With airlines and aircraft manufacturers working to curtail carbon emissions, the use of sustainable aviation fuel (SAF) is on the rise. Similar in its chemistry to fossil jet fuel, SAF is a ‘drop in’ kerosene product for today’s aircraft produced from sustainable feedstocks in place of crude oil.
What is a sustainable feedstock? Well, a broad range of criteria must be met, for example minimal impact on food production, appropriate use of land, water and maintaining biodiversity. Options include some vegetable oils, municipal waste, specific strains of algae, sugar and even carbon dioxide from steel mills. The carbon dioxide balance is also considered as energy is required to manufacture SAF and this can reduce the overall benefit.
Each new production pathway requires special approval to assure the reliability and performance of modern aviation turbine engines, taking many years of test data and assessment. Such efforts are overseen by ASTM International, a standards body that assures the testing and safety of new fuels and analysis methods. Once approved, full scale production and economics are key to viability which moves into the next topic, co-processing.
Co-processing is a method where vegetable oils, waste oils and fats, or similar sustainable feedstocks are processed along with crude oil feedstocks in existing refineries. Using an existing refinery can offer benefits in terms of cost savings and carbon reduction as it removes the need to build dedicated processing units. The fuel can also enter the standard distribution infrastructure to airport, again reducing transport and complexity.
In 2018, Air bp, working with Chevron and Phillips 66, gained approval for a co-processing pathway featuring vegetable oils or waste oils and fats for SAF production. This was a ground-breaking move as it opened the door for traditional refineries across the globe to enter SAF supply. Thoughts then turned to potential approval for co-processing Fischer-Tropsch syn-crude, an intermediate product featured in a municipal waste to SAF route. This would benefit the $30 million bp invested in 2016 in California-based Fulcrum BioEnergy, a company commercialising such a process. In July 2020 ASTM approval was gained, a significant success for Air bp and Fulcrum. As fuels and quality experts Air bp play a role in securing such approvals, or indeed challenging inappropriate technology, as part of the taskforces within ASTM.
As one of the most abundant elements on Earth hydrogen is sparking significant interest as an aviation fuel. In addition to removing carbon dioxide emissions entirely it may have the potential to reduce other environmental / greenhouse effects such as condensation trails.
Fuel cells have been developed where compressed hydrogen is combined with oxygen to generate electricity with water as the only biproduct. Lighter to transport and with a longer lifespan than conventional batteries, hydrogen fuel cells could play a significant role in making the concept of electric flight commercially viable.
Such technology is advancing today - in June, aviation start-up ZeroAvia saw the inaugural flight of its fuel cell electric aircraft at Cranfield Airport in the UK. The flight marked a significant milestone for the development of zero emissions hydrogen powered commercial aircraft.
What about liquid hydrogen, offering a higher energy density? Air bp was engaged in the recent European CleanSky 2 / FCH report which also examined this option for future flight. Liquid hydrogen is quite a different fuel compared to compressed hydrogen because it is cold, very cold. How cold is very cold? Imagine you are standing on Pluto, a tiny world at the outer limits of the Solar System. It’s a sunny day, however as a distant bright star in the sky the sun has little warmth to offer. The sun sets and the temperature falls to…. -240 °C. This is how cold hydrogen must be before it will liquify. Even air is solid at this temperature. Amazingly, both NASA and Russia have built and tested aircraft using liquid hydrogen as a turbine engine fuel. Handling the product is challenging due to the extreme temperature combined with the risk of boiling / venting, low ignition energy and wide flammability range. Like conditions on Pluto, a different world compared to more normal fuels.
Electric and hybrid-electric propulsion is rapidly revolutionising mobility technologies across different industries. Instead of using traditional fuel, electric light sport aircraft use re-chargeable batteries to power clean flight and significantly reduce noise pollution.
Last summer the two-seater motor glider e-Genius flew 300 miles on a single battery charge. It used just a fifth of the energy that a traditional two-seater fuel-powered plane would use to fly the same distance but with zero emissions. And in December 2019 Harbour Air and MagniX made history with the inaugural flight in Canada of the first all-electric aircraft built for commercial use.
Marking another milestone for electric flight, Pipistrel’s two-seater Velis Electro became the world’s first fully electric aeroplane ever to receive type certification from the European Aviation Safety Agency (EASA) in June 2020.
It’s not just small aircraft and start-ups that are pushing the boundaries of electric flight. In 2017 aviation giant Airbus launched the E-Fan X project in collaboration with Rolls Royce. Designed as a demonstrator E-Fan X was set to undergo its maiden flight in 2021. Although Airbus and Rolls-Royce made the decision to bring the E-Fan X demonstrator to an end in April this year, both companies will continue to leverage the knowledge gained through the project.
Will electric planes be commonplace within the next 20 years? Many experts believe they will. However, these will likely be small aircraft serving regional airports. The most obvious challenge to overcome for electric flight is battery capacity. Today’s batteries are simply not capable of storing sufficient energy to do anything other than fly a short distance. They need to be smaller and lighter before they can be used on commercial aircraft. Regulations also need to be adapted to enable commercially viable zero-emission electric aircraft to take to the skies.
Dating back to 1909 air racing is an adrenalin-rush sport involving aircraft competing over a fixed course at low altitudes. It was really brought into the limelight by the Red Bull Air Race Championship for which Air bp was the official fuel and carbon reduction partner for more than four years.
Although the Red Bull Air Race championships ended back in 2019, the enthusiasm for air racing is still soaring high. Now the focus is on racing electric aircraft with the first ever all-electric airplane race, Air Race E, due to go ahead in 2021.
Air Race E will see eight electric-powered aircraft racing directly against each other on a tight 5-km circuit. They will fly just 10 metres above the ground and at speeds faster than any land-based motorsport.
With huge potential to give rise to some interesting concepts for electric aircraft, electric air racing is one to watch.
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