Green Combustion for Air Transport: Putting the Cart before the Horse

As carbon-neutral electricity generation becomes price competitive with fossil-fuel electricity generation, an economy-wide transition from combustion to electrification is seen as a key means of addressing climate change. Air transport is too energy intensive for current batteries and fuel cells to power current airliners, which has given rise to proposals for sustainable aviation fuel (SAF) that would allow combustion-powered airliners to operate in a carbon-neutral fuel cycle. All SAF proposals could be labeled green combustion; however, the proposal examined here involves jet fuel synthesized from direct-air-capture (DAC) carbon dioxide and electrolysis-produced hydrogen. Green combustion is examined in the context of an economy that has incorporated a carbon dioxide removal industry that’s composed of many processes including DAC. It isn’t clear whether green combustion is better than fossil-fuel combustion with compensating carbon dioxide removal. Further, with carbon dioxide costs in the business calculus, the capital cost of combustion airliners will likely be dwarfed by the energy cost of propelling such airliners. A new horse is needed. That new horse is likely electricity, with airliners designed to suit. Until electric airliners are practical, the best type of carbon-neutral combustion for the old carts will depend on a robust carbon dioxide market.