Propulsion has been a strategic factor since the early days of aviation. Steam engine, like Clément Ader on the Eole or the Avion III, electric engine as for the balloon “la France” of Charles Renard and Arthur Krebs. At the birth of the automobile, and therefore of the combustion engine, oil was used very little, even though it had been known for 10 centuries that oil could be produced as a “lamp oil” very close to kerosene! The engine manufacturers used instead ethanol, peanut oil, like Rudolf Diesel, praising the advantages promised to agriculture, which was thus endowed with a new source of income! The famous Ford T (1903 – 1926) drove on alcohol. But oil, quickly abundant and cheap, conquered airplanes and cars, and put away the “biofuels” of the time. Durably. Today, their listing seems to have come to an end.
Here are a few reasons:

• global warming and the need to reduce greenhouse gas (GHG) emissions,
• the need to anticipate the inevitable decline in oil reserves and growing energy needs,
• the desire to recreate a certain energy independence, or to diversify sources of dependency,
• the usefulness of creating new opportunities for agriculture,
• the desire to pave the way for the recycling of waste and used products (oils, etc.).

And the fact that throughout their entire production and use chain, biofuels produce (or would produce) 80% less carbon emissions than oil!
Thus, for nearly 20 years now, the debate has been open, while research is increasing and tests and uses are multiplying. It has been shown that this is possible while maintaining flight safety. Moreover, it is estimated that 200,000 passenger flights have been made worldwide (i.e. 0.06%) since 2011 using a share (often more than 25%) of biofuels mixed with kerosene. However, it is not yet known up to what percentage it will be possible to climb? We are studying the possible longer-term consequences for engine seals and fuel lines, and further down the line, if the quantities on board were to decrease, on the centring of aircraft, the thermal exchanges in which fluids participate, etc.
Biofuels can be broadly classified into three generations: the first one is generally derived from agriculture, with vegetable oils (palm, sunflower, corn, wheat, etc.), animal fats, algae. The second, which adds the recycling of oils, waste, the production of alcohol derivatives, sugars, wood (lignite, cellulose). The third is the subject of research and incorporates micro-algae (algo-fuels) and other materials from biomass. Of course, all the products concerned must be subject to technical “certification” to assure air travellers that they are not at risk. It is also necessary to be able to demonstrate the “ecological” advantage induced by these fuels. Nor, on the grounds of reducing the carbon footprint of aviation, should other environmental or social disadvantages be created, such as drastically reducing the amount of arable land available for food, or making air fares impractical.

The aviation sector is estimated to be responsible for 2% to 2.5% of GHGs. This is 3% for the merchant navy. It is 4 to 5 times less than land transport. But, at the global level, the industrialists involved have committed to capping emissions by 2020. And by 2050, commercial aviation must have reduced its carbon footprint to 50% of what it was in 2005. This is a challenge that will have to be met despite a continuous growth in activity of around 5% per year. As a reminder, in 2019, there will be over 40 million flights, the world jet fleet will approach 30,000 aircraft, and the number of passengers will be close to 4.5 billion.
Of course, there are several ways to achieve the expected results. There is no denying that much has been achieved in the last 50 years, the jet age, with a remarkable reduction in noise, pollution, fuel consumption (and a considerable increase in safety and efficiency). However, while each generation of aircraft allows a gain of around 20% in fuel consumption and more in emissions, this is still not enough. In addition to the aerodynamics of aircraft, their lighter weight, which enables them to perform better, the marked improvement in engines, the increased efficiency of the means of piloting, navigation, control of navigation, taxiing and operator training, must be added environmental measures of another nature. The transition to clean propulsion systems is one way, notably through electricity. But there is still a long way to go in this area for wide-body aircraft. And the most serious prophets are only aiming for 2030 to see the serial appearance of an electric “switch”, probably a hybrid.
Until then, and more quickly accessible and efficient, there are (among other solutions under study) biofuels, mixed with jet fuel. Thus kerosene plus bio-kerosenes, should allow an active transition, a stabilization of emissions, and thus help to meet the commitments.
This requires the creation of a production (including refineries) and distribution (at all airports) chain for these new fluids. With an obligation to significantly reduce costs. Biofuels, while they should eventually have the advantage of a certain stability in their prices, compared to the political waltzes of the oil price, are today nearly three times more expensive than black gold!
This is why the French government decided in January to launch a Call for Expression of Interest (AMI). And by this to mobilize all national actors in the framework of the Commitment for Green Growth (ECV) signed in 2017. This CEI is a great pleasure for the parties concerned, Airbus, Air France, Safran, Suez and Total. It will encourage investment in sustainable biofuel production units for aviation and will also facilitate accompanying measures and incentives to promote these investments. The roadmap sets a target for biofuel incorporation of 2% by 2025, 5% by 2030 and 50% by 2050. Impressive!