The Azimuth Project
G. R. L. Cowan

I want cars to continue having internal combustion engines, but become zero-emission vehicles by ceasing to offload combustion products, except at refuelling time.

This favours a low per-unit-energy sum of oxygen mass and fuel mass, or otherwise said, a low ash mass. On this scale water and water-plus-CO2, the ashes respectively of hydrogen and gasoline, both lose to B2O3. This is among the reasons I believe motorists will eagerly upgrade to boron when they get the chance.

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