples of these are hydrophytes, lignocelluloses, starches and algae.

The biofuels derived from these types of biomass are considered more sustainable, as the CO2 consumed while they grow partly offsets the CO2 emitted during processing and burning; in the case of fossil fuels, there is no re-growth to re-absorb the CO2.

Agricultural residues and waste are sometimes referred to as second-generation feedstock too. These have the added advantage of reducing society’s environmental footprint while also reducing its dependence on fossil fuels. IATA calculates that if all current second-generation biomass sources were exploited, there would be the potential to produce 140 million barrels of oil a day (current global daily consumption is 90 million barrels). However, because there will be significant competition from other sectors of industry for energy, it doesn’t necessarily mean that biofuel will be able to meet all aviation fuel needs in the short to medium term.

One form of second-generation biomass identified by Airbus as having significant potential is Jatropha. This is a versatile plant with a number of sub-species that grow in a variety of conditions. Some species can grow in poor soil and tolerate drought, in conditions where little else grows. The seeds contain about 35% oil (relatively high) and the trees, which mature within three to five years of planting, can produce seeds for approximately 50 years. Yields can vary from one ton (seeds) per hectare per year to 10 tons/ha/yr, depending on the maturity of the plantation and growing conditions. With so many different species of Jatropha, it is important to select the correct species for the local environment. This process alone could take one to two years.

Typically, approximately 30% of each nut can be extracted as oil. Around 50% of the oil extracted can be converted to jet fuel (the remainder yields other products). Using Australia as an example, Mr Remy said that if its total jet fuel consumption of five million tons a year were to be replaced by Jatropha-based oil, it would require an area of approximately 300,000km² (roughly the size of Belgium) of immature plantations, reducing to 30,000km² for mature plantations. These represent relatively small areas in comparison to Australia’s large “interior” where little agricultural development exists.

Other second-generation biofuels are also showing promise. Algae-based fuel is currently the focus of much research as algae can be grown in sewerage plants and in salt water with potentially high yields. However, the technology for producing jet fuel from this source is not as advanced as for some other feedstocks. Mr Remy points out that no single feedstock will provide the “whole solution” and says that local solutions, compatible with local environmental conditions, will be more practical. Providing the final products all meet the same stringent standards, the resulting fuels should be inter-changeable, regardless of their source.

Generally speaking, with the exception of CTL and GTL produced via the FT process, there is currently a gap between “technology development” and “technology deployment” which—rather disingenuously—is sometimes referred to as “The Valley of Death”. Large scale production presents a number of challenges and risks, and is highlighted by IATA as an area where governments and other organisations must play their parts in minimising these risks, as well as streamlining policy and legislation so as not to impede progress.

Approval of alternative fuels

One area that must be developed before alternative fuels can be produced on a large scale is a framework for qualification and certification. A draft approval protocol, known as the Commercial Aviation Alternative Fuels Initiative (CAAFI), has been formulated by an industry team comprising SWRI (Southwest Research Institute), AA (Airworthiness Authorities), aviation gas-turbine manufacturers, OEMs (original equipment manufacturers) and ASTM (American Society of Testing and Materials). CAAFI has drafted a roadmap (see diagram) of the process, which consists of a test programme and an OEM internal review. Once these are completed, the specification can be changed.

The purpose of the test programme is to ensure that the candidate fuel or additive will have no negative impact on engine safety, durability or performance. This process is broken down into four stages, each of which must be passed in order. Firstly, the “specification properties” must be met. Examples of these are such things as appearance, composition, volatility and fluidity. Once these criteria are met, the fuel must pass a “fit for purpose properties” test. This includes such things as its performance properties, ground handling properties and compatibility. Following this, the fuel will undergo a “component or rig test”, where such things as cold starts and re-starts will be tested. Finally, an engine test will be carried out.

The next stage of the approval process will be the OEM’s internal review. The norm is to carry out a “controlled service introduction” (CSI), in which the new fuel or additive will be monitored over time for increases in things like numbers of defects and maintenance requirements.

The above process can often be lengthy. One of the characteristics of the ASTM system that makes it rigorous and robust is the balloting process. ASTM committee members representing all areas of the industry will soon be balloted on the adoption of the new protocols. One criterion is that there must be a unanimous vote. This poses the possibility that some members whose interests might conflict with the development of alternative fuels (for example, petroleum companies) could veto the move forward. However, Mr Remy believes this is unlikely to happen as there appears to be a genuine will among the aviation community and government bodies for the certification process to progress.

Certification also relies on the internal review of the OEM (in this case, engine and component manufacturers). In order to ensure safety is not compromised, they will need to have plenty of data. Once again, there will be an onus on all parties to provide all possible data, if the process is not to be protracted.

Timescales

In terms of approval of alternative fuels, it is fair to say generic synthetic fuels are very close. In December 2007, the UK Ministry of Defence granted approval for 100% Sasol full-synthetic fuel (Sasol is a South African based company) under its ‘Defence Standardisation’ system. The next stage will be certification of fuel blends containing a certain percentage of hydro-processed renewable (HRJ) jet fuel. This is anticipated by 2010, with 100% HRJ by 2013.

Of course, certification isn’t the only factor affecting the rate at which alternative fuels can be adopted. Selecting, planting and maturing of feedstock in quantities sufficient to meet the industry’s needs will take time. As already stated, Jatropha takes three to five years to mature. Realistically, 2015 would be the earliest that significant quantities of fuel could be derived from Jatropha—provided that land use policy does not impede planting. There is also the construction of the necessary processing plant, which, again, could take a number of years to plan and build.

Taking all of the above into account, Airbus estimates that up to 25% of jet fuel could be alternative fuel by 2025 and 30% by 2030. IATA’s goal is to have 10% by 2017.

Integrated solutions

The point has been made that the gap between technology development and technology deployment carries with it a number of risks. For example, the cost of infrastructure might be prohibitively high. As Mr Remy points out, it makes a great deal of sense to look at integrated solutions: “All the technologies we are studying need to be looked at in a broader perspective; they must have viable business cases and viable applications.”

He gave the example of algae. Because algae absorbs large quantities of CO2 as it grows, it would be sensible to position an FT plant (which produces CO2) adjacent to an algae farm and feed the excess CO2 from the FT process to the algae. Alternatively, algae or halophyte farms could be used as hosts for shrimps, thus providing a food source as a bi-product. The fuel from Jatropha need not only come from the oil in the nut; the resultant pulp (once the oil has been extracted) can be put through the gasification and FT process to provide BTL. The end result is likely to be a number of different “tailored” solutions to meet local conditions and needs.

The overall goal is to have a single fuel standard, but one that will be met with a number of different production solutions.

Demonstrations and tests

A number of biofuel demonstration and test flights have already taken place—one of the first being Airbus’s A380 flight which took place on 1 February 2008 . This was carried out in a flight-test aircraft fitted with full testing instrumentation. One Rolls Royce Trent 900 engine was supplied with a 40% GTL blend supplied by Shell. The fuel blend was at the lower limit of the permitted density range, which current jet fuels cannot reach. At 43,000 feet, the aircraft’s fuel pumps were switched off, allowing the engine to gravity feed. The importance of this was that it allowed Airbus to validate calibration of the aircraft’s fuel system model down at these low densities, giving them confidence that other types of alternative fuels could be compatible, providing they are within this density range.

On 30 December 2008, Air New Zealand completed a successful two-hour test flight in one of its Boeing 747s, using a 50% blend of Jatropha-based fuel in one of the aircraft’s Rolls Royce RB211 engines (see the news item on page xx of this issue). This flight was the first to use a sustainable second-generation biofuel in a commercial aircraft.

Other notable demonstration flights to date have included a flight by a Virgin Atlantic 747-400 in February 2008, using a 20% blend of babassu and coconut oil to power one of its GE engines. A number of US military flights have also taken place using biofuel, including a supersonic flight by a B-1B.

Airbus is planning other flight tests with second-generation biojet fuel in 2009.