Hydrogen fuel. All-electric propulsion. Hybrids. Open fan. Gasturbine. SAF. These are the new buzzwords that are now part of industry vocabulary as aircraft and engine manufacturers, airlines, and everyone in the supply chain race to meet the goal of carbon neutrality by 2050.

Alarming climate change data, public pressure, and the pandemic put new focus on the aviation sector’s estimated three per cent CO₂ contribution. Airlines have been quick to identify their most fuel inefficient fleet types and remove them from service. OEMs were equally quick to accelerate development of more environmentally-friendly products. The current emphasis is on propulsion systems that are powered by clean-burning sources – electricity, hydrogen, and sustainable aviation fuel (SAF.)

INTEREST IN BIOFUEL STARTED YEARS AGO

The move to SAF, in particular, is gaining the most momentum, yet research on SAF viability production started some two decades ago. Then, biofuels produced from plant matter offered cleaner-burning power. Embraer’s 202 Ipanema was the first aircraft in the world certified to run on biofuel back in 2004.

Since then, the source of biofuel production has expanded to include residues from cooking oil, municipal waste, plant oil, waste gases, and agriculture that would be left to decompose in the environment.

HOW IS SAF MADE?

A process called hydrodeoxygenation removes an oxygen atom from and adds hydrogen atoms to common renewable biogenic raw materials, like plants, and waste materials, such as animal fats and used cooking oil which are pre-treated to eliminate impurities. One of the most toxic of these is sulphur which is common in petroleum-based products. The result is a highenergy density hydrocarbon that can be isomerized. The modified hydrocarbon structure can then be branched and used to create new raw materials, including cleaner-burning jet fuel.

The overall sustainability of a new fuel is determined by its CO₂ output across its lifecycle, from production through consumption. Plants, for example, absorb CO₂ as they grow yet they produce an equal volume of CO₂ when they are burned as biofuel in a combustion engine. The net result is a carbon zero product. Yet the raw material-to-fuel production process itself generates CO₂ emissions. When that process is considered, lifecycle CO₂ emissions from SAF are up to 80 per cent lower than those from current fossil-based jet fuel.

SAF IS GAINING SPEED

SAF has been tested on commercial aircraft for years and is now routinely used by many of the world’s leading airlines. The latest carrier to start using SAF is Malaysia Airlines. On June 7, flight MH603, a B737-800, took off from Kuala Lumpur for Singapore fuelled by SAF provided by Neste MY. Neste (Finland), World Energy (USA), Alder Fuels, and SkyNRG are the world’s biggest SAF refiners and suppliers according to Earth.org, a non-profit environmental organization.

Today, however, the only SAF on the market certified for commercial use is a blend of half-Jet-A and half SAF. ASTM (formerly the American Society for Testing and Materials) specification D7566 governs requirements for the manufacture of nonpetroleum alternate drop-in jet fuels.

The goal of non-blended 100 per cent SAF is within reach but its widespread application will take some time.

WHY ALL THE HYPE OVER SAF?

Quite simply, it’s fast to implement and effective.

Raw materials for SAF can be sourced locally. Supporting local economies reduces dependence on big oil producers and can offset volatility in supply and pricing. Moreover, fuel sources from crops can be cultivated without impacting food production. The fast-growing camelina plant, for example, can grow on wheat fields that would normally be left fallow for a year. The lipid oil in the seeds from the jatropha plant are ideal for producing fuel but are toxic to humans and animals. Algae thrives on CO₂ and grows quickly, producing up to 15 times more oil per square kilometer than other crops.

SAF IS DROP-IN READY

Airlines are already using blended SAF. It can be “dropped in” to aircraft tanks to replace traditional fuel without any modifications to the airplane or fuel delivery systems. That’s welcome news for engine manufacturers, airports, and fuel suppliers. The next leap in application will be a 100 per cent unblended product.

Production needs to be on a massive scale so that cost comes down. Only then will we see SAF’s impact which could “contribute nearly 65 per cent to the reduction in emissions needed to reach the net-zero target in the next three decades,” according to Earth.org.

The volume of SAF needed for the industry to achieve its zero emissions target is daunting given the infancy of the product. Only 3,70,000 flights have used SAF over the last five years. Even considering projected growth in aircraft movements, a staggering 449 billion litres will be necessary by 2050. Only about 100 million liters of SAF were used in 2021.

SAF IS JUST ONE PART OF THE PLAN

Earth.org estimates that SAF production represents less than one per cent of global jet fuel and is more expensive than conventional jet fuel. The environmental benefits of SAF are clear. Its cost, however, will need to come down which may be forthcoming given the high price of crude oil and aviation turbine fuel.

In parallel, manufacturers are developing more fuel-efficient engines, including hybrid powerplants that use both electricity and SAF that could be in service by the mid 2030s. Engines that run on non-CO₂ producing hydrogen are already here. H2Fly of Germany flew its four-seat HY4 hydrogen-powered airplane from Stuttgart to Friedrichshafen at the Aero Friedrichshafen show in April.

Completely new aircraft designs are emerging which incorporate new propulsion systems. Electric power will likely be rolled out on smaller regional turboprops and jets, like Embraer’s Energia family and ATR’s EVO, before the technology is ready for bigger airplanes. That isn’t stopping the UK’s Easyjet from partnering with GKN Aerospace to explore hydrogen fuel cell technology for use on medium-range aircraft.

But SAF and new airplanes alone won’t get the industry to its 2050 carbon neutral goal. Improvements in infrastructure and greater efficiency moving aircraft through the air and on the ground will help lower CO₂ emissions.

The road to 2050 will be long, but every journey starts with a single step. And that first step is SAF.