Carbon Neutral Combustion for Aviation
Combustion enabled the modern world. Long chains of carbon bound to hydrogen provide unparalleled energy density and are readily transported, facilitating everything from power generation to heating to flight. Using petroleum fuel, however, also generates vast carbon emissions, driving the massive increase in atmospheric CO2 and corresponding warming throughout earth.
Of course, the best way to stop emitting carbon is to avoid combustion in the first place. Renewable electricity generation should indeed displace all fossil fuel power plants and electrified heating must replace every oil tank in every basement. But, in certain cases, direct electrification is impossible, particularly when the thing that needs energy is moving, and if it can’t be too heavy or too large.
For these reasons, carbon-based fuels will remain essential to aviation. And aviation, which fosters human connection and drives economic growth, will remain essential to humanity. A carbon-neutral future thus depends on providing access to carbon-neutral combustion. This creates an incredible challenge: every carbon atom in your fuel must come from the very CO2 in the atmosphere it will produce in flight.
We are therefore of the opinion that atmospheric CO2 is the only long-term carbon source for the production of sustainable aviation fuel (SAF). But even the range of pathways based on atmospheric carbon is, itself, surprisingly large. Carbon feedstocks from corn to agricultural waste or direct air capture CO2 are, in fact, all atmospherically derived. Despite sharing an ultimate source of carbon, the scalability, environmental impacts, and logistical challenges of each approach varies massively.
At present, waste cooking oil remains the only meaningful commercial source of SAF. Combining cooking oil – which looks not so chemically dissimilar from jet fuel – with hydrogen enables production of jet-range hydrocarbons (“HEFA”) through a process much like current petroleum refining. Unfortunately, the growth of HEFA production is constrained by the dramatic mismatch between potential feedstock and required fuel, precluding expansion much beyond its current <1% of the jet fuel market. There simply is not enough used cooking oil to meaningfully decarbonize aviation.
Alternative biologically sourced materials show similarly great challenges when envisioned at scale. The feedstocks are simply too limited and too diffuse, or they compete with food systems. They generate significant – often unaccounted for – associated emissions. The slow rate of plant-based carbon capture results in unreasonable land requirements. We believe they too do not provide a viable long-term solution to decarbonized aviation.
We thus insist that anthropogenic direct air capture is the only viable long-term source of carbon for SAF production, with one major problem: it remains prohibitively expensive. At Sora Fuel, we are addressing this challenge by removing the most energy intensive step from DAC. By integrating the carbon capture and conversion process, we can deliver CO2 from the atmosphere to our electrolyzer at <$25/ton. This solves the greatest challenge in the production of truly sustainable aviation fuel: finding a truly sustainable, cost-effective source of carbon. And by solving this problem, we will enable carbon neutral flight.