Reologia de Biodiesel de origens diversas e das misturas Diesel/Biodiesel

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Cost and depletion of petroleum derived fuels are increasing, thus alternative fuels are quite required. Biodiesel (B100), which is comprised of fatty acid methyl (or ethyl) esters (FAMEs/FAEEs) derived from vegetable oils, animal fats or waste oils mainly through transesterification, is an alternative source of energy. It is renewable, available locally, biodegradable and has proved to be a cleaner fuel. B100 viscosity is a critical physical property concerning the applicability of this fuel in direct injection diesel motors due to: a) B100 viscosity increases at low temperature ultimately leading to flow restrictions and/or filter plugging due to FAMEs/FAEEs crystallisation or gelation; b) An increasing in B100 viscosity diversely affects the atomization process bringing about the occurrence of competitive reactions, such as, charring or coking and polymerization. B100 viscosity is about 1.5 times higher than conventional diesel (B0). B100 and its blends with B0 display temperature-dependent viscosity behaviour similar of that of neat diesel, that is, it decreases with temperature in an exponential fashion. On the other hand, the viscosity of these fuels increases with chain length and saturation degree of FAMEs/FAEEs. This work aims was investigating the mechanical behaviour of B100 and its blends with B0 (B2 to B50) by studying their rheological behaviour and measuring their dynamic viscosity and density at a given temperature. In addition, predictive literature models for viscosity of non-associate liquid mixtures were applied to B100 (Andrade, Krisnangkura and Allen Models) and its blends (Andrade Model). The data obtained for the density of B100 and its blends were fit to the Liew Model. The B100 fuels used in this study were derivate from castor oil; cottonseed oil; oiticica oil and beef tallow. The castor oil B100, cottonseed oil B100 and oiticica oil B100 were produced in a batch transesterification unit (LaboratÃrio de CombustÃveis da Universidade Federal de Pernambuco), using methanol and sodium hydroxide as monohydric alcohol and catalyst, respectively. The B100 blends with diesel (Metropolitan - Type D) were prepared on mass-based. The average composition of B100 was determined by a CG Gas Chromatograph, CG Master Model. The density of B100 and its blends was measured by an Anaton-Paar Digital Densimeter, DMA 4500 model. The Brookfield Rheometer, LVDV-III model (spindles models: SC4-31 e SC14-18) was used for measuring the apparent viscosity of these fluids as well as elucidating their rheological behaviour. The operational conditions were: Temperature: 20oC to 60oC; Shear rate: 66s-1 to 333s-1. The dynamic viscosity was obtained using the apparent or Newtonian viscosity concept. The Andrade and Liew Models were used for predicting the vegetable oils/beef tallow, B100 and its blends viscosity and density values in function of temperature. Those models were fit to data by a non-linear regression. Model parameters were obtained. The Andrade and Liew Models predict viscosity and density of the vegetable oils/beef tallow, B100 and their blends with B0 with average errors of 3%. On the other hand, Krisnangkura and Allen Models were used for predicting the vegetable oils/beef tallow and B100 viscosity values in function of FAMEs composition. The Allen and Krisnangkura Models predict dynamic viscosity of the vegetable oils/beef tallow, B100 errors of 10% and 5%, respectively. An experimental data-base was created for the B100 studied and their blends with B0. The ANOVA technique was used for verifying the adequacy of models to the experimental data

ASSUNTO(S)

phenomenological models viscosity density biodiesel densidade engenharia quimica biodiesel fuel comportamento reolÃgico viscosidade rheological behaviour

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