Flight to sustainability

Sustainable aviation fuel has promise

The recent London-New York test flight of Virgin Atlantic is an important proof of concept for sustainable aviation fuel (SAF). A commercial, unmodified Boeing 787 made the 5,800-km flight using 100 per cent SAF. While jet engines are certified only to use a maximum of 50:50 mix of normal jet fuel and SAF, this flight received special clearance. If SAF procurement and production can be streamlined and scaled up to reduce costs, it would reduce emission considerably. Many Europe-based airlines are targeting a 10 per cent SAF fuel mix by 2030. This has to rise to about 65 per cent to meet the emission targets of 2050. Currently, civil aviation is reckoned to contribute 10-12 per cent of transport-related greenhouse gas emission. If audits included the carbon impact across the entire supply chain of aircraft manufacture, the impact would be much more.

SAF is produced by taking biomass such as used cooking oil, waste animal fat, manure and sewage, and broken or spoiled maize, foodgrains, rice and waste wood, and rendering these into synthetic jet fuel substitutes. Some SAF processes capture carbon dioxide from the air. Some versions of SAF may be “negative carbon” because they reduce free methane (found in manure and sewage) and capture atmospheric carbon dioxide. Methane is much worse than carbon dioxide in terms of greenhouse effects. Widespread use of high SAF mixes would obviate the expense and carbon impact of modifying, or replacing jet engines of fleets. Every form of SAF has a low carbon footprint compared to the mining and refining of crude oil and natural gas. However, it is at least three times as expensive as jet fuel and, at the moment, SAF contributes less than 1 per cent to the aviation fuel mix. The logic for SAF is analogous to that of German auto companies, which are developing synthetic petrol and diesel to run unmodified internal combustion engines. Replacing billions of internal combustion vehicles with electrical propulsion would have a large carbon impact even if the exhaust emission is zero. Instead, capturing carbon dioxide from the air and adding methane in some form could make such synthetic fuels net-zero-carbon if the exhaust emission is equivalent to or less than the carbon-equivalent removed in fuel production. Again, the issue is cost — synthetic petrol costs about five times mining and refining crude oil.

The technology and engineering challenges can be met if production is scaled up and engineering processes improve. There will always be questions about how much reduction occurs. But SAF and synthetic petrol would have a significantly lower carbon impact, especially so because existing transportation need not be replaced. It could also have other beneficial effects like waste recycling and, arguably, it would improve the environment, unlike with mining. Ideally, SAF production would use green energy. Policy support will be needed for research into better capture and collection of biomass and atmospheric carbon. Subsidies could also come into the picture as well to enable the synthetic fuel industry to take off. Decades of subsidies and policy support have worked with solar power, for example — solar is now cheaper than thermal in most places. It’s early days but this flight does indicate an alternative and, perhaps, more pragmatic route to emission reduction.