A method for reducing emissions from an engine includes generating a light hydrocarbon fuel fraction and combusting the light hydrocarbon fuel fraction in place of the fuel. The light hydrocarbon fuel fraction is generated by heating the fuel and flowing the fuel through a plurality of hollow fiber superhydrophobic membranes in a membrane module. Each hollow superhydrophobic membrane comprises a porous support and a superhydrophobic layer free of pores that extend from one side of the superhydrophobic layer to the other. Vapor from the fuel permeates the superhydrophobic membranes and enters a distillate collection chamber, producing a distilled fuel in the distillate collection chamber and a residual fuel within the hollow fiber superhydrophobic membranes. The residual fuel is removed from the membrane module and cooled to produce a cooled residual fuel. The cooled residual fuel flows through a plurality of hollow tubes in the membrane module and the distilled fuel is removed from the distillate collection chamber to produce the light hydrocarbon fuel fraction.