All previous presentation and discussion referred to solid nano-particles playing a catalytic role in the obtaining biofuels from algae, landfill methane and biomass. The following segments will examine the practical opportunities that exist for liquid nano-particles or droplets [21]. Consider multifunctional surface active liquid additives, whose lubricity enhancement is achieved via the formation of a monolayer over the surfaces in contact with additized fuel. [22] The treat rate for lubricity is determined by the adsorption saturation concentration. Speculate that the improved detergency and water co-solvency is obtained by the formation of nano emulsions. Also, postulate that the more complete combustion and consequent fuel efficiency increase is the result of the behaviour of nano droplets. These nano droplets result from the surfactant action of the additive in the fuel formulation and the presence of some water in all commercial fuel systems, usually due to evening condensation. Research by Wulff and colleagues [23] has shown that nano emulsions, which the authors call micro emulsions, with fuel (biofuel included most likely), water and surfactant are:

• Thermodynamically stable and

• Microscopically isotropic, and

• Nano-structured (thus, nano emulsions).

Their research concluded that:

• The use of these nano structures with fuel, water and surfactant is able to break the usual trade off between reduction of soot and NOx emissions, by achieving them simultaneously, and

• For the same fuel consumption, higher efficiency is obtained.

Strey and collaborators filed patent applications for what they call micro-emulsions used as fuel [24]. The interpretation offered for the behaviour of stable diesel (and most likely biodiesel)-water-surfactant nano emulsions is as follows:

• The surfactant components — oleic acid and nitrogen containing compounds (amines) — dissolve readily in diesel (and possibly in biodiesel) fuel and bind water to it without stirring;

• The water droplets are as small as a nanometer across, helping stabilize the emulsion

• The result is a "liquid sponge", can be stored indefinitely, like ordinary diesel fuel, without risk of phase separation

• This fuel formulation, when burned, results in the near-complete elimination of soot, and a reduction of up to 80% in nitrogen-oxide emissions

• The surfactant in the formulation also burns without creating emissions beyond water, carbon dioxide and nitrogen