The surface tension is one of the main properties for characterization of the quality of the fuel atomization process for its use in a diesel engine. There is a lack of published information about the values of surface tension of vegetable oils. The aim of this research is to obtain a mathematical model based on physical properties that establishes a relationship between the surface tensions of different vegetable oils and their fatty acid composition. For this reason, from literature reports, experimental data of oils related to the surface tensions was collected. Knowing that surface tension as a function of temperature, a total amount of 15 oils from different feedstocks at 20°C was selected. The obtained models were developed based in the use of artificial neural networks and multiple linear regressions fits, based on the experimental data available in the literature. Also, the obtained models present a good correlation between surface tension and the fatty acid composition, with a 95 % of confidence interval and coefficient of correlation higher than 0,95. The coefficient of correlation obtained shown a high correlation between the analyzed variables. According to the obtained results, the proposed models are a useful tool for the surface tension estimation from the oils fatty acid composition.

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Blends of Jatropha Curcas oil and standard diesel fuel were evaluated (without pre-heating). The engine tests for the blends were performed in a Petter single cylinder direct injection diesel engine under steady state conditions at high loads. Engine speeds between 1300-1700 rpm were selected for the engine tests. Torque, power output, specific fuel consumption, in cylinder pressure, ignition delay, rate of heat released and exhaust composition were evaluated. The tested blends between 10-20% of oil shown lower effective torque and power output joint to a higher specific fuel consumption related to the lower heating value of Jatropha oil compared to diesel fuel. Lower pressure peaks and rates or pressure rises were observed when Jatropha blends are used. A decrease in the rate of heat released and shorter ignition delay were observed for the blends. Decreases in HCand CO emissions were observed for blends compared to diesel fuel. Both alternatives assessed shown that the differences observed compared to diesel fuel, can be partially restored with engines regulation. The use of Jatropha oil in order to be a partial or full alternative to the use of diesel fuel for energy production was achieved.