Envirofuels claims that their product, DFC (Diesel Fuel Catalyzer), when added to diesel fuel, "improves the combustion process and reduces friction, increasing fuel economy while reducing emissions and engine wear." It does this with "a catalytic reaction and a surface conversion." How does this help?
Good question, and here is their answer: "The catalytic reaction optimizes the heat release rate, which leads to increased power, reduced emissions, and increased fuel efficiency. The surface conversion forms inorganic polymer complexes that converts the surfaces of ferrous and non-ferrous metals. These complexes smooth and passivate the metal surface, improve reflectivity (emissivity), and reduce oxygen reactivity, resulting in a reduction of friction and a more complete combustion reaction."
Honestly, their site is so full of information, via pdfs, links and charts, I suggest you check it out for yourself and make up your own mind about whether their product makes sense or not. It seems like an additive, like the ones you can get at any auto-parts store, except that they are targeting very large fleets and operations touting the savings and better emissions on a large-scale.