That is very, very cool. Thank you for posting the link and for the details on retrofitting the engines. I don't know if you're in Brazil, but my understanding is that they are way ahead of the US in renewable fuel usage. Most of our ethanol is corn based for technical and political reasons, and corn is a worse feedstock because it's more difficult for yeast to metabolize and it requires more fertilizer. So it's not nearly as economical here. And you are right, fertilizer is the non-renewable input. Most of the N (nitrogen) in NPK (nitrogen/phosphorus/potassium) is ammonia or urea derived from natural gas via something called the Haber Process.