Introduction
In the last 20 years it became very import to find renewable fuel sources that could be used in Diesel motors [1]. In this sense, methyl esters, which are produced by a catalytic transesterification reaction of vegetable oils with short-chain alcohols, have been pointed out as an alternative fuel for these engines [1] and [2]. Indeed, methyl esters are interesting alternatives because they show a decrease in CO2, SOx, and unburned hydrocarbons emissions during the combustion process when compared with fossil fuels [2] and [3]. However, the methyl esters present higher viscosities, densities, flash points, and lower cold-filter plugging point as compared to conventional diesel [1]. Conventional diesel engines can run using blends of diesel and methyl esters up to 20%, as B20 for instance [4]. The use of pure methyl esters is possible if some modifications are introduced in the diesel engine.