SUSTAINABLE FUTURE : THE NEXT GENERATION OF COMMERCIAL AIRCRAFT (PART III)

Sustainable Future : Biofuels and synthetic fuels

For a sustainable future, one of the ideas on which much work has been done is the use of sustainable fuels in lieu of the standard petrol-based jet fuel. This would help scale back carbon emissions without needing new aircraft.

Sustainable aviation fuel is usually a combination of waste products, raw materials from fuel manufacturing, and other sustainable sources, blended into standard aviation fuel. This mixture is then used as fuel, reducing the overall fossil fuel usage per flight. Several airlines are now testing biofuels, and it has the potential to catch on soon.

The aviation industry is actively exploring biofuels and synthetic fuels as viable alternatives to traditional fossil fuels, seeking to reduce its environmental impact. This section tries to review ongoing strategies for manufacturing these fuels, ongoing projects, and the technical limitations that shape the landscape of biofuels and synthetic fuels in aviation.

a) Manufacturing Strategies:

i. Biofuels from Biomass:

Biofuels derived from biomass, such as algae, plant oils, and waste, represent a significant strategy. These feedstocks are processed through various methods, including transesterification, hydro processing, and esterification, to produce bio-based jet fuels.

Transesterification is a chemical process to produce biodiesel. It involves the reaction of triglycerides (fats and oils) with an alcohol, typically methanol or ethanol, in the presence of a catalyst. This process results in the production of fatty acid methyl or ethyl esters (FAME or FAEE), which are the key components of biodiesel.
Hydro processing is a refining technique used in the conversion of bio-based feedstocks into advanced biofuels, including bio-based jet fuels. This method involves the use of hydrogen and a catalyst to remove impurities and saturate double bonds in the feedstock.

The result is a cleaner and more stable hydrocarbon fuel. It is employed to upgrade bio-oils or fats into hydrocarbons with properties suitable for aviation. The process enhances the overall quality of the bio- based fuel, improving its performance and compatibility with existing aircraft engines.

Esterification is a chemical reaction in which acids react with alcohols to form esters and water. In the context of bio-based jet fuels, esterification can involve the reaction of fatty acids or other bio-based acids with alcohols to produce esters. The reaction transforms bio-based acids into esters, which can contribute to the composition of the final fuel. The specific choice of acids and alcohols in esterification can be tailored to achieve desired fuel properties.

ii. Sustainable Future : Synthetic Fuels via Power-to-Liquid (PtL) Technology

Synthetic fuels are produced through Power-to-Liquid (PtL) technology, utilizing renewable electricity to generate hydrogen, which is then combined with carbon dioxide to produce synthetic hydrocarbons. Fischer-Tropsch synthesis is a common method for this process. Because of the relevance of this developing line, let us have a closer view of this technology:

Fischer-Tropsch (FT) process is a catalytic chemical reaction that converts synthesis gas (syngas), a mixture of carbon monoxide (CO) and hydrogen (H2), into liquid hydrocarbons. This transformative process has been historically utilized for coal-to- liquid (CTL) and gas-to-liquid (GTL) applications, and it holds significant importance in the production of bio-based jet fuels.

In the context of bio-based jet fuels, the Fischer-Tropsch process is employed to convert bio-derived syngas into liquid hydrocarbons. Biomass, such as agricultural residues, forestry waste, or dedicated energy crops, can serve as the feedstock for syngas production through gasification. The subsequent Fischer-Tropsch synthesis produces hydrocarbons with properties suitable for aviation fuel.

Syngas Production: Prior to Fischer-Tropsch synthesis, syngas is produced by gasifying biomass or other carbon-containing feedstocks. This gasification process typically involves reacting the feedstock with steam and oxygen at high temperatures, resulting in a mixture of carbon monoxide and hydrogen.

Sustainable Future : Advancing Bio-Based Jet Fuels with Fischer-Tropsch Technology

The syngas produced is then fed into Fischer-Tropsch reactors, which contain catalysts, often based on cobalt or iron. These catalysts facilitate the conversion of syngas into liquid hydrocarbons through a series of chemical reactions, including polymerization and hydrogenation.

Hydrocarbon Product Range: The Fischer-Tropsch process generates a range of hydrocarbons, from light gases to heavier liquid fractions. By adjusting process conditions, the distribution of hydrocarbons can be tailored to meet specific requirements, ensuring the production of aviation fuels with the desired properties.

Fischer-Tropsch bio-based jet fuels are characterized by high energy density, low sulfur content, and excellent thermal stability. These properties contribute to improved fuel efficiency, reduced emissions, and enhanced performance in aviation applications.

The Fischer-Tropsch process has gained commercial significance in the production of sustainable aviation fuels. Numerous pilot projects and initiatives aim to scale up the production of Fischer-Tropsch-based biofuels, showcasing the potential for integrating this process into the broader bioeconomy.

i. Advanced Feedstock Research:

Ongoing research explores advanced feedstocks for biofuels and synthetic fuels, including non-food crops and waste materials. Improving the efficiency of feedstock production is crucial for enhancing the sustainability of alternative aviation fuels.

b) Sustainable Future : Ongoing Projects

i. Commercial Aviation Alternative Fuels Initiative (CAAFI):

CAAFI is a collaborative initiative involving airlines, manufacturers, and government agencies working to advance the development and deployment of

alternative aviation fuels. The initiative supports various projects focusing on biofuels and synthetic fuels for commercial aviation.

ii. Sustainable Aviation Fuels (SAF) Projects by Airlines:

Numerous airlines have launched projects to integrate Sustainable Aviation Fuels (SAFs) into their operations. These projects often involve partnerships with biofuel producers and aim to demonstrate the feasibility of SAFs in regular commercial flights.

iii. EU’s Advanced Biofuels Flightpath Initiative:

The European Union has established the Advanced Biofuels Flightpath Initiative, setting ambitious targets for the deployment of advanced biofuels in aviation. This initiative supports research and development projects focused on scaling up the production of sustainable aviation fuels.

Biofuels and synthetic fuels offer promising avenues for reducing the carbon footprint of aviation. While manufacturing strategies continue to evolve, ongoing projects and initiatives demonstrate a collective commitment to integrating these alternative fuels into commercial aviation.

c)Sustainable Future : Addressing Technical Limitations

i. Feedstock Availability and Land Use:

The availability of suitable feedstocks for biofuels can be limited, and concerns about land use change arise. Striking a balance between biofuel production and food production and avoiding deforestation is crucial to ensuring the sustainability of these fuels.

ii. Energy Intensity and Cost:

The energy-intensive nature of biofuel and synthetic fuel production, especially through PtL processes, presents challenges. Additionally, the cost of producing these alternative fuels remains higher than traditional jet fuels, requiring ongoing technological advancements and economies of scale.

iii. Certification and Compatibility:

Ensuring that biofuels and synthetic fuels meet aviation safety and performance standards is a complex process. Certification for use in existing

aircraft engines and infrastructure compatibility are essential factors that influence the widespread adoption of these fuels.

d)Sustainable Future : Advanced aerodynamic design:

The next generation of commercial aircraft is set to look very different from our current ideas of an aircraft. Thinking of a plane today, we envision a fuselage with two wings and two (or four) engines mounted on those wings. However, concept designs from Airbus and Boeing point to a very different idea for future commercial aircraft.

Beyond engines and materials, advancements in aerodynamic design contribute substantially to fuel efficiency. This part of the article details how innovative design approaches are shaping the future of aviation, minimizing resistance, and maximizing performance.

a) Folding or Deployable Wings:

The implementation of folding or deployable wings involves the development of wings that can be adjusted in span. This innovative feature allows for a larger wingspan during cruise, enhancing fuel efficiency, and a reduced wingspan during takeoff and landing for improved maneuverability.

Those adaptable wings offer a dynamic solution to optimize aerodynamics based on the specific requirements of different flight phases (flight envelope), striking a balance between efficiency and flexibility.

b) Winglet Design:

This concept focuses in optimizing winglet designs or adding new types of wingtip devices. Winglets help minimize wingtip vortices, reducing induced drag and enhancing overall fuel efficiency. The improved winglet designs contribute particularly during long-haul flights, where the reduced fuel consumption ratio became maximized.

c) Streamlined Fuselage Shapes:

The advancements in aerodynamic shapes, and the new fuselages manufacturing methods, allows the design of sleeker and more streamlined profiles. A smooth and aerodynamically efficient fuselage reduces overall drag

during flight, by minimizing air resistance, and enhancing the overall aerodynamic performance of the aircraft.

The exploration of innovative materials and flexible structures focuses on creating wings and control surfaces with dynamic adaptability. These materials should allow morphing wing shapes and improved control surface effectiveness. This enhances aerodynamic efficiency by enabling real-time adjustments, optimizing the aircraft’s performance based on varying flight conditions.

d) Sustainable Future : Innovative Materials and Flexible Structures

This line of development constitutes a revolutionary breakthrough, as it would bring us closer to how birds handle aerodynamics. We only have to observe how a bird flies to realize that they are constantly modifying the geometry (and aerodynamics) of their wings and tail. Of course, we are a long way from achieving what every bird can do in this particular, but the path that opens up in front of us is impressive.

e) Sustainable Future : Adaptive Control Surfaces

Adaptive control surfaces involve the development of wings and control surfaces that can dynamically adjust their positions to optimize aerodynamics. This technology would enable a more precise and efficient control of the aircraft, providing enhanced control authority and efficiency, especially in challenging flight conditions.

f) Sustainable Future : Integrated Fuselage-Wing Design

An integrated approach to fuselage-wing design involves harmonizing the shape and structure of the fuselage and wings for optimal aerodynamic efficiency. This holistic design considers the entire aircraft as a unified aerodynamic system, enhances overall aerodynamic performance, reducing drag and improving fuel efficiency by creating a more streamlined and cohesive design.

g) Sustainable Future : Blended Wing Body (BWB) Concepts

Blended Wing Body (BWB) concepts is one of the more spectacular concepts to explore aircraft designs with a more seamless integration of the fuselage and wings. This innovative approach aims to enhance lift distribution and reduce drag for improved fuel efficiency. Perhaps the project that may illustrate better this

concept is the Airbus’ MAVERIC. For Airbus, the demonstrator tries to produce a real environmental performance benefit of significant interest. In accordance with their analysis, this concept may deliver approximately 20% less fuel burn compared to current single-aisle models with the same engine. In addition, the spacious configuration also opens the design space, enabling the possible integration of various other types of propulsion systems.

h) Sustainable Future: Active Flow Control Technologies

Active flow control involves the use of technologies such as air blowers and variable contour devices to actively manipulate airflow around the aircraft surfaces. This allows for precise control of boundary layer conditions by mitigating turbulence and controlling airflow, leading to reduced drag, and enhanced overall efficiency during various flight phases.

These advanced aerodynamic design principles collectively represent a significant step forward in creating more efficient, sustainable, and environmentally friendly aircraft for the next generation of commercial aviation.